Tuesday, July 4, 2023

Inlets from the SWMM 5.2.3 help file

 Inlets from the SWMM 5.2.3 help file 

The Storm Water Management Model (SWMM) is a powerful hydrological simulation program, used for planning, analysis, and design related to stormwater runoff, combined sewers, sanitary sewers, and other drainage systems. This software models various components of these systems, including pipes, channels, and inlets. When modeling inlets with SWMM, you should consider the following key concepts:

  1. Inlet Assignment: Inlets are assigned to conduit links that represent either streets or open channels. In this context, conduits are used to represent the physical structures that carry flow in the drainage system, such as pipes, channels, and tunnels. Therefore, each inlet, representing a point of entry for stormwater into the system, needs to be linked to a specific conduit.

  2. Inlet Type and Conduit Cross-section: The type of inlet you choose is determined by the cross-section of the conduit it is assigned to. For instance, curb and gutter-type inlets are designated to conduits with a street cross-section. Meanwhile, drop inlets are used with conduits that have either a rectangular or trapezoidal cross-section. Alternatively, custom inlets can be placed in any type of conduit, providing greater flexibility in modeling.

  3. Node Assignment: Each inlet is assigned to a node, typically part of a sewer line, that will receive the flow captured by the inlet. A node represents a junction point in the system where the flow may divide or combine.

  4. Multiple Inlets: Multiple inlets of the same design and receptor node can be assigned to a single conduit. This is particularly useful when modeling two-sided streets. For on-grade placement, the flow captured by each inlet is determined sequentially, which means the flow approaching the next inlet in line is the bypass flow from the inlet before it.

  5. Inlet Operation: Users can determine whether an inlet operates on-grade, on-sag, or let SWMM decide based on the street layout and topography. An on-grade inlet is situated on a continuous grade, while an on-sag inlet is located at a sag or sump point. The latter is an area where all adjacent conduits slope towards the inlet, leaving no place for water to flow except into the inlet.

  6. Flow Capture: Flow capture for on-grade inlets is determined by the approach flow seen by the inlet. However, for on-sag inlets, it is a function of the depth of water at the sag point node. This distinction is crucial for correctly modeling the flow behavior.

  7. Clogging and Flow Capture Restriction: Inlets can be assigned a degree of clogging and a flow capture restriction. These factors account for potential real-world conditions that may impede the flow into the inlet, providing a more accurate representation of the system’s functionality.

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