Thanks for the link, AC.

In case all this anchor tendon nonsense and cracks are confusing anyone, I'll add this observation ('opinion') best as I can recall by engineers from the old forums back in the days of spillway troubles:

1) The TOE edge (the downstream 'spillway' floor edge) of the gatehouse is slumping forward and rotating downhill when the reservoir is full. The internal stress on the vertical structural elements of the gatehouse are tremendous. That's what's stretching and busting the anchor tendons and cracking 5' thick structural concrete walls.

2) Previous high-pressure grouting under the head (upstream) edge and under the center of the gatehouse slabs in the 1960's and 70's made the problem worse. The grouting was necessary to mitigate water infiltration under the gatehouse through the hillside foundation rock, but expanding and filling the cracks put upward pressure under the headworks upstream edge. This 'helps' rotate (tip) the whole structure slightly forward when the reservoir is full from water pressure on the upstream side. Speculation is that this is the reason DWR engineers discontinued further grouting under the gatehouse and just accepted increased water infiltration/drainage under the gatehouse. Decades of erosion under the gatehouse toe made the whole problem worse.

3. Opening the gates at high reservoir levels relieves much of the upstream forces on the gatehouse and it will measurably rotate (tip) back towards the reservoir. Same thing when the reservoir is empty.

4. The headworks bottom slabs and piers are anchored to the hillside foundation bedrock by long rods cemented deep into the rock. Some of those anchors may have broken or become loose (cement deteriorating). Other anchors are still gripping sections of the bedrock, but that bedrock is known to be fractured and somewhat incompetent. There's a risk that sections of that rock are simply moving with the gatehouse when it tiles rather than anchoring it.

5. Worse yet, the anchoring and tipping problems are not uniform under the whole gatehouse structure. Slumping movement near the headworks left abutment (looking downstream) appears to be larger than along other sections, leading to the cracked pier above the trunion pin and anchors for Gate 8. This also contributed to the road deck slab spalling the edge of the pier it sits on. The headworks was built using two units - one of the left four gates and one for the right four gates. Racking of those structures during tipping may explain both pier 8 cracks and broken anchor tendons/gate racking at gate 4.

6. More evidence of this problem: the gigantic, bizarre concrete sarcophagus and wall. Supposedly to protect the main spillway from erosion if the e-spillway is used. Kind of like somewhere you would just build a simple, reinforced concrete wall. More skeptical engineers see this as a horrible hack to prop up the end of the e-spillway weir and headworks - FROM TILTING AND SLIDING DOWN THE HILL.

7. We're talking a fraction of a millimeter movement and microradians of tilt. The whole hill and dam deforms by those degrees when the reservoir is full and it wouldn't be unusual for large concrete structures built on it. It only becomes a problem when those structures are built using certain movement assumptions, and subsequent real-world performance later on are not measured or tracked. (Opinions vary on whether DWR does this at all or just keeps the results secret). Obvious future problems related to original design specification assumptions being exceeded later on are ignored - mostly because they are very costly and time-consuming to fix.

The above isn't MY technical assessment of the gatehouse. It's the collective assessment of some geezer engineers and geologists on forums that have been seeing these problems for decades. Other engineers disagree on the seriousness of the issues or suggest other underlying causes.


Measuring this kind of structural movement was difficult (but not impossible) 1960's technology. It's not, today. They can measure a millimeter of displacement and a fraction of a microradian of tilt on an active volcano with a few thousand dollars of equipment. DWR does not lack the technical means to do this, it's that they are paralyzed as far as any organizational desire to FIX anything they find regardless of measurement results, and they'll always use the quickest/cheapest fix when they ARE forced into action.

DWR isn't worried about 4" of displacement on a cracked 5' gatehouse structural pier. But they are outraged when pictures of it leak out and horrified dam engineers all over the world start discussing it and openly criticizing DWR and its engineering organizations. DWR *engineers* are not incompetent, stupid or immoral, but their bosses sure are. Must be a miserable place to work.

No problem for DWR though. DWR absolutely loves CEII restrictions allowing them to hide engineering problems like this affecting the public's safety. Unfortunate for DWR that the cracked pier photos got out, but those Goddam terrorist citizens will never be allowed to see the details on a host of other serious problems. Critical Electrical/Energy Infrastructure Information secrets. You don't NEED to know that secret stuff. And if you poke around too much, well... you'll end up under Sta. 23+00 where you can't cause any more trouble.