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