The rock-fill outlet is for modeling flow THROUGH the rock itself. Any water flowing over the top of the rock would be modeled as a weir. You can also use them together, to model the flow through the rock plus the weir overflow.


Peter Smart
HydroCAD Software
www.hydrocad.net

That's a plus; however, is it really accurate to model a weir with a crest breadth of 8' (for example) as a sharp-crested weir? That doesn't seem appropriate, based on the definition of a sharp-crested weir. Unless I missed something along the way, there isn't an option for a broad-crested vee/trap weir. Thanks for your help!

The only difference between the sharp-crested and broad-crested options is that the BC allows the coefficient to vary with head and the SC uses the same coefficient at all heads.

I agree that the roughness of your weir surface is likely to reduce the discharge, especially at low heads, so the BC option would seem appropriate. However, you will need to determine and enter suitable coefficients (C vs head) for your specific configuration. In general these values are determined from field studies. Another option is to enter a stage-discharge curve directly. Again, this would tend to be based on field studies rather than textbook flow calculations.

Another option would be to use a channel outlet (added in HydroCAD 10.1). This will allow for the roughness of the 8' long channel, and may be more appropriate than the weir equation.

Peter Smart
HydroCAD Software
www.hydrocad.net

Aha, I understand now! I did see your comment about using the channel option also, so I would assume HydroCAD may not have any plans to add a Broad-Crested Vee/Trapezoidal Weir to the list of available outlet options in the immediate future? Thanks!

With HydroCAD 10.1-7 a broad crested weir now supports trapezoidal and rectangular geometries.

Peter Smart
HydroCAD Software
www.hydrocad.net