| Product(s): | StormCAD, CivilStorm, SewerGEMS, OpenRoads Designer |
| Version(s): | 10.03.04.53 and earlier |
| Area: | Calculations |
Headwater results with culverts and headwalls are not matching HY-8.
The culvert (headwall) calculations in the above products are based on the HDS-5 standard methodology which is similar to HY-8. Results should be close.
First, ensure that you are viewing the "hydraulic grade" result in the properties of the upstream headwall element, which shows the headwater elevation upstream of any culvert headwall. The hydraulic grade shown in the culvert barrel (conduit element) is the hydraulic grade after (downstream of) any entrance losses.
Next, ensure that the headwater elevation is not exceeding the headwall ground elevation. If this happens, you will see a user notification about a flooding (overflow) condition. In short, the program assumes that you only want to look at headwater elevations below your structure ground elevation, otherwise a flooding/overflow condition has occurred and the results are approximated (and you see the notifications about this). You will need to ensure that the headwater elevation does not rise above the top (ground) elevation of the structure. See more here: Why is the HGL reset to rim elevation for flooded structures?
So, although you can raise the ground elevation to avoid this issue, it may indicate a larger problem that you'll need to address first. Meaning, the actual water surface may not be able to rise that high if it actually does exceed the ground elevation.
Improvements may be made in a future version to better handle this situation (and make it more obvious to the user). Reference #987818