Roman Buttress Dams

Esparragelejo
Whenever Roman engineers, often erroneously, judged the stability of a dam wall to be inefficient, they backed it up by irregularly spaced buttresses. But some dams were too thin. Buttress could not prevent the failure of the super thin, 0.9 m dam wall at Ituranduz. By contrast, some dams were over designed. The Olisipo dam was 6.5 m thick and didn't need help from its buttresses. The most remarkable of the Roman buttress dams is the one near the village of Esparragalejo. The 5.6 m high and 320 m long dam was supported in its central part with 12 buttresses averaging 1.2 m wide, 3.2 m thick and spaced 8.6 m apart. However, the novel feature was that the downstream face of the 2 m wide dam wall became curved between the buttresses. Thus, the first multiple arch dam was born!

Buttress Dams in Postmedieval Europe

Castellar
The Castellar storage dam in Spain was built around 1500 and had three water wheels to power its mill house. The sturdy end and walls of the mill house were actually buttresses ensuring the dam's stability. It is certainly no coincidence that this structural concept re-emerged in a region in which the Romans had built many buttress dams.

Evolution of the Modern Buttress Dam

Today we understand buttress dams as derivations from the massive gravity type with the introduction of intermediate spaces. These spaces allows the discharge of water seeping through the dam and its foundation, thus greatly reducing uplift pressures. Given the absence of uplift, more substantial savings were possible by inclining the upstream face, thereby mobilizing the vertical water load on the upstream face for sliding stability.

Multiple Arch
The first multiple arch dam of reinforced concrete had been completed in 1908. It impounded the Hume Lake fluming reservoir on the Ten Mile creek in the California Sierra Nevada Mountains. The dam was designed and supervised during constuction by John S. Eastwood (1857-1924). He also designed the Big Bear Valley dam in the San Bernardino mountains. Eastwood's designs were very economic: the required less concrete than an equivilant gravity dam and cost less, too. Overall, a dozen multi-arch dams were built in the following decade and a half according to Eastwood's design.

Check out a book on Eastwood.

A decidely larger arch span of 54.9 m was acheived in 1928 at the 76 m high Coolidge Dam in Arizona. This was the first application of the double-curved dome structure to buttress dams. Coolidge Dam provides water for irrigation, power, and recreation.

After World War II, large-span multiple-arch dams were pursued further by the prominent French dam designer Andre Coyne (1891-1960). After the war, several of them were built in France, among such sizable structures as the 88m high Grandval Dam built in 1959 with a 50 m span. However, Coyne's most important project of this type was built in the years from 1961 to 1968 in northern Canada. On the Manicougan river in Quebec was built the Daniel Johnson dam. It was an unprecedented 214 m high with a central span of 162 m and smaller side spans of 76 m each!! Unfortunately, the elegant structure was plagued by numerous cracks.

Flat Slab Buttress
The hottest competitor to multiple arch was the type of flat slab buttress designed and patened by Nils F. Abursen in 1903. Abursen's design took full advantage of the stabillizing effect of the vertical water load on the strongly inclined upstream face, which required a minimal buttress thickness per unit of dam length. The Abursen dam type soon became quite popular and, by the end of the 1920's, more than 200 had been constructed, thus outnumbering multiple arch dams by far.

Contiguous Butresses
There was an introduction of a new kind of design in which the arches or slabs as upstream closures of the intermediate spaces between the buttresses were replaced by a thickening of their heads to make them contiguous. The Dixence dam in Switzerland had II shaped buttresses. It was the world record in height for a buttress (87m) dam until after WWII. This dam has now been submerged by the reservoir from the Grand Dixence gravity dam in 1957.