Dam break flood wave arrival time

[Marulke]

I am doing a dam breach study, and I need to report the flood wave arrival time at each cross section. Flood wave arrival is defined as when the water level has increased 0.3 m above the initial water level.

I can pick the arrival time manually by inspecting each stage hydrograph, but it takes a lot of time.

Does anybody know a smarter way to do this?

I know the time for max stage can be tabulated in DSS Vue, but I have not found a way to pick the arrival time.

Thanks,
Marulke

[Chris G.]

Hmmm. Try this. It may or may not be faster than reading manually from the stage/flow hydrographs.

1. Set your detailed output interval to the smallest setting, 1 minute.
2. Rerun your model. It may take a LONG time to post-process with a 1 minute detailed output interval.
3. Open up your summary output table and select All Profiles (except Max WS).
4. Copy an paste to a spreadsheet. Each cross section will have a number of rows, each representing a different profile.
5. Then add a column that takes the difference between the first WS El in the block of data and each successive profile.
5. Look in that row for when you get to 0.3 ft. That’s your arrival time.

Like I said, this may not be much faster than manually reading off the hydrograph plots.

Your other option is to write a program that automates this process, but that would be too difficult unless you have programming experience and you know how to control RAS externally.

Good luck.
Chris

[Marulke]

Chris.

Using a spreadsheet to calculate the increase in stage is one way to do it. As you comment, it takes some time and may not be faster than doing it manually.

The DAMBRK model from National Weather Service (now obsolete?) automatically generated a table of flood wave arrival times.

Would have been nice if HEC-RAS had the possibility to tabulate a time-(user defined) event relationship for all cross sections, for example at what time the water level has increased by 1 ft, or the flow reaces a certain level.

Thanks,
Marulke

[Anonymous]

Travel time is one of the variables that RAS can put into an output table. Check out Appendix C of the RAS User’s Manual. This travel time is based on the RAS-computed velocity, so it might not represent the travel time for a target stage at a target location. Also, these travel times can be displayed with RAS Mapper

[Marulke]

Michael,
I was not avare of that HEC-RAS can report the travel time. I am not sure if this is what I need, but I will check the manual anyway.

Thanks for the info.

Marulke

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