HYDROLOGIC RESPONSE TO URBAN SPATIAL METRICS IN THE WHITE RIVER BASIN, IN

The White River watershed, which includes the city of Indianapolis, Indiana, has experienced significant urbanization in the past 30 years, resulting in a sharp increase in Impervious Surface Area (ISA). ISA has significantly different hydrological response characteristics from natural land cover and can potentially influence watershed hydrology. The role that urban land cover plays in local hydrology largely depends on the location of urban patches relative to the stream channel. For example, urban patches adjacent to wetland or forest may have little net impact since most of the urban runoff yield will flow through wetland or forest, rather than contributing directly to the outlet discharge. Urbanization in this region creates highly complex landscapes with human-dominated land uses and natural land covers scattered in a variety of patch shapes and configurations. Therefore, it is very important to examine how hydrological dynamics are influenced by urban spatial arrangements. Seventeen small watersheds with drainage areas between 20 and 300 km2 within the White River basin that have undergone different degrees of urbanization, are selected for hydrologic response analysis based on the availability of streamflow data between 1980 and 2003. The ISA fraction for each watershed is derived from 1983 and 2001 land use maps, where urban land use is separated into high density, low density and roads. Each category is assumed to consist of different ISA and turf grass fractions. The characteristics of urban patches are quantified using the spatial pattern analysis tools such as FRAGSTATS and ArcGIS. Edge density (ED), contagion (CONTAG), traversability (TRAVERS), largest patch index (LPI), number of patches (NP) and mean nearest neighbor (MNN) distance for each watershed are calculated in FRAGSTATS. The relationship of annual streamflow metrics such as flow distribution, daily variation, and high flow frequency are analyzed versus the above ISA spatial pattern metrics. The results of this work will increase our understanding of the impacts of urban spatial metrics to hydrological processes at regional scales, and can be beneficial to urban planners working on storm water management.