# flooding **URL:** \ **Category:** Factual Questions\ **Created:** [March 27, 2002, 2:56pm UTC](https://boards.straightdope.com/t/flooding/100376 "2002-03-27T14:56:29Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![vanilla](https://avatars.discourse-cdn.com/v4/letter/v/f19dbf/32.png) [@vanilla](https://boards.straightdope.com/u/vanilla)\ **Post date:** [March 27, 2002, 2:56pm UTC](https://boards.straightdope.com/t/flooding/100376/1 "2002-03-27T14:56:29Z")
How much snow would a city have to have for it to cause a flood when melting in a short period of time? We have about 8 inches here, and the sun just came out and its melting. I know it won’t flood here, but how much snow would there have to be? ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 27, 2002, 3:01pm UTC](https://boards.straightdope.com/t/flooding/100376/2 "2002-03-27T15:01:14Z")
Wow. This is more complicated than you’d think. Stream and rivers: capacity at this time? Ground: conditions? Hard from drought, moderately wet from normal precip? Run off areas: How prepared is the area in terms of drainage ditches? How fast will the melt be? Our company owns a database of “flood zones” which are used when people buy homes/insurance. Very involved, constantly needing updating. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 27, 2002, 3:03pm UTC](https://boards.straightdope.com/t/flooding/100376/3 "2002-03-27T15:03:55Z")
Insufficient information; how good is the city’s drainage system? is the city on a hill, or in a valley? Fresh, uncompacted snow is (apparently) about 90-95% air (or if you prefer, 5-10% water), so by that reckoning a foot of snow is equivalent to just over an inch of rainfall and it would all have to melt in the same time as it takes for that inch of rain to fall to have a similar effect. ---
**Author:** ![vanilla](https://avatars.discourse-cdn.com/v4/letter/v/f19dbf/32.png) [@vanilla](https://boards.straightdope.com/u/vanilla)\ **Post date:** [March 27, 2002, 3:05pm UTC](https://boards.straightdope.com/t/flooding/100376/4 "2002-03-27T15:05:09Z")
ground conditions? Ice under the snow. Rivers? not in my suburb. On a hill? nope. Use a flat area for example. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 27, 2002, 4:56pm UTC](https://boards.straightdope.com/t/flooding/100376/5 "2002-03-27T16:56:57Z")
Mangetout got to the point really. If an inch of rain in a day isn’t a problem in the area, then it is likely that melting of that amount of snow, even in a day shouldn’t be an issue. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 27, 2002, 5:00pm UTC](https://boards.straightdope.com/t/flooding/100376/6 "2002-03-27T17:00:33Z")
Sorry for two quick posts. Here, in the NorthEast, we have had 21 inches of snow from Nor’Easters followed by Bermuda High systems that propelled the temps into the 50s or 60s. Even in our flood prone areas, flooding wasn’t an issue with the fast melt. Flooding became an issue when rainfail exceeded 2 inhces in a 24 hour period. We had 33 inhces of snow followed by mild weather and there were no flood warnings for prone areas. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 27, 2002, 10:25pm UTC](https://boards.straightdope.com/t/flooding/100376/7 "2002-03-27T22:25:43Z")
> [@](#): > > \*Originally posted by Philster \* > \*\*Mangetout got to the point really. If an inch of rain in a day isn’t a problem in the area, then it is likely that melting of that amount of snow, even in a day shouldn’t be an issue. \*\* Except of course we should consider that snow can pile up into drifts in places where water would not collect, but this is only likely to be a problem when we’re talking about a settlement in the bottom of a valley. Since snow tends to be a pretty regular occurrence, people aren’t likely to have built (or been able to build) cities in places where meltwater deluges happen. ---
**Author:** ![vanilla](https://avatars.discourse-cdn.com/v4/letter/v/f19dbf/32.png) [@vanilla](https://boards.straightdope.com/u/vanilla)\ **Post date:** [March 28, 2002, 12:16am UTC](https://boards.straightdope.com/t/flooding/100376/8 "2002-03-28T00:16:55Z")
maybe Noah’s Ark was really just covered with 1,000 feet of snow that melted…😉 ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 28, 2002, 12:24am UTC](https://boards.straightdope.com/t/flooding/100376/9 "2002-03-28T00:24:54Z")
Hey, yeah, or the entire earth was covered with snow to a depth of (allowing for compaction, say) three times the height of everest. Remember, you heard it here first. ---
**Author:** ![vanilla](https://avatars.discourse-cdn.com/v4/letter/v/f19dbf/32.png) [@vanilla](https://boards.straightdope.com/u/vanilla)\ **Post date:** [March 28, 2002, 12:32am UTC](https://boards.straightdope.com/t/flooding/100376/10 "2002-03-28T00:32:07Z")
Yep, thats why there was extra room: the polar bears and penguins were outside.