The Dez Dam is a concrete hydroelectric dam in Andimeshk County and the first in a series of multipurpose dams built on the Dez River, located 23 kilometers northeast of Andimeshk. The Dez Dam and power plant were built to regulate water for agricultural use, generate electricity, and control flooding along the Dez River.

Preliminary surveying for the dam and power plant began in December 1959, excavation started in September 1960, and crews reached the riverbed in August 1961. Concrete placement for the dam wall began in November 1961 and was completed in December 1962. In the meantime, installation of the power plant equipment began and was finished in March 1963.⁠[1]

To control floods, two spillway tunnels were constructed on the eastern side of the reservoir, near the dam body, each capable of releasing 3,000 cubic meters of water per second. Two main intake tunnels were also built on the western side of the reservoir, each dividing into smaller branches that carry water from behind the dam to the turbines. At the center of the dam body, at an elevation of 222.7 meters above sea level, three cone‑shaped irrigation outlets provide water for farmland and help manage floodwaters. The power plant houses eight generator units, each rated at 65 megawatts, giving the plant a total capacity of 520 megawatts. The switchyard, located at an elevation of 577.5 meters above sea level, contains the high‑voltage switches and other equipment needed for 230‑kilovolt transmission. The control room is situated on the western side of the valley near the dam body at an elevation of 225 meters.⁠[2]

Construction of the Dez Dam created a reservoir 65 kilometers long with a final capacity of 3.3 billion cubic meters of water. The dam, a double‑curvature thin‑arch concrete structure standing 203 meters high, was at the time considered the sixth-tallest dam in the world.⁠[3]

Canadian Ontario Hydro, American Morrison‑Knudsen, and the Italian consortium Impresit– Girola– Lodigiani all took part in the construction of the Dez Dam and power plant.⁠[4]

The Dez Dam and power plant were inaugurated in March 1963 by Muhammad-Reza Pahlavi and named after him. After the Islamic Revolution, following a proposal by the Ministry of Energy and approval by the Cabinet on July 28, 1979, the name was changed to “ Dez”.⁠[5]

The first phase of the Dez power plant and the 230‑kilovolt Khuzestan transmission network went into operation in 1963, the second phase in 1970, and the third in 1972. As a result, the Dez Dam was able to supply a major share of the electricity needed in the provinces of Fars, Khuzestan, western regions, and Tehran.⁠[6]

With the start of the Iran– Iraq War, the strategic importance of the Dez Dam and power plant in supplying electricity to Khuzestan and part of the country made them a repeated target of Iraqi airstrikes. To prevent widespread power outages, transmission lines that had previously been concentrated along a single route were divided into several separate lines. This way, if one line was hit, the others could continue operating. Before this change, a single bomb hitting the switchyard could cut power to the entire region.⁠[7]

Air defense units were also deployed around the Dez Dam to counter enemy aircraft. Although the Iranian air defense units succeeded at times— such as on August 16, 1986, when they shot down two Iraqi aircraft that had dropped four bombs on the dam facilities, or on October 15, 1986, when they prevented six Iraqi aircraft from approaching the dam— the airstrikes continued and repeatedly caused damage. Among these were the attacks of September 19 and November 14, 1985, August 16 and November 25, 1986, and September 24 and November 29, 1987, which damaged the switchyard and water tanks.⁠[8] Even so, after every airstrike, repair teams immediately arrived on site, assessed the damage, and quickly carried out repairs and reconstruction, preventing disruptions to the power plant’ s operation.⁠[9] Despite the repeated Iraqi attacks, the Dez Dam and power plant remained operational thanks to the efforts of the facility’ s technical staff and continued supplying electricity to industries, military bases, and houses.⁠[10]

As part of the water‑warfare strategy, water from the Dez Dam was released during Nowruz 1981. As the water level rose, the Karun River was diverted through newly built channels into a wide plain stretching between the Karun and the Ahvaz– Khorramshahr Road, covering an area 130 kilometers long and 25 kilometers wide. Afterward, Iranian forces withdrew from their positions, and the enemy retreated to the paved Ahvaz– Khorramshahr Road, where it set up defensive lines.⁠[11] Meanwhile, the reservoir behind the Dez Dam became an ideal site for Iranian forces to conduct maneuvers and amphibious training. The 19th Fajr, 41st Tharallah (as), and 31st Ashura divisions sent their units to the reservoir area, where they received the necessary water‑and‑land training.⁠[12]

After the war, the Dez Dam and power plant continued operating as before, relying on domestic specialists. The dam plays a major role in regional agricultural development by irrigating 125,000 hectares of farmland. Moreover, it prevents flooding in downstream areas by controlling upstream floods. In 2016 and 2019, the dam successfully contained large volumes of floodwater, protecting downstream lands from being flooded.⁠[13]

The Dez hydroelectric plant continues to supply part of the country’ s electricity needs. In 2016, with its eight generating units, it provided 12.6 percent of Iran’ s total electricity. Under the Seventh Development Plan, the plant’ s capacity is expected to increase to 720 megawatts.⁠[14]

In the Ghadir water‑supply project, which began in early 2009, the Dez Dam serves as the main water source for the western, central, and southern regions of Khuzestan Province. Water will be drawn from the Dez reservoir through three concrete intakes, each 3.5 meters in diameter, installed in the right abutment of the dam.⁠[15]