The Zambezi Delta is vital to Mozambique's national economy and is a Wetland of International Importance. Large dams in the Zambezi catchment have substantially altered the magnitude, timing, duration, and frequency of flooding events in the delta, resulting in adverse ecological and socio-economic changes.We evaluated conflicts/trade-offs among various water uses and the potential for improving delta conditions through environmental flow releases from Cahora Bassa Dam, using the downstream response to imposed flow transformations (Brown, C.A. and Joubert, A., 2003. Using multicriteria analysis to develop environmental flow scenarios for rivers targeted for water resource development. Water SA, 29 (4), 365-374; King, J.M., Brown, C.A., and Sabet, H., 2003. A scenario-based holistic approach to environmental flow assessments for regulated rivers. Rivers Research and Applications, 19 (5-6), 619-640) model. Five variations in low flows, 18 alternatives for annual floods, and one extreme (1:5 year) flood were considered for a range of uses/concerns, including commercial and small-scale agriculture, estuarine ecology, coastal and freshwater fisheries, livestock, large mammals, waterbirds, vegetation, invasive species, natural resources, water quality, navigation, and groundwater recharge. The study revealed minimal trade-offs among different uses with regard to reinstating environmental flows. The majority of user-representatives perceive reinstatement of the annual flood to be beneficial and the perceived benefits increase with increased magnitude and prolonged duration, provided the timing of the annual flood occurs during the normal wet season. Simulation modelling of the Zambezi system dam operation indicates that these environmental flow releases can be realized within the constraints of firm power commitments and total energy demand. Of the 18 annual flood change levels considered, 7 can be generated with a firm power reliability >95% and hydropower reductions of <2.3%, and 16 require <10% reduction in annual energy production. This work illustrates the potential for environmental flows to overcome conflict in shared water resources and create opportunities for cooperation. © 2010 International Association for Hydro-Environment Engineering and Research.
