FY 2007 Proposed Budget - Arlingtonva
Subject: Lessons Learned from Little Pimmit Run Projects
FY 2015 Proposed Budget Budget Work Session Follow-up April 1, 2014 The following information is provided in response to a question raised by Mr. Tejada on March 20, 2014, regarding lessons learned from the Little Pimmit Run drainage improvement projects, including the downstream impacts study that was completed in 2010. Significant flood risk reduction work has been completed for the most vulnerable properties in the Little Pimmit Run stream corridor with completion of the culvert replacements at Old Dominion Drive and Williamsburg Boulevard in 2007 and 2010, respectively. Old Dominion Drive Culvert Replacement Project (2007):
Prior to construction
After construction
Williamsburg Boulevard Culvert Replacement Project (2010):
Prior to construction
During construction
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Subject: Lessons Learned from Little Pimmit Run Projects Phase 1 consisted of the replacement of the Old Dominion culvert. Construction started in spring of 2007. The construction cost was $900,000. Phase 2 included the replacement of the Williamsburg culvert and replacement of the concrete channel from Williamsburg Boulevard to Little Falls Road. The construction cost was $1,750,000. The Little Pimmit Run 'downstream impacts' study (Phase 3) was also completed in 2010 at a cost of approximately $200,000. The study included additional hydrologic and hydraulic analysis of Little Pimmit Run and work with an Advisory Committee to develop conceptual designs to improve flood protection and habitat downstream from the culvert projects. Lessons learned from the ‘downstream impacts’ study include the following: • Little Pimmit Run is a highly constrained stream corridor with limited opportunities for stream restoration and flood risk reduction because of stream alignment and proximity of homes to the stream. • Most property owners do not want the stream any closer to their homes, even if that means improved stream habitat and reductions in overall flood risks along the corridor. • Substantial implementation of watershed 'retrofit' projects like green streets has important stream habitat and pollution reduction benefits, but due to limited available locations, cannot reduce flooding from major storm events like the June 2006 flood. • The study provided significant knowledge about watershed, stream, and storm sewer capacity analytical tools. This information has greatly informed the storm sewer capacity analysis work that has been completed for the update of the Stormwater Master Plan, scheduled to be considered by the County Board in June 2014. Continued design and implementation of the stream and infrastructure improvement recommendations of the Little Pimmit Run 'downstream impacts' study has been shifted to later years in the draft FY 15-24 CIP. This is due to much higher priority stream and watershed improvement work driven by the County's new MS4 permit and Bay TMDL pollution reduction requirements; these priorities are reflected in the Stormwater Master Plan. Staff expects implementation of the key recommendations of the Little Pimmit Run study to occur at some point in the future, but given limited resources and staff throughput capacity, this work is currently not a top priority from a regulatory or flood risk reduction perspective. Additional information about the Phase 3 study, including the final report from the Little Pimmit Run Advisory Committee, is available on the following County website: http://www.arlingtonva.us/departments/EnvironmentalServices/Sustainability/page60407.aspx
L:\DMFBUD\Bud15\Worksessions\Follow up which has gone to the Board\J-1 DES Stormwater Pimmet Run.docx
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FY 2015 Proposed Budget Budget Work Session Follow-up April 1, 2014 The following information is provided in response to a question raised by Mr. Tejada on March 20, 2014, regarding lessons learned from the Little Pimmit Run drainage improvement projects, including the downstream impacts study that was completed in 2010. Significant flood risk reduction work has been completed for the most vulnerable properties in the Little Pimmit Run stream corridor with completion of the culvert replacements at Old Dominion Drive and Williamsburg Boulevard in 2007 and 2010, respectively. Old Dominion Drive Culvert Replacement Project (2007):
Prior to construction
After construction
Williamsburg Boulevard Culvert Replacement Project (2010):
Prior to construction
During construction
L:\DMFBUD\Bud15\Worksessions\Follow up which has gone to the Board\J-1 DES Stormwater Pimmet Run.docx
J-1
Subject: Lessons Learned from Little Pimmit Run Projects Phase 1 consisted of the replacement of the Old Dominion culvert. Construction started in spring of 2007. The construction cost was $900,000. Phase 2 included the replacement of the Williamsburg culvert and replacement of the concrete channel from Williamsburg Boulevard to Little Falls Road. The construction cost was $1,750,000. The Little Pimmit Run 'downstream impacts' study (Phase 3) was also completed in 2010 at a cost of approximately $200,000. The study included additional hydrologic and hydraulic analysis of Little Pimmit Run and work with an Advisory Committee to develop conceptual designs to improve flood protection and habitat downstream from the culvert projects. Lessons learned from the ‘downstream impacts’ study include the following: • Little Pimmit Run is a highly constrained stream corridor with limited opportunities for stream restoration and flood risk reduction because of stream alignment and proximity of homes to the stream. • Most property owners do not want the stream any closer to their homes, even if that means improved stream habitat and reductions in overall flood risks along the corridor. • Substantial implementation of watershed 'retrofit' projects like green streets has important stream habitat and pollution reduction benefits, but due to limited available locations, cannot reduce flooding from major storm events like the June 2006 flood. • The study provided significant knowledge about watershed, stream, and storm sewer capacity analytical tools. This information has greatly informed the storm sewer capacity analysis work that has been completed for the update of the Stormwater Master Plan, scheduled to be considered by the County Board in June 2014. Continued design and implementation of the stream and infrastructure improvement recommendations of the Little Pimmit Run 'downstream impacts' study has been shifted to later years in the draft FY 15-24 CIP. This is due to much higher priority stream and watershed improvement work driven by the County's new MS4 permit and Bay TMDL pollution reduction requirements; these priorities are reflected in the Stormwater Master Plan. Staff expects implementation of the key recommendations of the Little Pimmit Run study to occur at some point in the future, but given limited resources and staff throughput capacity, this work is currently not a top priority from a regulatory or flood risk reduction perspective. Additional information about the Phase 3 study, including the final report from the Little Pimmit Run Advisory Committee, is available on the following County website: http://www.arlingtonva.us/departments/EnvironmentalServices/Sustainability/page60407.aspx
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