Research Briefs

Research
Alternative approach to modeling salmonid spawning habitat in instream flow methods

Species concerned: Chum, pink, sockeye, coho, chinook salmon, steelhead, cutthroat, and bull trout.

Investigators: Hal Beecher, Bob Vadas, Alan Wald, Steve Boessow, Terra Hegy, and Perry Harvester, Science Team, Habitat Program.

Purpose of research: Determine channel form, channel unit, and mesohabitat features that characterize spawning habitat independent of stream size and stream flow. Instream flow determination often employs PHABSIM, a computer model that breaks up a stream into rectangular "cells" with a specified substrate (gravel, boulder, mud, etc.), then evaluates suitability of each cell based on the water velocity and water depth at different flows. A cell at the pool tail is treated the same as a cell in the deepest part of the pool: if it has gravel and enough depth and enough (but not too much) current velocity it is counted as good spawning habitat at a particular flow (e.g., at 25 cfs). We hope to develop rules that would allow us in the model to specify ,for example, that lateral bars ("slip banks") are better than the bottom of a pool if we are interested in chum salmon or that steelhead need areas of the channel that remain wetted as flow drops toward its summer low. Instream flow models are used extensively in water management, including watershed management planning under ESHB 2514 (RCW 90.82).

Geographic area: Salmonid spawning streams statewide.

Timeframe of study: Spring 2003 through 2004 (at least).

Joint partners: None.

Funding: Funding is limited to position budgets for technical assistance in watershed management planning. It comes out to a small fraction of an FTE (1-2%) - about three to four days a year for each person.

Are volunteers needed: No.