Definition of downstream routing extent

[Robert]

Hi everyone,

I would like to inform, how do you determine the downstream routing extent of dam breach study. I had studied a guideline : https://www.fema.gov/media-library/assets/documents/34193, but I don´t know to find these informations.

For example: When I solve a project dam breach analysis and I need to set a downstream extent of my project for the supplier of digitall terrain model. Because I can terminate the calculation in the place, where my peak flow of dam breach is equal or less as 100-years flow of channel. When I determine the extent/area less, when the peakflow of breach doesn´t decrease under 100-years flow, so I have to rebuy the DTM (high price).

thank you for your reply

regards!
Robert

[Anonymous]

There are two items here: 1. The agency requirements for modeling and, 2. Model use. Regarding the second item, there have been recommendations published for extending geometry for steady flows so that the unknown downstream boundary condition has negligible impact on the computed water surface profiles in the area of interest. Usually for dam breach studies the extent of the downstream modeling is determined by gage locations or chosen to be long enough so that the with/without failure converge to the same water surface elevation. The reproduction of the Teton event by the NWS addressed this issue.

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