Written by Doug Crouch
Swales in a Pattern Reflection
In a pattern sense, swales deal with pulses of energy also seen as a wave, just as sound frequency moves in waves. Their shape is a ditch and a mound and one summer in
Portugal we built a swale at the beach to demostrate the technique and take advantage of the easily moved substrate for teaching purpose. This reflection, seen in a picture below, became so evident after the onlookers stopped staring intently and we sat back and enjoyed our earth scultping in the soft material. In nature now, there are pulses of energy, wave in form and disturbance in function, flowing down landscapes often causing spirals of erosion. Water runoff in rain events lifts soil particulates which has a cascading affect of negativity in watersheds below and farm fields above. Hence the Permaculturists attitude that swales are so great as they can help to reinforce the pattern of the overbeck jet- growth and return, true regeneration. They infiltrate water that normally would runoff thus supporting perennial vegetation and a flourishing soil food web which helps to rebound bio-diveristy in general.
A swale indeed in practical terms is a ditch and mound, or berm and basin, on contour. Contour being the key here as swales, unlike diversion drains, are meant to infiltrate water not move them around such as what a canal or water channel would do. Be careful however in your terminology as some people around the world do refer to diversion drains as swales. So it’s important to distinguish this on contour factor whenever the word comes up so there is no confusion. Seen below are some aerial and topographic maps to aid this understanding.
Contour is established through using leveling devices and it is part of your design steps to ensure a successful implementation of this water harvesting feature. You can do this with the following tools in the field and are aided by detailed GIS maps:
- Bunyip Level
- Dumpy Level or Transit Level
They all can work well but it depends on the scale of the property and the unevenness of the terrain in a small-scale because of ground alterations. A-frames are a great small-scale device and can be made for the cheapest and done with basic things in a jungle if you have a saw. They use the A shape and walk through the landscape finding level with a dangling measuring tool which is calibrated at the onset of its completed construction. The bunyip level uses water itself inside a clear plastic tube with two measuring sticks on either end. Water is the ultimate teller of level and this device is very accurate and can be scaled-up for larger properties by making the tube longer. Transit levels and laser levels work on the same principle of having a stationary unit that looks out towards a person holding a very large measuring stick. With the laser level, no one has to be at the machine making it essentially a one person job whilst the other requires an operator of the transit level as well. Laser levels simply emit a laser and the stick has a receiver for the laser indicating which direction you need to go on the hillside to find level. The laser level can be extremely quick but the beeping is a bit annoying and the laser itself can be damaging to the eyes. GIS maps that have contour features also help us with our initial planning but remember “the map is not the territory”.
Water Sources for swale intervention
Swales are not fit for every site and climate context. However if you are observing overland flow that is causing erosion or noticing a lack of overall humidity to kickstart ecosystem regeneration, swales might indeed be the fix. I often use swales in conjunction with obvious roof, pavement, or compacted surface runoff; known as impervious surfaces. These all concentrate water in an unhealthy way and lead to a half hydrological cycle. To complete the cycle of hydrology, we need infiltration so that groundwater recharge can
happen and eventually springs reemerge. In sandier soils, such as half my families land in Northern Kentucky on the side closer to the Ohio River, there is very little overland flow even though lawn is the predominate land use because of the recreation business that is present. Even with roofs shedding water this portion of the land rarely has any visible need for a swale. There is a couple of obvious spots however, because compacted road surfaces issue huge volumes of water into concentrated points. Getting the water off the road and sinking it into swales is a great remediation trick and passive irrigation for future tree crops and windbreaks. On the other side of the valley farther from the Ohio River and its sandy outwashing, more typical clay soils of the area persist and give a great opportunity to catch higher flows of water and spread it across the landscape. Swales can be adjoined with pocket ponds in the keypoint to greatly aid this spreading effect. Furthermore, in my parents plot 15 minutes from the city center, a large swale (100 ft or 30 m) was created in the backyard suburban landscape to deal with the tremendous amount of water that comes from the roof. This lead to an edible landscape being created on the mound of the swale and with the ditch being the speed bump for the water as it previously came racing down from the pipes that brought guttered water into the backyard.
Ditch and mound on contour with perennial vegetation
Perennial vegetation should accompany all swales. These earthworks have non-compacted bottoms to facilitate water infiltration and also have a non-compacted mound which essentially becomes a raised garden bed. Depending on the climatic context, you can plant on top of the swale mound or just below it. In drylands you plant just below it, the toe of the swale where the earthwork hits the unaltered land. This is the best place for tree crops in the scarce water situations while hardy nitrogen fixers can go on top of the mound to pin the earthwork together and further increase the infiltration rate through accumulated organic matter percentage in the soil. In more humid climates planting on the mound is often warranted especially in heavy clay soils where you need more drainage. Tree crops thrive on these earthworks as water passively irrigates the mound or toe with the roots of the trees smartly searching for their essential watery nourishment.
Plants should be stacked in space in time, food forest style, especially with support species that fix nitrogen, slow wind and provide other useful resources such as animal or bee fodder, firewood, and medicinal plants. These nitrogen fixers and other biomass producing plants will help to repair soils after the earthwork is done.
Ditch and a mound on contour with perennial vegetation and soil food web stimulation
Soils that have been altered through earthworks like swales need to be accelerated in terms of soil food web succession and evolution as to support the infiltration and subsequent plantings. This can be done in a myriad of ways but most commonly done through adding compost to the mound, spraying compost tea or extract, adding microorganisms from EM sprays or lacto-ferment dilution sprays, and mulching the mound and in some contexts the depression. By chopping and dropping vegetation over time, soils are improved by the breakdown of organic material above and below ground.
When plants are chopped a portion of their roots also experience a slumping off to match the core model proportions of above and below ground plant material. This is one strategy of mulching in the long-term but short-term mulching may include bringing material in from the outside, which is a common Permaculture technique as to take
advantage of carbonaceous waste streams. Wood chips sometimes can be procured from utility companies or straw bales purchased. Leaves in the fall time are sometimes in abundance especially in North America where lawn owners happily rake them religiously each fall and conveniently set them bagged up curb side for our taking. Running these over with a lawn mower increases the edge thus breaking the material down faster and also preventing blow away, which is common in the dry winter areas where winds also whip due to the lack of leaves on trees. The depression can also be mulched and should be quite often because it represents an edge that can dry the whole earthwork out in the hotter and drier periods. This will also give better soil structure thus further increasing percolation to recharge groundwater.
A ditch and a mound on Contour with Perennial Vegetation, soil food web stimulation, and human interaction
Humans should creatively interact with swales over time to ensure their continued success. After the initial digging has been done either by humans or machines, again plantings should commence along with soil biology repair. Continued efforts to manage succession on the mound and in the soil should take place. Initial plantings can be further leveraged through plant propagation as subsequent phases of implementation come and succession changes. For example you may only have enough chives and comfrey to do a small section or specific guilds around the main tree crops known as anchor plants. You can continue to divide these plants out and further stabilize the cultivated ecosystem with their abundant plant material. I use both of these plants as edging plants where the top of the mound begins to drop off on either side to create a terracing affect all the while protecting the mound from erosion. Comfrey also greatly shades the mound on these edges as to protect it from drying out.
Furthermore one of the most important things humans must do over time is to manage the accumulation of soil in the bottom of the mound and check the spillway. Every swale needs a spillway, or exit point at which the water flows out. These need maintenance over the years to ensure that erosion doesn’t weaken the system and that they remain the low point for this designed exit. Over time the mound does erode so scooping soil out of the bottom and putting it back on top of the mound in low spots helps to maintain the wave pattern. Swales are implemented in degraded landscapes most often so there will be runoff that includes soil particles and organic matter. We can improve the longevity of the swale by creatively interacting with nature as this management regime should be planned into the design process.
Swales can be created on numerous scales from tiny hand dug backyard ones to kilometer long ones dug by a machine. On the smaller scale they are usually 3-5 ft wide (1-1.5 m) and 50-100 ft (15-30m) long. Their depth corresponds to the width and don’t make the sides too steep in hope of a greater water holding capacity as steep sides equal an increased rate of erosion which of course requires more maintenance. Remember 3:1 slope dimensions when creating and don’t try and go to deep, rather remember gentle
entry and exit angle. On the broad acre swales are created by heavy machinery and can be doubled in size as the previously mentioned length and width dimensions. However, the cost of doing swales on the broad acre rapidly builds and where possible keyline should be utilized as Darren Doherty claims that Keyline is 1/100 of the cost of implementing swales on the broad acre. I believe this to be true after project management on several big projects and seeing the cost of implementation and the follow-up of perennial vegetation, soil repair, human labour, and maintenance. Keyline is much softer on the landscape, creating more edge and lots of mini swales instead. Thus I believe swales are more of a zone 1-3 application but zone 2 seeming to be its best fit. Remember to start as high in the landscape as possible so that the earthworks can be downsized.
Finally, swale spacing is always a question of great importance. Again this is landform, slope, ctachment area, soil type, and climate contextually dependent. Peter Bane in his book the Permaculture handbook recommends in general swales be created at a rule of thumb spacing of five to six feet ( 1.6- 2 m) elevation change. In drier climates you tend to create swales spaced further apart but when big catchments are involved then they are spaced more closely. In more humid climates they are spaced closer together. In the Mediterranean dry summer/ wet winter I had the pleasure of implementing swales at the school I was teaching a PDC at in the winter of 2009 at Escola da Terra in Sintra, Portugal. Known for its heavy winter rains, in 2009 Sintra had an extremely wet winter. The school site topographically happened to receive heaps of runoff that formed a small stream from roads and roofs. Thus we implemented one swale during our PDC. Quickly we saw one it was not enough and instituted a second so that more water could be caught. The torrential rains persisted so we altered a raised bed to become our third swale. This herring bone design had swales really closely spaced but again we had plenty of catchment bringing huge volumes of otherwise polluting water. Watch this video on that project implementation or look at the pics and maps below.
Written by Doug Crouch
Header Art Bonita Edwards