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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 Area , Height, and  DischargeConduit Data must also be entered.

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


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]