# Where could the Mississippi River be dammed to create the largest possible lake? **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2011, 5:40pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038 "2011-09-29T17:40:46Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![drastic\_quench](https://avatars.discourse-cdn.com/v4/letter/d/e36b37/32.png) [@drastic\_quench](https://boards.straightdope.com/u/drastic_quench)\ **Post date:** [September 29, 2011, 5:40pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/1 "2011-09-29T17:40:46Z")
Think on the rough scale of China’s Three Gorges Dam and Reservoir. What stretch of the river has the right geography to make a mega lake? ---
**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\ **Post date:** [September 29, 2011, 6:02pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/2 "2011-09-29T18:02:39Z")
> [@drastic\_quench](#): > > Think on the rough scale of China’s Three Gorges Dam and Reservoir. What stretch of the river has the right geography to make a mega lake? On the Mississippi? You need a deep canyon to make a big lake with just a dam. If you want something the scale of the Three Gorges Reservoir, go to Lake Mead (which is, in fact, almost the same size in volume). ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [September 29, 2011, 6:21pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/3 "2011-09-29T18:21:32Z")
> [@panamajack](#): > > On the Mississippi? You need a deep canyon to make a big lake with just a dam. If you want something the scale of the Three Gorges Reservoir, go to Lake Mead (which is, in fact, almost the same size in volume). The Mississippi has very little drop it’s entire length. I think it only starts out 800 feet above sea level. That’s about the same as the height of the three gorges dam itself. In order to get something comparable you’d need to dig out a lake or creates one by pumping water up into a man made reservoir. Just building a dam across the Mississippi isn’t going to do what you want. An 800 foot dam is going to effectively reverse the Mississippi’s flow not create a big lake. Maybe lots of new swamp land and plenty of new little lakes popping up on the tributaries ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [September 29, 2011, 6:46pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/4 "2011-09-29T18:46:25Z")
1,475 ft (450 m), according to the wiki article on [Lake Itasca](http://en.wikipedia.org/wiki/Lake_Itasca). ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [September 29, 2011, 6:59pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/5 "2011-09-29T18:59:58Z")
> [@boytyperanma](#): > > Just building a dam across the Mississippi isn’t going to do what you want. An 800 foot dam is going to effectively reverse the Mississippi’s flow not create a big lake. Maybe lots of new swamp land and plenty of new little lakes popping up on the tributaries Not following you, are you saying that it would find a way around the dam? If so, you could just make a bigger dam. Or are you saying that at the 800 foot level, some of the water would be taking other paths to the ocean than the Mississippi? (Ignoring distributaries like the Atchafalaya.) ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 29, 2011, 7:14pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/6 "2011-09-29T19:14:37Z")
> [@Ludovic](#): > > Not following you, are you saying that it would find a way around the dam? If so, you could just make a bigger dam. And you’d end up with a giant puddle, only a few feet deep. There isn’t anything like the Three Gorges where you could create a deep reservoir. Your dam might end up being 10’s or even 100’s of miles long to get any significant depth to the reservoir. ---
**Author:** ![Foggy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foggy/32/1082_2.png) [@Foggy](https://boards.straightdope.com/u/Foggy)\ **Post date:** [September 29, 2011, 7:27pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/7 "2011-09-29T19:27:23Z")
Drop a couple of nukes on the river bed near Memphis until you have a deep enough crater and then let the river fill it up. Simple! ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [September 29, 2011, 8:52pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/8 "2011-09-29T20:52:50Z")
> [@Northern\_Piper](#): > > 1,475 ft (450 m), according to the wiki article on [Lake Itasca](http://en.wikipedia.org/wiki/Lake_Itasca). True, but the point about very little drop for most of its length remains valid, especially if we consider how large a river it is at various elevations. Cairo, IL has an elevation of 315 feet. At that point, the Ohio is very clearly the main branch, and if the names hadn’t already been established, you would probably consider the upper part of the Mississippi River the tributary. By the time the Mississippi even gets to Minneapolis, the elevation has dropped to around 800 feet. ---
**Author:** ![drastic\_quench](https://avatars.discourse-cdn.com/v4/letter/d/e36b37/32.png) [@drastic\_quench](https://boards.straightdope.com/u/drastic_quench)\ **Post date:** [September 29, 2011, 9:13pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/9 "2011-09-29T21:13:52Z")
> [@Foggy](#): > > Drop a couple of nukes on the river bed near Memphis until you have a deep enough crater and then let the river fill it up. Simple! Hmm. I might go with this. I’m not familiar with the topography for the entire length of the river. I just hoped their was a section of valley somewhere along the banks that’d work. ---
**Author:** ![AndyLee](https://avatars.discourse-cdn.com/v4/letter/a/898d66/32.png) [@AndyLee](https://boards.straightdope.com/u/AndyLee)\ **Post date:** [September 29, 2011, 9:40pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/10 "2011-09-29T21:40:55Z")
What do you mean the river would flow backwards? I’m having a hard time trying to visualize that ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [September 29, 2011, 10:02pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/11 "2011-09-29T22:02:32Z")
> [@AndyLee](#): > > What do you mean the river would flow backwards? I’m having a hard time trying to visualize that Try visualizing whirled peas first. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [September 29, 2011, 10:05pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/12 "2011-09-29T22:05:55Z")
The Mississippi floods rather easily, as anybody knows. That means the territory around the river is flat, bordering on the even flatter. There really is no place on the river to create that big a lake. The river would just flow around the dam and create new riverbed. ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [September 30, 2011, 12:00am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/13 "2011-09-30T00:00:41Z")
> [@AndyLee](#): > > What do you mean the river would flow backwards? I’m having a hard time trying to visualize that Take a 10 foot open ended section of gutter. To simulate the drop from the beginning to the end of the Mississippi, take a single penny and put it under one end. All things being equal gravity would tend to force most the water out the ‘lower’ end. If you blocked the lower end the waters going to be forced to reverse direction and instead flow out the upper end. The area that makes up the Mississippi watershed is massive, it could contain more water than water is circulating in the environment. Water evaporates it doesn’t just have to flow to sea level. A river can effective flow up hill provided water at the upper end is being removed fast enough. There are a number of real world examples where the flow of a river has been reversed. The Colorado River originally flowed west to east through the Grand Canyon area. The geology changed at some point due to tectonic shifting, the Rockies rose up creating a natural dam in that direction. This forced the river to reverse course cutting a new path east to west through the Grand Canyon. A man made example is the Chicago River. It used to flow from the Mississippi to Lake Michigan. The locals decided that didn’t work for them because their own pollution kept washing up on their beaches, it would be better to force it to flow into the Mississippi so someone else had to deal with their shit(literally). They built some dams and used the momentum generated by releasing water from those locks to force the water in the other direction. For the most part the Chicago river at it’s surface is always flowing south, the current underneath still varies seasonally. The floaty stuff still goes into the Mississippi though they’ve cleaned up their act a bit since the 1800’s ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [September 30, 2011, 4:09am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/14 "2011-09-30T04:09:01Z")
> [@silenus](#): > > The Mississippi floods rather easily, as anybody knows. That means the territory around the river is flat, bordering on the even flatter. There really is no place on the river to create that big a lake. The river would just flow around the dam and create new riverbed. Here’s a link to a map showing the different historical riverbeds of the lower Mississippi, illustrating how easily it shifts: [Shifting like a Snake: Ancient Mississippi Courses](http://bigthink.com/ideas/21260). ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [September 30, 2011, 5:48am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/15 "2011-09-30T05:48:14Z")
> [@silenus](#): > > The Mississippi floods rather easily, as anybody knows. That means the territory around the river is flat, bordering on the even flatter. There really is no place on the river to create that big a lake. … Sure there are. There are the Rockies to the west and the Appalachians to the east. Though you will need a VERY wide dam. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [September 30, 2011, 5:56am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/16 "2011-09-30T05:56:19Z")
I think you could dam the Mississippi at Memphis and create a very large lake. The dam would have to stretch from Chatanooga to someplace east of Santa Fe NM. ETA: **Boyo** ’s got the right idea. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 30, 2011, 11:28am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/17 "2011-09-30T11:28:32Z")
> [@Boyo\_Jim](#): > > Sure there are. There are the Rockies to the west and the Appalachians to the east. Though you will need a VERY wide dam. Just raise I-80 a few feet and you’re all set. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [September 30, 2011, 11:40am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/18 "2011-09-30T11:40:55Z")
While in theory you could build some sort of megastructure between the Ozarks and the Alleghenies and flood large parts of several states, this is turning into an absurdity. Let’s vary the question a bit: Using modern technology, I want to build a dam, plus any needed ancillary construction, somewhere in the world, no more than 3 km in span, which will confine the greatest amount of acre-feet of water. For our purposes, assume no issues of navigability, historical importance, cities needing relocation, etc., are issues – for whatever reason, this dam _must_ be built. Where would it be located to meet the criteria outlined above? ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [September 30, 2011, 11:51am UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/19 "2011-09-30T11:51:24Z")
> [@Boyo\_Jim](#): > > Sure there are. There are the Rockies to the west and the Appalachians to the east. Though you will need a VERY wide dam. > [@TriPolar](#): > > I think you could dam the Mississippi at Memphis and create a very large lake. The dam would have to stretch from Chatanooga to someplace east of Santa Fe NM. > > ETA: **Boyo** ’s got the right idea. Except there isn’t enough water in the system to actually fill such an area. I think the closest anyone’s come is dropping nukes next to Memphis to make a giant hole, that will give you something you could work with to make a lake. That and I like the idea of nuking Memphis. Blocking the Mississippi will make lots and lots of new swampland and little lakes. No giant lake. Where are the resident geologists? I’d love to hear what they have to say. I’m going off my knowledge from the high school, the history channel and NPR and feel I’m rather lacking. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [September 30, 2011, 1:33pm UTC](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038/20 "2011-09-30T13:33:17Z")
Og knows I’m all in favor of nuking Memphis, but if there’s no outlet to the ocean for water between the two big mountain ranges, it seems the space will eventually fill up, nukes or not. [Next page](https://boards.straightdope.com/t/where-could-the-mississippi-river-be-dammed-to-create-the-largest-possible-lake/598038.md?page=2)