ABSTRACT
This chapter discusses the approaches for estimating the pollutant removal by urban stormwater detention systems. Numerous simplifying assumptions must be made to use the statistical method including: restrictions on the type of probability density functions, ignoring the covariance between flow and concentration, a simple runoff coefficient, and simplistic treatment removal kinetics. A wide variety of methods exist for evaluating the effectiveness of detention systems for removing pollutants in urban runoff. Traditionally, a major justification for using a longer time step is computational expediency or necessity. However, the economics of computing have changed radically since the introduction of PCs. While the quantity of stormwater varies widely during a storm event, the quality varies even more widely. Depending on the nature of the storm and the sources of pollutants, the concentration of pollutants may exhibit a first flush, i.e. concentration decreases as the flow duration increases.
