Thursday, February 3, 2011

Creating hanging water for more sustainability

One might think that having a few pot plants at home may not have a very big effect in terms of sustainability. In this blog post I want to illustrate several things though. One is that we can have plants that manage water more efficiently, and hence grow better and more vigorously, that not only benefit the home environment, but that this idea is applicable to a much wider scale, and can be applied to whole cities and agriculture.

One would first have to explain what is "hanging water". Hanging water is literally water that hangs, one might think it could be perched water, however this is another concept, and is defined in the following way:
A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. We can illustrate it as in the photo that we see below:

The above situation then is water that sits on top of an impermeable surface. It is not really hanging.

Hanging water, as we had said, is water that hangs.
What does a hanging drop of water on a finger have to do with sustainability and good water management? This is the amazing thing of how small things can have enormous effects, I first understood a bit about this when my electronics professor who was an electronic engineer, like I would later become, loved to explain to his student that the difference between an Electrical Engineer and an Electronic Engineer was that the first can do big things with big voltages, and the the second does it with small voltages, hence having more merit. I cannot help but feel the same sort of thing and draw a simile with water, alas there is no real distinction as yet, to make a differentiation in water related careers. My experience with water engineers and professionals from around the world, shows that there is a tremendous amount of ground to be covered. Water engineering even till today focuses most of there effort on hydraulics managing volumes of water in quantities, paying very little attention to quality of water, and those that look at quality do so often with total disregard of undesired consequences.

Going back to hanging water then...
The fact that the water hangs in this way has tremendous implications in many applications. If the water had not found the end of my finger it would have continued it's journey downwards following the pull of gravity. What we are doing in essence is "conserving water".  If we are able to create similar "fingers" that hang water across vast areas we would be conserving huge amounts of water. How much? Experience has shown up to 76 litres per square metre. Quite a bit and just with a the same effect that a finger has with a drop of water.

The water hangs because it adheres to the surface it is on. This adhesion, that is much related to capillary action, poses a force that exceeds the pull of gravity. This adhesive power can be used to benefit.

The idea then is being able to hang water close to plan root structures, making it immediately available to vegetation. That the water should hangs arrests the "loss" of water travelling further down the soil profile. Water is conserved in the soil profile while it hangs in a state of "ideal" saturation, it is ideal because in the moment it becomes over saturated the hanging water drop will fall, plants will consume as much water as they need.

This hanging water can be created for a practical purpose in a "micro" implementation as is pot plant. One may say that what I am going to show is just another what have become to be called a "self watering pot", to an extent it is, though I think that the name is foolish to begin with. My design however does have a twist.

This is a typical pot for a plant. I am going to convert how we can apply hanging water.

In the base of the pot there are 2 small holes, which I insert with geotextile strips. This is to provide capillary action and a physical connection to the pot tray and the inside of the pot.
Here we can see the geotextile strip on the outside.

The base of the pot is lined with geotextile, this is to provide a layer of capillary action.

One cuts a piece of Atlantis Drainage Cell, to the size of the base of the pot.
The Drainage Cell gets a strip of geotextile for further capillary action.
The piece of Drainage Cell is placed on the bottom of the pot.
The piece of Drainage Cell is covered with another layer of geotextile, this serves the purpose of creating a separation media so that the soil we will add does not fill the drainage cell, and is what provides our much mentioned hanging water.
We fill around the plant with compost, here I very proudly show my own compost bin, where we can clearly see how the vegetable waste gets turned into very nutritive soil. Of course composting is something very sustainable, apart from being economical as one saves money on having to buy potting mix.
Here we can our pot plant ready with and Golden Cane or Areca Palm (Dypsis lutescens).
Here we can see 2 other pots that I had prepared and how the system works. One can observe that instead of thin strip connecting to the tray, I have laid a layer or square piece of geotextile. The plants can "never" be over watered, because as soon as the soil over saturates the excess water falls and is contained in the tray. In the measure that the plant needs water, through the capillary action infrastructure that we have provided, it access "sucks" that water. We have done in essence, for practical effects, is extend the root structure of the plant. On the left is pot where we see that the tray is dry and could with some water. This does not necessarily mean that the soil is dry as it could very well be at its point of saturation, what it does indicate is additional water capacity in the pot.

The ability to control soil humidity to "ideal" levels is something that some agricultural methods use extremely sophisticated sensor technology that then activates watering circuits and so on, here we have in a pot, created a much more effective, simple and sustainable method and technology that should never fail, that has no real moving parts, except for the water, that requires no power.

This sort of technology can be applied on mass scales and has already been done so in examples of roof garden technology. However this technology  that been used almost exclusively for roof gardens has to advance to another level, and that should be into agriculture.

I believe the way we do agriculture has to make its next step, what I would call Natural Sustainable Agriculture. Though one can argue that hydroponics is a step forward in agriculture, it can be said that it makes more efficient use of water, however I personally find few thing s more unsavoury that hydroponically grown tomatoes, that have a texture like plastic, not much colour, and less flavour. There is nothing like a succulent field grown tomato ripened on the stalk bursting with flavour, juice and texture.

To cover a last point and respond a question often asked, and respond to some raised eyebrows when we say that hanging water can mean providing storage of water of 76 litres per square metre. How can this be measured? Very simply, we get box with a base one square metre, on the bottom we put drainage cell, cover it with geotextile, and fill the box with soil media. Obviously the type of soil media will affect the result, but is to provide a typical soil profile that can be sand and organics. The depth could be any depth, but as we already have a reference it can be done with lets say 1 metre depth. We start filling the box with water and measuring the amount of water we are adding. The water should not drop down from the geotextile until it reaches a level of saturation, where the "weight" of the water exceeds that adhesive capacity of the water on the soil media, and capillary action of the same, and eventually a drop will fall. That falling drop will give the water bearing capacity that this concept, or rather implementation of creating hanging water has.

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