Fixing the Most Dangerous Dam in the World

Mosul Dam rises 370 feet or 113 meters above  the Tigris River in northern Iraq as one of the tallest dams in the Middle East. The dam was  built in the 1980s, but, in a way, construction never really stopped. That’s because ever since  the reservoir filled behind Mosul Dam, the ground

has literally been dissolving, nonstop, below  the structure. Almost immediately on filling, water started flowing through the foundation of  the dam and back out on the downstream side. Just a year later, the volume of seepage was measured  at 800 liters or about 200 gallons per second.

I usually hate to use the olympic-sized  swimming pool equivalent, but in this case it makes sense because it was enough  to fill one every hour of every day.

And the issue is that, once a process like this  gets started, it’s pretty hard to stop. So, for the past 40 years or so, the problem at  Mosul Dam has been ongoing, scrutinized by some of the most preeminent engineers across the  world and complicated by politics, bureaucracy,

and, of course, armed conflict. Failure of a  structure this large would be catastrophic; towns along the Tigris River would be fully wiped  off the map, and some estimate that the breach wave would be so massive that even major parts of  Baghdad, hundreds of miles downstream, would be

submerged. In 2006, the US Army Corps of Engineers  called it, unequivocally, “the most dangerous dam in the world.” That was 20 years ago, and Mosul  Dam is still standing, in better shape than ever.

And the story of how it got there is fascinating.  I’m Grady, and this is Practical Engineering.

Mosul Dam is an earthen embankment dam  not far from the City of Mosul in Iraq, built to generate hydropower and store water  for irrigation and drinking. The hydro plant is on the west side of the dam with four turbine  generators. You can see the massive surge tanks

sticking up from the plant that absorb changes in  pressure when the units are started and stopped.

The dam has an outlet structure through the  embankment here. It has a service spillway with radial gates here. And an auxiliary spillway with  earthen fuse plugs here. Check out my videos on spillway gates and fuse plugs if you want to learn  more about those types of structures after this.

The dam itself is impressive, but the rock that  serves as its foundation is extremely complex, and in many ways, far from ideal. The geology  of northern Iraq includes a lot of gypsum, a sedimentary rock that is widely used  for things like fertilizer, plaster,

and drywall. What it’s not widely used  for is the foundations of dams. In fact, the consensus of experts involved on Mosul  Dam throughout the years is that it was, all around, a terrible idea. One  consulting group said that, quote,