Putting Our New Swales to the Test
One of the first things we did when laying out our food forest was plan for water management. There is a shallow valley running through our property; most of the time, this valley is dry, but when it rains hard, it can turn into a river. Our goal was to slow down this water and allow it to soak into the soil, as well as reduce erosion. What would Bill Mollison and Geoff Lawton prescribe in this scenario? Swales on contour!
An on contour swale is essentially a ditch that is perfectly level. This allows water to run into the swale, but since it's level, the water simply stands in place. After a swale fills, it can take a few hours to a few days to soak into the soil and become dry again. The results are twofold... we're replenishing underground aquifers that had long dried up, and we're cleaning the water by slowly filtering it through our mycorrhizal rich soil and detoxifying plants & trees.
This winter, as weather permitted, we installed three swales where our food forest was planned. Each swale is about 130 feet long (a couple will be extended soon). They were dug with a front end loader on a Kubota tractor. Each swale ended up being about six feet wide by about four feet deep. The dirt that was dug was placed on the downhill side of the swale. We then tilled and planted the downhill side of the swale with an assortment of grasses, legumes, and flower mixes, as well as various trees. We're using a lot of red alder (Alnus Rubra) and black locust (Robina Pseudoacacia) in the food forest due to their nitrogen fixing qualities.
Up until now, our swales had only seen a couple inches of water sitting in them. But a recent storm brought in a crazy amount of rain and put the swales to the test. In the photo here, you can see the swale is full and has just reached the level sill spillway. This spillway provides one spot where excess water can drain out of the swale without damaging or eroding the rest of the swale. At the peak of the storm, this spillway was gushing with water, but no other part of the swale was breached - job well done!
This trial of our swales showed a lot of success and we were very happy with the results. However, it also pointed out a few spots in our swales that need to be touched up. In one spot, the swale wall is just a bit too short and needs to be built up a couple inches. In another spot, the spillway need to be leveled a bit. But the biggest need is new plant growth on the bare dirt. Thankfully, grass and crimson clover have already started to sprout and the lupines should be sprouting soon.