Faria,
The weir height extents to the upstream element's maximum elevation. In the case of a pond, it's the pond's top elevation. You can see the max/min headwater and tailwater (like in Pondpack) if you click "control structure" in the control structure dialog. The maximum, minimum and increment are computed automatically by CivilStorm based on the top and bottom of the adjacent elements.
If the weir does not extend to the top of the pond, then in what way does flow leave the pond for headwater elevations above the weir top? This still needs to be defined in CivilStorm. For example, if there's a sag in the dam at the weir location, then the weir essentially widens above the weir 'top'. In this case, you can model this with the irregular weir type.
Note that 4 inches seems too narrow for a weir length. The weir equation may not work with lengths that short. Did you mean 4 feet?
If you have any other questions like this, please submit a service ticket to technical support.
Regards,
Jesse Dringoli
Bentley Technical Support
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.