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MERCED RIVER WING DAM GRAVEL MONITORING 2000 - 2002 (FINAL REPORT)
Construction of dams on the Merced River has impeded the movement of coarse gravels through the river system. Consequently,areas downstream of dams lack recruitment of salmon spawning gravels from areas upstream of those sites. Chinook salmon require these coarse gravels for successful spawning. Addition of appropriately-sized gravel in riffles immediately below Crocker-Huffman Dam has shown an immediate response in salmon spawning activity. One strategy for increasing natural production of salmon on the Merced River is to replenish spawning gravel at key locations. As the rivers are continuously carrying this coarse sediment downstream, its replenishment is an ongoing need.
Current studies funded by CALFED are developing models to simulate sediment input needs and transport rates appropriate for the flows of the Merced River. This project is intended to provide data to supplement the modeling effort and to evaluate the use of
wing dams as gravel introduction sites. On the Merced River in the area around the town of Snelling, there are several riparian
diversions that are operated by the construction of wing dams in the spring. These wing dams are peninsulas consisting of streambed substrate that extend into the river to create partial hydraulic controls that raise the water surface elevation and enable gravity flow of water into the riparian diversion ditches. The dams typically wash out with winter and spring runoff flows, carrying the construction material downstream. The diversion operators, or riparian diverters, re-build the wing dams with miscellaneous fill or material from previous construction that has washed downstream into the river channel. They normally use any fill material available, including fine sediment which can be deposited downstream after mobilization and consequently impact spawning areas.
This project monitored movement of spawning-sized gravel from these wing dam sites under flow conditions experienced during the study period. To monitor gravel movement, two techniques were used: painted tracer rocks and radio-tagged telemetry rocks. This information may be useful in assessing whether these diversions are suitable locations for gravel introductions.
wing dams, salmon spawning gravel, sediment input, riparian diversions, streambed subtrate, hydraulic controls, gravel movement, tracer rocks, radio-tagged telemetry rocks, tracer gravel,
February 28, 2003 10:00 PM
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Snell
Merced River
Merced County