I ran across this sentence this morning:
here
Now it turns out that 99 percent of egyptians live within the Nile Valley and delta, but still that’s a large area, and rivers wander within their watershed over time. Would a collapse of the damn really kill most of egypt?
I know there’s at least one hydrologist on the SDMB, so I hold out some hope for an actual knowledgeable answer; maybe even a link to some online breach simulation software.
Lake Nasser has 157 km³ of water in it. Letting all that out at once, one would assume the Nile immediately north of the Aswan High Dam would burst its banks straight away, not having the capacity to hold that much water. So, the majority of it spills out over into desert in southern Egypt?
I wouldn’t like to test the theory, though.
You also have to assume the majority of Egypt lives in the north, which is more than 200 miles from Lake Nasser. Even if the water wave swept in at 100 MPH, which is not impossible but probably on the high end of things, the majority of Egypt would have more than 2 hours to evacuate.
If, like Mr Kobayashi said, the geometry is such that the banks are overflowed, then the water won’t reach northern Egypt. If the geometry is such that the water would all flow in a channel, then simply running when you hear the evac order would take most people far away enough. QED 
(which isn’t to say thousands of people wouldn’t die, or millions if there are that many people within a dozen or so miles of the dam, which I don’t know enough to say one way or the other.)
If we blast hole in a dam, we create a chokepoint, or bottleneck. How much water can get through that narrow bit in a period of time? This will help us see how high the deluge would be and how long it would last at any one moment. We also have to consider how much water would be lost in relatively uninhabited areas, such water would kill few people.
As the deluge moves downstream more and more of it would be slowed or lost from the main wave of destruction. So a huge wall of water at Asswan might be a long-lasting ripple at Alexandria.
Well, any major flooding even like that from a breached damn hold back an assload of water, involving a timeline of just a few hours warning and evacuating 10 of millions of people will certaintly not end well IMO. How not well is just details…
Here’s similar speculation on the potential damage the destruction of Mosul dam might do in the Tigris river valley. Lake Nasser however is a lot bigger than the water held back by the Mosul dam, I still think it’d lead to the ‘overflowing bath’ type model of flooding; water goes over the side as well as just down the Nile.
You always read that Israel doesn’t need nukes against Egypt 'cause they just have to simply take out the dam.
It would be an interesting computer model to see how much of the water would flow out like an overflowing tub.
I think another question that arises is, even if the people (or most of them) get to safe ground, what happens after. Do the people run into trouble without having the reserve of water? Does Sudan, Ethiopia and the other nations downstream reoppose Egypts efforts to rebuild the dam?
Just the fact that lots of valuable and useful stuff would be washed away or ruined would be enough of disaster.
Hell, look at Katrina and New Orleans. Statistically speaking, deaths were nearly zero for a “disaster”. Cost and aggravation? Nearly priceless.
At least it would cut the prevalance of bilharzia in the country.
(What do you know, something learned at school comes back for the boards…)
The flooding itself probably wouldn’t kill that many people, but it would render at least half the remaining population homeless and destroy virtually all the country’s arable land. What the water didn’t take, famine would.
The Nile Valley from the Dam north to Cairo averages @ 10 kilometers in width. It contains all the the populated, arable land of Egypt south of Cairo, and the entire population of the country that lives south of Cairo. The most likely scenario is that there would be a tsunami-like events down the valley up to Cairo (unless the Egyptian govt has constructed some diversionary paths, which is unlikely because they use the dam to control the flow of the river and consequent irrigation, etc. of the entire valley). Perhaps people living in the valley could flee to higher ground in the desert to the east and west of the valley. But it would mean going to a desert that has no water, no sanitation facilities, no power generation facilities (by the way the Dam supplies a significant percentage of the country’s electrical power), no means of sustaining life, etc. This would be a catastrophic disaster. The Egyptian government under Mubarak understood it was effectively held hostage by the Dam in the sense that the country could effectively be destroyed as an economically viable and politically functional society, and that it does not take a nuclear bomb to destroy the Dam. Hopefully, those who succeed him as “rulers” of Egypt will arrive at the same realization and that such realization will temper their inclination to try to “wipe Israel off the map.”
The dam only produces about 10% of Egypt’s electrical power requirements today, so that’s probably the smallest concern.
On a similar vien, what would happen if the Three Gorges Dam in China was breached? Does anybody know how many people live below it?
Probably not that many. It’s only been there for 5 years, and only 1.3 million people were displaced during construction, which suggests that the area isn’t all that populous.
Late to the party, sorry.
The floodwave resulting from a dam break is not easily predicted, because its volume/velocity/height would vary with things like the size and shape of the initial breach, height of the river downstream, volume of water in the reservoir at the time, etcetera.
That being said, a breach of a such a large dam would be quite destructive and the flood wave could be expected to propagate a long way downstream.
Unless it’s a zombie dam.
a delta is basically a “low energy” area, where the gradient of the ground has leveled, the main river splits and splays into several arms to empty into the sea. current action (both from the river and the sea) is low in areas protected by sand bars, mangroves, and natural levees. i can’t really predict how much energy the water from the aswan will have by the time it reaches the delta area bu i have a feeling it would have dissipated much of its energy (you’ll still have flooding though.)
What’s the largest dam to date that has broken, and what kind of devastation did it produce? Would what happened there be any help in trying to predict an Aswan catastrophe?
I know Egypt has had at least one dam break, but that was several thousand years ago >_>
Well, the Red Sea split went badly for the Egyptian army…
The largest dam collapse in history would have been the Banqiao Damthat failed in China during 1975. It killed ~171,000 people, and made ~11 million people homeless. Though I don’t think it would help much in predicting how much damage an Aswan dam failure would cause, as the amount of damage done by a damn failure is highly dependent on the particulars of the situation (how much water is released, how many people live downstream, how far away they are, time of the collapse, ect and so on. )
And here I am, reading the thread title and thinking, “that’s a weird name for an album…”