Late Holocene evolution of the Okavango River, Botswana

The Okavango Delta in the northern Kalahari Desert of Botswana is one of
the largest and most dynamic wetland systems in Africa. Understanding
the long-term evolution of the Okavango River and how it responds to external influences can help us to anticipate future trajectories of river adjustment due to climate and/or land use change. This research aims to investigate the timing and
hydroclimatic drivers of enhanced flow in Holocene palaeochannels of the Panhandle region of the Delta, particularly by comparing the morphology and discharges of palaeochannels with the modern-day channels. Palaeochannels in the Panhandle are up to 5-10 times the size of the modern channels and were active ~4 ka during a wet period that was also characterised by regional lake development. Increased Atlantic Ocean-sourced rainfall over the catchment due to an intensification or expansion of the Congo Air Boundary during the mid-Holocene is likely responsible for the enhanced flow. These large palaeochannels were actively laterally migrating (rates of at least 6 m/a). The modern channels are much smaller and only slowly laterally migrating but are prone to avulsion (abrupt channel relocation) leading to redistribution of water and sediment through a complex arrangement of intersecting channels. The complex relationships between climate and hydrology, discharge, and river character (morphology) and behaviour (laterally migrating versus avulsive) provide a template for understanding how future climatic and/or land use changes may influence the Okavango River.