Analysis of NYDEC guidelines for extended detention basins: Effectiveness in water quality improvement in western and central New York

The New York State Department of Environmental Conservation (NYDEC) has recently issued guidelines for stormwater management. One widely utilized management practice is the extended detention basin wherein improved water quality is achieved through sedimentation. NYDEC recommends these be designed so that the volume of storm runoff detained is equivalent to the first flush, defined as the first V of runoff or runoff from a 1-year, 24 hour storm event, whichever is greater, from all land areas for which the perviousness has been changed. It also suggests a minimum detention time of 24 hours. This thesis establishes if these generic criteria, generally adopted from studies in the Metropolitan Washington, D.C. area, are sufficient for the central and western New York state region. A computer model is developed to implement an existing technique to analyze the removal of particulate pollutants through sedimentation. The model uses local meteorological data, watershed characteristics and detention basin geometry as input. The results of the analysis, applied to a case study, show that a basin properly designed to the NYDEC guidelines is effective in providing water quality improvement. For the case study basin, an average of 86.4% of the suspended particulate pollutants were removed. It is, however, critical that the NYDEC specifications regarding storage volume are followed or the basin will not provide effective removal of suspended particulate pollutants