Thalweg profile maintenance for aquatic organism passage at roadway culverts

A countersunk culvert design variant was studied for maintenance of streambed stability, and fish and aquatic organism passage, at a roadway crossing. Previous studies and construction of countersunk and oversized culverts have mimicked adjacent riffle structures, and have considered—over brief time intervals—the initial placed and evolved sediment gradations, inscribed channel forms, and fish utilization of these channels and sediments. Challenges to these installations include the long-term stability of any placed sediments within a culvert section, and the potential reduction in base level due to the lowered culvert elevation within the channel profile.