The Big Darby Creek Watershed located near the Columbus, Ohio, metropolitan area, is widely recognized for its excellent quality of environmental health and high biological diversity in a Midwest agricultural landscape. The watershed has been affected by an increasing amount of runoff due to urban growth, causing occasional flooding, non-point pollution problems, and reduced biological diversity. This study focused on how urban growth in a once agricultural watershed impacted the surface hydrology. To accomplish this, an improved classification algorithm - the singular value decomposition method - for mapping land use/land cover (LULC) was developed using a hierarchical classification approach. The algorithm separately classifies urban and rural land using an object recognition technique. The GIS layers (road, streamline, park area shapefile, and golf course) were integrated with the LULC map in the post classification stage. The process produced high accuracy LULC maps with an overall accuracy of >89percent. To investigate the hydrologic impact of LULC change in the Big Darby Creek Watershed, the improved LULC maps were used in a distributed modeling scheme using HEC-GeoHMS/HEC-HMS. The hydrologic simulation results showed that there is a significant increase (15percent) in the peak hydrograph for Hellbranch Run, which is the most urbanized subwatershed in the Big Darby Creek Watershed. The sensitivity analysis of the LULC maps showed that the resulting hydrograph from the simulated LULC error would be minor for small urbanizing areas. A modeling framework was developed that can be used to study urbanizing watersheds for developing future efforts to understand the hydrological impact of LULC change in a watershed on a larger scale.
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