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cameronParticipant
There is good information on this in the user’s manual. In general, most people use 1:1 contraction upstream and 2:1 or 3:1 expansion downstream from the bridge opening, but it can change depending on the structure.
cameronParticipantI agree with Lonnie. I did not look at the figure close enough to notice it was the bridge editor.
cameronParticipantI would just copy the upstream and downstream cross-section data to the internal cross-sections to fix the problem.
cameronParticipantAre you using internal cross-sections for the bridges?
cameronParticipantWhat was the DEM created from? Have you compared the DEM to other elevation data sources to verify if it makes sense? Google Earth is a easy source to see if the terrain is roughly the same.
cameronParticipantIf you turn on the computation check box and set it up in the output options, HEC-RAS will create outputs at what ever your timestep is set at. To view the results you would have to go to the view pull down menu and select either the spatial or time series computational output.
cameronParticipantWhat is your topographic data based on? Does it have really good resolution to pick up the channel? Does the imagery line up with the topographic data?
cameronParticipantIt is based on the sediment properties you specify in the Sediment properties window under “Options”.
cameronParticipantThat the bank elevations don’t jump up or down a lot from one cross-section to the next.
cameronParticipantIn general I digitize them and then move them in HEC-RAS to what makes sense if it does not look correct in HEC-RAS. I also check in profile view the bank elevations to make sure they are consistent. Some people recommend placing the banks at bankfull flow which some say is around the 2 to 5-yr flood event or 20% of the 100-yr flood event.
cameronParticipantThere was no geometry file attached so I imported in the Geo-RAS file. If you look at the profile, the river is going in the wrong direction. Station 100 (west end of model) should be the upstream end of the model.
cameronParticipantWhat do your cross-sections look like? It would be easier if you posted your files and I could take a look.
cameronParticipantwhat did you set for your downstream boundary? Is the floodplain lower than the channel (channel bounded by levees)? Maybe if you post a picture or the files it might help.
cameronParticipantWhat build of HEC-RAS are you using?
April 2, 2015 at 7:29 pm in reply to: Multiple Reach Unsteady State Analysis- Model Instability #9238cameronParticipantHave you tried adjusting the time step to be lower or adjusting the minimum flow? Is there a steep drop in invert elevation from tributary to the main channel? Have you tried adding cross-sections?
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