October 2020

frankly, my dear


ansa khan

I have a fear of dams. (I also have a fear of pandemics, but now doesn't feel like the time.) Yet for a brief period in the early days of lockdown, for reasons that aren’t entirely clear to me, I found myself watching video after video about dams and dam construction.


I'm scared of dams because I'm scared of impending disaster, and that has always seemed pretty sensible. I grew up on the bad American disaster movies of the 1990s and, as anyone familiar with this genre will tell you, there is always that moment at the beginning when everything is still fine, before the sulphur has made the lake acidic, before the meteor has been detected, when the doors to the lab housing the deadly virus are still locked. Loosely speaking, it's the brief period in which the technician can carry on making out with his girlfriend, or the scientist listens to music with her earphones on; it’s the moment just before the traffic light moves from red to amber. This is what I think of when I look at a dam.


The first dam I remember recognizing from television or films was the Hoover Dam, which lies on the border of Nevada and Arizona in the U.S. Built in between the walls of the Black Canyon, it cuts off the flow of the Colorado River, one of the longest rivers in North America. It's obvious even to a child that this is something more suited to the American continent than our small set of islands: the scale is all wrong.


Originally known as Boulder Dam until it was renamed in 1947, construction took place between 1931 and 1936, during the Great Depression. We are so far from my area of expertise that it seemed important to come armed with facts, including that six million tonnes of concrete were used in its construction. This is my favourite one: the process by which concrete hardens is an exothermic reaction, meaning that it gives off heat as it happens. The heat generated as all the concrete used in the Hoover Dam hardened would have taken 125 years to cool if engineers hadn't devised a way of cooling the dam by pumping water through it. In the event, it only took twenty-two months. Another fact: It is a ‘concrete arch-gravity dam’, and while I know what all of those words mean individually, I can only guess at their meaning here. I mostly just imagine all that concrete succumbing to gravity and collapsing onto my head.


The reservoir formed by the dam is called Lake Mead and can hold up to 35 billion cubic metres of water (though this figure differs elsewhere: other sources cite 32.236 km3). Because of the extremely high demand for water in the area, it hasn't been full since 1983, and may never be full again. When you consider that the growth of Las Vegas was in part made possible by the infrastructure, water and power that the dam supplied, and when you imagine all those lights, you start to get an idea of just how large demand might be.


The dam is named after the president who definitely – to use overly simplified language – emerged from our GCSE History syllabus as the bad guy (F.D.R. being the requisite good guy). If you’re thinking that interpreting the U.S.'s descent into the Great Depression through good guy/bad guy optics is reductive, you’re not wrong. I'm just saying, the associations aren't good. 


I’ve tried to intellectualize my fear of dams by suggesting that I’m disturbed by the terrifying confrontation between human engineering and the natural world implied by their existence. They appear in the landscape like a painful abbreviation, as if nature was about to say something and we shoved a sock in her throat. But maybe I just saw the dam scene in The Fugitive at an inappropriately young age.


Did you know that in order to build the Hoover Dam they had to temporarily divert the Colorado River, which has been flowing across the United States long enough to have carved out the Grand Canyon? It established its present course 5 million years ago, before us humans took it upon ourselves to divert it, that is.


A river is dammed, and in revenge spreads out to flood any settlements it finds on hand. The water has to go somewhere, so the cities, towns and villages that lie in the path of where a new reservoir will form are sacrificed, offered up to the God of Progress.


I fell down a bit of a rabbit hole of watching videos about dams online; I'd recommend this to anyone looking to confuse search algorithms: YouTube now doesn't know whether to offer me outtakes from Pitch Perfect or documentaries about super tankers. I clicked link after link, until I finally found myself drawn into an episode of National Geographic's Big, Bigger, Biggest devoted to dams. It's there that I am introduced to the mother of all dams: the Three Gorges Dam, which spans the Yangtze River in China, now officially the largest hydroelectric dam in the world. As with so many things from childhood, it turns out the Hoover Dam is not the towering colossus I once thought it was.


The statistics I have for you here are gleaned from an episode of the series Megaprojects that was devoted to the construction of the Three Gorges Dam. Where figures from different sources were inconsistent, I've tried to give a range. The Three Gorges Dam contains either eight or ten times as much concrete as the Hoover Dam; it's 175 metres high and 2.4km long. Its reservoir holds 39.3 cubic kilometres of water. According to some news outlets, NASA scientists think that the elevation above sea level of such a large collection of water has slowed the rotation of the Earth. Earth days are now, apparently, 0.06 microseconds longer than they were before the dam was built. So, if you've ever felt like there weren’t enough hours in the day, the builders of the Three Gorges Dam have sort of done you a solid. It's also visible from space.


The figures on the number of settlements that the reservoir flooded seem to vary, but around a dozen cities, over one hundred towns, and over one thousand villages were inundated when the dam was built. The figure for the number of people uprooted also varies according to the source; the Chinese news site China.com.cn cited 1.4 million as the number of people uprooted. That's a lot of people in need of new homes.


There seems to be a counter-intuitive amount of destruction involved in dam construction. The term 'cofferdam' refers to a temporary dam—or two—built to cordon off the river at various stages, to allow building to take place on a dry, exposed riverbed. These warm-up dams (a prelude to the main event if you will) are later either flooded or blown up. An augury of their destruction is in fact built into the cofferdams: engineers include spaces for the demolition charges in their structure. Thus, they fulfil their destiny.


Yet let it not be said that there isn’t a great deal of beauty in dam design. Hear the poetry in the following description from Big, Bigger, Biggest: 'This sends the water shooting down the spillway into a tumbling vortex, which dissipates its energy. As the water cascades off the ramp, it loses much of its destructive power.' Dissipation, tumbling vortexes, cascades . . . It reminds me of Stéphane Mallarmé's description of a dancer in his poem Billet à Whistler as a 'tourbillon de mousseline ou/Fureur éparse en écumes' (a whirlwind of muslin or/A furious scattering of spray). 


There's also something beautiful about the human ingenuity on display. For every obstacle there's a solution: rivers can be diverted, concrete can be cooled, a giant ‘shiplift’ can raise shipping containers (and the water they're floating in) 113 metres into the air and over the dam. Dams are also, themselves, an ingenious solution not only to the problem of how to generate enough power to satisfy mankind's thirst for electricity, but also as a way of controlling flooding. That's what the builders of the Three Gorges Dam had in mind: trying to put an end to the regular and often catastrophic floods caused by the Yangtze bursting its banks.


That was also the motivation behind the construction of the Aswan Dam across the Nile in Egypt. The unforeseen consequence of that, however, was a failure of harvests downstream from the dam, as soil was no longer enriched by the plant nutrients of nitrogen, phosphorus, magnesium and potassium that were previously carried in the floodwater. Silt is no longer mixed-up and carried with the water down-river. Instead, it sinks to the bottom and builds up in front of the dam. Engineers at the Three Gorges have designed sluice gates that they open periodically to move the silt on. It turns out there's no solution to moving all the silt downstream, but the view seems to be that on balance, this is a price worth paying. 


That's maybe my big take-away from this immersion in dam history: the risk of disaster is worth it. I've excised the section I had on dam failures, but they are as devastating as you might expect. Modern engineers have apparently found solutions to the problems that caused dams to collapse in the past (if they're going to build a dam near you, ask what shape the spillway is), but we've always been a bit over-confident as a species, haven't we? I suppose it's part of our charm. To its credit, the Three Gorges Dam looks pretty solid; if I stood underneath it, I'm not sure I'd feel like it would topple onto my head. However, two months of heavy rainfall meant that earlier this year, the level of water in the dam approached capacity, so let’s all agree to keep an eye on it.


To be honest, the whole thing sort of makes me wish I'd been an engineer, not because I think I'd be any good at it—I dropped Maths at school like a hot potato—but because I worry about how future-proof my current (home) office job is, and they must always be in need of people to keep a structure as complex as a dam up and running. I wouldn't want too much responsibility; maybe I could drive the little boat that scoops up the rubbish that also gathers behind the dam, and in that way make myself useful.


Perhaps my favourite among all the things I watched were the videos of water being purposefully, and in a controlled manner, released by dams. In these videos, the water escapes at such high pressure, it looks more like smoke. When you watch these, you’re literally watching disaster being averted: the releases control the level of water behind the dam and prevent the reservoir from exceeding its capacity. In these stressful times, it is a very cathartic and oddly reassuring viewing experience. I highly recommend it.

ANSA KHAN is a book editor and lives in London. Twitter


(Image credit: The Damn Dam (Glen Canyon Dam), 2017, by John Gibbons)