The safe thing here would be to let Daren respond, but here is my addition to the discussion and I certainly welcome corrections
Your observations/ summary seem basically correct. I'm a beginner also, and as I walk back and forth doing my hrs of observation I think I finally understood what PA meant when he had that revelation and saw how simple and elegant the whole thing was.
In my mind, I use the stated formula for locating a keyline dam as a general explanation, but on the ground, especially when trying to locate dams as high as possible, those high dams will likely be above the formulaic key line, and the things to consider are many when determining spacing etc.
The main reason for the keypoint is to determine the best place to obtain the material for the dam wall.if the Valley continues to slope away from the proposed water level , you have less and less material but more needed to fill in the deeper area at the wall, so prospects of getting
enough clay for a dam wall diminish as the slope from the (proposed)water level increases.
Going from convex (hump) to concave (indented) in my
experience is often not straightforward as if there was a specific point that would determine the final water level. Looking at the overall--how steep is the convex, how shallow is the concave, or if there is no well defined point, find the flattest part of the gully floor. Think about looking at the gully contour sideways, the concave part of the gully even looks like a small natural
pond
I have also done a bit of digging/ dam building on my own property and there is also the nature of the material down in the valley and especially at those key points. As water rushes down and hits those flatter areas it will tend to slow and stuff will settle out--primarily the clay, which of
course is just what you want
The idea of the key point may also connect geologically to earth strata laid down in layers over time, and without dramatic upheaval in the landscape there can often be observed the colocation of key points where going around the ridge on contour and into the next valley will find you at another keypoint in the new valley. Or at least close enought to make the connection between dams
This is all theory, but helps me tie together some of the observations of Geoff and PA that I've heard.
PA's idea of plowing downhill to the ridge likely originated as part of a broad acre design to promote instant irrigation just by turning a valve at a dam--PA had this thing about fireproofing the landscape. For smaller spaces between tree belts on contour, I would think just direct contour plowing for most applications would be fine, and more efficient to maintain.
Swales and planting
trees of course go together--it's a quick, no extra trouble needed way to supply water to the trees
root zone encouraging the
roots to go down.
If there was a reason why the straight level swale wasn't desired, net and pan would work, but from now on I want to make sure when planting trees I get water under the tree root and not water from the surface. After a few years of doing it half assed, I start to understand the value of that extra consideration when planting. so Whether it's the natural deep watering of a swale, a drip box at the bottom of the hole, or some way to funnel water
underground naturally in the pan planting, watering deep is the way to go
So let's see about your questions
1.The key point (depending on the slope of the valley may not exist or be very poorly defined. My valley/gully is a case in point it slopes almost uniformly, no convex or concave too much, so at that point I look for other features (which might include other possible dam sites, so one of my points includes a contour dam which has a nice fairly flat field out from the contour that connects to the main gully dam. As that goes around the ridge it naturally connects into another reasonably good site in the next Gully so it becomes an integrated system with water from both gullys available to that entire swale.
The swales coming off the dam are level, not the "downhill to the ridges" plowing method of keyline-- this might be altered to suit a specific design, but a level swale allows water to flow both ways, and if you want to direct water one way a few sandbags at one end or the other can do that
water does flow in a level swale, but in a rain event it is likely to fill first from runoff, then if there is excess flow in the gully, the flow in the swale (from the dam overflow) will be more like a rising tide than an energetic erosive flow
2. The sloped grade for plowing is applicable in some cases, but in others contour/level lines are more appropriate, a lot depends on just how intensive the management will be and what other features are in play. Keyline is a great way to provide easy, quick water access to broad acre plantings and for hydrating ridgelines more evenly. But as a design evolves to include tree belts, those belts are built on swales designed around level contours (at least by geoff's methods)
3. already answered
4. again tree planting might be designed on a strict keyline method, but Geoff really doesn't teach to use that downhill gradient for swales, which is the most convenient way to deep water trees without pipes and special consideration. Keeping the compacted level part of the swale on contour allows water to flow from either end and when water moves down the slope it goes under the loose earth of the swale watering the deeper roots of the trees. If your irrigation only comes from one water source the slope of your keyline downhill slope would likely insure more water got out to the ridge (but then would not go around it).
In fact, having water passively sitting in a swale line and soaking into the loose earth at the downhill side of the swale is really what a tree planting swale is all about. mostly the water is not supposed to run at all, it is just supposed to sit and soak
Remember , in
Permaculture we use all the tools, keyline is a tool, not an absolute. become familiar with how water behaves, get real knowledgeable and think your design through over and over, do a couple small tests and think it through again ,, don't get hung up on keyline, although understanding the how and why of keyline is a very useful tool to have.
1
On steeper slopes use a trenching machine to dig trenches along contour lines. Sink trenches as deep as machinery allows. Space trenches every 50 feet along slope contours. You can also dig trenches on gentle slopes and flat areas to trap water for subsoil storage.
