Evaluating the Flow Regulating Functions of Natural Ecosystems in the Zambezi River Basin

Abstract

"This report summarizes the findings of a literature review conducted to find evidence of the flow regulating functions of the major ecosystems in the Zambezi River Basin. It also describes a pragmatic approach for quantifying the flow regulating functions of floodplains, headwater wetlands and miombo forests in the basin. The method utilizes observed streamflow records and flow duration curves to derive a simulated time series of flow in the absence of the ecosystem. This can then be compared with an observed time series to evaluate the impact of the ecosystem on the flow regime. The method has been applied to 14 locations in the basin. Results indicate that the different ecosystems affect flows in different ways. Broadly: i) floodplains decrease flood flows and increase low flows; ii) headwater wetlands increase flood flows and decrease low flows; iii) miombo forest, when covering more than 70% of the catchment, decreases flood flows and decreases low flows. However, in all cases there are examples which produce contrary results and simple correlations between the extent of an ecosystem type within a catchment and the impact on the flow regime were not found."