Water Harvesting Earthworks “Design To Reality” . Part 1
So, you have been contacted by a client and you’ve discussed the client’s brief. You’ve started to look at the contour map, aerial images, whatever data you can find on the site. And with the client brief in mind, always remembering WATER IS LIFE, you set to the task of patterning the landscape using functional forms.
You start to look at what’s the most economical way to hold water in the landscape, move water around the landscape passively and make it perform as many duties as possible before it leaves the site.
Next is to develop the mainframe design theme. A big part of this is looking for high water storage sites. So we take the approach of looking at the contour map to take into account where the highest possible spot is, where water can safely be stored on the site in dams, (always considering how much catchment area is above the potential dam site or if there are any hard-surface run-off areas above the dam site).
Reader’s will understand catchment area, but hard surface run-off areas aren’t so well utilised and it’s just a bit of pattern recognition to identify when you look at a new site.
Identifying hard surface run off areas
Hard surface run-off areas with a bit of design thinking, can brought into our water harvesting systems. At times it doesrequire good observation skills to identify them, but there are generally clues for the observer.
There are many examples of hard surface run-off areas, sometimes called ‘hard-ware’. Your roof, a road, any compacted surface or a rock outcrop are all examples of ‘hard-ware’.
Gravel roads run off 85% of the water that hits the surface. Concrete areas 100% minus whatever evaporates, and your roof 100%.
These areas can represent a significant volume of water to be harvested and any designer should pay careful attention to these hardware runoff areas.
BASIC MATH: 1 meter x 1 meter x 1 millimetre = 1 litre
(Consider roughly $3 a bottle if bought in a shop!)
Surveying the site: Site survey is critical…so, does the design fit?
This is one of the most critical parts of the design to installation process. Surveying the site to know that we can harvest water in swales from roads and terraces, directing the surplus water towards dams.
Things that we’re looking at when we are surveying the levels in readiness for the earthworks
Difficult slope/s not seen on the contour map, i.e.: We must survey a line out to see if it’s possible.
- Is it safe to do the earthworks on that slope for the site and any machines utilised.
- Consider whether there are any rare or endangered species,
- or if there is a rock out-crop that would require us to adjust the height of the level we are working with.
(That’s why I like to say, “Design to reality!”)
Why? Because when we start to survey out heights and we survey around the landscape, we start find out (in reality) how we can pick water up from one catchment area or from some hard surface run-off and bring it around all on one level and put it into a dam.
At times it’s just not possible to do this on just one level. We must walk the water into the landscape by placing a swale or some other impoundment to hold the water, then over-flow at the desired point with our spillway to be pick up by the next swale line lower down the slope and into a dam before it over-flows.
By surveying the landscape it often highlights other opportunities that you didn’t see within the subtleties of the landscape itself.
Landscape form is hard to see with strong day light. If you want to look at landscape to get the best representation or image, early morning or late afternoon, or a full moon is the best from my experience.
It’s a very soft light you’re after and it will show you some things in the landscape that you will not see in bright daylight, which may present other opportunities.
A level line can be very deceptive and the contour map is just a guide.
– Remember, don’t get discouraged by your design not fitting on the landscape! Adapt it. I always do!
– Your design is merely the theme. Don’t get caught up on imposing your design on a site. Allow the design to evolve as new information becomes available, and don’t trust your eye.
I have done many jobs that I’ve looked at a level line and thought “that can’t be right”, but it is. Double checking your heights is always a good practice.
I always request photos from my clients after large rain events when I know the system is working, and it is working with often very subtle height differences imperceptible by the human eye!
Next week in part 2 David will cover how to determine the start point surveying and also explain the “Key Points” in the landscape and their relevance to water harvesting.
Having taught and worked on various projects extensively within Australia and internationally, such as Morocco, Jordan, Palestine and New Caledonia, David Spicer has covered a broad array of different soil types, topography and climatic zones.
David is a valued member of the Permaculture Sustainable Consulting team headed up by Geoff Lawton.
He is a master of practical and logical mainframe permaculture design which allows him to give his extensive experience of life and the cost involved to change a site. He has majored in the design water harvesting and storage earthworks which frames all regenerative farming, fo more information you can see his work on docspicepermaculture.com
David has the distinction of being Registered Teacher #5 with the Permaculture Research Institute of Australia.
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