WRIA 54 Instream Flow Assessment
Final Instream Flow Report:
Instream Flow Final Report
Appendix A Cover and Substrate
Appendix B Calibration Tables
Appendix C Spokane Toe Width Final Report
Appendix D Spokane Riffle Photographs
Appendix E Letters of Support or Objection
The term Instream Flow is used to identify a specific stream flow (typically measured in cubic feet per second, or cfs) at a specific location for a defined time, and typically following seasonal variations. Instream flows are usually defined as the stream flows needed to protect and preserve instream resources and values, such as fish, wildlife, habitat, and recreation. Instream flows are most often described and established in a formal legal document, typically an adopted state rule.
The Science Behind Instream Flows (Flow Measurement Methods)
IFIM/PHABSIM and Toe-width are the two most commonly used flow measurement methodologies used in Washington State.
Instream Flow Incremental Methodology / Physical Habitat Simulation (IFIM/PHABSIM)
The IFIM/PHABSIM is the most commonly used method for determining how much water fish need. IFIM is a series of computer-based models that quantify the amount of fish habitat at different flow levels in a river or stream. By matching those depths and velocities to fish preferences for those factors, the model will tell you how many square feet of habitat will be available at different flow levels. Physical Habitat Simulation (PHABSIM) is the subset of IFIM used extensively in Washington State.
Toe-width is a quick habitat assessment tool used primarily for small streams. The measurement from the toe of one stream bank to the toe of the other is put into an equation and an estimation of flows needed for fish spawning and rearing is derived.
Why should we worry about low stream flows?
Sufficient water in streams is necessary to sustain both the natural environment and our community water supplies. Washington State is known for its natural beauty and quality of life, both of which are affected by limited water. Fish and wildlife depend on adequate water, as do many recreational activities. Flows affect water levels in wetlands, lakes and ponds, and are an important aspect of water quality. Out-of-stream water uses, including farming, irrigation, domestic water supplies, and hydroelectric power can also be affected by low stream flows.
Who determines instream flows?
The authority to adopt instream flows by rule rests with the Washington State Department of Ecology (Ecology). WRIA planning Units and watershed groups are evaluating water quantity and other water issues, and many have and may in the future present instream flow recommendations to Ecology. These groups are developing plans to protect and restore stream flows, while also making water available for out-of-stream uses needed by society.
The WRIA 54 instream flow (ISF) assessment is being conducted concurrently with additional ISF assessment in the lower WRIA 57 reach of the Middle Spokane River by TetraTech/KCM Inc. and their group of technical consultants. The detailed scope of work (Step A) was prepared by the Instream Flow Technical Team (IFTT) during three meetings on February 22, 2006, March 8, 2006 and March 29, 2006. Approval to proceed to Step B (work collecting field measurements) was granted by the Department of Ecology on June 30, 2006.
The high-flow measurements on the Spokane River occurred on June 23, 2006, mid-flow measurements on July 6, 2006, and low-flow measurements on August 15, 2006 and September 12, 2006. The toe-width measurements on the selected WRIA 54 tributaries occurred on August 16th and 17th.
Now with all the field work completed, the report preparation and ultimately instream flow recommendations are next. A draft report (Step C) is expected by January 2007.