You know, filling in the hole and fixing the spillway below the main break is not the most important issue on the spillway.
Prioritizing it to me would be like this:
1a) Clear the river of a lot of the debris. Couple of big clam shell passing it to track excavators just to get it out of the river bed, simultaneous with —
1b) Cut a new pathway for water below the break that would not continue to add as much debris to the river channel.
1c) Get above the break with maintenance vehicles and crews and make all repairs to the slab areas above the break. If the spillway has to be put back into action, we need a spillway that will not have its concrete surface break up above the current break and create an entire new source of debris and sub terrain damage.
2) After those items are address simultaneously, then move to cutting out the canyon ( I think I will name it Moonbeam Canyon ) and benching it back for engineered fill considerations. If in mucking it out, it is found to be unable to get back to some bedrock, then consider an engineered drop and eliminate the rock mountain below Moonbeam Canyon.
One of the weather guys on Fox 2 in the bay area has a degree in geology as well as a doctorate in meterology.
For years he has warned areas in common flooding area to get rid of the upstream debris/often dead trees in the river plain and dead brush.
Then, they need to dredge down stream to the bay to prevent flooding down stream an a regular if not yearly basis.
Exactly your #1 and #2.
1a) Clear the river of a lot of the debris. Couple of big clam shell passing it to track excavators just to get it out of the river bed, simultaneous with —
1b) Cut a new pathway for water below the break that would not continue to add as much debris to the river channel.
Not surprising is how some of the local environazis fight his suggestions and yours.