Ever since we arrived here in 2015, we’ve been thinking about how to improve the water situation on the farm. Sweden has been drying out for the last ten years or so, with 2016 the dryest year in 40 years. This year, so far, it’s quite a bit worse. So the need for good water management was never as great as it is now. Likely it will be greater next year. This is why we have dug our first swales and pond this summer.
What’s the problem?
The problem is not just that less water falls out of the sky, but also that what falls does not seep into the soil to end up in aquifers any more. Reasons for this are that ever more surface area is covered in concrete, that land that isn’t paved (yet) is ever more compacted, and that there are ever fewer deep-rooting plants creating channels for water to follow deep down into the soil.
This leads to land that is not capable of absorbing water the way it used to. So when it doesn’t rain, the soil dries out very quickly, but if it does rain, the water cannot go down into the soil. Instead it runs straight downhill over the surface. This means that much of the land basically stays dry no matter how much it rains. But water running downhill fast will gather somewhere, eventually. The areas through which it runs can flash flood and erode dramatically, and the areas where it eventually accumulates can flood.
What is the solution?
The conventional solution to the problem of water shortage is irrigation. When energy is (relatively) cheap, you can fairly easily pump up water from somewhere onto your land to keep plants growing. Never mind that the water you use comes from somewhere where it is necessary as well. Water inequality is a result of this, but also drying out of rivers and areas which used to be kept moist by those rivers. Irrigation is certainly usually not a lasting improvement in the water situation.
On the other hand, the conventional solution to the problem of flooding is drainage. If farmland gets flooded, the desire is to get that water off the land as soon as possible, so that plants don’t die. Draining the land, however, simply leads to more flooding downhill, because water flowing downhill faster means that it will accumulate faster in the places where drainage has not or cannot be improved. And once the water has gone again, the soil is still left dry. Consider a spunge. When it has dried up completely, you can hold it under a running tap, but all the water will simply run off. Nothing will be absorbed. Only if the spunge is somewhat damp already will it absorb more water.
Shortly put, irrigation leads to more drought, and drainage leads to more flooding. And then drought.
What is the real solution?
The real solution is one where the water retention ability of the land increases. This means that when water falls, it will not run off immediately. Instead it will seep into the soil, which will hold it for a long time. This can replenish ground water and aquifers again. If the weather is dry, the land and the plants on and in it can use this stored water. Very healthy soil, which almost automatically must be soil with a well-established perennial plant cover, can absorb so much water, that flooding might only happen during truly horrendous weather events. And if flooding does occur, soil will not or hardly be washed away, because the structure of the soil and the plant root and fungal mycelium networks in it keep everything knitted together. And because the water does not rush from up high to down low, there will be no flash floods.
There are several ways to achieve this. There are swales. There are keylines. There are ponds/dams. There is the planting of suitable plants. There is adding organic matter to soils to act like spunges. And there are many other things which can play a role as well in water management.
For a truly deep analysis of especially the differences between swales and keylines, I will recommend you to do some serious searching online and in books. There is a lot available, and discussions can get pretty heated. Often those in favour of swales abhor keylines, and vice versa.
Our swales and pond
We decided to go for the option which we understood best, and which we could find and afford the required tools for most easily: swales. All we needed was a mini digger. We’ve only put swales in on a fairly small area of our land so far, so it’s not impossible that we’ll consider keylines next year for the remaining land.
A swale can be defined as a water-harvesting ditch on contour. The effect is that water running downhill over the surface or through the topsoil gets trapped in the ditch, and from there infiltrates deeper into the subsoil. If it would keep running over the surface or through the topsoil only, it would never replenish ground water, let alone aquifers. But if it is given a chance to go down into the subsoil, it can and will.
It is really rather amazing what such a relatively simple thing as a ditch can do. Sure, it’s not cheap to rent a digger, nor is having such a heavy machine burn diesel for a few days very nice. But… sometimes the positive effects of doing something can overcompensate the destructive (both to wallet and, more importantly, planet) elements of those actions. We have damaged the world so badly by millennia of destructive agriculture, and many decades of industrial development with heavy machines, that by now it’s quite possible that to remedy the destruction caused is no longer something we can do with bare hands. Not in time, anyway.
I dug part of the first swale by hand. Sure, it’s possible, but to dig all the ones that we may want on our land would take years, and would probably cost several backs. And all the time until it’s finished, the land itself will not be able to function optimally. Functioning optimally includes sequestering carbon! The carbon emitted by the digging, if all is well, will be compensated by the growing of soil and plants and other living beings. None of this is to say, though, that anything requiring a (military) industrial complex can ever be sustainable. It can not. Paradoxical? Not really, but it takes a while to see it.
Swales and pond in the making
First, let’s take a look at a map (click on it for a larger view). You’ll see that it’s only a very small area we’ve tackled so far. The reason why we chose that area was that by far the wettest patch where the pond now is was… where the pond now is. Last year we dug a few small test holes by hand to see if they’d hold water. They filled up quite nicely after rain, and even hold water for a few weeks with very little or no rain. This was promising enough to get that digger in, although we were never truly certain that a big hole would ever fill up with between 30 and 50.000 liters of water.
To make it a bit more likely that the hole would fill up with water, we did a few things. First of all, it’s worth noting that this is an unlined hole in fairly sandy soil. The fact that it was always damp seemed to suggest that groundwater is coming to the surface there, which is a good start. But there is a chance that once you make a big hole there, the water gets a quick way out as well. This is why we paid attention to the soil as we dug. If we’d suddenly have found an area with much looser soil, we would have stopped digging there, as it might well become a way for any water flowing in to flow out just as quickly. But fortunately we didn’t find an area like that. If anything, driving around with the digger while working, compacted the already pretty compacted subsoil even more. A second thing we did was to dig a narrow trench on the downhill side of the pond until we got to the really compact layer about half a meter to a meter down. This trench we then filled up with the densest material we dig out of where the pond was to be, and compacted this as well as we could by driving over it with the digger and/or pounding it with the bucket.
Thirdly, we made the swales above the pond. They are almost completely on contour, apart from where they hit the path. Here they slope down ever so slightly, so that water running down the path is diverted into the swales. So instead of running straight down the path into the woodland, and then straight on into the lake, that water is now led onto the land, where it gets the time to soak into the subsoil. Of course water falling on the land above the swales will also end up in them, as it runs down over the soil, or, slower, down through the topsoil.
The subsoil in this part of the land (but probably in many parts) is really very compacted after years of only growing hay, and heavy tractors riding over it to harvest it. We’ll be planting many perennial plants (trees, bushes) and deep-rooted annuals on the land, and their roots will break open the subsoil and add topsoil. More water in the subsoil will help this process a lot. Not only will the plants grow better, but the moisture will partly freeze in winter, and expand, and thus break open the soil in another way than roots do. All this will increase the ability of the soil to contain and retain water. And, to come back to why the swales so far are only above the pond, this increased moisture above the pond will mean that more water can seep into that pond.
Due to financial and temporal constraints, we could not continue beyond this point this year. Also, it made sense to first see how this small beginning worked out. If the hole would just remain a dry or merely damp hole, and if the swales would not gather much water to speak of, then making more of both would not be that great a way to invest money and time. But… we could never have imagined how well it all does work!
The photo above shows a very uneven distribution of water. This is because of inexperience using a digger. The top of the ditch is very close to level, but the bottom isn’t. It’s a lot easier to determine where to begin digging than how deep you dig… This means that there is still quite a lot of work to do to get this evened out. I’ll do part of that by hand, but maybe we can afford getting a digger in before winter, and taking care of it a lot quicker then. Even in this suboptimal situation, the water you see there has not run down the path, but has soaked into the subsoil, adding to the ground water. A big improvement already.
Despite the soil being so compacted, the water that runs into the swales sinks into the soil very quickly. After an hour or two, it’s all gone into the subsoil. Thousands of liters of water that otherwise would have run off, evaporated, or at best only shortly wetted the topsoil.
The top of the swale (where the dug-out material is dumped as a dam) we planted as soon as possible with hundreds of young bushes and trees, and put seeds of many annuals on as well. This ensures that the dam is kept together well by the roots, and is less likely to wash away in extreme weather. But it also makes it more than merely a water-harvesting feature; it makes it a productive area, and a very biodiverse one at that, with many different microclimates.
And how about the pond? We finished digging the pond on the ninth of July. On the fourth of August, it looked like this:
Firstly, yeah, it’s a mess. We had to bring back the digger before we could make anything like a nicely finished dam on the downhill side. This I’m working on bit by bit by hand these days, and again, maybe we’ll be able to afford one or two more days with a digger to do it a bit quicker and easier.
The pond is very long and narrow. I haven’t actually measured it yet, but I estimate 15 x 4 meters on average. It’s narrower than we’d have liked, but we were constrained by a steeper bit of land right above the pond, and a 10,000V electricity cable inconsiderately buried just downhill of the lowest shore of the pond. We know… we very nearly hit that cable while digging. Fortunately there was a lower voltage cable right above it, which we did hit. Sparks flew, and so we halted immediately. Someone from the electricity company came to take a look, and had to fix that cable. Whilst working on that, he saw that the 10,000V cable was only centimeters below it. Hitting that might have led to some rather permanently charred (ex)workers. But hey… this is how you learn that when you want to dig, you have to ask all kinds of authorities where they might have burried things like cables and tubes. Who’d think someone would want to bury something as lethal as that underneath farmland?!
But even if we’d have been able to make the pond a bit less narrow, it would still have been quite a bit longer than wide. This, and the fact that it runs roughly between north east and south west (the prevailing wind direction is south west), and that there are deeper and undeeper areas, means that wind will have the optimal effect on the water, making it move. That will even out temperature differences, and maximise oxygen in the water.
And as time progressed, and an extremely dry winter, spring, and first part of summer turned into a wetter August, the pond filled up both painfully slowly ànd infinitely faster than we had dared dream.
At this point, on the 16th of August, the deepest part of the water was about a meter deep, and that after no more than 15cm of rain since we finished digging. It was a good time to dig up some waterplants from the lake, and plant them in the pond. Also, I added some of the mud from the lake bottom, and some water to the pond to infuse it with life. Hard to see on the photograph, but there are some waterlilies and reeds in the far end now.
This is roughly how far it has come so far, although as I write this, there’s a few more millimeters of rain coming down, so tomorrow it’ll be higher again. And so, within two months after digging the pond and the swales which feed it, I have to seriously start considering what should happen when it overflows. It’s not a question any more, I think, of whether or not it will overflow, but how soon, and how much. And overflow is what I want! That way, the water that flows into this pond can feed another one a bit further downhill. In a few years time we intend to have ponds, some a good bit larger than this one, dotted over the land. How that will work on much dryer parts of the land remains to be seen. But with more swales and ponds installed, the soil should hold ever more water ever better, and this makes a next successful pond much more likely. In other words, we’re confident enough now to think that adding more swales will help make it much more likely that we’ll get lucky.
It’s hard to describe how excited we are after this initial success. When we started digging, a neighbour came to take a look, and when asked whether he thought he’d be able to take a bath in that hole one day, he said that he was pretty sure that wouldn’t be possible. When I recently confronted him with the fact that the water now was more than a meter deep at the deepest point, his reply was.. “Yes, well, that’s logical. That’s because of rain!”. Goes to demonstrate that it’s pretty tough to explain what you’re trying to achieve sometimes.
Last but not least, here’s a video showing how the swales work during heavy rain: