The United States Environmental Protection Agency now considers pollution from all diffuse sources to be the most important source of contamination in the nation's waters (USEPA, 1997). These pollutants cause dramatic changes in hydrology and water quality that result in a variety of problems. Hydrologic impact due to urbanization is reported to cause water quality problems such as sedimentation, increases temperatures, habitat changes, and loss of fish population. There is widespread recognition that these problems are caused by increased runoff volumes and velocities from urbanization and associated increases in watershed imperviousness. Imperviousness represents the imprint of land development on the landscape. The second aspect of urbanization that contributes to urban stormwater pollution is the increased discharge of pollutants. Oil, grease, landscape practices, construction, illicit connection, leaking sanitary sewers and countless other aspects of daily life in urban areas contribute to polluted runoff (NRDC, 1999, Chap. 2). The degradation caused by urban stormwater pollution is serious, and affects a significant proportion of the nation's population. The most dramatic consequence of increases in the volume and rate of stormwater runoff is flooding, property damage and erosion.
With the spread of development and intensified agricultural practices across watersheds, pollutant runoff, nonpoint source pollution and unmanaged development have become the greatest threats to drinking water sources (TPL, 1997, p.5). From small towns to big cities to entire states, there is a growing recognition that land conservation may be the best and cheapest way to guarantee drinking water supplies. Watershed development does not necessarily have to be synonymous with the degradation of aquatic resources. When new growth is managed in a watershed context, homes and businesses can be located and designed to have the smallest possible impact on streams, lakes, wetlands and estuaries. In the watershed protection approach, communities can apply basic tools that guide where and how new development occurs. Watershed planning has provided several municipalities the opportunity to consider all the resources in the watershed as a single, interrelated system.