The first phase of construction is wrapping up this month on the salmon-safe clean water retrofit that Otak designed at Mt. Hood Community College. This project, led by the Sandy River Watershed Council, will improve water quality and salmon habitat in Gresham’s Beaver Creek by treating 1.9 million gallons of polluted runoff per year. Older parking lots like this college campus were built without the stormwater treatment that is typically required in new development today.
Otak’s water and natural resources engineers designed the retrofit project to treat as much runoff as possible while keeping costs down, minimizing loss of parking spaces, and protecting the mature trees that shade the parking lots. Stormwater swales and planters fit into slivers of available space, with drywells added to increase infiltration. A large raingarden creates the focal point of the retrofit, providing a visible opportunity to educate campus visitors about stormwater and watershed health. New signs designed by students will help spread the word about the project’s environmental benefits, and the City of Gresham installed devices to monitor water quality and flow rates before and after construction.
The project is funded by East Multnomah Soil and Water Conservation District, Metro regional government, the City of Gresham, Spirit Mountain Community Fund, and the Oregon Department of Environmental Quality. In 2016 the partners came together to identify retrofit projects on the college campus that would maximize environmental benefits and public education opportunities. These parking lots got top priority and are expected to be the first of many future improvements. Mt. Hood Community College is the first Salmon Safe certified community college in the country, and the stormwater retrofits will help the college maintain its certification.
On October 27, volunteers will plant the portions of the project that were built by the nonprofit group Depave. Contractors for the project are Britton Excavating and Grow Construction. The second phase of the project is expected to be built next summer, pending funding.
Close collaboration with the Columbia River Estuary Study Taskforce aimed to restore estuary function and wildlife habitat to the Buckmire Slough near Vancouver Lake, Washington. The slough had poor water quality conditions and two large berms blocking fish passage.
An Improved Floodplain Habitat with Fish-Friendly Features
The removal of four in-stream barriers restores full estuarine tidal processes and improves juvenile salmon access to the slough and wetland habitat. Installing two new bridges led to an improved floodplain habitat while placed logs and other low-lying features support native vegetation (e.g., Sedges and Wapato) and prevent juvenile fish from getting stranded. The design includes fish-friendly features, ecological features to support native Wapato, and large wood habitat structures. In developing the design, the Otak team used hydraulic modeling to assess water quality, fish passage conditions, and scour potential at the bridge sites.
Uphill of Lake Sammamish, the 40th Street stormwater trunk was originally built in the 1980s to intercept stormwater runoff from commercial properties and send it to the lower reach of Villa Marina Creek. The complete master plan includes a unique water quality facility. After years of erosion threatened water quality downstream, upgrades were designed to accommodate a 50-year flood event and redirect peak flows with the addition of a new outfall dissipation structure.
Diverting Peak Flows of Stormwater Runoff to Improve Water Quality and Erosion Control
In an area experiencing high growth, the City of Redmond aimed to put in place more sustainable stormwater management infrastructure and practices for future development. Stakeholder outreach provided a forum for feedback and built consensus around the project’s importance throughout development of the lake outfall plan. Upgrades to the trunkline includes over 1,400 linear feet of 42-inch HDPE pipe and 300 linear feet of 12-inch water line relocation. The design also accounts for the restoration of the roadway and sidewalk including signal modifications, the relocation of utilities. To divert damaging peak flows from Villa Marina Creek to the outfall at Lake Sammamish, an interactive flow splitter progressively increases peak flow rates as a new submerged channel is formed and shoreline plantings establish healthy root systems.
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