GIS Techniques for Watershed Delineation of SWAT Model in Plain Polders

Watershed delineation based on digital elevation models (DEMs) is the prerequisite to set up SWAT model. With topography and hydrologic processes different from the mountainous area, the watershed delineation in plain polders faces three problems: (1) the subbasins and reaches delineated from the DEM do not agree well with the realistic ones; (2) the braided streams cannot be identified by SWAT model; (3) routing processes are affected by the water-control projects seriously. Based on ArcGIS and ArcSWAT, improved DEM-based method and pre-defined method were applied in watershed delineation. In the first method, “Burn-in” and drawing reach and subbasin boundary manually were applied. First, the digital channel network (DCN) was imported using the “Burn-in” function, and the streams and subbasins were delineated based on DEM and DCN. Then the “watershed” and “reach” layers were edited in ArcGIS, where the location, range, and hydrologic connection could be adjusted. In the second method, streams and subbasins could be drawn manually or re-edited. In conclusion, the watershed delineation results using both methods agreed well with the realistic hydrologic processes in polder area and could meet the demands of the following model setup.