Rush Creek Watershed Study Technical Support ... AWS
Rush Creek Watershed Study Technical Support Data Notebook (TSDN) May 24, 2017
TBPE Firm Reg No. F-312
In Cooperation with:
TBPE Firm Reg No. F-3043
TBPE Firm Reg No. F-6548
Brown & Gay Engineers, Inc. EBG Engineering, LLC
TBPE Firm Reg No. F-3075
TBPE Firm Reg No. F-2677
Nathan D Maier Consulting Engineers, Inc. Surveying And Mapping, Inc.
Rush Creek Watershed Study Final Report
CONTENTS Executive Summary ................................................................................................................................. ES 1 1. Introduction ............................................................................................................................................... 1 1.1 Study Purpose and Scope ................................................................................................................. 1 1.2 Location of Study ................................................................................................................................ 3 1.3 Community Description ..................................................................................................................... 3 1.4 Floodplain Mapping Extents ............................................................................................................. 3 2. Data Collection ........................................................................................................................................ 6 2.1 Survey and Mapping .......................................................................................................................... 6 2.1.1 Digital Projection Information ...................................................................................................... 6 2.1.2 Field Survey...................................................................................................................................... 6 2.2 Previous Reports and Studies ............................................................................................................ 6 2.2.1 Report Summaries .......................................................................................................................... 8 2.2.1.1 Floodplain Information; Rush and Village Creeks; Arlington, Texas; USACE; February 1971 ..................................................................................................................................... 8 2.2.1.2 Flood Insurance Study Arlington Texas, Volume 2; Fort Worth District, USACE; July 1972 ............................................................................................................................................. 8 2.2.1.3 Rush Creek Watershed Management Development Document; Espey, Huston & Associates, Inc; April 1989 ............................................................................................................ 8 2.2.1.4 Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report; USACE; 1991 – 1992 ............................................................................................................................ 9 2.2.1.5
Rush Creek Tributary 1 Report; USACE; August 1992 ............................................... 10
2.2.1.6 State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180; August 1993 ........................................................... 10 2.2.1.7 Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report; Fort Worth District, USACE; March 1994 ............................................................................................... 11 2.2.1.8 1994
Rush Creek Tributary 1; 205 DPR Study; Fort Worth District, USACE; November ........................................................................................................................................... 11
2.2.1.9 Rush Creek Flooding and Sedimentation Study (Final Report); Nathan D. Maier Consulting Engineers, Inc.; January 2001 .................................................................................... 11 2.2.1.10 Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition; G.A. Dixon & Associates; June 2006 ............................................................................................. 12 2.2.1.11 Flood Study of Rush Creek for Valista Estates in Arlington, Texas; Nave Engineering, Inc.; June 2007 .......................................................................................................... 12
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2.2.1.12 Letter of Map Revision Based on Fill (LOMR-F); Morrison Hydrology Engineering, Inc.; Table for Summary of Discharges and Floodway Data ........................... 13 2.2.1.13 Flood Study for Property Located at 2224 Wanda Way, Rush Creek, City, Tarrant County; Morrison Hydrology Engineering, Inc.; November 2008 .............................. 13 2.2.1.14 Rush Creek and Tributary RC-2; Conditional Letter of Map Revision (CLOMR); Nathan D. Maier Consulting Engineers, Inc.; October 2009 .................................................... 14 2.2.1.15 Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1; Caffey Engineering, Inc.; January 2010....................................................................................... 14 2.2.1.16
Rush Creek Letter of Map Revision (LOMR); Wier & Associates; March 2010 16
2.2.1.17 Blue Binder: Information on Flood Data Elevation; John D. Zimmerman P.E., R.P.S.; October 2010 ........................................................................................................................ 17 2.2.1.18 Comprehensive Stream Management Plan; Phase 1 and Phase 2 Report; Jacobs Engineering; March 2011 ................................................................................................. 19 2.2.1.19 Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary Number 7 – Grace preparatory Academy Addition, Charles Crook Consulting, Inc., May 2016 ....................................................................................................................................... 19 2.3 Flood Insurance Study ...................................................................................................................... 19 2.4 Hydrologic and Meteorologic Data.............................................................................................. 20 2.5 Public Meeting................................................................................................................................... 23 3. Hydrologic Analysis ................................................................................................................................ 24 3.1 Subbasin Delineation ....................................................................................................................... 24 3.1.1 Topographic Data Acquisition and Evaluation ..................................................................... 24 3.1.2 Terrain Processing ........................................................................................................................ 26 3.2 Precipitation Data............................................................................................................................. 26 3.3 Depth-Area Reduction Factors ...................................................................................................... 27 3.4 Runoff Volume ................................................................................................................................... 27 3.4.2 Land Use Classification ............................................................................................................... 28 3.4.2.1
Existing Conditions Land Use ........................................................................................ 29
3.4.2.2
Ultimate Conditions Land Use...................................................................................... 29
3.4.3 Hydrologic Soil Groups ................................................................................................................ 29 3.5 Runoff Hydrographs .......................................................................................................................... 32 3.6 Routing ................................................................................................................................................ 33 3.7 Hydrologic Analysis Results .............................................................................................................. 33 3.8 Quality Control .................................................................................................................................. 33 4. Hydraulic Analysis ................................................................................................................................... 34 4.1 Introduction ........................................................................................................................................ 34
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4.2 HEC-RAS Model Development ....................................................................................................... 36 4.2.1 Stream Centerlines and Cross-Sections ................................................................................... 36 4.2.2 Structures ....................................................................................................................................... 36 4.2.3 Manning Roughness Coefficients ............................................................................................. 36 4.2.4 Ineffective Flow ............................................................................................................................ 38 4.2.5 HTab Parameters.......................................................................................................................... 38
4.3
4.2.5.1
HTab Parameters for Cross-Sections ........................................................................... 38
4.2.5.2
HTab Parameters for Structures ................................................................................... 38
Boundary Conditions & Flow Input ........................................................................................... 39
4.3.1 Unsteady Flow Input .................................................................................................................... 39 4.3.1.1
Initial Flow ........................................................................................................................ 39
4.3.1.2
Minimum Flow ................................................................................................................. 39
4.3.2 Steady Flow Input ........................................................................................................................ 39 4.4 Quality Control .................................................................................................................................. 39 4.5 Results .................................................................................................................................................. 40 4.5.1 Modeled Flows and Stages ....................................................................................................... 40 5. Updated Floodplain Map/Physical Map Revision ........................................................................... 45 5.1 Base Map ............................................................................................................................................ 45 5.2 Floodplain Delineation ..................................................................................................................... 45 5.3 Flood Profiles ...................................................................................................................................... 45 5.4 Floodway Computations ................................................................................................................. 45 5.5 FIS Report Section ............................................................................................................................. 46 5.5.1 Hydrologic Analysis ...................................................................................................................... 46 5.5.2 Hydraulic Analysis ........................................................................................................................ 47
FIGURES Figure 1-1. Location Map ............................................................................................................................. 2 Figure 2-1. Tarrant County 24-hr Distribution of 100-yr Storm (based on the frequency storm method) .................................................................................................................................... 22 Figure 2-2. Arlington Airport, September 7-8, 2010 Storm Event (15 minute) ................................... 23 Figure 3-1. Subbasin Delineation .............................................................................................................. 25 Figure 3-2. Existing Land Use ...................................................................................................................... 30 Figure 3-3. Soils ............................................................................................................................................. 31 Figure 4-1. Modeled Stream Reaches ..................................................................................................... 35
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TABLES Table 1-1. Rush Creek Watershed Study Modeled Streams .................................................................. 4 Table 2-1. Watershed Study Reports .......................................................................................................... 7 Table 2-2. Detailed Study Streams. .......................................................................................................... 20 Table 2-3. Estimated 24-hour Storm Depths (inches) for Tarrant County Texas. .............................. 21 Table 3-1. Rainfall Depth-Duration-Frequency Data (inches) ............................................................ 26 Table 3-2. Rush Creek ARF Estimates ....................................................................................................... 27 Table 3-3. Land use and Percent Impervious ........................................................................................ 28 Table 3-4. Watershed Soil Classification .................................................................................................. 32 Table 4-1. n values ....................................................................................................................................... 37 Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges ....... 41
APPENDICES Appendix A: Technical Standards Appendix B: Hydrologic Parameter Summary Appendix C: Public Meeting Information Appendix D: Lidar Quality Assurance Report Appendix E: Floodway Data Tables and Profiles Appendix F: Hydraulic and Hydrology Database Appendix G: Hydraulic and Hydrology Models Appendix H: QA/QC Forms Appendix I: Survey Data Appendix J: Floodplain Work Maps
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Rush Creek Watershed Study Final Report
Executive Summary The Rush Creek Watershed is the largest watershed in Arlington, Texas and includes portions of Kennedale, Mansfield, Fort Worth and the entirety of Pantego and Dalworthington Gardens. The watershed has developed significantly over the past 40 years from the time when the original floodplain mapping was produced by FEMA. The City of Arlington has undertaken a comprehensive study of the Rush Creek Watershed. The purpose of this report is to revise Federal Emergency Management Agency (FEMA) flood maps so that flooding risk is better defined for Arlington residents. To meet this objective, this study included hydrologic and hydraulic modeling compliant with FEMA guidelines and standards. The new hydrologic analysis of the entire Rush Creek Watershed included subbasin delineation, runoff characterization, rainfall input calculations, and development and validation of a HEC-HMS model (version 3.5). HEC-RAS models (version 4.1) were built for all current effective Zone AE and Zone A streams in the watershed for the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent annual chance event and the 1 percent annual chance event for future development conditions. A September 2010 flood event (Tropical Storm Hermine) was also modeled. Revised floodplains were delineated based on computed water surface elevations in the HECRAS models. For tributaries studied in limited detail, a floodplain was delineated based on the 1% annual-chance water surface elevations. For the detailed study streams (including Rush Creek), both the 1- and 0.2 percent annual-chance floodplains were mapped including floodways. Floodplain work maps showing the revised floodplain delineations can be seen in Appendix J. Water surface profiles for the 10-, 4-, 2-, 1-, and 0.2 percent annual-chance floods were prepared in FEMA format for all detailed study streams associated with this study. All profiles maintained the same horizontal and vertical scales used in the effective FIS report in accordance with FEMA standards for restudied streams. The profile plots are included in Appendix E.
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Rush Creek Watershed Study Final Report
1.
Introduction
The Rush Creek-Village Creek Watershed in southeast Tarrant County is mainly comprised of area located in west Arlington, but also includes portions of Kennedale, Mansfield, and Fort Worth and the entirety of Pantego and Dalworthington Gardens as shown on Figure 1-1. Rush Creek Watershed contains approximately 35 square miles and approximately 56 miles of main channel and tributary. Rainfall is the major contributor to flow in Rush Creek, but there are a small number of natural springs from the Woodbine Aquifer that also contribute to the total flow. Channels within the watershed range from natural to concrete lined. Research indicates that major floods most likely occurred in April 1922, May 1949, April 1957, May 1965, March 1968, March 1977, May 1989, April 1990, June 2004, June 2007, and September 2010 (when over 200 homes were reported to have flooded in the Rush Creek Watershed). While lake levels have been maintained for Lake Arlington upstream of Lower Village Creek since 1988, no records of streamflow are available on Rush Creek. The watershed has developed significantly over the past 40 years. During this time frame City stormwater ordinances allowed development without considering cumulative downstream impacts. This has had an enormous impact on the floodplains and creeks and has led to increased volumes, velocities and base flood elevations as well as decreased water quality. The effective watershed hydrologic modeling has not been updated to take this period of development into account. Due to flooding concerns and the lack of knowledge of the true volumes and flood elevations in the watershed, the City of Arlington has completed a comprehensive watershed study for the Rush Creek Watershed in compliance with Federal Emergency Management Agency (FEMA) guidelines and standards. CDM Smith acted as the Project Management Consultant (PMC), wrote the project’s technical standards and provided quality assurance and control. AECOM, Dewberry, and Michael Baker completed the initial hydraulic analyses. Halff Associates completed the hydrologic analysis, final hydraulic model revisions, and completed the final FEMA mapping and applications.
1.1
Study Purpose and Scope
There central purpose of the Rush Creek Watershed Study was to Revise FEMA flood maps so that flooding risk is better defined for Arlington residents.
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Rush Creek Watershed Study Final Report
Figure 1-1. Location Map
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Rush Creek Watershed Study Final Report
The City of Arlington and sub-consultants completed the following tasks for this study: Data Collection: included information such as previous watershed studies, existing topography and photography (contours, aerial mapping, watershed delineations, and existing surveys of physical features), hydrologic and hydraulic models, and FEMA floodplain delineations. Develop Standards: standards were developed for both work products and technical analysis since five engineering firms were involved. The Technical Standards document is included as Appendix A.
Terrain Data – an ESRI Terrain geodatabase, compatible with ArcGIS Desktop version 9.3.1, was created using Light Detection and Ranging (LiDAR) data collected in 2009 and 2010 and made available by the Texas Natural Resources Information System.
Survey – cross sections were surveyed to supplement the LiDAR-based terrain data.
Hydrologic Modeling – a new hydrologic analysis of the entire Rush Creek Watershed was completed. This effort included subbasin delineation, runoff characterization, rainfall input calculations, and development and validation of a HEC-HMS model (version 3.5).
Hydraulic Modeling – new HEC-RAS models (version 4.1) were built for all currently effective Zone AE and Zone A streams in the watershed for the 50%, 20%, 10%, 4%, 2%, 1%, and 0.2% annual chance event and the 1% annual chance event for future development conditions. A September 2010 flood event was also modeled.
1.2
Location of Study
As noted above, the Rush Creek-Village Creek Watershed is in southeast Tarrant County, Texas and is mainly comprised of area located in west Arlington, but also includes portions of Kennedale, Mansfield, and Fort Worth and the entirety of Pantego and Dalworthington Gardens. The City of Arlington has taken the lead on this study but has coordinated with Pantego, Dalworthington Gardens, and the general public through meetings to discuss the project’s goals and progress.
1.3
Community Description
The City of Arlington, with a population of over 360,000, lies wholly within Tarrant County, Texas. The City covers approximately 100 square miles, is served by four independent school districts, and is home to three institutions of higher learning.
1.4
Floodplain Mapping Extents
Detailed unsteady HEC-RAS models were prepared to define base flood elevations and regulatory floodways along approximately 35 miles of open channel streams that are currently mapped as Zone “AE” in the Rush Creek Watershed. Streams currently mapped as Zone A in the watershed were modeled in steady HEC-RAS but with limited detail. Modeled and mapped streams are shown in Table 1-1. Streams noted as “Not Studied” in Table 1-1 were typically entirely within the backwater from the main stem and were not modeled. Stream centerlines were delineated based on aerial photography and cross-section surveys and then georeferenced in HEC-RAS. Additional streams needed to define overflows and diversions were included to provide additional floodplain mapping extents.
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Rush Creek Watershed Study Final Report
Table 1-1. Rush Creek Watershed Study Modeled Streams Stream Name
Study Area
Stream
Reach ID
Study Type
Length (ft)
Forest Park Tributary
UR
RUS
RUS_FPT
Detailed (AE)
1945
Kee Branch
KB
KEE
KEE_000
Detailed (AE)
30744
Kee Branch Tributary 1
KB
KEE
KEE_001
Limited Detail (A)
2543
Kee Branch Tributary 1.1
KB
KEE
KEE_001_001
Limited Detail (A)
428
Kee Branch Tributary 2
KB
KEE
KEE_002
Limited Detail (A)
2070
Kee Branch Tributary 3
KB
KEE
Kee Branch Tributary 4
KB
KEE
KEE_004
Limited Detail (A)
6173
Kee Branch Tributary 5
KB
KEE
KEE_005
Limited Detail (A)
3888
Northeast Tributary
UR
RUS
RUS_NET
Detailed (AE)
2610
Pantego Branch
LR
PAN
PAN_000
Detailed (AE)
9153
RUS
RUS_000
Detailed (AE)
76098
RUS
RUS_RCH
Detailed (AE)
4218
Rush Creek
Not Studied
Rush Creek Relief Channel
LR
Rush Creek Tributary 3
LR
RUS
Rush Creek Tributary 4
LR
RUS
RUS_004
Limited Detail (A)
4981
Rush Creek Tributary 4.1
LR
RUS
RUS_004_001
Limited Detail (A)
4074
Rush Creek Tributary 5
LR
RUS
RUS_005
Limited Detail (A)
7814
Rush Creek Tributary 5.1
LR
RUS
Rush Creek Tributary 5.2
LR
RUS
Not Studied
Rush Creek Tributary 5.3
LR
RUS
Not Studied
Rush Creek Tributary 6
LR
RUS
Not Studied
Rush Creek Tributary 7
MR
RUS
RUS_007
Limited Detail (A)
5406
Rush Creek Tributary 7.1
MR
RUS
RUS_007_001
Limited Detail (A)
543
Rush Creek Tributary 8
MR
RUS
Rush Creek Tributary 9
MR
RUS
RUS_009
Limited Detail (A)
6595
Rush Creek Tributary 10
MR
RUS
RUS_010
Limited Detail (A)
5682
Rush Creek Tributary 10.1
MR
RUS
RUS_010_001
Limited Detail (A)
1636
Rush Creek Tributary 10.2
MR
RUS
RUS_010_002
Limited Detail (A)
2424
Rush Creek Tributary 10.3
MR
RUS
RUS_010_003
Limited Detail (A)
1182
Rush Creek Tributary 10.4
MR
RUS
RUS_010_004
Limited Detail (A)
2717
Rush Creek Tributary 11
MR
RUS
RUS_011
Limited Detail (A)
1348
Rush Creek Tributary 12
MR
RUS
RUS_012
Limited Detail (A)
1145
Rush Creek Tributary 13
MR
RUS
RUS_013
Limited Detail (A)
4512
Rush Creek Tributary 14
MR
RUS
RUS_014
Limited Detail (A)
2891
Rush Creek Tributary 15
MR
RUS
RUS_015
Limited Detail (A)
2848
Rush Creek Tributary 15 Overflow Rush Creek Tributary 16
MR
RUS
Polo_Club
Limited Detail (A)
1232
UR
RUS
RUS_016
Limited Detail (A)
3338
Rush Creek Tributary 16.1
UR
RUS
Rush Creek Tributary 17
UR
RUS
Not Studied
Not Studied
Not Studied
Not Studied RUS_017
Limited Detail (A)
1566
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Rush Creek Watershed Study Final Report
Table 1-1. Rush Creek Watershed Study Modeled Streams Study Area
Stream
Rush Creek Tributary 18
UR
RUS
Rush Creek Tributary 18.1
UR
RUS
Rush Creek Tributary 19
UR
RUS
Rush Creek Tributary 20
UR
RUS
Ryan’s Branch
MR
RYA
RYA_000
Detailed (AE)
6632
Ryan’s Branch Tributary 1
MR
RYA
RYA_001
Limited Detail (A)
1108
Stream KB-1
KB
KEE
KEE_KB1
Detailed (AE)
5157
Stream KB-1.1
KB
KEE
KB1_001
Limited Detail (A)
1496
Stream RC-1
RC1
RCO
RUS_RC1
10185
Stream RC-1A
RC1
RCO
RCOT1A
Stream RC-1 Tributary 1
RC1
RCO
RCO001
Detailed (AE) / Limited Detail (A) Detailed (AE) / Limited Detail (A) Limited Detail (A)
Stream RC-1 Tributary 2
RC1
RCO
RCO002
Limited Detail (A)
2120
Stream RC-1 West Diversion Stream RC-1 North Diversion Stream RC-2
RC1
RCO
RCO_WST
Limited Detail (A)
2493
RC1
RCO
RCO_NOR
Limited Detail (A)
820
LR
RUS
RUSRC2
Detailed (AE) Detailed (AE) / Limited Detail (A) Limited Detail (A)
Stream Name
Reach ID
Study Type
Length (ft)
Not Studied Not Studied RUS_019
Limited Detail (A)
2623
Not Studied
7566 1057
6731
Sublett Creek
UR
SUB
SUB_000
Sublett Creek Tributary 1
UR
SUB
SUB_001
Sublett Creek Tributary 1.1
UR
SUB
SUB_001_001
Sublett Creek Tributary 2
UR
SUB
SUB_002
Limited Detail (A)
873
Sublett Creek Tributary 3
UR
SUB
SUB_003
Limited Detail (A)
4541
Sublett Creek Tributary 4
UR
SUB
Twin Springs Draw
MR
TWI
Twin Springs Draw Tributary 1 Twin Springs Draw Tributary 1.1 Twin Springs Draw Tributary 2 Twin Springs Draw Tributary 3 Twin Springs Draw Tributary 4 Twin Springs Draw Tributary 5
MR
TWI
Not Studied
MR
TWI
Not Studied
MR
TWI
MR
TWI
MR
TWI
TWI004
Limited Detail (A)
3768
MR
TWI
TWI005
Limited Detail (A)
628
Limited Detail (A)
23895 2032 1208
Not Studied TWI000
TWI002
Detailed (AE)
Limited Detail (A)
6594
702
Not Studied
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Rush Creek Watershed Study Final Report
2.
Data Collection
Information and data related to the Rush Creek Watershed was collected in compliance with FEMA guidelines and standards. This information includes previous watershed studies, recently collected terrain data and photography, GIS data, hydrologic and hydraulic models, and approved Letters of Map Revision (LOMRs/CLOMRs). This section includes a catalog of the data collected and a brief synopsis of each piece of data.
2.1
Survey and Mapping
One of the purposes of this study is to update estimated flood elevations using recent sources of physical data. For model building and floodplain mapping the key physical system data consists of base map, terrain and field survey. The date and sources of this data are as follows:
Base Map – Streets – ArcGIS Online World Transportation
Aerial Photography – 2015 TNRIS
Terrain – The terrain was prepared by Halff Associates in 2012 from LiDAR that was flown in 2009.
Survey – Cross-sections and bridge dimensions were obtained during the spring of 2012 under the direction of the hydraulic modeling consultants (AECOM, Dewberry, and Michael Baker). Additional open channel and bridge surveys were performed by Halff Associates along Kee Branch, Rush Creek, and Twin Springs Draw Tributary 5 (Arbrook Channel) during the spring of 2015.
2.1.1
Digital Projection Information
All spatial data uses the NAD_1983_StatePlane_Texas_North_Central_FIPS_4202_Feet projection.
2.1.2
Field Survey
Field survey of channel cross-sections and hydraulic structure dimensions was conducted along all detail study streams. No data from the effective model was deemed to be usable given that the models were prepared in 1985. All survey data was obtained and documented according to FEMA data capture standards including required photos and field sketches of each surveyed structure and cross-section. All data was georeferenced and incorporated into the project database. See Appendix I for survey data including photos and field sketches. The horizontal and vertical datums used were:
Vertical Datum: North American Vertical Datum of 1988 (NAVD88)
Horizontal Datum: North American Datum of 1983 (NAD83)
2.2
Previous Reports and Studies
Table 2-1 below lists watershed study reports that have been collected by the City. Section 2.2.1 contains a short summary of each report.
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Rush Creek Watershed Study Final Report
Table 2-1. Watershed Study Reports Report Name Floodplain Information Rush and Village Creeks Arlington, Texas Flood Insurance Study Arlington Texas, Volume 2 Rush Creek Watershed Management Development Document Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report Rush Creek Tributary 1 Report State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180 Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report Rush Creek Tributary 1; 205 DPR Study Rush Creek Flooding and Sedimentation Study (Final report) Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition Flood Study of Rush Creek for Valista Estates in Arlington, TX Letter of Map Revision Based on Fill (LOMR-F) 2224 Wanda Way, Arlington, Texas Table for Summary of Discharges, floodway data Flood Study for Property located at 2224 Wanda Way Rush Creek, City, Tarrant County Rush Creek and Tributary RC-2 Conditional Letter of Map Revision (CLOMR) Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1 Content Rush Creek Letter of Map Revision (LOMR) Blue Binder: Information on flood data elevation. Comprehensive Stream Management Plan Phase 1 and Phase 2 Report (including photographs and geodatabase) Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary No. 7 – Grace Preparatory Academy Addition
Author U.S. Army Corps of Engineers (USACE) Fort Worth District, USACE Espey, Huston & Associates, Inc.
Date February 1971 July 1972 April 1989
USACE
1991 – 1992
USACE
August 1992 August 1993
Fort Worth District, USACE Fort Worth District, USACE Nathan D. Maier Consulting Engineers, Inc.
March 1994 November 1994 January 2001
G.A. Dixon & Associates
June 2006
Nave Engineering, Inc
June 2007
Morrison Hydrology Engineering, Inc Morrison Hydrology Engineering, Inc
November 2008
Nathan D. Maier Consulting, Engineers, Inc.
October 2009
Caffey Engineering, Inc.
January 2010
Wier & Associates
March 2010
John D. Zimmerman P.E., R.P.S
October 2010
Jacobs Engineering
March 2011
Charles Crook Consulting, Inc.
May 2016
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Rush Creek Watershed Study Final Report
2.2.1
Report Summaries
2.2.1.1
Floodplain Information; Rush and Village Creeks; Arlington, Texas; USACE; February 1971
The Floodplain Information report contains information on the flood conditions along Village Creek below Lake Arlington and Rush Creek. The report is based on rainfall data, runoff data, historical flood heights, current flood heights, and other technical data bearing upon the occurrence and size of floods in the Rush-Village Creek Watersheds. This report includes the following data:
Watershed map
Tables with flood elevations along the studied area
Photos from Rush Creek bridges
Maximum known flood discharges table
Floodplain cross section figure
Index map for flooded areas
Individual flooded areas map for all the locations on the index map
High water profiles for Rush Creek, Village Creek
Cross sections for Rush-Village Creeks
2.2.1.2
Flood Insurance Study Arlington Texas, Volume 2; Fort Worth District, USACE; July 1972
The Flood Insurance Study (FIS) compiles and presents flood risk data for Rush Creek and its tributaries. The FIS revised and updated information regarding the severity of flood hazards in Tarrant County, which includes the Rush Creek Watershed. The FIS contains data relevant to the Rush Creek Watershed Study, including a map index and a preliminary floodway map. 2.2.1.3
Rush Creek Watershed Management Development Document; Espey, Huston & Associates, Inc; April 1989
The study focused on improving the watershed by reducing flood risks. Each reach was summarized for existing and future flooding problems. The study used the U.S. Army Corps of Engineers computer model NUDALLAS (USACE, 1980). This study includes the following data:
Physiographic description of the Rush Creek Watershed
Description of Watershed’s climate, vegetation, wildlife, land use, subsurface geology, soils, erosion, and cultural features.
Table for water quality standards for unclassified streams
Table for water quality data summary for Rush Creek
Reach descriptions and maps for Sublett Creek, Kee Branch, Pantego Branch, Rush Creek and Tributaries KB-1, RC-2, RC-1A, and, RC-1.
Maps for vegetation, geology, soils, cultural features, open space concept
Typical section at all span bridges drawing
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Rush Creek Watershed Study Final Report
Linear park trail – street connection at bridge drawing
Trail & creek in box culvert at street crossing drawing
Natural channel section with linear park improvements drawing
Longitudinal section – typical ramp at bridges drawing
Concrete lined channel section drawing
Grass lined channel section drawing
Maps for the proposed watershed improvement plan, fully-developed conditions flooded structures, and drainage area.
NUDALLAS output for Rush Creek
HEC-2 Outputs for Kee Branch, Pantego Branch, Rush Creek Tributary No. 1, Rush Creek Tributary No.1A, Rush Creek and Sublett Creek.
Flood Profiles for Rush Creek, Stream RC-1, Stream RC-1A, Pantego Branch, Stream RC-2, Kee Branch, Stream KB-1, Sublett Creek,
The study proposed four plans to reduce the flooding in the area. Plan 1 represents a fullydeveloped watershed without watershed flood control improvements. Plan 2 represents a fully-developed watershed with bridge and channel improvements. Plan 3 represents onsite detention in the upper portion of the watershed and fully-developed conditions. Plan 4 contains a regional detention in the upper portion of Rush Creek, Kee Branch and Sublett Creek with fully-developed conditions. Channel and bridge improvements included in Plan 2 are the most cost-effective components of the final plan. 2.2.1.4
Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report; USACE; 1991 – 1992
This report provides detailed information on flooding problems along Rush Creek (Tributary 1) including environmental assessment, findings of no significant impact, US fish and wildlife coordination act, archeological assessment, public notice, and exhibits. This report includes the following data:
Photos of flooded areas
Topographic Map of the study area
Channel analysis performed on HYDRA
HEC-2 output files for existing and improved conditions
Calculations and drawings for culverts, drop inlets
Cross-section drawings
Area map
Survey data
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Rush Creek Watershed Study Final Report
2.2.1.5
Rush Creek Tributary 1 Report; USACE; August 1992
The Rush Creek Tributary 1 Report is a detailed project report, environmental assessment, and feasibility study for Rush Creek Tributary 1. The report includes appendices that include the following data:
Hydrology analysis with SWFHYD Program – input on file
Hydraulics – water surface profiles, 100-year flood limits for existing and with project
Civil Design and Cost Estimating – Site plan drawing, plan and profiles, drop structure plan and profile, and calculations
Geotechnical Data – plan of borings, subsurface profile, logs of borings, environmental site assessment
U.S. Fish and Wildlife Final Coordination Act Report
Real Estate – channel improvement easement, temporary work area easement, road easement
Cultural Resources
Economic Analysis
2.2.1.6
State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180; August 1993
The report provided the following data to support the Rush Creek Watershed Study:
Roadway details sheet
Quantity Summary sheet
General notes and specification data sheets
Plan profile sheet
Culvert layout SH180 at Tributary to Rush Creek sheet
Inlets and storm drains sheet
Culvert end details sheet
Traffic control plan sheet
Permanent Pavement Markers sheet
Precast concrete box culverts sheets
Multiple box culverts sheet
Temporary barrier barrel-mounted guard fence sheet
Metal beam guard fence sheet
Raised pavement markers, reflective pavement markers, traffic buttons and jiggle bar tile sheet
Typical standard pavement markings sheets
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Rush Creek Watershed Study Final Report
Work zone barrier delineation sheet
Combination rail sheet
2.2.1.7
Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report; Fort Worth District, USACE; March 1994
The report provided the following data to support the Rush Creek Watershed Study:
Photos – downstream end of Tributary No. 1, confluence of Tributary No. 1 and Rush Creek
Improvement channel drawings
Bridge computations using WASURO
HEC-2 Outputs – lower subcritical reach, supercritical reach
Design Calculations, existing conditions profiles
High water profile and HEC-2 output
2.2.1.8
Rush Creek Tributary 1; 205 DPR Study; Fort Worth District, USACE; November 1994
The report provided the following data to support the Rush Creek Watershed Study:
Basic storm water pollution prevention plan for construction of Rush Creek Tributary No. 1
HEC-2 outputs for with project conditions and without project conditions
Drop inlet design calculations and profiles
One drop model – drawings and HEC-2 outputs
Basin HEC-2 outputs
Lower Trap drop HEC-2 outputs
Trapezoidal Stilling Basin HEC-2 output, calculations and drawings
Stilling Basin Design HEC-2 output
Hydraulic Design Chart for California Institute Technology type drop structure HEC-2 output and cross-sections profiles
2.2.1.9
Rush Creek Flooding and Sedimentation Study (Final Report); Nathan D. Maier Consulting Engineers, Inc.; January 2001
The study identified 14 elements that can be used to improve the area. Elements 1 to 6 focused on reducing the flood potential in the downstream portion of the study. Elements 8 – 10 focused on a reduction in the upstream portion and Elements 7 and 11 – 14 provided benefits throughout the project area. These elements consisted of sedimentation removal in Rush Creek Channel, removal or modification of the existing dam, modifications in the channel (widening), creation of a levee/floodway system downstream of Pioneer Parkway, maintenance of Rush Creek Relief Channel, expansion of the relief channel, improvements on the relief channel/bridge, channel restoration upstream of Pioneer Parkway, widening the Woodland Park Boulevard bridge,
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Rush Creek Watershed Study Final Report
channel improvements upstream of Pioneer Parkway, on-channel detention, sedimentation basin, debris removal, and structure relocation. The study describes all the alternatives in detail. HEC-1 was used to analyze the alternatives. Each alternative is composed of a combination of the 14 elements. The report contains:
Topographic Map with Cross Section Locations
Flood photographs along Shady Valley, Woodland Park Bridge, Rush Creek Channel (in 1980 and 1999)
Exhibits with Floodplain Limits and Local Flooding Information
Exhibits with improvement elements
Exhibit for the main (i.e. bank to bank) channel configuration of Rush Creek
Exhibits showing Rush Creek floodplain – existing Conditions
Exhibits showing the Selected Alternative
The study concluded that these alternatives will provide a reduction of the 100-year floodplain elevation. The alternatives providing the greatest benefit in reducing the existing flood elevation contains restoration upstream of Pioneer Parkway with the main channel. 2.2.1.10 Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition; G.A. Dixon & Associates; June 2006
Study established the 100-year floodplain limits and the easement to satisfy city criteria for SWSMP and establish minimum finished floor elevations.
Existing channel hydraulics description for the channels immediately south and north of the Wanda Way Bridge and Wanda Way Addition.
Cross-Sections along the study area
FIRM map of the study area
25 year, 100 year floodplain and easement of Wanda Way Addition
CD – HEC-RAS model
HEC-RAS output report
2.2.1.11
Flood Study of Rush Creek for Valista Estates in Arlington, Texas; Nave Engineering, Inc.; June 2007
Study delineated the existing and ultimate conditions for 100-year floodplain through the Valista Estates. The flood study was performed for the existing, proposed (with development), and ultimate (the watershed fully developed) conditions for the 25-year and the 100-year storm events. The study provides sufficient data to delineate the ultimate development 100year floodplain in addition to the following data:
HEC-1 output for existing and proposed 10-year, 25-year, 50-year, 100-year, and 500-year conditions
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Rush Creek Watershed Study Final Report
HEC-1 output for ultimate 100-year
HEC-2 effective and effective floodway outputs.
HEC-RAS effective and effective floodway outputs
HEC-RAS revised existing condition and floodway outputs
HEC-RAS for proposed condition and floodway outputs
HEC-RAS for ultimate condition output
HEC-RAS for unnamed tributary output
Location, drainage area, effective FIRM, land use, soil and work map
HEC-2 and HEC-RAS for Rush Creek and Unnamed Tributary
2.2.1.12 Letter of Map Revision Based on Fill (LOMR-F); Morrison Hydrology Engineering, Inc.; Table for Summary of Discharges and Floodway Data
This LOMR-F provides the following data to support the Rush Creek Watershed Study:
FIRM
HEC-2 Partial FEMA effective model output
Property Information Form
FIRM with location of the property
Elevation Form
Survey Map
Community Acknowledgement Form
2.2.1.13 Flood Study for Property Located at 2224 Wanda Way, Rush Creek, City, Tarrant County; Morrison Hydrology Engineering, Inc.; November 2008
This study was conducted to fill an area under a proposed structure to ensure that the lowest adjacent grade is above the FEMA 100-year floodplain and the finished floor is 2 feet above the 100-year ultimate condition floodplain. The study concluded that the structure should be elevated on the property compacted fill to the required elevation. This study provided the following data to support the Rush Creek Watershed Study:
Table comparing FEMA and Proposed Fill condition flood elevations
HEC-2 Partial FEMA effective model output
Table for Summary of Discharges, floodway data
FIRM
Preliminary FIRM
Ultimate Condition 100 year HEC-2 output
Ultimate Development Map
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Rush Creek Watershed Study Final Report
Ultimate Condition Floodplain and Floodway Delineation for 100 year and 100 year ultimate map
Proposed Condition With Fill HEC-2 output
Proposed Condition with Fill Cross-sections map showing 100 year and 100 year ultimate
Proposed Condition with Fill water surface profiles for 100 year and 100 year ultimate
Proposed Condition with Fill 100 year floodplain and floodway delineations
2.2.1.14 Rush Creek and Tributary RC-2; Conditional Letter of Map Revision (CLOMR); Nathan D. Maier Consulting Engineers, Inc.; October 2009
The project provided flood control and protection against erosive forces for Rush Creek and Tributary RC-2. The study area for Rush Creek extends from the downstream side of Pioneer Parkway to 1,200 feet upstream of Woodland Park Blvd with Tributary RC-2 extending from the center of Rush Creek to 650 feet upstream to Creekside Drive. The proposed flood reduction plan includes a flat lined channel bottom with a varying bottom width of approximately 120 feet to 60 feet with 4:1 side slopes. The modifications reduced the water surface elevation throughout the reach and reduced the risk of flooding residential structures. The project provided the following data:
Location of the project map
Comparison of HEC-2 and Pre-Project HEC-RAS
Floodway analysis performed for post-project HEC-RAS
Includes the CLOMR
Riverine Hydrology & Hydraulic Forms
Riverine Structures Form
Pre-project and Post-project FIRMs
Effective FEMA Model - HEC-2 Results from 27 August 1986
Pre-Project and Post Project HEC-RAS results for Rush Creek and Tributary RC-2
Digital data – CD containing:
USACE.pdf with the HEC-2 results
HEC-RAS models for Rush Creek and RC-2
CLOMR workmap.dwg
2.2.1.15 Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1; Caffey Engineering, Inc.; January 2010
This report is a LOMR for significant modifications along the north of the Union Pacific Railroad. Modifications include construction of new culverts, replacement of the natural channel with a trapezoidal structure. The upper portion of the channel is lined with pavement while the lower portion is unlined; an industrial park was also developed in this area. This report provided the following data to support the Rush Creek Watershed Study:
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Rush Creek Watershed Study Final Report
Basin Map
CD and printed output containing:
RushCreek.pdf – multiple profiles and floodway output files.
P20RC1.OH2 – duplication multiple profile output report.
P21RC1.OH2 – duplication floodway output report.
HEC2RAS.rep – HEC-RAS report for multiple-profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
RC1HEC2RAS.rep – HEC-RAS report for floodway profile HEC-2 conversion to HECRAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
FixedQs.rep – Existing conditions multiple-profile model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street, and channelization downstream of Division Street.
RC1FW.rep – Existing conditions floodway model for RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street, and channelization downstream of Division Street
IndPkBp3.rep – Multiple-profile model of Division Street weir flows that enter the industrial park rather than returning to the main channel for existing conditions.
ZoneAbypass.rep – Existing conditions: Multiple-profile model of bypass flows that leave the main channel and flow westward along the south side of the Union Pacific Railroad not to return to the main channel. This model facilitates detailed mapping of the bypass channel which is currently mapped Zone A.
P20RC1.DAT – Duplication multiple profile output report.
P21RC1.DAT – Duplication floodway output report.
HEC2RAS – HEC-RAS report for multiple-profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
RC1HEC2RAS – HEC-RAS report for floodway profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
FixedQs – Existing conditions multiple-profile model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street and channelization downstream of Division Street.
RC1FW – Existing conditions floodway model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street and channelization downstream of Division Street.
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Rush Creek Watershed Study Final Report
IndPkBp3 – Multiple-profile model of Division Street weir flows that enter the industrial park rather than returning to the main channel for existing conditions.
ZoneAbypass – Existing conditions: Multiple-profile model of bypass flows that leave the main channel and flow westward along the south side of the Union Pacific Railroad (UPRR) not to return to the main channel. This model facilitates detailed mapping of the bypass channel which is currently mapped Zone A.
Overview and Concurrence form, Riverine Hydrology & Hydraulics Form, and Riverine Structures Form.
Rush Creek Tributary No. 1(RC-1) Photos, Zone A Photos
RC-1 copy of the currently effective FIRM
RC-1 FIRM and Flood Profiles for existing conditions
Delineation Map for Rush Creek Tributary 1 and Zone A
Newspaper from Sunday, May 8, 2011 with the Public Notice
Rush Creek RC-1 01-2011 CD contains pdfs of maps in the report
Rush Creek RC-1 CD contains CAD drawings in the report
2.2.1.16 Rush Creek Letter of Map Revision (LOMR); Wier & Associates; March 2010
The study showed that prior to the construction of the Pleasant Ridge Road improvements some single family residential lots upstream were at a great risk of flooding. The revisions included the removal of an old bridge and the construction of a twin leaf concrete arch bridge with a span of 66 feet and an estimated height at the center line of over 22 feet. The study provided the following data:
HEC-2 CD containing input files for Rush Creek pre-project and post project for the project area and floodway.
Overview and Concurrence Form
Riverine Hydrology & Hydraulics Form
Riverine Structures Form
FIRM
Tables and flood profiles from FIS
Property owner notification letters
NGS data sheet
Swiss Avenue grading plan and LOMR-F
Site gradating and pond layout
Pre-project and post Profile
Fill Compaction and Soil Boring Report
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Rush Creek Watershed Study Final Report
2.2.1.17 Blue Binder: Information on Flood Data Elevation; John D. Zimmerman P.E., R.P.S.; October 2010
The binder contains printed pictures, flooding data information and four CDs for impacted residences. The flooding information contains state plane coordinates, elevation of high water, and finish floor elevations for all residences listed below. The flooding information sheet is also provided in pdf format on the CD. The binder includes an article on the flood of 1989.
Pictures CD Flood Data Pictures 5-11-2011 2905 Lakeshore Dr 3434 Indian Trail 4700 Westhaven Rd 7600 Sharon Lee
Rush Creek Tributary 1 Flood – Sep. 8, 2010 CEI/JEC CD
Photos from different locations
Cit of Arlington additional files CD
Flood Photos 1841 South Park 1845 South Park 1847 South Park 1901 Woodridge
CD
Rush Creek Flood 2010 Castle Pines Valleywood Houses 2015, 2115, 2121, 2127 Woodland Park Houses 4028, 4038, 4042, 4044 Creekside Creekside Houses 2001, 2101, 4304, 4306 Division Street Forest Edge north and south Hill Valley
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Rush Creek Watershed Study Final Report
1817 Hillvalley Shady Creek Shady Creek Houses 3701, 3807 Shady Valley Shady Valley Houses 4150, 4152, 4155, 4157, 4159, 4161, 4166, 4168 Sheffield Sheffield Houses 3309, 3401, 3403 3403 contains a movie South Park South Park Houses 1821, 1823, 1824, 1825, 1828, 1829, 1831 – 1841, 1845, 1847 Valley Crest Valleycrest Houses 2101 – 2112, 2114, 2115 Valleywood Valleywood Houses 2000 – 2002, 2004 – 2006, 2008 – 2010, 2012 – 2014,
2016 – 2018, 2100 – 2102, 2104 – 2106, 2108 – 2110, 2112 – 2114 West Fork WestFork Houses 407, 411, 416 Willows at Shady Valley Apartment Apartments 1700, 1702, 1704, 1706, 1710, 1712, 1714, 1800, 1802, 1804, 1806,
1808, 1810, 1812, 1814, 1900, 1902, 1904, 1906, 1908, 1910, 1914, 1916, 1918, 1920, 1922, 1924, 1926, 1928 Winewood Winewood House 1902 Woodland Park Ct Woodland Park Houses 4200 – 4209 Woodland Park Dr Woodland Park Houses 4225, 4228, 4230, 4300, 4301 – 4304, 4306, 4308 Woodridge Woodridge Houses 1818, 1820, 1901, 1903, 1905
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Rush Creek Watershed Study Final Report
2.2.1.18 Comprehensive Stream Management Plan; Phase 1 and Phase 2 Report; Jacobs Engineering; March 2011
Phase 1 of the Comprehensive Stream Management Plan involved collecting information on existing storm water related programs, updating the drainage concern database, evaluating existing design criteria, development of a repetitive loss structure inventory, as well as Hazard Mitigation Grant Program (HMGP) and Repetitive Flood Claims grant applications. Phase 2 consists of system condition assessments.
Watersheds addressed in the report: Cottonwood Creek, Fish Creek, Johnson Creek, Kee Branch, Lower Rush Creek, Lynn Creek/Bowman Branch, Upper Rush Creek, Village Creek, West Fork Trinity
Interviews were conducted with the following municipalities: City of Austin, City of Dallas, City of Denton, City of Farmers Branch, Town of Flower Mound, City of Fort Worth, City of Garland, City of Grand Prairie, Harris County Flood Control District, City of Killeen, City of Mesquite, City of Plano, City of Richardson, and, City of San Antonio
Each watershed has a section that includes a description of the watershed, the drainage concern, threatened structures, infrastructure, utilities, retaining walls, trees, and, amenities. A brief conclusion for each watershed is also included.
In addition, the report includes a table with a summary of municipal natural channel maintenance programs, photographs and a geodatabase.
2.2.1.19 Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary Number 7 – Grace preparatory Academy Addition, Charles Crook Consulting, Inc., May 2016
The report details hydrologic and hydraulic impacts of an addition to Grace Preparatory Academy. The development primarily affects Rush Creek Tributary No. 7 and has a minimal impact on Rush Creek. The project included relocation and channelization of 290 linear feet of Tributary No. 7, construction of several buildings in the Tributary No. 7 overbank, and minor grading changes in the Rush Creek floodplain. This report provided the following data to support the Rush Creek Watershed Study:
2.3
Existing conditions workmap
Proposed condition workmap
Storage exhibits for existing and proposed conditions
Cross Sections
Grading Plan
CD containing supporting hydraulic and hydrologic modeling
Flood Insurance Study
The current effective Flood Insurance Study (FIS) for Rush Creek is the Tarrant County, Texas FIS dated September 25, 2009. According to the study, the underlying hydrologic and hydraulic analysis was completed in September 1985. The FIS identified thirteen Rush Creek tributaries as “Detailed Study Streams”. These streams and their reported studied lengths are listed in Table 2-2.
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Rush Creek Watershed Study Final Report
Table 2-2. Detailed Study Streams. Detailed Study Streams
Length (miles)
Rush Creek
14.0
Sublett Creek
4.4
Northeast Tributary
0.1
Forest Park Tributary
0.1
Rush Creek Relief
0.7
Stream RC1
1.7
Stream RC1A
0.7
Stream RC2
1.0
Ryan’s Branch
0.9
Twin Springs Draw
0.5
Pantego Branch
1.8
Kee Branch
5.4
Stream KB-1
0.9
The detailed study streams are mapped with defined Base Flood Elevations (BFE) and have regulatory floodways. Floodways were not defined for Northeast Tributary and Forest Park Tributary. These streams were redelineated during the 2009 countywide remapping and no additional engineering analysis was conducted. An Engineering Data Request (EDR) was submitted to FEMA to attempt to obtain the original hydrologic models, but the models were not included in the data provided. Digital copies of an HEC-2 model of the Rush Creek Mainstem were provided that appeared to be part of a 1998 LOMR.
2.4
Hydrologic and Meteorologic Data
Searches of the web sites of the National Weather Service and the US Geological Survey were conducted to gather historical stream flow and rainfall data that could prove to be useful in the study. Design rainfall depths were obtained from the National Weather Service and North Central Texas Council of Governments (NCTCOG) and reviewed for use in the study. There are no USGS stream gauging stations in the Rush Creek Watershed nor are there any hourly rain fall recording stations. The nearest rainfall station with sub-daily data is located at Arlington Airport.
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Rush Creek Watershed Study Final Report
The 24-hour design storm rainfall estimates for Tarrant County are provided in Table 2-3. Estimates have been obtained from TP-40 (Hershfield, 1961) and the NCTCOG iSWM Hydrology manual (2010). Although the TP-40 estimates are extremely old, recent studies such as Asquith (2004) indicate that the TP-40 extreme rainfall depths are clearly within the margin of error for such estimates. If anything, it appears that estimates of extreme rainfall in north Texas has decreased slightly in the past 50-years. Due to the future uncertainty posed by long-term climate variability, it is recommended that the TP-40 estimates be employed in the Rush Creek Study. Table 2-3. Estimated 24-hour Storm Depths (inches) for Tarrant County Texas. Storm
NWS TP-40
iSWM
1-year
3.15
2.64
2-year
3.95
3.36
5-year
5.33
4.56
10-year
6.32
5.52
25-year
7.47
6.72
50-year
8.45
7.92
100-year
9.47
9.12
500-year
11.47
12.96
For the 24-hour evaluations, rainfall will be distributed using a nested frequency storm distribution as shown in Figure 2-1; this distribution was created using the TP-40 100-year storm frequencies.
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Rush Creek Watershed Study Final Report
2.2 2.0 1.8 1.6 Rainfall (inches)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0:00
2:00
4:00
6:00
8:00
10:00 12:00 14:00 16:00 18:00 20:00 22:00
0:00
Time
Figure 2-1. Tarrant County 24-hr Distribution of 100-yr Storm (based on the frequency storm method) Rainfall for September 7-8, 2010 event (Tropical Storm Hermine recorded at Arlington Municipal Airport) is shown in Figure 2-2 and this storm may be used for model calibration/validation purposes.
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Rush Creek Watershed Study Final Report
Arlington Airport, September 7-8, 2010 Storm Event (15 minute) 0.50 0.45 0.40
Rainfall (inches)
0.35 0.30 0.25 0.20 0.15 0.10 0.05 0:00 1:15 2:30 3:45 5:00 6:15 7:30 8:45 10:00 11:15 12:30 13:45 15:00 16:15 17:30 18:45 20:00 21:15 22:30 23:45 1:00 2:15 3:30 4:45 6:00 7:15 8:30 9:45 11:00
0.00
Time
Figure 2-2. Arlington Airport, September 7-8, 2010 Storm Event (15 minute)
2.5
Public Meeting
On February 16, 2012 the City Department of Public Works and Transportation: Stormwater Management Division hosted a public meeting at the City Fire Training Center. The purpose of this public meeting was to inform the public of the purpose of the Rush Creek Watershed Study and to collect information. A handout provided at the meeting (see Appendix C) said: “What You Can Do to Help: Your knowledge of flooding and erosion is indispensable to making our study as accurate as possible. Please tell us flooding or erosion issues on your property, on properties around you or on public property/streets near you. Photos or information about depth of the water during past floods are also welcome.” Information collected during this meeting was used to locate high water marks, flooding concerns, and to understand residents’ view of flooding risks in the watershed. A second public meeting will be scheduled to present study results to the public and to explain the significance of these results to the public.
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Rush Creek Watershed Study Final Report
3.
Hydrologic Analysis
This section summarizes the study methods and results of the hydrologic modeling effort performed by Halff Associates, Inc. The purpose of the hydrologic modeling is to simulate flooding and evaluate existing land use conditions for the 50, 20, 10, 4, 2, 1, and 0.2 percentannual-chance storm events and the ultimate land use conditions for the 1 percent-annualchance flood event. Hydrologic analyses have been conducted for the Rush Creek Watershed as part of the comprehensive watershed study and model updates. The entire watershed was analyzed for the following hydrologic scenarios:
Existing Land Use Conditions, and
Ultimate Land Use Conditions.
HEC-HMS v3.5 was utilized to create hydrologic models. The results of this modeling effort were utilized to develop steady and unsteady hydraulic models to determine flood elevations corresponding to the 50, 20, 10, 4, 2, 1, and 0.2 percent-annual-chance events. Significant rainfall events considered for the hydrologic models were the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent-annual-chance events. Detailed watershed delineations, existing and ultimate land use determinations, and the hydrologic soil coverage were used to develop HEC-HMS hydrologic computer models for the respective tributaries’ watershed. The Rush Creek Watershed Technical Standards along with Urban Hydrology for Small Watersheds, Technical Release 55 (TR-55) Second Edition were used as guidelines for developing parameters used in the new 2012 hydrologic analyses.
3.1
Subbasin Delineation
Subbasin delineations were generated using ESRI’s ArcGIS Version 10.0 based on the Texas Natural Resource Information Systems (TNRIS) 2009 Light Detection and Ranging (LiDAR) Terrain Data. Digital storm sewer lines supplied by the City, supported by current aerial photography, aided in the subbasin delineation process. Subbasins in the range of 60 to 100 acres were recommended by the Technical Standards; the majority of basins fell within this range. Figure 3-1 depicts the subbasin delineations.
3.1.1 Topographic Data Acquisition and Evaluation Topographic data covering the project extent was obtained from the TNRIS 2009 LiDAR acquisition project. This data was available as LiDAR point clouds in the American Society of Photogrammetry and Remote Sensing (ASPRS) common LiDAR Data Exchange Format (LAS 1.1) with 1.0 meter post spacing.
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Rush Creek Watershed Study Final Report
Figure 3-1. Subbasin Delineation
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Rush Creek Watershed Study Final Report
Data was acquired in March 2009 by Fugro Earth Data, Inc. Fugro performed this work under subcontract to Dewberry who served as the prime contractor to the Texas Water Development Board for the LiDAR Acquisition Project. The LiDAR Quality Assurance Report provided by Dewberry is included in Appendix D. This data was acquired and processed to meet 0.185 meter Root Mean Square Error (RMSEz) vertical accuracy and was tested to have an RMSEz of 0.040 meters using National Standards for Spatial Data Accuracy (NSSDA) and FEMA methodology (see Table 1 of the LiDAR Quality Assurance Report).
3.1.2
Terrain Processing
The LiDAR data was processed with ESRI’s ArcGIS software. The LiDAR data was acquired in Universal Transverse Mercator (UTM), North American Datum of 1983, (NAD83 Meters) with heights in the 1988 North American Vertical Datum (NAVD88 Meters). Each LiDAR tile was projected to State plane NAD83, Texas North Central zone with horizontal units of feet and the vertical units were also converted from meters to feet. The project LiDAR point clouds were then processed in ArcGIS and the ground points were placed into a multipoint feature class within a file geodatabase. The multipoint feature class was then used to generate a seamless terrain dataset within the same file geodatabase. From the terrain dataset, a ground surface Digital Elevation Model (DEM) was generated to support basin delineations and hydrologic modeling.
3.2
Precipitation Data
Rainfall data was obtained from TP-40 (Hershfield, 1961) for the 24-hour storm events corresponding to the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent-annual-chance storm events. The rainfall data is summarized in Table 3-1. Table 3-1. Rainfall Depth-Duration-Frequency Data (inches) Storm Duration
Frequency (Percent Annual Chance)
5 Min
15 Min
1 Hr
2 Hr
3 Hr
6 Hr
12 Hr
24 Hr
50%
0.40
1.02
1.77
2.15
2.37
2.86
3.43
3.95
20%
0.54
1.38
2.39
2.90
3.19
3.86
4.63
5.33
10%
0.64
1.64
2.84
3.44
3.79
4.58
5.49
6.32
4%
0.76
1.94
3.35
4.06
4.48
5.41
6.49
7.47
2%
0.86
2.19
3.79
4.59
5.06
6.12
7.34
8.45
1%
0.96
2.46
4.25
5.15
5.67
6.86
8.23
9.47
0.2%
1.16
2.98
5.15
6.24
6.87
8.31
9.96
11.47
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Rush Creek Watershed Study Final Report
3.3
Depth-Area Reduction Factors
Typically, areal reduction factors (ARF) are applied to rainfall depths when the tributary area exceeds 10 square miles to account for the fact that average storm depths over a large area are less than a point rainfall of equal probability of occurrence. Potential reduction factors for Rush Creek were estimated according to the method of Leclerc and Schaake (1972) which is a formula designed to reproduce the graphed values in TP-40. These estimates are shown in Table 3-2 and ARF for areas less than 10 square miles have been set equal to 1.0. Table 3-2. Rush Creek ARF Estimates 1
Location
Cumulative Drainage Area (acres)
Rush Creek at Sublett Road Rush Creek at Indian Trail Rush Creek above the Kee Branch Confluence Rush Creek at W Division Street
1
Cumulative Drainage Area (sq. miles)
Storm Duration (hours)
Estimated Areal Reduction Factor
5,880
9.2
24
1.00
11,070
17.3
24
0.97
15,640
24.4
24
0.96
19,830
31.00
24
0.95
Kee Branch (outfall)
4,570
7.1
24
1.00
RC-1 (outfall)
2,280
3.6
24
1.00
As indicated in Table 3-2, the ARF is 1.0 for most of the modeled reaches and varies from 0.97 to 0.95 along the Rush Creek mainstem between Sublett Road and the confluence. In unsteady flow there is no possible way to vary a rainfall reduction factor along a reach as can be done in steady flow. Furthermore, in steady flow studies, peak flows are assumed to occur simultaneously throughout the entire reach which produces a conservative outcome. As this study is using unsteady flow, it is determined that the 3 to 5 percent reduction in rainfall was not justified nor necessary for the limited area over which it would be applied. Doing so would require multiple model runs to obtain flows and stages for particular reaches. A test analysis showed that the maximum ARP would reduce maximum discharges in lower Rush Creek by about 1,000 cfs and maximum stages by about 0.3 feet. These values are well within the estimation error for modeled stream discharges and stages consistent with the differences between steady and unsteady flow.
3.4
Runoff Volume
The loss rate of rainfall, caused by evaporation, interception, depression, storage, and infiltration, is typically evaluated and subtracted from the rainfall to determine rainfall excess for each time increment of a storm. For this study, the SCS Curve Number Method, developed by the Natural Resources Conservation Service (NRCS), was used to develop flood hydrographs based on land use, soil classification, and antecedent moisture conditions. Baseline Curve Numbers were obtained from TR-55, Table 2.2c, for pasture, grassland, or
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Rush Creek Watershed Study Final Report
range land. Curve Numbers (CN) were computed based on a composite percentage of soil types within each subbasin. Group A soils were defined as having a CN of 39, Group B soils were defined as having CN of 61, Group C soils were defined as having CN of 74, and Group D soils were defined as having CN of 80. The antecedent moisture condition (AMC) defines the soil moisture condition prior to a storm. AMC-II, average soil moisture conditions, was used for the watershed study. Basin parameters are presented in Appendix B. The initial abstraction (I.A.) for all watersheds was computed for AMC-II, average soil conditions using the following equation from TR-55:
1000 IA = 0.2 − 10 CN 3.4.2 Land Use Classification Land use for the Rush Creek Watershed has been determined for both existing and ultimate conditions. Table 3-3 shows the land use categories and corresponding impervious percentages used for this study. Refer to the Technical Standards in Appendix A for sources of these impervious area percentages. Watershed conditions dictated that the percent impervious values provided in the Technical Standards be supplanted by the values shown in Table 3-3 for Extremely Low Density Residential, Very Low Density Residential, Major Transportation, Institutional, and Mobile Home land use categories. A composite percentage of impervious area was computed using the land use contained in each subbasin for both existing and ultimate conditions. Table 3-3. Land use and Percent Impervious Impervious (%) Conditions
Land Use Description Extremely Low Density Residential (2+ acre lots)
15
Very Low Density Residential (1 acre lots)
25
Low Density Residential (1/2 acre lots)
40
Medium Density Residential (1/3 acre lots)
45
High Density Residential (1/4 acre lots)
50
Major Transportation
50
Industrial
72
Institutional
50
Group Quarters
40
Hotel/Motel
85
Mobile Home
35
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Rush Creek Watershed Study Final Report
Table 3-3. Land use and Percent Impervious Impervious (%) Conditions
Land Use Description
3.4.2.1
Multi-family
65
Office
85
Parks/Recreation
6
Retail
85
Under construction
50
Utilities
60
Vacant
3
Water
100
Existing Conditions Land Use
The existing land use conditions were based on 2005 NCTCOG existing land use data provided in shapefile format. The land use shapefile was updated to reflect current development conditions shown on the City aerial photography (2011). The existing conditions land use for the Rush Creek Watershed is illustrated in Figure 3-2. 3.4.2.2 Ultimate Conditions Land Use
Ultimate conditions land use data was not available for the project area. Based on discussion with the project team and the City, an impervious value of 75 percent was applied to all vacant and extremely low density residential land use to estimate the ultimate build out conditions of the watershed. All other land use remained consistent with the existing land use conditions.
3.4.3 Hydrologic Soil Groups The NRCS Soil Survey of Tarrant County (2009) was used to evaluate the hydrologic soils in the Rush Creek Watershed. In general, the watershed is underlain by B, C, and D soils in nearly equal proportions. The most prevalent soil type in the watershed is Group D which consists of clayey soils with slow infiltration rates and high potential for runoff. The second most prevalent soil type is Group B which consists of soils characterized as having some content of gravelly sand with moderate infiltration rates and low to moderate runoff potential. The third most prevalent soil type in the watershed is Group C which indicates soils having moderately fine to fine texture and slow infiltration rates. A small percentage of soils in the watershed are identified as Group A which indicates soils having high infiltration rates and low runoff potential. Table 3-4 includes a list of the NRCS Soil Survey Geographic Database (SSURGO) Hydrologic Soil Group (HSG) classifications for each Rush Creek sub-watershed. Hydrologic soils in the Rush Creek Watershed are illustrated on Figure 3-3.
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Rush Creek Watershed Study Final Report
Figure 3-2. Existing Land Use
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Figure 3-3. Soils
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Table 3-4. Watershed Soil Classification Hydrologic Soil Type Percentage A
B
C
D
Kee Branch
3
38
29
30
Lower Rush Creek
13
43
18
26
Middle Rush Creek
4
25
18
53
Stream RC-1
2
41
28
28
Upper Rush Creek
3
29
17
50
3.5
Runoff Hydrographs
The SCS Dimensionless Unit Hydrograph method was used and SCS lag times were computed for each subbasin to generate runoff hydrographs. A different time of concentration was computed for existing and ultimate conditions. Both were based on the NRCS TR-55 methodology for overland (sheet) flow, shallow concentrated flow, and channel flow. Overland flow length was limited to a maximum of 100 feet for unpaved surfaces and 50 feet for paved surfaces. Travel times for channel flow were based on velocities from the HEC-RAS routing models, where available. Channel flows for non-routed reaches were estimated based on Manning’s equation, assuming a bankfull depth that was selected based on the channel geometry and the elevation corresponding to the natural channel banks. For improved channels, it was often difficult to estimate the bankfull depth from the channel geometry and some consideration was given to the expected bankfull (2-year) discharges and anticipated velocities associated with bankfull flow. Storm drain velocities were assumed to be six feet per second for the purposes of this study. Based on the recommendation of the project team, the stream channels being modeled using unsteady HEC-RAS were removed from the time of concentration calculations. A memorandum, entitled “Flow paths for estimating Basin Lag Time”, supporting this decision is provided in Appendix B. The time of concentration is the summation of these phases, where: Tc = tsheet + tshallow concentrated + tstorm drain + tchannel Lag times were computed using the following equation: Tp = 0.6*Tc The ultimate conditions times of concentration were estimated by changing overland flow located in vacant land use to be a maximum of 50 feet and paved. All shallow concentrated
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Rush Creek Watershed Study Final Report
flow was changed to paved for ultimate conditions. These two changes were intended to estimate the impacts of future development to times of concentration.
3.6
Routing
The Modified Puls routing method was utilized in HEC-HMS for all steady state, Zone A reaches. In addition to the studied Zone A reaches, a handful of channel reaches that were not included in the study were also included in the HEC-HMS analysis to facilitate modeling of unsteady HEC-RAS reaches. The Modified Puls routing method was also used for these additional reaches. HEC-RAS v4.1 was used to develop storage-discharge relationships for a range of routing flows for studied and unstudied steady state reaches. The HEC-RAS models were generated using cross sections based on the TNRIS LiDAR data. The sub-reaches (routing step) calculations are provided in Appendix B. Channel routing was performed in HEC-RAS for all unsteady reaches. The Muskingum-Cunge method was used to route flows through storm drain reaches outside of the new unsteady hydraulic study reaches. An equivalent pipe diameter size was calculated for most reaches based on a weighted average of the pipe size and length through the reach. The equivalent pipe diameter was input in the HEC-HMS models and a note was added in the description of these routing reaches to specify when this method was applied. Routing parameters are presented in Appendix B.
3.7
Hydrologic Analysis Results
The hydrologic model results from the Rush Creek HEC-HMS models consist primarily of unrouted runoff hydrographs through the detailed, Zone AE studied reaches. As such, the results from the HEC-HMS models used for the detailed study reaches are not directly comparable with previous hydrologic studies that included routed hydrographs. Therefore, the resulting maximum discharges for the detailed study reaches are presented with the hydraulic analysis in Table 4-2.
3.8
Quality Control
The project team established a rigorous set of quality assurance and quality control procedures for the development of the Rush Creek Watershed Study. Quality control for the hydrologic analysis met requirements established in the Technical Standards and the Rush Creek Quality Control Plan. All submittals were reviewed by the PMC to ensure quality work products. In addition, Halff Associates, Inc. implemented internal quality control to ensure deliverables were accurate and of the highest quality prior to submitting to the PMC.
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Rush Creek Watershed Study Final Report
4.
Hydraulic Analysis
Hydraulic modeling was performed in 2013 by AECOM, Dewberry, and Michael Baker Corporation utilizing unsteady HEC-RAS and subsequently reviewed by CDM Smith (the Project Management Consultant). Halff Associates was contracted by the City of Arlington to finalize the HEC-RAS models, beginning with the HEC-RAS models completed by the referenced hydraulic modeling consultants. All streams were initially studied using unsteady HEC-RAS and consisted of 5 total HEC-RAS models; one for each major sub-watershed. Halff Associates separated out each study stream to individual HEC-RAS models and converted all Zone A study streams to steady state. This section of the report summarizes the final study methods and results of the hydraulic modeling performed by Halff Associates.
4.1
Introduction
All 1-D hydraulic modeling was performed using HEC-RAS version 4.1.0 while a single 2-D hydraulic model was performed in HEC-RAS version 5.0.3. Unsteady HEC-RAS was chosen for the detailed study streams for its flexibility and convenience in complex systems, particularly those containing flow diversions and storage facilities. The extent and location of each modeled reach is shown in Figure 4-1. The detailed study models were all newly constructed from the survey data and GIS data assembled for this project. All modeling was performed to comply with Appendix C of the FEMA guidelines and standards. Additional modeling guidelines for this study were written to supplement the FEMA guidelines in matters specific to unsteady HEC-RAS. These guidelines are provided in the Rush Creek Watershed Technical Standards (see Appendix A).
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Rush Creek Watershed Study Final Report
Figure 4-1. Modeled Stream Reaches
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Rush Creek Watershed Study Final Report
4.2
HEC-RAS Model Development
4.2.1
Stream Centerlines and Cross-Sections
The model geometry development process began with defining the extents to be modeled as depicted in Figure 4-1 and then defining the stream centerline for each modeled reach. Initially, the stream centerlines were developed to follow the flow path defined in the topography. Later, during cross-section input, several differences in channel location between the 2011 terrain data and the 2012 survey were identified. The stream centerlines were adjusted where needed to match the 2012 survey and keep them within the channel banks. With preliminary stream centerlines established, the next step was to determine the hydraulic structures that would be represented and to lay out the model cross-section locations. All significant hydraulic structures were to be included in the models. Field reconnaissance walks were conducted along each reach to identify significant structures. Next, cross-section locations were located along each reach. Cross-sections were required at the approach and departure of each structure and within 500 feet of any confluence (junction of two streams). Once these cross-section locations were established, additional channel cross-sections were laid out at 500 - 800 foot intervals. Cross-sections were cut from the project topography using HEC-GeoRAS which was also used to extend the survey cross-sections. Stream reaches studied in limited detail were not surveyed, and instead used GeoRAS cross-sections derived from the terrain data.
4.2.2 Structures Bridge, culverts and in-line structures were represented in the model according to the procedures described in the HEC-RAS Hydraulic Reference Manual (HRM) and Application Guide. In the detail study reaches the geometric data describing each structure was obtained from the field survey data. This data includes culvert sizes and spacing, low and high chords of bridges and pier shapes and sizes. Culvert entrance and exit coefficients and drag coefficients for piers were determined from tables in the HRM. Weir coefficients for the overflow sections on bridges and culverts were generally set to a value of 2.6 or less. Inline structures with well-defined crest sections were assigned a weir coefficient of 3.0. In limited detail reaches, bridges and culverts were input based on measurements in the field during the field reconnaissance and the overtopping section was measured from the project topography.
4.2.3 Manning Roughness Coefficients Manning roughness coefficients (“n values”) for the Rush Creek Watershed Models were assigned in accordance with Table 3-1 of the HEC-RAS Hydraulics Reference Manual. Proper assignment of Manning roughness coefficients begins with well-defined bank stations. These were located in each cross-section at a break in ground slope that divides the channel from the floodplain. A single n value was assigned to each channel section and one or more n values were assigned to the floodplain or overbank sections. The n values assigned to each study stream are listed Table 4-1.
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Rush Creek Watershed Study Final Report
Table 4-1. n values Stream Reach
Channel “n” Value
Overbank “n” Value
Forest Park Tributary Kee Branch Kee Branch Tributary 1 Kee Branch Tributary 1.1 Kee Branch Tributary 2 Kee Branch Tributary 4 Kee Branch Tributary 5 Northeast Tributary Pantego Branch Rush Creek Rush Creek Relief Channel Rush Creek Tributary 4 Rush Creek Tributary 4.1 Rush Creek Tributary 5 Rush Tributary 7 Rush Tributary 7.1 Rush Tributary 8 Rush Tributary 9 Rush Tributary 10 Rush Tributary 10.1 Rush Tributary 10.2 Rush Tributary 10.3 Rush Tributary 10.4 Rush Tributary 11 Rush Tributary 12 Rush Tributary 13 Rush Tributary 14 Rush Tributary 15 Rush Creek Tributary 16 Rush Creek Tributary 17 Rush Creek Tributary 19 Ryan’s Branch Ryan’s Branch Tributary 1 Stream KB-1 Stream KB-1.1 Stream RC-1 Stream RC-1 North Diversion Channel Stream RC-1 West Diversion Channel Stream RC-1 Tributary 1 Stream RC-1 Tributary 2 Stream RC-1A Stream RC-2
0.045 – 0.055 0.045 – 0.065 0.065 0.065 0.050 – 0.065 0.055 0.020 – 0.055 0.050 – 0.065 0.035 – 0.055 0.015 – 0.065 0.025 – 0.050 0.017 – 0.055 0.040 – 0.050 0.045 0.020 – 0.050 0.045 0.050 0.025 – 0.100 0.045 – 0.100 0.045 0.025 – 0.050 0.030 – 0.050 0.045 0.045 0.045 0.045 0.045 0.025 0.050 – 0.060 0.050 – 0.080 0.045 – 0.055 0.050 – 0.052 0.045 0.035 – 0.065 0.055 – 0.065 0.030 – 0.045 0.055 – 0.060 0.060 0.055 0.055 0.015-0.065 0.035 -0.047
0.065 – 0.100 0.050 – 0.500 0.070 – 0.100 0.100 0.080 – 0.100 0.070 – 0.100 0.080 – 0.100 0.050 – 0.200 0.015 – 0.500 0.015 – 0.500 0.015 – 0.500 0.030 – 0.500 0.040 – 0.500 0.150 – 0.500 0.030 – 0.500 0.100 – 0.500 0.030 – 0.500 0.045 – 0.500 0.050 – 0.500 0.100 – 0.500 0.050 – 0.500 0.065 – 0.500 0.100 – 0.500 0.050 – 0.500 0.100 0.060 – 0.500 0.050 – 0.500 0.080 – 0.500 0.050 – 0.080 0.060 – 0.100 0.055 – 0.085 0.050 – 0.500 0.065 – 0.075 0.040 – 0.500 0.065 – 0.100 0.045 – 0.500 0.035 – 0.070 0.035 – 0.500 0.500 0.100 – 0.500 0.045 – 0.100 0.020 – 0.500
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Rush Creek Watershed Study Final Report
Table 4-1. n values Stream Reach
Channel “n” Value
Overbank “n” Value
Sublett Creek Sublett Creek Tributary 1 Sublett Creek Tributary 1.1 Sublett Creek Tributary 2 Sublett Creek Tributary 3 Twin Springs Draw Twin Springs Draw Tributary 2 Twin Springs Draw Tributary 4 Twin Springs Draw Tributary 5
0.050 – 0.062 0.045 – 0.055 0.050 – 0.060 0.040 – 0.050 0.030 – 0.060 0.030 – 0.055 0.045 0.050 0.035
0.050 – 0.500 0.055 – 0.200 0.080 – 0.200 0.080 – 0.200 0.050 – 0.200 0.045 – 0.500 0.100 0.100 – 0.500 0.050 – 0.100
4.2.4 Ineffective Flow Ineffective flow areas occur in cross-sections adjacent to structure embankments and in isolated low areas in floodplains. These were defined as needed throughout the models to prevent overestimating the channel conveyance capacity.
4.2.5 HTab Parameters Unsteady HEC-RAS uses Hydraulic Tables (HTabs) to store cross-section properties and structure rating curves. The design of these tables is specified by the user so that each table is consistent with the model scale because large streams and small streams need to use different HTab parameter sets. For the Rush Creek models, the following parameter values were used. 4.2.5.1
HTab Parameters for Cross-Sections
The HTAB parameters for cross-sections were set to 100 increments (points) for all crosssections. The starting value was generally set to 0.5 feet above the invert and the elevation increment was set to the smallest value that provides sufficient tabulated depth to reach the top of the cross-section. 4.2.5.2 HTab Parameters for Structures
The HTAB parameters for bridges and culverts were initially set to the following values:
Number of Points on Free Flow (FF) Curve: 40
Number of Rating Curves (RC): 50
Number of Points on RC: 40
Reasonable maximum headwater elevations and maximum flows were also assigned for each structure. Occasionally, it was necessary to adjust these initial values during model debugging.
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Rush Creek Watershed Study Final Report
4.3
Boundary Conditions & Flow Input
The boundary conditions for the unsteady flow models include:
A time boundary -- an initial condition for every element in the model
Extent boundaries -- a time series at the upstream model terminus and normal depth as the downstream boundary condition
The downstream boundary condition was set to normal depth for all steady flow simulations.
4.3.1
Unsteady Flow Input
The hydrology model generates flow hydrographs for each modeled subbasin. As needed, subbasin hydrographs were routed and combined within the hydrology model until flow arrives at a reach represented in the HEC-RAS model, at which point the hydrograph is loaded into the HEC-RAS model. There are four situations where hydrographs must be applied in a HECRAS model:
Flow at the upstream end of a modeled reach
Flow distributed along a reach representing a subbasin transited by the reach
Lateral inflow at a point representing the inflow from a tributary
Flow from an adjacent watershed model.
4.3.1.1
Initial Flow
A set of initial flows was developed for each model because HEC-RAS requires non-zero flow in all reaches at all times. Initial flows were set as low as possible and to obey continuity at every junction. The small magnitudes of the initial flows do not influence the resulting water surface elevations for the simulated flood flow conditions. 4.3.1.2
Minimum Flow
Minimum flows were assigned to load points, as needed, to prevent zero flows in a reach and assure continuity is maintained in every reach under low flow conditions.
4.3.2 Steady Flow Input Peak discharges from the hydrologic model were applied at key flow change locations (cross sections) in HEC-RAS for each study stream. Typical flow change locations include:
Peak flow contributing at the most upstream HEC RAS cross section
Immediately downstream of inflow from a tributary
At a point where approximately 2/3 of the local subbasin transited by the study reach contributes to the stream.
4.4
Quality Control
Multiple technical reviews of the hydrologic analysis were conducted by CDM Smith, while Halff Associates performed internal reviews for both the hydrologic and hydraulic analysis. All hydrologic and hydraulic Quality Assurance/Quality Control (QAQC) certification forms can be found in Appendix H of this report.
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Rush Creek Watershed Study Final Report
4.5
Results
The HEC-RAS models were run and debugged for each of the flow scenarios specified and flows and elevations were obtained. Several steps were taken to verify and validate the results and adjustments were made to improve correlation with known data. Then final production runs were performed for floodplain mapping and problem identification.
4.5.1
Modeled Flows and Stages
The completed models were used to determine BFEs for all of the modeled flooding sources and to generate flood profiles for detailed studied streams as presented in Appendix E. Table 4-2 below provides a comparison between effective 1% annual chance water surface elevations and discharges at key locations along each of the detailed study streams.
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Location
At confluence with Rush Creek Downstream of confluence of Tributary 2
Drainage WS Area Elevation (Sq. Mi.) FIS
Kee Branch
136
Kee Branch
6,505
Kee Branch
10,493
Kee Branch
15,743
Kee Branch
16,088
Kee Branch
18,094
At interstate Route 20 Downstream of confluence of Tributary 4 Upstream of confluence of Tributary 4 Downstream of confluence of Tributary 5
Kee Branch
21,238
At U.S. Route 287
1.09
Kee Branch
25,758
At Kennendale Sublett Road At confluence with Kee Branch
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
7.23
539.8
534.60
10,920
11,587
6.96
556.3
556.23
9,970
10,531
4.44
572.6
575.45
7,300
6,615
3.55
593
592.30
6,420
7,828
2.85
593.05
5,020
6,058
1.40
602.51
2,140
5,757
610.6
616.45
1,640
4,054
0.89
637.6
638.45
1,840
2,256
1.52
573
568.04
3,670
5,471
At Oak Springs Road
1.26
585.5
586.59
3,120
4,383
At confluence with Rush Creek
1.68
499.9
494.16
3,710
4,030
Stream KB-1
68
Stream KB-1 Pantego Branch Pantego Branch Pantego Branch
2,395
3,131
At West Park Row
1.43
522.5
521.20
3,310
3,567
7,499
At Smith-Barry Road
0.94
556.5
557.98
2,290
3,206
Rush Creek
9,094
At confluence of Pantego Branch
29.01
499.8
500.68
4,704
6,959
Rush Creek
13,423
At State Route 303
28.77
510.7
511.82
27,060
28,088
Rush Creek
15,008
At Woodland Park Boulevard
27.59
516
517.41
26,670
28,153
Rush Creek
18,067
At Arkansas Lane
27.17
523.3
525.02
27,180
27,984
Rush Creek
24,444
Below confluence of Kee Branch
25.24
538.15
537.42
25,280
26,669
Rush Creek
24,900
At confluence of Kee Branch
18.01
538.15
538.46
16,850
15,953
275
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Rush Creek
5
Rush Creek
29,181
Rush Creek
5
Rush Creek
33,663
Rush Creek
33,974
Rush Creek
36,148
Rush Creek
37,789
Rush Creek
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
Below confluence of Ryan’s Branch
17.83
Above Kee Branch
17.52
At confluence of Ryan’s Branch Below confluence of Twin Springs Draw At confluence of Twin Springs Draw Downstream of confluence of Tributary 7 and Tributary 9
16.57
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
16,950 543.51
17,600
15,206
16,350
16.30
552.11
16,340
15,191
15.16
552.93
15,700
13,654
14.74
561.80
15,780
13,846
564.53
14,770
14,838
573.20
15,190
12,984
42,647
At interstate Route 20 Downstream of confluence of Tributary 10
13.07 12.78
Rush Creek
42,821
At confluence of Tributary 10
11.51
Rush Creek
47,930
10.82
Rush Creek
52,976
At Green Oaks Boulevard Downstream of confluence of Sublett Creek
Rush Creek
53,787
4.22
Rush Creek
54,743
At confluence of Sublett Creek Downstream of confluence of Tributary 16
Rush Creek
55,388
Rush Creek Rush Creek
565.9
573.36
14,010
10,480
587.54
13,890
11,819
596.62
13,179
11,518
598.55
6,270
5,723
3.04
600.40
5,490
5,867
585.1
9.51 595.5
2.54
601.99
4,610
5,713
67,236
At confluence of Tributary 16 Below confluence with Tributary 20
1.90
635.83
3,850
4,065
67,471
At confluence with Tributary 20
1.00
636.70
1,980
2,493
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location Forest Park Tributary of Rush Creek Northeast Tributary of Rush Creek Rush Creek Relief Channel
HEC-RAS Station
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
164
At confluence with Rush Creek
0.18
612.30
609.41
610
895
130
At confluence with Rush Creek
0.11
613.20
606.66
361
610
4
498.00
30,374
3
3.56
491.50
488.21
6,850
2,777
1.95
530.00
529.63
3,630
5,332
5
Upstream of convergence with Village Creek
Stream RC-1
455
Stream RC-1 Stream RC1A Stream RC1A
3,592
At confluence with Rush Creek Immediately upstream of Union Pacific Railroad
632
At confluence with Stream RC-1
1.36
528.00
523.82
3,180
4,439
At Bowen Road
0.93
562.00
564.16
2,480
3,976
Stream RC-2
480
At confluence with Rush Creek
1.18
516.50
517.64
2,790
494
Stream RC-2 Ryan's Branch Ryan's Branch Sublett Creek Sublett Creek Sublett Creek
5
At headwaters
0.64
At confluence with Rush Creek
1.29
545.00
541.46
3,100
3,562
At Roosevelt Drive
0.99
576.50
579.84
2,800
1,807
554
At confluence with Rush Creek
5.29
599.50
599.15
7,500
5,873
7,517
D/S Calendar Road (US Trib 1) Below confluence with Sublett Creek Tributary 3
4.57
624.25
623.49
7,060
5,652
3.66
638.60
637.87
5,790
5,478
3,836
851 5,439
12,975
1,930
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Sublett Creek Sublett Creek Twin Springs Draw
16,601
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
2.99
650.50
650.38
5,170
4,415
22,270
At U.S. Route 287 Below confluence with Sublett Creek Tributary 4
1.83
669.00
666.11
3,800
2,966
87
At confluence with Rush Creek
1.17
554.00
551.10
2,850
4,418
1
Source: Federal Emergency Management Agency Flood Insurance Study, Tarrant County, Texas Volume 1
2
From Hydraulic Models
3
Not likely the same location
4
Data not available
5
Location could not be determined from the information available in the effective FIS
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Rush Creek Watershed Study Final Report
5.
Updated Floodplain Map/Physical Map Revision
The hydraulic models described in Section 4 were developed update the FEMA floodplain maps which are currently based on modeling completed in 1985. FEMA has two processes for revising floodplain maps:
Letter of Map Revision (LOMR), and
Physical Map Revision (PMR).
Generally, LOMRs are used to revise a part of a stream system while PMRs are used to revise entire map panels. In a PMR, all components of a map are revised, including the base map, flood elevations, and floodway extents. Clearly the size and extent of the Rush Creek revisions warrant the use of the PMR option even though it is more expensive and will have a fairly long review and republication timeline. The primary elements of a PMR submitted are the base map, the base flood and 0.2% flood elevations, the floodway delineations and the model documentation. These elements are described in the following sections.
5.1
Base Map
The FEMA FIRM panels were used as the base map for the floodplain work maps. Base map information used for the FIRM panels was provided in digital format by NCTCOG. This information was digitized at a scale of at least 1:12,000 from aerial photography dated 2003.
5.2
Floodplain Delineation
Updated floodplains were mapped based on water levels computed in the HEC-RAS model. For tributaries studied in limited detail, a floodplain was delineated based on the 1% annualchance water surface elevations. In the detailed study streams (including Rush Creek), both the 1- and 0.2 percent annual-chance floodplains have been mapped. In each case, a spatial data format (sdf) file was exported from HEC-RAS and imported into ArcGIS to begin the mapping. The resulting line work was then smoothed and adjusted along the length of the stream to achieve a floodplain delineation that follows the detail of the topography and bends around solid objects such as bridge abutments. Additionally, Zone A mapping for one area adjacent to Stream RC-1 was delineated based on a 2-D HEC-RAS model of the area. Floodplain work maps showing the revised floodplain delineations can be seen in Appendix J.
5.3
Flood Profiles
Water surface profiles for the 10-, 4-, 2-, 1-, and 0.2 percent annual-chance floods were prepared in FEMA format for all detailed study streams associated with this study. All profiles maintained the same horizontal and vertical scales used in the effective FIS report in accordance with FEMA standards for restudied streams. The profiles were prepared from the HEC-RAS computed maximum water surface elevation output with the assistance of the FEMA RAS-Plot software. The profile plots are included in Appendix E.
5.4
Floodway Computations
FEMA requires definition and delineation of a regulatory floodway on all streams that have an effective floodway. For Rush Creek, this includes all of the detailed study streams except for
45
Rush Creek Watershed Study Final Report
Northeast Tributary, Forest Park Tributary, and Stream RC-1 West Diversion. In some cases, the floodway was extended farther upstream to match the detailed study stream length. Each unsteady HEC-RAS model was converted to steady state in order to develop floodway encroachments limits for the Rush Creek Watershed Study. The following procedures were used to define the floodway limits for Rush Creek studied streams. 1. Converted unsteady flow values related to the max water surface elevation profile to steady state flow change locations at all cross sections. 2. Computed steady state run and compared to unsteady 100-year max water surface elevations. 3. Identified cross section locations where the water surface elevation difference was greater than 0.5’ between the steady state and unsteady runs. 4. Revised the HEC-RAS geometry with the goal of eliminating differences to the extent practical, focusing mainly on differences greater than 0.5’ between the unsteady and steady 100-year water surface elevations. Typical geometry changes for the Rush Creek Watershed Study included revisions to cross section alignment, ineffective flow areas, and expansion/contraction coefficients, but may have included other model revisions. The goal was to produce one HEC-RAS model geometry that was utilized for the unsteady and steady state analyses. 5. Optimized floodway encroachments ensuring no greater than 1.0’ rise compared to the steady and unsteady 100-year water surface elevations. Floodway delineations can be seen in the Floodplain Work Maps in Appendix J. Floodway Data Tables are included in Appendix E.
5.5
FIS Report Section
For the flooding sources studied by detailed methods in the Rush Creek Watershed, standard hydrologic and hydraulic study methods were used to determine the flood-hazard data required for this study. Flood events of a magnitude that is expected to be equaled or exceeded with a 10-, 4-, 2-, 1-, and 0.2 percent annual-chance, respectively, during any year were determined. The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study.
5.5.1
Hydrologic Analysis
Hydrologic methods used for this study are in accordance with Appendix C of FEMAs Guidelines and Specifications for Flood Hazard Mapping Partners dated November 2009. The analytical approach generally followed the Natural Resources Conservation Service (NRCS), formerly the SCS, procedures as outlined in Technical Release Number 55 (TR-55). The hydrologic rainfall/runoff model developed by the USACE Hydrologic Engineering Center
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Rush Creek Watershed Study Final Report
(HEC), HEC-HMS Version 3.5, was used to estimate runoff discharge hydrographs from individual subbasins. The primary source of terrain data used for this study was developed by processing the 2009 Light Detection and Ranging (LIDAR) topographical data obtained from Texas Natural Resources Information System (TNRIS) for the Rush Creek Watershed. The terrain data was used along with the HEC-GeoHMS extension to generate the subbasin delineations. Rush Creek rainfall totals for the frequency floods were obtained from the NWS Technical Paper No. 40. These rainfall depths were compared with other sources including USGS Atlas of Depth-Duration Frequency of Precipitation Annual Maxima for Texas, Scientific Investigations Report 2004-5041 and it was determined that the TP-40 data were consistent with recent studies. A 24-hour duration nested frequency hypothetical storm was used for the various frequency event simulations in HEC-HMS. Soils information was obtained from the U.S. Department of Agriculture, NRCS Soil Survey Geographic (SSURGO) database for Tarrant County published in 2009. Hydrologic Soil types B, C and D are nearly evenly distributed throughout the watershed with a little bit of type A soil in places. Type D is the most common soil in the Rush Creek and RC-1 watersheds. A shape file of existing (2010) land use was obtained from the North Central Texas Council of Governments (NCTCOG). Runoff losses were computed using the NRCS Loss Rate Method. Composite, soil based curve numbers were computed for each subbasin using GIS Tools. Percent impervious values were computed based on the composite land use for each subbasin. The NRCS dimensionless unit hydrograph was selected to compute the unit hydrograph. The time of concentration calculations were split into three sections including overland, shallow, and channel flow. Overland flow was calculated using the coefficient of velocity. Times of concentration (tc) were computed using a modified velocity method outlined in the NRCS Technical Release 55 for shallow, and channel flow. Lag time (tlag) for each watershed was calculated by using the equation tlag = (0.6)tc . The Modified-Puls routing method was utilized in HEC-HMS for all steady state reaches. HEC-RAS v4.1 was used to develop storage-discharge relationships for each Modified-Puls routing reach. Channel routing was performed in HEC-RAS for all unsteady reaches. The Muskingum-Cunge method was used to route flows through storm drain reaches outside of the unsteady hydraulic study reaches.
5.5.2 Hydraulic Analysis Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected flood frequencies. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data tables in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS report in conjunction with the data shown on the FIRM.
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Rush Creek Watershed Study Final Report
Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Appendix E). For stream segments for which a floodway was computed (Section 5.4), selected cross-section locations are also shown on the FIRM. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the Flood Profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Detailed study streams are listed in Section 1 and shown in Table 1-1. Hydraulic methods used for this study are in accordance with the Guidelines and Specifications for Flood Hazard Mapping Partners dated April 2003 and Appendix C of the Guidelines dated November 2009. The following is a summary of data sources, assumptions, and procedures used to create the hydraulic models for the study streams. The primary source of terrain data used for this hydraulic study was developed from TNRIS 2009 LIDAR data. Roughness coefficients (Manning’s “n” values) used in the hydraulic computations were estimated on the basis of field inspection and NCTCOG 2011 aerial photography. The channel and overbank “n” values are shown in Table 4-1, “Summary of Roughness Coefficients.” A triangulated irregular network (TIN) was created by Halff Associates utilizing the 2009 LiDAR mass points and break lines in order for HEC-GeoRAS to extract cross-section geometry data for use in HEC-RAS. All floodplains were mapped using the 2009 LiDAR data. Water surface profiles for the 10-, 4-, 2-, 1- and 0.2 percent annual-chance events were computed using the River Analysis System HEC-RAS Version 4.1.0., dated January 2010. Cross-sections, taken from field surveys conducted as part of this study, were supplemented with HEC-GeoRAS cross-sections cut from the TIN’s generated using the 2009 LiDAR. Bridge data used for the hydraulic models were taken from field surveys. Profiles (Appendix E) were generated using RAS-PLOT. Profiles were plotted at the same scale as the previous FIS profiles.
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Rush Creek Watershed Study Final Report
Appendix A: Technical Standards
A1
Rush Creek Watershed Study Final Report
Appendix B: Hydrologic Parameter Summary
A2
Rush Creek Watershed Study Final Report
Appendix C: Public Meeting Information
A3
Rush Creek Watershed Study Final Report
Appendix D: Lidar Quality Assurance Report
A4
Rush Creek Watershed Study Final Report
Appendix E: Floodway Data Tables and Profiles
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Rush Creek Watershed Study Final Report
Appendix F: Hydraulic and Hydrologic Database Provided in digital format (DVD)
A6
Rush Creek Watershed Study Final Report
Appendix G: Hydraulic and Hydrologic Models Provided in digital format (DVD)
A7
Rush Creek Watershed Study Final Report
Appendix H: QA/QC Forms
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Rush Creek Watershed Study Final Report
Appendix I: Survey Data
A9
Rush Creek Watershed Study Final Report
Appendix J: Floodplain Workmaps
A10
TBPE Firm Reg No. F-312
In Cooperation with:
TBPE Firm Reg No. F-3043
TBPE Firm Reg No. F-6548
Brown & Gay Engineers, Inc. EBG Engineering, LLC
TBPE Firm Reg No. F-3075
TBPE Firm Reg No. F-2677
Nathan D Maier Consulting Engineers, Inc. Surveying And Mapping, Inc.
Rush Creek Watershed Study Final Report
CONTENTS Executive Summary ................................................................................................................................. ES 1 1. Introduction ............................................................................................................................................... 1 1.1 Study Purpose and Scope ................................................................................................................. 1 1.2 Location of Study ................................................................................................................................ 3 1.3 Community Description ..................................................................................................................... 3 1.4 Floodplain Mapping Extents ............................................................................................................. 3 2. Data Collection ........................................................................................................................................ 6 2.1 Survey and Mapping .......................................................................................................................... 6 2.1.1 Digital Projection Information ...................................................................................................... 6 2.1.2 Field Survey...................................................................................................................................... 6 2.2 Previous Reports and Studies ............................................................................................................ 6 2.2.1 Report Summaries .......................................................................................................................... 8 2.2.1.1 Floodplain Information; Rush and Village Creeks; Arlington, Texas; USACE; February 1971 ..................................................................................................................................... 8 2.2.1.2 Flood Insurance Study Arlington Texas, Volume 2; Fort Worth District, USACE; July 1972 ............................................................................................................................................. 8 2.2.1.3 Rush Creek Watershed Management Development Document; Espey, Huston & Associates, Inc; April 1989 ............................................................................................................ 8 2.2.1.4 Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report; USACE; 1991 – 1992 ............................................................................................................................ 9 2.2.1.5
Rush Creek Tributary 1 Report; USACE; August 1992 ............................................... 10
2.2.1.6 State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180; August 1993 ........................................................... 10 2.2.1.7 Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report; Fort Worth District, USACE; March 1994 ............................................................................................... 11 2.2.1.8 1994
Rush Creek Tributary 1; 205 DPR Study; Fort Worth District, USACE; November ........................................................................................................................................... 11
2.2.1.9 Rush Creek Flooding and Sedimentation Study (Final Report); Nathan D. Maier Consulting Engineers, Inc.; January 2001 .................................................................................... 11 2.2.1.10 Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition; G.A. Dixon & Associates; June 2006 ............................................................................................. 12 2.2.1.11 Flood Study of Rush Creek for Valista Estates in Arlington, Texas; Nave Engineering, Inc.; June 2007 .......................................................................................................... 12
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Rush Creek Watershed Study Final Report
2.2.1.12 Letter of Map Revision Based on Fill (LOMR-F); Morrison Hydrology Engineering, Inc.; Table for Summary of Discharges and Floodway Data ........................... 13 2.2.1.13 Flood Study for Property Located at 2224 Wanda Way, Rush Creek, City, Tarrant County; Morrison Hydrology Engineering, Inc.; November 2008 .............................. 13 2.2.1.14 Rush Creek and Tributary RC-2; Conditional Letter of Map Revision (CLOMR); Nathan D. Maier Consulting Engineers, Inc.; October 2009 .................................................... 14 2.2.1.15 Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1; Caffey Engineering, Inc.; January 2010....................................................................................... 14 2.2.1.16
Rush Creek Letter of Map Revision (LOMR); Wier & Associates; March 2010 16
2.2.1.17 Blue Binder: Information on Flood Data Elevation; John D. Zimmerman P.E., R.P.S.; October 2010 ........................................................................................................................ 17 2.2.1.18 Comprehensive Stream Management Plan; Phase 1 and Phase 2 Report; Jacobs Engineering; March 2011 ................................................................................................. 19 2.2.1.19 Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary Number 7 – Grace preparatory Academy Addition, Charles Crook Consulting, Inc., May 2016 ....................................................................................................................................... 19 2.3 Flood Insurance Study ...................................................................................................................... 19 2.4 Hydrologic and Meteorologic Data.............................................................................................. 20 2.5 Public Meeting................................................................................................................................... 23 3. Hydrologic Analysis ................................................................................................................................ 24 3.1 Subbasin Delineation ....................................................................................................................... 24 3.1.1 Topographic Data Acquisition and Evaluation ..................................................................... 24 3.1.2 Terrain Processing ........................................................................................................................ 26 3.2 Precipitation Data............................................................................................................................. 26 3.3 Depth-Area Reduction Factors ...................................................................................................... 27 3.4 Runoff Volume ................................................................................................................................... 27 3.4.2 Land Use Classification ............................................................................................................... 28 3.4.2.1
Existing Conditions Land Use ........................................................................................ 29
3.4.2.2
Ultimate Conditions Land Use...................................................................................... 29
3.4.3 Hydrologic Soil Groups ................................................................................................................ 29 3.5 Runoff Hydrographs .......................................................................................................................... 32 3.6 Routing ................................................................................................................................................ 33 3.7 Hydrologic Analysis Results .............................................................................................................. 33 3.8 Quality Control .................................................................................................................................. 33 4. Hydraulic Analysis ................................................................................................................................... 34 4.1 Introduction ........................................................................................................................................ 34
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Rush Creek Watershed Study Final Report
4.2 HEC-RAS Model Development ....................................................................................................... 36 4.2.1 Stream Centerlines and Cross-Sections ................................................................................... 36 4.2.2 Structures ....................................................................................................................................... 36 4.2.3 Manning Roughness Coefficients ............................................................................................. 36 4.2.4 Ineffective Flow ............................................................................................................................ 38 4.2.5 HTab Parameters.......................................................................................................................... 38
4.3
4.2.5.1
HTab Parameters for Cross-Sections ........................................................................... 38
4.2.5.2
HTab Parameters for Structures ................................................................................... 38
Boundary Conditions & Flow Input ........................................................................................... 39
4.3.1 Unsteady Flow Input .................................................................................................................... 39 4.3.1.1
Initial Flow ........................................................................................................................ 39
4.3.1.2
Minimum Flow ................................................................................................................. 39
4.3.2 Steady Flow Input ........................................................................................................................ 39 4.4 Quality Control .................................................................................................................................. 39 4.5 Results .................................................................................................................................................. 40 4.5.1 Modeled Flows and Stages ....................................................................................................... 40 5. Updated Floodplain Map/Physical Map Revision ........................................................................... 45 5.1 Base Map ............................................................................................................................................ 45 5.2 Floodplain Delineation ..................................................................................................................... 45 5.3 Flood Profiles ...................................................................................................................................... 45 5.4 Floodway Computations ................................................................................................................. 45 5.5 FIS Report Section ............................................................................................................................. 46 5.5.1 Hydrologic Analysis ...................................................................................................................... 46 5.5.2 Hydraulic Analysis ........................................................................................................................ 47
FIGURES Figure 1-1. Location Map ............................................................................................................................. 2 Figure 2-1. Tarrant County 24-hr Distribution of 100-yr Storm (based on the frequency storm method) .................................................................................................................................... 22 Figure 2-2. Arlington Airport, September 7-8, 2010 Storm Event (15 minute) ................................... 23 Figure 3-1. Subbasin Delineation .............................................................................................................. 25 Figure 3-2. Existing Land Use ...................................................................................................................... 30 Figure 3-3. Soils ............................................................................................................................................. 31 Figure 4-1. Modeled Stream Reaches ..................................................................................................... 35
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Rush Creek Watershed Study Final Report
TABLES Table 1-1. Rush Creek Watershed Study Modeled Streams .................................................................. 4 Table 2-1. Watershed Study Reports .......................................................................................................... 7 Table 2-2. Detailed Study Streams. .......................................................................................................... 20 Table 2-3. Estimated 24-hour Storm Depths (inches) for Tarrant County Texas. .............................. 21 Table 3-1. Rainfall Depth-Duration-Frequency Data (inches) ............................................................ 26 Table 3-2. Rush Creek ARF Estimates ....................................................................................................... 27 Table 3-3. Land use and Percent Impervious ........................................................................................ 28 Table 3-4. Watershed Soil Classification .................................................................................................. 32 Table 4-1. n values ....................................................................................................................................... 37 Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges ....... 41
APPENDICES Appendix A: Technical Standards Appendix B: Hydrologic Parameter Summary Appendix C: Public Meeting Information Appendix D: Lidar Quality Assurance Report Appendix E: Floodway Data Tables and Profiles Appendix F: Hydraulic and Hydrology Database Appendix G: Hydraulic and Hydrology Models Appendix H: QA/QC Forms Appendix I: Survey Data Appendix J: Floodplain Work Maps
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Rush Creek Watershed Study Final Report
Executive Summary The Rush Creek Watershed is the largest watershed in Arlington, Texas and includes portions of Kennedale, Mansfield, Fort Worth and the entirety of Pantego and Dalworthington Gardens. The watershed has developed significantly over the past 40 years from the time when the original floodplain mapping was produced by FEMA. The City of Arlington has undertaken a comprehensive study of the Rush Creek Watershed. The purpose of this report is to revise Federal Emergency Management Agency (FEMA) flood maps so that flooding risk is better defined for Arlington residents. To meet this objective, this study included hydrologic and hydraulic modeling compliant with FEMA guidelines and standards. The new hydrologic analysis of the entire Rush Creek Watershed included subbasin delineation, runoff characterization, rainfall input calculations, and development and validation of a HEC-HMS model (version 3.5). HEC-RAS models (version 4.1) were built for all current effective Zone AE and Zone A streams in the watershed for the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent annual chance event and the 1 percent annual chance event for future development conditions. A September 2010 flood event (Tropical Storm Hermine) was also modeled. Revised floodplains were delineated based on computed water surface elevations in the HECRAS models. For tributaries studied in limited detail, a floodplain was delineated based on the 1% annual-chance water surface elevations. For the detailed study streams (including Rush Creek), both the 1- and 0.2 percent annual-chance floodplains were mapped including floodways. Floodplain work maps showing the revised floodplain delineations can be seen in Appendix J. Water surface profiles for the 10-, 4-, 2-, 1-, and 0.2 percent annual-chance floods were prepared in FEMA format for all detailed study streams associated with this study. All profiles maintained the same horizontal and vertical scales used in the effective FIS report in accordance with FEMA standards for restudied streams. The profile plots are included in Appendix E.
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Rush Creek Watershed Study Final Report
1.
Introduction
The Rush Creek-Village Creek Watershed in southeast Tarrant County is mainly comprised of area located in west Arlington, but also includes portions of Kennedale, Mansfield, and Fort Worth and the entirety of Pantego and Dalworthington Gardens as shown on Figure 1-1. Rush Creek Watershed contains approximately 35 square miles and approximately 56 miles of main channel and tributary. Rainfall is the major contributor to flow in Rush Creek, but there are a small number of natural springs from the Woodbine Aquifer that also contribute to the total flow. Channels within the watershed range from natural to concrete lined. Research indicates that major floods most likely occurred in April 1922, May 1949, April 1957, May 1965, March 1968, March 1977, May 1989, April 1990, June 2004, June 2007, and September 2010 (when over 200 homes were reported to have flooded in the Rush Creek Watershed). While lake levels have been maintained for Lake Arlington upstream of Lower Village Creek since 1988, no records of streamflow are available on Rush Creek. The watershed has developed significantly over the past 40 years. During this time frame City stormwater ordinances allowed development without considering cumulative downstream impacts. This has had an enormous impact on the floodplains and creeks and has led to increased volumes, velocities and base flood elevations as well as decreased water quality. The effective watershed hydrologic modeling has not been updated to take this period of development into account. Due to flooding concerns and the lack of knowledge of the true volumes and flood elevations in the watershed, the City of Arlington has completed a comprehensive watershed study for the Rush Creek Watershed in compliance with Federal Emergency Management Agency (FEMA) guidelines and standards. CDM Smith acted as the Project Management Consultant (PMC), wrote the project’s technical standards and provided quality assurance and control. AECOM, Dewberry, and Michael Baker completed the initial hydraulic analyses. Halff Associates completed the hydrologic analysis, final hydraulic model revisions, and completed the final FEMA mapping and applications.
1.1
Study Purpose and Scope
There central purpose of the Rush Creek Watershed Study was to Revise FEMA flood maps so that flooding risk is better defined for Arlington residents.
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Rush Creek Watershed Study Final Report
Figure 1-1. Location Map
2
Rush Creek Watershed Study Final Report
The City of Arlington and sub-consultants completed the following tasks for this study: Data Collection: included information such as previous watershed studies, existing topography and photography (contours, aerial mapping, watershed delineations, and existing surveys of physical features), hydrologic and hydraulic models, and FEMA floodplain delineations. Develop Standards: standards were developed for both work products and technical analysis since five engineering firms were involved. The Technical Standards document is included as Appendix A.
Terrain Data – an ESRI Terrain geodatabase, compatible with ArcGIS Desktop version 9.3.1, was created using Light Detection and Ranging (LiDAR) data collected in 2009 and 2010 and made available by the Texas Natural Resources Information System.
Survey – cross sections were surveyed to supplement the LiDAR-based terrain data.
Hydrologic Modeling – a new hydrologic analysis of the entire Rush Creek Watershed was completed. This effort included subbasin delineation, runoff characterization, rainfall input calculations, and development and validation of a HEC-HMS model (version 3.5).
Hydraulic Modeling – new HEC-RAS models (version 4.1) were built for all currently effective Zone AE and Zone A streams in the watershed for the 50%, 20%, 10%, 4%, 2%, 1%, and 0.2% annual chance event and the 1% annual chance event for future development conditions. A September 2010 flood event was also modeled.
1.2
Location of Study
As noted above, the Rush Creek-Village Creek Watershed is in southeast Tarrant County, Texas and is mainly comprised of area located in west Arlington, but also includes portions of Kennedale, Mansfield, and Fort Worth and the entirety of Pantego and Dalworthington Gardens. The City of Arlington has taken the lead on this study but has coordinated with Pantego, Dalworthington Gardens, and the general public through meetings to discuss the project’s goals and progress.
1.3
Community Description
The City of Arlington, with a population of over 360,000, lies wholly within Tarrant County, Texas. The City covers approximately 100 square miles, is served by four independent school districts, and is home to three institutions of higher learning.
1.4
Floodplain Mapping Extents
Detailed unsteady HEC-RAS models were prepared to define base flood elevations and regulatory floodways along approximately 35 miles of open channel streams that are currently mapped as Zone “AE” in the Rush Creek Watershed. Streams currently mapped as Zone A in the watershed were modeled in steady HEC-RAS but with limited detail. Modeled and mapped streams are shown in Table 1-1. Streams noted as “Not Studied” in Table 1-1 were typically entirely within the backwater from the main stem and were not modeled. Stream centerlines were delineated based on aerial photography and cross-section surveys and then georeferenced in HEC-RAS. Additional streams needed to define overflows and diversions were included to provide additional floodplain mapping extents.
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Rush Creek Watershed Study Final Report
Table 1-1. Rush Creek Watershed Study Modeled Streams Stream Name
Study Area
Stream
Reach ID
Study Type
Length (ft)
Forest Park Tributary
UR
RUS
RUS_FPT
Detailed (AE)
1945
Kee Branch
KB
KEE
KEE_000
Detailed (AE)
30744
Kee Branch Tributary 1
KB
KEE
KEE_001
Limited Detail (A)
2543
Kee Branch Tributary 1.1
KB
KEE
KEE_001_001
Limited Detail (A)
428
Kee Branch Tributary 2
KB
KEE
KEE_002
Limited Detail (A)
2070
Kee Branch Tributary 3
KB
KEE
Kee Branch Tributary 4
KB
KEE
KEE_004
Limited Detail (A)
6173
Kee Branch Tributary 5
KB
KEE
KEE_005
Limited Detail (A)
3888
Northeast Tributary
UR
RUS
RUS_NET
Detailed (AE)
2610
Pantego Branch
LR
PAN
PAN_000
Detailed (AE)
9153
RUS
RUS_000
Detailed (AE)
76098
RUS
RUS_RCH
Detailed (AE)
4218
Rush Creek
Not Studied
Rush Creek Relief Channel
LR
Rush Creek Tributary 3
LR
RUS
Rush Creek Tributary 4
LR
RUS
RUS_004
Limited Detail (A)
4981
Rush Creek Tributary 4.1
LR
RUS
RUS_004_001
Limited Detail (A)
4074
Rush Creek Tributary 5
LR
RUS
RUS_005
Limited Detail (A)
7814
Rush Creek Tributary 5.1
LR
RUS
Rush Creek Tributary 5.2
LR
RUS
Not Studied
Rush Creek Tributary 5.3
LR
RUS
Not Studied
Rush Creek Tributary 6
LR
RUS
Not Studied
Rush Creek Tributary 7
MR
RUS
RUS_007
Limited Detail (A)
5406
Rush Creek Tributary 7.1
MR
RUS
RUS_007_001
Limited Detail (A)
543
Rush Creek Tributary 8
MR
RUS
Rush Creek Tributary 9
MR
RUS
RUS_009
Limited Detail (A)
6595
Rush Creek Tributary 10
MR
RUS
RUS_010
Limited Detail (A)
5682
Rush Creek Tributary 10.1
MR
RUS
RUS_010_001
Limited Detail (A)
1636
Rush Creek Tributary 10.2
MR
RUS
RUS_010_002
Limited Detail (A)
2424
Rush Creek Tributary 10.3
MR
RUS
RUS_010_003
Limited Detail (A)
1182
Rush Creek Tributary 10.4
MR
RUS
RUS_010_004
Limited Detail (A)
2717
Rush Creek Tributary 11
MR
RUS
RUS_011
Limited Detail (A)
1348
Rush Creek Tributary 12
MR
RUS
RUS_012
Limited Detail (A)
1145
Rush Creek Tributary 13
MR
RUS
RUS_013
Limited Detail (A)
4512
Rush Creek Tributary 14
MR
RUS
RUS_014
Limited Detail (A)
2891
Rush Creek Tributary 15
MR
RUS
RUS_015
Limited Detail (A)
2848
Rush Creek Tributary 15 Overflow Rush Creek Tributary 16
MR
RUS
Polo_Club
Limited Detail (A)
1232
UR
RUS
RUS_016
Limited Detail (A)
3338
Rush Creek Tributary 16.1
UR
RUS
Rush Creek Tributary 17
UR
RUS
Not Studied
Not Studied
Not Studied
Not Studied RUS_017
Limited Detail (A)
1566
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Rush Creek Watershed Study Final Report
Table 1-1. Rush Creek Watershed Study Modeled Streams Study Area
Stream
Rush Creek Tributary 18
UR
RUS
Rush Creek Tributary 18.1
UR
RUS
Rush Creek Tributary 19
UR
RUS
Rush Creek Tributary 20
UR
RUS
Ryan’s Branch
MR
RYA
RYA_000
Detailed (AE)
6632
Ryan’s Branch Tributary 1
MR
RYA
RYA_001
Limited Detail (A)
1108
Stream KB-1
KB
KEE
KEE_KB1
Detailed (AE)
5157
Stream KB-1.1
KB
KEE
KB1_001
Limited Detail (A)
1496
Stream RC-1
RC1
RCO
RUS_RC1
10185
Stream RC-1A
RC1
RCO
RCOT1A
Stream RC-1 Tributary 1
RC1
RCO
RCO001
Detailed (AE) / Limited Detail (A) Detailed (AE) / Limited Detail (A) Limited Detail (A)
Stream RC-1 Tributary 2
RC1
RCO
RCO002
Limited Detail (A)
2120
Stream RC-1 West Diversion Stream RC-1 North Diversion Stream RC-2
RC1
RCO
RCO_WST
Limited Detail (A)
2493
RC1
RCO
RCO_NOR
Limited Detail (A)
820
LR
RUS
RUSRC2
Detailed (AE) Detailed (AE) / Limited Detail (A) Limited Detail (A)
Stream Name
Reach ID
Study Type
Length (ft)
Not Studied Not Studied RUS_019
Limited Detail (A)
2623
Not Studied
7566 1057
6731
Sublett Creek
UR
SUB
SUB_000
Sublett Creek Tributary 1
UR
SUB
SUB_001
Sublett Creek Tributary 1.1
UR
SUB
SUB_001_001
Sublett Creek Tributary 2
UR
SUB
SUB_002
Limited Detail (A)
873
Sublett Creek Tributary 3
UR
SUB
SUB_003
Limited Detail (A)
4541
Sublett Creek Tributary 4
UR
SUB
Twin Springs Draw
MR
TWI
Twin Springs Draw Tributary 1 Twin Springs Draw Tributary 1.1 Twin Springs Draw Tributary 2 Twin Springs Draw Tributary 3 Twin Springs Draw Tributary 4 Twin Springs Draw Tributary 5
MR
TWI
Not Studied
MR
TWI
Not Studied
MR
TWI
MR
TWI
MR
TWI
TWI004
Limited Detail (A)
3768
MR
TWI
TWI005
Limited Detail (A)
628
Limited Detail (A)
23895 2032 1208
Not Studied TWI000
TWI002
Detailed (AE)
Limited Detail (A)
6594
702
Not Studied
5
Rush Creek Watershed Study Final Report
2.
Data Collection
Information and data related to the Rush Creek Watershed was collected in compliance with FEMA guidelines and standards. This information includes previous watershed studies, recently collected terrain data and photography, GIS data, hydrologic and hydraulic models, and approved Letters of Map Revision (LOMRs/CLOMRs). This section includes a catalog of the data collected and a brief synopsis of each piece of data.
2.1
Survey and Mapping
One of the purposes of this study is to update estimated flood elevations using recent sources of physical data. For model building and floodplain mapping the key physical system data consists of base map, terrain and field survey. The date and sources of this data are as follows:
Base Map – Streets – ArcGIS Online World Transportation
Aerial Photography – 2015 TNRIS
Terrain – The terrain was prepared by Halff Associates in 2012 from LiDAR that was flown in 2009.
Survey – Cross-sections and bridge dimensions were obtained during the spring of 2012 under the direction of the hydraulic modeling consultants (AECOM, Dewberry, and Michael Baker). Additional open channel and bridge surveys were performed by Halff Associates along Kee Branch, Rush Creek, and Twin Springs Draw Tributary 5 (Arbrook Channel) during the spring of 2015.
2.1.1
Digital Projection Information
All spatial data uses the NAD_1983_StatePlane_Texas_North_Central_FIPS_4202_Feet projection.
2.1.2
Field Survey
Field survey of channel cross-sections and hydraulic structure dimensions was conducted along all detail study streams. No data from the effective model was deemed to be usable given that the models were prepared in 1985. All survey data was obtained and documented according to FEMA data capture standards including required photos and field sketches of each surveyed structure and cross-section. All data was georeferenced and incorporated into the project database. See Appendix I for survey data including photos and field sketches. The horizontal and vertical datums used were:
Vertical Datum: North American Vertical Datum of 1988 (NAVD88)
Horizontal Datum: North American Datum of 1983 (NAD83)
2.2
Previous Reports and Studies
Table 2-1 below lists watershed study reports that have been collected by the City. Section 2.2.1 contains a short summary of each report.
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Rush Creek Watershed Study Final Report
Table 2-1. Watershed Study Reports Report Name Floodplain Information Rush and Village Creeks Arlington, Texas Flood Insurance Study Arlington Texas, Volume 2 Rush Creek Watershed Management Development Document Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report Rush Creek Tributary 1 Report State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180 Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report Rush Creek Tributary 1; 205 DPR Study Rush Creek Flooding and Sedimentation Study (Final report) Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition Flood Study of Rush Creek for Valista Estates in Arlington, TX Letter of Map Revision Based on Fill (LOMR-F) 2224 Wanda Way, Arlington, Texas Table for Summary of Discharges, floodway data Flood Study for Property located at 2224 Wanda Way Rush Creek, City, Tarrant County Rush Creek and Tributary RC-2 Conditional Letter of Map Revision (CLOMR) Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1 Content Rush Creek Letter of Map Revision (LOMR) Blue Binder: Information on flood data elevation. Comprehensive Stream Management Plan Phase 1 and Phase 2 Report (including photographs and geodatabase) Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary No. 7 – Grace Preparatory Academy Addition
Author U.S. Army Corps of Engineers (USACE) Fort Worth District, USACE Espey, Huston & Associates, Inc.
Date February 1971 July 1972 April 1989
USACE
1991 – 1992
USACE
August 1992 August 1993
Fort Worth District, USACE Fort Worth District, USACE Nathan D. Maier Consulting Engineers, Inc.
March 1994 November 1994 January 2001
G.A. Dixon & Associates
June 2006
Nave Engineering, Inc
June 2007
Morrison Hydrology Engineering, Inc Morrison Hydrology Engineering, Inc
November 2008
Nathan D. Maier Consulting, Engineers, Inc.
October 2009
Caffey Engineering, Inc.
January 2010
Wier & Associates
March 2010
John D. Zimmerman P.E., R.P.S
October 2010
Jacobs Engineering
March 2011
Charles Crook Consulting, Inc.
May 2016
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Rush Creek Watershed Study Final Report
2.2.1
Report Summaries
2.2.1.1
Floodplain Information; Rush and Village Creeks; Arlington, Texas; USACE; February 1971
The Floodplain Information report contains information on the flood conditions along Village Creek below Lake Arlington and Rush Creek. The report is based on rainfall data, runoff data, historical flood heights, current flood heights, and other technical data bearing upon the occurrence and size of floods in the Rush-Village Creek Watersheds. This report includes the following data:
Watershed map
Tables with flood elevations along the studied area
Photos from Rush Creek bridges
Maximum known flood discharges table
Floodplain cross section figure
Index map for flooded areas
Individual flooded areas map for all the locations on the index map
High water profiles for Rush Creek, Village Creek
Cross sections for Rush-Village Creeks
2.2.1.2
Flood Insurance Study Arlington Texas, Volume 2; Fort Worth District, USACE; July 1972
The Flood Insurance Study (FIS) compiles and presents flood risk data for Rush Creek and its tributaries. The FIS revised and updated information regarding the severity of flood hazards in Tarrant County, which includes the Rush Creek Watershed. The FIS contains data relevant to the Rush Creek Watershed Study, including a map index and a preliminary floodway map. 2.2.1.3
Rush Creek Watershed Management Development Document; Espey, Huston & Associates, Inc; April 1989
The study focused on improving the watershed by reducing flood risks. Each reach was summarized for existing and future flooding problems. The study used the U.S. Army Corps of Engineers computer model NUDALLAS (USACE, 1980). This study includes the following data:
Physiographic description of the Rush Creek Watershed
Description of Watershed’s climate, vegetation, wildlife, land use, subsurface geology, soils, erosion, and cultural features.
Table for water quality standards for unclassified streams
Table for water quality data summary for Rush Creek
Reach descriptions and maps for Sublett Creek, Kee Branch, Pantego Branch, Rush Creek and Tributaries KB-1, RC-2, RC-1A, and, RC-1.
Maps for vegetation, geology, soils, cultural features, open space concept
Typical section at all span bridges drawing
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Rush Creek Watershed Study Final Report
Linear park trail – street connection at bridge drawing
Trail & creek in box culvert at street crossing drawing
Natural channel section with linear park improvements drawing
Longitudinal section – typical ramp at bridges drawing
Concrete lined channel section drawing
Grass lined channel section drawing
Maps for the proposed watershed improvement plan, fully-developed conditions flooded structures, and drainage area.
NUDALLAS output for Rush Creek
HEC-2 Outputs for Kee Branch, Pantego Branch, Rush Creek Tributary No. 1, Rush Creek Tributary No.1A, Rush Creek and Sublett Creek.
Flood Profiles for Rush Creek, Stream RC-1, Stream RC-1A, Pantego Branch, Stream RC-2, Kee Branch, Stream KB-1, Sublett Creek,
The study proposed four plans to reduce the flooding in the area. Plan 1 represents a fullydeveloped watershed without watershed flood control improvements. Plan 2 represents a fully-developed watershed with bridge and channel improvements. Plan 3 represents onsite detention in the upper portion of the watershed and fully-developed conditions. Plan 4 contains a regional detention in the upper portion of Rush Creek, Kee Branch and Sublett Creek with fully-developed conditions. Channel and bridge improvements included in Plan 2 are the most cost-effective components of the final plan. 2.2.1.4
Trinity River and Tributaries; Rush Creek Tributary 1; Detailed Project Report; USACE; 1991 – 1992
This report provides detailed information on flooding problems along Rush Creek (Tributary 1) including environmental assessment, findings of no significant impact, US fish and wildlife coordination act, archeological assessment, public notice, and exhibits. This report includes the following data:
Photos of flooded areas
Topographic Map of the study area
Channel analysis performed on HYDRA
HEC-2 output files for existing and improved conditions
Calculations and drawings for culverts, drop inlets
Cross-section drawings
Area map
Survey data
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Rush Creek Watershed Study Final Report
2.2.1.5
Rush Creek Tributary 1 Report; USACE; August 1992
The Rush Creek Tributary 1 Report is a detailed project report, environmental assessment, and feasibility study for Rush Creek Tributary 1. The report includes appendices that include the following data:
Hydrology analysis with SWFHYD Program – input on file
Hydraulics – water surface profiles, 100-year flood limits for existing and with project
Civil Design and Cost Estimating – Site plan drawing, plan and profiles, drop structure plan and profile, and calculations
Geotechnical Data – plan of borings, subsurface profile, logs of borings, environmental site assessment
U.S. Fish and Wildlife Final Coordination Act Report
Real Estate – channel improvement easement, temporary work area easement, road easement
Cultural Resources
Economic Analysis
2.2.1.6
State of Texas Department of Transportation; Plans of proposed state highway improvement for Tarrant County S.H. 180; August 1993
The report provided the following data to support the Rush Creek Watershed Study:
Roadway details sheet
Quantity Summary sheet
General notes and specification data sheets
Plan profile sheet
Culvert layout SH180 at Tributary to Rush Creek sheet
Inlets and storm drains sheet
Culvert end details sheet
Traffic control plan sheet
Permanent Pavement Markers sheet
Precast concrete box culverts sheets
Multiple box culverts sheet
Temporary barrier barrel-mounted guard fence sheet
Metal beam guard fence sheet
Raised pavement markers, reflective pavement markers, traffic buttons and jiggle bar tile sheet
Typical standard pavement markings sheets
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Rush Creek Watershed Study Final Report
Work zone barrier delineation sheet
Combination rail sheet
2.2.1.7
Trinity River and Tributaries, Rush Creek, Tributary 1 Reconnaissance Report; Fort Worth District, USACE; March 1994
The report provided the following data to support the Rush Creek Watershed Study:
Photos – downstream end of Tributary No. 1, confluence of Tributary No. 1 and Rush Creek
Improvement channel drawings
Bridge computations using WASURO
HEC-2 Outputs – lower subcritical reach, supercritical reach
Design Calculations, existing conditions profiles
High water profile and HEC-2 output
2.2.1.8
Rush Creek Tributary 1; 205 DPR Study; Fort Worth District, USACE; November 1994
The report provided the following data to support the Rush Creek Watershed Study:
Basic storm water pollution prevention plan for construction of Rush Creek Tributary No. 1
HEC-2 outputs for with project conditions and without project conditions
Drop inlet design calculations and profiles
One drop model – drawings and HEC-2 outputs
Basin HEC-2 outputs
Lower Trap drop HEC-2 outputs
Trapezoidal Stilling Basin HEC-2 output, calculations and drawings
Stilling Basin Design HEC-2 output
Hydraulic Design Chart for California Institute Technology type drop structure HEC-2 output and cross-sections profiles
2.2.1.9
Rush Creek Flooding and Sedimentation Study (Final Report); Nathan D. Maier Consulting Engineers, Inc.; January 2001
The study identified 14 elements that can be used to improve the area. Elements 1 to 6 focused on reducing the flood potential in the downstream portion of the study. Elements 8 – 10 focused on a reduction in the upstream portion and Elements 7 and 11 – 14 provided benefits throughout the project area. These elements consisted of sedimentation removal in Rush Creek Channel, removal or modification of the existing dam, modifications in the channel (widening), creation of a levee/floodway system downstream of Pioneer Parkway, maintenance of Rush Creek Relief Channel, expansion of the relief channel, improvements on the relief channel/bridge, channel restoration upstream of Pioneer Parkway, widening the Woodland Park Boulevard bridge,
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Rush Creek Watershed Study Final Report
channel improvements upstream of Pioneer Parkway, on-channel detention, sedimentation basin, debris removal, and structure relocation. The study describes all the alternatives in detail. HEC-1 was used to analyze the alternatives. Each alternative is composed of a combination of the 14 elements. The report contains:
Topographic Map with Cross Section Locations
Flood photographs along Shady Valley, Woodland Park Bridge, Rush Creek Channel (in 1980 and 1999)
Exhibits with Floodplain Limits and Local Flooding Information
Exhibits with improvement elements
Exhibit for the main (i.e. bank to bank) channel configuration of Rush Creek
Exhibits showing Rush Creek floodplain – existing Conditions
Exhibits showing the Selected Alternative
The study concluded that these alternatives will provide a reduction of the 100-year floodplain elevation. The alternatives providing the greatest benefit in reducing the existing flood elevation contains restoration upstream of Pioneer Parkway with the main channel. 2.2.1.10 Hydrology and Hydraulic Analysis on Little Rush Creek Wanda Way Addition; G.A. Dixon & Associates; June 2006
Study established the 100-year floodplain limits and the easement to satisfy city criteria for SWSMP and establish minimum finished floor elevations.
Existing channel hydraulics description for the channels immediately south and north of the Wanda Way Bridge and Wanda Way Addition.
Cross-Sections along the study area
FIRM map of the study area
25 year, 100 year floodplain and easement of Wanda Way Addition
CD – HEC-RAS model
HEC-RAS output report
2.2.1.11
Flood Study of Rush Creek for Valista Estates in Arlington, Texas; Nave Engineering, Inc.; June 2007
Study delineated the existing and ultimate conditions for 100-year floodplain through the Valista Estates. The flood study was performed for the existing, proposed (with development), and ultimate (the watershed fully developed) conditions for the 25-year and the 100-year storm events. The study provides sufficient data to delineate the ultimate development 100year floodplain in addition to the following data:
HEC-1 output for existing and proposed 10-year, 25-year, 50-year, 100-year, and 500-year conditions
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Rush Creek Watershed Study Final Report
HEC-1 output for ultimate 100-year
HEC-2 effective and effective floodway outputs.
HEC-RAS effective and effective floodway outputs
HEC-RAS revised existing condition and floodway outputs
HEC-RAS for proposed condition and floodway outputs
HEC-RAS for ultimate condition output
HEC-RAS for unnamed tributary output
Location, drainage area, effective FIRM, land use, soil and work map
HEC-2 and HEC-RAS for Rush Creek and Unnamed Tributary
2.2.1.12 Letter of Map Revision Based on Fill (LOMR-F); Morrison Hydrology Engineering, Inc.; Table for Summary of Discharges and Floodway Data
This LOMR-F provides the following data to support the Rush Creek Watershed Study:
FIRM
HEC-2 Partial FEMA effective model output
Property Information Form
FIRM with location of the property
Elevation Form
Survey Map
Community Acknowledgement Form
2.2.1.13 Flood Study for Property Located at 2224 Wanda Way, Rush Creek, City, Tarrant County; Morrison Hydrology Engineering, Inc.; November 2008
This study was conducted to fill an area under a proposed structure to ensure that the lowest adjacent grade is above the FEMA 100-year floodplain and the finished floor is 2 feet above the 100-year ultimate condition floodplain. The study concluded that the structure should be elevated on the property compacted fill to the required elevation. This study provided the following data to support the Rush Creek Watershed Study:
Table comparing FEMA and Proposed Fill condition flood elevations
HEC-2 Partial FEMA effective model output
Table for Summary of Discharges, floodway data
FIRM
Preliminary FIRM
Ultimate Condition 100 year HEC-2 output
Ultimate Development Map
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Rush Creek Watershed Study Final Report
Ultimate Condition Floodplain and Floodway Delineation for 100 year and 100 year ultimate map
Proposed Condition With Fill HEC-2 output
Proposed Condition with Fill Cross-sections map showing 100 year and 100 year ultimate
Proposed Condition with Fill water surface profiles for 100 year and 100 year ultimate
Proposed Condition with Fill 100 year floodplain and floodway delineations
2.2.1.14 Rush Creek and Tributary RC-2; Conditional Letter of Map Revision (CLOMR); Nathan D. Maier Consulting Engineers, Inc.; October 2009
The project provided flood control and protection against erosive forces for Rush Creek and Tributary RC-2. The study area for Rush Creek extends from the downstream side of Pioneer Parkway to 1,200 feet upstream of Woodland Park Blvd with Tributary RC-2 extending from the center of Rush Creek to 650 feet upstream to Creekside Drive. The proposed flood reduction plan includes a flat lined channel bottom with a varying bottom width of approximately 120 feet to 60 feet with 4:1 side slopes. The modifications reduced the water surface elevation throughout the reach and reduced the risk of flooding residential structures. The project provided the following data:
Location of the project map
Comparison of HEC-2 and Pre-Project HEC-RAS
Floodway analysis performed for post-project HEC-RAS
Includes the CLOMR
Riverine Hydrology & Hydraulic Forms
Riverine Structures Form
Pre-project and Post-project FIRMs
Effective FEMA Model - HEC-2 Results from 27 August 1986
Pre-Project and Post Project HEC-RAS results for Rush Creek and Tributary RC-2
Digital data – CD containing:
USACE.pdf with the HEC-2 results
HEC-RAS models for Rush Creek and RC-2
CLOMR workmap.dwg
2.2.1.15 Request for a Letter of Map Revision (LOMR) for Rush Creek Tributary No. 1; Caffey Engineering, Inc.; January 2010
This report is a LOMR for significant modifications along the north of the Union Pacific Railroad. Modifications include construction of new culverts, replacement of the natural channel with a trapezoidal structure. The upper portion of the channel is lined with pavement while the lower portion is unlined; an industrial park was also developed in this area. This report provided the following data to support the Rush Creek Watershed Study:
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Rush Creek Watershed Study Final Report
Basin Map
CD and printed output containing:
RushCreek.pdf – multiple profiles and floodway output files.
P20RC1.OH2 – duplication multiple profile output report.
P21RC1.OH2 – duplication floodway output report.
HEC2RAS.rep – HEC-RAS report for multiple-profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
RC1HEC2RAS.rep – HEC-RAS report for floodway profile HEC-2 conversion to HECRAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
FixedQs.rep – Existing conditions multiple-profile model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street, and channelization downstream of Division Street.
RC1FW.rep – Existing conditions floodway model for RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street, and channelization downstream of Division Street
IndPkBp3.rep – Multiple-profile model of Division Street weir flows that enter the industrial park rather than returning to the main channel for existing conditions.
ZoneAbypass.rep – Existing conditions: Multiple-profile model of bypass flows that leave the main channel and flow westward along the south side of the Union Pacific Railroad not to return to the main channel. This model facilitates detailed mapping of the bypass channel which is currently mapped Zone A.
P20RC1.DAT – Duplication multiple profile output report.
P21RC1.DAT – Duplication floodway output report.
HEC2RAS – HEC-RAS report for multiple-profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
RC1HEC2RAS – HEC-RAS report for floodway profile HEC-2 conversion to HEC-RAS corrected to reflect two culverts rather than the nonexistent railroad trestle bridge.
FixedQs – Existing conditions multiple-profile model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street and channelization downstream of Division Street.
RC1FW – Existing conditions floodway model for the RC-1 main channel reflecting culverts at the railroad, new culverts at Division Street and channelization downstream of Division Street.
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Rush Creek Watershed Study Final Report
IndPkBp3 – Multiple-profile model of Division Street weir flows that enter the industrial park rather than returning to the main channel for existing conditions.
ZoneAbypass – Existing conditions: Multiple-profile model of bypass flows that leave the main channel and flow westward along the south side of the Union Pacific Railroad (UPRR) not to return to the main channel. This model facilitates detailed mapping of the bypass channel which is currently mapped Zone A.
Overview and Concurrence form, Riverine Hydrology & Hydraulics Form, and Riverine Structures Form.
Rush Creek Tributary No. 1(RC-1) Photos, Zone A Photos
RC-1 copy of the currently effective FIRM
RC-1 FIRM and Flood Profiles for existing conditions
Delineation Map for Rush Creek Tributary 1 and Zone A
Newspaper from Sunday, May 8, 2011 with the Public Notice
Rush Creek RC-1 01-2011 CD contains pdfs of maps in the report
Rush Creek RC-1 CD contains CAD drawings in the report
2.2.1.16 Rush Creek Letter of Map Revision (LOMR); Wier & Associates; March 2010
The study showed that prior to the construction of the Pleasant Ridge Road improvements some single family residential lots upstream were at a great risk of flooding. The revisions included the removal of an old bridge and the construction of a twin leaf concrete arch bridge with a span of 66 feet and an estimated height at the center line of over 22 feet. The study provided the following data:
HEC-2 CD containing input files for Rush Creek pre-project and post project for the project area and floodway.
Overview and Concurrence Form
Riverine Hydrology & Hydraulics Form
Riverine Structures Form
FIRM
Tables and flood profiles from FIS
Property owner notification letters
NGS data sheet
Swiss Avenue grading plan and LOMR-F
Site gradating and pond layout
Pre-project and post Profile
Fill Compaction and Soil Boring Report
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Rush Creek Watershed Study Final Report
2.2.1.17 Blue Binder: Information on Flood Data Elevation; John D. Zimmerman P.E., R.P.S.; October 2010
The binder contains printed pictures, flooding data information and four CDs for impacted residences. The flooding information contains state plane coordinates, elevation of high water, and finish floor elevations for all residences listed below. The flooding information sheet is also provided in pdf format on the CD. The binder includes an article on the flood of 1989.
Pictures CD Flood Data Pictures 5-11-2011 2905 Lakeshore Dr 3434 Indian Trail 4700 Westhaven Rd 7600 Sharon Lee
Rush Creek Tributary 1 Flood – Sep. 8, 2010 CEI/JEC CD
Photos from different locations
Cit of Arlington additional files CD
Flood Photos 1841 South Park 1845 South Park 1847 South Park 1901 Woodridge
CD
Rush Creek Flood 2010 Castle Pines Valleywood Houses 2015, 2115, 2121, 2127 Woodland Park Houses 4028, 4038, 4042, 4044 Creekside Creekside Houses 2001, 2101, 4304, 4306 Division Street Forest Edge north and south Hill Valley
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Rush Creek Watershed Study Final Report
1817 Hillvalley Shady Creek Shady Creek Houses 3701, 3807 Shady Valley Shady Valley Houses 4150, 4152, 4155, 4157, 4159, 4161, 4166, 4168 Sheffield Sheffield Houses 3309, 3401, 3403 3403 contains a movie South Park South Park Houses 1821, 1823, 1824, 1825, 1828, 1829, 1831 – 1841, 1845, 1847 Valley Crest Valleycrest Houses 2101 – 2112, 2114, 2115 Valleywood Valleywood Houses 2000 – 2002, 2004 – 2006, 2008 – 2010, 2012 – 2014,
2016 – 2018, 2100 – 2102, 2104 – 2106, 2108 – 2110, 2112 – 2114 West Fork WestFork Houses 407, 411, 416 Willows at Shady Valley Apartment Apartments 1700, 1702, 1704, 1706, 1710, 1712, 1714, 1800, 1802, 1804, 1806,
1808, 1810, 1812, 1814, 1900, 1902, 1904, 1906, 1908, 1910, 1914, 1916, 1918, 1920, 1922, 1924, 1926, 1928 Winewood Winewood House 1902 Woodland Park Ct Woodland Park Houses 4200 – 4209 Woodland Park Dr Woodland Park Houses 4225, 4228, 4230, 4300, 4301 – 4304, 4306, 4308 Woodridge Woodridge Houses 1818, 1820, 1901, 1903, 1905
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Rush Creek Watershed Study Final Report
2.2.1.18 Comprehensive Stream Management Plan; Phase 1 and Phase 2 Report; Jacobs Engineering; March 2011
Phase 1 of the Comprehensive Stream Management Plan involved collecting information on existing storm water related programs, updating the drainage concern database, evaluating existing design criteria, development of a repetitive loss structure inventory, as well as Hazard Mitigation Grant Program (HMGP) and Repetitive Flood Claims grant applications. Phase 2 consists of system condition assessments.
Watersheds addressed in the report: Cottonwood Creek, Fish Creek, Johnson Creek, Kee Branch, Lower Rush Creek, Lynn Creek/Bowman Branch, Upper Rush Creek, Village Creek, West Fork Trinity
Interviews were conducted with the following municipalities: City of Austin, City of Dallas, City of Denton, City of Farmers Branch, Town of Flower Mound, City of Fort Worth, City of Garland, City of Grand Prairie, Harris County Flood Control District, City of Killeen, City of Mesquite, City of Plano, City of Richardson, and, City of San Antonio
Each watershed has a section that includes a description of the watershed, the drainage concern, threatened structures, infrastructure, utilities, retaining walls, trees, and, amenities. A brief conclusion for each watershed is also included.
In addition, the report includes a table with a summary of municipal natural channel maintenance programs, photographs and a geodatabase.
2.2.1.19 Hydrologic and Hydraulic Analysis of Rush Creek and Rush Creek Tributary Number 7 – Grace preparatory Academy Addition, Charles Crook Consulting, Inc., May 2016
The report details hydrologic and hydraulic impacts of an addition to Grace Preparatory Academy. The development primarily affects Rush Creek Tributary No. 7 and has a minimal impact on Rush Creek. The project included relocation and channelization of 290 linear feet of Tributary No. 7, construction of several buildings in the Tributary No. 7 overbank, and minor grading changes in the Rush Creek floodplain. This report provided the following data to support the Rush Creek Watershed Study:
2.3
Existing conditions workmap
Proposed condition workmap
Storage exhibits for existing and proposed conditions
Cross Sections
Grading Plan
CD containing supporting hydraulic and hydrologic modeling
Flood Insurance Study
The current effective Flood Insurance Study (FIS) for Rush Creek is the Tarrant County, Texas FIS dated September 25, 2009. According to the study, the underlying hydrologic and hydraulic analysis was completed in September 1985. The FIS identified thirteen Rush Creek tributaries as “Detailed Study Streams”. These streams and their reported studied lengths are listed in Table 2-2.
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Rush Creek Watershed Study Final Report
Table 2-2. Detailed Study Streams. Detailed Study Streams
Length (miles)
Rush Creek
14.0
Sublett Creek
4.4
Northeast Tributary
0.1
Forest Park Tributary
0.1
Rush Creek Relief
0.7
Stream RC1
1.7
Stream RC1A
0.7
Stream RC2
1.0
Ryan’s Branch
0.9
Twin Springs Draw
0.5
Pantego Branch
1.8
Kee Branch
5.4
Stream KB-1
0.9
The detailed study streams are mapped with defined Base Flood Elevations (BFE) and have regulatory floodways. Floodways were not defined for Northeast Tributary and Forest Park Tributary. These streams were redelineated during the 2009 countywide remapping and no additional engineering analysis was conducted. An Engineering Data Request (EDR) was submitted to FEMA to attempt to obtain the original hydrologic models, but the models were not included in the data provided. Digital copies of an HEC-2 model of the Rush Creek Mainstem were provided that appeared to be part of a 1998 LOMR.
2.4
Hydrologic and Meteorologic Data
Searches of the web sites of the National Weather Service and the US Geological Survey were conducted to gather historical stream flow and rainfall data that could prove to be useful in the study. Design rainfall depths were obtained from the National Weather Service and North Central Texas Council of Governments (NCTCOG) and reviewed for use in the study. There are no USGS stream gauging stations in the Rush Creek Watershed nor are there any hourly rain fall recording stations. The nearest rainfall station with sub-daily data is located at Arlington Airport.
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Rush Creek Watershed Study Final Report
The 24-hour design storm rainfall estimates for Tarrant County are provided in Table 2-3. Estimates have been obtained from TP-40 (Hershfield, 1961) and the NCTCOG iSWM Hydrology manual (2010). Although the TP-40 estimates are extremely old, recent studies such as Asquith (2004) indicate that the TP-40 extreme rainfall depths are clearly within the margin of error for such estimates. If anything, it appears that estimates of extreme rainfall in north Texas has decreased slightly in the past 50-years. Due to the future uncertainty posed by long-term climate variability, it is recommended that the TP-40 estimates be employed in the Rush Creek Study. Table 2-3. Estimated 24-hour Storm Depths (inches) for Tarrant County Texas. Storm
NWS TP-40
iSWM
1-year
3.15
2.64
2-year
3.95
3.36
5-year
5.33
4.56
10-year
6.32
5.52
25-year
7.47
6.72
50-year
8.45
7.92
100-year
9.47
9.12
500-year
11.47
12.96
For the 24-hour evaluations, rainfall will be distributed using a nested frequency storm distribution as shown in Figure 2-1; this distribution was created using the TP-40 100-year storm frequencies.
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Rush Creek Watershed Study Final Report
2.2 2.0 1.8 1.6 Rainfall (inches)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0:00
2:00
4:00
6:00
8:00
10:00 12:00 14:00 16:00 18:00 20:00 22:00
0:00
Time
Figure 2-1. Tarrant County 24-hr Distribution of 100-yr Storm (based on the frequency storm method) Rainfall for September 7-8, 2010 event (Tropical Storm Hermine recorded at Arlington Municipal Airport) is shown in Figure 2-2 and this storm may be used for model calibration/validation purposes.
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Rush Creek Watershed Study Final Report
Arlington Airport, September 7-8, 2010 Storm Event (15 minute) 0.50 0.45 0.40
Rainfall (inches)
0.35 0.30 0.25 0.20 0.15 0.10 0.05 0:00 1:15 2:30 3:45 5:00 6:15 7:30 8:45 10:00 11:15 12:30 13:45 15:00 16:15 17:30 18:45 20:00 21:15 22:30 23:45 1:00 2:15 3:30 4:45 6:00 7:15 8:30 9:45 11:00
0.00
Time
Figure 2-2. Arlington Airport, September 7-8, 2010 Storm Event (15 minute)
2.5
Public Meeting
On February 16, 2012 the City Department of Public Works and Transportation: Stormwater Management Division hosted a public meeting at the City Fire Training Center. The purpose of this public meeting was to inform the public of the purpose of the Rush Creek Watershed Study and to collect information. A handout provided at the meeting (see Appendix C) said: “What You Can Do to Help: Your knowledge of flooding and erosion is indispensable to making our study as accurate as possible. Please tell us flooding or erosion issues on your property, on properties around you or on public property/streets near you. Photos or information about depth of the water during past floods are also welcome.” Information collected during this meeting was used to locate high water marks, flooding concerns, and to understand residents’ view of flooding risks in the watershed. A second public meeting will be scheduled to present study results to the public and to explain the significance of these results to the public.
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3.
Hydrologic Analysis
This section summarizes the study methods and results of the hydrologic modeling effort performed by Halff Associates, Inc. The purpose of the hydrologic modeling is to simulate flooding and evaluate existing land use conditions for the 50, 20, 10, 4, 2, 1, and 0.2 percentannual-chance storm events and the ultimate land use conditions for the 1 percent-annualchance flood event. Hydrologic analyses have been conducted for the Rush Creek Watershed as part of the comprehensive watershed study and model updates. The entire watershed was analyzed for the following hydrologic scenarios:
Existing Land Use Conditions, and
Ultimate Land Use Conditions.
HEC-HMS v3.5 was utilized to create hydrologic models. The results of this modeling effort were utilized to develop steady and unsteady hydraulic models to determine flood elevations corresponding to the 50, 20, 10, 4, 2, 1, and 0.2 percent-annual-chance events. Significant rainfall events considered for the hydrologic models were the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent-annual-chance events. Detailed watershed delineations, existing and ultimate land use determinations, and the hydrologic soil coverage were used to develop HEC-HMS hydrologic computer models for the respective tributaries’ watershed. The Rush Creek Watershed Technical Standards along with Urban Hydrology for Small Watersheds, Technical Release 55 (TR-55) Second Edition were used as guidelines for developing parameters used in the new 2012 hydrologic analyses.
3.1
Subbasin Delineation
Subbasin delineations were generated using ESRI’s ArcGIS Version 10.0 based on the Texas Natural Resource Information Systems (TNRIS) 2009 Light Detection and Ranging (LiDAR) Terrain Data. Digital storm sewer lines supplied by the City, supported by current aerial photography, aided in the subbasin delineation process. Subbasins in the range of 60 to 100 acres were recommended by the Technical Standards; the majority of basins fell within this range. Figure 3-1 depicts the subbasin delineations.
3.1.1 Topographic Data Acquisition and Evaluation Topographic data covering the project extent was obtained from the TNRIS 2009 LiDAR acquisition project. This data was available as LiDAR point clouds in the American Society of Photogrammetry and Remote Sensing (ASPRS) common LiDAR Data Exchange Format (LAS 1.1) with 1.0 meter post spacing.
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Rush Creek Watershed Study Final Report
Figure 3-1. Subbasin Delineation
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Data was acquired in March 2009 by Fugro Earth Data, Inc. Fugro performed this work under subcontract to Dewberry who served as the prime contractor to the Texas Water Development Board for the LiDAR Acquisition Project. The LiDAR Quality Assurance Report provided by Dewberry is included in Appendix D. This data was acquired and processed to meet 0.185 meter Root Mean Square Error (RMSEz) vertical accuracy and was tested to have an RMSEz of 0.040 meters using National Standards for Spatial Data Accuracy (NSSDA) and FEMA methodology (see Table 1 of the LiDAR Quality Assurance Report).
3.1.2
Terrain Processing
The LiDAR data was processed with ESRI’s ArcGIS software. The LiDAR data was acquired in Universal Transverse Mercator (UTM), North American Datum of 1983, (NAD83 Meters) with heights in the 1988 North American Vertical Datum (NAVD88 Meters). Each LiDAR tile was projected to State plane NAD83, Texas North Central zone with horizontal units of feet and the vertical units were also converted from meters to feet. The project LiDAR point clouds were then processed in ArcGIS and the ground points were placed into a multipoint feature class within a file geodatabase. The multipoint feature class was then used to generate a seamless terrain dataset within the same file geodatabase. From the terrain dataset, a ground surface Digital Elevation Model (DEM) was generated to support basin delineations and hydrologic modeling.
3.2
Precipitation Data
Rainfall data was obtained from TP-40 (Hershfield, 1961) for the 24-hour storm events corresponding to the 50-, 20-, 10-, 4-, 2-, 1-, and 0.2 percent-annual-chance storm events. The rainfall data is summarized in Table 3-1. Table 3-1. Rainfall Depth-Duration-Frequency Data (inches) Storm Duration
Frequency (Percent Annual Chance)
5 Min
15 Min
1 Hr
2 Hr
3 Hr
6 Hr
12 Hr
24 Hr
50%
0.40
1.02
1.77
2.15
2.37
2.86
3.43
3.95
20%
0.54
1.38
2.39
2.90
3.19
3.86
4.63
5.33
10%
0.64
1.64
2.84
3.44
3.79
4.58
5.49
6.32
4%
0.76
1.94
3.35
4.06
4.48
5.41
6.49
7.47
2%
0.86
2.19
3.79
4.59
5.06
6.12
7.34
8.45
1%
0.96
2.46
4.25
5.15
5.67
6.86
8.23
9.47
0.2%
1.16
2.98
5.15
6.24
6.87
8.31
9.96
11.47
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3.3
Depth-Area Reduction Factors
Typically, areal reduction factors (ARF) are applied to rainfall depths when the tributary area exceeds 10 square miles to account for the fact that average storm depths over a large area are less than a point rainfall of equal probability of occurrence. Potential reduction factors for Rush Creek were estimated according to the method of Leclerc and Schaake (1972) which is a formula designed to reproduce the graphed values in TP-40. These estimates are shown in Table 3-2 and ARF for areas less than 10 square miles have been set equal to 1.0. Table 3-2. Rush Creek ARF Estimates 1
Location
Cumulative Drainage Area (acres)
Rush Creek at Sublett Road Rush Creek at Indian Trail Rush Creek above the Kee Branch Confluence Rush Creek at W Division Street
1
Cumulative Drainage Area (sq. miles)
Storm Duration (hours)
Estimated Areal Reduction Factor
5,880
9.2
24
1.00
11,070
17.3
24
0.97
15,640
24.4
24
0.96
19,830
31.00
24
0.95
Kee Branch (outfall)
4,570
7.1
24
1.00
RC-1 (outfall)
2,280
3.6
24
1.00
As indicated in Table 3-2, the ARF is 1.0 for most of the modeled reaches and varies from 0.97 to 0.95 along the Rush Creek mainstem between Sublett Road and the confluence. In unsteady flow there is no possible way to vary a rainfall reduction factor along a reach as can be done in steady flow. Furthermore, in steady flow studies, peak flows are assumed to occur simultaneously throughout the entire reach which produces a conservative outcome. As this study is using unsteady flow, it is determined that the 3 to 5 percent reduction in rainfall was not justified nor necessary for the limited area over which it would be applied. Doing so would require multiple model runs to obtain flows and stages for particular reaches. A test analysis showed that the maximum ARP would reduce maximum discharges in lower Rush Creek by about 1,000 cfs and maximum stages by about 0.3 feet. These values are well within the estimation error for modeled stream discharges and stages consistent with the differences between steady and unsteady flow.
3.4
Runoff Volume
The loss rate of rainfall, caused by evaporation, interception, depression, storage, and infiltration, is typically evaluated and subtracted from the rainfall to determine rainfall excess for each time increment of a storm. For this study, the SCS Curve Number Method, developed by the Natural Resources Conservation Service (NRCS), was used to develop flood hydrographs based on land use, soil classification, and antecedent moisture conditions. Baseline Curve Numbers were obtained from TR-55, Table 2.2c, for pasture, grassland, or
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Rush Creek Watershed Study Final Report
range land. Curve Numbers (CN) were computed based on a composite percentage of soil types within each subbasin. Group A soils were defined as having a CN of 39, Group B soils were defined as having CN of 61, Group C soils were defined as having CN of 74, and Group D soils were defined as having CN of 80. The antecedent moisture condition (AMC) defines the soil moisture condition prior to a storm. AMC-II, average soil moisture conditions, was used for the watershed study. Basin parameters are presented in Appendix B. The initial abstraction (I.A.) for all watersheds was computed for AMC-II, average soil conditions using the following equation from TR-55:
1000 IA = 0.2 − 10 CN 3.4.2 Land Use Classification Land use for the Rush Creek Watershed has been determined for both existing and ultimate conditions. Table 3-3 shows the land use categories and corresponding impervious percentages used for this study. Refer to the Technical Standards in Appendix A for sources of these impervious area percentages. Watershed conditions dictated that the percent impervious values provided in the Technical Standards be supplanted by the values shown in Table 3-3 for Extremely Low Density Residential, Very Low Density Residential, Major Transportation, Institutional, and Mobile Home land use categories. A composite percentage of impervious area was computed using the land use contained in each subbasin for both existing and ultimate conditions. Table 3-3. Land use and Percent Impervious Impervious (%) Conditions
Land Use Description Extremely Low Density Residential (2+ acre lots)
15
Very Low Density Residential (1 acre lots)
25
Low Density Residential (1/2 acre lots)
40
Medium Density Residential (1/3 acre lots)
45
High Density Residential (1/4 acre lots)
50
Major Transportation
50
Industrial
72
Institutional
50
Group Quarters
40
Hotel/Motel
85
Mobile Home
35
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Table 3-3. Land use and Percent Impervious Impervious (%) Conditions
Land Use Description
3.4.2.1
Multi-family
65
Office
85
Parks/Recreation
6
Retail
85
Under construction
50
Utilities
60
Vacant
3
Water
100
Existing Conditions Land Use
The existing land use conditions were based on 2005 NCTCOG existing land use data provided in shapefile format. The land use shapefile was updated to reflect current development conditions shown on the City aerial photography (2011). The existing conditions land use for the Rush Creek Watershed is illustrated in Figure 3-2. 3.4.2.2 Ultimate Conditions Land Use
Ultimate conditions land use data was not available for the project area. Based on discussion with the project team and the City, an impervious value of 75 percent was applied to all vacant and extremely low density residential land use to estimate the ultimate build out conditions of the watershed. All other land use remained consistent with the existing land use conditions.
3.4.3 Hydrologic Soil Groups The NRCS Soil Survey of Tarrant County (2009) was used to evaluate the hydrologic soils in the Rush Creek Watershed. In general, the watershed is underlain by B, C, and D soils in nearly equal proportions. The most prevalent soil type in the watershed is Group D which consists of clayey soils with slow infiltration rates and high potential for runoff. The second most prevalent soil type is Group B which consists of soils characterized as having some content of gravelly sand with moderate infiltration rates and low to moderate runoff potential. The third most prevalent soil type in the watershed is Group C which indicates soils having moderately fine to fine texture and slow infiltration rates. A small percentage of soils in the watershed are identified as Group A which indicates soils having high infiltration rates and low runoff potential. Table 3-4 includes a list of the NRCS Soil Survey Geographic Database (SSURGO) Hydrologic Soil Group (HSG) classifications for each Rush Creek sub-watershed. Hydrologic soils in the Rush Creek Watershed are illustrated on Figure 3-3.
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Rush Creek Watershed Study Final Report
Figure 3-2. Existing Land Use
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Figure 3-3. Soils
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Table 3-4. Watershed Soil Classification Hydrologic Soil Type Percentage A
B
C
D
Kee Branch
3
38
29
30
Lower Rush Creek
13
43
18
26
Middle Rush Creek
4
25
18
53
Stream RC-1
2
41
28
28
Upper Rush Creek
3
29
17
50
3.5
Runoff Hydrographs
The SCS Dimensionless Unit Hydrograph method was used and SCS lag times were computed for each subbasin to generate runoff hydrographs. A different time of concentration was computed for existing and ultimate conditions. Both were based on the NRCS TR-55 methodology for overland (sheet) flow, shallow concentrated flow, and channel flow. Overland flow length was limited to a maximum of 100 feet for unpaved surfaces and 50 feet for paved surfaces. Travel times for channel flow were based on velocities from the HEC-RAS routing models, where available. Channel flows for non-routed reaches were estimated based on Manning’s equation, assuming a bankfull depth that was selected based on the channel geometry and the elevation corresponding to the natural channel banks. For improved channels, it was often difficult to estimate the bankfull depth from the channel geometry and some consideration was given to the expected bankfull (2-year) discharges and anticipated velocities associated with bankfull flow. Storm drain velocities were assumed to be six feet per second for the purposes of this study. Based on the recommendation of the project team, the stream channels being modeled using unsteady HEC-RAS were removed from the time of concentration calculations. A memorandum, entitled “Flow paths for estimating Basin Lag Time”, supporting this decision is provided in Appendix B. The time of concentration is the summation of these phases, where: Tc = tsheet + tshallow concentrated + tstorm drain + tchannel Lag times were computed using the following equation: Tp = 0.6*Tc The ultimate conditions times of concentration were estimated by changing overland flow located in vacant land use to be a maximum of 50 feet and paved. All shallow concentrated
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Rush Creek Watershed Study Final Report
flow was changed to paved for ultimate conditions. These two changes were intended to estimate the impacts of future development to times of concentration.
3.6
Routing
The Modified Puls routing method was utilized in HEC-HMS for all steady state, Zone A reaches. In addition to the studied Zone A reaches, a handful of channel reaches that were not included in the study were also included in the HEC-HMS analysis to facilitate modeling of unsteady HEC-RAS reaches. The Modified Puls routing method was also used for these additional reaches. HEC-RAS v4.1 was used to develop storage-discharge relationships for a range of routing flows for studied and unstudied steady state reaches. The HEC-RAS models were generated using cross sections based on the TNRIS LiDAR data. The sub-reaches (routing step) calculations are provided in Appendix B. Channel routing was performed in HEC-RAS for all unsteady reaches. The Muskingum-Cunge method was used to route flows through storm drain reaches outside of the new unsteady hydraulic study reaches. An equivalent pipe diameter size was calculated for most reaches based on a weighted average of the pipe size and length through the reach. The equivalent pipe diameter was input in the HEC-HMS models and a note was added in the description of these routing reaches to specify when this method was applied. Routing parameters are presented in Appendix B.
3.7
Hydrologic Analysis Results
The hydrologic model results from the Rush Creek HEC-HMS models consist primarily of unrouted runoff hydrographs through the detailed, Zone AE studied reaches. As such, the results from the HEC-HMS models used for the detailed study reaches are not directly comparable with previous hydrologic studies that included routed hydrographs. Therefore, the resulting maximum discharges for the detailed study reaches are presented with the hydraulic analysis in Table 4-2.
3.8
Quality Control
The project team established a rigorous set of quality assurance and quality control procedures for the development of the Rush Creek Watershed Study. Quality control for the hydrologic analysis met requirements established in the Technical Standards and the Rush Creek Quality Control Plan. All submittals were reviewed by the PMC to ensure quality work products. In addition, Halff Associates, Inc. implemented internal quality control to ensure deliverables were accurate and of the highest quality prior to submitting to the PMC.
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4.
Hydraulic Analysis
Hydraulic modeling was performed in 2013 by AECOM, Dewberry, and Michael Baker Corporation utilizing unsteady HEC-RAS and subsequently reviewed by CDM Smith (the Project Management Consultant). Halff Associates was contracted by the City of Arlington to finalize the HEC-RAS models, beginning with the HEC-RAS models completed by the referenced hydraulic modeling consultants. All streams were initially studied using unsteady HEC-RAS and consisted of 5 total HEC-RAS models; one for each major sub-watershed. Halff Associates separated out each study stream to individual HEC-RAS models and converted all Zone A study streams to steady state. This section of the report summarizes the final study methods and results of the hydraulic modeling performed by Halff Associates.
4.1
Introduction
All 1-D hydraulic modeling was performed using HEC-RAS version 4.1.0 while a single 2-D hydraulic model was performed in HEC-RAS version 5.0.3. Unsteady HEC-RAS was chosen for the detailed study streams for its flexibility and convenience in complex systems, particularly those containing flow diversions and storage facilities. The extent and location of each modeled reach is shown in Figure 4-1. The detailed study models were all newly constructed from the survey data and GIS data assembled for this project. All modeling was performed to comply with Appendix C of the FEMA guidelines and standards. Additional modeling guidelines for this study were written to supplement the FEMA guidelines in matters specific to unsteady HEC-RAS. These guidelines are provided in the Rush Creek Watershed Technical Standards (see Appendix A).
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Rush Creek Watershed Study Final Report
Figure 4-1. Modeled Stream Reaches
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4.2
HEC-RAS Model Development
4.2.1
Stream Centerlines and Cross-Sections
The model geometry development process began with defining the extents to be modeled as depicted in Figure 4-1 and then defining the stream centerline for each modeled reach. Initially, the stream centerlines were developed to follow the flow path defined in the topography. Later, during cross-section input, several differences in channel location between the 2011 terrain data and the 2012 survey were identified. The stream centerlines were adjusted where needed to match the 2012 survey and keep them within the channel banks. With preliminary stream centerlines established, the next step was to determine the hydraulic structures that would be represented and to lay out the model cross-section locations. All significant hydraulic structures were to be included in the models. Field reconnaissance walks were conducted along each reach to identify significant structures. Next, cross-section locations were located along each reach. Cross-sections were required at the approach and departure of each structure and within 500 feet of any confluence (junction of two streams). Once these cross-section locations were established, additional channel cross-sections were laid out at 500 - 800 foot intervals. Cross-sections were cut from the project topography using HEC-GeoRAS which was also used to extend the survey cross-sections. Stream reaches studied in limited detail were not surveyed, and instead used GeoRAS cross-sections derived from the terrain data.
4.2.2 Structures Bridge, culverts and in-line structures were represented in the model according to the procedures described in the HEC-RAS Hydraulic Reference Manual (HRM) and Application Guide. In the detail study reaches the geometric data describing each structure was obtained from the field survey data. This data includes culvert sizes and spacing, low and high chords of bridges and pier shapes and sizes. Culvert entrance and exit coefficients and drag coefficients for piers were determined from tables in the HRM. Weir coefficients for the overflow sections on bridges and culverts were generally set to a value of 2.6 or less. Inline structures with well-defined crest sections were assigned a weir coefficient of 3.0. In limited detail reaches, bridges and culverts were input based on measurements in the field during the field reconnaissance and the overtopping section was measured from the project topography.
4.2.3 Manning Roughness Coefficients Manning roughness coefficients (“n values”) for the Rush Creek Watershed Models were assigned in accordance with Table 3-1 of the HEC-RAS Hydraulics Reference Manual. Proper assignment of Manning roughness coefficients begins with well-defined bank stations. These were located in each cross-section at a break in ground slope that divides the channel from the floodplain. A single n value was assigned to each channel section and one or more n values were assigned to the floodplain or overbank sections. The n values assigned to each study stream are listed Table 4-1.
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Rush Creek Watershed Study Final Report
Table 4-1. n values Stream Reach
Channel “n” Value
Overbank “n” Value
Forest Park Tributary Kee Branch Kee Branch Tributary 1 Kee Branch Tributary 1.1 Kee Branch Tributary 2 Kee Branch Tributary 4 Kee Branch Tributary 5 Northeast Tributary Pantego Branch Rush Creek Rush Creek Relief Channel Rush Creek Tributary 4 Rush Creek Tributary 4.1 Rush Creek Tributary 5 Rush Tributary 7 Rush Tributary 7.1 Rush Tributary 8 Rush Tributary 9 Rush Tributary 10 Rush Tributary 10.1 Rush Tributary 10.2 Rush Tributary 10.3 Rush Tributary 10.4 Rush Tributary 11 Rush Tributary 12 Rush Tributary 13 Rush Tributary 14 Rush Tributary 15 Rush Creek Tributary 16 Rush Creek Tributary 17 Rush Creek Tributary 19 Ryan’s Branch Ryan’s Branch Tributary 1 Stream KB-1 Stream KB-1.1 Stream RC-1 Stream RC-1 North Diversion Channel Stream RC-1 West Diversion Channel Stream RC-1 Tributary 1 Stream RC-1 Tributary 2 Stream RC-1A Stream RC-2
0.045 – 0.055 0.045 – 0.065 0.065 0.065 0.050 – 0.065 0.055 0.020 – 0.055 0.050 – 0.065 0.035 – 0.055 0.015 – 0.065 0.025 – 0.050 0.017 – 0.055 0.040 – 0.050 0.045 0.020 – 0.050 0.045 0.050 0.025 – 0.100 0.045 – 0.100 0.045 0.025 – 0.050 0.030 – 0.050 0.045 0.045 0.045 0.045 0.045 0.025 0.050 – 0.060 0.050 – 0.080 0.045 – 0.055 0.050 – 0.052 0.045 0.035 – 0.065 0.055 – 0.065 0.030 – 0.045 0.055 – 0.060 0.060 0.055 0.055 0.015-0.065 0.035 -0.047
0.065 – 0.100 0.050 – 0.500 0.070 – 0.100 0.100 0.080 – 0.100 0.070 – 0.100 0.080 – 0.100 0.050 – 0.200 0.015 – 0.500 0.015 – 0.500 0.015 – 0.500 0.030 – 0.500 0.040 – 0.500 0.150 – 0.500 0.030 – 0.500 0.100 – 0.500 0.030 – 0.500 0.045 – 0.500 0.050 – 0.500 0.100 – 0.500 0.050 – 0.500 0.065 – 0.500 0.100 – 0.500 0.050 – 0.500 0.100 0.060 – 0.500 0.050 – 0.500 0.080 – 0.500 0.050 – 0.080 0.060 – 0.100 0.055 – 0.085 0.050 – 0.500 0.065 – 0.075 0.040 – 0.500 0.065 – 0.100 0.045 – 0.500 0.035 – 0.070 0.035 – 0.500 0.500 0.100 – 0.500 0.045 – 0.100 0.020 – 0.500
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Rush Creek Watershed Study Final Report
Table 4-1. n values Stream Reach
Channel “n” Value
Overbank “n” Value
Sublett Creek Sublett Creek Tributary 1 Sublett Creek Tributary 1.1 Sublett Creek Tributary 2 Sublett Creek Tributary 3 Twin Springs Draw Twin Springs Draw Tributary 2 Twin Springs Draw Tributary 4 Twin Springs Draw Tributary 5
0.050 – 0.062 0.045 – 0.055 0.050 – 0.060 0.040 – 0.050 0.030 – 0.060 0.030 – 0.055 0.045 0.050 0.035
0.050 – 0.500 0.055 – 0.200 0.080 – 0.200 0.080 – 0.200 0.050 – 0.200 0.045 – 0.500 0.100 0.100 – 0.500 0.050 – 0.100
4.2.4 Ineffective Flow Ineffective flow areas occur in cross-sections adjacent to structure embankments and in isolated low areas in floodplains. These were defined as needed throughout the models to prevent overestimating the channel conveyance capacity.
4.2.5 HTab Parameters Unsteady HEC-RAS uses Hydraulic Tables (HTabs) to store cross-section properties and structure rating curves. The design of these tables is specified by the user so that each table is consistent with the model scale because large streams and small streams need to use different HTab parameter sets. For the Rush Creek models, the following parameter values were used. 4.2.5.1
HTab Parameters for Cross-Sections
The HTAB parameters for cross-sections were set to 100 increments (points) for all crosssections. The starting value was generally set to 0.5 feet above the invert and the elevation increment was set to the smallest value that provides sufficient tabulated depth to reach the top of the cross-section. 4.2.5.2 HTab Parameters for Structures
The HTAB parameters for bridges and culverts were initially set to the following values:
Number of Points on Free Flow (FF) Curve: 40
Number of Rating Curves (RC): 50
Number of Points on RC: 40
Reasonable maximum headwater elevations and maximum flows were also assigned for each structure. Occasionally, it was necessary to adjust these initial values during model debugging.
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4.3
Boundary Conditions & Flow Input
The boundary conditions for the unsteady flow models include:
A time boundary -- an initial condition for every element in the model
Extent boundaries -- a time series at the upstream model terminus and normal depth as the downstream boundary condition
The downstream boundary condition was set to normal depth for all steady flow simulations.
4.3.1
Unsteady Flow Input
The hydrology model generates flow hydrographs for each modeled subbasin. As needed, subbasin hydrographs were routed and combined within the hydrology model until flow arrives at a reach represented in the HEC-RAS model, at which point the hydrograph is loaded into the HEC-RAS model. There are four situations where hydrographs must be applied in a HECRAS model:
Flow at the upstream end of a modeled reach
Flow distributed along a reach representing a subbasin transited by the reach
Lateral inflow at a point representing the inflow from a tributary
Flow from an adjacent watershed model.
4.3.1.1
Initial Flow
A set of initial flows was developed for each model because HEC-RAS requires non-zero flow in all reaches at all times. Initial flows were set as low as possible and to obey continuity at every junction. The small magnitudes of the initial flows do not influence the resulting water surface elevations for the simulated flood flow conditions. 4.3.1.2
Minimum Flow
Minimum flows were assigned to load points, as needed, to prevent zero flows in a reach and assure continuity is maintained in every reach under low flow conditions.
4.3.2 Steady Flow Input Peak discharges from the hydrologic model were applied at key flow change locations (cross sections) in HEC-RAS for each study stream. Typical flow change locations include:
Peak flow contributing at the most upstream HEC RAS cross section
Immediately downstream of inflow from a tributary
At a point where approximately 2/3 of the local subbasin transited by the study reach contributes to the stream.
4.4
Quality Control
Multiple technical reviews of the hydrologic analysis were conducted by CDM Smith, while Halff Associates performed internal reviews for both the hydrologic and hydraulic analysis. All hydrologic and hydraulic Quality Assurance/Quality Control (QAQC) certification forms can be found in Appendix H of this report.
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Rush Creek Watershed Study Final Report
4.5
Results
The HEC-RAS models were run and debugged for each of the flow scenarios specified and flows and elevations were obtained. Several steps were taken to verify and validate the results and adjustments were made to improve correlation with known data. Then final production runs were performed for floodplain mapping and problem identification.
4.5.1
Modeled Flows and Stages
The completed models were used to determine BFEs for all of the modeled flooding sources and to generate flood profiles for detailed studied streams as presented in Appendix E. Table 4-2 below provides a comparison between effective 1% annual chance water surface elevations and discharges at key locations along each of the detailed study streams.
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Location
At confluence with Rush Creek Downstream of confluence of Tributary 2
Drainage WS Area Elevation (Sq. Mi.) FIS
Kee Branch
136
Kee Branch
6,505
Kee Branch
10,493
Kee Branch
15,743
Kee Branch
16,088
Kee Branch
18,094
At interstate Route 20 Downstream of confluence of Tributary 4 Upstream of confluence of Tributary 4 Downstream of confluence of Tributary 5
Kee Branch
21,238
At U.S. Route 287
1.09
Kee Branch
25,758
At Kennendale Sublett Road At confluence with Kee Branch
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
7.23
539.8
534.60
10,920
11,587
6.96
556.3
556.23
9,970
10,531
4.44
572.6
575.45
7,300
6,615
3.55
593
592.30
6,420
7,828
2.85
593.05
5,020
6,058
1.40
602.51
2,140
5,757
610.6
616.45
1,640
4,054
0.89
637.6
638.45
1,840
2,256
1.52
573
568.04
3,670
5,471
At Oak Springs Road
1.26
585.5
586.59
3,120
4,383
At confluence with Rush Creek
1.68
499.9
494.16
3,710
4,030
Stream KB-1
68
Stream KB-1 Pantego Branch Pantego Branch Pantego Branch
2,395
3,131
At West Park Row
1.43
522.5
521.20
3,310
3,567
7,499
At Smith-Barry Road
0.94
556.5
557.98
2,290
3,206
Rush Creek
9,094
At confluence of Pantego Branch
29.01
499.8
500.68
4,704
6,959
Rush Creek
13,423
At State Route 303
28.77
510.7
511.82
27,060
28,088
Rush Creek
15,008
At Woodland Park Boulevard
27.59
516
517.41
26,670
28,153
Rush Creek
18,067
At Arkansas Lane
27.17
523.3
525.02
27,180
27,984
Rush Creek
24,444
Below confluence of Kee Branch
25.24
538.15
537.42
25,280
26,669
Rush Creek
24,900
At confluence of Kee Branch
18.01
538.15
538.46
16,850
15,953
275
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Rush Creek
5
Rush Creek
29,181
Rush Creek
5
Rush Creek
33,663
Rush Creek
33,974
Rush Creek
36,148
Rush Creek
37,789
Rush Creek
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
Below confluence of Ryan’s Branch
17.83
Above Kee Branch
17.52
At confluence of Ryan’s Branch Below confluence of Twin Springs Draw At confluence of Twin Springs Draw Downstream of confluence of Tributary 7 and Tributary 9
16.57
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
16,950 543.51
17,600
15,206
16,350
16.30
552.11
16,340
15,191
15.16
552.93
15,700
13,654
14.74
561.80
15,780
13,846
564.53
14,770
14,838
573.20
15,190
12,984
42,647
At interstate Route 20 Downstream of confluence of Tributary 10
13.07 12.78
Rush Creek
42,821
At confluence of Tributary 10
11.51
Rush Creek
47,930
10.82
Rush Creek
52,976
At Green Oaks Boulevard Downstream of confluence of Sublett Creek
Rush Creek
53,787
4.22
Rush Creek
54,743
At confluence of Sublett Creek Downstream of confluence of Tributary 16
Rush Creek
55,388
Rush Creek Rush Creek
565.9
573.36
14,010
10,480
587.54
13,890
11,819
596.62
13,179
11,518
598.55
6,270
5,723
3.04
600.40
5,490
5,867
585.1
9.51 595.5
2.54
601.99
4,610
5,713
67,236
At confluence of Tributary 16 Below confluence with Tributary 20
1.90
635.83
3,850
4,065
67,471
At confluence with Tributary 20
1.00
636.70
1,980
2,493
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location Forest Park Tributary of Rush Creek Northeast Tributary of Rush Creek Rush Creek Relief Channel
HEC-RAS Station
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
164
At confluence with Rush Creek
0.18
612.30
609.41
610
895
130
At confluence with Rush Creek
0.11
613.20
606.66
361
610
4
498.00
30,374
3
3.56
491.50
488.21
6,850
2,777
1.95
530.00
529.63
3,630
5,332
5
Upstream of convergence with Village Creek
Stream RC-1
455
Stream RC-1 Stream RC1A Stream RC1A
3,592
At confluence with Rush Creek Immediately upstream of Union Pacific Railroad
632
At confluence with Stream RC-1
1.36
528.00
523.82
3,180
4,439
At Bowen Road
0.93
562.00
564.16
2,480
3,976
Stream RC-2
480
At confluence with Rush Creek
1.18
516.50
517.64
2,790
494
Stream RC-2 Ryan's Branch Ryan's Branch Sublett Creek Sublett Creek Sublett Creek
5
At headwaters
0.64
At confluence with Rush Creek
1.29
545.00
541.46
3,100
3,562
At Roosevelt Drive
0.99
576.50
579.84
2,800
1,807
554
At confluence with Rush Creek
5.29
599.50
599.15
7,500
5,873
7,517
D/S Calendar Road (US Trib 1) Below confluence with Sublett Creek Tributary 3
4.57
624.25
623.49
7,060
5,652
3.66
638.60
637.87
5,790
5,478
3,836
851 5,439
12,975
1,930
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Rush Creek Watershed Study Final Report
Table 4-2 Flooding Source Comparison of Representative 1% Annual Chance Discharges Flooding Source and Location
HEC-RAS Station
Sublett Creek Sublett Creek Twin Springs Draw
16,601
Location
Drainage WS Area Elevation (Sq. Mi.) FIS
WS Elevation Model
Peak Discharge (cfs) 1% Annual Chance1
Revised Discharge (cfs)2
2.99
650.50
650.38
5,170
4,415
22,270
At U.S. Route 287 Below confluence with Sublett Creek Tributary 4
1.83
669.00
666.11
3,800
2,966
87
At confluence with Rush Creek
1.17
554.00
551.10
2,850
4,418
1
Source: Federal Emergency Management Agency Flood Insurance Study, Tarrant County, Texas Volume 1
2
From Hydraulic Models
3
Not likely the same location
4
Data not available
5
Location could not be determined from the information available in the effective FIS
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Rush Creek Watershed Study Final Report
5.
Updated Floodplain Map/Physical Map Revision
The hydraulic models described in Section 4 were developed update the FEMA floodplain maps which are currently based on modeling completed in 1985. FEMA has two processes for revising floodplain maps:
Letter of Map Revision (LOMR), and
Physical Map Revision (PMR).
Generally, LOMRs are used to revise a part of a stream system while PMRs are used to revise entire map panels. In a PMR, all components of a map are revised, including the base map, flood elevations, and floodway extents. Clearly the size and extent of the Rush Creek revisions warrant the use of the PMR option even though it is more expensive and will have a fairly long review and republication timeline. The primary elements of a PMR submitted are the base map, the base flood and 0.2% flood elevations, the floodway delineations and the model documentation. These elements are described in the following sections.
5.1
Base Map
The FEMA FIRM panels were used as the base map for the floodplain work maps. Base map information used for the FIRM panels was provided in digital format by NCTCOG. This information was digitized at a scale of at least 1:12,000 from aerial photography dated 2003.
5.2
Floodplain Delineation
Updated floodplains were mapped based on water levels computed in the HEC-RAS model. For tributaries studied in limited detail, a floodplain was delineated based on the 1% annualchance water surface elevations. In the detailed study streams (including Rush Creek), both the 1- and 0.2 percent annual-chance floodplains have been mapped. In each case, a spatial data format (sdf) file was exported from HEC-RAS and imported into ArcGIS to begin the mapping. The resulting line work was then smoothed and adjusted along the length of the stream to achieve a floodplain delineation that follows the detail of the topography and bends around solid objects such as bridge abutments. Additionally, Zone A mapping for one area adjacent to Stream RC-1 was delineated based on a 2-D HEC-RAS model of the area. Floodplain work maps showing the revised floodplain delineations can be seen in Appendix J.
5.3
Flood Profiles
Water surface profiles for the 10-, 4-, 2-, 1-, and 0.2 percent annual-chance floods were prepared in FEMA format for all detailed study streams associated with this study. All profiles maintained the same horizontal and vertical scales used in the effective FIS report in accordance with FEMA standards for restudied streams. The profiles were prepared from the HEC-RAS computed maximum water surface elevation output with the assistance of the FEMA RAS-Plot software. The profile plots are included in Appendix E.
5.4
Floodway Computations
FEMA requires definition and delineation of a regulatory floodway on all streams that have an effective floodway. For Rush Creek, this includes all of the detailed study streams except for
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Rush Creek Watershed Study Final Report
Northeast Tributary, Forest Park Tributary, and Stream RC-1 West Diversion. In some cases, the floodway was extended farther upstream to match the detailed study stream length. Each unsteady HEC-RAS model was converted to steady state in order to develop floodway encroachments limits for the Rush Creek Watershed Study. The following procedures were used to define the floodway limits for Rush Creek studied streams. 1. Converted unsteady flow values related to the max water surface elevation profile to steady state flow change locations at all cross sections. 2. Computed steady state run and compared to unsteady 100-year max water surface elevations. 3. Identified cross section locations where the water surface elevation difference was greater than 0.5’ between the steady state and unsteady runs. 4. Revised the HEC-RAS geometry with the goal of eliminating differences to the extent practical, focusing mainly on differences greater than 0.5’ between the unsteady and steady 100-year water surface elevations. Typical geometry changes for the Rush Creek Watershed Study included revisions to cross section alignment, ineffective flow areas, and expansion/contraction coefficients, but may have included other model revisions. The goal was to produce one HEC-RAS model geometry that was utilized for the unsteady and steady state analyses. 5. Optimized floodway encroachments ensuring no greater than 1.0’ rise compared to the steady and unsteady 100-year water surface elevations. Floodway delineations can be seen in the Floodplain Work Maps in Appendix J. Floodway Data Tables are included in Appendix E.
5.5
FIS Report Section
For the flooding sources studied by detailed methods in the Rush Creek Watershed, standard hydrologic and hydraulic study methods were used to determine the flood-hazard data required for this study. Flood events of a magnitude that is expected to be equaled or exceeded with a 10-, 4-, 2-, 1-, and 0.2 percent annual-chance, respectively, during any year were determined. The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study.
5.5.1
Hydrologic Analysis
Hydrologic methods used for this study are in accordance with Appendix C of FEMAs Guidelines and Specifications for Flood Hazard Mapping Partners dated November 2009. The analytical approach generally followed the Natural Resources Conservation Service (NRCS), formerly the SCS, procedures as outlined in Technical Release Number 55 (TR-55). The hydrologic rainfall/runoff model developed by the USACE Hydrologic Engineering Center
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Rush Creek Watershed Study Final Report
(HEC), HEC-HMS Version 3.5, was used to estimate runoff discharge hydrographs from individual subbasins. The primary source of terrain data used for this study was developed by processing the 2009 Light Detection and Ranging (LIDAR) topographical data obtained from Texas Natural Resources Information System (TNRIS) for the Rush Creek Watershed. The terrain data was used along with the HEC-GeoHMS extension to generate the subbasin delineations. Rush Creek rainfall totals for the frequency floods were obtained from the NWS Technical Paper No. 40. These rainfall depths were compared with other sources including USGS Atlas of Depth-Duration Frequency of Precipitation Annual Maxima for Texas, Scientific Investigations Report 2004-5041 and it was determined that the TP-40 data were consistent with recent studies. A 24-hour duration nested frequency hypothetical storm was used for the various frequency event simulations in HEC-HMS. Soils information was obtained from the U.S. Department of Agriculture, NRCS Soil Survey Geographic (SSURGO) database for Tarrant County published in 2009. Hydrologic Soil types B, C and D are nearly evenly distributed throughout the watershed with a little bit of type A soil in places. Type D is the most common soil in the Rush Creek and RC-1 watersheds. A shape file of existing (2010) land use was obtained from the North Central Texas Council of Governments (NCTCOG). Runoff losses were computed using the NRCS Loss Rate Method. Composite, soil based curve numbers were computed for each subbasin using GIS Tools. Percent impervious values were computed based on the composite land use for each subbasin. The NRCS dimensionless unit hydrograph was selected to compute the unit hydrograph. The time of concentration calculations were split into three sections including overland, shallow, and channel flow. Overland flow was calculated using the coefficient of velocity. Times of concentration (tc) were computed using a modified velocity method outlined in the NRCS Technical Release 55 for shallow, and channel flow. Lag time (tlag) for each watershed was calculated by using the equation tlag = (0.6)tc . The Modified-Puls routing method was utilized in HEC-HMS for all steady state reaches. HEC-RAS v4.1 was used to develop storage-discharge relationships for each Modified-Puls routing reach. Channel routing was performed in HEC-RAS for all unsteady reaches. The Muskingum-Cunge method was used to route flows through storm drain reaches outside of the unsteady hydraulic study reaches.
5.5.2 Hydraulic Analysis Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected flood frequencies. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data tables in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS report in conjunction with the data shown on the FIRM.
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Rush Creek Watershed Study Final Report
Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Appendix E). For stream segments for which a floodway was computed (Section 5.4), selected cross-section locations are also shown on the FIRM. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the Flood Profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Detailed study streams are listed in Section 1 and shown in Table 1-1. Hydraulic methods used for this study are in accordance with the Guidelines and Specifications for Flood Hazard Mapping Partners dated April 2003 and Appendix C of the Guidelines dated November 2009. The following is a summary of data sources, assumptions, and procedures used to create the hydraulic models for the study streams. The primary source of terrain data used for this hydraulic study was developed from TNRIS 2009 LIDAR data. Roughness coefficients (Manning’s “n” values) used in the hydraulic computations were estimated on the basis of field inspection and NCTCOG 2011 aerial photography. The channel and overbank “n” values are shown in Table 4-1, “Summary of Roughness Coefficients.” A triangulated irregular network (TIN) was created by Halff Associates utilizing the 2009 LiDAR mass points and break lines in order for HEC-GeoRAS to extract cross-section geometry data for use in HEC-RAS. All floodplains were mapped using the 2009 LiDAR data. Water surface profiles for the 10-, 4-, 2-, 1- and 0.2 percent annual-chance events were computed using the River Analysis System HEC-RAS Version 4.1.0., dated January 2010. Cross-sections, taken from field surveys conducted as part of this study, were supplemented with HEC-GeoRAS cross-sections cut from the TIN’s generated using the 2009 LiDAR. Bridge data used for the hydraulic models were taken from field surveys. Profiles (Appendix E) were generated using RAS-PLOT. Profiles were plotted at the same scale as the previous FIS profiles.
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Rush Creek Watershed Study Final Report
Appendix A: Technical Standards
A1
Rush Creek Watershed Study Final Report
Appendix B: Hydrologic Parameter Summary
A2
Rush Creek Watershed Study Final Report
Appendix C: Public Meeting Information
A3
Rush Creek Watershed Study Final Report
Appendix D: Lidar Quality Assurance Report
A4
Rush Creek Watershed Study Final Report
Appendix E: Floodway Data Tables and Profiles
A5
Rush Creek Watershed Study Final Report
Appendix F: Hydraulic and Hydrologic Database Provided in digital format (DVD)
A6
Rush Creek Watershed Study Final Report
Appendix G: Hydraulic and Hydrologic Models Provided in digital format (DVD)
A7
Rush Creek Watershed Study Final Report
Appendix H: QA/QC Forms
A8
Rush Creek Watershed Study Final Report
Appendix I: Survey Data
A9
Rush Creek Watershed Study Final Report
Appendix J: Floodplain Workmaps
A10
