Pond Boss Forums POND CONSTRUCTION Soil questions Pond overflow runoff erosion problem

Thanks for all the input - I'm open to anything that will work. I'd like to see a pic of the cinder block drop stucture. I'm aware of water
running under a concrete slab - I've experienced , it first hand, the water ran under the slab and than washed it down into the large gulley. But, the spillway slab will have an 8" x 4" footing on the flow entry back side. Thie recessed footing will be 11" below grade .
I'm limited in the size and amount of rock that is available. Most of the rock that I get comes from Sawyer, Ok, and I'm not certain that they have anything larger than the oversized limestone rocks. Also, only a Bobtail truck(12 yds) could access the erosion area.

I've included a couple of pics from 18 months ago of the original fix to the first headcut erosion problem - worked fine for nearly 18 months before washing out. The embankment had an 18" angled culvert pipe, that I told the contractor was not near large enough,
but what do I know ( 4 of those pipes wouldn't have been enough). Incidently, the concrete structure shown earlier, is equivalent to 8.6 18" culvert pipes

Oldfix by lee harvey, on Flickr