But they have to keep the spillway above the hole from failing by being undercut by the water.
As a retired contractor, viewing the pictures I have some observations. If the main spillway runs for a few hours and lowers the lake where the emergency spillway is no longer draining and damaging its outflow, as you say, the main spillways damaged outflow structure could have its gaping sinkhole filled.
The problem is access. There is no road or stable access to the damaged spot. Instead, big rip-rap boulders, high-strength / early set concrete and massive helicopter delivery is the only feasible method I can see if the window is only about 48 hours. Even then, that spillway running again will tear out all the temporary fix in short order.
What about bridging steel sheeting over the spillway erosion hole to stop the water from entering the hole. I’m thinking of that interlocking marine pier sheeting that is driven into the ground. At the angle of the hill and velocity of the water there should not be that much water weight that the steel would need to support. Not sure how large the hole is though.
What about bridging steel sheeting over the spillway erosion hole to stop the water from entering the hole. I’m thinking of that interlocking marine pier sheeting that is driven into the ground. At the angle of the hill and velocity of the water there should not be that much water weight that the steel would need to support. Not sure how large the hole is though.
Are there low power lines above the spillways? If so, that would make copter access iffy.
I believe that's what is being tried. Helicopters, flying low, were heard last night near Carson City. Seems they were called in to help lower large boulders in the crevace in the spillway.
But they have to keep the spillway above the hole from failing by being undercut by the water.