I’ve read elsewhere that it IS anchored, and that they shaved away looser rock so that they had something solid to anchor it to. I don’t think that the weir was about to slide away, but there appears that some of that rock might not have been as solid as it was thought some 40 years ago. The erosion at the parking-lot end of the weir shows that things could have gotten pretty dicey pretty fast.
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The weir will go nowhere.
It rests on drilled piers that go more than 25 feet into the native rock.
The concern at the weir was errosion below its bottom near the main spillway.
That was the very first thing that was reinforced with the grout and rock.
The dam is not an issue; flooding and storm flow management is. This has actually been true all of the time, but there was great concern for more possible damage to the main spillway before the erosion was addressed.
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See pics at link in post #6 by gubamyster
http://www.freerepublic.com/focus/f-news/3526879/posts?page=6#6
Grabbed wrong post; pix are here
http://www.freerepublic.com/focus/f-news/3526879/posts?page=23#23
H/t blueplum