Pattern and Variation in Development of Small Urban Watersheds

Abstract

Increased urbanization has been correlated with hydrologic, chemical, geomorphologic, and biologic changes to receiving streams. Therefore, the status quo in watershed management has been to control the amount of impervious surface area. However, because various measures of development and impervious surface area are correlated, it is hard to discern what aspects of development cause adverse ecological impacts: impervious surface area is correlated with stormwater infrastructure, natural vegetation cover, road density, and so on. In practice, the level of variability in any of these parameters can be high at any intensity of development. We can take advantage of that variability to choose landscape configurations that minimize watershed impacts for any given level of urbanization. To do so, we must understand how watershed land cover parameters co-vary with development intensity (percent impervious surface) and which aspects of configuration most directly impact urban streams. To this end, I examined 14 specific aspects of development configuration and stormwater infrastructure for 235 small watersheds in the Piedmont region of North Carolina. For both landscape metrics and infrastructure features, there was a high degree of variability at almost any level of development intensity. In the case of road density for central ranges of development, there was so much variation that the expected positive correlation of roads with development was no longer significant. Our results set the stage for future exploration of the hydrologic and chemical processes that are altered in urban streams. Relation of development pattern to ecological process in this way will support more nuanced methods for management of watershed development so that hydrologic impacts might be minimized for any given level of development intensity.