Sustainable soil structure management and water conservation for small farm Permaculture can be achieved using strategic earthworks.
We’ll show you the basic types of earthworks to make the most of the water that falls on your farm property and how to plan and build them to maximize soil and surface storages.
As they are disruptive to the landscape, you’ll want to have your small farm earthworks in place before undertaking any planting, fencing or soil reconditioning work. It makes sense to plan them all in advance and have them constructed at the same time, to save money on earthworks contractors.
A STRATEGIC APPROACH TO SMALL FARM EARTH WORKS:
Australian farmer P A Yeomans revolutionized farm earth work strategy when he applied clever water conveying practices learned in the gold mining industry to agriculture. His work was a major innovation for sustainable soil structure management and water conservation on farms, and an inspiration to the development of Permaculture.
In the ensuing decades, the resulting Keyline approach to farming has been widely embraced as a practical, low-cost means of:
- Planning the logical layout of roads, irrigation areas, fences, dams, forestry belts and farm buildings
- Building soil fertility
- Making best use of rainfall by storing water in the soil
- Preventing water-caused soil erosion
- Integrating the placement and use of dams on-farm
While the Keyline approach is easiest to implement on larger properties, it has many aspects that can be applied directly or modified to fit into a smaller farm. Over the fence cooperation with your neighbors to enable its fuller utilization can reap benefits for all concerned.
We do not have room to do full justice to the Keyline approach here, but its basic principles are relatively simple and straightforward:
Every hillslope or valley has a midline Keypoint above which the slope is steeper, producing a convex profile, and below which the slope is gentler, with a concave profile.
A contour (a line on the ground each point of which is the same height above sea level) surveyed from this Keypoint produces a Keyline for the valley.
The position of the Keypoint and its Keyline influences all further development on the land:
Deeply ripping the soil – using a non-inverting chisel plough (e.g. a Graham Hoehme Chisel Plough or the specially developed Yeomans Plough) – always perfectly parallel to the Keyline, both up and down slope of it, will tend to spread rainfall away from wet areas and towards dry areas, improving soil moisture, fertility and productivity.
As it is the natural point for water to be directed towards in the landscape topography, the Keypoint is the ideal site for building dams. These are built incorporating a large valve at the base that can be opened as needed to release water.
The water can be conveyed by low gradient (with as little as a 1:500 or even a 1:1000 fall) banks to passively irrigate soil or top up dams also placed on the Keypoints of lower valleys.
Irrigation is achieved simply and cheaply by using canvas to temporarily block the bank, causing it to overflow down the slope to be irrigated. The design of the banks allows for a single person to shift the canvas along every few minutes, progressively irrigating along the length the bank.
The ideal placement for access roads is alongside dam spillway banks and on the crest of major hilltop ridgelines.
The ideal placement for forestry belts is along the graded banks that link the dams in the landscape.
The ideal placement for homestead buildings is at or just below the Keypoint of a valley.
TYPES OF EARTH WORKS:
Building Site Excavation
If you are like us and have a sloping building site, significant earth moving will be needed to establish a level area for buildings and vehicle access.
- From our preliminary surveying work using a simple home-made Hose Level we were able to work out where the best site with minimal work was, how deep the contractor would need to cut into the hill and how high the resulting pad would be above the natural soil surface. We drew this up and showed it to contractors to inform their cost of job quotes.
As the most desirable site was outside of our allotted building envelope we had to also apply to our local council for their approval to move the building envelope to the new location.
This can take a few months so keep you good humor and be prepared to do some of the legwork yourself for gathering evidence to support your application (we managed to get a “no objection” letter from the state department of environment to overcome issues raised by our council officer).
- Once this was decided we measured and marked out the area with surveying stakes.
- It would be a shame to waste beautiful topsoil by burying it beneath tons of excavation. So have your contractor carve off and stockpile topsoil from the building site at a convenient spot out of the way, before the excavation work begins!
- If at all possible, you should arrange to be present while the building site is excavated. Have your site drawings and plans on hand and be prepared to make adjustments to your plan as the work progresses to accommodate unforeseen complications such as areas of solid rock. We used roadmarker paint to show the contractor where the new cut lines should go.
A principle of Permaculture is that dams ideally constitute 10% of the land area of your small farm. They potentially perform many functions in your property beyond simple water storage, including aquaculture, moderating climate and acting as a barrier to fire. The bund of earth that bounds them can also form a convenient access way for vehicles across gullies.
Water storages should begin as high up in the landscape as possible, allowing greater use downslope via passive gravity-fed irrigation as well as overflow to lower dams.
Good dam sites for harvesting surface water flows on small farms occur in natural storm-water drainage lines and gullies, ideally at the Keypoint of the slope. If not placed in a natural gully, Graded banks can be built to funnel surface water into these types of dam.
Potential soak filled dams may also be found where there is natural soil seepage, often marked by the growth of water reeds and rushes on a slope.
The foregoing dam types require the presence of good clay soils to create an impervious lining to retain the water. It makes sense, therefore, to have the sites you have in mind test-drilled for the presence of suitable soils, and also to ascertain if there is excessive rock below the surface. Water can leak out of dams via rock seams, and they also may defeat the abilities of the machine used to dig the dam.
In areas with a high groundwater level, (especially valley floor sands) a soak can be simply build by excavating down to groundwater.
Small farm dams can be built using either excavator or bulldozer. Avoid construction when the surrounding soil is waterlogged or much compression of and damage to soil and land surface may result.
Remember to check with your local council before construction for application and permission guidelines governing your property!
Graded Banks or Levees
Graded banks are surface channels formed by using a grader to cut a channel along a slope and depositing the earth to form a downslope bank to retain the water. The bank should be a minimum of 0.5 m high, and follow the contour with a gentle slope gradient of 1:50 to 1:120. They are often used on slopes to prevent surface runoff from building up volumes and velocity that may cause erosion, and divert it to stable waterways or dams.
To avoid overwhelming water flow, the catchment of each bank should be less than 3 hectares, and their length limited to 400 m or less. Until grass reestablishes on the bank they will be susceptible to erosion, a risk that is increased for slopes that may have shallow topsoil over dispersive (e.g. clay) subsoil.
Swales are simply level sills that are surveyed to precisely follow the contour of your land. Because they have no slope, much of the runoff water that flows onto them spreads and slows down, allowing it to infiltrate into the ground. This forms an underground “water lens” of moist soil below the swale that can support the growth of trees and bushes, boosting the amount of rainfall effectively available to horticulture or agroforestry.
Swales form a convenient pathway on sloping land for access or harvesting your trees. They can be widened over time by further cutting into the upslope side.
They can be constructed on farmland or backyards and arranged to receive water collected by downpipes off buildings, roads or culverts. Laying mulch (e.g. slashed grass) on the swale improves its soil conditions and moisture holding capacity.
Small farm swales are most conveniently built using a GRADER. Whatever machine is used, it must be able to angle the earth cutting blade so that earth is simultaneously cut from the upslope and deposited downslope. Don’t let a bulldozer push build your swales or they will end up as long dams and may even worsen downslope salinity problems.
Swales for small farms can also be hand dug with mattock (grubber), pick or spade. It can also be quite effective to simply arrange rocks and logs along a contour. Over time soils, manure and vegetable matter will accumulate behind them and passively form a swale.
The photo shows swales constructed by a grader on our own small farm property. They expose a shallow layer of heavy soil that is not ideal for horticulture. We will use our stockpile of topsoil to add about 30 cm of good soil onto the swales which will then be ideal for growing a wide range of crops.
Water that infiltrates into soil moves very slowly through the landscape. Unlike surface water, soil water is well shielded from evaporative losses, making it a secure storage option. Such delayed water is a valuable source for topping up dam levels, long after the rainy season has ended, as an effective “drought-proofing” strategy.
Water can be encouraged into the soil upstream of small farm dams by the building of leaky micro-dams.
Designed to leak into the soil (i.e. not clay-lined), leaky dams on small farms can be simply constructed with a mattock and shovel, by scooping earth to form a depression and mini-dam wall along where water naturally flows. The dam wall should be bolstered with logs or rocks.
This practice also slows stormwater flows, reducing erosion, and traps sediments and organic matter creating a fertile mini-aquaculture area for the benefit of frogs and other life.
Consider the potential of all of these earthworks for your small farm early in the planning process. They are effective for many years and are best installed prior to any other small farm improvements.