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Drainage division, DEM, GIS, wetlands, riparian buffers, concentrated flow


In a complex watershed, isolated wetlands, riparian wetlands and riparian buffers provide important functions such as flood attenuation and water quality improvement. For conservation purposes, it is critical to properly delineate drainage areas for these features such that their impacts on runoff, sediment and pollutant transport can be reasonably simulated. However, traditional methods for watershed delineation typically fill depressions or ignore riparian features in order to maintain the continuity of surface flow pattern. In this study we develop an ArcView geographic information system (GIS) interface for watershed delineation that accounts for wetlands and riparian buffers. Based on digital elevation model (DEM), wetland distribution, and stream network GIS data, a subwatershed is further divided into isolated wetland drainage, concentrated flow drainage, riparian wetland drainage, and direct stream drainage. Outflow from isolated wetlands forms a source of concentrated flow that may contribute to riparian wetlands or bypass riparian buffers depending on its outlet location. This approach of drainage division makes a contribution in linking watershed models and field- based models through divided drainage areas. The developed interface provides a tool for simulating hydrologic processes of these features and assessing different restoration scenarios. The drainage division interface is applied to the Fairchild Creek watershed of southern Ontario in Canada where numerous isolated wetlands, riparian wetlands and riparian buffers exist. A comparison of runoff and sediment simulation results before and after drainage delineation shows the importance of the interface in facilitating watershed modeling.