oa Botswana Notes & Records - Physical and biological processes controlling the Okavango Delta : a review of recent research

Volume 24, Issue 1
  • ISSN : 0525-5090



Over the last six years, a multidisciplinary team from the University of Witwatersrand has been carrying out research to establish the nature of the processes which underpin the Okavango Delta. From this work it has become evident that the environmental factors controlling the Delta can be divided into two broad categories. (i) External variables, which include graben faulting, which is the ultimate reason for the Delta's existence; the geology of the catchment area of the Okavango River, which controls water quality and the nature of particulate sediment; the semi-arid nature of the environment, which is responsible for the high evapotranspirational rate and the ground water leakage which prevents the accumulation of hypersaline ground water; (ii) Internal processes which operate within the constraints imposed by the external variables and have produced the present form of the Delta. Biotic processes dominate this latter category, with specialised plant communities fulfilling specific functions. These various communities regulate the dispersal of particulate sediment and water. They also control water loss through transpiration, thereby regulating chemical sedimentation, which is the dominant aggradational process in the Delta at present. The action of biological agencies induces even aggradation of the land surface and shapes the topography of the Delta, ensuring widespread distribution of water, and localising, and hence minimising the impact of, the accumulation of toxic salts. Far from being catastrophic, changes in water distribution are actually brought about by plant communities and constitute an essential self-renewal strategy in the system.

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