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World's Shortest Irrigation Ditch

Posts: 2780
Location: Central Oklahoma (zone 7a)
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As I've explained elsewhere, for the first ten years I lived on this 40-acre patch of my inlaws' land I mostly didn't try to grow anything on it. One of the ways I rationalized this was by clinging to the belief that nothing worth growing would survive the hot rainless summers we've been having, not without irrigation.

Once I started reading up on permaculture, I came to understand the possibilities of water management. There's water here; a lot of it falls as rain in the winter, and considerable quantities are accumulated in various ponds and ravines, even during summer drought. Lack of water is no reason not to plant. I just need to manage it a little.

I have zero interest in hand-carrying irrigation water, not unless I was a lot hungrier than I am now. But I don't mind doing a little shoveling if it lets me bring water and plants into happy proximity.

So, today I decided to do some experimental digging. We've got a stock pond, and in one corner it's got a gently-sloped muck-on-gravel beach:

There's rock close to the surface (you can see a highlighted sandstone outcrop nearby) but I wanted to find out just HOW close. When I was a kid, we did old-fashioned pick-and-shovel gold mining in Alaska; and one of the techniques was digging a special ditch called a "drain". Basically it was a level trench that starts at the water's edge and proceeds upstream through shore gravels. Eventually if you keep the drain level, you'll meet the rising bedrock as you go upstream, and when you get there, the bedrock will be dry because you're draining away all the surplus water down your "drain" ditch. So you can do your gold-mining work (scraping nuggets out of cracks in the bedrock) without having to work underwater.

So I know a little about gold mining and nothing about irrigation. But I thought "Why not dig a drain into the hillside near my pond?" If I keep the trench level a few inches below the pond level, I should be able to carry an unlimited supply of irrigation water as far from the pond as I can dig before I'm too deep in the rising hillside; and then I could make soil beds on both side of the drain (irrigation micro-canal) for plants whose roots would be able to reach unlimited water. As the pond level drops in summer, I'll need to deepen my drain, but that's no big deal.

I knew going in that my irrigation canal would be no more than six feet long at best, because of the rising slope. And it turned out to be a lot shorter. In fact, I'd call this experiment a failure, because the bedrock was only a few inches down, even at the water's edge. And it starts sloping up just a few feet from the water. Well, that's what exploratory digging is for, right? I've gone looking for bedrock many times when I was gold mining, so it's no surprise that it should find ME when I start digging irrigation canals.

Even so, I'll get some use out of this:

I've already scattered some seeds Fukuoka-style on the upturned soil, but my plan is rework it into proper small beds and plant some legumes. The soil has a bit of organic muck, but it's mostly clay and small gravel; not promising stuff. It needs improvement. I piled all the excavation material on the south side of the ditch, because that's the direction of the prevailing winds; I figure that I can grow a few things in the lower untilled topsoil on the north side, and they'll have wind protection against drying, provided by the berm of taller, poorer soil (and whatever grows in it) on the south side.

I'm not going to invest much more effort than that, because in the hot season, the pond will drop, my canal will be dry, and short of chipping at sandstone with an iron bar, I'm not going to get water back into that trench. Still, I'll get something to grow there in April and May.

Exploratory digging is something that gold miners do a lot of. I hadn't realized its value in agriculture before today, though.
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