How to Easily Use the DWF Allocator with your Lots Shapefile in InfoSWMM
The goal of this document is to show how you can use a shapefile with polygon loadings to a link in the InfoSWMM DWF Allocator to create DWF loadings to the nodes in InfoSWMM that are the sums of the flows in the polygons. In other words, we are not areally weighting the polygons but summing the flows to a node from each polygon.
Step 1. We will examine the shapefile Export_Output_18.shp to find out which data fields we can use or modify for the DWF Allocator. We will use the DWF value field L_s and create a valid ID for the Field HX_JNTID which is currently empty by creating Thiessen polygon around each Node or Manhole in the model.
Step 2. Use the DWF Allocator tool Thiessen Polygon creator to make a shapefile for the HX_JNTID connection.
Step 3. View the created Thiessen Polygons that now have a valid ID for the Field HX_JNTID. The polygons are now too large so we will interset the original polygon shapefile Export_Output_18.shp with the created Thiessen Polygons.
Step 4. Use the Arc Toolbox tool Intersect to intersect the Thiessen Polygons and the shapefile Export_Output_18.shp. The Thiessen Polygon shapefile should be first on the list.
Step 5. View the created shapefile and show the flow loading per polygon. We now want to use the DWF Allocator to sum up the flow from each polygon to the InfoSWMM DWF DB table. Use properties to show the DWF in L/s for each of the intersected polygons centered around Node or Manholes.
Step 6. Open the intersected polygon shapefile using the Open Attribute Table command in Arc GIS.
Step 7. Use the Statistics tool in the Open Atribute Table for L_s to find the total DWF – it should be 255.646218 l/s
Step 8. We are not going to use the area of the polygons so we will make a new Field in the intersect polygon shapefile called BOR which will be the inverse of the polygon layer.
Step 9. Use the Field Calculator to find the inverse of the polygon layer BOR = 1/Shape_Area.
Step 10. Register the created and modified polygon shapefile. It will be layer type Intersected, use HX_JNTID and BOR as the Junction Connection and Usage Type, respectively.
Step 11. Use the DWF Allocator using 1 for the scaling factor and the Field L_S as the population. We will use the Intersected Layer option. Population – If you have a field in the Secondary Layer that is populated with the human population for each polygon, you can specify this field and DWF Allocator will be calculated as: DWF Allocator = (intersected polygon area fraction) X (intersected polygon Population) X (Load Factor for the Usage Type) X (Allocation Scaling Factor. In effect we are setting the area to 1 for all of the polygons.
Step 12. Save or Allocate the flow – we should have a DWF total of 255.646 which matches the total in Step 7.
Step 13. Check the Inflow Icon in the Attribute Browser to see the allocated flows – each row matches one polygon loading to a node.
Step 14. Finally, check the created DB table for DWF. The sum of the DWF should again equal or be close to the total in Step 7.