What's the weight of all that rain?

What's the weight of all that rain?

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Discussion

Thankyou4calling

Original Poster:

10,707 posts

180 months

Monday 14th September 2015
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After a lovely day yesterday I left my car out with the roof down overnight only for it to start raining at about 4am, interior was soaked but there you go.

It got me thinking. If it rained for say 2 hours over an area of 100 square miles, pretty heavy say 10mm how much actual rain would fall?

Would it fill an Olympic swimming pool? How many?

And how much would it weigh?

God knows why but I was just wondering.

Thanks for replies.

Leptons

5,317 posts

183 months

Monday 14th September 2015
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A hundred square miles is fking big area. My small brain suggests that would fill many swimming pools.

PositronicRay

27,535 posts

190 months

Monday 14th September 2015
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Calculator out time. I think 1sq m is a tonne.

torqueofthedevil

2,088 posts

184 months

Monday 14th September 2015
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Calling a mile 1600m would result in 2.56m litres of water. Which is 2.56m tons. And coincidently an Olympic sized swimming pool contains around 2.5m litres of water


Vaud

52,411 posts

162 months

Monday 14th September 2015
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With some assumptions, I think my units are right but happy to be corrected.

Lotus Notes

1,240 posts

198 months

Monday 14th September 2015
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PositronicRay said:
Calculator out time. I think 1sq m is a tonne.
May I suggest that 1m3 is a tonne smile

ViperDave

5,572 posts

260 months

Monday 14th September 2015
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my guess is about 2,589,988.11 kg



Edited by ViperDave on Monday 14th September 22:18

deckster

9,631 posts

262 months

Monday 14th September 2015
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Vaud said:


With some assumptions, I think my units are right but happy to be corrected.
Out by a factor of 1,000 I'm afraid. 1sqkm == 1 million sqm.

Lotus 50

1,014 posts

172 months

Monday 14th September 2015
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Vaud said:


With some assumptions, I think my units are right but happy to be corrected.
With apols in advance if I'm wrong but aren't there 1,000,000 sq. metres in 1 sq.km? so shouldn't it be 258,999,000 sq.m (call it 259,000,000)? Which would be 2,590,000 cubic metres (so 2,590,000 tonnes of water and over 1000 pools).

...above post got there before me!

Vaud

52,411 posts

162 months

Monday 14th September 2015
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Yup, I'm wrong.

That will teach me to multitask. Just change the lower rows...

Timsta

2,779 posts

253 months

Monday 14th September 2015
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Lotus Notes said:
PositronicRay said:
Calculator out time. I think 1sq m is a tonne.
May I suggest that 1m3 is a tonne smile
Yep, 1sq m is 0g.

Weight of a rainstorm: https://what-if.xkcd.com/12/

NRS

22,978 posts

208 months

Monday 14th September 2015
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Timsta said:
Yep, 1sq m is 0g.

Weight of a rainstorm: https://what-if.xkcd.com/12/
After reading that I have to say the OP was being a lot more responsible putting his water in swimming pools rather than letting it fall out of the sky together on lots of innocent people.

ApOrbital

10,155 posts

125 months

Monday 14th September 2015
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Ark at you lot trying to suss it out.

Thankyou4calling

Original Poster:

10,707 posts

180 months

Tuesday 15th September 2015
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Thanks for the replies. I'm going to read them again to see if I've got a definitive answer but either way that's a lot of rain in weight and volume terms.

Vaud

52,411 posts

162 months

Tuesday 15th September 2015
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I had another go...

cv01jw

1,136 posts

202 months

Tuesday 15th September 2015
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Assuming 100 square miles is taken as 10 miles by 10 miles (as opposed to 100 by 100), then the catchment area is 16.09km x 16.09km = 258.89km². This is 258,890,000m².

Rainfall of 10mm (0.01m) over this catchment would generate 2,588,900m³ of water.

An olympic pool taken as 25m x 50m x 2m will hold 2,500m³ of water, therefore the rainfall above would fill 1,035 pools.

To put these figures into another perspective, 10mm of rainfall over 2 hours is not particularly high. An industry standard 'typical' rainfall event used for fag-packet type calculations would use 50mm per hour.

When undertaking detailed designs of drainage systems the actual rainfall used varies depending on lots of factors, but peak intensities in excess of 200mm per hour are not uncommon.

Smokehead

7,703 posts

235 months

Tuesday 15th September 2015
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What about evaporation rates? hehe

Thankyou4calling

Original Poster:

10,707 posts

180 months

Tuesday 15th September 2015
quotequote all
cv01jw said:
Assuming 100 square miles is taken as 10 miles by 10 miles (as opposed to 100 by 100), then the catchment area is 16.09km x 16.09km = 258.89km². This is 258,890,000m².

Rainfall of 10mm (0.01m) over this catchment would generate 2,588,900m³ of water.

An olympic pool taken as 25m x 50m x 2m will hold 2,500m³ of water, therefore the rainfall above would fill 1,035 pools.

To put these figures into another perspective, 10mm of rainfall over 2 hours is not particularly high. An industry standard 'typical' rainfall event used for fag-packet type calculations would use 50mm per hour.

When undertaking detailed designs of drainage systems the actual rainfall used varies depending on lots of factors, but peak intensities in excess of 200mm per hour are not uncommon.
I think your calculations are right BUT.

50mm of rain in an hour is nearly two inches. London, as an example gets two inches A MONTH!! So in an hour that's an absolute deluge.and far from typical.

smg916

18 posts

169 months

Tuesday 15th September 2015
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The 50mm/hr figure is what is typically quoted (for fag packet calculatoins) as rainfall intensity for a 1 in 30 year 'design' rainfall event; which is the level of protection that the water company regulator requires the industry to provide protection from internal property flooding against. The only trouble is that 1 in 30 year events seem to be happening every few years...

anonymous-user

61 months

Tuesday 15th September 2015
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What if the rain fell on sloping ground? You'd have to reduce the volume to allow for that?