Publication Summary

The Washington State Department of Ecology (Ecology) conducted an instream flow study in the Big Quilcene River using the Instream Flow Incremental Methodology. The study provides information about the relationship between streamflows and fish habitat which can be used in developing minimum instream flow requirements for fish in the Big Quilcene River. One site, composed of eight transects, was chosen. The site was located at approximately River Mile 1.1. Streamflow measurements and substrate information were recorded at high, medium and low flows. This information was entered into the IFG4 hydraulic model to simulate the distribution of water depths and velocities with respect to substrate and cover under a variety of flows. Using the HABTAT model, the simulated information was then used to generate an index of change in available habitat relative to changes in flow; this index is referred to as "weighted usable area" (WUA).

The Washington State Department of Ecology (Ecology) conducted an instream flow study in the Big Quilcene River using the Instream Flow Incremental Methodology. The study provides information about the relationship between streamflows and fish habitat which can be used in developing minimum instream flow requirements for fish in the Big Quilcene River. One site, composed of eight transects, was chosen. The site was located at approximately River Mile 1.1. Streamflow measurements and substrate information were recorded at high, medium and low flows. This information was entered into the IFG4 hydraulic model to simulate the distribution of water depths and velocities with respect to substrate and cover under a variety of flows. Using the HABTAT model, the simulated information was then used to generate an index of change in available habitat relative to changes in flow; this index is referred to as "weighted usable area" (WUA).

Determination of a minimum instream flow for the Big Quilcene River will require setting priorities for river reaches, fish species and lifestages. Different fish species and lifestages exist simultaneously in the river and each has a different flow requirement. There is no single flow that will simultaneously provide optimum habitat for all fish species and lifestages.

In addition, minimum instream flows must include flows necessary for incubation of fish eggs, smolt out-migration, fish passage to spawning grounds, and prevention of stranding fry and juveniles. Other variables to be considered include water temperature, water quality, and sediment load. These variables were not addressed in this study.

No instream flow recommendations are made in this report. This would require an evaluation of the environmental variables listed above on the river and the long-range fishery management objectives of the state and federal natural resource agencies and affected Tribes.