Characterization and Determination of Nonpoint Pollution in Streams Caused by Stormwater Runoff

The water stress that can be seen in different regions are generally related to the excessive use of water by human activities and to the improper wastewater treatment and disposal. In this aspect, periods of drought are considered critical because of the low volume available for pollutants dilution. However, surface runoff has been identified as responsible for significant impacts on water and aquatic habitats due to amount of pollutants washed during storm events. Differently from punctual pollution, which is easy to quantify and even predict, nonpoint source pollution is strongly connected with economic, cultural and social aspects of land use and vary widely with site characteristics. Those complex variables make essential to develop methods and concepts to quantify the pollutant load present in surface runoff considering the great variability of the constituents and its quantities. Concentrations can vary by orders of magnitude between river basins, different precipitation events and along the same event. The graph that explains the behavior of the concentration of the pollutant in the storm event versus time is known as pollutograph and is essential for the studies of non-source point pollution. Nonpoint loads can be quantified and estimated by several methods, such as Exports Coefficients (EC) or Unit Loads, Event Mean Concentration (EMC) as well as Mathematical Models and two approaches are identified. The most widely used are the lumped-parameter models, while more complex models are based on the distributed-parameter concept. In this article, four models (USGS, HSPF, STORM, SWMM) were described briefly and it is shown that computer simulation models which combine the processes that water undergoes (in terms of quantity and quality) in the watershed surface and downstream waterbodies are highly needed. Comparison between computed and measured concentrations in a real urban area highlight the need for further extensive research on this subject.