VEGETATION, HYDROLOGY AND SEDIMENTATION PROCESSES AS DETERMINANTS OF CHANNEL FORM AND DYNAMICS IN THE NORTHEASTERN OKAVANGO DELTA, BOTSWANA

The relationships between vegetation, hydrology, and the landscape-forming processes of erosion and deposition are examined in channels of the northeastern Okavango Delta, Botswana. Channel development appears to be due to the confinement of rapid water movement by vegetation processes and peat formation in backswamp areas. The channels have sandy beds and densely vegetated banks composed of erosion-resistant peat deposits between 1.5 m and 4 m thick. Sediment introduced into the delta is transported as bed-load, is unable to escape from the peat-lined channels and is therefore deposited along the channel floor. Channels that receive their water supply directly from source areas are therefore dominated by depositional processes. In contrast, channels that receive their water supply as overspill from these aggrading source channels do not receive bed-load sediments from source areas, and their beds tend to be erosional. Channel switching is therefore suggested to be due to a combination of erosional and depositional processes, rather than simply the result of depositional processes as has previously been suggested. A conceptual model of channel development and change within the northeastern Okavango Delta is presented.