 So, another thing I'm commonly asked on courses is, should I make swales? So the first thing you need to know is, what is a swale? Perhaps you know already, but a swale is a ditch on contour with the idea that when water runs down the slope, it gets trapped in the ditch and soaks into the ground. So there's no liner here, we're not trying to hold the water, we're just trying to slow it, temporarily hold it so it can soak into the ground. And swales are best suited for dry landscapes, particularly if you've got a slope which has no vegetation on it, so there's no roots of trees and plants to slow that water and create their infiltration, no root systems to feed the life in the soil where it creates a good structure and allows the water to penetrate the ground, and particularly land that has no cover because land that's uncovered, when it's hot in a dry landscape, that land gets hot, the air in the soil gets hot, the air rises out and when you do get rain it pushes the rain away. So swales are good for dry lands, slopes particularly, I mean anywhere up to a metre of rainfall a year, which is quite a lot, but in Britain, the east side of Britain is drier and so you might have situations where slopes that have been eroded might need a swale system in order to allow that water to penetrate in and get the vegetation going. But very much a temporary, almost a one-off intervention in the sense that what you're trying to do is to establish plants and trees to stabilise that slope, you shouldn't be needing to dig swales on a regular basis. So here I'm standing in a ditch, it's actually not a swale, but it's here and I can talk about it in a way that perhaps it was, so if this was level on contour rather than a slope, then instead of the water on Dartmoor, instead of the water coming down, being collected here and draining gently away rather than going at speed, the water would be held and would soak into the ground. Now here on Dartmoor we don't need that, it's about two metres of rain a year, there's a lot of precipitation and there's no need for holding the water, there's plenty of water in the soil and here particularly there are trees in the landscape here and some vegetation behind. But what this does show is that when water comes into a place like this, so there's a fairly steep drop into the swale and then a gentle fall away, you'll get an accumulation of material like this, so a lot of leaves here from the trees, but also we get a bit further down, it's a very nice material and over time this will fill up, this whole area will fill up and we'll end up with a terrace, now that will take quite a lot of time and the thing is that a terrace is actually a good thing as well because then the water is slowing down on the terrace, it doesn't need to have this ditch in the long term. Now when we plant swales we also put trees on the bank, top of the swale and also often trees behind and those trees will be able to take advantage of that extra water that's being held here that seeps into the soil and into the water table and then they can support, the water supports the tree and in turn the trees support the structure that you've created, so when we make the swale we take a little bit of the soil from here and we put it slightly downhill okay and they can be, swales can be quite small or they can be really quite big if you have a lot of rainfall that falls in a short period of time, sort of monsoons and things then swales need to be able to accommodate that water without overflowing and then disappearing down the slope, so a swale has to be able to take the water from above and hold it for long enough for it to soak in, now if you're, if you have quite a long slope then you need a series of swales down the slope so there would be this one and then some distance down there'll be another one and so on so the water that falls between this one and the next one down is collected in that one and it has the ability to capture that and hold it and soak it in. How do you know how big your swales need to be? How far apart? Well you just need to know things like your geology and the slope of the and how much rainfall you have and there is actually a website called the swale calculator and you can just go there and type the numbers in it does all the sums for you which is great. So do you need swales? If you've got a fairly dry landscape you don't have a lot of rainfall and when it rains it runs off then almost certainly yes because that's about remediating your soil if you get plenty of rain then really there is no need you may even need to put in drainage but certainly not swales.