Swales

A swale is a tree growing system.

It's made by excavating a trench, on contour. The bottom of the trench is the same level from one end to the other.

The soil and subsoil excavated from the trench are placed on the downhill side of the trench. This is where the trees are planted.

Visualise if you will, rain hitting the ground. After a number of raindrops hit the ground in the same spot, their natural tendency is to flow downhill as quickly as possible at a right angle to the elevation contour.

A swale trench will stop that water that's flowing down the hill. Being that the bottom of the trench is perfectly level, the raindrops that flow into the trench will stop and create a level puddle. The puddle will be as long as the trench. This spreading of water is important, as it will evenly feed the next step in the route of the raindrop.

The soil and subsoil that were cast on the downside of the trench are placed loosely. This allows the water in the trench the ability to soak into this mound. The trees planted here receive the water that has soaked into the mound right where they need it, at their roots.

Some of the water that ends up in the trench also sinks down into the ground. This is a good thing too. Deeper roots can access this water. An even better result is that the sinking water feeds aquifers.

As aquifers fill with water provided by swales, they occassionally find their way to the surface in the form of springs.

While the spring is a very valuable result of swale creation, and a filled aquifer are a very valuable result of swale creation, the most important result of swale creation is the establishment of a droughtproof environment for growing trees.

Trees planted on the downhill slope of a swale will be able to access moisture in the ground for growth much longer during the year than a tree not planted on the downhill slope of a swale.

This enhanced access to water can act like a supercharger for tree growth. When local other forests are completely dried out during summer droughts, forests that are designed with swales are working overtime with all the water that swales make available to their roots.

Geoff Lawton, my Permaculture teacher, describes swales better than I ever could. Here's his video on Swales.