I am curious if anyone has had much success on tall (~400 feet) earth dams using RTK (horizontal) to measure monitoring points on benches below the crest of the dam? I noticed that the 2018 USACE manual does not discuss RTK, but I have heard of surveyors using it for monitoring. I am not sold one way or another on GPS or TS for this type of survey; however, I am curious to learn what others have done on similar types of dams.
How much movement do you need to be able to detect?
The answer is dependent on the project's requirements, such as relative accuracy or absolute accuracy, error budget and the geometry of the monitoring points. If I could put a total station in one spot and see everything, I'd likely do that as it's accuracy and precision is something I have more control over than a particular day's satellite geometry and the effects of CMEs such as last week's G4 event. If the earthen dam was oriented in a way that would require a ton of setups and the error budget was a tenth of a foot (I'm aware higher precision can be obtained via base/rover RTK), I might use RTK.
Generally, though, I suspect I'd slap R980s on two intervisible monitoring points and run a static session. Then I'd hit them with a VRS occupation because throwing away redundant data bothers me less than lingering doubts about Trimble RTX or OPUS solutions. After that, I'd set the S5 up on one of the MPs and backsight the other; then turn three, maybe even five, D&R rounds & sets to it and other MPs because again, the extra 3 minutes per location isn't that concerning to me and requires no more effort on the part of the crew than to change a "1" to a "3" in the number-of-rounds dialogue box. I'd run a Network Adjustment in TBC Enterprise, one of my favorite things to do though I miss Star*Net, and pat myself on the back for being both efficient and precise in my field measurements. Afterward, I'd bask in the glory of an automated accuracy report displaying relative positioning errors that would require a jeweler's loupe to visualize.
@murphy - thanks for the perspective, appreciate it. The tolerances required are less than 0.1 of a foot. Previous surveys did alignment-offset surveys, which are amazingly quick to accomplish. I have heard of some that traversed across similar dams, but I have not attempted it.