Tailwater effect on a broad crested weir

[DuckEngineer]

How does HydroCAD calculate the tailwater effect on a broad crested weir? I am trying to model a ditch plug that doesn't come to the top of the existing ditch. I don't have any downstream data, so any tailwater I put in has to be Stor-Ind routed. I played with the differential tailwater setting on the advanced tab and was wondering where the numbers came from.

 

[psmart]

To allow for tailwater effects on a broad-crested weir, HydroCAD uses a submergence adjustment as discussed in Handbook of Hydraulics by Brater & King (p.5-18)

You will find full details in HydroCAD help. See "Submerged,Weir" in the help index.

This information is also included on page 90 of the HydroCAD-8 Owner's Manual.

 

[psmart]

If you have other tailwater effects that need to be modeled you should probably use the Dynamic Storage-Indication method. Although the manual tailwater options are disbled when using DSI, you can use a link to define a manual tailwater elevation (constant, tidal, or elev.vs.time) For details see

http://www.hydrocad.net/dsi.htm