Swales and Water Retention
What is a Swale?
So according to this definition any low lying area of ground could become a swale. How can we use this to our advantage, let’s take a look. As water is a finite resource we want to be mindful of our responsibilities to conserve those resources using it to the fullest of our ability within our own land. First we want to conserve the consumption within the house, but that is for a separate post at a later date, today we will focus only on the outside of the house. So the rain that falls within our property runs across our property from the highest point of our land to the lowest point. As it does so a portion of the water is absorbed by the land based on the soil absorption rate, the amount of water that is running across the surface of the land, the amount of absorption material on the surface of the land, and the amount of vegetation on the land.
By determining the contour of the land you will be able to understand how the water flows and where we need to place the swales for maximum efficiency. The contour of the land can be determined using a transit, surveyor’s level, sight level, or an a-frame level. The a-frame is the cheapest of the options so that is what I used on my own property. I fashioned the a-frame from scrap wood in just a few minutes, a picture of my creation is shown below.
Now that we have the contour of our land determined we will be able to create our swales. Our land has the highest point at the rear of the property on the left so our contours will run like the picture below.
Now that we have the contours established we can start to add our swales. Because we are in a municipality, I do not want to create large berms with swales as I would in an rural setting. So we have decided to build our swales as our paths running across the property. We will use a system of smaller depth swales as feeder swales to join the system together and direct the water where we wanted it to go. Our contour swales will be 2 foot wide by 1 foot deep with 4 inches of gravel in the bottom of the swale. This will help to slow down the water captured within the swale allowing it to be absorbed within the ground. The rest of the swale will be filled with mulch specifically wood chips. This will help to absorb the water also slowing it down and at the same time providing a soft cushioned path to walk on almost like cork. Because we planned to use wood chips, we also added 4 inches of compressed leaves between the gravel and the wood chips. We hoped this would offset any leaching of nitrogen caused by the wood chips while also saving us a little money purchasing the wood chips.