Figures 2-1 and 2-2 display the pre- and post-development SWMM model layouts from Example 1. In Figure 2-1, the pre-development region was depicted by a single subcatchment, sized according to a 500 ft overland flow limit. The post-development scenario (Figure 2-2) involved seven subcatchments, with widths based on area-weighted averages of flow distances per area type. All subcatchments discharge overland flow to node O1 at the site’s outlet.

Figure 2-1

Figure 2-2

Objective: This case aims to integrate a basic surface drainage system into the post-development site. Using gutters, grass swales, and culverts, the system will be designed to manage the 100-year storm. Through three SWMM hydraulic routing methods, runoff from the 2-year, 10-year, and 100-year storms will pass through this system. We’ll then compare the resulting outflow hydrographs at the site’s outlet to those from Example 1, which lacked hydraulic routing.