I’ve been scouring around for the past 2 hours, trying to look for a way to properly model a v-notch weir in HEC-RAS. So far I’ve got nothing to show for it.
Presumably, for flat, rectangular broad-crested lateral weirs, I understand that HEC-RAS just uses the standard weir equation, Q = Cd * L * H^(3/2), where Cd is discharge coefficient, L is weir length, and H is the effective depth. This equation assumes that your weir and water surface elevation are parallel with each other.
For a 90deg V-notch weir, the approximate flow equation is, Q = 2.5 * H^(2.5). The caution that I have with just manipulating the weir geometry in HEC-RAS is that the value of Cd will be different for the V-notch weir.
My question is this: Can I model the V-notch in HEC-RAS by just manipulating the weir geometry and keep the same Cd? Or is there an adjustment to the Cd that needs to be accounted for?