Modeling the impacts of climate extremes and multiple water uses to support water management

What is it about?

The hydropower production, water supply and aquaculture services of the Itaparica Reservoir are of immense importance for the Brazilian Northeast. Uncontrolled water resources consumption (e.g. irrigation, water supply), climate and land use change effects deteriorated the water quantity and quality in the reservoir, leading to socioeconomic and environmental problems. In this work, a depth-averaged shallow water model was set up for the Icó-Mandantes Bay, one major branch of the reservoir, using the open TELEMAC-MASCARET system. The aim was to assess the impacts of the newly built water diversion channel, as well as the effects of a flood and tracer transport from an intermittent tributary, both located in the bay. An alternative approach to estimate the water retention times was additionally implemented. The simulations showed that though the diversion channel did not influence significantly the hydrodynamics of the bay, it is necessary to continuously monitor water quality parameters in the withdrawal, especially during rainy periods after droughts, because of the nutrient inputs from the tributary and the overflows of the nearby drainage systems. Management measures adapting to the continuously changing natural conditions and anthropogenic impacts are thus indispensable and the model presented can be a valuable supporting tool for this purpose.

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Why is it important?

The article presents two-dimensional (depth-averaged) modeling tool for the Icó- Mandantes Bay, one of the major off-stream branches of the Itaparica reservoir (Sub- Middle São Francisco River, Northeast Brazil), proposed for management support. The aim of the research was to assess the impacts of climate extremes, such as floods and droughts, and the multiple uses of water on the hydraulics and on the transport of contaminants, investigating as well the exchange processes between the two different behaving complex systems. The water body investigated is stressed out by the effects of climate change (e.g., the still lasting drought started in 2012), the multiple uses of water, often unregulated, and has a high eutrophication potential (nutrients overload after rain events and algae blooms). Moreover, the eastern channel of the highly debated water diversion project for the Northeast will withdraw water directly from the bay. The manuscript provides a CFD tool first available for the region, which gives a deeper insight of the complex dynamics of the water body studied and may be used and refined in the next future by academia and water managers, e.g. coupling it with a water quality module. Last but not least, the research integrates the results of the ecohydrological model SWIM and the new decennial plan for the São Francisco River Basin produced by the Lisbonsettled company NEMUS with (all references may be found in the article), both at the basin scale.

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