GoKawiil[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.
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