Hydrological Modelling and Detention Ponds Evaluation at Paranoa Lake - Brazil

Abstract

Paranoá Lake is an urban lake and since last year Brasilia started to use its waters for human consumption. Until the 1990’s algae and cyanobacteria blooms occurred and improvements on wastewater treatment plants brought the water quality to very good conditions in the 2000’s. Recently water quality is starting to deteriorate mainly due to diffuse pollution. Thus, the evaluation of urban drainage waters entering the lake and the proposition of technological alternatives to minimize impacts are important for the analysis of diffuse urban pollution flowing into the lake. Quantitative and qualitative behaviour of the urban drainage waters were analysed by means of monitoring the precipitation amount and runoff flow and quality. Mathematical modelling using the SWMM and PCSWMM programs was carried out, and good results were obtained for flow modelling. However, in water quality simulations, poorer response was obtained. It was also evaluated the implementation of 13 alternatives of detention ponds to study the effects of their location on the removal of pollutants, as well as influences on the network flow support. It was observed that ponds allocated in the downstream part of the network are more efficient, but requireconstruction in environmentally and urbanistically problematic areas and high commercial value. Alternatives with smaller volumes in areas areas near the center ofthe basin can meet flood-damping needs of the presently constructed drainage network.