Call me ignorant but I have no idea what swales are. I've seen the word a lot on this site and others but have no clue as to what they are and how they prevent erosion or if that is their main function.....
Can someone help????
Until I started reading up on permaculture, I had no idea what swales were either! Don't feel bad!
A swale is a slight depression that runs along the contour of the land. That is to say, it is level all along its length. It can be deep or shallow, or even hidden (a ditch filled with gravel and capped with topsoil), and the dirt from digging the swale is usually used to make a berm on the downhill side. A common sized swale is two or three feet wide. Of course, you can make them any size you want. An important distinction is that a swale is not a drain. It is a water collection device. The cheapest way to store water is in the soil. And of course, by stopping the run-off, it prevents erosion as well.
How it works is this: Rain falls on your property, and instead of running straight down the slope, it runs to the swale and gathers. There it soaks in slowly, forming a lens of water underneath the swale. This provides a plume of shallow sub-surface water downslope from it for an amazingly long time, so your grass will stay greener, and you won't need to water very often.
Eric in Japan
eric has got it one, but swales can be constructed (if that's the right word) in many ways ie.,. you could run rows of hay bails end to end if the slope is steep drive a garden stake through the middle of each as it takes time for this type of swale to settle in; or use a single tine ripper behind a tractor and rip along the contours (my favourite way less cost & physical input & they can be used as temporary so you can put a new swale elsewhere plus if you are planting trees planting them along the rip line is better for all concerned), we ripped ours and it has worked very well indeed, just simply didn't realise how well it would work; or you could plant rows of the tall clump like grasses eg.,. lemon grass/citronella grass, you will have 2 or 3 rows of plants staggered to form the swale as with the hay bails they will trap debris and act as a swale plus their root systems will give the key for the water to soak underground.
the trench swales to me are more labour intensive to install and pretty much a permanent aspect of you landscape, where as all the other ideas can be temporary depending on your changing needs. from my observations if you have heavy clay soil using grasses or rips will work better as if you dig a trench in particular this willa ct more like a dam and the ability for the water to soak in may be restricted, just something to take into account. also with the otehr type constructions you don't need to be so exacting with constructing along the contours just a by eye level will do.
lens garden page
silly me forgot my most important consideration in developing swales, i have planted all our food trees along the contours and as well as mulching around the trees have muched between the trees this forms a row that also acts as a permanent swale it is not inconvient in the landscape and as it breaks down improving the micro-system we keep adding to it & feeding the food trees. this setup in our system is now taking over from the rips, so you can see if you plant along the rips you still have that benefit as well though out of sight.
Suggest visit to Yorkshire for a whole dale of swales.