They can...try...to control flow thru small breaches in the cofferdams, and hopefully increase output more than before, but less than if losing the dams totally.
That they would chance this, implie the dams are at risk.
I don’t know how much silt behind those dams. If none, figure on a full toe to crest breach opening a 35 foot head of water, times ever how wide both dams are, minus destructive interference where outflow from each, along I-10, results in non-laminar flow.
Minus 50%...probably. Unlikely to lose both embankments at once.