“Earthen emergency spillways are designed to erode gradually and release dangerous volumes of water in a controlled manner to prevent down stream catastrophe. Oh, by the way, the emergency spillway is designed to be destroyed in the process, draining the body of water behind it.”
I’ve designed a few dams. You never, ever, never, never, never want the dam to be overtopped in any way, or to erode in any fashion.
And the spillway is meant to be armored (grass, rip-rap, concrete..whatever the velocity merits) so it does not get destroyed.
I have no idea how erosion from an overtopped dam can be considered gradual or controlled.
I guarantee that this Oroville dam is experiencing an event beyond its design parameters, and it is not at all eroding slowly or gradually...and frankly nobody knows what might happen. I pray it holds long enough to draw down - but its gonna rain again soon :(
Agreed. You never want your dam to be overtopped. The fact is that earthen emergency spill ways WILL erode once they function. Don’t care what you’ve topped or armored it with. I had the unfortunate opportunity to watch a minor but fairly large earthen dam with emergency spillway function during a tropical depression back in 94-the spillway was over topped and in 5 hours the lake was drained. The Choctawhatchee river downstream was already at flood stage and if the dam proper had failed-it would have likely killed hundreds or thousands downstream. Since it eroded and drained the lake over time, it did little damage that the flood waters had already begun.
What you don’t want is a catastrophic breach of any dam....
I had designed and built a few civil projects too, only one dam- the one that replaced the lost one a few years later. As a combat engineer officer, I spent more time planning destruction than construction- so much more satisfying when it’s an enemy’s infrastructure....