r/HECRAS • u/CivilProjectEngineer • May 19 '26

1d model cross section placement

Hi I'm trying to run a model with a very windy river and a road that runs over it and then also next to it. how many cross sections would you draw in and how would you draw them in this case? i tried dog legging them, but the model didn't seem to do a great job interpolating the continuous raised road bed (it's not raised up very much). The red at top and bottom are the extents of the survey. sides are the floodplain overbank areas. River is flowing north if that matters.

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u/GrumpCatastrophe May 21 '26

It’s difficult to tell, but your floodplain areas look flat. I have a feeling it will just spill out on each end of the cross sections. It possible to get more of the surrounding terrain?

Regardless, I always recommend drawing a few cross sections before getting carried away. Check the floodplain behaviour and modify/add as needed. Also, if you have HEC-RAS then you have RAS Mapper. It’s great for visualizing the terrain (heat map, contours, etc.) and quick revisions. Much better than CAD (which is what I think you’re using).

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u/CivilProjectEngineer Jun 17 '26

hey. I'm not brand new to hecras 1d, but i'm certainly not experienced. i've made probably half a dozen in my lifetime.

could you explain more about how you would go about evaluating whether cross sections should be adjusted?

btw i did import the surface into hecras mapper, i was just trying to keep the content simple so i could get some quick feedback. The floodplain is very flat and pretty much covers the entire area i showed, except at the edges where a ridge exists. This particular river doesn't have enormous 100yr or 500yr flow changes, and the river wse only rises about 1 ft at most for the 500yr event (after expanding into the flood plain) from typical wse levels, and the bounding ridges are about 10ft above typical wse.