Storage Capacity and Sedimentation of Loch Lomond Reservoir, Santa Cruz County, California, 1998By Kelly R. McPherson and Jerry G. Harmon
U.S. GEOLOGICAL SURVEY
Prepared in cooperation with the Sacramento, CA 2000 |
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FIGURES
1. Map showing location of Loch Lomond Reservoir, Santa Cruz County, California
2. Photograph showing vegetation typical in the area of Loch Lomond Reservoir, Santa Cruz County, California
3. Photograph showing depth-sounding equipment and global positioning system used to survey the topography of Loch Lomond Reservoir in Santa Cruz County,
4. Map showing location of data points measured for depth from a moving boat on Loch Lomond Reservoir, Santa Cruz County, California
5. Map showing elevation of reservoir bed produced from November 1998 bathymetric survey of Loch Lomond Reservoir, Santa Cruz County, California
6. Thalweg profiles showing valley floor elevations of Loch Lomond Reservoir, Santa Cruz County, California, 1982 and 1998
7. Cross-section profiles showing changes in elevation of the bed of Loch Lomond Reservoir, Santa Cruz County, California, 1998 and 1982
8. Map showing location of upstream reach used for comparison of 1982 and 1998 storage capacity surveys, Santa Cruz County, California
TABLE
ABSTRACT
In 1998, a bathymetric survey was done to determine the storage capacity and the loss of capacity owing to sedimentation of Loch Lomond Reservoir in Santa Cruz County, California. Results of the survey indicate that the maximum capacity of the reservoir is 8,991 acre-feet in November 1998. The results of previous investigations indicate that storage capacity of the reservoir is less than 8,991 acre-feet. The storage capacity determined from those investigations probably were underestimated because of limitations of the methods and the equipment used.The volume of sedimentation in a reservoir is considered equal to the decrease in storage capacity. To determine sedimentation in Loch Lomond Reservoir, change in storage capacity was estimated for an upstream reach of the reservoir. The change in storage capacity was determined by comparing a 1998 thalweg profile (valley floor) of the reservoir with thalweg profiles from previous investigations; results of the comparison indicate that sedimentation is occurring in the upstream reach. Cross sections for 1998 and 1982 were compared to determine the magnitude of sedimentation in the upstream reach of the reservoir. Results of the comparison, which were determined from changes in the cross-sectional areas, indicate that the capacity of the reservoir decreased by 55 acre-feet.