Bathymetric Changes of Lake Chivero, Zimbabwe, as a Result of Sedimentation

Abstract

Major dams in Zimbabwe are losing more than half of their design capacity in the first 11 to 12 years of operation. Despite these obvious impacts of sedimentation in the country's reservoirs, sedimentation studies have only been conducted once for 90% of the reservoirs. Thus, a sedimentation estimation study was conducted in November 2014 in Lake Chivero to quantity storage loss due to sedimentation, determine the spatial distribution of sediment deposition in the reservoir, update its elevation-capacity curves and estimate its useful life. The study used a dual beam echo sounder for determining depth measurements. Depth measurements were converted to digital elevation models in a Geographic Information System environment. A comparison of the 1953 and 2014 digital elevation models indicated that the lake was losing depth uniformly. The highest deposition depths were observed towards the dam wall and the deep central parts of the lake along the old river channel. Minimal sediment deposition was generally observed at the shallower parts of the lake, on the north-east and south-western locations. A total of 49126170.34 m³ (18%) of the lake's storage capacity has been lost to sedimentation, which translates to an average annual capacity loss of 792,357 m³ year⁻¹ (0.295% per year) since construction in 1953. The lake's specific sediment yield and remaining useful life were calculated at 352.31 m³ year⁻¹ km⁻² and 106.63 years; respectively. This loss of storage in the lake will impact the operational and economic benefits for which it was built. It will also affect the habitats of its varied flora and fauna. In the absence of original topographic maps produced at the inundation, the dual frequency echo sounder can be used to generate data to estimate sediment loads into the reservoir as well as update elevation-capacity curves.