Barkley lake was formed by Barkley Dam on the Cumberland River back in the early 60's. Corps bought up to elevation 367, summer pool is 359, winter pool is 354. Project I'm working on requires establishing the winter pool level for a water intake. Project is on a creek approximately 5 miles upstream of where the creek enters the main lake, which is about another 10 miles upstream of the dam. Winter pool backs up the creek pretty much to the site, summer pool backs it up within about 3 ft of the top of the creek bank. Have a concrete pad that, based solely on my observations during a 3 day period last year when the published lake elevation held at 363, was level with the water. Question is, at this location, how would you establish winter pool?
Corps did not buy up to 367 at this location, only have a flowage easement. Typical where the 367 line went a long way up a creek, they stopped buying at the next property line after 359 or thereabouts.
At the local COE lakes, we would get the lake level from the management office of the lake. A lot of this information is available now online from the COE website.
The COE will probably have an elevation on or around the dam (in this case it is a lock and dam system). They maintain an hourly record of the water level.
Around here we use the posted elevation of the emergency overflow spillway as a bench mark.
Before GPS we would transfer that to the water and then to a point around the lake by the level of the water. When the bridge crossing monitor stations were bettered, that was used in addition to the dam readings. Now we use GPS.
That elevation does not always adjust to actual MSL for every lake. It is however the most likely source of reference for elevations used for the lake that dam is on.
Lake Barkley is along a river and would probably have a defined difference in water level given as a ratio per mile of riverbed from the dam.
Check with COE information and ask them about their requirements. I have always found them especially helpful when you are doing something beneficial to them.
I guess my question is, much like the low water thread the other day, is winter pool elevation level? Winter pool is 354, is that only at the dam, or is it for the entire lake? Is the better indication of winter pool at this site the use of the concrete pad at the site for a BM, observed at the top of water level when the published lake elevation was 363? Or is it 354MSL, regardless of the observed water elevation? Or is it 354 based on GPS observations tied to the 354 gauge at the dam?
All of the COE elevation levels I have worked with are based on contour lines.
That would be my guess here also, but I'm thinking it would need to be tied to whatever they called 354 at the dam location in the early 60's. Wonder how close that would be to 354 now if established by GPS? Like I said, this site is probably 15 miles upstream of the dam.
Be very careful about the lake being level (or unlevel). You might be surprised how a thunderstorm on one end of the lake, or a thunderstorm downdraft, or localized barometric pressure can knock the lake out of level. Also, winds can cause the lake surface to get out of level. This is called "set up." My recommendation is to set a TBM in the region you are surveying and correlate the changes in elevation of the water level near your TBM as compared to the water levels at the main lake gauge. This will give you the effects caused by conditions that can knock the lake out of level. I did a fairly extensive experiment on a 30,000-acre lake, and I found out that if the winds were calm, and there was no bad weather late at night, that the correlation was withing a couple hundredths of a foot. During the day with a light breeze, the level would quickly get out of whack by over a tenth and sometimes a lot more. Make sure the lake doesn't have any substantial current in it--something like a big river flowing into it rapidly. The gauge differentials won't pick this up. There is a way to approximate lake set up using calculations, but nothing is as good as differential gauge/TBM comparison over a couple days and nights. My $0.02 anyway.
Frank.....
My recommendation is to set a TBM in the region you are surveying and correlate the changes in elevation of the water level near your TBM as compared to the water levels at the main lake gauge.
Trying to think how it would go if somebody were to question the elevation of the intake in the future. Barkley Lake is about 60,000 acres. This site is 10 miles upstream on the Cumberland River, and another 5 miles upstream in a creek. When they purchased the properties they inundated, the deeds call for 367 MSL, although they actually set pins they call for in their descriptions, which may or may not be at 367.
They say summer pool is 359 MSL. Winter Pool is 354 MSL. I would assume they based their gauge at the dam on MSL back in the early 60's. So it would seem that the 354 contour, based on their gauge, would be the most reasonable basis to use to establish winter pool at the site. IMHO
I don't think that I would hold anything as reported of the water elevation. Presumably, there is a "spill way" or some other object at some purported level. This is what I would use.
Then, the rest of the exercise is fairly academic. You could use OPUS and differential elevations to "transfer" the known elevation to an unknown location, or just hub jump a base station and roll on.
The next guy in line will have to do at least that to prove you are wrong. If someone else says you're wrong and they didn't go to the monumentation for the lake datum, well, that's akin to saying the corner is in the wrong location without ever setting the gun up.
Frank Willis has VERY sound advice on the fact that lakes can have HUGE elevation differences on one end versus the other. Kent McMillan some years back on Lake Travis (I think) used a coffee can to transfer elevations holding the premise that the water elevation inside the can is static (if I remember correctly) and then using the water as a TBM to transfer the elevation.
Personally, I'd opt for the high dollar gear and do it right the first time.
High-dollar standard survey is obviously the best, but I can tell you that if lake levels when done right are extraordinarily accurate. A lot of the Red River Navigation Project (huge project) was done using gradient levels of the water surface in Red River. When i check into them with OPUS and optically, I am often stunned at how accurate they are. We did that work for two full years, following predecessors.
Many times I have set an iron rod in the edge of a lake spanning 12 miles, and monitored it 10 times a day, and compared it to a real-time satellite gauge, and found that late at night it is more accurate than I think I could run with a Wild NA-2. I think a number of papers have been published on this technique.