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March 28, 2020 at 4:09 am in reply to: hec ras 5.0 training workshop guide 1D/2D tutorial model #12766cameronParticipant
The link below has some training material on 1D/2D modeling
https://www.hec.usace.army.mil/training/materials.aspx#ADVANCED_1D_2D_UNSTEADY_FLOW_MODELING
cameronParticipant30 seconds is to large of a timestep. I would use a variable timestep with Courant set to 1.
If it is really steep, you may need to go smaller on your cell size to get reasonable looking results.
cameronParticipantYour model is going unstable. This could be due to your time step, ineffective flow areas, cross-section spacing, roughness, bridges, dam breach parameters, or HTAB inputs.
Dam breach models in 1D can be unstable and it is hard to give any advice without having more information about the model.
cameronParticipantWhat is your discharge?
What does the bridge/cross-section geometry look like?
cameronParticipantThe warning message for the 10yr states it is using the energy solution and not the pressure weir. This is probably why the 25yr is below the 10yr. What are the larger events using (50yr and 100yr)? Not sure what your bridge geometry/cross-section look like and how much flow is in the overbanks, but it may be worth while to just use energy for all of them.
cameronParticipantYour 10yr event has a higher wse upstream of the bridge than the 25yr which isn’t good. It is hard to determine the actual reason without looking at your model.
By how much are they both overtopping the bridge?
Are both the 10yr and 25yr events using the pressure/weir as their solution method or is one pressure and the other doing pressure/weir?
What is your weir coefficient over the bridge?
Do you get any errors/warnings/notes for the bridge?
cameronParticipantWhat bridge methodology is being calculated for each flow and bridge? If it transitions between low flow to high flow or energy/full momentum to pressure/weir differently at the Q25 for each bridge then you can get results similar to what you mention.
What does the blue line in the overbank represent (second opening)? If it is a second opening, are you modeling it as a multiple opening or with two culverts (one for main opening and one for secondary)?
cameronParticipantHEC-RAS calculates one water surface elevation for each cross-section. There is no way for it to have more than one.
You would either need to do a 1D/2d model or an all 2D model to get different results in the overbanks.
cameronParticipantYour results show that everything is hitting critical depth. This is not normal usually and would be something I would look into.
How is the bridge solution being calculated? Is it energy, pressure/weir? It looks like the bridge is causing backwater and changing the results.
cameronParticipantThis is normal for how HEC-RAS maps flooding.
You would need to go finer on your grid cell size. I would also switch to the full momentum solver as you have steep slopes with high velocities.
cameronParticipantThe current version of HEC-RAS 5.0.7 cannot handle infiltration. Drainage systems can sort of be modeled, but not in a straight forward method and includes a lot of assumptions.
cameronParticipantwhere are you importing your data from?
cameronParticipantYou can import them into mapper, select them, copy them, and then paste them to the layer you want (river or bank lines). This is all done by right clicking on the line, selecting copy, and then selecting the layer you want to copy and selecting paste.
February 6, 2020 at 4:26 am in reply to: Raising / lowering cross sections from the inversion elevation #12719cameronParticipantYou would need to write a script to modify the cross-section to do what you would like.
cameronParticipantIn Mapper you can create Flowpath lines which will calculate the reach lengths.
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