Sediment transport dynamics in a semi-arid reservoir environment: A case study of the Weija dam

Abstract

The provision and control of water resources is becoming increasingly expensive with semi-arid regions experiencing significant issues with soil loss, sedimentation, and river erosion. This paper sought to investigate the current rate of sediment transport, capacity and bathymetry of the Weija reservoir by establishing discharge and sediment rating curves at the upstream of the reservoir using empirical equations together with suspended sediment data collected through a one-year (03/2019 - 02/2020) monitoring programme. In realising this, impeller current meters and echo sounders were deployed in the field. Equally, sediment samples were analysed at the laboratory of Water Research Institute, Accra-Ghana. The results indicate minimum and maximum suspended sediment concentrations of 34.67 mg/L and 239.69 mg/L respectively in January 2020 and June 2019. Within the reservoir, the suspended sediment concentrations range from 34.75 mg/L to 124.92 mg/L with gross annual sediment yield estimated at 104,539 t/yr. The current reservoir capacity stands at 86.67x10⁶ m³ indicating a 25% reduction over the designed storage capacity of 116.04 x 10⁶ m³. With increasing changes in land uses, sediment yield is anticipated to worsen within the Weija reservoir and thus the buffer zone policy needs to be enforced to curtail depletion of the reservoir capacity.