InfoDrainage 2021.1 Help Documentation infodrainage2021v1

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Gate Outlet allows a gate control to be modelled. The gate outlet uses the Torricelli's equation to calculate the flow when the gate is surcharged. When unsubmerged, the flow through the gate is calculated using the weir formula.


Height - Enter the size of the gate.

Width - Enter the size of the gate.

Coefficient of Contraction - Enter the coefficient of contraction of the gate. A default value of 0.61 is given and is suitable for a vertical gate

Invert Level - Enter the invert level of the gate.


When gate is submerged the flow rate is calculated using Torricelli's equation:


Ao = Area of the gate opening 

He= The effective head seen by the gate.

Cd = Coefficient of contraction.

Weir behaviour occurs when the inlet water level is below the top of the gate opening:


Cd = Coefficient of contraction

b = Gate width

h = Depth of water above the invert level of the gate.


More details can be found in the SWMM Reference Manual Volume II - Hydraulics which is available Here.