Non-Point Pollution Modelling and Water Quality Modelling Using Unit Loads. A Case Study in Hedberg Reservoir, São Paulo.

In urban areas disorganized expansion, inefficiency of drainage infrastructure, poor public cleaning and the dissenting use of the support capacity of the environment are causes of progressive degradation of the environmental conditions. Similar scenarios can be found in rural areas, as the excessive use of pesticides, natural vegetation removal also causes strong negative impacts. Much is known about punctual pollution, that can be more easily quantified, predicted and controlled as their locations are well-established. However, surface runoff has been identified as the cause of significant impacts on water and the aquatic habitat. This aspect points to the necessity to develop and upgrade quantifying, monitoring, and modelling the pollutants load for different conditions. One of the most used methods to predict non-point pollution is through Unit Loads that has the major advantage to be found in literature and calibrated after local sampling. Once pollutants’ load is known, water quality simulations can be used to predict the fate of constituents and its consequences over the water environments. The Hedberg Reservoir (106 m3) is in a environmental protected area in the state of São Paulo. Its catchment area is partially rural and suffers an intense process of degradation resulting from human activities. This has caused a substantial development of phytoplankton and macrophytes that compromise water quality and its uses. This work was carried out to quantify the amount of incoming load of pollutants in Hedberg Reservoir through the calibration of the appropriate unit loads against local monitoring. The procedure employed a hydrological spatial model coupled to a water quality model and the results were compared to the literature values according to the specific soil characteristics and land use. The results obtained in the case study showed that Unit Load’s Method is a useful tool to represent diffuse pollution build-up, when comparing modelling outputs.