What makes a dam spectacular is usually the site, not the dam itself

Photograph any dam from downstream and you get the same picture: a wall, some water, a lot of concrete. The ones that end up in collections of the world’s most spectacular dams are almost all the same type, and the reason is structural rather than aesthetic.

Four shapes, four sites

A dam’s form is dictated by the valley, not by the designer’s preference.

Arch dams are curved in plan, convex upstream, and they work by transferring the water load sideways into the canyon walls. They require competent rock on both flanks. Given that, they can be astonishingly thin relative to their height, which is exactly why they photograph well: a slender curved sheet wedged into a gorge, with a long drop beneath it. The tallest engineered dams are almost all of this type.

Gravity dams resist water by weight alone. They are massive triangular sections that stay in place because they are too heavy to move. They do not need strong flanks, so they can go where an arch dam cannot, and they need much more material to do the same job.

Buttress dams are a compromise: a relatively thin upstream face braced by a series of ribs. Less concrete than a solid gravity dam, more formwork and more complexity.

Embankment dams are heaps of engineered earth and rock, with an impermeable core. They are the default where there is no gorge at all — a wide valley floor, weak foundations, or simply a lot of local fill and no cement plant nearby.

Which is the tallest

Among engineered dams, Jinping-I: a concrete arch dam on the Jinping Bend of the Yalong River in Liangshan, Sichuan, completed in 2013 at 305 metres. Behind it, the tallest embankment dam and second tallest engineered dam of any type is Nurek in Tajikistan at 300 metres, built in the Soviet period. The tallest gravity dam is the Grande Dixence in Switzerland at 285 metres. Then a run of Chinese arch dams: Xiaowan on the Lancang at 292 metres, finished in 2010, and Baihetan on the Jinsha at 289 metres.

Note the type distribution. Of the five tallest structures named there, four are arch or embankment dams in mountain terrain, and the one gravity dam is in the Alps.

The overall record holder is not engineered at all. The Usoi Dam in Tajikistan, on the Murghab, was formed by a landslide in 1911 and stands 567 metres — nearly twice Jinping-I. It impounds a large lake and nobody designed it.

Which is the biggest

Change the measure and the list changes completely. By volume of material placed, the largest is Tarbela in Pakistan, completed in 1976: about 153 million cubic metres of earth and rock fill, and only 143 metres high.

Behind it come the Grand Ethiopian Renaissance Dam, completed in 2023 at an estimated 130 million cubic metres, then Fort Peck in the United States, 1940, at 96 million cubic metres and just 76.4 metres high, then the Atatürk Dam in Turkey, 1990, at 84.5 million cubic metres.

Almost none of those is spectacular in a photograph, and they are the largest structures on the list. The full accounting of which superlative applies to which dam is set out in our explainer on the biggest dam in the world.

The measurement caveat

Compilations of the largest dams carry a warning that is easy to skip: structure-volume figures are less readily available and less reliable than height or reservoir data, and they are often published as estimates rather than as surveys. Tailings dams — embankments retaining mining waste, some of them enormous — are kept on separate lists, which removes a set of genuinely vast structures from contention on a definitional rather than a physical basis.

National bodies that maintain these records, such as the Japan Commission on Large Dams, publish by category for exactly this reason. Any single ranked list of “the biggest” has already made a choice on the reader’s behalf.

What to look for instead

If you want to read a dam rather than admire it, the useful question is what the site made necessary.

A thin curved wall means the engineers found sound rock on both sides and exploited it. A vast earth embankment means they did not, and paid for it in volume. A buttressed face means they were trying to save concrete and had the labour to build the formwork. The valley wrote the specification; the dam is the answer.