The Rivers That Still Run Underneath Major Cities

Every old city is built on water, and most of that water is still there.

Rivers that were once open — fished in, washed in, built beside — were progressively enclosed during the nineteenth and twentieth centuries, and the cities grew over the top of them. They were not filled in. They were roofed, and they are still flowing.

Why it happened

The usual assumption is that rivers were buried because they were dirty. That is part of it, and it is worth being precise about the sequence.

As cities grew, small urban rivers became the obvious place to put waste, because they already flowed away. Household waste, industrial effluent and eventually sewage all went in. The result was an open watercourse running through a densely populated area that was, by the middle of the nineteenth century, an obvious public health problem and an unbearable smell.

The engineering answer was to enclose them: build a brick arch over the channel, culvert the flow, and connect it into the growing sewer network. That freed up valuable land for building, removed the smell, and solved the immediate sanitary problem.

It also created a second, less obvious benefit. A culverted river can be routed, controlled and combined with other drainage in a way an open one cannot.

How to find one from the pavement

Culverted rivers leave a remarkably consistent set of traces.

Street names. This is the easiest one. Anything containing bridge, ford, brook, bourne, well, mill, fleet or holm is worth investigating, and the name often survives centuries after the feature has gone.

The shape of the road. Rivers curve, and streets laid along a buried watercourse curve with them. In a district of otherwise straight or gridded streets, a single meandering road is frequently a river.

The gradient. Walk the area and pay attention to your feet. A shallow valley, often only a few metres deep, is usually still detectable even when it has been built over. If the road dips and rises and there is no obvious reason for it, there may be one underneath.

Boundaries. Rivers were used as parish, borough and ward boundaries for centuries. Administrative boundaries that wander eccentrically across a modern street pattern are frequently following a watercourse nobody can see any more.

Drainage. Manhole covers, grilles and outfalls follow the line. In some cities the outfall into the main river is visible at low tide.

What happens when it rains

This is the part with real consequences.

Culverted rivers are sized for the flows that were expected when they were built, and the catchment above them has since been covered in roofs, roads and car parks. Rain that would once have soaked into fields now runs straight into the drainage network within minutes.

The result is that buried rivers are a significant flood risk, and the flooding is often surprising because nobody can see the river. Properties get water in the basement and the cause is a watercourse the owners did not know existed.

Flood risk mapping in a number of countries now explicitly includes culverted watercourses for this reason, and buying a property without checking it is a well-known trap.

Bringing them back

The direction of travel has reversed in the last few decades.

Deculverting — reopening a buried river into a designed channel — is now a recognised approach in urban regeneration, and has been carried out in a number of cities. The arguments for it are practical rather than sentimental: an open channel with planted banks slows water down, reduces peak flood flows, improves water quality, supports wildlife and, incidentally, makes land next to it considerably more valuable.

It is expensive, and it is only possible where the surface above is not built on, which limits it to parks, car parks, industrial land and redevelopment sites.

Where to start looking

The best single source for any city is a historic map. Compare a map from before the culverting with a modern one and the line usually becomes obvious immediately: a blue thread that runs through what is now a shopping street.

Most national mapping agencies and many city archives now have historic maps online, and local history societies have often done the work already.