Outlets are flow control devices that are typically used to control outflows from storage units. They are used to model special head-discharge relationships that cannot be characterized by pumps, orifices, or weirs. Outlets are internally represented in SWMM as a link connecting two nodes. An outlet can also have a flap gate that restricts flow to only one direction.
Outlets attached to storage units are active under all types of flow routing. If not attached to a storage unit, they can only be used in drainage networks analyzed with Dynamic Wave flow routing.
A user-defined rating curve determines an outlet's discharge flow as a function of either the freeboard depth above the outlet's opening or the head difference across it. Control Rules can be used to dynamically adjust this flow when certain conditions exist.
The input parameters for an Outlet are listed in the table below:
| Field | Description |
| Name | User-assigned outlet name. |
| Start Node | Name of node on inflow side of outlet. |
| End Node | Name of node on discharge side of outlet. |
| Inlet Offset | Depth or elevation of outlet above inlet node invert (ft or m). |
| Flap Gate | YES if a flap gate exists which prevents backflow through the outlet, or NO if no flap gate exists. |
| Rating Curve |
Method of defining flow (Q) as a function of freeboard depth or head (y) across the outlet.
FUNCTIONAL/DEPTH - uses a power function
Q = AyB FUNCTIONAL/HEAD - uses a power function Q = AyB where y is the head difference across the outlet. TABULAR/DEPTH - uses a tabulated curve of flow versus freeboard depth values. TABULAR/HEAD - uses a tabulated curve of flow versus freeboard depth values. |
| FUNCTIONAL | |
| Coefficient | Coefficient (A) for the functional relationship between depth or head and flow rate. |
| Exponent | Exponent (B) used for the functional relationship between depth or head and flow rate. |
| TABULAR | |
| Curve Name | Name of Rating Curve containing the relationship between depth or head and flow rate (double-click to edit the curve). |