Sediment Transport Monitoring and Short Term Modeling in the Okavango Delta, Botswana

The Okavango Delta of northern Botswana comprises large wetlands that spread over an alluvial fan of 150km in length. Only part of the fan is covered with wetlands but the repeated shifting of the zones prone to inundation has led to a regular distribution of sediments and eventually to the formation of a smooth fan surface. We conducted repeated solute and bedload transport measurements at the inlet and within the wetlands proper to quantify sediment input and channel aggradation rates. The relationship between flow velocity and bedload transport was used to simulate channel erosion and aggradation, and a bedload transport component was built into a numerical hydrological model of the Okavango Delta. The model was used to assess the impact of a hypothetical dam in the upstream of the wetlands on channel bed elevations and the distribution of flooded areas. Our results suggest that the contribution of solute inputs to the overall sediment accumulation of the fan has been overestimated relative to bedload inputs. The numerical simulations reveal that a dam would have an impact on channel elevations only in its immediate downstream, but an impact on the distribution of flooding would be felt over the entire wetland syste