How are you doing contour or topo map of your pond. Anyone figured a way to do it with a hanheld gps?
Is it better to have surveyed w the structure in place?

If you are lucky and Google Earth happens to take a satellite picture at the right time, you can have a record of where you place structure.

I got partially lucky. After placing structure the pond filled about 2/3 when the picture was taken. I don't have a record of all the structure placed, but I do at least have the picture that shows the tops of the major structure that comes within about 3' of full pool.

If you have a hand held GPS with at least WAAS correction, you can probably record the location within about 3 feet. It takes a higher accuracy correction signal (higher cost GPS plus subscription service for correction signal) to get down to within a few inches. And surveyor grade correction to get down to property line accuracy (= very big bucks).

I have not messed with hand held gps for quite some time, so they are probably much better now. But used to be if you got within 15' of repeatability you were lucky.

We use WAAS for correction on our planting farm tractors and get acceptable pass to pass accuracy. But not near good enough if we were wanting to come back a day or week later and hit the same spot. To have high repeatable accuracy, it requires a fixed base station signal from a known point of reference to give the differential correction the satellites need to take into account tropospheric anomalies (The change in phase as the signal is bent going through the troposphere). It would take an expensive hand held gps with a radio receiver receiving a differential signal from a fixed base station (with a paid up subscription to the correction signal) to provide such accuracy. They make them. They are not cheap.

No they are cheap. But handheld gps should work for general purpose I am after. I will draw map also and best measure locations. I have access to excavator level w detectors ill meaure depth with that.
Thanks

You can get a mapping card with either Humminbird or Lowrance fish finders that will build countours as you run around the lake. The cards are about $200 in addition to the cost of the fish finder. If your lake is not on there base map, it will not show it in blue, or the boarders of the lake, but just as contour lines on "land".

I've been contemplating the card, I already have the finder, but I just haven't bit the bullet.