Rainwater Harvesting For Outdoor Landscaping | Green Living

By Haley Paul

With the coming of every summer monsoon season are high hopes for abundant rainfall. When you live in the desert, a little bit of rain can go a long way to making or breaking your outdoor landscape, and knowing how to harvest that rain is a great way to maximize those summer storms.

Your rainwater harvesting potential varies depending on where you live in Arizona. In the more arid parts of the state, such as Phoenix, the average 7 inches of precipitation per year can act as a nice supplemental drink for the trees in your landscape. If you live in Tucson or Sierra Vista, where it rains an average of 12 and 14 inches per year, respectively, it is possible, with careful plant selection and rainwater harvesting techniques, to irrigate an entire landscape on rainwater.

Back of the envelope calculation

To calculate how much rainwater you can capture in your landscape, first assess the surface area from which you will be harvesting. In a residential setting, this is most likely your house?s roof.? Next, find your yearly average rainfall. (see the resource section below for a good website)

Multiply the collection surface area (for example, a 2,000-square-foot roof) by your average annual rainfall (for Phoenix, 7 inches) by 0.6 (a conversion factor) to see what you could collect in a year. For example: 2,000 ft² x 7in x 0.6 = 8,400 gallons per year of captured rainwater

In most of Arizona, our bimodal rainfall pattern means that precipitation comes with the summer monsoon storms and the slow, steady winter rains. Since all the rain doesn?t fall at once, you?ll also need to consider how you want to collect the?rainwater.

Types of rainwater catchment

Passive rainwater collection is typically the contouring of your landscape to capture and store rainwater. By directing rainwater to the plants in your landscape through the shaping of basins, berms, or swales, rainwater remains on site instead of running off and down the street. Slowing the rainwater down and letting it slowly soak into the soil is a great method for irrigating landscape plants. Be careful, though?you do not want to flood the base of your house, and you always need to plan for overflow. Overflow areas ensure that, in the event a heavy rain overpowers your planned rainwater-capturing capacity, excess water has a place to go.

Active rainwater harvesting is probably the more recognizable of the two methods, as it utilizes cisterns, barrels, or some other retrofitted container to harvest and store rainwater for a later use. Gravity-fed rainwater collection containers are simplest and cheapest. Attach a hose to the bottom of the container, turn open the valve, and irrigate your landscape plants. Note that as you add in underground storage tanks and pumps, the cost of your rainwater harvesting system will start to climb.

Before you embark on your rainwater harvesting home improvement project, consult the additional resources below.

Use it in the Landscape!

Because a majority of residential water usage is devoted to outdoor projects such as pools and landscapes, using captured rainwater for your yard is a great way to offset your use of potable (drinkable) water. However, it takes some management to turn off the irrigation clock for a certain amount of time after a rain event to actually save water.

Another way to approach rainwater harvesting is to use it as a supplemental source of water. Sometimes, especially with drip irrigation, mature trees in landscapes do not receive sufficient water. Trees like Aleppo pines, for example, tend to fail from inadequate winter irrigation.? Directing rainwater to the root zones of mature trees can provide a much-needed boost to these large specimens and keep them healthy in your?landscape.

Please note that using captured rainwater for the edible garden is not recommended because the quality of the water coming off your roof, parking lot, or street is unknown.

Resources on rainwater harvesting in Arizona

Harvesting Rainwater for Landscape Use: cals.arizona.edu/pubs/water/az1344.pdf

Using Rainwater in Urban Landscapes-?Quick Guide for Maricopa County:
cals.arizona.edu/pubs/water/az1566.pdf

Rainwater Harvesting Infographic: tinyurl.com/rainwater-infographic

Tips to conserve water in Southern Arizona: waterwise.arizona.edu

Arizona precipitation averages: wrcc.dri.edu/summary/climsmaz.html

Source: http://www.greenlivingaz.com/2013/07/09/rainwater-harvesting/

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