# 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:** 20\ **Page:** 1
**Author:** ![Artemis\_Tardis](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Artemis\_Tardis](https://boards.straightdope.com/u/Artemis_Tardis)\ **Post date:** [March 31, 2014, 1:37am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/1 "2014-03-31T01:37:07Z")
I have a post-grad assign mentwith the following scenario: A small town is 18 km away from a big dam and we have to create a system to evacuate the town if something bad happens. For instance, a huge explosion. What I have no idea of how to do is to calculate how much time do the citizens have to run away before they are flushed away… Any help with that? ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [March 31, 2014, 1:41am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/2 "2014-03-31T01:41:28Z")
> [@demian\_travis](#): > > I have a post-grad assign mentwith the following scenario: A small town is 18 km away from a big dam and we have to create a system to evacuate the town if something bad happens. For instance, a huge explosion. What I have no idea of how to do is to calculate how much time do the citizens have to run away before they are flushed away… Any help with that? way too many unknowns. And what do you mean by explodes? Are you postulating that the dam will literally explode? How might that be imagined? I doubt even a nuclear weapon under a dam would “explode” the dam. The dam will fail of course, but not explode in any sense. ---
**Author:** ![nevadaexile](https://avatars.discourse-cdn.com/v4/letter/n/eb8c5e/32.png) [@nevadaexile](https://boards.straightdope.com/u/nevadaexile)\ **Post date:** [March 31, 2014, 1:50am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/3 "2014-03-31T01:50:48Z")
A dam exploding would have to be caused by an act of sabotage or the dam itself being struck by a weapon,a meteor impact or large aircraft flying at a high rate of speed into it. It cannot “explode” in any other manner as there no volatile chemicals or hydrocarbons routinely used inside the dam’s structure which could cause it to do so. Also, if it did “explode” the denotation or the resulting shockwave would likely cause as much damage to the nearby town as the eventually flooding and mudslides created when the water the dam was holding back reached it. Now if a dam _ **failed** _, due to sabotage, poor maintenance, a natural disaster,etc, then how long it would take for the water to reach the town would likely depend upon: [ol] [li]How much water was released.[/li][li]The terrain between the dam and the town[/li][li]Whether there were one or more natural channels at or in the town to divert the flow[/li][li]The exact location of the town in reference to the dam (if it was on a hillside above the river controlled by the dam or on a plain alongside the river,etc)[/li][/ol] You would probably get a better answer if you provide the size of reservoir behind the dam, the height/width of the dam,the terrain around the dam and the town,etc. ---
**Author:** ![BlakeTyner](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@BlakeTyner](https://boards.straightdope.com/u/BlakeTyner)\ **Post date:** [March 31, 2014, 1:54am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/4 "2014-03-31T01:54:49Z")
You might start here: > **[Johnstown Flood](https://en.wikipedia.org/wiki/Johnstown_flood)** > > The Johnstown Flood, sometimes referred to locally as Great Flood of 1889, occurred on Friday, May 31, 1889, after the catastrophic failure of the South Fork Dam, located on the south fork of the Little Conemaugh River, 14 miles (23 km) upstream of the town of Johnstown, Pennsylvania, United States. The dam ruptured after several days of extremely heavy rainfall, releasing 14.55 million cubic meters of water. With a volumetric flow rate that temporarily equaled the average flow rate of the Mis Th... 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. ---
**Author:** ![El\_Kabong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/el_kabong/32/496_2.png) [@El\_Kabong](https://boards.straightdope.com/u/El_Kabong)\ **Post date:** [March 31, 2014, 1:56am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/5 "2014-03-31T01:56:49Z")
In the 1889 Johnstown, PA flood, which resulted from the catastrophic failure of a dam upriver, water from the breached reservoir traveled the 14 mile (approx. 22.5 km) distance to the city in 57 minutes. Items to consider, obviously, would be the average width of the channel and the slope of the river bed, but this may provide a rough baseline. > **[Johnstown Flood](https://en.wikipedia.org/wiki/Johnstown_Flood)** > > The Johnstown Flood, sometimes referred to locally as Great Flood of 1889, occurred on Friday, May 31, 1889, after the catastrophic failure of the South Fork Dam, located on the south fork of the Little Conemaugh River, 14 miles (23 km) upstream of the town of Johnstown, Pennsylvania, United States. The dam ruptured after several days of extremely heavy rainfall, releasing 14.55 million cubic meters of water. With a volumetric flow rate that temporarily equaled the average flow rate of the Mis Th... ETA: heh, ninja’d as usual. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [March 31, 2014, 1:59am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/6 "2014-03-31T01:59:56Z")
Here’s another example: > [@](#): > > Five minutes after the collapse, having traveled one and a half miles (2.4 km) at an average speed of 18 miles per hour (29 km/h) > > At a speed of 12 mph (19 km/h) the water continued on and entered the valley > > The flood had taken only 5 hours and 27 minutes to travel the 54 miles (87 km) from the dam site to the sea. At that time it was almost two miles (3 km) wide and traveling at a speed of 6 mph (9.7 km/h) > **[St. Francis Dam](https://en.wikipedia.org/wiki/St._Francis_Dam)** > > The St. Francis Dam, or the San Francisquito Dam, was a concrete gravity dam located in San Francisquito Canyon in northern Los Angeles County, California, United States, that was built between 1924 and 1926. The dam failed catastrophically in 1928, killing at least 431 people in the subsequent flood, in what is considered to have been one of the worst American civil engineering disasters of the 20th century and the third-greatest loss of life in California history. > The dam was built to serve ... Looks like you’ve got anywhere between 20 minutes and an hour and a half as a reasonable guesstimate. ---
**Author:** ![nevadaexile](https://avatars.discourse-cdn.com/v4/letter/n/eb8c5e/32.png) [@nevadaexile](https://boards.straightdope.com/u/nevadaexile)\ **Post date:** [March 31, 2014, 2:04am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/7 "2014-03-31T02:04:20Z")
There’s also this:[Teton Dam - Wikipedia](http://en.wikipedia.org/wiki/Teton_Dam) But each dam is different so each scenario would be different. ---
**Author:** ![Twoflower](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/twoflower/32/22_2.png) [@Twoflower](https://boards.straightdope.com/u/Twoflower)\ **Post date:** [March 31, 2014, 2:34am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/8 "2014-03-31T02:34:33Z")
Is this a theoretical town and dam, or a real-life example? If it’s real, look for the “dam inundation map” associated with the dam in question. If the map is not available online due to terrorism paranoia, try contacting FEMA and/ or the Army Corps of Engineers. ---
**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, 2:35am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/9 "2014-03-31T02:35:24Z")
In 1993 a Missouri River levee failed at [Chesterfield, Mo](http://www.drj.com/drworld/content/w3_080.htm), flooding an approximately 4,000 acres. > [@](#): > > On July 30 at 10:17 p.m. the surging Missouri River muscled its way through the Monarch Levee. A wall of flood waters spilled through a 100 foot section of the gaping rupture, filling the Chesterfield Valley with thousands of gallons of flood waters. Authorities closed both directions of Highway 40 at 12:50 a.m. Saturday, July 31. In addition to the businesses affected, the Spirit of St. Louis Airport, and the county’s Adult Correctional Institution were deluged with the murky flood water. By dawn the valley was completely flooded with over eight feet of water and debris. Truck trailers floated like toys in a bathtub. Considering Highway 40 was not just a major route but the primary evacuation path for the entire valley, they would have kept it open until the very last minute, so 2.5 hours was about the maximum time they could push it. At the same time [NOAA said the Mississippi River at St. Louis was flowing at 1.08 million cubic feet per second](http://www.crh.noaa.gov/lsx/?n=1993_flood), which would fill a bowl the size of Busch Stadium in 69 seconds. ---
**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, 2:43am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/10 "2014-03-31T02:43:56Z")
Too late for the edit. When the Taum Saulk reservoir dam failed in 2005, the lake level dropped by approximately [90 feet in 15 minutes.](https://www.bpa.gov/power/PG/NW-HydroOperators-Forum/Materials/CaseStudyT-Sauk_Ehasz-Paul.pdf) ---
**Author:** ![Enginerd](https://avatars.discourse-cdn.com/v4/letter/e/bcef8e/32.png) [@Enginerd](https://boards.straightdope.com/u/Enginerd)\ **Post date:** [March 31, 2014, 3:06am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/11 "2014-03-31T03:06:07Z")
> [@demian\_travis](#): > > I have a post-grad assign mentwith the following scenario: A small town is 18 km away from a big dam and we have to create a system to evacuate the town if something bad happens. For instance, a huge explosion. What I have no idea of how to do is to calculate how much time do the citizens have to run away before they are flushed away… Any help with that? Are you supposed to give a best guess answer from analogous cases, or are you supposed to actually calculate it? If you need to calculate it, you’re probably looking at transient flood routing using the Saint Venant equations - check out dynamic wave modeling. ---
**Author:** ![Artemis\_Tardis](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Artemis\_Tardis](https://boards.straightdope.com/u/Artemis_Tardis)\ **Post date:** [March 31, 2014, 3:20am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/12 "2014-03-31T03:20:25Z")
Sorry for the terrible english and lack of details. I had a terrible night of sleep. And a hangover. It is a theoretical dam and city, and the city needs a system to evacuate its citizens in case of a disaster (a failure on the dam). The data you guys provided is really helpful! Question: What would you do if you were on a city 18 km away from a dam that just burst open? Is there any chance of survival if one escapes right after the disaster? ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [March 31, 2014, 3:29am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/13 "2014-03-31T03:29:07Z")
Climb the nearest hill at the fastest possible speed ? ---
**Author:** ![Beauregard\_Porkypine](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@Beauregard\_Porkypine](https://boards.straightdope.com/u/Beauregard_Porkypine)\ **Post date:** [March 31, 2014, 4:12am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/14 "2014-03-31T04:12:13Z")
Another variable is the amount of pre-planning was done by both the government and the towns citizens. A town that sits in the path of an upstream dam and reservoir will have a government that has done, or should have done, specific pre-disaster mitigation planning. This would include how to give sufficient warning to all citizens, evacuation routes and alternate routes and sheltering. How do you contact citizens who don’t have phones or internet? How do you evacuate special needs and non-ambulatory citizens? Where will they go when they evacuate? Do you have special shelters that except pets? Most shelters don’t and most people will not go if they can’t take their pets. What transportation will you use to evacuate hospitals, nursing homes and assisted living centers? How will you evacuate the jail or prison? Can you, in an hours time, have enough responders to go door to door and clear every household, school, hospital and business? Even if you give an hours notice many citizens will struggle unless they too have done some pre-planning. Have they, at some time in the past, collected any non replaceable items and made a evacuation Go Kit? Do they know where they will meet up with other family members if they’re away at work or school at the time of the emergency? Do they have transportation to evacuate? Some citizens will have mobility issues. Some will need medical oxygen, dialysis, special medications or other critical needs to stay alive. Have these citizens done their pre-planning? As you can see, even if you are given the luxury of a one hour, the evacuation of even a small town is very challenging. If they haven’t done any pre-planning then…Surfs Up! ---
**Author:** ![nevadaexile](https://avatars.discourse-cdn.com/v4/letter/n/eb8c5e/32.png) [@nevadaexile](https://boards.straightdope.com/u/nevadaexile)\ **Post date:** [March 31, 2014, 4:26am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/15 "2014-03-31T04:26:34Z")
> [@demian\_travis](#): > > Sorry for the terrible english and lack of details. I had a terrible night of sleep. And a hangover. > > It is a theoretical dam and city, and the city needs a system to evacuate its citizens in case of a disaster (a failure on the dam). The data you guys provided is really helpful! > > Question: What would you do if you were on a city 18 km away from a dam that just burst open? Is there any chance of survival if one escapes right after the disaster? This again depends upon a number of variables, including: [ol] [li] **The conditions of the roads** - Two lanes vs. four.? State highway vs. interstate? Any bridges or tunnels? Mountainous terrain?[/li][li] **What time of day it is** - Morning ( better), afternoon ( maybe a lot of traffic, not so good) Evening/early morning before day ( Worst as teh darkness and the people being tired or having to wake up will delay their response time)[/li][li] **Planning** - If there’s a solid warning and evacuation plan, things may go well. If there isn’t, there will be mass casualties.[/li][li] **History** - Has this ever occurred before? Johnstown,Pennsylvania for example has experienced two major floods. The one in the 19th century was one of the worst natural disasters in American history. They would expect a dam incident. A town where there has never been a serious natural disaster, night still get caught off guard even with warming.[/li][/ol] Some free advice: Sit back and really plot out the details on this before you make a decision or a plan. This isn’t going be a simple process. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [March 31, 2014, 10:11am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/16 "2014-03-31T10:11:32Z")
The most famous incident of catastophic failure that springs to mind is the [Vaiont Dam](http://en.wikipedia.org/wiki/Vajont_Dam) in Italy. It was a landslide that caused a massive wave of water to overtop the dam and it killed thousands in many of the villages down the valley. It has been extensively studied so I’d image it’d be a good starting point to give you a feel for the sort of “worst-case” timings for evacuations (unfortunately, in this case there was no warning at all) ---
**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, 10:38am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/17 "2014-03-31T10:38:08Z")
> [@demian\_travis](#): > > Question: What would you do if you were on a city 18 km away from a dam that just burst open? Is there any chance of survival if one escapes right after the disaster? Move as fast as possible to high ground in a direction about 90 degrees from the direction of flow. If you have, say, 45 minutes warning, you can get two miles away at a brisk, but sustainable walking speed. In reality though, the warning may come late and you may not be in a position to evacuate immediately (if your kids are at school, for example). ---
**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, 11:14am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/18 "2014-03-31T11:14:12Z")
How tall and how sturdy is the tallest building around? If it’s a steeple in an old wood church I head for the hills. If it’s a 30 story concrete and steel Hyatt Regency I’m headed for the rooftop bar. ---
**Author:** ![Ken001](https://avatars.discourse-cdn.com/v4/letter/k/43a26b/32.png) [@Ken001](https://boards.straightdope.com/u/Ken001)\ **Post date:** [March 31, 2014, 11:16am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/19 "2014-03-31T11:16:08Z")
> [@Novelty\_Bobble](#): > > The most famous incident of catastophic failure that springs to mind is the [Vaiont Dam](http://en.wikipedia.org/wiki/Vajont_Dam) in Italy. > > It was a landslide that caused a massive wave of water to overtop the dam and it killed thousands in many of the villages down the valley. It has been extensively studied so I’d image it’d be a good starting point to give you a feel for the sort of “worst-case” timings for evacuations (unfortunately, in this case there was no warning at all) How interesting. I was a young child and yet I remember the news reports of that horrifying event. ---
**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, 11:19am UTC](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950/20 "2014-03-31T11:19:18Z")
> [@zoid](#): > > How tall and how sturdy is the tallest building around? > If it’s a steeple in an old wood church I head for the hills. > If it’s a 30 story concrete and steel Hyatt Regency I’m headed for the rooftop bar. 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. [Next page](https://boards.straightdope.com/t/how-fast-will-water-spread-id-a-dam-explodes/684950.md?page=2)