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Thanks again for the detailed reply, ER333.

You are going to have me give away some of my secrets... :-)

I wouldn't mind prying a few more out of you if I thought the Oroville Dam guys would take note, but horse-water-drink, etc.

TIR/FLIR inspection is interesting - never thought of the utility of that method. A search online produced no images I could post here as an example, but I noticed a few inspection firms had specifically mentioned the service. The cameras/scanners are getting better every year. It would be great to see a time series over days-weeks of the spot in the fall as the reservoir rises.

The metrology toys just keep getting better.

InSAR imagery for those interested (because I'm a picture/cartoon kind of primate):

Source: Norwegian Geotechnical Institute captioned "Deformation analysis of the Svartevatn dam, based on the InSAR technique, shows a settlement rate of approximately 3 mm/year at the centre of the dam. Satellite scans were taken by the ERS satellite between 1992 and 2000. (Satellite data: Copyright © European Space Agency)"

And a study of the Mosel Dam subsidence:

From Space geodetic monitoring of engineered structures: The ongoing destabilization of the Mosul dam, Iraq

I was hoping to find an good image of terrestrial RADR or LIDAR interferometry studies of an embankment dam, but couldn't locate anything. I know they have issues with rough surfaces, but should still be useful with the image processing software currently available. Visible monument markers would probably be needed too, but I think they 'lost' some of them on Oroville if I remember right from one of the inspection reports.

Electrical resistivity tomography is also mentioned by some dam inspection firms. It's done by taking a series of measurements from electrical probes inserted at the surface. This appeals to that Break-it-down-Barney-style mentality: blue = leaks (well, sort of...).

Source: Geophysical investigation of earth dam using the electrical tomography resistivity technique

Chinese engineers love the fact that resistivity tomography can also help locate those pesky 'termite chew cavities' in small earthen dams. Apparently, the voids are significant enough to compromise the structures. That's some aggressive termites!

It's also sort of sad about the state of the piezometers at Oroville. I remember reading about the proud claims of it being one of the most heavily-instrumented dams at the time of construction. I wonder how the long-gone original engineers would feel about the missing geometry monuments and the dam only having three of the 50 piezometers functional? You can't out-engineer poor maintenance (or termite chew cavities) unless you have a good time machine.

Hi PavewayIV, DWR has ran into the exact issue that the InSAR images reveal. Settlement can be very delicate to precisely monitor. Especially in shorter time periods. DWR ran into difficulty with the GPS uncertainty in the millimeters. Thus they didn't know if the quality of the data was accurate for trending or even an absolute. InSAR provides very high precision verses the thorn in the side of GPS in dealing with scintillation error from the ionosphere + the orbital correction reprocessing of the GPS satellites. Even the USGS has "error bars" on their high precision fixed GPS monitoring station readings. They "average" the noise out to a degree with numerous measurements throughout a long period of time.

Have you seen one of the USGS GPS precision monument antenna stations? They are bulky. I can't imagine these installed in a matrix array on the dam. Too invasive + FERC might have a heart attack.

The TIR/FLIR imagery for dams are mostly on "research paper" sites. You have to pay to get these research papers. You can tell when something is a hot field and where people are willing to invest in paying for research - is when you can't find much open info (with good data) except on the "pay" for research papers websites.

The electrical resistivity method has a few variants. They still involve inserting probes into the surface. A big no-no for US dam safety regulations. The non-invasive version of this (magneto-electroresistive) is not 100% until you follow-up with a verification drill. Another no-no. But its good that other entities, such as the Chinese and the Australians have more flexible test standards. This environment can help prove out any new tech that the US may adopt quicker than if tried in the US trying to fight through the red-tape bureaucracy.