Dam Breach into depression with HEC-RAS?

[jdavis]

I am performing a dam breach. The dam is small with a very small drainage area (was a quarry) and empties into a depression see inserted profile photo

The model will run without errors. However, the initial condition downstream is a bank full. I would like to model the depression downstream of the dam as dry since this is realistic.. as sunny day breach.

Another issue is the output for the dam breach does not calculate the dam breach Q, area or velocity. HEC-RAS file is located on dropbox at:

https://dl.dropboxusercontent.com/u/50339437/DamBreach_01.p02.zip

I have provided a small minimum flow and a pilot flow.

Any pointers on how I can model so that the initial condition is dry downstream of the dam so I can take into account this storage?

Is this an option in HEC-RAS?

Thanks,

JD

[Anonymous]

RAS 1D does not allow for completely dry cross sections. You could try adding a small pilot channel. Start it at the low point in the depression and end it downstream say around a channel distance of 200 feet or so.

On second thought, you might want to start the pilot channel immediately downstream of the dam at an elevation that is similar to the bottom of the depression.

[jdavis]

Thanks! I increased the initial elevations at downstream side of the dam and that worked. Starting too “dry” did not work even with the pilot flow. It was handling the low flow but not the low depth.

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