Integrated Watershed Management

Before stormwater control programs can be selected and evaluated, it is necessary to understand the problems in local receiving waters. The lists below give typical receiving water problems, both those associated with the long-term accumulation of pollutants and those caused by short-term (event-related) problems. Long-term problems associated with accumulations of pollutants in waterbodies include: 1) Sedimentation in stormwater conveyance systems and in receiving waters, 2) Nuisance algal growths from nutrient discharges, and 3) Inedible fish, undrinkable water, and shifts to less sensitive aquatic organisms caused by toxic heavy metals and organics (such as with contaminated sediment). Short-term problems associated with high pollutant concentrations or frequent high flows (event related) include: 1) Swimming beach closures from potentially pathogenic microorganisms, 2) Water quality violations, especially for bacteria and heavy metals, 3) Property damage from increased flooding and drainage system failures, and 4) Habitat destruction caused by frequent high flow rates, although actual stream bed enlargement may take place over several years (bed scour, bank erosion, flushing of organisms downstream, etc.). Many of these problems have been commonly found in urban receiving waters in many areas of the U.S. Because these problems are so diverse, a wide variety of individual stormwater controls usually must be used together to form a comprehensive wet weather management strategy, and in conjunction with suitable wastewater collection and treatment methods. The integration of water use considerations also can be an important tool in an integrated watersheds management program. Unfortunately, combinations of controls are difficult to analyze either using most available stormwater models or directly from the results of monitoring activities. These difficulties will require new modeling techniques that will enable an effective evaluation of a wide variety of control practices and land uses that may affect the entire suite of receiving water problems, while at the same time the design and implementation of these practices must meet the over-riding storm drainage objective of flood control.