The story suggests there is a 300 foot wide canal that can be used to let water go in casse of an emergency. Well, how about doing so now? Rather than using the turbines, use the canal to let the water out, but without it generating electricity...
Next time you are near a dam look around and you will find that most have three paths for the water to leave the reservoir. The first is through the power generating turbines, second is the sluice gates which control water level, and third is the emergency spill way which is designed to fend off catastrophic failure.