NAD83/94

is that as wrong as it looks?

Probably. Time to ask for some clarification.

I aggree with Rover.  But Maybe an adjustment was done around 94 and they kinda have a typo.  What state are you in.  I bet if i have to guess someone established the system as nad83 cors 96  or they could mean nad83 HARN. .  Edit. The HARN were done in each state starting in the 90’s. So maybe Thats what the mean. 

Assuming the project has been completed, areas have been purchased for the dam, topo is done and the dam is designed, then this is your task:

They are asking you to verify if the control is still valid. Are the points still there? Are the values used still tight between the points? Elevations are paramount, especially near the dam.

What they are not asking is for a new resurvey of the control to the most modern values that CORS/OPUS will produce. The horse left the barn on that one. If they are 83(94) NAVD29, then they better stay that way. 

However, if the dam hasn't been designed, there are not topo maps produced, ariel flights haven't been done, land hasn't been purchased based on the old control, then go ahead and maybe modernize the control. 

You need to know what is going on, what do they really need, but going out and OPUSing control previously run from HARN points and changing the numbers to make it easy for some button pushing surveyors can be a disaster. For a dam, the top of dam and top of spillway heights are critical. A few tenths can cost a huge amount. Figure it out this way, the elevation for the spillway is .4' feet off in height, the spillway holds back a reservoir that covers 300 acres. That is 100 acre/feet of water. For some storage, water is selling for 10-20K per acre feet or a 2 million dollar bust because of a few tenths. 

If the project is getting ready for construction its basically irrelevant how the control was run. You need to check to see if it's internally consistent. I would also suggest some topo checks on the mapping, particularly at the dam site, but also along the valley. 

NAD83/94 (2011)

Somebody is copying various spec sources and mixing them. Ask them if they mean NAD83(1994) which is the Nevada HARN realization and maybe what the design was based on, or if they want NAD83(2011) epoch 2010.0.

Those are both horizontal, so if there is elevation measurement involved as well you need to ask if they want measurements based on the latest geoid model.

@mightymoe You are the second person I have seen state NAVD 29.  I have used NAVD88 and NGVD29.  But is navd29 = to ngvd29. Wondering if someone uses it that way. I have seen it twice now and have to ask.

@bill93 great point.  I would assign the correct geoid to the correct horizontal datum. They do not need to be mixed either. Had a similar situation not long ago nad83 harn but they stated geoid 18. I had to make a call and get the correct info.  They had not updated the text asinged to the north arrow block. So it was nad83 harn. In the notes Vertical datum was navd88 and later a note stTing geoid 12b. It ended up being nad83 2007 I believe and such. Not a big deal but i am glad i made the call. Assuming makes a you know what out of me.

@olemanriver 

Yes, my bad, a typo, should have been NGVD29. Many newer dams would be based on NGVD29 because of local FEMA maps still not being updated to NAVD88. This assumes dams in more populated areas.

Hopefully, by now all FEMA maps and control have been updated. But locally that happened only a decade ago and prior to the new maps everything connected to flood plains were based on NGVD29.

Dams, particularly large ones, will go through years of permitting before they get to the construction phase. Just the water rights phase is going to be 1-1/2 years if you're lucky. So, the control will probably be years old. And if you're coming in after topo, design, you're stuck with the given control, whatever the basis of it is.

There is no changing it now.

Elevations are the most critical component. It's important to get the finished dam, spillway, glory hole heights precise. After construction the monitoring phase kicks in and then horizontal locations become very important. 

All the monitoring we do is level and TS using control on and off dam. John Hamilton can speak to it better than I can, but it's important to set up a system that will track small movements. We do a series of local dams and check them yearly. They are 29 and 88 based. 

Somebody is copying various spec sources and mixing them. Ask them if they mean NAD83(1994) which is the Nevada HARN realization and maybe what the design was based on, or if they want NAD83(2011) epoch 2010.0.

I'd bet my next paycheck that's what is going on. Someone without any knowledge of datums is writing those statements.

You'd think it would be SOP to actually leave that sort of thing to someone who knows what they are doing...

We have both HARN and FBN datums here in WA, designated as NAD83(91) and NAD83(98). Even surveyors get them screwed up way more than they should. You also occasionally get the yahoos using our RTN noting their datum as simply "WSRN" (acronym for Washington State Reference Network) and nothing more.

@mightymoe gotcha. The whole longterm project thing is a issue. I am dealing with projects like that myself. Since being back on this side and learning that one in done mindset someone else stated on this site. I have been shaking the bushes and rattling the bell as If all raw data is stored and documented properly and all meta data it doesn’t take long to take a design file and get it to the latest realization and most problems are solved. But the lack of metadata and the just use these two points and re traverse mentality causes me to invest in tums and rolaids lol.