Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices in SWMM5

Note: Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices
The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414. All of the units are based on the internal SWMM 5 units of American Standard.
For a circular orifice the Critical Height is:
Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4
For a rectangular orifice the Critical Height is:
Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width))
The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice. The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice.

Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices in SWMM 5 by dickinsonre Note:  Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414.  All of the units are based on the internal SWMM 5 units of American Standard. For a circular orifice the Critical Height is: Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4 For a rectangular orifice the Critical Height is: Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width)) The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice.  The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice. via Blogger http://www.swmm5.net/2013/07/orifice-critical-depth-for-separating.html