Dynamic drawdown breach

[BobC]

I am modeling a breach of a small dam on a relatively small river. I’ve defined the storage upstream using cross sections, as opposed to a storage area. When I breach the dam, the WSEL at the cross section immediately upstream (~40 Ft) drops, but does not completely drawdown (plus or minus 5 feet above the WSEL at the breach). I’ve done the math, and the breach width is not restricting flow and causing the impoundment, so it would appear I have not modeled something correctly. I’ve tried redefining the geometry for level pool, and that does not help either. Suggestions? Any help would be much appreciated.

[Marulke]

The drop in WSEL may be caused by the flow accelerating towards the breach opening (increase in velocity head) and head loss between the two sections.

I suggest you run a constant flow and compare the energy levels at the two sections. The difference should be equal to the sum of friction and singular losses between them.

Marulke

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