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Rock Chute/Rock Weir capability in HydroCAD

Rock Chute/Rock Weir capability in HydroCAD

Rock Chute/Rock Weir capability in HydroCAD

Is the new flow-through rock-fill option for a pond outlet (available in version 10.1-7a) something that could be used to model a broad-crested, trapezoidal weir rock weir type of outlet? The existing options for weirs (through version 10.0-22) don't seem to match up too well with the rock weirs we typically use. Any help would be appreciated!

RE: Rock Chute/Rock Weir capability in HydroCAD

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

RE: Rock Chute/Rock Weir capability in HydroCAD

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!

RE: Rock Chute/Rock Weir capability in HydroCAD

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

RE: Rock Chute/Rock Weir capability in HydroCAD

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!

RE: Rock Chute/Rock Weir capability in HydroCAD

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

Peter Smart
HydroCAD Software

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