New Approach for Evaluation of a Watershed Ecosystem Service for Avoiding Reservoir Sedimentation and Its Economic Value: A Case Study from Ertan Reservoir in Yalong River, China
A model was established to simulate an ecosystem service of avoiding reservoir sedimentation and its economic value based on the process of sediment delivery in a watershed. The model included fabricating the watershed of the study reservoir. The sediment retention coefficient of different land cover types were used to simulate the spatial patterns of the annual quantity of the sediment that were prevented from entering the reservoir by the vegetation in each cell followed the flow path in watershed. The economic value of the ecosystem service in this model was determined by the marginal cost of reservoir desilting. This study took the Ertan reservoir as an example. The results showed that most eroded soil was intercepted by different types of ecosystems in the process of sediment delivery in a watershed. The region with a higher quantity of sediment retention was around the reservoir. The absolute quantity of average sediment retention in forestland was lower, so the sediment retention ability of forestland failed to be brought into fullest play in watershed. 1. Introduction The erosion of soil and its generation of sediment in a watershed can cause significant sedimentation in associated reservoirs. The subsequent decrease in storage capacity not only decreases the effective operation of the reservoirs but also causes other problems. Sedimentation spread to the upper river regions can affect the environment. Sedimentation in backwater regions can alter the navigational conditions for ships and boats. Sullage at the bottom of reservoirs can cause deterioration in water quality. Extreme build-up of sediment behind a dam wall can threaten the safety of the dam. Reservoir sluicing can change the river course in the lower reaches of a river [1]. Regular sediment removal is a common solution for avoiding long-term sedimentation problems, but it results in a costly maintenance budget. The ecosystem provides a natural service or function of soil retention by using roots to hold soil in place, and the processes of interception, absorption, and saturation can reduce the scouring power of runoff [2]. The service or function of the avoided reservoir sedimentation is a very important aspect of soil retention [3–5]. In China the current approaches to evaluating the efficacy of the ecosystem service for avoiding reservoir sedimentation are all quite similar. They calculate the amount of soil retention in the whole landscape based on the universal soil loss equation (USLE) or the revised universal soil loss equation (RUSLE) and then multiply it by a coefficient
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