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Colorado State University (2007)

Application of the Water Evaluation And Planning (WEAP) model to assess future water demands and resources in the Olifants Catchment South Africa

Arranz, Roberto

Titre : Application of the Water Evaluation And Planning (WEAP) model to assess future water demands and resources in the Olifants Catchment South Africa

Auteur : Arranz, Roberto

Université de soutenance : Colorado State University

Grade : Master of Science (MS) 2007

Résumé
The Olifants Catchment is one of the 19 Catchment Managent Areas (CMA) existing in South Africa. Different water users (i.e., rural, urban, mining, subsistence and commercial irrigated agriculture, commercial forestry, industry and power generation) are present in the catchment. The Olifants River is a tributary of the Limpopo River, an international river shared by South Africa, Botswana, Zimbabwe and Mozambique. The development of the mining industry (mainly platinum group metals and coal) and the construction of new power generation plants, along with the population growth, the implementation of the Environmental Reserve, the International responsibilities, the improvement of the accessibility to water in the rural areas, etc are going to increase the water demands in this already water stressed catchment. Being able to assess the ability of the catchment to satisfy its future water demands is crucial in order to plan for the future and make wise decisions. In this study a Scenario Analysis approach was used in conjunction with the Water Evaluation and Planning (WEAP) water allocation model, in order to assess the impacts of possible future water demands on the water resources of the Olifants catchment. For each scenario, the main outputs of the model were analyzed : unmet water demands for the different water sectors, streamflows at the outlet of the Olifants catchment and the water stored in the reservoirs. The model results show that for the different 2025 water demand scenarios considered in this study the implementation of the Environmental Reserve (an instream requirement to guarantee the health of the riverine ecosystems) will increase the shortages of other sectors. The construction of the main water storage infrastructure proposed by the Department of Water Affairs and Forestry (DWAF), in conjunction with the application of water conservation and demand management (WC&DM) practices, can reduce the unmet demands and shortages to levels lower or similar, depending on the scenario, to those experienced for the 1995 water demand baseline. However, in all the cases these interventions won’t be able to meet completely the demands of all the sectors. A tight control of the growth of the future demands will be needed, although this may be difficult in a rapidly growing developing country like South Africa. Another interesting output of the simulations performed is that, even for the most severe scenario, the mean annual streamflow released to Mozambique (i.e., the country downstream) will exceed 60% of the mean annual naturalized streamflow. This result reflects the inability of the existing storage infrastructure in South Africa to regulate interannual flows (total storage capacity is less than the mean annual naturalized flow) and explains in part the efforts of Mozambique to increase the development around the Massingir dam.

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