I’m so pleased with the reception to my previous glossary article, “10 (or More) Common Garden Terms in Permaculture”, that I’ve decided to try another list of 10-plus words centred around water-harvesting. With that in mind, it might behoove us all to define water-harvesting as seen in permaculture, which is a bit more expansive than the 55-gallon barrel beneath a rain gutter spout.
From that quick overview, we’ll get into some of the jargon that comes up repeatedly in permaculture design, which focuses hugely on stopping, spreading, and soaking water throughout the landscape. Harvesting water is often one of the first issues a designer tackles when looking at creating a site, so to understand why a design is as it is, it’s important to appreciate what’s happening in terms of water.
Basically, the permaculture notion of water harvesting runs contrary to the conventional agricultural (and development) method of draining the landscape quickly when it rains. Rather than installing ditches and other methods to whisk water away, permaculture design will try to capture and hold as much water as possible before allowing it to leave a site. In this way, it’s far more than filling a tank of water from the roof. It involves hydrating the entire landscape.
In addition to using rooftops, permaculturalists must be aware of the natural drainage of a property, as well as look to other hard surface, such as driveways, for opportunities to direct and catch more water in a rain event. On top of rainwater, this water-harvesting effort also includes methods for conserving and reusing water so that we maximise the water we use and continually cycle and naturally clean it.
A huge part of harvesting water is recognising slope, aka gradient, in order to choose the correct water harvesting technique to fit the landscape. Slope is expressed in a fraction, derived by putting rise (the vertical change) over run (the horizontal change). So, if a landscape rises one foot for every three feet of run it has 1/3 slope, also sometimes put in the ratio form of 1:3. Gradient (or grade) is a means of expressing slope via percentage, converting the rise over run fraction into a decimal and multiplying it by 100. In the case above 1/3 equals 0.33, so when we multiply that by 100, we get a gradient of 33%
With that in mind, a contour line moves along the landscape at the same vertical (rise) position, which makes it a level line. The reason these contour lines are important to recognise and locate in water harvesting is because, when water is level, it doesn’t then drain or move in a specific direction. Rather, it fills up a space equally, as happens in a bathtub. Catching water along level contour lines pacifies water flows, preventing erosive damage from water runoff and distributing the water evenly over the area for infiltration into the earth.
Swale and Berm
Swales are a commonly used and hugely important water harvesting technique in permaculture. Swales—in permaculture terms—are level-bottomed trenches dug along a contour line in the landscape. This level trench, or basin, interrupts the downhill flow of water, disperses it along that contour line (often over long distances), and allows the water to permeate into the ground rather than drain away. Often swales are used in conjunction with dams and/or ponds both to increase the catchment area feeding the dam and as an overflow system to protect the dam wall.
A berm is just a raised section of earth, often used to contain water. Berms—in this case—are created with the earth excavated when digging a swale. This soil is piled into a continuous mound along the entire downslope side of the swale, helping to hold the water in the swale. Berms (and the slopes immediately below them) are planted with trees, which can benefit from and help moderate the water held in the earth. The swale-and-berm combination is used as a tree growing system for orchards and reforestation.
Here, the terminology becomes a little confusing because they are used differently depending on what country one is in. In either case, what we are talking about is a landlocked body of freshwater.
In order to clarify, first, we are going to go with the Australia version because that’s where permaculture originates. In this scenario, there is a dam wall holding back water to create a dam. The dam is the actual body of water. A pond is a subterranean body of water with a water surface at land level, and it can be either naturally formed or dug into the earth by man. A dam is never natural, save for when beavers create them.
In the US, the terms get a bit more muddled. The term pond typically applies to any landlocked body of water that doesn’t qualify as a lake, and the term dam is used to reference what is actually the dam wall. In other words, what Australians would refer to as a dam, Americans would likely call a pond. Furthermore, what Americans would call a dam, Australians would differentiate as a dam wall.
Another thing that permaculture designers should be aware of is that there are many types of dams, such as check dams, turkey nest dams, keypoint dams, ridgepoint dams, saddle dams, and so on. Explaining the differences between all of these would be an article all on its own.
Gabions are kind of like intentionally porous dams. They are stacks of rocks congregated and held together in wire baskets. Gabions are commonly used for erosion control where land has been cut away on hillsides, holding the upslope earth in place. In permaculture, particularly in drylands designs, gabions are used in gullies where water flows. Rather than holding the water back to create a dam, the gabion slows the water down but allows it to flow through, dropping sediment behind it rather than causing further erosive damage. These sediment deposits then behave like sponges, in essence storing moisture in the desert soil, safe from the sun and evaporation.
Level Sill Spillway
A spillway is like a safety valve for different water storage situations, and characteristically dams, ponds, and even swales have one. Not only do they insure that a rush of water, say from a serious storm, doesn’t threaten the integrity of the berm, dam wall, or pond edge, but also strategically designing a spillway allows the excess water to be directed to another water catchment. Permaculture landscapes will often have a series of spillways and catchments that work down a slope, catching and storing water all over the place.
A level sill spillway is a type of spillway that helps to pacify water flows as much as possible. Rather than something tall and narrow, like a ditch, a level sill spillway is wide and completely level so that water moves over it evenly. This is very useful because it prevents the draining water from building up a huge head of steam and wrecking the landscape downslope. Instead, the level sill spillway disperses the overflow, mitigating much of its destructive power.
Hydroponics, Aquaponics and Aquaculture
Often these terms are misapplied. Hydroponics is growing plant crops in water that has nutrient added to it. “Aquaculture”, as used in the mainstream, is synonymous with fish farming: Fish in tanks or controlled ponds fed fish food. Aquaponics combines these two, cycling the water fertilised with fish manure to grow plants (hydroponics) and feeding the fish to harvest them for meat (“aquaculture”). In short, this makes aquaponics well-suited for urban areas, where space is confined, because plants and fish are often grown in the same square footage.
True aquaculture, as defined in permaculture (via Geoff Lawton), is the ideal option. This is essentially creating an ecosystem with a body of water at the heart of it. Then, plant food can be grown in and around it. Fish can be harvested from it. No fish food is required to feed the fish because they can eat insects, wild plants, and other fish (depending on the type of fish). Wild animals can use it for habitat, as can domesticated water fowl like geese and ducks. And, once in place, it requires very little interference from humans.
Greywater and Blackwater
Making the most of the fresh water we have is part of water-harvesting in permaculture, and knowing the difference between greywater (still usable) and blackwater (highly contaminated) is important.
In the simplest of terms, greywater is the household water that has been used to wash dishes, clothes, bodies, floors, and so on. With simple filtration systems, it can be safely repurposed for irrigation, after which it returns to the natural water cycle. Greywater systems will often either release this water subterraneously where soil biota cleans it up or filter it through reedbeds to remove any fats, oils, or soaps that might be problematic.
Blackwater is what we create in the toilet or when using toxic chemicals, and that isn’t safe. Generally, full-on permaculture systems will opt for dry composting toilets instead of flush toilets to avoid creating this blackwater waste, which is difficult to deal with. Instead, composting toilets create rich compost that can be added to the base of fruit trees as fertiliser. Toxic chemicals are avoided as well.
Reeds, which grow in water, are efficient absorbers of excess nutrients, and that makes them fantastic filter systems for greywater. Greywater from homes is sent into small, open tanks (or even lined ponds on the large scale) filled with gravel or soil so that the reeds can grow in them. These are meant to mimic wetland ecosystems, which are great cleaners of water.
The roots of the reeds create complex networks the soiled water must move through, as well as the ideal habitat for aerobic microbes, which are the key to cleaning the water. The reeds can periodically be cut back and harvested for mulch material to add to gardens. While there are other greywater filtering systems, reed beds are a common, biological solution in permaculture designs.
Mulch Pit/Infiltration Basin
Mulch pits, also known as infiltration basins, are large holes dug in the earth so that water can congregate and soak in. They are often put near trees that will, as with swales, benefit from the extra moisture, as well as help to mitigate the amount of groundwater in the landscape. The infiltration basins are often filled with organic materials, especially bulky stuff, hence “mulch pit”. The mulch in the pits not only shields the water from evaporation, it also adds nutrients to the water, as well as absorbs and holds a lot of the moisture itself.
One of the better-known uses for mulch pits is creating banana circles. The pit is dug roughly two metres across and one metre deep. The excavated earth is piled in a ring around the hole, and the hole is filled with mulch. Bananas, yucca (cassava), and sweet potato are planted in the ring. These crops benefit from the rich, moist growing environment, and they also provide enough organic material to continually recharge the mulch in the centre. This works especially well in the wet-dry tropics, where six-month droughts are commonplace.
For more information on water harvesting specifically, Brad Lancaster wrote something of three-volume bible on the topic: Rainwater Harvesting for the Drylands and Beyond. It’s worth checking out and is frequently referenced by permaculture designers.