Imperviousness and Land-Use Policy: Toward an Effective Approach to Watershed Planning

Urban impacts to water quality and quantity have been a major focus of resource and ecosystem protection efforts since the early 1960s, focusing in the last decade on the impact of impervious thresholds. These are now commonly used as benchmarks of water quality planning and protection in local, watershed, and regional planning efforts. However, the relationship between urbanization and hydrologic impacts is much more complex than this cause-and-effect model would indicate, containing some weaknesses for effective growth management planning. This paper reviews the current literature to synthesize the development-related variables of hydrologic impairment, placing them in a context that is useful in growth management and development mitigation. Through this critical review of the literature, the paper focuses on an outstanding question in land planning: which best management practices, individually or in concert, are the most effective in dealing with the water quality impacts of urban growth and development? Research indicates two largely overlooked areas of potential improvement in water protection efforts: the location of impervious surfaces in the watershed, and the maintenance of adequate areas of forest stands and native vegetation.