Abstract
Over the years, sedimentation has posed a great danger to the storage capacity of hydropower reservoirs. Good understanding of the transport system and hydrological processes in the dam is very crucial to its sustainability. Under optimal functionality, the Shiroro dam in Northern Nigeria can generate ∼600 MW, which is ideally sufficient to power about 404,000 household. Unfortunately, there have not been reliable monitoring measures to assess yield in the upstream, where sediments are sourced into the dam. In this study, we applied the Soil and Water Assessment Tool (SWAT) to predict the hydrological processes, the sediment transport mechanism and sediment yield between 1990 and 2018 in Kaduna watershed (32,124 km2) located upstream of the dam. The model was calibrated and validated using observed flow and suspended sediment concentration (SSC) data. Performance evaluation of the model was achieved statistically using Nash-Sutcliffe (NS), coefficient of determination (r2) and percentage of observed data (p-factor). SWAT model evaluation using NS (0.71), r2 (0.80) and p-factors of 0.86 suggests that the model performed satisfactorily for streamflow and sediment yield predictions. The model identified the threshold depth of water (GWQMN.gw) and base flow (ALPHA_BF.gw) as the most sensitive parameters for streamflow and sediment yield estimation in the watershed. Our finding showed that an estimated suspended sediment yield of about 84.1 t/ha/yr was deposited within the period under study. Basins 67, 71 and 62 have erosion prone area with the highest sediment values of 79.4, 75.1 and 73.8 t/h respectively. Best management practice is highly recommended for the dam sustainability, because of the proximity of erosion-prone basins to the dam.
Highlights
The greatest challenge of dam construction is a reduction in storage capacity due to reservoir sedimentation (WCD, 2000; Gottschalk, 1964; Petts, 1984; Cogollo and Villela, 1988; Evans et al, 2000)
The streamflow data of the four reaches that constituted Kaduna watershed were obtained from the African Flood and Drought Monitor developed by Princeton Climate Analytics (PCA)
The flow sensitive hydrological modelling parameters for the studied watershed starting with the most sensitive are threshold depth of water in the shallow aquifer required for return flow to occur mm H2O (GWQMN.gw), effective hydraulic conductivity in main channel alluvium mm/hr (CH_K2.rte), soil available water capacity (SOL_AWC(.).sol), plant uptake compensation factor (EPCO.hru) and surface runoff lag coefficient (SURLAG.bsn)
Summary
The greatest challenge of dam construction is a reduction in storage capacity due to reservoir sedimentation (WCD, 2000; Gottschalk, 1964; Petts, 1984; Cogollo and Villela, 1988; Evans et al, 2000). Reservoir sedimentation, according to Morris and Fan (1998) is the process by which stream transports and deposits sediments in the reservoir behind the dam. Sediments affect the useful life of reservoirs as well as damage the aesthetic quality of the environment. It serves as a distribution medium for certain toxins and a source for the overlying water column and biota within a reservoir (Juracek and Stiles, 2010; Alemayehu et al, 2014). According to Reza (2011), reservoir sedimentation increases the risk of water runoff during floods, reduces the quality of consumed water, decreases reservoir water volume and decreases the dam's life cycle
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