Irrigation Dams

A steady supply of water for irrigation is extremely important for any civilization to thrive. Heavy flooding in the wet season and long droughts in the dry season makes farming very difficult. However, if the water is contained during the wet season and released periodically through the dry season, a constant water supply will be present.

Ancient Dams

The first dam designed for irrigation purposes was the Marib dam in Yemen Capital City of Saba. The Marib was an embankment dam constructed about 510 BC. It reached a height of 20m and was about 700m long. The embankment slopes on each side were 1:1.8 with no road crest along the top. The most interesting aspect of this dam is that the fill was placed in layers parallel to the slopes, instead of the typical horizontal layer configuration. This dam also did not have any type of impermeable element in its design. On each end of the dam an outlet structure was built of excellent aslar masonry. The sills of both outlets were almost located at the same height from the riverbed. A 50m long spillway, with a sill height was also included in the dam design located in the northern section of the dam. the capacity of the Marib dam was 30 milliom m3, about 15% of the average annual rainfall for the area. the final failure came about 1,300 years after the completion of the dam. It was not repaired and lead to immigration of about 50,000 people that depended on the water supply. Recently, a modern embankment dam with a capacity of 400 million m3 was built in 1986, 3 km upstream of the ancient dam site.

The Kirsi dam of Iraq was built under the Assyrian king of Sennacherib about 355 km north of Baghdad. This dam was also a diversion dam, used to direct the river flow into a 15 km long canal for irrigation purposes. It was designed as a gravity dam constructed rubble masonry weirs. The upstream face was vertical with a board overflow crest and a stepped downstream face.

Romans

The Romans were highly advanced in hydraulic engineering from their many engineering feast such as aqueducts. However, they did not attempt dam construction until around 150 BC when they annexed Greece. One advantage the Romans had, was that they already possessed fully developed construction technique based on traditional tools such as levers, picks and shovels. The Romans also used pulleys in multiple configurations to lift heavy objects vertically and horizontally. Some of the Romans advance tools included rules, squares, plumblines, and spirit levels. Traditional building materials were used in their design however, the Romans also added concrete to their dams. This allowed them to develop new shapes using formwork and concrete. They added volcanic ash or ground brick into the concrete mix to ensure that it would harden, even when submersed under water.

Medieval and Postmedieval Europe

Damming for irrigation purposes was practiced throughout this era. Irrigation was used throughout Europe, however, it was essential in the southern countries of Europe like Italy and Spain and required storage reservoirs. The dams in these southern countries were mostly of masonry, which contrast to dams built in northern Europe that were built mainly of soil embankments. The reason for dams built in Italy and Spain being masonry is most likely an inheritance from Roman civilizations who used embankments primarily for supporting elements.

The first true arch dam built in Europe since the Roman time, was built in 1632-1640 near Elche. The arch stretched across the main section of the gorge and butted into wing walls directed upstream on either side of the gorge. The arch thrust was directed downwards, since it did not have much support at the crest level. The main arch was 75m long and 9m wide at the crest and had a curve radius of 62m and a curve angle of 70°. The design of this dam was later tested using the crown-cantilever computer analysis that determined it to be satisfactory.

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