The act of water harvesting is not a way of gardening, it is a way of life. The importance of water harvesting is simple…to create a sustainable way to use rain water. If created correctly, your water harvesting area could be used not only to house a beautiful garden, but for your showers, and even drinking water. The benefits are enormous from creating a water harvesting system. By simply setting up tanks in strategic places, you can have yourself a wonderful and quite useful water harvesting system…in your own backyard! First, allow me to compare the benefits of creating a system just out of earthworks, or the benefits of adding cisterns to collect water. Below is a picture of rainwater cistern.
Comparing Earthworks and Tanks:
1. Water uses:
Earth works: Provide large quantities of high-quality rainwater to garden and landscape
Cisterns: Provide water for drinking, washing, fire control, and supplemental irrigation. Click here for more details on supplemental irrigation: http://www.icarda.cgiar.org/
2. Water collection areas:
Earth works: Can collect water from roof, streets, vegetation, bare dirt, greywater drains, air conditioner condensate, etc. Click here for the definition of greywater: http://greywateraction.org/
Cisterns: Need relatively clean collection surface (typically metal, tiled or slate roof) located above the cistern.
3. Water storage capacity:
Earthworks: Very large potential to store water in soil
Cisterns: Limited to size of tank
Earthworks: Inexpensive to construct and maintain. Can build with hand tools
Cisterns: Cost varies with size, construction material, above or below ground placement, self built, etc.
Earthworks: Do not locate 10 feet away from a wall or building fountain. May be very difficult if garden is in very small yard, with adjacent nearby roofs.
Cisterns: No limit to where you can place the cisterns. Can be used in very small yards with adjacent nearby roofs.
6. Time period water is available:
Earthworks: Water available for limited periods after rainfall depending on soil type, multch, climate and plant uptake. Click here for more information on mulch and its uses: http://soilutions.net/
Cisterns: Water available for extended periods of time after rainfall
Earthworks: Work passively, require some maintenance after heavy rainfalls
Cisterns: Maintenance required, must turn valve to access water and may need pump to deliver water
8. Erosion Control:
Earthworks: Very effective
Cisterns: Can assist with erosion control
9. Grey Water Collection:
Earthworks: Very effective at harvesting grey water from household drains
Cisterns: Not appropriate to harvest grey water in tanks due to water quality issues.
10. Water quality impacts to environment:
Earthworks: Pollutants in grey water and street runoff intercepted in the soil stay out of regional waterways
Cisterns: Less impact than Earthworks to the broad environment
11. Impacts on urban infrastructure and flooding:
Earthworks: Can capture large volumes of water, reducing need for municipal water (click here for municipal water definition: http://watereducation.utah.gov/ ), storm-water drains, storm-water treatment and decreasing of flooding.
Cisterns: Can capture low to moderate volumes of water, reducing demand for municipal water, storm-water drains, storm-water treatment and decreasing of flooding.
12. Groundwater recharge:
Earthworks: Sometimes can recharge very shallow groundwater tables
Cisterns: Not an efficient use of tank water
Based off of this information, you can choose whether water cisterns or earthworks are a better fit for your yard. Once you have decided, it is time to get to work. To create a simple water-harvesting system in your backyard, you must follows these eight steps. First, you must begin with long and thoughtful observation. It is important to observe where the water flows, where it collects, where it drains away, and where it drains from. By knowing these principles, you can create a more efficient water-harvesting system. Secondly, you must start at the top or highpoint of your watershed and work your way down. This is very useful because it is ultimately much easier to harvest water high in the water shed than low in the watershed because the volume and velocity of flow is less, and more manageable, at the top. By doing this, you can then use the free power of gravity to redistribute the harvested water to areas around your garden containing a downslope. Below is a picture of using your rooftop for a water cistern:
Thirdly, you want to start small and simple. This is because small and simple water harvesting systems are easier to take care of and maintain rather than large and complex ones. It is also far more effective to have large amounts of small systems rather than a few large ones. Fourth, you want to slowly spread and infiltrate the flow of water. It is important to zig-zag and calm the flow of water to reduce destructive erosion and increase the time and distance the water flows. This is important because it increases the infiltration of the soil. Fifth, you always want to plan an overflow route, and manage that overflow as a resource. It is important to create an overflow system right next to your cistern, so any excess water will simply be placed into a growing garden. Therefore, no water is wasted in this process.
Sixth, you need to create a living sponge. As discussed in my previous posts, soil sponges are holes dug in the ground that are filled with organic materials (such as cardboard, paper and mulch). They essentially help hold water in the ground and redistribute it throughout the land. Below is a picture of a soil sponge being constructed in the desert oasis garden:
Seventh, you need to essentially do more that just harvest water. Yes, harvesting water is important, but there needs to be multiple other factors that create the system into a success. You need to “stack functions”. In other words, you need to have cisterns and earthworks that provide high quality irrigation water and serve as on site stormwater control strategy. Furthermore, you need to have rain irrigated vegetation and above ground cisterns that can passively shade and cool the eastern and western sides of the landscape in the summer.
Finally, you need to continually reassess your system. Focus on how the land is responding to your work. How are your strategies performing? Create any changes if necessary.
Last photograph is by Mrs. Beamish