Karin:
Note that DAMBRK considers the effects of contraction and expansion losses of the flow as it is routed downstream. However, the breach mechanics of the DAMBRK software does not account for contraction and expansion losses at the breach itself.
If you have severe contraction and expansion effects at the dam, then you need to add transition cross sections close to the dam.
Sincerely,
Chris E. Maeder, M.S., P.E.
Senior Technical Engineer
chris.maeder@bossintl.com