Problem

What do the rectangular weir output variables H, Htw, and Qfree refer to?

Solution

These variables are listed in the Individual Outlet Curves report. H is the depth above the weir crest on the upstream side of the weir. Htw is the TW depth on the downstream side of the weir. Qfree refers to the discharge flow rate under free outfall conditions. Whenever Htw = 0, then the reported weir flow will equal Qfree. If Htw > 0, then the reported weir flow will be less than Qfree due to tailwater effects.