Sediment Yield and Reservoir Sedimentation in Highly Dynamic Watersheds: The Case of Koga Reservoir, Ethiopia

Abstract

Soil erosion is exacerbated by unsustainable land-use activities and poor management practices, undermining reservoir storage capacity. To this effect, appropriate estimation of sediment would help to adopt sustainable land-use activities and best management practices that lead to efficient reservoir operations. This paper aims to investigate the spatial variability of sediment yield, amount of sediment delivery into the reservoir, and reservoir sedimentation in the Koga Reservoir using the Soil and Water Assessment Tool (SWAT). Sediment yield and the amount entered into the reservoir were also estimated using a rating curve, providing an alternative approach to spatially referenced SWAT generated suspended sediment load. SWAT was calibrated from 1991 to 2000 and validated from 2002 to 2007 using monthly observations. Model performance indicators showed acceptable values using Nash-Sutcliffe efficiency (NSE) correlation coefficient (R2), and percent bias (PBIAS) for flow (NSE = 0.75, R2 = 0.78, and PBIAS = 11.83%). There was also good agreement between measured and simulated sediment yields, with NSE, R2, and PBIAS validation values of 0.80, 0.79, and 6.4%, respectively. The measured rating curve and SWAT predictions showed comparable mean annual sediment values of 62,610.08 ton/yr and 58,012.87 ton/yr, respectively. This study provides an implication for the extent of management interventions required to meet sediment load targets to a receiving reservoir, providing a better understanding of catchment processes and responses to anthropogenic and natural stressors in mixed land use temperate climate catchments. Findings would benefit policymakers towards land and water management decisions and serve as a prototype for other catchments where management interventions may be implemented. Specifically, validating SWAT for the Koga Reservoir is a first step to support policymakers, who are faced with implementing land and water management decisions.

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Monitoring Evolution of Coastline along Mto Tamamba Delta in Kenya North Coast Using Satellite Images

“…The fact that land is seen prograding towards the ocean is an indication that sediment is pilling in this region. The 8 Journal of Sensors vegetation and bare land have a favorable link because eroded soil contains fertile alluvial deposit, which encourages the growth of sparse and dense vegetation such as mangrove forest [33]. It should be noted that in this region, water is advancing into the land on a daily basis between noon and 6 p.m.…”

Land use, management and climate effects on runoff and soil loss responses in the highlands of Ethiopia

“…Furthermore, catchment-scale studies in semi-arid (Haregeweyn et al, 2006;Girmay et al, 2012) and humid (Lemma et al, 2017;Moges et al, 2018;Kebedew et al, 2020;Lemma et al, 2020;Ayele et al, 2021) regions reported that water storage sites such as reservoirs and lakes have silted up owing to excessive runoff and associated sediment transport from various non-point sources in upland areas despite extensive implementation of various soil and water conservation (SWC) measures in croplands and non-croplands in the catchments (Haregeweyn et al, 2015). This can reflect that SWC measures have been implemented across watersheds without evaluating their effectiveness under specific land use and biophysical conditions.…”