Water

 
 
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Water, combined with soil, provides the essential medium for plant growth. It is one of the prime wild energy sources reaching our site. It is both a design element and a source of energy as it runs across a piece of land. We try to counter the erosive power of water through land modification and planting; we retain water to let it gradually feed plants or to tap its energy for work as needed.


Water is part of an endless system of change and transport known as the hydrologic cycle. Water from the Earth's surface, lakes, oceans and vegetation is moved into the atmosphere through evaporation and transpiration. Water vapor is moved around the Earth by air masses until it falls out as precipitation to run off into streams and rivers and to be collected again in soil, ground water, lakes, oceans, glaciers and plants. Water, in the form of vapor, liquid or ice is the life-blood of the planet.


While the Earth is known as the water planet much of our water is not available for direct human and plant use. Almost 94 percent is in the salty oceans and only 3 percent is freshwater. Seventy-five percent of that freshwater is tied up in ice and glaciers and 24. 5 percent in groundwater. Of the remaining one-half percent, only one third is available in lakes and rivers, the rest being held in soil and atmosphere. Fresh, pure water is a scarce entity and one we must conserve and respect.


In a permaculture design we try to capture, conserve and reuse water many times as it moves through our design. On an urban or suburban site this might be as simple as collecting water that runs off a roof for use in watering plants and trying to design the site so it has zero runoff. In more rural areas or on larger sites we may go to greater extremes to store and control water flow and erosion. Water may be stored in the soil, infiltrated by earthworks, held in ponds and farm dams, retained in biological systems or placed in tanks. (Permaculture, pg. 155)


 

 

P. A. Yeoman was one of the most influential thinkers on use of water planning in the landscape. His book, Water for Every Farm/The Keyline Plan, written in 1954, is the pioneering text on landscape design for water conservation and gravity-fed flow irrigation. (Permaculture, pg. 156, map pg. 161)

The concept of water use is to collect it and connect it across a site using combinations of dams, terraces and swales to control flow. For example, saddle dams catch the water at the highest levels, ridgepoint dams collect water on the sub-plateaus of flattened ridges, keypoint dams are located in the valleys of secondary streams, contour dams collect water off relatively flat slopes, and barrier dams retain flow in intermittent stream beds. Additional structures such as turkey's nest dams, check dams, and gabion dams will further collect or store water. (Permaculture, pg. 158-160) Erosion, the down side of water flow, can be controlled by low gradient grass swales along the contours, terracing to reduce slope pitch, sheet mulching, check structures of rock or logs, rock aprons, and a number of other bioengineering techniques.

Water is subject to contamination as it is used for industry and commerce, aquaculture, agriculture and waste transport. It is contaminated as it runs across urban building surfaces, parking lots, roads, lawns and golf courses. Partially contaminated water may be reused in 'greywater' systems for toilet flushing, washing and irrigation. More seriously contaminated water may have to be treated through use of treatment plants, wetland treatment systems or living machines.