Meadowlark - I have seen some of your other posts and appreciate your input. On calculating volume how tight of a grid would recommend for depth recordings. I know the tighter the more accurate and we are looking for +/- 15%. We are doing this for someone else and I have a general idea of what the bottom looked like during 2011 and it did still had some water in it.
I'm still laughing that someone in the pond business actually questioned why you needed that data...LOL.
If the bottom is a typical bowl shaped like a lot of ponds, accuracy will be generally high with relatively few data points and of course likewise, if it is irregular bottom with channels and cuts and underwater islands, many more data points will be required.
You can certainly get well within the +- 15% on area by using appropriate geometric shapes(circles, squares, trapezoids, rectangles) and the roller I mentioned. A hand held GPS will nail that down very accurately, much more than 15% and will even calculate the area for you.
The depth is where it gets more tricky...especially from the bank. One rule of thumb for most regular shaped ponds is to calculate average depth by multiplying the max depth by .4. This would be good for regular shaped bottoms....but for irregular and/or precise calculations, the more data points you get, obviously, the more accurate the volume calculation.
You can do some "sensitivity" analysis to get a feel for how much error in your depth measurements affects the volume calculation. Let’s say, for example, you had a 3 surface acre pond and 6 ft average depth that would equate to a volume of about 5.9 million gallons. Now, if you missed the average depth by 15%, that would equate to about .9 million gallons less or more, for example.
Wish I was nearby as that would be fun to do that calculation.