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Rain Water Collection Converting inches of rainfall into gallons of potential irrigation water.
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Transcript of Rain Water Collection Converting inches of rainfall into gallons of potential irrigation water.
Rain Water Collection
In most landscapes rainfall is diverted into drain lines and directed through a hole in the curb then flushed to the sea as quickly as possible
Rain Water Collection
Most any flat, impermeable surface within a landscape can be a source of potential, future, irrigation water
Definition: impermeable—not allowing fluid to pass through
Rain Water Collection
This includes:Rooftops using rain gutters and
downspouts Patios & patio coversDriveways & sidewalks
Rain Water Collection
Water from these flat surfaces can be channeled and captured in large, closed collection tanks for future use
Rain Water Collection
First – determine the potential for water savings per year
Ex. water costs in Westminster are $2.29/unit (as of summer 2012)
1 unit = 100 cu.ft. of water or 748 gallons of water
Rain Water CollectionMy bill for 3 residences averages
about 18 units/month or about 13,464 gallons per month
For 6+ people3 toilets3 kitchen sinks3 tub-showersAnd whatever yard watering
Rain Water Collection
We average about 14 inches per year of rainfall in the Orange/LA County areas (more or less)
How much usable, potential irrigation water does that amount to?
Rain Water Collection
Let’s say we have a storm that deposits 1” of rainfall on your roof and your roof covers 1,000 square feet of area
How many gallons of water does that amount to?
Rain Water Collection
The first thing we need to do is to convert the amount of rainfall into a comparable measurement—to something we get billed for
Rain Water Collection
We start by asking ourselves: “How many gallons of water are
there in 1” of rainfall over an area of 1,000 sq.ft.?”
Rain Water Collection
Since we are ultimately dealing with cubic “FEET” of water – we should probably begin by turning inches of rainfall into “FEET” of rainfall
Rain Water CollectionSo 1” of rainfall equals how many
“FEET” of rainfall? 1 foot = 12 inches so we could divide: 1” rainfall = 0.083 ft.
12”/foot(don’t forget the inches cross-cancel and feet come to the top)
So 1” of rainfall = 0.083 ft. of rainfall
Rain Water CollectionNext figure out just how many cubic
feet of rainfall in our 1000 sq.ft. area that amounts to:
Remember that cubic feet represents a volume
Volume = Area x Depth orV = L x W x D provides an answer in
“cubic ‘something’”Remember: Area = L x W
Rain Water Collection
So if we take the area (in sq.ft.) covered by rainfall and multiply it by the depth of rainfall (in ft.) that will give us the amount of cubic feet of rainfall
Volume = area x depth (V = A x D)
Rain Water Collection
We started with an area of 1,000 sq.ft. covered by rainfall and 0.083 ft. of rainfall
1,000 sq.ft. X 0.083 ft. = 83.3 cu.ft. of rainfall
Rain Water CollectionHow many gallons does that convert to? Since there are 7.48 gallons per cubic
foot of waterWe could divide:
7.48 gallons/cu.ft. X 83.3 cu.ft.= 623.3 gal. 1 cu.ft.
(don’t forget the cu.ft. cross-cancel)
Rain Water Collection
So . . . For every 1” of rainfall on an
impermeable area of 1,000 sq.ft. we could conceivably collect 623 gallons of possible
Rain Water CollectionAnd in an average year, with an
average of 14” of rainfall, that means about 8,727 gallons per year of potential irrigation water!
Almost 12 units per yearOr about $28 yearIs it worth it?
Rain Water CollectionNow how much water does that lawn
need to stay green? On average of about 1” of irrigation
per weekOr 624 gallons per 1,000 sq.ft. per
week At 38 weeks per year (arbitrary
number assuming 14” of rainfall over 14 weeks)
Rain Water Collection
That’s about 25,000 gallons of irrigation water per 1,000 sq.ft. of lawn per year
About 33 units per yearAbout $75 per year
Rain Water Collection
It probably wouldn’t be practical to irrigate lawns using captured rainfall
It might make sense to use that captured rainfall in a “gravity fed” drip system in the planters
Wouldn’t that offset water costs for residential landscape irrigation uses?
Rain Water Collection
The costs may not sound like much now, but water rates continue to rise!
The future price of tap water:Tap water = bottled waterThat might make it worth it.