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<br />The stepped, experimental discharge was effective at flushing sediment out of the <br /> <br />pools. and once the snowmelt discharge began, bed scour and channel widening achieved <br /> <br /> <br />nearly complete channel recovery, Given the structural limitations of Halligan dam, <br /> <br /> <br />maximum release capacity at the outlet valves is approximately 3.4 m3/s (140 fe/s). <br /> <br /> <br />Larger magnitude discharges are dependent on the annual snowpack, filling the reservoir <br /> <br /> <br />until spill-over occurs. As such, discharges prior to snowmelt runoffwill be limited to <br /> <br /> <br />the 3.4 m31s (140 ft3/s)maximum. A sustained snowmelt has the capability of entraining <br /> <br /> <br />and transporting large volumes of fine sediment out of pools. In September 1997, the <br /> <br /> <br />resurvey indicated that greater than 80% of the pool volume within the Tick Pool was <br /> <br /> <br />restored by the high magnitude, long duration runoff. <br /> <br />Recommendations <br /> <br />Prevenling Fuwre Hazards <br /> <br /> <br />If sediment must be released from Halligan Reservoir to maintain storage capacity <br /> <br /> <br />within the reservoir. the timing of a release must consider the pertinent life cycles of <br /> <br /> <br />downstream biota to minimize degradation of the aquatic ecosystem. Although the focus <br /> <br /> <br />of this report was not on the aquatic organisms. an integrated approach to reservoir <br /> <br /> <br />management which considers both the biotic and abiotic factors of a river system is <br /> <br /> <br />recommended, Most importantly. a release of sediment must be accompanied by a <br /> <br /> <br />continual discharge of clear water, to Hush sediment well into or through the system. <br /> <br /> <br />More trequent sediment releases are recommended rather than one voluminous release, to <br /> <br /> <br />more readily mobilize and transport a smaller quantity of sediment into downstream <br /> <br /> <br />reaches of the river, <br /> <br />.'vliligaling Exisling Hazards <br /> <br /> <br />If existing hazards along the North Fork continue, such as another sediment <br /> <br /> <br />release ofa similar scale, mitigation might include applying one-dimensional models, <br /> <br />with the knowledge of sediment movement characteristics from tield data for model <br /> <br /> <br />calibration, Also. a stepped-discharge. or multiple discharges show promise in <br /> <br />1-1 <br />