# how fast will water spread id a dam explodes? **URL:** \ **Category:** Factual Questions\ **Created:** [March 31, 2014, 1:37am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950 "2014-03-31T01:37:07Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [March 31, 2014, 11:36am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/21 "2014-03-31T11:36:48Z")
> [@BlakeTyner](#): > > You might start here: > > [Johnstown Flood - Wikipedia](http://en.wikipedia.org/wiki/Johnstown_flood) > > Johnstown was 23km downstream from a major dam that failed. It took the water 57 minutes to travel that distance. At least that gives a bit of precedent, although there are, as noted, LOTS of variables. If anyone ever finds themselves in Johnstown, the Flood Museum is worth part of a day. ---
**Author:** ![zoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zoid/32/336_2.png) [@zoid](https://boards.straightdope.com/u/zoid)\ **Post date:** [March 31, 2014, 11:45am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/22 "2014-03-31T11:45:01Z")
> [@Mangetout](#): > > Concur - almost. Solid, tall buildings would be the best compromise if the warning comes late, but high ground is always preferable to any built structure, if you can get there in time. [No damn break in the world is knocking this down.](http://zannaland.com/wp-content/uploads/2013/07/Signature-Exterior-Hyatt-Regency-Grand-Cypress-2013-SMALL.jpg) Probably safer than running because it requires less time to reach a safe location. ---
**Author:** ![Meurglys](https://avatars.discourse-cdn.com/v4/letter/m/258eb7/32.png) [@Meurglys](https://boards.straightdope.com/u/Meurglys)\ **Post date:** [March 31, 2014, 1:30pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/23 "2014-03-31T13:30:16Z")
In WW2 the Mohne Dam in Germany was destroyed by a British bombing raid and [Wiki](http://en.wikipedia.org/wiki/Operation_Chastise#Bomb_damage_assessment) says (under the section ‘effect on the war’) > [@](#): > > The two direct mine hits on the Möhnesee dam resulted in a breach around 250 feet (76 metres) wide and 292 feet (89 metres) deep. The destroyed dam poured around 330 million tons of water, equivalent to a cube measuring 687 metres, into the western Ruhr region. A torrent of water around 32.5 feet (10 metres) high and travelling at around 15 mph (24 km/h) swept through the valleys of the Möhne and Ruhr rivers. which gives 45 minutes to reach your hypothetical town (if it were there!) Several other dams were destroyed or damaged; I expect there will be similar info for the others on Wiki as well… ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [March 31, 2014, 1:37pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/24 "2014-03-31T13:37:39Z")
The Lake Murray Dam is about 14 miles from downtown Columbia. I have read that after a dam failure the Gervais Street bridge would be 20 feet underwater in 20 minutes. (I, personally, would try to get off it before that 20 foot mark, you know, given the choice.) Considering that most people here never even think about the dam and the big honking lake behind it, a true dam disaster would be absolutely catastrophic. There’s no way they could evacuate - I don’t even know what the signal would be and I pay attention and have lived here almost all my life. Thankfully a few years ago they did a bunch of earthquake-proofing work on it. But hey, I work on the second floor at least. ---
**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 31, 2014, 1:54pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/25 "2014-03-31T13:54:14Z")
> [@zoid](#): > > [No damn break in the world is knocking this down.](http://zannaland.com/wp-content/uploads/2013/07/Signature-Exterior-Hyatt-Regency-Grand-Cypress-2013-SMALL.jpg) I honestly wouldn’t be so sure about that - it may look solid, but it’s a lattice of reinforced concrete beams - designed primarily for load under compression. Demolition of a structure like that often only requires a comparatively small amount of damage to the supporting members at ground level - if the water arrives fast and is carrying a lot of large debris, even quite a large concrete building could end up collapsing into the flood. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [March 31, 2014, 2:53pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/26 "2014-03-31T14:53:23Z")
As earch for the 1982 floods in Valencia brought me a wiki article on “[dam failure](http://en.wikipedia.org/wiki/Dam_failure)” and these: [The Tous Dam disaster](http://link.springer.com/article/10.1007/s11069-012-0458-0#page-1) – from what I’ve skimmed, it talks mostly about the sociopolitical consequences, the creation of evacuation plans etc [Description of the Tous Dam break case study](http://www.tandfonline.com/doi/abs/10.1080/00221686.2007.9521832#.UzmAG_l_vWw) — this one appears to be more about the engineering/physics end of things My flat is downstream from a pretty large dam; if it failed without warning there wouldn’t be time to evacuate the town. Instructions in case evacuation is not possible (and for those who for some reason can’t evacuate) is to get to the highest floors. The river is pretty low from the village, though: unless the dam shatters, the water should barely lick the church (which is the building closest to the river itself). ---
**Author:** ![Kent\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kent_clark/32/105_2.png) [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)\ **Post date:** [March 31, 2014, 5:32pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/27 "2014-03-31T17:32:03Z")
The USGS actually did [measurements when the flood gates were opened at Hoover Dam.](http://pubs.usgs.gov/fs/FS-168-97/pdf/fs-168-97.pdf) Short answer, “it depends.” ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 31, 2014, 6:43pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/28 "2014-03-31T18:43:29Z")
One of Johnstown’s responses to the Great Flood was to build the steepest inclined railway in the world, both to facilitate development up on the hills, and to evacuate citizens in the event of another flood (a job that it actually performed in two subsequent floods, though those weren’t nearly as severe as the 1889 one). ---
**Author:** ![zoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zoid/32/336_2.png) [@zoid](https://boards.straightdope.com/u/zoid)\ **Post date:** [March 31, 2014, 7:31pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/29 "2014-03-31T19:31:12Z")
> [@Mangetout](#): > > I honestly wouldn’t be so sure about that - it may look solid, but it’s a lattice of reinforced concrete beams - designed primarily for load under compression. Demolition of a structure like that often only requires a comparatively small amount of damage to the supporting members at ground level - if the water arrives fast and is carrying a lot of large debris, even quite a large concrete building could end up collapsing into the flood. The tsunami that hit japan demonstrated that reinforced concrete [is pretty damn strong.](http://geol105naturalhazards.voices.wooster.edu/files/2012/03/japan-earthquake-tsunami-nuclear-unforgettable-pictures-ship_33287_600x450.jpeg) Those are simple 2 story buildings. There’s no way a hotel, properly constructed, is going anywhere. ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [March 31, 2014, 10:17pm UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/30 "2014-03-31T22:17:22Z")
Doesn’t it predominantly depend on the difference in height between the dam and town? I am pretty sure that water over Niagra Falls drops at 32ft/(sec)(sec), and that if there is a mountain between the damn and the town then the water would only reach there after it has evaporated and rained down. [Previous page](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950.md?page=1)