Slope and Aspect

Following on from last month’s concept of energy flow, in this Part 5 of this exclusive Equine Permaculture Design Series, Mariette van den Berg explains the design tool that permaculture design consultants use when deciding the best placement and layout of a property. This time focusing on the shape of the land and how we can find ways to use it to our advantage. 

When it comes to horse property layout, it pays to consider the permaculture design approach because it aims to build systems that are easier to manage, more efficient and sustainable, whilst considering the health and wellbeing of all – people, horses, plants and the soil that sustains them. 

When we design the layout of our horse properties, we cannot ignore the importance of the shape of the land. When we are dealing with uneven ground, such as slopes, hills and valleys, further design considerations need to be taken into account because the contour of the land has a pronounced effect on the flow of energy in our overall system.

If you are managing horses on a hilly property, you will have experienced the effect of the slopes on water flow, soil condition and grass cover.

With any slope, gravity will move things from the highest point to the lowest and we can take advantage of the work performed by gravitational forces to make our system more energy efficient.

The main emphasis of designing with slope is efficient energy flow. In this article, we will describe how the shape of the land affects natural energies, such as water, materials, heat, erosion control, fire control and aspect.

Water capture and flow

Put simply, water is the world’s most valuable life-sustaining commodity!

Without water, we don’t get very far on a property. We need water for plants, animals and ourselves. Therefore, water and how it flows over your land is one of the first energies you have to identify, so you can design in terms of maximising harvesting.

Since water flows from the highest point to the lowest, any slope can be used to move water downhill.

We can exploit gravity by situating water storage, such as tanks or dams, uphill on the higher points of a site, as this allows natural forces alone to supply a flow of water without needing additional energy to power a pump.

In addition, we can place our dams on the ‘key point’, which is not only the highest ideal placement for water catchment in a valley, but is also a likely place to find both a spring and good clay as it is the initial point of deposition in the landscape.

The keypoint referred to in the diagram on Page 36 is the area or plateau that lies between the convex slope above it and the concave slope below it.

Important to note is the keypoint is not actually on the inflection point, but a little further downhill from the actual inflection point, still along this central path of the valley, where the force of water movement changes from erosive to deposition. This where you can place your so-called keypoint dams. Here you can capture more efficiently water and prevent erosion.

Another way to capture more water on a slope is by the use of swales. Swales are on-contour, level banks that store water and soak it to deeper underground reservoirs.

A swale is not a drain! The words on-contour and level are very important because this helps with slowing down the movement of the water and preventing erosion.

Swales have a special width and depth, and on the lower end a little mound is made. This area is typically vegetated with a cover crop and, later on, shrubs and trees can be planted to stabilise the banks – and, at the same time, you can use it to grow fodder! In a future issue, we will discuss this in more detail.

Another way to capture water or redirect water flow is by using gravel pits with reeds growing in them, which can serve as a wastewater (grey water) treatment system. The idea is to build these grey water reed beds downhill from the house or horse stables, so waste or soiled water can flow by gravity into the reed beds, where it is cleaned and then directed into a pond or swale situated further down the slope.

As an alternative to using a reed bed wastewater treatment system, the greywater from the kitchen, bathroom and laundry can be directed to an orchard that is located downhill from the house.

Structures that have a large roof areas for rainwater harvesting, such as horse shelters, sheds, workshops and other such buildings that people don’t live in, can be located uphill from the house, to capture rainwater, which is collected in water tanks located next to these structures, and fed via gravity to the house and/or stables.


Like water, the movement of resources and materials from the high areas to the lower ones uses less energy than moving them across level ground, and considerably less energy than moving materials uphill.

By locating access roads uphill of the house, less energy is expended distributing any materials throughout.

Similarly, growing timber for firewood or plants for mulch uphill from the house makes it easier to bring the material back to where it will be used because the load is carried downhill.

How heat moves

Another very important aspect to consider when designing is how the slope affects the air temperature.

Heat behaves in an opposite manner to water, as heat rises upwards, as does warm air. Conversely, cold air, being more dense, sinks and flows downward.

Dams and bodies of water situated downslope can reflect heat, as well as act as a thermal mass, heating up during the day and releasing the heat at night. Since heat rises, the heat emanated will rise upwards and warm the upslope area.

Similarly, we can place plantings of tall trees on a slope to retain heat, to warm the incoming cold night air that flows down the slope.

When the warm air moves through the forested area, it will have warmed up as much as it can and, on reaching a plateau at the end of the forest, all the warm air will begin to rise, creating a thermal belt, which will be warmer than the surrounding area.

If we place a house in this thermal belt, it will be warmed naturally (see next page), which shows a thermal belt at the keypoint on the property design.

We can also take advantage of the fact that hot air and hot water rise to set up the collection point downhill, which allows us to use the energy above the collection point. For example, if we set up a solar water heater on a lower level, the hot water will naturally rise upwards by convection, it can then be stored and accesses from an elevated tank.

A solar hot water heater is basically a thermosiphon, a passive heat exchanger that works by convection to circulate water without a pump. The water starts to move when the water inside the collector is heated by the sun. It expands, becomes less dense and, therefore, lighter, and rises to float above the cooler, denser, heavier cold water. As the convection moves the hot water upwards, out of the collector, cold water flows by gravity into the collector where it, in turn, is warmed up and continues the cycle.

Erosion control

Most horse owners will be aware of the importance of erosion control, especially on hilly properties. Having vegetation, such as shrubs and trees, will help control soil erosion and a forested steep slopes also warm the cool night air to create a thermal belt as described previously.

When water runs downhill, it will carve its own watercourses and gullies, washing away the soil in the process. Trees, vegetation and ground covers absorb the flow of the water and, by creating a buffer between the flowing water and the soil, they control erosion.

This is why it’s also important to maintain  good grass cover in your pasture areas. Healthy topsoil and good grass cover will act like a sponge, soaking up the water, and reducing direct and fast run-off.

Water flows fastest straight down a slope and the effects of erosion will be most pronounced when water has the most direct path down a slope. Additionally, when water flows fast down a slope, very little of it is absorbed into the soil.

As mentioned earlier, by digging trenches along the contours of the slope (swales), the flow of water can be slowed down and diverted sideways on its downhill journey, slowing it down and allowing it to soak into the soil.

Likewise, when constructing paths, tracks, laneways – for example, for paddock paradise set-ups – and fences, it is best to have these run along the contours of the site, rather than down the hill. Downhill running paths will create significant soil erosion, because there are no ground cover plants protecting the soil on a cleared path.

Fences holding horses will become tracks as horses walk the fence-line day after day, so its best to avoid running any fences straight downhill, if possible.

Fire control

If you are located in a bush fire prone area, it is very important to include a fire sector in your design.

In addition, you should also have a fire management and evacuation plan in place for your property, in case a bushfire strikes you! Your state government and horse industry websites offer emergency plan advice, and have information about how to best manage horses in bushfire-prone areas.

If your house is located on a slope, the greatest danger is from fires running from the downhill area up the slope. These are called upslope fires. The steeper the slope, the higher the risk. The speed and intensity of the fires doubles for every 10 degree increase in the slope angle. This is happens for two reasons:

The angle of the slope allows the fire to dry the material uphill, making it more flammable when the fire reaches it, and

The updraught effect – when a fire strikes, hot air rises fast and the fire pulls in more oxygen-rich air from lower down the hill to feed it. The more air that feeds in, the hotter it gets and the fiercer it burns.

As a consequence, the worst places to site a house is on sharp rigdetops or hilltops. Such a house is exposed from all sides to the threat of fire and fire will race quickly up the slope.

Another risky spot is the lee side of a hill, that is, the side of the hill sheltered from the wind. As the wind blows over the crest or top of the hill, it creates a low pressure area on the lee side, which creates a lot of air movement. During a fire, this powerful air movement can drive a fire cyclone, which will be burning directly over the house!

To reduce the risk of fire, houses and horse stables need to be sited:

  • Away from the tops of hills or ridges,
  • Preferably on downslope plateaus (level areas),
  • If the house is located on a slope of a hillside, excavate a shelf, a flat area and locate the building on the shelf, well back from the edge to protect it from radiant heat coming from the downhill area, and
  • If excavating a shelf, build a pond as a firebreak or an earthbank to protect the building from radiant heat.

Aspect of a slope

The aspect of a slope is simply the direction it faces. A sun-facing slope is facing north in the southern hemisphere and facing south in the northern hemisphere.

Good orientation can increase the energy efficiency of your home, making it more comfortable to live in and cheaper to run.

Ideally, choose a site or home with good orientation for your climatic and regional conditions, and build or renovate to increase the site’s potential for passive heating and passive cooling; adjusting the focus on each to suit the climate.

For those sites that are not ideally orientated, there are strategies for overcoming some of the challenges.

In hot, humid climates and hot, dry climates with no Winter heating requirements, aim to exclude direct sun by using trees and adjoining buildings that give shade year round, while capturing and channelling cool breezes.

In all other climates, a combination of passive solar heating and passive cooling is desirable. The optimum balance between capturing sunlight (solar access), and capturing cooling breezes is determined by heating and cooling needs.

A northern aspect is generally desirable in climates requiring Winter heating, because the position of the sun in the sky allows you to easily shade northern parts and the ground near them in Summer with simple horizontal devices, such as eaves, while allowing full sun infiltration in Winter.

Similarly, the aspect of the slope or orientation should also be considered in your design when placing horse buildings and facilities.

When building stables, shelters, loafing areas, arenas and even when planting vegetation, you should take the aspect of the slope into consideration.

You want to have your horse shelters positioned in such a way they offer protection against the severe (gust) winds/rains. During Summer, you want to have enough shade to protect your horses from the midday sunlight, while still allowing sunlight during Winter.

All this can be achieved by using a combination of natural and man-made structures which offer these features.


Permaculture places an enormous emphasis on sustainable design concepts for our homes and properties, with the aim to capture energy that facilitates the growth of our living systems and to set in place cycles, which eventually lead to greater energy and chore efficiency.

To accomplish this, we need to have a close look at the layout of our horse properties and, in our design process, we need to:

Determine the zones within the site to optimise the distances where elements are located (see Part 3 in the July issue of Horses and People),

Analyse our sectors carefully to account for all the ‘wild energies’ moving through our site, and locate design elements to harness or reduce them as necessary (see Part 4 in the August issue), and

Assess the sun angle and slope to gain maximum benefit from them.

After this analysis, we will have a fairly sound and potentially successful design in terms of making the most efficient use of energy for our site.

It is a fairly simple and straightforward exercise to systematically step through each of the areas covered under Zone, Sector and Slope, and attend to each part of the design as a separate task.

Breaking up even the largest site into smaller sections makes it much easier to design. Dividing up the site into zones does this for us. Sector planning involves observation of nature to see where the elements come into our site design and slope is a really a creative exercise where we see how much free energy you can use from what nature offers!

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