One end of our property has a stream bed that is dry almost all of the time, accept when we have heavy rains. It is fed by uphill runoff and springs to some degree. In 2010 heavy water flow, most likely increased by logging done uphill and off property started to cause erosion and extend the stream bed in a new path. In 2011 a wet spring and the tropical storm Irene later that season tore a massive gully. Since that time when we have had several inches of rain in a short duration more erosion has happened and the gully gets wider as the sides fall in. The gully is headed out toward our lower field where we had hoped to continue rotating our animals for grazing and eventually have more garden space. When flood water hits the field it carries a lot of sediment, floods certain sections of the field then rushes to the lowest point and off property where it does damage to a neighbor’s logging road.
Our soil is very sandy and well drained. Generally when the rain stops, it is quickly absorbed and water logged soil is not an issue. So, we hoped to find a solution to this flood/drought situation with a little earthwork. Our intention was to decrease the erosive force of water entering the field by slowing it down, spreading it out, and giving it opportunity to soak in where we want to store it. We had done some consultation with Mark Krawczyk of Keyline VT a couple of years ago. He suggested trying to slow the water flow as high on the landscape as possible by creating step dams, which we have done to some degree over the years. He also suggested digging swales on contour in the field. We tried tackling this by hand and did dig two shorter swales by hand, but they did not connect to the water flow. This spring we decided to step it up a notch and rent an excavator and hire Mark to lay out the swales and dig them.
Swale is a term that can mean different things. From the permaculture perspective it generally means a water harvesting ditch that is built on contour. A swale is different than a ditch that is intended to carry water away as fast as possible off a property or away from something like a road. Here is a good article that explains swales more in depth. As water from the gully or from general rain runoff runs into each swale it will follow the low point along the contour and sink in under the berm. If there is enough water to fill the swale, it will overflow at the spillway which is a lower place in one section of the berm. It will then move onto the next swale. We constructed a series of 4 swales with enough space in between to be able to graze animals and allow for mobile fencing and housing structures as needed. Hopefully enough capacity is built into these swales to be able to diffuse the force of water in extreme weather events, and allow us to hold on to as much of that precious resource on site as possible.
Next spring we plan on planting trees all along the berms of these swales. We still have some planning to do regarding what types of trees we choose, but they will most likely be a mix of fruit trees and bushes, nitrogen fixers, nuts, and some that can be chopped for mulch and forage.
We hope to have just the right amount of rain to germinate the seeds and get good plant cover growing before any testing of the swales happens. We’ll keep you posted.