An orifice 
is a command, usually located at the outlet, to reduce, measure, or restrict a flow.
Orifices serve as representations of outlet and diversion structures in drainage systems, typically manifesting as openings in manhole walls, storage facilities, or control gates. Internally within VOSWMM, they are depicted as links connecting two nodes. Orifices may take on either circular or rectangular forms, positioned at the bottom or along the side of the upstream node, and equipped with a flap gate to prevent backflow.
These orifices can function as outlets for storage units in various flow routing scenarios. If not associated with a storage unit node, they are exclusively applicable in drainage networks analyzed with Dynamic Wave flow routing.
The computation of flow through an orifice relies on factors such as the area of its opening, discharge coefficient, and the head difference across the orifice.
Dynamic control of the opening height of an orifice can be achieved through user-defined Control Rules, facilitating the modeling of gate openings and closings.
| Parameter Name | Description | Default Value |
|---|---|---|
| NHYD | Hydrograph number. | — |
| NAME | Name of the component. | — |
| From Node | The name of the from node. | — |
| To Node | The name of the destinated node. | — |
| COMMENT 1, 2, and 3 | Comment for the command. | — |
| Tag | Optional category or classification. | |
| System Type | Specifies the junction’s system type, whether it belongs in the overland, storm, or sanitary system. | Blank |
| Height [m] | Height of orifice opening when fully open (ft or m). Corresponds to the diameter of a circular orifice or the height of a rectangular orifice. | 1 |
| Width [m] | Width of rectangular orifice when fully opened (ft or m). | 1 |
| Inlet Offset [m] | Depth or elevation of the bottom of the orifice above the invert of the inlet node (feet or meters). | 0 |
| Type | Type of orifice (Side/Bottom). | |
| Shape | Orifice shape. | |
| Discharge Coeff. | Discharge coefficient (unitless). A typical value is 0.65. | 0.65 |
| Flap Gate | YES if the flap gate exists that prevents flow back through the orifice, or NO if no flap gate exists. | |
| Time to open/close | The time to open a closed (or close an open) gated orifice in decimal hours. Use 0 or leave blank if timed openings/closings do not apply. |
Key input parameters for an orifice encompass:
- Names of its inlet and outlet nodes
- Configuration (bottom or side)
- Shape (circular or rectangular)
- Height above the inlet node invert
- Discharge coefficient
- Time to open or close (optional)
