[cameron]

Why don’t you just create a 2D connection line where you want to extract the discharge? It would then be stored in the dss file.

[cameron]

Colorado DWR has a great document that discusses what happens (page 19). Below is a link to the document and the text that discusses it.

https://dnrweblink.state.co.us/dwr/ElectronicFile.aspx?docid=3566962&dbid=0

HEC-RAS has the capability to model the pipe with an initial piping elevation set at the bottom of the dam (most piping failure situations); the piping hole is modeled as a rectangular hole, which is more consistent with the final trapezoidal shaped breach section, thereby reducing discontinuity. The bottom width of the hole enlarges proportionally to the final bottom width according to the selected progression, as does the height of the hole toward the final breach depth. This will make the hole height/width ratio greater than one if the final breach parameters chosen show a bottom width narrower than the dam height, but since the orifice flow is based upon the area of the orifice and not the width versus the height, this is a valid assumption.

Once the water level drains down to the top of the enlarging piping hole, the crest is assumed to collapse and the algorithm transitions to weir flow. The bottom width and the top width of the breach continue to enlarge laterally until the final defined width and side slopes are reached. Unlike HEC-HMS, HEC-RAS never assumes orifice flow with a reservoir level below the top of the piping hole. It should be noted that in several modeled case studies, the crest collapses when the height of the piping hole reaches near 0.6Hb and the peak flow occurred in the weir flow portion of the failure soon after the crest collapses. This is dependent on the drawdown rate versus the breach progression, and selected final parameters, but helps support the reasonableness of the program.

[cameron]

You can have smaller cell sizes than that. The HEC-RAS validation document has cell sized of 0.05m for some of the laboratory experiments.

https://www.hec.usace.army.mil/software/hec-ras/documentation/RD-52_HEC-RAS%20Verification%20and%20Validation.pdf

[cameron]

The question would be, due the oscillations impact results downstream. As the hydrograph travels downstream, it will attenuate and volume from the hydrograph is more important than the peak flow.

You could try a test where you either cut off the hydrograph at say time 0.4 hours or adjust the flow after 0.4 hours and run the simulation. Then do a test with the unmodified hydrograph to see how results compare. If the depths are within a few tenths or arrival time is similar, then probably not a big deal.

[cameron]

What I normally do is make a copy of the my original geometry (like to have backups) in the Geometry Data window with a save as. I then open Mapper and edit geometry and save edits.

When you are doing this, are your files saved locally or on a network? Did you try a different machine?

[cameron]

did you look into changing the different calculation tolerances to be smaller?

[cameron]

Breach flow is the flow that goes through the breach, it does not account of outlet works or spillway.

[cameron]

2D Connection lines are more accurate than profile lines drawn in Mapper. The 2D connection lines are grabbing results along the cell faces where as most of the time profile lines are not along cell faces and have to interpolate from the results.

[cameron]

do your cross-sections only intersect one river? If you have cross-sections intersecting a single river more than once or more than one river then this can happen.

You can just delete the River in the Geometric Editor and not Mapper.

[cameron]

I would switch to using the most recent version of HEC-RAS (5.0.7) and see if that makes any difference.

When you turned of modified pulse, did you just uncheck the box or did you delete all of the regions as well?

[cameron]

Can you share a picture of what you are talking about? Is this only occurring between cross-sections and not at cross-sections? What do your bank lines look like in Mapper?

[cameron]

from my understanding, that is how the roughness factor is supposed to work.

[cameron]

Can you model this in 2D? That would be the easiest option.

[cameron]

when you say you have station and elevation data is that x, y, and z data in a coordinate system? You can read in x, y, and z data in HEC-RAS to create cross-sections under import geometry data.

[cameron]

If you look at the 2D Users Manual, there is a table (Table 3-1) that lists appropriate weir coefficients. If the ground is not elevated then you should be using a value from 0.11 to 0.28 for SI units.

Generally the model is more stable when using the 2D equations so I find it interesting that the model crashes.

Did you turn on the 1D/2D Iteration option at all?

[Author]

Posts