Mounting an RTK on the 3 point hitch would be awesome! Sorry, but my tractors are the wrong color. I’d appreciate your help if you can stand green and yellow. Now, I do have a neighbor with a MF I can borrow…
That makes sense, but I don’t follow a 1 cm requirement. Sounds like 30cm at least from low point along slope to top of berm, and if you had 2, 3, even 4 cm accuracy probably that would be fine, and you could probably smooth things out a touch later if there were a local issue.
You should also understand that GNSS measures “height above ellipsoid” (purely geometric), and that people use “orthometric height” (relative to gravity). The standard orthometric height in the US is NAVD88, and there are geoid models to estimate that from NAD83 HAE. The big point is that water flows downhill in orthometric height, not in HAE – but the difference changes slowly and I seriously doubt that is perceptible across a tens of acres site.
I "think" the 1cm goal is focused on the top of the berm during the final grading. The terrace follows a contour to maximize infiltration. If the rain event produces more water than infiltration can handle, then it must be discharged. If the top of the terrace berm is truly level, the discharge will maintain sheet flow downhill, in a gentle fashion. If there is a lower section of the berm, the flow will concentrate there as a point discharge instead of a gentle sheet flow, with potential erosion.
I could easily be wrong, but that’s my understanding after Dan’s explanations. Seems like designing a curb & gutter but you want your Top of Curb to maintain a constant elevation when your done, to overtop as sheet flow.
@gdt - Great point about HAE ! Ortho would be a requirement.
That 100% makes sense to me. I would think one would want to touch up elevations of top of berm (+/- dirt) after major construction and maybe use an optical level. But for the broad-scale of the feature, RTK is probably just about ok, more or less. It’s interesting that absent things like pouring concrete and buildings, tight vertical accuracy is only really of interest in relation to water flow. (Plus of course nerds need to know, even when they don’t.)
Great feedback from gdt and Ryan. Ryan’s explanation is very helpful. He must truely be a farmer or have great water flow knowledge. Everyday gentle rainfall is easy to deal with, but my measurements and work are mostly done to insure that this doesn’t result in erosion when we get the occasional 3 inches in an hour downpour. Being as accurate as possible is important to me because that is how I work on all projects. For this purpose, having a little more error than a cm means it still can work, but it could be problem if a hurricane comes inland in NC this year.
Thanks!