The Use Of LID As An Alternative To Traditional Stormwater ...
The Use Of LID As An Alternative To Traditional Stormwater Management Practices In Takoma Park, Maryland Richard L. Stanford, 1
1 P.E.
President, ATR Associates, Strasburg, Virginia 22657
2
and Ali Khalilian,
2 P.E.
City Engineer, City of Takoma Park, Maryland 20910
“Cleveland Avenue Rain Garden ” - Phase I
Alternative Designs
The City of Takoma Park, Maryland successfully installed a sustainable stormwater management alternative to standard storm drains and pipes within a neighborhood with no existing stormwater management system. The properties located at the downgradient end of Cleveland Avenue received run-off that caused local yard flooding and erosion, sediment from the street washoff, and to some extent water intrusion into basements.
FINAL
INITIAL
Conventional stormwater run off management would have required the installation of over 1,000 linear feet of stormwater sewer pipe through difficult terrain along a tree-lined street, across private properties, and along a State Highway. The City held several public outreach meetings where environmentally sensitive solutions to the stormwater management problems were discussed and contrasted with conventional pipe placement. A landscaping design firm, Natural Resources Design, Inc., and an ecological engineering firm, ATR Associates, Inc., in conjunction with the City Engineer, developed the concept and plans for a low-impact stormwater management system for the neighborhood. A key component of the system is a 1,300 S.F. bioretention (“Rain Garden”) unit located on a residential property at the downgradient end of the street. The rain garden is designed with a capacity sufficient to retain the runoff from a 10-year storm event. This phase was completed in July of 2007. The resident on whose property the rain garden was built participated in a partnership with the City for construction of the rain garden. According to the agreement worked out between City stormwater staff and the property owner, the facility will be maintained cooperatively. Initial design included two roadside infiltration trenches, one end-ofpavement interceptor trench, and two rain gardens
Cleveland Avenue Infiltration Basin - Phase II Phase II of the Cleveland Ave Stormwater Management Project consisted of constructing an infiltration basin to capture, detain and infiltrate runoff from the neighborhood. The basin is installed beneath the pavement at the downgradient end of the street. The asphalt and concrete street pavement was removed and replaced with permeable pavers that allow the run-off to enter the underlying infiltration basin.
Final design included one end-of-pavement interceptor gallery, one endof-pavement interceptor trench, and one rain garden
DRAINAGE AREA 25,315 SQ. FT. (0.58 AC.)
The infiltration basin includes 36 Rainstore3® units embedded in gravel and underlain by a layer of geo-grid to reinforce granular sub base material and to provide a pavement structure capable withstanding H-20 (Heavy Trucks) vehicular loading. If the storm event generates runoff sufficient to fill the infiltration basin’s reservoir course the overflow is discharged through a series of pipes into an abutting collection trench which in turn discharges into the 1,300 S.F. rain garden constructed during Phase I.
SIZING CRITERIA WQV
11,573 SQ. FT. IMPERVIOUS (45.7%)
Water Quality Volume
SOILS – HSG B
WQv Subarea
Soil Properties Depth (in)
Soil name
Sand (%)
Silt (%)
Clay (%)
Moist bulk density (g/cc)
Saturated hydraulic conductivity (µm/sec ; in/hr)
Linear extensibility* (%)
P
I
Rv
A (ac.-ft.)
ft³
Northern
1.0
43.3
0.44
0.326
0.012
521
Southern
1.0
53.7
0.53
0.23
0.010
442
TOTAL
The infiltration basin is capable retaining runoff generated from a 2-year storm event (3.2”). It has been shown that 99% of the storms in Washington area result in less than 3“ of rainfall in a 24 hour period. The Phase II project was designed by ATR Associates, Inc., which also oversaw the construction of the system.
Gaila
Glenelg
When combined, the Phase I and Phase II stormwater management system at Cleveland Avenue is design to store runoff generated by a 75-year storm event.
0–8 8 – 17 17 – 20 20 – 76
---------
---------
10 – 25 18 – 30 10 – 25 5 – 20
1.20 – 1.40 1.30 – 1.50 1.25 – 1.50 1.25 – 1.50
4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98 14.00 – 42.00 ; 1.98 – 5.95 14.00 – 42.00 ; 1.98 – 5.95
0.0 – 2.9 0.0 – 2.9 0.0 – 2.9 0.0 – 2.9
0–8 8 – 28 28 – 60
-------
-------
15 – 25 20 – 32 5 – 20
1.10 – 1.40 1.20 – 1.60 1.20 – 1.40
4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98
0.0 – 2.9 0.0 – 2.9 0.0 – 2.9
* Linear extensibility is used to determine the shrink-swell potential of soils. The shrink-swell potential is low if the soil has a linear extensibility of less than 3 percent; moderate if 3 to 6 percent; high if 6 to 9 percent; and very high if more than 9 percent. If the linear extensibility is more than 3, shrinking and swelling can cause damage to buildings, roads, and other structures and to plant roots. Special design commonly is needed.
TRENCH DRAIN
963
ReV Recharge Volume Percent Volume Method Subarea
I
Rv
A
S
Northern
43.3
0.44
0.326
Southern
53.7
0.53
0.23
TOTAL
Percent Area Method Rev
Ai
S
Rev (ac.)
135
0.047
0.26
0.012
115
0.037
0.26
0.010
(ac.-ft.)
ft³
0.26
0.003
0.26
0.0026
250
BIORETENTION
POROUS PAVERS & INFILTRATION GALLERY
ELEVATION – CROSS SECTION
ELEVATION – CROSS SECTION 1"
6" MAX DEPTH
HARDWOOD MULCH
4"
THE POROUS PAVEMENT WAS CONSTRUCTED OF 775 SQ. FT. OF E.P. HENRY ECO-II PAVING STONES AND No. 8 GRAVEL.
6" DIA. SCHEDULE 40 SOLID PVC RISER
UTILITIES DETAIL
THE INFILTRATION GALLERY IS COMPOSED OF GRAVEL AND RAINSTORE3® UNITS BY INVISIBLE STRUCTURES, INC. THE MODULAR DESIGN OF THE RAINSTORE3 UNITS ALLOW THE UNITS TO BE SEPARATED TO ACCOMMODATE THE EXISTING WATER AND GAS UTILITY MAIN AND LATERAL LINES THAT ARE BELOW THE STREET.
ENGINEERED SOIL
THE TRENCH DRAIN IS A POURED-IN-PLACE CONCRETE DRAIN WITH A NEENAH GRATING. IT INTERCEPTS RUNOFF THAT MAY FLOW OVER THE PERMEABLE PAVER AREA AND ACCEPTS OVERFLOW FROM THE INFILTRATION GALLERY. A SINGLE 8” DIAMETER SOLID PVC PIPE CONVEYS WATER FROM THE TRENCH TO THE BIORETENTION UNIT.
SUBGRADE SOILS WERE NOT COMPACTED BELOW THE ‘MAIN’ INFILTRATION AREA, BUT SUBGRADE SOILS WERE COMPACTED IN THE PARKING SHOULDERS. WATER IS COLLECTED IN THE INFILTRATION AREA UNTIL THE HEIGHT REACHES THE FOUR PERFORATED PIPES INSTALLED DIRECTLY BELOW THE ROADWAY PERMEABLE PAVERS. WATER COLLECTED IN THE PERFORATED PIPES IS TRANSMITTED TO THE TERMINAL TRENCH DRAIN.
6" DIA. SCHEDULE 40 SOLID PVC PIPE @ >= 0.5% SLOPE
2'-6"
ASTM C-33 CONCRETE SAND OR VDOT FINE AGGREGATE CLASS A OR B 6"
PARKING SHOULDER DETAIL
ELEVATION – CROSS SECTION
THE 1,300 SQ. FT. RAIN GARDEN IS A VERY SIMPLE DESIGN – MADE POSSIBLE BY THE SANDY HSG “B” SOILS AT THE SITE. THE 6” DIAMETER PVC UNDERDRAIN IS IMBEDDED IN A SAND ‘RESERVOIR’ LAYER – NO GRAVEL IS USED. THE UNDERDRAIN IS NOT CONNECTED TO A STORM SEWER, NOR IS IT DAYLIGHTED. THE UNDERDRAIN IS STUBBED OFF IN ORDER TO ALLOW CONNECTION IF WARRANTED. IF AN UNDERDRAIN EXTENSION IS NEEDED, IT WILL BE DAYLIGHTED ONTO PINEY BRANCH ROAD – APPROXIMATELY 150’ DOWNHILL. AT PRESENT, ANY OVERFLOW FROM THE RAIN GARDEN IS RELEASED THROUGH AN ‘EMERGENCY SPILLWAY’ WITH AN EMBEDDED LEVEL SPREADER. TO DATE, ONLY THE LARGEST STORMS (I.E., HURRICANES) HAVE PRODUCED ENOUGH RUNOFF IN A SHORT A PERIOD OF TIME TO PRODUCE AN OUTFLOW OVER THE LEVEL SPREADER.
1 P.E.
President, ATR Associates, Strasburg, Virginia 22657
2
and Ali Khalilian,
2 P.E.
City Engineer, City of Takoma Park, Maryland 20910
“Cleveland Avenue Rain Garden ” - Phase I
Alternative Designs
The City of Takoma Park, Maryland successfully installed a sustainable stormwater management alternative to standard storm drains and pipes within a neighborhood with no existing stormwater management system. The properties located at the downgradient end of Cleveland Avenue received run-off that caused local yard flooding and erosion, sediment from the street washoff, and to some extent water intrusion into basements.
FINAL
INITIAL
Conventional stormwater run off management would have required the installation of over 1,000 linear feet of stormwater sewer pipe through difficult terrain along a tree-lined street, across private properties, and along a State Highway. The City held several public outreach meetings where environmentally sensitive solutions to the stormwater management problems were discussed and contrasted with conventional pipe placement. A landscaping design firm, Natural Resources Design, Inc., and an ecological engineering firm, ATR Associates, Inc., in conjunction with the City Engineer, developed the concept and plans for a low-impact stormwater management system for the neighborhood. A key component of the system is a 1,300 S.F. bioretention (“Rain Garden”) unit located on a residential property at the downgradient end of the street. The rain garden is designed with a capacity sufficient to retain the runoff from a 10-year storm event. This phase was completed in July of 2007. The resident on whose property the rain garden was built participated in a partnership with the City for construction of the rain garden. According to the agreement worked out between City stormwater staff and the property owner, the facility will be maintained cooperatively. Initial design included two roadside infiltration trenches, one end-ofpavement interceptor trench, and two rain gardens
Cleveland Avenue Infiltration Basin - Phase II Phase II of the Cleveland Ave Stormwater Management Project consisted of constructing an infiltration basin to capture, detain and infiltrate runoff from the neighborhood. The basin is installed beneath the pavement at the downgradient end of the street. The asphalt and concrete street pavement was removed and replaced with permeable pavers that allow the run-off to enter the underlying infiltration basin.
Final design included one end-of-pavement interceptor gallery, one endof-pavement interceptor trench, and one rain garden
DRAINAGE AREA 25,315 SQ. FT. (0.58 AC.)
The infiltration basin includes 36 Rainstore3® units embedded in gravel and underlain by a layer of geo-grid to reinforce granular sub base material and to provide a pavement structure capable withstanding H-20 (Heavy Trucks) vehicular loading. If the storm event generates runoff sufficient to fill the infiltration basin’s reservoir course the overflow is discharged through a series of pipes into an abutting collection trench which in turn discharges into the 1,300 S.F. rain garden constructed during Phase I.
SIZING CRITERIA WQV
11,573 SQ. FT. IMPERVIOUS (45.7%)
Water Quality Volume
SOILS – HSG B
WQv Subarea
Soil Properties Depth (in)
Soil name
Sand (%)
Silt (%)
Clay (%)
Moist bulk density (g/cc)
Saturated hydraulic conductivity (µm/sec ; in/hr)
Linear extensibility* (%)
P
I
Rv
A (ac.-ft.)
ft³
Northern
1.0
43.3
0.44
0.326
0.012
521
Southern
1.0
53.7
0.53
0.23
0.010
442
TOTAL
The infiltration basin is capable retaining runoff generated from a 2-year storm event (3.2”). It has been shown that 99% of the storms in Washington area result in less than 3“ of rainfall in a 24 hour period. The Phase II project was designed by ATR Associates, Inc., which also oversaw the construction of the system.
Gaila
Glenelg
When combined, the Phase I and Phase II stormwater management system at Cleveland Avenue is design to store runoff generated by a 75-year storm event.
0–8 8 – 17 17 – 20 20 – 76
---------
---------
10 – 25 18 – 30 10 – 25 5 – 20
1.20 – 1.40 1.30 – 1.50 1.25 – 1.50 1.25 – 1.50
4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98 14.00 – 42.00 ; 1.98 – 5.95 14.00 – 42.00 ; 1.98 – 5.95
0.0 – 2.9 0.0 – 2.9 0.0 – 2.9 0.0 – 2.9
0–8 8 – 28 28 – 60
-------
-------
15 – 25 20 – 32 5 – 20
1.10 – 1.40 1.20 – 1.60 1.20 – 1.40
4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98 4.00 – 14.00 ; 0.57 – 1.98
0.0 – 2.9 0.0 – 2.9 0.0 – 2.9
* Linear extensibility is used to determine the shrink-swell potential of soils. The shrink-swell potential is low if the soil has a linear extensibility of less than 3 percent; moderate if 3 to 6 percent; high if 6 to 9 percent; and very high if more than 9 percent. If the linear extensibility is more than 3, shrinking and swelling can cause damage to buildings, roads, and other structures and to plant roots. Special design commonly is needed.
TRENCH DRAIN
963
ReV Recharge Volume Percent Volume Method Subarea
I
Rv
A
S
Northern
43.3
0.44
0.326
Southern
53.7
0.53
0.23
TOTAL
Percent Area Method Rev
Ai
S
Rev (ac.)
135
0.047
0.26
0.012
115
0.037
0.26
0.010
(ac.-ft.)
ft³
0.26
0.003
0.26
0.0026
250
BIORETENTION
POROUS PAVERS & INFILTRATION GALLERY
ELEVATION – CROSS SECTION
ELEVATION – CROSS SECTION 1"
6" MAX DEPTH
HARDWOOD MULCH
4"
THE POROUS PAVEMENT WAS CONSTRUCTED OF 775 SQ. FT. OF E.P. HENRY ECO-II PAVING STONES AND No. 8 GRAVEL.
6" DIA. SCHEDULE 40 SOLID PVC RISER
UTILITIES DETAIL
THE INFILTRATION GALLERY IS COMPOSED OF GRAVEL AND RAINSTORE3® UNITS BY INVISIBLE STRUCTURES, INC. THE MODULAR DESIGN OF THE RAINSTORE3 UNITS ALLOW THE UNITS TO BE SEPARATED TO ACCOMMODATE THE EXISTING WATER AND GAS UTILITY MAIN AND LATERAL LINES THAT ARE BELOW THE STREET.
ENGINEERED SOIL
THE TRENCH DRAIN IS A POURED-IN-PLACE CONCRETE DRAIN WITH A NEENAH GRATING. IT INTERCEPTS RUNOFF THAT MAY FLOW OVER THE PERMEABLE PAVER AREA AND ACCEPTS OVERFLOW FROM THE INFILTRATION GALLERY. A SINGLE 8” DIAMETER SOLID PVC PIPE CONVEYS WATER FROM THE TRENCH TO THE BIORETENTION UNIT.
SUBGRADE SOILS WERE NOT COMPACTED BELOW THE ‘MAIN’ INFILTRATION AREA, BUT SUBGRADE SOILS WERE COMPACTED IN THE PARKING SHOULDERS. WATER IS COLLECTED IN THE INFILTRATION AREA UNTIL THE HEIGHT REACHES THE FOUR PERFORATED PIPES INSTALLED DIRECTLY BELOW THE ROADWAY PERMEABLE PAVERS. WATER COLLECTED IN THE PERFORATED PIPES IS TRANSMITTED TO THE TERMINAL TRENCH DRAIN.
6" DIA. SCHEDULE 40 SOLID PVC PIPE @ >= 0.5% SLOPE
2'-6"
ASTM C-33 CONCRETE SAND OR VDOT FINE AGGREGATE CLASS A OR B 6"
PARKING SHOULDER DETAIL
ELEVATION – CROSS SECTION
THE 1,300 SQ. FT. RAIN GARDEN IS A VERY SIMPLE DESIGN – MADE POSSIBLE BY THE SANDY HSG “B” SOILS AT THE SITE. THE 6” DIAMETER PVC UNDERDRAIN IS IMBEDDED IN A SAND ‘RESERVOIR’ LAYER – NO GRAVEL IS USED. THE UNDERDRAIN IS NOT CONNECTED TO A STORM SEWER, NOR IS IT DAYLIGHTED. THE UNDERDRAIN IS STUBBED OFF IN ORDER TO ALLOW CONNECTION IF WARRANTED. IF AN UNDERDRAIN EXTENSION IS NEEDED, IT WILL BE DAYLIGHTED ONTO PINEY BRANCH ROAD – APPROXIMATELY 150’ DOWNHILL. AT PRESENT, ANY OVERFLOW FROM THE RAIN GARDEN IS RELEASED THROUGH AN ‘EMERGENCY SPILLWAY’ WITH AN EMBEDDED LEVEL SPREADER. TO DATE, ONLY THE LARGEST STORMS (I.E., HURRICANES) HAVE PRODUCED ENOUGH RUNOFF IN A SHORT A PERIOD OF TIME TO PRODUCE AN OUTFLOW OVER THE LEVEL SPREADER.
