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Harvest Rain!

Rainwater cache photo

Monsoon rains should be a great benefit to landscape plants.

But if the rainwater simply runs off of your property, you're not getting the full benefit of all that moisture!

Think there isn't enough rain? A one-inch rain will collect 600 gallons from a 1,000 square foot roof, while 4,500 square foot lot will receive 2,800 gallons!

 

Two easy ways to collect rainwater:

  1. "Passive" collection where you catch stormwater as it moves across your property
  2. "Active" collection where you catch rainwater in a container.

HOW MUCH RAIN CAN YOU CATCH?

Here is an easy formula:
  1. Measure the square footage of the collection area (for example a roof that is 30 feet wide x 50 feet long = 1500 sq. ft.)
  2. Multiply the area by the amount of rain in inches
  3. Multiply that number by 0.623 (that is the amount of water in gallons one inch deep in one square foot of space)

= amount of gallons that can be collected.

Example: 1500 square feet of roof area x 15 inches of rain x 0.623 = 14,017 gallons

Landscapes and hard surfaces can be designed and modified to hold, direct and distribute rainwater to plants with rainwater harvesting.

Preventing water from rapidly running off of the landscape is of primary importance. Porous paving materials such as bricks and special asphalt can allow water to penetrate. Angling hard surfaces to drain to planted areas instead of off the property can supplement irrigated areas..

Many back yards of urban properties are bordered by privacy walls. These walls have openings at the base to allow water to drain out.

Partially blocking these openings for a time can hold in rainwater, giving it a chance to soak into the ground. Caution must be taken, however, not to block the escape of the water to the extent that flooding of the home occurs.

During a heavy rain, partially block the openings to determine the amount of water held in.

To increase the water-holding capacity, depressions in the landscape can be created. These depressions can be shallow, but the more area they encompass, the more water will be held. These depressions, also called swales, should be designed to hold enough water to penetrate to the roots of trees and shrubs. One inch of water will penetrate the soil about one foot

.

Groundcover plants have roots that grow down to only about one foot in the soil. A shallow depression of 1 inch in the area of groundcovers would be sufficient. Shrubs and tree roots will grow down to about 2 and 3 feet respectively. Depressions under or in the vicinity of these plants would require a minimum of 2-3 inches. Consider making your berms higher - 6 inches - so you do not have to rebuild them as often as they erode down.

Consider also the placement of rainwater catching barrels or tanks. By placing gutters around the roof perimeter and connecting them to downspouts, large amounts of water can be directed where needed in the landscape. A great advantage to collecting rainwater from the roof is that it can be saved for use in dry periods. Downspouts can be emptied into plastic trash cans (you will eventually want to use something more permanent as they will split), wooden wine barrels, stock tanks and even corrugated metal pipes standing on end. Make sure you put wire mesh over the downspout opening in the gutter to prevent debris from entering your barrels.

A corrugated metal pipe cistern

 

and multiple connected trash barrels

 

 

 

 

Gutters 5 inches wide at a minimum should be used, and slope them 1/16 inch per foot. Place hangers every 3 feet. In choosing downspouts, keep in mind that for each 100 square feet of roof area, you will need 1sq. inch of downspout. You will want to space your downspouts about 20 feet apart.

It's a good idea to elevate the storage container a foot or so off the ground, especially if the water is intended to fill watering cans or buckets. Hose or piping also can be connected to the storage container and funneled directly to the garden or landscape.

To begin water harvesting, try a few simple techniques here and there in the landscape. As you see the positive results in plant health and water savings, you'll be encouraged to expand your efforts and save even more.

Useful Information:

2.31 feet in elevation = 1 psi

1 gallon water = 8.34 pounds

1 foot elevation = 0.43 psi 7.48 gallons in 1 cubic foot

1000 sq ft of roof = 623 gallons/1” rain

National average indoor usage gallons/person/day: 40

(shower: 8.8; faucets: 10.8; toilets: 8.2; clothes washers: 10; dishwashers: 0.7; other domestic: 1.6. NOTE: Leaks and baths are not included)

(Article modified from "Landscaping Features Assist Wise Water Use" by John Begeman, Pima County Extension Agent)

 

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