Weirs

[CivilSurveyor]

Peter,
I need your help. I have to prove to the Local agency that my weir(s) will be able to handle 1.25 times the 100 year flow. I need to calculate the depth through the emergency spillway to make sure the depth will not exceed the freeboard of the pond, as well as the velocity through the spillway for counter measures.

I would like the equation(s) for the different weirs used by HydroCAD and I will solve them for depth. Can you give me the equations for the following:
Rectangular Weir
V-Notch Weir
Trap Weir
Compound Weir
Custom Weir

I know this will very a bit due to the Head as it increases but since this is for the emergency spillway sizing and my typical freeboard depth is or will be only about 2 feet. This should not come into play.

Thank you,
CivilSurveyor

 

[psmart]

All the weir calculations are documented in the help system. Just press the help key on the applicable weir screen. Or consult any basic hydraulics text.

However, an easier solution is to examine the stage-discharge curve in HydroCAD for each scenario you wish to evaluate. No inflow hydrograph or storage data is required - just select the "zero storage" option and enter an outlet weir. You can set the "Flood Elevation" for the pond to extend the range of the stage-discharge curve to the desired elevation.

As far as discharge velocity, this is most easily determined by routing the applicable hydrograph through the pond, and HydroCAD will display the maximum velocity for each device. Or you can just divide the flow rate by the flow area.


Peter Smart
HydroCAD Software

http://www.hydrocad.net