Day 80 (part 1 of 2)
Today's topic of the
permaculture design course was
Water. Jeremy started off the discussion with some of what water does for us. Water fosters life processes, can be used to develop productive food systems, and to develop hydraulic means of
energy production.
97% of the water on Earth is saltwater. Of the 3% remaining freshwater, 75% is frozen as ice or snow, 13.5% is deep (800+ meters deep) groundwater, 11% is shallow (less than 800 meters deep,) groundwater, 0.3% is in lakes and ponds, 0.06% is in the soil, 0.035% is in the atmosphere, and 0.03% is in rivers.
Aquifers are deep groundwater, the deep storage basins of the earth's freshwater supply. Aquifers can't be recharged effectively and so are a relatively finite and precious resource. The water table is where our
wells usually draw from, the shallow groundwater, and it can be recharged.
Water wants to take the shortest route downhill, following gravity and running perpendicular to contour lines. But as permies we want to keep water on our land for as long as possible.
Forests recycle about 74% of the water passing through. Evaporation rates are extremely low in a fully shaded
canopy, the
roots of trees are highly efficient at capturing and storing water, and the layers of deep leaf litter and natural hugels act like a massive sponge that holds water and releases it very slowly. Water coheres to itself, and adheres to other surfaces, making biological storage, and thereby life itself, possible.
There are several ways to store water in ponds, and understanding the landscape is key to determining which methods to use. A saddle is the area between two ridges, and if you have such a landform, you can build a saddle dam. A ridgepoint dam is built on a descending ridgeline. A keypoint is the place in a landscape where a slope meets flatter land, or where the land goes from convex to concave. Keypoint dams often offer the greatest catchment for the least work, and once established can be easily used to irrigate slopes lower down. Contour dams are built on contour where the slope is 8 degrees or less. A barrier dam is built across running water, like a stream or river, and needs a fish ladder. A check dam is built across swales or channels. A gabion is a kind of dam constructed of stacked stone or a stone-filled wire cage. And a turkey nest is a kind of donut-shaped dam that can be built on flat land and is mainly for storage rather than catchment.
Ponds can be sited to reflect sunlight, causing a sort of double-sun effect, and if placed uphill can be used to passively gravity-feed water downhill. When building a
pond, first dig down a bit both where the
pond will be and also where the dam will be. You're looking for soil with a clay content of at least 30%. A model can be built and tested using the materials you plan to use for the actual pond. Plan your spill ways to be able to deal with maximum rainfall and overflow. Ponds can be aligned long ways to the prevailing winds to increase aeration and to reduce evaporation. By the time the wind reaches the middle of a long pond, the air is saturated and so you lose less water to evaporation. Keep the pond shaded to reduce evaporation as well. Use rocks along the edges to hold heat and provide habitat, and be sure to seed the banks to minimize erosion and evaporative losses, and to take advantage of this saturated soil for growing.
A dam
should be slightly crowned on the crest, like a road, so that water doesn't pool there and wash the dam away. Freeboard is the distance between the top of the dam and the top of the water in the pond, and your freeboard should be at least 3 ft. The key of a dam is a compacted, impervious layer tied into a clay layer underneath. The key runs through the core of a dam. A pipe, like
Sepp's monks mentioned a few posts back, can be used to drain water out of a pond. A spillway designed to handle overflow should be located off to the side of, rather than through, the dam, and should be low
enough to maintain your 3 ft freeboard. Spillways can divert overflow to swales or other elements of the system.
Water can be siphoned into or out of ponds, and roads can be used to catch and divert rainwater into ponds. Islands can give ducks sanctuary from predators. Too much nitrogen or fertilization in ponds can cause eutrophication. The more edges a pond has, the more opportunity for production, habitat, and filtration.
Ponds can be sealed a number of ways. Gleying is the process of using animal manure to create a soppy, anaerobic layer 6 to 9 inches deep. Ducks,
cattle, and especially pigs can be used to seal ponds this way. Clay, especially Bentonite clay, is great for sealing ponds. An excavator with an articulating
bucket, like a giant fist, can grind, vibrate, and pound the bottom of a pond to compact and seal it. Explosives have also been used to seal ponds.
Understanding contour is important to siting ponds, dams, and other water features. An a-frame level can be used to find contour.
There are many effective ways to acquire water besides simple wells. Rainwater catchment systems can be built with first-flush diverters so that the water collected has less debris in it. Airwells are large stacks or piles of rocks; the outer rocks are in the sun and heat up, while the inner rocks are shaded and stay cool, so condensation forms on the inner rocks and causes moisture to collect. Fog collectors are like giant nets drained to gutters that trap and store the moisture of fog and mist. Humus wells utilize deep-rooted trees to catch water.
Greywater can be diverted from showers, laundry, and sinks, and reused in the landscape. It can be sent to mulch basins around woody species that filter the water while using it to produce fruit, into artificial wetlands where species like cattail efficiently convert the contained nutrients to soil, into mycofiltration systems with fungi that bind up or break down toxins, or any combination of the above. Ultimately, once biologically filtered, it can re-enter your productive water systems.
Other water systems include chinampas, (highly productive garden systems that maximize edge,) curb cuts, (an urban technique for collecting street run-off,) wicking beds, (a garden irrigation system where water is added down low, causing plants to grow deeper roots,) ollas, (a similar irrigation method where a sub-surface pot is filled with water that is seeped into the soil lower down to encourage deep
root growth,) drip irrigation, (a method of irrigation that attempts to minimize water use,) and aquaponics, (intensive hydroponic systems that grow plants and fish together in symbiosis.)
Cyanobacteria are a highly prolific and successful nitrogen-fixing form of aquatic life that can be used to increase fertility in, for example, rice paddies.
Riparian buffers are densely vegetated strips of land along rivers and streams that can protect waterways from pollution and also shade the water to prevent evaporative losses.
Natural swimming pools use plants to clean and filter water rather than toxic chemicals like chlorine. They can be used for food production as well as swimming.
Microhydro systems utilize flowing or falling water to generate electricity or run machines. A ram pump is a device that uses the water hammer effect to develop pressure that lifts a portion of the input water to a higher elevation than it started. A trompe is a water-powered gas compressor.
Howard gave us a few formulas:
Spillway lengths should be equal in meters to the square of the catchment area in hectares.
Rainwater harvested from a solid surface (gallons) = (catchment area in sq. ft.) x (max inches of rainfall) x (conversion factor 0.623) -Or- 1 inch of rainfall on 1 sq. ft. surface = approximately 0.6 gallons
A water tank at 10 meters high gives 1 BAR of pressure, (which is the typical water pressure in cities.)
Other things to consider when building a dam include: Clay should be packed on the inner and pond-side of the dam, as well as the bottom of the pond, but leave the ground uphill of the pond natural to store water in the soil uphill. Try not to site ponds or dams on rock, sand, or gravel, as these materials are too-well-draining. A dam slope should be at least 2:1, but 5:1 is better. Don't plant trees or plants with
deep roots on a dam.
The cheapest way to store water is in the soil. The next cheapest is to store it in ponds/dams. And storing it in tanks is expensive.
For water security, utilize as many different sources as possible: rainwater, wells, springs, ponds, soakage, condensation, and greywater.
To summarize the
permaculture approach to water, we want water to take the longest path, over the most distance, over the most time, traveling as slowly as possible, with the most passive friction, rubbing up against as many living things as possible.
3
-Art Donnelly
