Background
The Cedar River is the source of  70% of Seattle’s municipal and industrial water supply. Below the City’s diversion, the river supports a large spawning population of sockeye salmon and a valued run of steelhead trout. These two competing demands have given the Cedar River fisheries studies a very high profile with City officials, agency heads, and purveyors.

Scope
Senior scientists from EES Consulting were contracted by the City to conduct extensive fisheries studies, including the Instream Flow Incremental Methodology (IFIM), to determine the instream flow needs of the Cedar River’s anadromous salmonid populations. The investigations and analysis performed by EES Consulting biologists are a critical component of the Cedar River Habitat Conservation Plan (HCP) developed for the City of Seattle.

Work Completed
The Cedar River Instream Flow Project has been recognized by state and federal fisheries agencies as one of the best and most comprehensive instream flow studies conducted in Washington State.

Application of instream flow and fisheries studies on this project involved:

• Thorough consultation and comprehensive scrutiny of study design, methods and results by 14 representatives of seven different state, federal, tribal and municipal agencies.
• Extensive use of aerial video for study design, habitat mapping and weighting, and agency consultation.
• Development of site-specific habitat suitability curves for spawning sockeye and spawning and rearing steelhead.
• Modeling of a spawning “risk zone analysis” using radio transmitters buried in sockeye redds integrated with the results of the hydraulic simulations from PHABSIM. The threshold discharge for bed movement at redds was determined.
• Modeling of effective and cumulative spawning potential using the results of the IFIM.
• Development of analytical models that integrate WUA, hydrology and municipal water demand.