Hi EarthResearcher333.
Regarding issues you raised in post 3717:
LIDAR
The LIDAR used for the “Google car” and many other autonomous vehicles has a stated accuracy of 2cm http://velodynelidar.com/hdl-64e.html , although it does sample millions of times a second, yielding a point cloud resolution better than that for flat surfaces like roadways. Measurement of the large cobbles on the upstream slope of the dam would be noisy, but this could be partially mitigated by oversampling. As you say, the grassy downstream slope would be more of a issue, especially with the Green Spot grass at varying heights.
However, I think such a point cloud resolution should be sufficient to investigate if there are substantial settlement discontinuities across the dam. This would not have the resolution of InSAR, but would be faster/cheaper/more available for a preliminary investigation. Either measurement technique would have to tie into the same survey monuments used for the 1975 DWR Settlement Report cited in post 3624 (or others as available) to determine the past time rate of settlement.
Microprocessors
I suggested the use of an array of microprocessor based moisture sensors to determine if the Green Spot moisture is correlated with reservoir elevation. These are COTS items commonly used in California during the drought - simple and cheap enough that they can be quickly installed. To me, the most critical question is “Dose reservoir water seep through the face of the dam”, and these embedded micro controllers would help determine that question one way or another.
I also suggested that some type of access to instrumentation be embedded in the new spillway as it is being constructed so as to better diagnose problems before they manifest. In lieu of dragging chains over the spillway in the hope that a trained ear will pick up subtle changes over the years, perhaps it might be better to have embedded microphones detect any acoustic changes as a function of spillway flow? My post was more concerned with the types of detection that might be useful, rather than how to write C code to collect the data.
Lighting can fry any outdoor electronics, but that’s not real common in that area of California. However, critical instrumentation should be accessible and replaceable if it fails for any reason.
Another non-starter with LIDAR is that you cannot tell a differential settlement progression from a single pass at a single date & time. There has to be a period of time elapsed sufficient between samples to get an accurate assessment reading in an "interferometric" comparison of the two.
AS the original reason for bringing up "what to do" in the most effective way to discern information on the Green Wet Area, satellite InSAR data may already be available in mapping runs from years prior. If so, another single mapping run would provide the two samples to compute the precision interferometric results.
Of course, any survey data of the dam would be useful. But this depends on how many monuments are being sampled, where on the dam, and how accurately. There was documentation I've run across where DWR was debating the issues of portable GPS units (error bars in accuracy). If they have been using these systems, the ionospheric scintillation and post processing errors could degrade the precision of a "differential" assessment.
But one of the more important tests that could be performed is TIR/FLIR. It would be able to quickly identify if there is a thermal heat sink of moisture/seepage deeper below the Zone 3 layer. Not only that, it could give a mapping pattern to the source(s) and extent of the thermal heat sink.
The TIR/FLIR is non-invasive, aircraft capable, and would give swift information to the full area of the downslope surface of the dam. No piezometers needed for this first assessment.
The challenge with using Piezometers at this moment, is that they require a careful construction operation to emplace. DWR should have had instruments in the ground years ago. Right now they don't have the luxury of referencing instruments that are not there. The other question is how many and what location(s) should these be placed. Remember, the Zone 3 fill backside of the dam should have zero pore pressure. So all of these carefully well drilled, grouted, and sealed emplacements would be in a part of the dam that would be just for this Green Wet Area investigation. The sensor may be affordable, but the engineering construction & emplacement is very expensive and time consuming (if done on the downslope face).
If you are wondering about "does reservoir water seep through the face of the dam", I'd suggest you go talk to DSOD inspectors. They have written this fact into their report. So you don't have to take my word for it. This DSOD report was when there was a severe drought with 81 straight days of no rain - yet they identified seepage still coming out of the wet area. If this data is not acceptable to anyone as extremely strong evidential proof (from DSOD themselves in a personal inspection AND stated "from the reservoir"), then I don't know that if you'll ever convince that "anyone". Best not to discuss it with them at all.
Spillway: The first defense is a good offense. Build it right with a high factor of safety. The BOC has already had DWR work to get a piezometer into the upper spillway area (in the recent repairs). I'm not sure if it is already installed & running or if it will soon be operational. Piezometers are useful in detecting water where it shouldn't be, or detecting water pressures that are unexpected. There are sensors that may assist in monitoring the massive area of the spillway. This is not disputed. However, the choice of the technology should be with wisdom as electronics can be poorly designed without the user being aware of its FIT rate or MTBF (Failure in Time or Mean Time Between Failure).
The modularity, serviceability, and accessibility are important. But the wiring & power is critical to insure integrity for a long span distance (3000+ feet). That is where the dv/dt fast transient earth voltage/current gradients may couple into electrical sensory wiring systems. Fiber optics provides an isolation to this effect, but you have to have good & reliable power supplies at the tx/rx repeaters & transceivers.
In critical Hospital operating rooms, in doing heart procedures such as atrial fibrillation ablation, they have multiple computer systems that overlap in their ability to detect & monitor conditions. This makes it fault tolerant (i.e. if the old Windows operating system blue screens on you the patient won't "blue screen"). [btw= I've been through 5 ablations & when wheeling into the operating room I immediately saw the computer array & screens - then asked what OS were they running & what happens if it "blue screens" - they laughed knowing what I was asking and assured me that they had redundancy - yes, their systems sometimes crashed back then]. So too should be the strategy in monitoring.
I brought up the C++ code to assembly language to code branch anomalies as a real life example of rare "glitches" in microcontroller code. I have spent decades in this field. It is only getting worse at times just as I mentioned in the EEPROM case where the engineers were oblivious to the soft error rate risk to the floating gate charge leakage loss (soft bit error).
The key is to leverage experts. Just as you are doing good "out of the box" thinking, when coupled with "what if's" with "experts in the field", that is when the continuing innovation occurs. A good tip: The best experts are the ones who can tell you every conceivable way something can fail.... :-).