Optimization of water allocation networks in highly engineered basins: The case of Guandu River basin, Rio de Janeiro State, Brazil

Abstract

During the last decades, metropolitan areas with a large population and economic size have mushroomed, modifying the urban geography and natural environment. Along with the rising of megacities, highly engineered basins have been created, providing resource security regarding water and energy. The coastal Guandu River basin in Brazil represents an artificial basin that has been heavily intervened for decades. The basin receives almost ∼80% of the water by transfers from the Paraiba do Sul River Basin System and has an associated hydroelectric complex that generates power for the national network. It is the primary source of water and energy for the Rio de Janeiro Metropolitan Area, home to ∼13 million people. Recently, water availability for this region has been jeopardized by drought conditions due to changing rainfall patterns and competition for water resources with other users such as Sao Paolo Metropolitan Area. This study focuses on the development of an optimization framework (WANAB model) for water resources management at the macroscopic level in the Guandu Basin to guarantee economic viability and water resources sustainability. The model incorporates parameters and equations for hydrological, and engineered water and hydropower processes to determine the optimal water allocation network. Also, a multi-criteria analysis is proposed to evaluate the water availability considering different scenarios. The results show that through optimization, it is possible to have a water availability of up to ∼24 m3/s in the Guandu River basin by integrating elements such as water storage systems, grey and blackwater treatment plants with capacities up to ∼39 m3/s and ∼9 m3/s, respectively. The results show that it is possible to reach a water availability of 21 m3/s in the scenario, considering the reduction of water transfers from outside the basin due to climate change. However, the major impact is observed in the hydropower generation, decreasing from ∼2270 GWh/y to ∼1950 GWh/y. The WANAB model represents a decision-making and policy tool for optimizing water allocation networks and may be adapted for other highly engineered basins.