Cedar Mill Creek is subject to frequent flooding, but has extensive floodplain habitat potential. Due to this, roadway improvement projects (of Washington County) were required to mitigate impacts by enhancing the steam corridor, in lieu of stormwater detention vaults. Concurrent to those efforts, Clean Water Services is replacing a sanitary force main along Cedar Mill Creek near a main road and through a nearby park.
W2r is leading the design and supporting permitting efforts of the corridor enhancement which includes roughly 1,400 linear feet of creek between Jenkins Road and the THPRD Nature Park. The design will offset hydromodification impacts, improve stream and floodplain resilience, and increase habitat diversity.
To help alleviate the frequent flooding W2r’s design will provide increased floodplain connectivity and side channels in conjunction with an improved trail system in the nature park. By facilitating temporary flow diversion through strategically locating side channel habitat enhancements W2r was able to reduce the cost of the sanitary sewer line construction by over $1M by eliminating borings and enabling open-cut stream crossings.
This project is incorporating the use of the Oregon Flood Attenuation Impact Mitigation (FAIM) Tool (Beta version, December 2018) as a pilot project for hydromodification offsets.
Client
Clean Water Services
Keywords
Flood risk reduction, sanitary sewer mitigation, hydromodification offset, stormwater detention alternative, channel bed and bank stability, permitting, hydraulic modeling
