Channels, wetlands and islands in the Okavango Delta, Botswana, and their relation to hydrological and sedimentological processes

Abstract

AbstractThe Okavango wetland in northern Botswana is one of the world's largest inland deltas. The delta is a dynamic environment with shifting channel routes, causing growth and decay of flanking wetlands, and giving birth to islands. Primary island nuclei are formed by fluvial processes and bioengineering, and subsequently grow into secondary larger islands of irregular shape by clastic and chemical sedimentation, and later by coalescence. This article presents classifications and quantitative estimations of channels, wetlands and islands of the Okavango Delta. Islands were classified dependent on composition, pattern of composition, shape and juxtaposition. 90 per cent of all islands in the entire wetland were identified, with a classification accuracy of 60 to 85 per cent. Smaller islands of the nucleus types dominate the upper parts of the delta, whereas larger secondary islands are more common in the distal part, a reflection of the age of the islands. Islands in the entry valley of the delta, the Panhandle, are larger in the top end – the primary region of recent clastic sedimentation. The overall size distribution of islands in the delta, however, shows no clumps, indicating that island growth is a uniform process over time and space. The total area flooded at least every decade is approximately 14 000 km2, of which 9000 km2 is classified as actual wetland. Channel meandering decreases from the Panhandle to the distal part of the delta, with the abandoned Thaoge channel as an exception. Occurrence of fluvially formed islands in the distal delta indicates that the water flow and area of inundation must once have been much larger. Copyright © 2004 John Wiley & Sons, Ltd.