Why Rivers Help Great Cities Grow

People need reliable fresh water for drinking, cooking, washing, farming and making goods. A river can supply all of these needs, so settling nearby reduces the time and effort spent carrying water. Farmers can also use river water to irrigate fields when rain is not enough.

Rivers often leave fine sediment on nearby land during floods. This material can make floodplains very fertile, which helps farms produce more food. A strong food supply supports a larger population, and a larger population can support markets, crafts, government and other parts of city life.

River water can support industry as well as daily life. Mills once used flowing water for power, while later factories needed water for cooling, cleaning and processing. These benefits attracted jobs and workers. Over time, however, untreated waste could make the same river unhealthy, so sanitation became a central challenge for growing cities.

Before railways and motor roads, moving heavy goods over land was slow and expensive. Boats could carry far more grain, stone, timber or pottery with less effort. A river acted like a natural transport route linking inland settlements to one another and, in some cases, to the sea.

Where routes met, trade grew. River crossings, bends, ports and confluences became useful places to exchange goods and collect taxes. A small market could slowly become a town, then a city, because geography kept bringing people through the same spot.

Rivers also shape the exact form of a city. Bridges pull streets towards crossing points, docks create working waterfronts, and islands or steep banks limit where neighbourhoods can spread. Even after cars and trains arrive, the old river pattern often remains visible in roads, districts and place names.

Living beside a river is useful, but it is never completely safe. Floods can destroy homes, spread pollution and force people to move. Cities often respond with embankments, dams, drainage systems and rules about where building is allowed.

Those choices can create new problems. A wall that protects one neighbourhood may push water towards another, while straightening a river can damage habitats. Good river planning tries to work with the landscape rather than pretending water can always be controlled. Useful questions include:

• •Where does floodwater naturally spread?
• •Which areas need open ground to absorb water?
• •How can transport and wildlife share the river?
• •Who gains protection, and who carries the risk?

London shows how a single river location can shape a city for two thousand years. When the Romans founded Londinium in the first century, they chose a place on the Thames where the river was narrow enough to bridge but still deep enough for seagoing ships to reach. Geographers call this kind of site a lowest bridging point, the crossing closest to the sea. Roads from different parts of the province could meet at the bridge, while ships from continental Europe could unload goods at the same spot.

Firm gravel ground on the north bank, raised slightly above the marshy floodplain, gave builders somewhere drier to settle. Over the centuries docks spread downstream as ships grew larger, and the old port areas were later redeveloped when container shipping moved to deeper water nearer the estuary. You can look for the same pattern elsewhere. Many river cities began at the first practical crossing inland, the highest point ships could reach, or a confluence where two valleys met, and their old centres often still sit beside that original feature.

Rivers are not fixed lines on a map. They carry sediment, build up their beds, cut new channels and sometimes change course altogether, and a city built around one can lose its reason for existing. Ur, one of the great cities of ancient Mesopotamia, once stood near the Euphrates and close to the waters of the Gulf. Over many centuries the river shifted away and the coastline crept south as sediment built up, leaving the city stranded in dry land, and it was eventually abandoned.

A later example comes from Bruges in Flanders, which grew rich in the Middle Ages through a channel connecting it to the North Sea. As that inlet silted up, larger ships could no longer reach the city, and much of its trade moved to Antwerp on the deeper Scheldt. Modern cities face the same forces on a different scale. Ports dredge their channels constantly, and engineers build banks and barriers to hold rivers in place, because the location that made a city successful can quietly drift out of reach.

Not every big city needs a large river, and the exceptions show which advantages matter most. Johannesburg is often described as one of the largest cities in the world not built on a major river, lake or coast. It grew rapidly after gold was found on the Witwatersrand in 1886, because the wealth lay underground rather than beside a waterway, and railways rather than boats carried goods to the ports. The ridge it sits on is a watershed, sending streams towards the Indian Ocean on one side and the Atlantic on the other, so much of the city's water is now piped from distant dams, including some in Lesotho.

Los Angeles shows another route. The city does have a river, but it is small and carries little water in dry months, nowhere near enough for millions of people. Its rapid growth in the twentieth century depended on engineering. An aqueduct completed in 1913 carried water more than 300 kilometres from the Owens Valley, and later projects drew on the Colorado River and northern California. The lesson is that rivers gave early cities a head start, but once people could build railways, pumps and long pipelines, gold, oil, harbours, climate or government could matter more, and water could be brought to wherever the city happened to be.

Chicago grew where a sluggish river met Lake Michigan, close to a low ridge separating the Great Lakes from the Mississippi basin. A canal opened in 1848 linked the two systems, making the city a hub between the east coast and the interior. Growth brought a dangerous problem. The city drew its drinking water from the lake, while its sewage and industrial waste drained into the Chicago River, which flowed into the same lake. Outbreaks of waterborne diseases such as typhoid and cholera were a recurring threat, and moving the water intakes further offshore was only a partial answer.

The solution was bold. Engineers dug the Chicago Sanitary and Ship Canal, opened in 1900, deep enough to make the river flow backwards, away from the lake and towards the Illinois River and eventually the Mississippi. Downstream, St Louis objected that Chicago was sending its sewage its way, and Missouri took Illinois to the United States Supreme Court, which ruled in 1906 that the harm had not been proved. Treatment works were added later. The reversal still has consequences today, because the canal links two great river systems, and electric barriers are now used to stop invasive fish passing between them.

Rivers help cities grow because they provide water, food, fertile land and transport. The same river can also flood, so successful cities must respect both its usefulness and its power.