---
title: "Runoff Orifice Diversions"
canonical: "https://help.innovyze.com/space/xps/19661205/Runoff%20Orifice%20Diversions"
format: markdown
---
**In Runoff,** an orifice is a control structure at the bottom of a conduit which affects the outflow characteristics of the conduit. Data must be entered for both the orifice and the conduit.

---

The orifice is defined in terms of its

> Macro (tooltip)

,

> Macro (tooltip)

, and 

> Macro (tooltip)

. [Conduit Data](https://help-innovyze.atlassian.net/wiki/spaces/xps/pages/19661186) must also be entered.

![image](media://3df3cce0-deec-4c31-8c38-82301b291b31)

An orifice is either a dropout or sump orifice, or a side outlet orifice. A standard orifice equation is used for both types:

Q = Cd . A . (2 . G . (H - Hc))^0.5

**where:**

Q = outflow, cfs [cms]

Cd = orifice discharge coefficient, dimensionless

A = orifice cross-sectional area, ft^2 [m^2]

G = gravitational acceleration = 32.2 ft/sec^2 or 9.8 m/sec^2

H = hydraulic head above the orifice, ft [m]

Hc = orifice centreline depth, ft [m]