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Hi Ray, Yes, there is a berm type of a wall in front of the curved "approach wall".

Dam design construction blueprints show this incoming waterflow channel as the "approach channel". The far side wall of this waterway "approach channel" is the "Cut escarpment".

This enlarged image shows trees growing in the berm/embankment that what looks like a concrete wall that joins to the upside down "J" of the curved "approach wall" inlet.

What is of note is that the composition of this apron, with trees growing in a "soil or aggregate/soil" base is not a protected surface if turbulence were to occur (notice the grooving in the berm from equipment).

This turbulence, brown discoloration in other images, and the soil/aggregate design of this inlet has been the source of heated discussions in whether there is a risk of an "erosion scouring" at the entrance to the Main Spillway inlet (approach wall). This would be a serious condition.

Of course, the huge "bubbles" that were caught by the Fox10 helicopter crew overflight in front of the Emergency Spillway weir suggests that there is a porosity potential via the soil -in front of - and the now known layer of "fractured rock" that the ES rests upon.

The approach channel likely has this same substructure. Laminar flow is very important to prevent scouring with any non-armored surfaces.

It’s difficult to tell from the photo but it looks like the approach wall ends near where the berm’s equipment scarring begins. I think it’s not an earthen berm but a rocky ledge, a piece of the escarpment the channel cuts through. From the end of the approach wall the ledge decreases in height above the channel floor in the upstream direction, and toward the gate it rises above the wall then abruptly ends at the “J” wall. In the photo water is flowing around all but the highest parts of the ledge. Due to the way the escarpment hooks around in front of the approach channel water enters the channel at an angle, some of the water entering directly toward the gate and some flowing over the submerged rising ledge and entering the channel nearly perpendicular to the main flow. Both the ledge and the confluence of the flows causes turbulence. I agree it might be causing some scouring, particularly since the approach channel floor appears to be aggregate.

I’ve read several comments about bubbles but haven’t seen any photos.

I’ve been thinking about the rock bags dumped in the holes at the far corner of the parking lot. Where did that water go? There appears to be a seasonal, or perhaps now defunct due to the dam, stream about 2000 feet away. Perhaps there is a seam the water followed. A few days ago there was a small earthquake about 200 feet underground where the stream joins the river. It’s marked on this map https://www.google.com/maps/place/39%C2%B032’31.4%22N+121%C2%B030’35.4%22W/@39.5432017,-121.5071578,1356m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d39.54206!4d-121.50984 I mention this because it supports the “rotten rock” concerns.

“This enlarged image shows trees growing in the berm/embankment that what looks like a concrete wall that joins to the upside down “J” of the curved “approach wall” inlet.”

Comparing this image with the image you posted in #1320 showing the turbulence before the spillway gate, it appears to me that the “upside down J” approach wall is gone, and may have collapsed.

The concrete wall that joined it remains, and the earth that abutted it on the near side has eroded away allowing water to flow on both sides of it, but at least two of the trees remain.

If true, could this be the cause of the turbulence you circled in #1320?