Reservoir Storage: New Methods to Measure Capacity, Sedimentation
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A new method of measuring the storage capacity and sedimentation of Loch Lomond Reservoir, Santa Cruz shows promise to help water managers more effectively assess changes in water-storage capacity in similar basins with steep, narrow drainages in mountainous terrain. The method employs a combination of bathymetric scanning using multibeam-sidescan sonar, and topographic surveying using laser scanning. The techniques employed in the study help improve understanding of the quantitative effects of increased sedimentation rates on reservoir storage capacity. Understanding the resulting reductions in storage capacity can also help water managers more effectively adjust storage dynamically to prevent flooding.
Completed Newell Creek Dam and Loch Lomond Reservoir, Santa Cruz County, California, about 1961. Photograph provided by Chris Berry, Water District of the city of Santa Cruz, California. |
Several methods have been used to monitor the storage capacity of, and the rate of sedimentation in, Loch Lomond Reservoir over the years of its operation since 1961. Each of these methods requires different equipment for data collection and different techniques for data processing, and therefore has a different accuracy level. In an effort to accurately define the storage capacity of the reservoir, the USGS examined each of these methods to determine the most accurate and cost-effective approach for performing bathymetric and topographic surveys of the reservoir bed. The report discusses each of these methods and its limitations, and describes the application of a new state-of-the-art method for combined bathymetric and topographic surveying to establish a new baseline for calculations of reservoir stage capacity. This study has been a cooperative effort between the USGS California Water Science Center and the City of Santa Cruz. The new report, "Analysis of Methods to Determine Storage Capacity of, and Sedimentation in, Loch Lomond Reservoir, Santa Cruz County, California, 2009" documents these advanced methods and can be found online at http://pubs.usgs.gov/sir/2011/5141/.
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