Even if a highly organised army of religious fanatics wasn’t planning to destroy it, the Mosul dam will eventually collapse anyway due to a fundamental design flaw that was known when the Hochtief Aktiengesellschaft consortium began construction in 1980. It’s built on a soluble foundation. Underground rivers develop and grow, continually washing away the stone, much as they do in the Burren and other karst regions around the world, but with two big differences.
Firstly, unlike most other karst strata, some of the Iraqi bed is submerged beneath 300 metres of pent-up water. That’s 1,000 feet of vertical weight, giving rise to a vast unrelenting driving force that tears away at the underground caverns and channels, removing huge amounts of material from the dam’s foundations.
Secondly, the material under the Mosul dam is not only limestone but also marl, gypsum and anhydrite, which are highly soluble.
Of course, gypsum karst is not unusual. It occurs all over the world, from the Black Hills of Dakota to the Canadian Maritimes, from Andalusia to Lower Saxony. Dams built on soluble substrates do exist and they all share the same problems. For example, Quail Creek dam in Utah USA collapsed in 1989 due to seepage through a soluble substrate, but no dam anywhere is on the scale of Mosul, with the potential to cause so much damage in the event of a failure. Mosul dam holds back 11.1 cubic kilometres of water, with several major cities in its path if the dam should happen to fail, which means that nobody in their right mind would build such a dam unless they happen to be a despotic tyrant like Saddam Hussein, more intent on solidifying his own power than listening to boring scientists and engineers.
As this excellent analysis from the US Army Corps of Engineers laconically puts it,
The site was chosen for reasons other than geologic or engineering merit.
One study has estimated that if the dam collapsed, Mosul, a city of 2 million people, would be inundated by the melt-waters of the Turkish mountains to the height of a six-storey building and that after 72 hours, Baghdad would be submerged beneath 4 metres of water. These are apocalyptic figures, and yet, that’s precisely what the Mosul dam threatens unless something is done.
But what exactly can be done?
In the case of the dam itself, the answer is nothing. Right from the start, it was part of the design to continuously pump concrete into the foundations in the hope that it would somehow plug the gaps caused by the rushing waters eating away at the soft, soluble under-layer, but that isn’t working. Either the grout is immediately washed away, or else a new channel opens up which, of course grows bigger and bigger as the water rushes through it. The amazing thing is that the German-Italian consortium who built the dam ever thought grouting had a long-term future, but perhaps that reflects their assessment of the political situation in Iraq. And besides, they did make €2 billion out of it, so there are some winners.
Even though the grouting goes on six days out of every seven, pumping thousands of tons of concrete into the dam’s base, it’s unsustainable. It can’t go on and it won’t go on. This dam will collapse sooner or later. Some estimates suggest that the dam would begin to crumble within two weeks if grouting stopped, which explains why ISIS brought in their own engineers to keep the process going, and even though that might seem counter-intuitive, it makes perfect sense. Anyone trying to establish a new state needs control of water supplies and power-generation, so it was in the interests of ISIS to keep the dam intact. (Of course, that didn’t stop them from planting explosive charges throughout the structure, just in case they needed a Doomsday option, and with their access to the best of old Iraq’s technologists, they would without doubt be able to destroy the structure at the touch of a button).
There has been talk of constructing a cut-off wall – a subterranean dam within a dam cut deep into the foundations to prevent percolation into the soft, soluble base, but the sheer scale of the effort is staggering and probably outside the scope of what is physically achievable. There is no precedent for action on this scale anywhere in the world, there are no studies, no theoretical basis and crucially, no machinery to do it. Remedial curtain walls have been installed in other dams using secant piling, which means drilling deep holes beside each other and filling them with concrete to form a continuous barrier, but nobody has yet tried to do it on the scale of Mosul. Soft walls have also been proposed using “soilcrete” or drilling mud, but again, the equipment doesn’t exist to dig such huge trenches under 300m of water, and yet the erosion continues.
If the substrate was purely limestone, the timescale to collapse would be centuries, but since it’s also gypsum, which is essentially Plaster of Paris, it could be a matter of weeks. All around the site, sink-holes continue to open, just as they have done from the outset, proving that the bed of this dam is disappearing. Eventually, the whole thing will be washed away by the 11 cubic kilometres of water it holds back, and then there will be Armageddon, unless something else happens.
That something else is the Badush dam, downstream of the Mosul dam, designed with two purposes: to generate electricity and to prevent utter catastrophe when the Mosul dam inevitably collapses. It was started when Saddam realised the folly of his decision on the Mosul dam, but unfortunately, construction was halted just before the 2003 invasion, and the dam remains unfinished.
There’s another snag.
In order to completely neutralise the consequences of a collapse upstream, the Iraqis would need to widen and deepen the Badush dam but that would cost another $10 billion, a sum they might have regarded as chickenfeed before their country was invaded, but which they now are unable to afford.
Hence, Mosul is now the most dangerous unstable dam in the world, while at the same time being attacked by the most dangerous, unstable political movement in the world.