Forest impact on flood peak discharge and sediment yield in streamflow

Abstract

Two recent studies help to define the extent to which forest cover, compared with a cover of shorter vegetation, can reduce flood peaks and sediment yields at the catchment scale as part of an integrated flood control programme. First, field data analysis and model analysis tested the hypothesis that, as the size of the rainfall event increases, the effect of forest cover on peak discharge becomes less important. Second, a systematic model analysis assessed the relationship between specific sediment yield and catchment area for various land use scenarios. The results show that the change in forest cover must apply to 20-30% of the catchment area to affect the hydrological response; forest cover can affect the peak discharges for small to moderate floods but has little effect on large floods; increased cultivation in headwater areas can increase sediment yield, but the effect becomes attenuated over an order of magnitude increase in catchment area. In an Indian context, these results suggest that altered land use in the Himalayas has little immediate effect on flood magnitude and sediment yield in Bangladesh. However, forests can have a role in controlling floods and sediment yield in smaller headwater catchments.