Mossyrock Project—River Diversion and Care of Fish

The preservation of the anadromous fish in the Cowlitz River was an essential feature of the Mossyrock Project. The final solution to this problem included the construction of a salmon and a trout hatchery downstream of the project. However, during construction of the dam and prior to completion of the hatcheries it was necessary to maintain the natural fish runs to spawning areas upstream of the damsite. This was accomplished by designing two gothic shaped unlined diversion tunnels such that they satisfied the requirements essential to the passage of fish as well as satisfied requirements for diversion of the Cowlitz River. The unlined tunnels were constructed with no difficulty and successfully passed three large floods. The fish runs were maintained during construction and are now being maintained with the aid of the two hatcheries downstream.