Determination of Rainfall

Your math looks good to me. That's a lot of water!

mightymike-bonaire,

What did you use as a value for pi?

Using 3.1415927, I calculated 41,999.167 (say 42,000) cubic meters of rainwater...

3.14 is ok for pi because the diam is approx. You can bargain on at least 40,000 m3.

yes i used simply 3.14 for pi.

And i`m "guessing" 250 mm of recoverable water.... the rest of the 250 mm may not be recoverable (evaporation etc.) still a hefty 20,000 m3. about 8 Olympic size swimming pools ? .

Anyway thanks very much for the verification. I`m working on a project to use this water. If there is anyone willing and able to advise on semi arid agriculture and horticulture..... I`m all ears...

If the water isn't contaminated from contact with the oil, etc. and depending on whether the need exists, perhaps it could be used (with minimal purification/disinfection) for potable water.

Thats really nice work for water conservation , you will have to get it more to use in agriculture , when you caculate 50% loss in evaporation and attempting to do agriculture you will have to further calculate and find ways of preserving that collected water

there are floating balls used to reduce pool loss

Hendrik,

I used 3.1415927, because that is the value that my calculator provides when you depress the "pi" key.

Yep, that's A LOT OF WATER...

Around 88 million pounds worth.

I was relieved from my 1980 model HP71 scientific calculator at gunpoint and haven't found something nice to replace it yet. At the moment i use anything that comes to hand. mostly 24 key pocket jobs made in China. Over here you get one for free when you buy a laser cartridge or similar. I miss my pi but get along very well with 3.14 for guesstimates or 355/113 for better accuracy.

I am not fighting with you about the value af pi.

It is some mighty expensive water you are talking about. At 2 pounds per litre it would be out of reach for agriculture. Say one can produce 20000 x 10 kg bags of potatoes the income could then be 3 (wild guess) x 20000 = 60000 pounds

At the moment this water goes to waste.... it is drained off the roofs.. flows to the sea.

Here in Bonaire we pay approx 5$ per m3 (desalinated water).... and getting higher, as oil prices are rising.
let`s say 20,000 m3 X 5$ = 100,000$ per year.. 1000,000$ in 10 years.. enough to pay for infrastructure to recover this water I guess..

500 MM/year = 20 inches annually. Not very much, but it may pay to have large catchments and use that water for non sanitary uses

nice flat floating roofs, water gathering might work as long as you have a birdshit filter. That might ruin the economics of it.

The water will also get stinked up by the oil/gas etc in the tanks.

As oil goes up, the economics shift in favor of it.

the type and area of the crop will depend on evaporation etc.

at ±1000 mm for fodder, 600mm for grain, 400mm for potatoes (wild guesses) for conventional irrigation your irrigated area will be small (2 to 5 ha) and maybe not viable.

you may have to go for freshwater (or mixed) aquaculture or hydroponics.

Can I ask, "What is the point of your analysis? Are you calculating runoff? Retention? Are you intending to harvest the rainwater for other applications? Is this for drainage?

For harvesting, total rainfall is relevant.

For drainage, rainfall rate is relevant.

yes, harvest the rainwater for other applications.

I was thinking of constructing a park with local fruit trees (long term), a part organic green house for vegetables (short term) swimming pool (gathering of young and old), a building with enough space for lectures, small scale conferences, a couple of studios for guests or students contributing to this project ,a small space to sell products produced in this complex (fruits vegetables,artwork etc.) a garage (oil recovery) also a separate project to educate and inform people about using rain water at home, soil erosion, prevention contamination of groundwater (garage for oil recovery). this will be paid for in part by the oil company and government. All projects should be self sufficient over a period of time. But first I need to know if there is enough water to make this all possible in the first place.

Ps. The oil company must "donate" this water to make it all possible.

Hope this helps:

Formulaic projections of one inch of rainfall x 1 sq ft of roof= .62 gal of fresh water, based on a conservative 50 ins. per annum, yield a typical fresh water harvest of around 77,000 gallons per year per 2,500 sq ft roof

I don't know your location, but does evaporation matter. Also when does the rain happen - all in one huge monsoon/all at mid-day etc ? 'Average' sounds a bit dodgy when we don't know an approx location/rainfall pattern.. What do you do with the run-off, or is that a question for a theoretical question ?