STREAM RESTORATION PROJECTS
Rock Creek/Fenwick Branch Stream Restoration
District Department of Transportation (DDOD)
District Department of the Environment (DDOE)
Problem: The total Fenwick Branch and Portal Branch tributary catchment area discharging through the Kalmia Road culvert is 714.5 acres (1.11 square miles). Both the Fenwick and Portal Branch streams are buffered on either side by 100 feet or less of forested parkland (owned in-part by the National Park Service). Mean flow was calculated between 1 and 3 cfs. However, given the developed and sewered urban characteristics of the Fenwick Branch watershed, runoff can generate quickly from significant rainfall storm events. Back to back extreme storm events caused the branch to surcharge and severely damaged the existing Kalmia Road culvert in 2010. The Fenwick Branch southwest bank has also historically experienced slow and steady degradation from the excessive discharges of the existing Kalmia Culvert structure. The ongoing erosion of the bank and flow migration has created gravel shoaling which the National Park Service requested to remove by a realignment of the Branch main flow away from the SW bank.
Solution: WRMA, as part of the MCI team, was retained to perform hydrologic watershed assessment and hydrologic/hydraulic modeling to determine optimum replacement culvert opening area and streambank restoration including a structural design to achieve the desired bank stabilization and sediment/gravel shoaling removal by channel realignment. This included the provision of imbricated rip rap wall as guidance for low flow realignment. The existing shoaling would be removed and mix with backfill to be placed onsite or re-graded between the wall and the existing SW bank of Fenwick Branch. WRMA also performed hydrologic watershed assessment and hydrologic/hydraulic modeling to determine water quantity regime for fish passage and sediment/bank erosion control design. WRMA assisted with permitting coordination with DDOT, DDOE, and the National Park Service.
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