SWMM 5.2.3 Inlet Workflow from the Help File
The process of conducting an inlet analysis using the Storm Water Management Model (SWMM) is quite thorough and systematic. Here, we provide a detailed expansion of the general workflow you've presented, demonstrating how to apply it to a simple street and sewer drainage system:
Layout both the street and sewer networks: Begin by designing and sketching your street and sewer networks. This involves determining the locations of your roads, open channels, and sewer lines, as well as their interconnections. This layout forms the fundamental skeleton for your model. You can use GIS (Geographical Information System) data or manual drafting to aid in creating the layout.
Assign subcatchment runoff and user-defined inflows to individual street nodes: Next, designate the runoff from surrounding land areas (subcatchments) and any user-defined inflows to the nodes within your street network. Runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. User-defined inflows could be point sources of water other than the subcatchment runoff. This assignment takes into account how rainfall will be distributed in the area and which roads it will likely flow down.
Create a collection of Street cross-sections: Design a collection of street cross-sections. These cross-sections represent a vertical slice through the street, showing elements such as the roadway, sidewalks, and gutters. The cross-sections provide a detailed view of the street’s shape and slope, which are key factors influencing how stormwater flows.
Assign specific Street cross-sections to individual street conduits: Each conduit in your street network should be assigned a specific cross-section from your collection created in the previous step. The assignment should accurately represent the actual structure of the street at the conduit's location.
Create a collection of Inlet designs: After dealing with the streets, focus on creating a variety of inlet designs. These inlets are structures that allow stormwater to enter the drainage system from the street surface. They can have different designs depending on their size, shape, and the specific conditions they will be handling.
Assign specific Inlet designs to selected streets: Once you have a collection of inlet designs, assign them to the specific streets within your network. Inlet placement depends on factors such as street slope, expected water flow, and city planning guidelines.
Set appropriate analysis options and run a simulation: Configure the parameters for the SWMM analysis according to the objectives of your study, including the simulation duration, time steps, and any specific routing or runoff methods. Then, execute the simulation, which will use the SWMM algorithms to model how stormwater will flow through your designed network.
Review the simulation results to see if flow spread and depth values are acceptable: After the simulation has run, assess the results. Examine key outputs like flow spread (the width of water flow on a street) and depth values at each inlet and node. Ensure that these values are within acceptable ranges as defined by your design standards. If the results are not satisfactory, you may need to revisit and revise your design, which may include altering the street layout, changing the assigned cross-sections, or modifying the inlet designs.
This detailed procedure offers a step-by-step guide to designing and analyzing a basic street and sewer drainage system using SWMM. It's essential to remember that real-world scenarios may require additional steps or considerations, depending on the specificities of the site, climate conditions, and regulatory requirements.
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