If only everything about Permaculture was exciting as trenches and swales. Knowing the different surface water management tools such as a swale, trench or channel improves every permaculture plan. It prepares us for drought as much as flooding rains.
Channels know where they are going, and get on with it. Whereas, a trench needs to get full before it looks for an exit. But the humble swale hugs the land, and lets it all sink in.
Let’s start with the humble trench a trench is a long hole in the ground it can capture the water and it can hold it whereas a ditch can capture and hold water but it usually gets the water to run away. To move away, for example, from a road or paddocks. In permaculture design we want to use the water at least three times before filtering it and sending it away.
Hugelkultur uses berms made out of wood and leaf litter. These berms run slightly off the contour so that the water, frost and snow can keep moving down the hill.
Berms (mounds) when positioned well can trap or guide water. In this instance, the water originally ran straight down towards the house. So, ta berm worked to trap the water and made the garden more productive. In another example a berm became a swale instend of digging. On our property is very difficult to dig. It takes hours to dig a trench or swale. The soil is solid clay which is good for making pottery. So mounds are easier to construct.
In the 1970s Emile Hazeslip coined the term synergistic gardens. She created diverse microclimates and different levels of moisture for the different plants. These gardens were productive and almost doubled the surface area for growing.
A swale is a combination of a trench and a berm and it sits on the contour line. The water in swale doesn’t travel downhill. It just sits there and seeps into the berm below.
Often a swale is shaped as a wide shallow trench (like a pan) with a berm below. Conveniently, the soil dug out of the trench creates the berm. When the trench is shallow and wide it forms a gentle pathway.
Making the pathways inside a shallow trench is handy for compacting that soil and to keep the garden accessible. That’s because we tend to clear the pathways as we work. We actively reduce any trip hazards. also, we rarely go in the garden when it’s raining heavily. So, when the pathway fills with water but move off quickly. Meanwhile we relax indoors as the flow of water works to clear away debris.
At this farm called Conscious Ground in Mullumbimby, the berm looks really tall. But in fact it’s on a steep slope. This food forest has a wide level trenches and berms on contours across the slope. [If you want help understanding contours, see our student tutorial on mapping and elevation].
The trench is wide enough for several people to walk along together and is accessible by machinery.
Ditches are common water management devices for flatlands with little runoff but they can also be the start of erosion channels. When there’s nothing holding the soil together, the ditch is destructive. Drip by drip, the life in the soil washes away. In this patch of sparsely covered lawn a gully has started. In fact, erosion commonly starts with just a little ditch between a road and a fence
What makes the best swale?
A swale needs three things: a trench, a downhill berm and plants. It needs plants uphill to stop the swale from silting up. And the swale needs plants downhill to prevent erosion by wind, water or animals.
Water distribution channels
Channels work well on large properties (housing developments or broadacre farms). Keyline designs channels to move water from wet areas to dry ridges. Unlike a swale, trench or berm, Keyline channels slowly distribute water. Keyline planning works closely with the contours, the rainfall and soil type.
Plant growth is dependent on access to water. Creating a plans to manage the water naturally builds abundance. And your food forest journey begins.