Why are the new culverts so big?
The short answer is because of requirements established by the regulatory agencies in interpreting the Endangered Species Act (ESA) as well as Oregons migratory fish passage rules. In 1998, the National Marine Fisheries Service listed the Lower Columbia River Steelhead Trout as a threatened species. This was followed in 1999 by an additional listing of the Columbia River Chum Salmon and the Lower Columbia River Chinook Salmon. A significant loss in habitat was one reason contributing to the decline in numbers that led to the listings. Development was considered to be a major contributor to this habitat loss, and the ESA required steps to improve conditions. Beginning in the early 20th century, “correct” engineering design was to size culverts according to the required flow capacity. This led to the relatively small culverts we are accustomed to seeing. While these culverts usually pass storm waters with no problem, they are not very accommodating to migratory fish. As a result, public
