The Subcatchment Manager of InfoSWMM will help calculate most of the physical parameters associated with a Watershed or Subcatchment in SWMM 5 from a Digital Elevation Data (Step 1). The Subcatchments slope is estimated from a slope raster (Step 2) and the Slope Calculator (Step 4). The created watershed area are calculated using the command Update DB from Map (Step 6) along with the Subcatchment Width (Step 3) and the Impervious Area (Step 5). The physical parameters estimated from the DEM are shown in Figure 1.
Figure 1. Physical Data Estimated from a DEM using the Subcatchment Manager in InfoSWMM.
Step 1. Use the command Create Flow Stream to create a Flow Stream for the DTM or DEM that can be used later.
Step 2. Create a Slope Raster from the DEM for later usage in the Slope Calculator.
Step 3. Calculate the Width of the Subcatchment using one of five methods.
Step 4. Calculate the Slope in percent from the Slope Raster created in Step 2.
Step 5. Populate the Impervious area percentage using a Parcel shape file and the Created Subcatchments.
Step 6. Use Arc Map to calculate the area of the Subcatchments using the command Update DB from Map and the following Operation Flags.