In order to reduce the likelihood of a dam failure, consideration should be given to constructing a separate emergency fuseplug spillway (or auxiliary spillway) to carry part of the spillway discharge at maximum flows.
As the flood increases in size and exceeds the capacity of the dam's standard spillway, the fuseplug is overtopped and washes out. For the maximum probable flood, both the standard dam spillway and fuseplug spillways will discharge at the design discharges.
However, of concern is how to construct the fuseplug so that when it’s overtopped the fuseplug will not wash out suddenly--thereby greatly increasing the downstream discharge (like a mini-dam failure). Various materials should be considered for the fuseplug filler material, so that the fuseplug can withstand 2 to 3 feet of water over the top of it before it starts to wash out, and then continue to wash out at a slow rate until it is completely washed out.
Sincerely,
Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com