Reservoir volumetric and sedimentation survey data: A necessary tool for evaluating historic sediment flux and appropriate mitigation response
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Multi-frequency reservoir survey techniques offer a technological means to verify historic sediment delivery estimates and to quantify the effectiveness of conservation implementation. A multi-year, multi-frequency acoustic survey of Granger Lake, Texas, was undertaken to demonstrate the application of this technology and the value of its derivatives. Granger Lake is a drinking water resource for surrounding cities, perceived as being threatened by agriculture-driven sedimentation, and the focus of a watershed conservation implementation programme. Objectives of the present study were to (i) conduct sub-bottom profiling to verify the pre-impoundment capacity of the reservoir; (ii) plot historic bathymetric datasets, including pre-impoundment surface determined by low-frequency acoustics, identifying any changes in annualized sediment delivery curve to date; and (iii) quantify changes in sediment delivery resulting from agricultural conservation practices implemented as part of the Granger Lake Watershed Assessment and Implementation Project. The sediment-profiling results indicated that the pre-impoundment design estimates were overstated, thereby skewing historic sediment delivery estimates. Adjusting the 1980 pre-impoundment volume of Granger Lake indicated that the historic trend in Granger Lake sedimentation/water storage loss was markedly less acute. Although sedimentation did accelerate somewhat in the mid-1990s, the intervals following the 1995-2002 survey period revealed a trend of decelerating sedimentation. Reduced sedimentation as a response to conservation implementation is not distinguishable beyond what is seen as a steady downward trend in sediment delivery. Insights from this study highlight the important role of multi-frequency reservoir survey techniques for refining watershed conservation and/or reservoir sustaining strategies. 2013 Wiley Publishing Asia Pty Ltd.
