Appendix-A: Storm Network Representation in GeoSWMM
GeoSWMM models a conveyance network as a series of nodes connected by links (Figure 2.1). Links control the rate of flow from one node to the next and are typically conduits (e.g. open channels or pipes) but can also be orifices, weirs or pumps. Nodes define the elevation of the drainage system and the time- varying hydraulic head applied at the end of each link it connects. The flow conveyed through the links and nodes of the model is ultimately discharged to a final node called the outfall. Outfalls can be subjected to alternative hydraulic boundary conditions (e.g. free discharge, fixed water surface, time varying water surface, etc.) when modeled with Dynamic Wave.
All hydraulic elements modeled in SWMM are classified as either nodes or links. The hierarchy of these elements is shown below along with both the required and optional properties that characterize each element’s hydraulic behavior.
Type of Hydraulic Element | Category of Element | Tutorials or Types | Required Properties | Optional Properties |
|---|---|---|---|---|
Nodes | Junction
| · Manholes · Points of Change in conduit slope or cross section | · Invert elevation · Maximum depth · Initial depth | · Surcharge depth · Treatment · Inflows · Ponded area |
Divider
| · Cutoff · Tabular · Weir · Overflow | · Invert elevation · Diversion link · Type · Maximum depth · Initial depth | · Ponded area · Surcharge depth · Treatment · Inflows | |
Storage Unit
| · Reservoirs · Peak shaving detention ponds · BMPs | · Invert elevation · Storage curve · Maximum depth · Initial depth | · Treatment · Inflows · Evaporation factor | |
Outfall
| · Free · Normal · Fixed · Tidal · Time series | · Invert elevation · Type | · Inflows · Treatment · Tide gate | |
Links | Conduit
| · Natural channels · Closed conduits · Open Channels | · Inlet node · Outlet node · Shape and section geometry · Length · Roughness · Inlet offset · Outlet offset | · Initial flow · Maximum flow · Entry loss coefficient · Exit loss coefficient · Average loss coefficient |
Pump | · Off-line · In-line incremental · Variable speed in-line | · Inlet node · Outlet node · Pump curve | · Initial status · Startup depth · Shutoff depth |
Type of Hydraulic Element | Category of Element | Tutorials or Types | Required Properties | Optional Properties |
|---|---|---|---|---|
Nodes | Orifice
| · Circular orifice · Rectangular orifice | · Inlet node · Outlet node · Type · Geometry · Inlet offset · Discharge coefficient | · Flap gate · Time to open/close |
Links | Weir
| · Transverse · Side-flow · V-notch · Trapezoidal | · Inlet node · Outlet node · Type · Geometry · Inlet offset · Rating curve · Inlet offset · Discharge coefficient | · Flap gate · End contractions · End coefficient |
Outlet
| · Used to model special head discharge relationships | · Inlet node · Outlet node · Inlet offset · Rating curve | · Flap gate |
