DIY Permaculture Landscape Design:
How to Use Slope, Elevation and Aspect.
Now that you are familiar with the
of Permaculture Landscape Design, and have sketched out the
for your property plan, its time to take it 3-D!
This is where we consider the actual characteristics of your site, its slope, aspect, elevation and orientation, and work out how you can use them to your advantage in creating the perfect small farm or backyard for sustainable living.
Gravity sucks! So the slope of your site offers all sorts of potential for harnessing its energies.
It naturally flows from high elevation points to low without needing any additional energy inputs. So it makes sense to store water resources high on your property and let it gravity feed to where you want to use it. It also makes sense to place access roads for heavy vehicles high in the landscape above the lower areas that may become boggy due to accumulated water.
The same goes for storages of heat…
Because hot air or water naturally rises (the thermosiphon effect) these can be placed above their collection points (e.g. solar hot water panels) and they’ll flow to their storage point by natural physics.
By the same principle, cool air being heavier (more dense) will tend to flow downslope where it will accumulate in frost pockets. High chilling varieties of fruiting trees need a minimal amount of frost to set fruit and can be located in areas of your site that naturally collect cold air.
This cold air can be diverted and held where you want it using hedgerows of thick vegetation, or allowed to flow away from where you don’t want it (e.g. around your house, or the warmer microclimate plants in your system) by the absence of such barriers.
Wind and slope
Wind speed intensifies as it flows up a slope, in a similar way that the pressure of water flow through a hose increases when reduce the size of the outlet with your thumb. Conversely, wind slows down when it travels downslope.
Since the speed and ferocity of fire is directly related to wind speed, protection from downslope fire sectors justifies the introduction of more fire barrier elements into your design than do upslope fire sectors.
Planning and Hillslope Profile
In climates where rainfall exceeds evaporation, such as temperate and humid tropic regions, hillslope profiles tend to have a flattened “S” shape as shown above.
Traditional peoples with sustainable cultures placed their settlements on the inflection point of change in slope profile, shown above as the “key point”. Above the key point, the slope is concave, below it, it is convex.
Such placement with respect to slope enabled traditional cultures to draw resources from the different ecosystems existing up and down slope. The junction of different ecosystems always offer access to greater biodiversity, ecological niches and yield than either alone.
Ideal housesite placement…
The key point is also a fortuitous place for Zone 0 – the home or settlement centre – using Permaculture principles to capitalize on the different characteristics and dynamics operating up and down slope.
Forest upslope areas…
Planting the steeper lands above the key point preserves the soil from water erosion (to this end, any slopes steeper than 18 degrees should be forested) and adds warmth and moisture to cold air sliding downslope towards the house site, creating a thermal belt.
Such forests are good water catchment areas, with the potential for rainfall runoff to be captured in midslope (key point) dams. These relatively small storage dams can then be used frugally in the home and food production areas.
Since the travel speed of wind and hence fire slows as it goes downhill,
upslope forests present only modest fire danger to Zones 1 and 2.
Positioning of tracks and fencelines…
Tracks and fencelines running down a slope increase the risk of soil loss through water erosion. Animals walk along such fences and make their own tracks that are, like man-made access tracks, exposed soil unprotected from the energy of water running downslope.
The ideal alignment of such structural elements on your small farm are on the contour, following relatively level ground as much as possible.
It is OK to cut across a slope providing you layout your fence or track structure so that its elevation changes only gradually (up to 1:20 i.e. 1 metre maximum elevation change for every 20 metres track length – more for fences).
Tracks are also ideal runoff areas for rainfall and can be integrated with dams to deliver top-up water even in light rain.
Siting sustainable agriculture…
The gentler concave slopes generally found below the key point are at low risk of water erosion and so are ideal for placement of access tracks to the house site, crop cultivation and livestock grazing.
With sound soil conditioning and water interception (e.g. using swales), they support the most sustainable and viable agriculture if the forests above are preserved.
They, along with downslope dams, can passively receive, utilize and filter wastes from the homestead zones, converting them into useful fruits, timber and aquatic life.
Because of their position in the landscape such areas are also most suited to irrigated horticulture, the water stored in header tanks and high dams at the key point able to be passively fed to them without the need for energy inputs.
Low elevation dams…
Low elevation areas with gentle slope offer cheap sites for water storage, with a minimal amount of earth having to be moved to effect large storage volume.
Dams both store heat and reflect light upslope, warming the winter microclimate. Air thermosiphoning (hot air rises) transmits such warmth naturally upslope to the home site. In summer they cool hot breezes, again moderating climate.
At the lowest elevation, valley plains can remain productive if protected from their vulnerability to wind erosion and salting by no tillage cropping practices and judicious plantings of hedgerows and copses.
As we have seen in our analysis of solar sectors, the position or angle of the sun relative to the horizon in the sky changes from high in summer to low in winter.
This annual variation in sun angle can be utilized to good effect in the design of houses, deciding placement of eaves and windows, shade, as well as reflection or absorption angles of surfaces such as dams and solar heat collectors.
Site aspect is simply its angle of orientation with respect to the sun.
In the southern hemisphere, north facing sites are described as having a solar aspect, and in the northern hemisphere the same is true of south facing sites.
A sun facing slope will receive significantly more direct solar radiation than a shaded slope, hastening thaw and providing usable energies to homes and gardens.
To Sum Up…
A great small farm or property design results from following the simple steps we’ve described:
• Thoughtful zoning of all design elements
• Element placement in accord with properly analyzed sectors, and
• Optimized slope and sun aspect benefits.
Even you are a novice, by following a commonsense Permaculture landscape design approach, a successful plan for sustainable living will be achieved.
Indeed, you can not fail to do better than those who overlook such essential factors to planning for sustainable living!
Return from PERMACULTURE SLOPE AND ASPECT
to PERMACULTURE DESIGN