One Man Crew Fun

any snakes?

When you said lake I envisioned a larger body of water. Is this a backwater of a large lake? Large enough to be concerned about seiche?

Looks pretty calm. In places with waves do you use a stilling bucket?

I'd probably use the total station for this sort of work and set it to read ΔZ. As long as the rod height remains fixed for both backsight and foresight it cancels out of the equation. You note exactly as for levelling, but keep track of and account for the negative readings. 

Posted by: @hpalmer

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any snakes?

No. This lake is actually a retention pond, but I always keep an eye out for snakes.

Posted by: @bill93

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Is this a backwater of a large lake?

No. Actually, it's a retention pond. Most of our lakes are true lakes.

Posted by: @norman-oklahoma

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I'd probably use the total station for this sort of work and set it to read ΔZ.

I like your idea. Our total station does have a reflectorless distance mode, but I doubt the office would accept that in lieu of a rod reading. 

Posted by: @field-dog

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Our total station does have a reflectorless distance mode,

I do not suggest using reflectorless for this. Use a rod and glass, just keep the rod at the same height for both backsight and foresight. 

1. shoot the benchmark. Note the ΔZ in the BS column.

2. with the rod at exactly the same height shoot the edge of water. Note the ΔZ in the FS column.

3. change the rod height. Shoot the water level again. Note the ΔZ in the BS column.

4. without changing the rod height again, return to the benchmark, reshoot, and note the ΔZ in the FS column.

Resolving the level notes can be a bit confusing but it really is nothing more than common level note reduction except that you SUBTRACT the backsights and ADD the foresights, with the negative numbers on some of the readings accounted for.  And the accuracy of this method in in the ±0.01' area. More than good enough for lake water levels.

Fun fact that makes 0.01' accuracy moot. A pond of water (big or small) with no shade in 90 to 100F summer heat will drop 0.02' to 0.04' in elevation per day due to evaporation. Low humidity and wind will make it drop even more.

@landbutcher464mhz and water levels rise with florida's rains.  And as you point out, measurements to the hundredth are 'significantly' misleading.  Without knowing the survey accuracy specifications, I would use trig levels or GNSS for this task with accuracy to tenth of a foot - would change with relative hard surfaces/benchmarks/weirs/concrete inverts.

There isn't a real need for precision for this task. RTK GPS would be good for it, Total Station better, levels are the best but since you're not locating a "thing" such as a weir, gaging station, outlet, I don't see the need to level it. Water heights are subject to many influences. They aren't really precise, and will rise and fall. 

Interesting timing as I have on my plate about a dozen or so lakes where I'm at that I've been tasked to develop a water level monitoring plan for. They all include benchmarks, spike in a tree typically. I was planning on just using my robot to trig level to a hub driven flush with the water surface. I'll just break my setup and trig back to the BM as a check. Don't think anyone cares much about a few hundredths. Some of these lakes have no outflows and are tied to ground water levels and they've risen as much as five feet in recent years. I'm going to need to do some test sampling of the local trout populations while at it, y'know, for science.

Posted by: @williwaw

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I'll just break my setup and trig back to the BM as a check.

Changing the rod height serves the same purpose and takes far less time. 

Is there a question of ethics here?

If the client indicates the water level will be needed on a repeat basis, do you .....

Say you're available anytime needed.

or

Do you suggest you do your work just once to establish the datum for

something like this ....

Posted by: @norman-oklahoma

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Posted by: @williwaw

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I'll just break my setup and trig back to the BM as a check.

Changing the rod height serves the same purpose and takes far less time. 

Government work. If it buys me a few more minutes outside before I have to return to my office in the catacombs, I'm really okay with it, but your point is valid.

From what I understand, the primary purpose for checking lake elevations is to prepare for hurricanes. Most of our lakes are checked on a monthly basis while others are checked quarterly. We have no established tolerances for elevations; however, I hold myself to +/- 0.05' on measure-downs and staff gauges. We only use a level when our lake benchmarks cannot be used due to low lake levels. These lake benchmarks can be a nail and disc in a boat dock, a channel iron, a disc on a headwall, or a square-cut on a headwall. Maybe one day the county will let us use RTK and record data digitally.

My 25' fiberglass rod has a standard 5/8" threaded hole in the top so I put a threaded stud in there and can attach a small prism. I have used it with the prism to reach roof heights thru trees when the reflectorless will not work. Never had to measure water levels before but with my robot I would shoot the bench then hold the rod arms length out in the water (keeping my boots dry), read the water level on the rod and subtract it from the actual rod height. That would eliminate setting a hub at water level. Also, like @bill93 said, if there is some wind you will need a calming or stilling bucket. A 5 gallon paint bucket with the bottom cut out would work. Stick the bucket in the water, put the rod inside and presto, a steady water level reading that is not jumping up and down with little waves.

Posted by: @williwaw

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Government work. If it buys me a few more minutes outside

Spend the time you save sitting on the bank "working on your notes".

Posted by: @norman-oklahoma

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Posted by: @williwaw

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Government work. If it buys me a few more minutes outside

Spend the time you save sitting on the bank "working on your notes".

I'll take that under advisement. One of the big adjustments for me going back to work for government, has been the utter futility of trying to work efficiently. For example, I'm not allowed any admin privileges, so a simple update to my Carlson can take over an hour of back and forth with IT. I can't connect any external devices directly to a domain computer, which means that to upload or download data from my controller, I have to go through a non-domain laptop through MS OneDrive through a web portal, which means just downloading a days work can easily take half an hour of trying to log in, repeated phone calls to verify I am who I say I am, just to get one file downloaded. 

No. Don't even get me started because that's just the tip of the iceberg. Ever see the movie 'Office Space'? Yea. That's me, in the basement, guarding my stapler.

@williwaw 

I remember that kind of experience from my days of working for a large consulting firm contracted to the Department of the Army.  This was in the early days of having any kind of electronic data capability.  The clerk-typists had typewritters and five sheets of carbon paper to provide the required six copies of everything.  Correcting a typo was a time consuming event.  There was one superduper copy machine controlled and operated only by a certain employee.  One Division had somehow acquired one Radio Shack TRS-80.  Two people were assigned to it in order to develop a master plan for planned equipment maintenance scheduling.  That summed up the entire use of modern capabilities.  Being in the Engineering Division, I sent through a purchase order to charge one of my project accounts to buy an HP-whatever number programmable calculator.

The purchase order was bounced back to me from the Purchasing Department in the Finance and Adminstration Division because their Division Director rejected it as being hazardous to security.  I knew the Director quite well, so I promptly strolled into his office carrying my personal HP some other number.  I demonstrated how I could use my own calculator to determine the volume of fuel in a horizontal storage tank based on a stick reading for depth.  What we wanted to do was install a floating depth device to be read continuously as a means of determining leak loss quickly.

He was concerned that somehow my HP whatever might be able to be used to "hack in", a term he didn't know, to sensitive information that might be stored somewhere else at our facility.  I assured him I knew of no way to link up the HP whatever to their little TRS-80.  He then approved my purchase order.