Dan J.S. wrote:
"Warren" wrote in message
Well, let's say you want to put down 3cm of water per week, and you're
not loosing significant amounts to leakage, run-off (from poor draining
soil), evaporation (you're not watering in the heat of the sun), or
forgetting to turn off the water once enough is delivered, and, of
course, a reasonably even distribution. 75 sq meters is 750,000 sq cm.
Make it 3cm deep and you have 2,250,000 cubic cm per week. Multiply that
times 20 weeks and you get 45,000,000 cubic cm, or 4,500 cubic meters.
There are 1,000 liters in a cubic meter, so that would be 4,500,000
liters a season.
I think there is something wrong with this calculation... a lawn that
small would be a lake if you watered it with 4.5 million liters a
season...
You're right. I made a mistake converting back from cubic centimeters to
cubic meters that resulted in a 100-fold mistake! (Mark your calendars,
folks. I'm admitting to a mistake.)
Let's try it again then.
1 meter equals 100 centimeters. 1 square meter equals 100 centimeters x 100
centimeters, or 10,000 square centimeters.
Take that 10,000 square centimeters, and make it 3 centimeters deep, and you
get 30,000 centimeters.
You don't just have 1 square meter, you have 75 of them, so 30,000 x 75 =
2,250,000 cubic centimeters.
There are May to October is 5 months. Go with 4 weeks per month, and that's
20 weeks, or 20 times you have to put down 2,250,000 cubic centimeters of
water. That's a total of 45,000,000 cubic centimeters.
A cubic meter would be 100cm x 100cm x 100cm, or 1,000,000 cubic
centimeters. So 45,000,000 cubic centimeters is 45 cubic meters. (This is
where I made my mistake the first time.)
There are 1,000 liters in a cubic meter, so 45,000 liters is the correct
answer.
To check that for reasonableness, let's try the English measurements. He
stated 680 sq. feet, and I'll use 1.2 inches instead of just the standard 1
inch because that's closer to 3 cm.
There are 144 square inches in a square foot, so 680 square feet is 97,920
square inches. Make that 1.2 inches deep, and we have 117,504 cubic inches.
Times 20 weeks we have 2,350,080 cubic inches for the season. There are
about 231 cubic inches in a gallon, so that's about 10,174 gallons for the
season.
Very roughly speaking, there are 4 liters in a gallon, so 10,174 x 4 =
40,696, which is in the same ballpark as the 45,000 liters we came up with
in the other calculation, so now we've got some reasonable numbers.
To put this further in perspective, the area being spoken about, if it were
square, would be about 26 x 26 feet. Over 10,000 gallons of water are needed
for a 26 x 26 foot lawn. My water rate is $1.83/cubic foot. There are 1,728
cubic inches in a cubic foot, so 2,350,080 cubic inches is 1,360 cubic feet.
So if I had to water a 26 x 26 foot lawn every week for five months, it
would cost me almost $2,500 a year.
Even without figuring in anything for fertilizer, gas (or electricity) for a
lawn mower, or anything for the labor involved, that means a 26 x 26 foot
lawn is a pretty darn expensive luxury unless you get lots of help from
Mother Nature, or let it go dormant.
Thankfully where I live I only need to water about 1/3 that many weeks, with
Mother Nature handling the rest. And I let my back and side lawns go
dormant. That means I only water a small front lawn. I water with a timer,
so I water before dawn so there's less evaporation, and the timer means I'll
never forget to turn it off, either. So I don't have to spend anywhere near
$2,500 a year, but I have neighbors who try to keep a large, monolithic
lawn, and they complain about how their summer water bill is more than their
winter gas bill.
Lawns are expensive. Very expensive if Mother Nature isn't chipping in a big
share!
--
Warren H.
==========
Disclaimer: My views reflect those of myself, and not my
employer, my friends, nor (as she often tells me) my wife.
Any resemblance to the views of anybody living or dead is
coincidental. No animals were hurt in the writing of this
response -- unless you count my dog who desperately wants
to go outside now.
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