The case of the Zambezi River in Mozambique: Some investigations on solid transport phenomena downstream Cahora Bassa Dam

摘要

The Zambezi River is the fourth largest river in Africa (after Congo, Nile and Niger) and it is the largest river flowing into the Indian Ocean. The Lower Zambezi in Mozambique is strongly influenced by the presence of two very large reservoirs (Kariba Dam and Cahora Bassa Dam) that have modified the natural seasonal flows, as well as the sediment balance and morphology of the river. In particular, the downstream of the Cahora Bassa Reservoir non negligible effects are taking place, such as local scour, bank collapse and shore-line progressive erosion, together with economic and ecologic consequences on shrimp production and biodiversity alteration. In order to assess and possibly mitigate those effects, a quantitative and qualitative analysis of the erosion/sedimentation/sediment transport phenomena along the Zambezi seems to be urgently needed. The main constraint is represented by the scanty and unreliable data available: the Mozambican hydrometric monitoring network is very scarce and no long-historical and systematic measures of flow, sediment transport and reservoir sedimentation are available. The objective of the present study is trying to integrate the disposable data with a simplified model of sediment transport applied to the reach downstream of Cahora Bassa Dam.