Boss breach difficulties

Hi Bob, as per your request I am forwarding this information to find some answers with regards to Boss Breach.

The dam that I am trying to model with breach is composed of two materials with one of the two materials also comprising the face of the dam. The dam is a rockfill dam with an inner impervious core. I described the dam with the inner and outer core descriptions. For the inner core which is glacial till I described it as per the pertinent data. The outer core is rockfill with a D50 of 10 inches. I used the rockfill for the dam face as well. When I try to run the program I don't get a breach of the dam. Even if I change the initial piping width to something like 10 feet I still don't get a breach. I tried changing my outer core to false descriptions with D50's ranging from 1/3 inches to 10 inches. However, any D50 after 3 inches didn't result in a breach. Here is my problem. As the dam material has a D50 of 10 inches and anything over 3 inches doesn't breach, I am getting stuck. I don't think that it is inconceivable that the dam will breach with that size of stone, so I would like to determine a way to model the dam and resulting breach. I hope that you can help me on this matter and I hope to hear from you soon.

Thanks for your time and effort,
Chris.

Dear Chris Murphy :

Note that BOSS BREACH probably is failing to run your model because the erosion equations that are used by the NWS BREACH model were not meant for grain sizes as large as you have defined. Therefore, the fundamental problem here is that BREACH can't model a rockfill face, it was not designed to model that. The only suggestions I can provide is to either ignore the rockfill face (not a very good assumption) or try to find a different model that works in these conditions.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com

Gary my consultation with Chris Maeder of Boss International led to the discovery that Breach couldn't model a dam with the rockfill grain size that this dam has. I have a planned approach in mind but would appreciate remarks from you both before I proceed.

What I plan to do is to model the dam and breach with grain sizes for the rockfill from 1/3" - 3" by 1/3" increments. I will then have a table of values for breach width, flow, etc. for their corresponding grain sizes. When I graph the results I will perform a regression analysis and try to extrapolate breach characteristics for grain size of 10". I will then compare the breach characteristics to width = 2 to 5 times height of dam

time to breach(hrs) = H(m)/30

If the results are somewhat reasonable I will go with that. If you have any suggestions on my planned approach I would appreciate some feedback.

Thanks,
Chris.

Dear Chris Murphy :

What you have come up with sounds like good approach. I won't have thought of it. Please let me know what you come up with and the success of this method.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com