Ben Bishop wrote:This is supposed to guide water away from the valley and into the ridges right? I can't quite wrap my head around that part. Why wouldn't you just plow a bunch of lines on contour around the keyline to hold in the rainwater?
Because then you'd have more water in the valleys than in the ridges. Even if the water only travels, say, a meter before soaking into the ground, it will tend to flow toward the valleys unless something intervenes. The goal of keyline plowing is to even it out by making it flow that meter toward a dry spot instead of toward a wet spot.
Ben Bishop wrote:-Can you do this type of work on a home-scale with shovels and pitch forks?
Sure! But it may not make sense to break out the surveying gear for a small scale; just go out in a heavy rain and see where the puddles accumulate and where they don't, and move some dirt around as necessary to relieve the situation. I've had great success with this on my 1/10 acre -- I don't get puddles anymore even during the heaviest rains.
Ben Bishop wrote:-If the parallel plow lines aren't on contour wouldn't they cause water to accumulate in one area?
Only if they congregate somewhere. What you're missing here is that if they were
on contour, that would cause water to accumulate in the valleys (keeping in mind that we're talking about valleys and ridges within the context of a larger slope), because that's what water naturally does on a sloping landscape. By plowing slightly off contour, you're spreading that water back the other way, toward the dry spots.
Ben Bishop wrote:Can the land be TOO flat to even need to consider the keypoint?
I would say yes, personally.
Geoff Lawton says no landscape is too flat to use swales on contour (see: Greening the Desert, or his interview with Paul Wheaton where he talks about flat land), but finding the keypoint when there's no perceptible slope is a tricky business and probably futile IMHO.
