Clean Water Services and the City of Tigard collaborated on an ambitious infrastructure rehabilitation and habitat improvement project along Derry Dell Creek, which has suffered severe channel incision and bank instability, threatening an important sewer main and rapidly eroding adjacent residential properties.
This is a quintessential multi-disciplinary, multi-objective design that will restore natural stream, floodplain, and wetland processes, while protecting critical utility systems and increasing public access.
This project not only improved the resilience of critical utility infrastructure and private property, but it also restored 1,000 feet of stream channel, enhanced 3.5 acres of floodplain wetland, restored fish passage at an undersized culvert crossing, and created a valued recreational amenity and trail connection for the community.
Beginning with a series of field assessments, ESA helped Clean Water Services conceptualize this challenging project. ESA engineers conducted initial site reconnaissance and geomorphic field investigation, identified threats to critical infrastructure and private property, and developed a stream realignment design to naturalize the stream and protect infrastructure. The project grew to encompass Tigard-owned park land and improvements at the SW Walnut Street/Derry Dell Creek crossing, leading to a partnership with the City of Tigard.
The ESA engineering team designed the stream relocation, roadway and right-of-way improvements, storm sewer, sanitary sewer, and water line relocations to accommodate a roadway lane expansion and a new fish passage culvert crossing. ESA's landscape architecture team developed an alignment and design for a trail with boardwalk and bridge components that cross the restored stream with minimal wetland, buffer, and floodplain impacts. The trail provides a safe off-street neighborhood connection as well as access to the existing natural area and future neighborhood park.
Permitting assistance included HEC-RAS modeling to support a no-rise analysis. ESA prepared a wetland delineation and Joint Permit Application to secure permits from the U.S. Army Corps of Engineers and Division of State Lands; a Biological Assessment to facilitate Endangered Species Act consultation with the National Marine Fisheries Service; a Fish Passage Plan to obtain fish passage approval from Oregon Department of Fish and Wildlife; and a Natural Resources Assessment to obtain a Service Provider Letter from Clean Water Services. The project generated advance wetland mitigation credits for CWS and Tigard to use on future projects, and it was the first project in Oregon to be awarded stream mitigation credits.
ESA also provided bid-phase and construction-phase services, including utility coordination and construction observation, working directly with the owners and contractor to resolve challenges during construction.