side piers on the upstream face to more correctly channel water over the dam so that each spillway discharges the same amount of water. The spillways release their water slightly above the actual bed of the river, creating a waterfall effect when they are fully open. A spillway tunnel carved from granite in the right bank of the river augments the spillways and provides for additional overflow. The total spillway capacity is half that of Grand Coulee Dam in the United States. The Export-Import Bank of the United States provided $8.9 million (about $67.2 million in 2010 inflation-adjusted dollars) in credits in 1958 to Iberduero to enable it to purchase six 120 Megawatt (MW) turbines and other electrical equipment for the power generating station, all of which were supplied by American firms. The dam won Spain an international reputation as a builder of very large dams. The dam's eye-catching, "ski jump" style spillways are its most noted feature, and have been called "outstanding" by leading dam engineers. The canyon through which the Duero River flows is exceptionally deep and narrow, resulting in a reservoir that has a relatively small surface area for its immense size. In some ways, this limits use of the reservoir for recreational activities. However, the Aldeadávila Dam reservoir is a popular one for boating. Power plant Until the Alcántara Dam, also in Spain, was built in 1969, the Aldeadávila Dam was the largest hydroelectric power plant in Europe. As of 2018, and after some upgrades, it remains the largest in Spain, with a total output generating power of . The dam's original Aldeadávila I Power Station houses six Francis turbines for a total generating output of . In 1986, the Aldeadávila II Power Station extension was completed, adding two Francis pump-turbines, boosting generating capacity by . During periods when the demand for electricity is low (such as evenings, weekends, or during seasonal fluctuations), the dam's two pumped-storage generators can use its excess power-generating capacity to pump water back into the reservoir—enhancing reservoir capacity and storing water for periods when the demand for electricity is high. At the time it was constructed, the Aldeadávila Dam had the largest pumping station capacity in Europe. The dam has two diversion tunnels, each in length. Each tunnel has a high surge tank. The dam also contains more than of tunnels which divert water to the electrical generation turbines. There are