Mathematical Modeling of Watersheds as a Subsidy for Reservoir Water Balance Determination: The Case of Paranoá Lake, Federal District, Brazil

Abstract

Paranoá Lake, Federal District (DF), Brazil, is one of the most important urban lakes in the country and it receives inputs from basins with different characteristics, from natural and preserved to intensely urbanized and agricultural areas. The study of the hydrological processes in these basins, as well as the water balance in each of them, is fundamental for planning current and future water uses in Paranoá Lake. Using an extensive database (35 years) and the Soil and Water Assessment Tool (SWAT) model, we modelled five sub-basins. The outflow rates of the model for each sub-basin served as input for determining the water balance of Paranoá Lake, which recently became part of the DF public water supply system. Despite extensive flow monitoring in the main lake tributaries, about 20% of the lake basin is composed of direct contribution or non-monitored tributaries. Additionally, the lake outflow is composed of a spillway and a hydropower generation unit that does not have proper flow measurements, and thus a correct basin hydrological simulation is essential for water balance aiming to water management scenarios. The results show an average long-term balance of 18.073 m3/s, with minimum flows around 13 m3/s and maximum flows close to 30 m3/s. This is a pioneering study that associates the extensive monitored database and the hydrological simulation of all affluent basins with the water balance of Paranoá Lake. The results obtained are essential to water management and hydrodynamic modeling of the lake.