The states around the Persian gulf are, at least currently, filthy rich and mostly at low elevation. If they pooled their resources to dam the strait of Hormuz to combat raising sea levels, could it be done?
Since I find even “regular” construction projects around the world absolutely staggering I don’t trust my own judgment of “That probably couldn’t be done, right?”
The Strait of Hormuz is about 55 km wide at its narrowest point. The longest seawall/dyke in the world is about 33 km long, so the distance to be spanned is about two-thirds as long again as that. In addition, the Strait of Hormuz is about 150 meters deep at its deepest, while the Saemangeum Seawall is about 54 meters tall at its tallest.
In addition, you would have to construct locks in this hypothetical seawall, since the reason these gulf states are rich is that they can ship oil to the rest of the world, and they would not want to turn off that particular pipe. And you’d need to get cooperation between all of the Gulf states, some of which hate each other’s guts (particularly Iran vs. Iraq and Iran vs. Saudi Arabia), so in the current political climate it would be a non-starter.
There would be a lot of challengng problems.
First, there would have to be a shipping channel through it, since 1/3 of all the worlds maritime-shipped oil passes through there. Then, that opening (or any other breach) would inundate any economic development on protected or reclaimed land. And there will be, for some time to come, unpredictable political implications. So defending it would be almost as problematic as building it.
As for building it, it is about 32 miles across, and the engineering should not present any problems except sheer magnitude. The maximum depth is 100 meters. It would be Iran on one end, and Oman, currently one of the more liberal nations, on the other. But there are eight nations whose shorelines would be affected, and it wold seem impossible for them to all agree on the terms.
Also, would damming the straits lower sea levels, or raise them? There a number of major rivers that empty into the Straits, after all.
My guess is that building dikes along the coastline (similar to the Netherlands) would be a both less expensive and more politically expedient way to protect the coastlines.
Good question.
Well that’s one major issue. You’d need pumps capable of continuously removing that much water. Even more if you want to preserve salinity.
Really? Even if we only protect the cities we’re talking at least half a dozen large cities, and many smaller ones, that’s a lot of dikes and long ones too if we’re not going to leave them isolated from the remaining dry land. A modest sea level increase of just seven meters would be a major problem for all of the small states around the gulf. If we posit a more significant rise, say 30 meters, the most populous areas of multiple states go completely under water and Iraq gets inundated almost up to Baghdad. Lowest Land Points Below Sea Level Map | Depression Elevations
Really. Building on a wall on land is extremely cheap compared to building a wall at the bottom of the sea.
You think they’d rather drown?
I can see that, but we’re talking a few tens of miles versus hundreds, and most of the building is just dumping landfill, which, depending on the source, would be transported by sea anyway.
Not trying to claim any expertise mind you.
No, they’d just build their own independent dike system (a la the Netherlands). Since OP’s actual proposal is infeasible, as likely to provoke flooding from land-based inflows as from rising external sea levels, and require nearly-impossible diplomatic accomplishments.
[quote=“naita, post:8, topic:780544”]
You think they’d rather drown?[/QUOTE
I think they’d rather politically posture. Drowning is not the only option. Like everyone else in the world, people in low-lying coastal areas have the expedient of just moving to higher ground, which might be cheaper than this kind of a public works project.
Multi-lateral agreements in the world are pretty hard to come by. It takes a generation just to get a country approved into an existing treaty. Even progressive western democracies agonize for decades over membership into a pact to defend then from Stalin, who died before 90% of us were born.
In the past century, two million people have figured out how to move to and ive in Clark County, Nevada.
Some perhaps relevant data points: the Mediterranean once mostly dried out, the Black Sea probably did something similar much later, and the Caspian Sea surface is at present well below ocean level (and the Dead Sea even more so, with surface level steadily dropping).
You’re obviously not familiar with the Middle East.
If we’re positing 30m sea level changes than a hefty fraction of worldwide human habitation is inundated.
Facing that, the rest of the world is gonna be busy saving its own butt. Which means massive planet-wide economic dislocation. So that the currently comfy situation of the Gulf oil exporters is likely to be disrupted too.
My definitely non-expert take is that as a matter of straight engineering humanity could build an earthen dam across Hormuz. As a matter of politics and economics it’s a non-starter.
As well, ref the folks upthread, it seems the straits are about 100m deep at the deepest. So we might need to build the dam up 105m or 110m at that point to have enough freeboard above current sea level plus tide range plus wave and storm action. If we bump the sea level 30m we’re talking about adding ~1/3rd to the overall height. Considering the broad pyramidal cross section of earthen dams, that 1/3 increment in height might require 3x the total material. Which might put the project out of reach.
A funny thought: Rising sea level, taken to its (il-)logical conclusion, results in Waterworld. At a time of rapidly rising sea level inundating coastal habitations, would we have a political backlash where any efforts to build dams and walls in or near the water are opposed by know-nothings who are afraid that by excavating from our high ground and dumping it into the water we’re further raising sea levels and simultaneously losing our only refuges? I can see fundamentalist demagogues of all stripes attracting quite a following to their “preserve the hills” mania.
The two closest points on the strait are the Iranian coast near Bandar Abbas and the Mussandam peninsula, which is a tiny non-contiguous part of Oman largely dominated by US and UK military installations. Oman is wealthy, but not as wealthy as the UAE, and Iran is not wealthy. The dam wouldn’t benefit Oman at all, because the rest of its coastline is out beyond the strait.
Expanding on this line of thought…
Let’s say we want to build a wall 10m above sea level. For ease for calculation, let’s say the angle of repose of the material we use to build it is 45 degrees. The coastal wall will have a cross section of (10m)(10m)/2 = 50sqm. The wall across the strait will have a cross section (110m)(110m)/2 = 6050sqm. That means the coastal wall of 120 times the length of the strait will have the same volume. If the strait is 50km, we can protect 6000km of coastline given the same volume of material. How long is the Gulf coast?
It depends on the length of your measuring stick. 
So for a 10m wall the dam makes absolutely no sense, but for a 30m wall the project is equivalent to 1000km of coastline protection, and for 40m we’re down to 600km. Still, that’s a lot of cubic meters of fill. I guess I’m not going to invest in this project … 
Well the good news is you’d have a long time to save up the money for the project. 30 meters is about 15,000 to 20,000 years worth of sea level rise at current rates. So, Deposit a dollar in a compound interest account in the Galactic Bank and wait patiently for compound interest to do its magic…
if the angle of repose is 45 degrees an earthen dam 10m tall will be 20m wide at the base. It would be 10 high & 10 wide as you said only if one side was a sheer vertical face.
So the cross sections will be 10 * 20 / 2 = 100 and 110 * 220 / 2 = 12,100. The 120:1 ratio still applies. But the absolute volume of material is 2x what you estimated.
A more realistic angle for an earthen dam is flatter than 45. Further increasing the total volume.
All in all, it’ll be a metric shitload of material.