Reservoir sedimentation is one of the problems facing managers of small reservoirs (with ≤5m height of embankment). The main methods used to understand sedimentation process in the Makoye reservoir included sediment coring, onsite measurements using Sedimeter SM3A, use of Elevation Change Method (EMC), laboratory analysis of sediment core, 3D Spatial Analyst Tools (3DSATs) in ArcGIS 10.3 as well as mathematical models. The reservoir had been silting at a significant rate of 3,112.97 m 3 yr -1 leading to average accumulation of 87,163 m 3 of sediment, which had eventually reduced the reservoir's storage capacity by 53.5%. The EMC methods also revealed that Makoye reservoir tapped 79,749.38 m 3 of sediment giving rise to the between method average sediment volume of 83,456.26 m 3 . Reservoir's useful life was found to be 24 years. Results from Sedimeter SM3A showed that a total depth of 0.688cm of sediment had accumulated during a period of 309 hours in the 2015/2016 rainy season as compared to 1.56 cm in the 2016/2017 rainy season. The long term average depth of sediment was found to be 2.4 cm. It was concluded that sedimentation in the Makoye Reservoir is a serious problem which may lead to complete loss of reservoir storage capacity.Keywords: Sedimentation rate, reservoir capacity, Sediment yield, Useful life, Sedimeter-SM3A
BackgroundReservoir sedimentation is one of the problems facing managers of small reservoirs (with ≤5m height of embankment) (Nissen-Petersen, 2006) and, it has persisted in literature (Meade, 1982;Walling, 1988;Sichingabula, 1997;Collins and Walling, 2004;Lu et al., 2013;Sichingabula et al., 2014;Chomba and Sichingabula, 2015) such that it still needs further studies particularly in Zambia where sediment data is quite scanty. Due to very low velocity (<0.035ms -1 ) of water in reservoirs, they tend to be very efficient sediment traps leading to untimely loss of reservoirs' useful life, storage capacity as well as reduced water quantity and quality (Lu et al., 2013). Rainfall, runoff and river channel erosion provide a continuous supply of sediment that is finally deposited into reservoirs, if sediment inflow is large relative to the reservoir storage capacity, then the useful life of the reservoir may be drastically shortened (Randle et al., 2008). Collins and Walling (2004) noted that information on sedimentation is an important data requirement for reconstructing historical catchment erosion patterns and assist in the interpretation of sediment loads in small reservoirs. Moreover, the capacity to manage current and predicted sedimentation problems depends, in part, upon an improved understanding of sediment load (Collins and Walling, 2004). This study aimed at determining quantity of sediment and rate of sedimentation in the Makoye reservoir.