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Landsburg Dam during high flows
Instream flow monitoring and research is used to monitor the strategy for instream flow management and to develop a better understanding of aquatic and riparian habitat in the lower Cedar River.
Stream flow regulation by the City's water storage and diversion facilities affect fish habitat in many ways, including: the amount and distribution of spawning and rearing habitat; the risk of damaging incubating eggs or larval fish by scour or desiccation; risk of stranding fish in low flows, conditions for up and downstream migration; the biophysical factors that form and maintain stream channels.
Instream flow monitoring and research is used to monitor and inform the strategy for instream flow management. The program will ensure flow compliance, verify accretion flows downstream of Landsburg, improve flow-switching criteria, and develop a better understanding of relationships between stream flow and aquatic habitat.
The measurement point for minimum and supplemental instream flows is located at the existing USGS stream gauge (USGS #12117600) located 1.4 miles downstream of the Landsburg diversion dam. This gauge is also used to monitor compliance of upstream City facility water management operations with downramping prescriptions, regulating the rate at which stream flows may be reduced.
New measurement points have been added along the length of the Cedar River to allow more accurate assessment of instream flow compliance. A new measurement point has been added just upstream of the Cedar Falls hydroelectric facility tailrace. The gauge (USGS #12116400) has been installed to monitor compliance with the City’s commitment to provide rearing flows for anadromous fish in the bypass reach between Lower Cedar Falls and the hydroelectric project, once fish passage facilities are completed at the Landsburg dam.
An improved-flow switching criteria study will be used to develop robust, measurable, reliable and independently verifiable criteria to allow a timely switch from normal to critical instream flows and high-normal to low-normal flows. The analyses will involve evaluation of various switching criteria, including measured stream flows and reservoir conditions, forecasted stream flows and reservoir conditions, refill success, system-wide conditions, biological conditions and watershed conditions.
During the steelhead incubation period, the City will provide supplemental flows to minimize the risk of dewatering of steelhead redds. Annual steelhead redd monitoring will take place to locate and monitor steelhead redds from the time of their construction through the completion of fry emergence. The results of the study will be useful for real-time instream flow management and developing analytical tools that may be used to support subsequent decision making in later years.
Although instream flow management has been studied for more than 30 years on the Cedar River, we still have more to learn. Supplemental studies are being carried out to address several emerging questions related to Sockeye salmon and threatened Chinook salmon. The studies also further examine the role of stream flow in sustaining the natural biophysical processes that shape and maintain aquatic and riparian habitat.
The study is expected to help generally advance the scientific basis for managing stream flow in altered fluvial systems. Successful implementation of the study will require coordination and collaboration with other tribal, state, county and federal parties in the basin. All major aspects of planning, implementation, and coordination with other related studies will be carried out under the direction of the Instream Flow Commission.
Read about proposed supplemental studies (pdf).
Specifically, this study will investigate the effects of stream flow on:
Current accretion flow assumptions have a significant impact on fish habitat and future flow management decisions. However, these assumptions need to be verified and updated. The City will therefore conduct a long-term monitoring study of accretion flows in the lower Cedar River between Landsburg dam and Renton.
If this study concludes that actual local inflow patterns are considerably more or less than previously assumed patterns, the Instream Flow Commission may act to adjust the agreed-upon minimum flow regime up or down accordingly.
This study will:
Water Resources Manager
Seattle Public Utilities
Phone: (206) 615-0021