This study is evaluating the ecological impacts of culvert replacements on Padden Creek near Bellingham, Washington. Padden Creek supports runs of coho and chum salmon and migrating Chinook salmon and steelhead trout. WSDOT began construction in April 2021 to replace two culverts that have slopes that prevent fish passage to improve habitat for migratory species and other wildlife along the 2.7 miles of Padden Creek between Padden Lake and Bellingham Bay. A contractor is replacing the existing concrete box culvert at I-5 with two fish passable bridges and the double concrete box culvert at SR 11 with a 20-foot single span concrete box culvert. To evaluate the impacts of those replacements, UW researchers are sampling the water for DNA at Padden Creek and two control creeks monthly through September 2022. They will develop molecular assays for three to five species that are a priority for WSDOT, such as salmonids, lamprey, and freshwater mussels, by using CRISPR-Cas12a technology. The goal is to hand off these assays to WSDOT and other state agencies so that they may autonomously use these techniques in the future for evaluating these and other waterways.

Principal Investigator: Ryan Kelly, School of Marine & Environmental Affairs, UW
Sponsor: WSDOT

WSDOT Technical Monitors:
Tammy Schmidt  
Susan Kanzler 

WSDOT Project Manager: Jon Peterson  
Scheduled completion: March 2023

Stream simulation culverts (SSCs) are engineered into road-stream crossings to promote fish passage. Current design guidelines focus on the construction of SSCs with “clean,” granular, non-cohesive sediments such as sand, gravel, and boulders, but natural stream corridors also contain significant amounts of organic matter that is not currently part of SSC design and construction. Roots, decaying plant matter, trees, grasses, and other similar organic materials can also significantly contribute to the stability of sediments and play an important role in the ecological functioning of a streambed. Such natural organic matter (NOM) could likely provide stabilization in a low-cost, naturally adaptive manner that would boost ecosystem function. However, it is not clear how NOM can be efficiently incorporated into a simulated streambed during SSC construction. The objective of this project is to study in detail how organic materials can be used in SSCs to help promote their long-term stability. To facilitate the recovery of fish populations, agencies will need to prevent or minimize the formation of barriers to fish passage when they replace SSCs. In addition, ensuring that SSCs function like natural streambeds will increase the likelihood that they can function properly for years without incurring large maintenance costs.

Principal Investigator: Nicholas Engdahl, Civil and Environmental Engineering, WSU
Sponsor: WSDOT
WSDOT Technical Monitor: Julie Heilman  
WSDOT Project Manager: Jon Peterson
Scheduled completion: September 2023

This project is working to establish guidelines for placing coarse bands in streambed simulation culverts to maintain the form of the stream channel and enhance fish passage. At road crossings, restoring fish passage is recognized as a key priority. Stream simulation is one of the design methods that are allowed, and one kind of stream simulation utilizes coarse bands, which are relatively thin regions of sediment that are coarser than the natural streambed material and are placed horizontal to the flow to enhance stream channel stability. They are intended to simulate the natural stream in terms of both bed material and geometry. Of the 3,175 fish passage structures that WSDOT owns, the Washington Department of Fish and Wildlife has determined that 60 percent are barriers to fish passage. More than 800 of these structures must be fixed by 2030, and many will be replaced with stream simulation culverts. Results of this project will include recommendations for the layout, dimensions, and composition of the coarse bands to maximize longevity of the simulated streambed. A key component of this project will also be a standardized procedure for quantifying the performance of a simulated streambed.

Principal Investigator: Nicholas Engdahl, Civil and Environmental Engineering, WSU
Sponsor: WSDOT
WSDOT Technical Monitor: Julie Heilman
WSDOT Project Manager: Jon Peterson
Scheduled completion: December 2020