I have put together a slideshow on the swale work done at pointReturn. A link to the slideshow appears at the end of this article as it is best viewed after reading this.
That I had fallen in love with the word ‘swale’ helped. It kept buzzing at the back of my mind like some tempting movie I must see someday. ‘Swale’ is a decidedly lovelier sounding word than Continuous Contour Trench- or its abominable abbreviation, CCT, the usual tag for a swale in India.
How I eventually came to love swales, is a story worth telling in some detail. Long time visitors to this site know most of what I will quickly summarise in next few paras. I had gone out of the way to seek a land that was abandoned, bereft of top soil, water and any agricultural activity. I wanted a blank canvas on which to demonstrate restoration from levelZero. My goal was to make 18 acres self-sufficient in water, food, energy and cash for forty people.
In 2007, I installed a windmill to pump water based on a logic that went as follows: ‘No doubt the groundwater is likely to be little, since the bald sloping land must have shed all rainwater -and topsoil- as runoff. There must have been very little groundwater recharge over the years. Still, being so close to a hill, there must be some water down there. Maybe it cannot sustain a multiple horsepower pump- but a windmill? A windmill sucks but under a litre per stroke or about 50litres per minute. Surely, there must be a sustained water supply down there to feed such a windpump’.
With the counsel of a water diviner I picked a spot as being worthy of a borewell, and drilled one 200′ deep. Late May 2007, a windpump was installed over it. And I thought I was done with water self-sufficiency. The windmill’s suction was 60′ into the borewell, a depth I thought enough to support the gentle pump. But no! My education on the ways of water was about to begin.
I realised my search for a land bereft of water had been more successful than I had hoped! The urgent requirement was that the borewell be recharged with rainwater. So I decided to dig a big pond, nearly encircling the borewell. Not a man given to doing things by half, I planned a 1.6million litre pond.
It was stretching my money. But as I sat pondering the road I had taken thus far, I underwent a shift in my perception of money. True wealth is not money in the bank but water under the ground and fertile soil on top. Money used as a tool to create these will eventually result in sustained surpluses of money. How I wish this perception was shared by economists, starting with the celebrated one now leading India!
So the pond was dug. In about ten days starting from Oct 13, 2007, it was almost done. When there was about 10% to go for completion, the skies opened up and filled it. It was a sight to behold.
This pond has given me a satisfaction that my money has seldom brought me. I gazed on the million litres arrived from heaven, and felt a very wealthy princ
As 2007, drew to a close I had planted 26 species of trees, 200 in all. We were watering the plants without a care. 2008 saw the pond refill again in September. I told myself -for the second time and again in error as it turned out- that I was done with water self-sufficiency. Surely a million litres stored by the borewell will steadily recharge the ground and take me home! Apparantly, not; at least, not sufficiently.
By early 2009, it was clear we were headed for a drought year. The windmill began to struggle by March, a good four months before the usual time. As the drought progressed, the pond depleted and many of the 300 trees planted in 2008 began to wilt, I was to be whispered new lessons to learn.
What I had was a large storage pond which collected runoff from its western uplands. The expectation was that it would recharge the collected water into the aquifer from which the windpump drew. The windpump delivered the lifted water into an overhead storage, from which I had laid pipelines all over the planted area.
Conceptually this system is flawed and no different from dams which gather water and distribute it via canals. The main action in this system is to collect runoff. The objective of a true watershed design however should be to *prevent* runoff and encourage recharge. My pond had a clayey bottom and so it probably lost more water by evaporation than due to recharge. Rest of the property remained dry and needed piped water. It’s not just more work; it’s also bad design- and therefore, my woes.
One can see this bad design in every centralised system- in every farm, government works and municipal systems. Entire urbanisation is based on centralised supply of water and power. Nature on the hand creates distributed systems, with millions of microstorages in ditches, leaf litter and aquifers. Nature further creates canopies to reduce evaporation. Clouds floating above do not rain on dams and rivers alone, but everywhere, increasing distribution. What I needed to do at pointReturn was to trap water all over the property and encourage it to percolate at the point of capture. With tens of places distributed all over for collecting and gravitating the water into the ground, I would be rehydrating the whole land [less work with pipelines] and awakening more underground pathways for water to flow to the pond [steady supply to the pond]. Differently put, the surface area of contact between collected water and the earth determines the quantity of recharge. Holding a million litres distributed over 10 acres will always beat 5 million litres held in one acre, given of course the porosity of the soil is the same. Again distributed bodies will even out the odds of impervious bottoms found in some of them.
Awareness of pointReturn’s situation and the needed course correction dawned on me as the hot months sizzled by and the pond drained . How do I implement RWH on multiple acres? The answer had lain in me waiting for the right question to be asked. It now popped up: swales.
I scrambled to revisit all the pages, notes, websites and videos I had idly browsed tossing this swale-thing about my mind. Now they all made immediate sense, quickening me to action. A swale is a means to percolate water into the ground rather than hold it, as a pond does. We will come to the sizing of swales a bit later, but for now a quick description: soil excavated to make the swale is piled on the downward edge on the slope. The mound is planted out successively with legume, cover and tree crops. Since a swale is located on contour line -meaning that its bottom is dead level- water entering the swale spreads throughout its length.
Speed of the runoff having been arrested by one or several swales, water has nowhere to go but down. It slowly progresses down slope filling inter-particulate voids. It is said that on a sloping land, water on the surface can travel a kilometer in a few minutes, while the same water trapped and sent into the ground, will take a couple of years to travel the same distance, depending of course on the geology of the underground.
The following clip from Geoff Lawton’s video ‘Harvesting Water – The Permaculture Way’, quickly and vividly illustrates how a swale works.
I surprised myself by deciding to fairly bust my wallet and buy a mini excavator. [The new attitude to money had obviously taken hold.] I could operate this myself and patiently sculpt out swales over months. When I am done with them, there would be other jobs I can use the machine for.
As the banks of the swale would eventually be planted out fairly thickly, I decided that the swale bottom should be wide enough to let the excavator to traverse it, during the summer months when its without water. I will have access to desilt the swale or scoop out leaf litter for use as mulch elsewhere. I might even grow a crop on the swale floor until it’s shaded out.
Size and number of swales depend on rainfall patterns. If it rained almost daily, you probably need no swales at all. In a forum post on the subject, a contributor Paul Cereghino has summed up the sizing issue succinctly: “distance between swales decreases as slope and rainfall rate increases and ability of soil/swale system to absorb water decreases.” If like around pointReturn, the entire annual rainfall of 900mm came down a week each, six months apart, more swales need to dug. I picked on a width of 7′ and depth of 2′, as a good size for motorable access. Since swales are absorption and not storage bodies, they would be empty most of the year. There would be ramps at either ends and the excavator or a tractor can traverse it.
The Yanmar VIO20 arrived to much local adulation. It was everything I had hoped for and a joy to operate. Using an A-frame, I marked out the first contour line to the west of the main pond and got to work. I dug a swale all right but the operator’s inexperience showed: the swale had to be hand dressed by members of the A-Team. “We are cleaning up after you,” they might have justifiably muttered under their breath.
In a spookily serendipitous happening, Ringo hove over the horizon on September 1, 2009. A more befitting person could not have been sent my way: Ringo, aka Paul Kean, is an itinerant Australian, a Permaculture designer, a land surveyor, an earth works operator with 30 years experience and above all a passionate swale lover. How pat is that! Ringo stayed a few days at pointReturn and dug a swale putting out a virtuoso performance. What came out was a text-book swale. Pertinently for the A-Team, Ringo’s swale, as it has come to be called, needed no hand dressing. To boot, it turned out to be pretty too, as lovingly built swales invariably are.
The swale mound should always be planted with ‘something’ soon as it’s piled up on the lower edge. Needless to say, it should not be compacted. When it’s still fluffy, it can be sown with a pioneer ground cover or legume crop. The piled soil, as at pointReturn bereft of any worthwhile topsoil, is likely to be infertile. So a pioneer crop serves as a green manure that can be chopped and dropped before it seeds. The residual roots become feed stock for soil animals and the dropped biomass becomes mulch. It may then be ready to be planted out with chosen tree crops.
If on the other hand, the swale is being dug on a fertile property, the topsoil is carefully removed and placed on the upper edge. Digging and piling up of the undersoil proceeds as before. Finally, the reserved topsoil is transferred on top of the mound, created on the lower edge. It may then be sown with a pioneer crop.
Getting the swale mound quickly covered has three benefits. One, cover crop roots anchor the soil against erosion and prevent compaction. Two, the soil is fertilised naturally and quickly. And three, when trees are planted out, the mound comes readily mulched to retain moisture.
It’s been just over 3 months since my affair with swales began. In that time three swales have emerged spread over a 3 acre area. They take up 0.2 acres and have a total capacity to trap 400,000 litres of rainwater, every time they are filled. And they have been filled once already. They constitute about 20% of the planned swale work. As I write, my heart and the pond are full; the road ahead looms clear. Swales are the way to go and reach water security at pointReturn.
Why do I love swales? Let me count the ways:
- Swales, strategically dispersed on a property will increase water security
- Swales can make a property drought proof
- Swales store water underground, a storage that is the lowest in cost, clean, secure, accesible and of nearly infinite capacity.
- Benefits of a medium sized swale network can radiate to fileds miles around
- Swales enable effortless integration of aquaculture
- Trees on swale mounds require little or no irrigation
- A series of swales planted out with trees, enhance transpiration activity, which in turn increases humidity, decreases temperature and encourages greater rainfall
- Swale trenches can be used as access paths or as crop areas
- Swales locations can be triggers to determine other farm facilities to be placed in mutually beneficial relationships.
- Swales unveil and blend with the natural landscape of a given property with effortless ease.
- Areas between swales can be developed as ever-hydrated pastures, crop areas or orchards
- Swales become ready windbreaks for crops like bananas and slender trees planted in their lee
- As swale mounds discourage trespass, they develop into reserve habitats for small animals, nesting birds and soil fauna, ever enriching the soil.
- When built with well designed escape sills, swales manage floods without damage
- Where wildfire risks exist, swales can mitigate them.
- Swales can be effectively deployed everywhere- from backyards to multiple square mile watersheds. What limits them are our imagination and will
“In most countries, 80% of rainfall runs off or evaporates. Thus only 12% is available for agriculture or domestic needs. We must legislate for the construction of thousand of miles of swales on farms, as large contour ditches that fill in every heavy rain (>10mm/day). In 3 to 6 hours, such water soaks in, and is immune to evaporation or run-off! This water, over years and centuries, feeds tree roots, springs, and valley streams. Swales enable forests, and forests are both passive condensers of night air, and active cloud generators for rainfall. If we clear the ridges, 40% of orographic rain ceases. If we clear the plains, most condensation and clouds fail to form. Thus, swales precede forests. Forests precede precipitation.”
Haven’t you fallen in love yet?
No comments:
Post a Comment