Bill Husa of the ChicoER took this great Google 360 image from the top of the gate house on June 1st (h/t Dan Reidel on Twitter).
If you pan over to the downstream side of the e-spillway weir, you can see a series of three little pads, each with a ground-level square white cover with some metal tubes protruding - the tallest of which looks like a gooseneck vent.
Screen caps from the image:
A closer view below with a nearby railroad tie included for scale. A common U.S. railroad tie is 8' (2.4m) long.
I don't have any specific information on what these are - piezos/flow gauges is just a guess. For all I know, they might be vent holes to DWR's secret underground lair. But that would be CEII, so you didn't hear that from me.
Plans are to add a pretty substantial RCC apron on the downstream side of the weir, so these would eventually be under several feet of concrete. They would have to build some kind of access to them or just remount higher on the surface of the new apron.
On old blueprints, the weir was shown to have a rectangular open box drain at grade that runs along the center of it's length, with T's every 40' or so emptying to the downstream side of the weir at the very bottom. They were not visible because the bottom edge of the monoliths were a few feet below the ground surface.
There appeared to be some kind of piping related to these drains washed out after the spill, but you couldn't make out much on how many there were or how they were accessed. The one blurry photograph that gave any clue suggested that at least one under-weir drain was piped to a small, square concrete basin, maybe 4'x4' and a foot deep, topped with a manhole cover. That manhole cover was never visible in any old photographs, so this may just have been something like a buried junction box for more than one drain.
I don't know if the new little access points are actually related to the under-weir drains or if they're piezometers to measure underground seepage independent of the drains. Either would make sense.
No wonder this is CEII - in either case noted above, these are obvious attack vectors for terrorists. How many times have we read about jihadis going after under-weir drains? Why, if I had a nickel for every time I read about these kind of tragic attacks...
