draining the fields…

…in Southern Norway…

failing drainage…

We have some low-lying fields that are quite problematic in the sense that water from everywhere else ends up there – creating soaked and almost swampy soil. Two channeled creeks pass through, but the channels are shallow and the deep soil on both sides of these will hold enormous amounts of water for long periods after rainy periods. These fields can then neither carry farm-machines nor animals for months, which anyone can understand is pretty impractical on a farm.

The old stone-built ducts for draining these fields are partly in bad shape – have caved in and become blocked by mud. Many have also been cut and thereby blocked by later drainage-attempts. Blocked ducts most often means the water has to rise to get out as more water pours in from higher levels, which of course often results in swampy areas and small lakes in the middle of fields. Not a good situation.

We let professional drainage-diggers loose on some of the most problematic areas a few years ago, but the results were less than satisfying. Some more of the old drainage-ducts got damaged – with disastrous effects, and some of the new drainage-pipes and ditches turned out to be almost “water-resistant” – they didn't let the water in even if it rose well above the inlet-holes, and whole pipe-systems acted more like barriers than drainage-ducts.

Badly manufactured pipes with too small inlet-holes in combination with too much fine sand in the gravel brought in for use as filter in the ditches, caused the failure. The pipes became sealed and acted as barriers instead of water-outlets – which definitely was not what we paid for. Needless to say we do not intend to let others be in control of such jobs in the future.

We solved the problems by digging down alongside the failing drainage-pipes at strategic places, and simply used a knife to cut bigger holes in the pipes. These holes was then covered by thick layers of the kind of plastic-mesh silage bales are held together with – creating large filter-areas so the water can get through while the soil is held back.

Additional branch-pipes surrounded by thick layers of really coarse gravel took care of the rest. The drainage-systems immediately started to work, and the surface sank noticeable as the soil dried out. So far so good.

dig deep, drain shallow…

Now we have our own little digger, and I've reverted to “the old methods” for draining problematic fields. In short: dig deep and drain shallow, and let nature do most of the work.

What this means is that we dig clean-cut ditches and/or holes as deep as we can – 2½meters in places, and surround the drainage pipes with coarse gravel almost all the way up to the surface. This coarse gravel channel water so well that it does in fact make pipes almost redundant, but not quite.

We use long-lasting double-walled plastic drain-pipes with an inner diameter of 5 cm. These pipes are slick-surfaced on the inside and corrugated on the outside, and don't collapse under outside pressure. This means we do not have to be particularly careful while placing them and filling up the ditches, and can immediately run heavy machines over them to pack the gravel and steady the soil around the ditches and holes.

These slick pipes are also easy to clean up if they get clogged by mud once covered, we simply blow them with water under pressure in through the outlets – effectively reversing the water-flow direction. Using a small tank-vagon normally used for transporting and spreading maneur to dump and suck a few cubic-meters of water in and out of the drainage-system in carefully controlled bursts, clears out any clogging well into the surrounding soil down there.

dig deep

Waterlogged soil has natural channels made by the water itself, since the water is under pressure down there and has to disperse and escape as more water pours in. These natural channels consist of thin layers that disperse water over wide areas deep down. Under normal conditions these layers act like baloons, making the surface rise when there's much water and high pressure down there, and then it sinks slowly during dry periods.

By cutting through these natural water-layers to some depth, and filling the holes with gravel to hold back the soil, the pressure is released and the water will naturally rise throught the gravel and pipes towards the surface, and preferably escape through the outlets of our drainage-systems instead of soaking the top soil.

Releasing the pressure means the water won't make the surface rise and fall the same way as before, but if all water gets drained out the soil will dry out too much in periods and the fields will sink into a bowl-shape that'll contain surface-water once it starts raining again. That's like going to the other extreme, and we don't want that to happen on a farm. Consequently: we want to achieve “partial release” of the water-pressure down there.

drain shallow

So, now comes the slightly tricky part – only letting excess water out so as to prevent waterlogging, while keeping a balanced water-reservoir in the soil so the surface doesn't sink too much, and – most important – so the natural water-channeling layers don't collapse and stop working.

There's no way we can replace nature's own drainage-systems, so we want to keep it intact and make it work to our advantage.

In theory this is easy to achieve, but since nature doesn't always play along with our theories and we can't see how the water disperses and creates its own channels deep down in the soil, some trial and error has to become part of the problem-solving process. If it doesn't work well enough first time around, one simply has to figure out why and where, and correct it.

The trick is to lift the drain-pipe outlets to the right level, which means they must let water out a bit higher than the drain-pipes go through the soil so the ground-water keeps the pipes full and under a slight pressure at all times. Drainage-pipes that periodically dry out tend to clog up after a few seasons, so having water in them is important. The pressure from the soil on the water-channeling layers below, will push excess water up and out.

If the levels for the man-made drainage channels and outlets are right, the surface will dry up and be strong enough to carry farm-machines and animals pretty soon after rainy periods, and the water is available to the plant-roots at a somewhat stable level around 30 cm below the surface. That's the ideal, and hardly ever achievable.

variable soil and ground conditions…

What I referred to as “the old methods”, do work fine. In the old days they could achieve near perfect drainage of large fields by digging ditches by hand and build ducts with stones or fill the ditches with gravel or branches. We have access to better technology and materials today.

lost knowledge

However, a few generations of knowledge and experience with a particular piece of land, is a necessary ingredient if one wants success. That knowledge and experience is mostly lost by our generation, so some level of failure is to be expected despite our improved materials and technology.

One has to know what type of soil one is dealing with, and how deep it goes. Any larger rocks in the soil changes the local conditions, and the surrounding terrain and ground conditions play a major role. Give me a few hundred years in the area, and I'll sort it all out to near perfection – locally. Well, I don't think God will let me stay here that long, so let us look at the options.

technicality

One can probe for water-saturation and look for natural water-channeling layers by driving steel pipes (prepared with small drainage-holes along the first half meter) into the the ground. By checking how the water rises one can estimate amounts of water and pressure one has to deal with down there, and create somewhat realistic plans for how to deal with it. This is a working method on many farms, but it can be time-consuming.

One can use Ground-Penetrating Radar (GPR) to map the ground to some depth. However, GPR isn't exactly household equipment on a farm since it's quite expensive and one needs a bit of training in use of such equipment and to interpret the data correctly. Not realistic on the average farm.

One can also remove all soil to a suitable depth – say 1½ meters, create a drainage-layer by pouring in half a meter or more of gravel, and put quality-controlled soil (around 20% humus and 80% sand) back on top again. May work well on golf-courses where one can put in a few millions (any currency) and expect users to pay the bill, but will simply cost too much on most farms. Guess that's why so many farms end up as golf-courses and/or waste-land.

practicality

In real farm-life one has to weigh the cost of perfecting drainage in a field, up against the gains in production and income on a farm. If it doesn't pay off, than there's no reason to do much to improve things.

Since it is often better to drain too little than too much, fixing the largest areas to an acceptable level and to the lowest possible cost, and leave the most problematic areas to nature, is often the best and most practical approach to drainage-problems. This often means use of some areas are very weather-dependent, but that's quite normal in farming in our part of the world anyway.

natural probing

Our animals naturally test the fields they're let loose on, and mark weak areas with hoof-holes – no further probing necessary. If there's no hoof-holes then the area is good enough. If on the other hand there are nothing but hoof-holes, we may have to do something about it – some day.

Some places the easiest solution is to strengthen the surface by pouring fine, preferably natural river-sand, on top, and leave drainage below entirely to nature. A 15-20cm layer of sand will make wonders on most pastures. The sandy layer will carry the animals and farm-machines, and grass doesn't need much organic material to grow in as long as there's water below and regular deposits of cow-dung on top.

Even our regular gravel-roads are green with grass in the midst of summer, and we use layers of coarse gravel to create more solid paths for animals and machines across problematic areas. After a year or two these paths look like the rest of the fields, apart from that their surface does not become water-logged. Problem solved to a degree.

good enough is good enough…

So, we accept some weak spots and failures, and correct things as best we can – when we can. Some of our newly dug drainage-ducts work well, and some don't. This means some of our fields are good for farming, and some aren't so good. No big deal as long as our animals get fed and have somewhere to go.

Since we can attack the problematic areas with our own machinery, we're able to keep things working. Only thing is: we may have to wait for the right conditions so our machines don't sink in too deep and get permanently stuck in the mud.
No chance we'll run out of something to do and things to improve on our farm anytime soon.

sincerely 

Hageland 30.may.2008
last rev: 22.jul.2008