Abstract
Small dams for power generation are increasingly being built around the world, and the reported impact caused by these structures on sediment transport varies widely, ranging from substantial to minimal or non-existent alterations among different dams. Such variability is still poorly understood. In this study, we present an original application of fuzzy inference systems (FIS) to extract knowledge concerning the effect of small dams on sediment transport, providing understandings of how different variables related to watershed characteristics, dam characteristics and hydrological variations can affect sedimentological responses of these structures. Numerous small dams have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned tropical wetland, where we apply the methodology. Data on 23 hydropower facilities from the uplands of the Pantanal region were used, with a total of 535 records. The models presented very good results (NS equal to 0.92 for the most detailed FIS model) and provided a better understanding of the phenomenon through their explicit linguistic rules. The upstream suspended sediment concentration (SSC) is the most determinant variable for the alteration caused by dams. Higher SSC entering the reservoir is related to higher sediment retention. Vegetation cover and soil type of the drainage area of dams also influence the alterations on SSC caused by these structures. Dams located in basins with greater vegetation cover tend to affect less sediment transport, and dams located in basins with high percentages of agriculture and pasture tend to alter more. FIS models also confirmed that the size of dams is directly proportional to their capacity to alter sediment transport. The methodologies developed for the interpretation of fuzzy rules proved to be useful for assessing how small dams affect sediment transport along river systems.
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