Sustainable water and land management of the Okavango Delta, Botswana

A distributed model for coupled surface and groundwater flow in the Okavango–Delta was constructed, based on MODFLOW with new extensions developed in the project. The model reproduces the annual flooding patterns as a function of inflows and climate. It was calibrated against the patterns of the water-covered area as determined from satellite images. The fate of salt, which can serve as a tracer, was tracked through the system. It was found that the long coastline removes water with salt through infiltration and evapotranspiration thus leaving the surface water remarkably fresh. The evapo-concentration process leads to salt accumulation on islands and may eventually produce fingering of dense water under islands. One such island was analysed in detail with geophysical methods. The existence of a salt finger could be shown with down-hole geoelectrics. With the model, scenarios of the impact of future interventions both in the upstream where dams are to be built as in the delta itself where dredging and papyrus cutting is considered, were calculated. The distance from project results to practical use is short as the Department of Water Affairs was our partner in this project from the beginning. The results of the project will further flow into the Okacom, an international commission of the riparian states of the Okavango Delta.

In the continuation of the project an airborne TEM survey of the whole delta will be performed. The model will be adjusted according to the sizes of the observed freshwater lenses. The thickness of the Kalahari sand aquifers will be estimated from airborne geomagnetic data already available. Sediment transport will be incorporated into the model.

More detailed information can be found in the following posters.

• Monitoring and Modelling of Sediment Transport in the Okavango Delta, Botswana
• Hydrological and sedimentological modelling of the Okavango Delta, Botswana
• Semi-automated interpretation of aeromagnetic data as a means of determining the geometry of the Kalahari Sands aquifer below the Okavango Delta, Botswana
• Flooding in the Okavango Delta, Botswana
• Salt Transport in the Okavango Delta, Botswana

Main publications

Bauer, P., Held, R., Zimmermann, S., Linn, F. and Kinzelbach, W. (2004) Coupled Flow and Salinity Transport Modelling in Semi-Arid Environments: The Shashe River Valley, Botswana. Submitted to Journal of Hydrology.

Bauer, P., Gumbricht, T. and Kinzelbach, W. (2004) A large-scale coupled surface water/groundwater model of the Okavango Delta, Botswana, Submitted to Water Resources Research.

Bauer, P. and Kinzelbach W. (2004) Wassernutzungskonflikte am Okavango: Szenarios als Entscheidungshilfe. GAIA, 13(1), 50-60.

Bauer, P., Thabeng, G., Stauffer F. and Kinzelbach W. (2004) Estimation of the evapotranspiration-rate from diurnal groundwater level fluctuations in the Okavango Delta, Botswana. Journal of Hydrology, 288(3-4), 344-355.

Bauer, P., Zimmermann, S. and Kinzelbach, W. (2004) Salt Transport on Islands in the Okavango Delta: 1. Large-Scale Salt Balance and the Role of Density Fingering. Submitted to Water Resources Research.

Bauer, P., Zimmermann, S., Supper, R. and Kinzelbach, W. (2004) Salt Transport on Islands in the Okavango Delta: 2. Mapping the salinity distribution beneath Thata Island by electrical resistivity tomography. Submitted to Water Resources Research.

Brunner, P., Bauer, P., Eugster, M. and Kinzelbach W. (2004) Using Remote Sensing to regionalize local precipitation recharge rates obtained from the Chloride Method. Journal of Hydrology, 294, 241-250.

Gumbricht, T., McCarthy, T.S. and Bauer, P. (2004) The micro-topography of the wetlands of the Okavango Delta, Botswana, Earth Surface Processes and Landforms, in press.

Zimmermann, S. Bauer, P., Held, R., Walther, J. and Kinzelbach, W. (2004) Salt Transport on Islands in the Okavango Delta: Numerical Investigations. Submitted to Advances in Water Resources.

Contacts

W. Kinzelbach, P. Bauer

Agency/Funding

First phase: ETH/238 kCHF;
Second phase: SNF/240 kCHF.

Partners

Department of Water Affairs, Botswana, Water Resources Consultants, Botswana

Status

First phase finished in 2004, second phase started in October 2004.