HEC RAS Internal Bridge Sections
HEC RAS Internal Bridge Sections
(OP)
Does anyone know for sure how the program creates the two internal bridge sections? I know it copies them from upstream and downstream, but where are the actual "cut lines" located with respect to the stream centerline? And how are they oriented? Notice how if the two upstream and downstream sections are different lengths, the bridge, as shown on the geometric plot looks as if as trapezoid has been formed using the 0 and last station points of the upstream and downstream sections--and that the bridge was formed inside those boundaries. Better yet!! It asks for a distance from upstream section and deck width, but is the deck actually the same width all the way across when the two upstream and downstream sections are not parallel? Where is that distance measured along? the centerline? or is it just a straight distance? Any insight?





RE: HEC RAS Internal Bridge Sections
See this page for explanation of the image.
Between your downstream reach lengths and the bridge station/width/geometry, I believe HEC-RAS can calculate it sufficiently for its purposes. Remember that HEC-RAS is a one-dimentional model and all your inputs are reduced to a head loss calculation, effectively.
Also try the Hydraulic Reference Manual as it's better than the user manual.
RE: HEC RAS Internal Bridge Sections
RE: HEC RAS Internal Bridge Sections
Also contributing are the up- and downstream expantion lengths.
RE: HEC RAS Internal Bridge Sections
It is important to note that while there are items such as Width in Hec-RAS, they may not actually do anything. Width for structures is typically just so it shows up on the plan view and is not used in calculations.
As for meanders, you really have to have the survey data for those. All the squiggles on your plan view don't mean anything between cross sections.
RE: HEC RAS Internal Bridge Sections
Thanks for your posts everyone. Unfortunately, it seems that no one has delved into HEC RAS the way my collegues and I have.
RE: HEC RAS Internal Bridge Sections
Something I am curious of, are people running sensitivity analysis on the roughness values? It seems that the uncertainty of roughness is often larger than geometry changes. I am curious how this is done for frequent events? Especially if you have a lot of debris dropped in your channels.
I get to estimate bulking now, which can add up to 50% for some areas, so my models have a pretty wide range for expected flow depths, more fun but less precision.
RE: HEC RAS Internal Bridge Sections
RE: HEC RAS Internal Bridge Sections