Basic principles of water harvesting
By Nigel Shemanski
There are many forms of rainwater harvesting on the University of Arizona campus. The landscapes in which they are found, serve as examples for what can be done at the residential level.
Both large and small scale water harvesting techniques follow the same principles to create the most effective ways of capturing water. The principles described here come from the University of Arizona Water Harvesting course taught by James Riley and from the textbook used in the class, written by Tucsonan Brad Lancaster.
Start with observing the site
Start with careful observations of where the water flows, how the water flows, and what is already working on the site. This will save large amounts of time and effort when installing harvesting techniques.
Start at the top
Allow gravity to assist in water harvesting. Begin by working on the highest area of the site. (This may be the roof of a house.) By doing this, the water is controlled before it can gain speed and volume.
Keep it simple
Install techniques that can be done by hand, and can be easily fixed if damaged. Installing numerous small harvesting techniques rather than one big project allows for better infiltration of the water.
Slower is better
Try to slow the flow of water as much as possible and spread it across the site, rather than allowing the water to run off the site.
The more the better
In locations where abundant water can flow, plan an overflow route. The overflow water should be harvested, rather than directed off the site. A series of check dams and basins is an effective way to manage overflow.
Green is good
Try to maximize the ground cover by adding plants to the site. Plant roots loosen the soil and allow easier infiltration of water into the soil.
Use multi-functional techniques
This is the most advanced principle, but it can have the most impact to a site. Turn berms and check dams into walking paths and bridges. Select plants that can provide shade and cool your home, or even provide food.
Always critique the site
As with the careful observation of the site prior installation, it is always important to observe the site even after the initial harvesting techniques are placed on the site. Keep track of what the water is doing and how the site can be improved.
With a little time and effort, any site can be transformed into a sustainable oasis using these eight principles. It is important to remember that rainwater harvesting on a site is never finished and can always be improved.
For more information, see the website and books of Brad Lancaster, author of Rainwater Harvesting for Drylands and Beyond.