Reservoir phosphorous sources evaluation and water quality modeling in a transboundary watershed

The Alqueva dam, constructed in the Portuguese section of the Guadiana River, is the centre of a multipurpose project under development in Alentejo, Portugal, which includes strategic water storage, hydropower production, irrigation and urban water supply. Aiming to adequately evaluate nutrient control strategies along the Alqueva watershed in Portuguese territory, total phosphorous (P) quantification methodologies were implemented for urban, industrial and diffuse (nonpoint) sources and used as input to the two-dimensional hydrodynamic and water quality model CE-QUAL-W2. As a first approach two scenarios of pollution reduction in Portuguese territory were simulated: 90% reduction of urban waste water pollution sources (scenario 2) and 100% reduction of all pollution sources (scenario 3). According to the results of the ongoing study, even a theoretical 100% reduction of the pollution loads originated in Portuguese territory would not insure an overall satisfying water quality in the Alqueva reservoir. Nevertheless, simulation results show not only that urban waste water discharges are yet a significant contribution for unsatisfactory water quality, but also that the overall contribution from the Portuguese area may be an important factor on biomass control. Also, water quality deterioration has been observed along reservoir branches, which are probably only affected by loads originated in Portuguese territory.