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Optical Target placed on Spillway to Identify further downslope movement of Corner of Main Spillway… A "two piece" black and white striped optical target has been bolted to a Main Spillway Side wall. Any further movement would reveal a shift in the black and white stripes. This wall & nearby main spillway slab has already shifted a number of inches as noted by the significant width of the gaps that were repaired.

This reveals that there is a concern regarding this section of the upper main spillway where they want to carefully monitor any early warning sign of further downslope sliding. Erosion has compromised some of the lower end of this wall's anchor bars, including significant voids of subsurface rock.

It was expected that drilling/coring would be done. This allows access below the spillway concrete slab to subsurface rock and zones. A common practice to facilitate pumping of "backfill" material to repair voids or to improve the integrity of subsurface conditions (pumping grout). The image denotes a light blue colored "line" marked on the concrete slab. (note: this line angles to the spillway wall, not unlike the drain pipe alignment).

A "two piece" black and white striped optical target has been bolted to a Main Spillway Side wall. Any further movement would reveal a shift in the black and white stripes. This wall & nearby main spillway slab has already shifted a number of inches as noted by the significant width of the gaps that were repaired.

Hard to see how that slab stays in place under the two months or more of constant pounding its likely to see this spring.

When/if it goes the slabs to its side are likely to go shortly thereafter.

If it goes, let’s hope the next slab up from there stays put. It’s easy to see a domino effect if the slabs in general are not anchored well enough for that slope and volume of water.

Wildcard: If the rock underneath the slabs has been exposed to “weathering” over the last few decades it may no longer be as strong as it was when the spillway was first built. Based on the great pictures you have so kindly provided, portions of that rock look pretty fractured.

Another wildcard: Significant new erosion is certain if that slab goes. Lots more debris in the channel. At some point the generators would have to be shut down again, leading to the need for even higher flow through the spillway. A bit like an unstable feedback loop I heard about recently...