Impact of the Mpatamanga dam on sediment budget of the Shire River in Malawi

The Shire River, originating in Lake Malawi, is an important water resource for irrigation, water supply, ecological functioning of several protected areas and electricity production. A new 358 MW Mpatamanga hydropower project is proposed on the river. This paper describes the sediment studies that were carried out with the aim to (a) improve understanding of the present sediment dynamics in the river system and (b) identifying and quantifying the future sediment impacts of the project. The quantification was achieved by construction of a sediment budget, for which a new method, suitable for circumstances where little information about observed sediment flows is available, was developed. The study was supported by Revised Universal Soil Loss Equation–type sediment yield and soil erosion modelling and long-term reservoir sedimentation modelling to evaluate sediment trapping efficiency. The identified impacts included bed and water level rise affecting assets in the upstream end of the reservoir, storage loss and interrupted sediment continuity towards downstream, in particular for sand-sized particles.