The Los Angeles Aqueduct Is Wild

[Note that this article is a transcript of the video embedded above.]

On the northern edge of Los Angeles, fresh water spills down two stark concrete chutes perched on the foothills of the San Gabriel Mountains, a place simply called The Cascades. It’s a deceptively simple-looking finish line: the end of a roughly 300-mile (or 500 km) journey from the eastern slopes of the Sierra Nevada into the city.

On November 5, 1913, tens of thousands of people climbed these hills to watch the first water arrive. When the gates finally opened, water trickled through, but that trickle quickly became a torrent. The project’s chief engineer, William Mulholland, leaned over to the mayor and shouted the line that’s been repeated ever since: “There it is, Mr. Mayor. Take it!”

That moment was profound for a lot of reasons, depending on where you live and how you feel about water rights. LA didn’t become LA by living within the limits of its local resources. Its meteoric growth into the metropolis we know was enabled by an early and extraordinary decision to reach far beyond its own watershed and pull a whole new river into town. Today, roughly a third of LA’s water comes from the Eastern Sierra through the Los Angeles Aqueduct system. That share swings with snowpack, drought, and environmental constraints, but this one piece of infrastructure helped turn a water-limited town into a world city. It’s one of the most impressive and controversial engineering projects in American history.

But to really appreciate that water in the cascades, you have to look way upstream and see what it took to get it there. It’s gravity, geology, politics, and human ambition all in a part of the state that most people never see. Let’s take a little tour so you can see what I mean. I’m Grady and this is Practical Engineering.

When most people think about aqueducts, this is what they picture: a bridge carrying water over a valley or river. And, just to be clear, these are aqueducts. But engineers often use the term more broadly to describe any type of conveyance system that carries water over a long distance from a source to a distribution point. Could be a canal, a pipe, a tunnel, or even just a ditch. In the case of the LA aqueduct, it’s all of them, plus a lot of supporting infrastructure as well.

From the center of the city, it’s about a four hour drive to the Owens River Diversion Weir. It’s not accessible to the public, but it is the official start of the LA Aqueduct, at least when it was originally built. Here, all the snowmelt and rain from a huge drainage system between the Sierra Nevada and Inyo Mountains funnel down into the Owens River, where a large concrete diversion weir peels nearly all of it out of its natural course and into a canal. This point is roughly 2,500 feet (or 750 meters) higher in elevation than the bottom of the Cascades at the downstream end, which makes it obvious why LA chose it as a source. The entire aqueduct is a gravity machine. There are no pumps pushing the water toward the city. Half a mile of elevation change feels like a lot until you realize you have to spread it out over 300 miles. It’s all achieved through careful grading and managing elevations along the way to keep the flow moving.

That care is particularly important in this upper section of the aqueduct, where the water flows in an open canal. To do this efficiently, you need a relatively constant slope from start to finish. That’s a tough thing to achieve on the surface of a bumpy earth. Following a river valley makes this easier, but you can see the twists and turns necessary to keep the aqueduct on its gentle slope toward LA.

If it seems kind of wild that a city would buy up the land and water rights from somewhere so far away, it did to a lot of the people who lived in the Owens Valley, too. A lot of the acquisitions and politics of the original LA Aqueduct were carried out in bad faith, souring relationships with landowners, ranchers, farmers, and communities in the area. The saga is full of broken promises and shady dealings. Then when the diversion started, the area dried up, disrupting the ecology of the region, making agriculture more difficult and residents even more resentful. Many resorted to violence, not against people but against the infrastructure. They vandalized parts of the aqueduct, a conflict that later became known as the California Water Wars. In one case in 1924, ranchers used dynamite to blow up a part of the canal. Later that year, they seized the Alabama Gates.

About 20 miles or 35 kilometers downstream from the diversion weir, a set of gates sits on the eastern bank of the aqueduct canal. Because it runs beside the river valley, the aqueduct captures some of the water that flows down from the surrounding mountains in addition to what’s diverted out of the Owens River, particularly during strong storms. That means it’s actually possible for the canal to overfill. The Alabama Gates serve as a spillway, allowing operators to divert water back down to the river. This also helps drain the canal for maintenance or repairs when needed.

Those Owens Valley ranchers understood exactly what the Alabama Gates controlled. Open them, and the water would run back where it had always run, down the Owens River, instead of south to Los Angeles. The resistance simmered and flared for years, but it didn’t end in the dramatic showdown at the aqueduct. Instead, it ended at a bank counter. The Inyo County Bank was run by two brothers who were also key organizers and financiers of the resistance campaign. In August 1927, an audit revealed major shortfalls and ongoing embezzlement, and the bank quickly collapsed. Residents across the valley saw their savings wiped out or frozen overnight, shattering what was left of the community’s ability to keep fighting.

The Alabama Gates weren’t just a political flashpoint though. They also marked an important dividing line in the aqueduct’s design. LA knew that even if the ranchers didn’t release the water to the river in protests, a lot of it would end up there anyway through seepage. As the canal climbed away from the valley floor and crossed more porous soil, it would naturally lose its water through the ground. So, at the Alabama Gates, the aqueduct transitions from an unlined canal to a concrete-lined channel. It’s still open to the air, so there’s no protection against evaporation or contamination, but the losses to the ground are a lot less.

This design continues for about 35 miles (or 55 kilometers) through the valley. Along the way, the aqueduct passes the remains of Owens Lake. Once a large body of water, it quickly dried up with the diversion of the Owens River. Of course, there were impacts to wildlife from the loss of water, but the bigger problem came later: dust. All the fine sediment that settled on the lakebed over thousands of years was now exposed to the hot desert sun. When the wind picked up, it filled the air with fine particulates that are dangerous to breathe. Over the years, there have been times when Owens Lake is the single largest source of dust pollution in the entire country, and LA has spent more than a billion dollars just trying to fix this problem alone. The aqueduct passing along the hillside past the lake and its challenges is a reminder that the true cost of water is often a lot more than the infrastructure it takes to deliver it.

So far, it might be obvious that this aqueduct system is pretty fragile to be making up a major part of a city’s fresh water supply. Even beyond the vandalism and political resistance, there are a lot of things that could go wrong along the way, from bank collapses, earthquakes, diversion failures, and more. That’s why Haiwee Reservoir was originally built in a narrow saddle between two hills as a kind of buffer. With a dam on either side, it stored water up so the aqueduct could keep running even during a disruption upstream. It also slowed the water down, exposing it to th