I have a fairly simple and straightforward 1D only model that I’m doing some inundation mapping with RasMapper. I’m looking at how the mapped flood water levels encroach on 2 bridges within the model domain. I’ve used the technique described in this blog and manuals to “burn-in” the in-channel HECRAS geometry to make a modified DEM.
When I compare the model result WSE from the cross section editor to the WSE map layer in RasMapper, I get perfect agreement throughout the model domain, except just upstream and beneath my 2 bridges. At cross sections ~25+ft upstream of the bridge, the WSE matches no problem. But once I get closer to the bridge (i.e. I have a cross section just 5′ upstream of a bridge) the WSE does not match the results shown in the cross section editor. Looking at RasMapper alone, this caused me to initially think that a 100 year flood event does not overtop the bridge. Yet looking at the cross section editor shows that to be incorrect.
I know bridge hydraulics are tough with HECRAS and 1d certainly cannot correctly model the complex hydraulics that occur. But I am concerned how model results differ between what’s shown in RasMapper and traditional cross section and profile results. Any one run into this, or know what’s going on? Thanks!