By Andy Williams.
From the very beginning of planning this site, I knew we’d need to do some serious earth moving. The site is intermittently wet because the subsoil is clay, so when it rains heavily there’s nowhere for the water to go once the topsoil is saturated. We’ll be improving this by increasing the organic matter in the soil by planned grazing, but it can only achieve so much. We plan to plant fruit and nut trees, which struggle with consistently waterlogged roots for the most part. The solution is a permaculture classic, almost a cliche really: swales.
A swale is a ditch dug along the line of contour, with the removed topsoil forming a berm on the downhill side of the ditch. Their purpose is usually to catch overland water flow and hold it, so it can be absorbed into the ground instead of running off the property. In dry climates they’re fantastic, and allow people to grow tree varieties without irrigation that would be impossible otherwise. Of course nobody would describe the north of Scotland as a dry climate, but here they’ll serve another purpose. The berm will allow us to plant trees in soil that’s higher above the water table, giving them a better chance. We’ll be able to plant other, smaller, water loving shrubs like wax myrtle lower down the berm where the soil is wetter and other productive species like ramsons in the bottom of the swale ditch. We’ll be able to create really interesting, productive polycultures because of the different niches on different parts of the swale with differing amounts of moisture and shade. An often overlooked benefit of swales is that they effectively increase the acreage of land. If a piece of A4 paper is representative of an acre of land, imagine a sheet of corrugated card the same size. Now imagine pulling that corrugated card from each end to flatten it out. Free land! Of course swales aren’t dug at the same concentration as the ridges in corrugated card, but the principle still holds. The swales will of course infiltrate a great deal of moisture into the ground during rain, after all it’s what they’re generally used for, so even during dry summers we shouldn’t get water stressed trees and shrubs. Not bad for a glorified ditch eh?
Ponds, even small ones, have a positive effect on natural ecosystems. The same is true within diverse agricultural systems. They have a moderating effect on microclimate because of their thermal mass. They encourage natural biodiversity, for example frogs and toads, which feed on slugs. Who’s ever grown food in a damp climate without wishing there were fewer slugs? Ponds can also be used more directly for food production of meat such as ducks and geese, plants such as watercress and large ponds can be used for aquaculture of fish. Our swales will be designed to fill relatively small ponds, but they’ll still be useful. I have a niggling little plan in the back of my mind that integrates water culture with a greenhouse that should be interesting but that’s for a different blog, far in the future.
Swales, as I’ve already said, need to be dug perfectly on contour. Water shouldn’t flow along them but remain static until infiltrated. Careful levels need to be marked out before any digging begins. Earthworks permanently change the hydrology of any landscape and need to be carefully thought out. In the case of our top field, we need to establish the way the ground slopes before finalising any design. Just looking at a field is never accurate enough. We know it slopes generally to the north of course, but is that north with a bit of west, or east? The human eye just isn’t good at estimating slight changes in slope.
There are many ways of setting levels within landscape. A laser level is beautifully accurate, but is expensive. I tend to buy good quality tools but only if they’ll be used regularly, and once we’ve marked out the contours in the field we’re not likely to need one often enough to justify the cost. One cheap alternative is an ‘A’ frame level. It’s simple to make and reasonably accurate, but doesn’t work well going through undergrowth. At the moment the top field is bare, but we may well need to set some levels after the swales have been put in. For us, the best option is the bunyip or hose level.
At its most basic, it’s a length of clear hose clamped or taped to a wooden stake at each end. With the hose mostly filled with water, when the stakes are put side by side on a flat and level surface the water level in each end of the hose will be exactly the same. If that level is marked on both stakes and one of the stakes is moved up, the water will remain level but will now be below the mark on the stake. It will of course be above the level on the other stake, because that’s how water always behaves. If the hose is a long one and two people have a stake each, they can ascertain whether the stakes are at the same height even if they can’t see each other just by telling each other whether the water level in the hose is above or below the line. It’s beautifully simple, and cheap.
I built ours a little fancier. The hose must have no airlocks in it, or it’s just not accurate. Airlocks are difficult to eliminate in a thin diameter hose, so I used 25mm braided hose. The thicker diameter also eliminates a lot of drag on the inner surface of the pipe which also should increase accuracy. Instead of marks drawn on the stakes I cannibalised a pair of cheap tape measures and screwed a tape to each stake. Hose is somewhat flexible, so if it’s squashed at all it changes the internal volume. This could lead to two people trying to describe just how much above the line their water level is. With tape measures on the stakes you can use figures that actually mean something to both people, nice and accurate.
We’ve had a bit of a play with it this afternoon, and it really does seem to work as well as the literature suggests. Tomorrow we’re going to survey the slopes in the top field and work out where the swales will run and the retention ponds will logically go. After years of study and planning, this is the start of the exciting stuff. As a bonus, there’s nothing quite like dragging a pipe full of water stuck to a couple of tape measures around a field, sticking in bamboo canes and waving your arms around, for entertaining your neighbouring farmers. Who knows, I might even crack out the new video camera!