Sandalwood Swale Tualatin, Oregon

In developing a comprehensive solution to the water quality impacts of the Tualatin Moving Forward bond program, the Sandalwood Swale – along with two smaller sites – provides water quality mitigation for all 36 projects associated with the program. Stormwater facility analysis and design for this regional water quality facility was provided by Otak, including conceptual stormwater facility layout and construction cost estimates.

A Bond Program’s Regional Approach to Water Quality Mitigation

As part of the city’s stormwater master plan, the Sandalwood Swale takes a regional approach to water quality mitigation for a number of transportation and pedestrian-focused improvements involving impervious surfaces. With 11.6 acres required by Clean Water Services design to be covered, the swale exceeds that requirement, providing water quality treatment for 19.49 acres of impervious area. The facility itself is a vegetated swale with native plants selected specifically for the area’s environmental conditions that cover its 12-foot-wide bottom and 189-foot length. With multiple parcels coming into the facility, the regional approach is more cost-effective and requires less maintenance than several smaller facilities would offer, while a water quality manhole added upstream is designed to further reduce maintenance. In a location where the community often reported the impacts of flooding, the improved grated inlet is also designed to better collect debris from storm runoff and eliminate flooding issues in the area.