After nearly nine years of work, four hundred thirty million dollars in construction cost, four hundred fifty thousand cubic yards of concrete, and eight hundred forty-nine miles of reinforcing steel, Roosevelt Dam was modified because the largest probable flood that could flow into the reservoir was determined to be far greater than originally thought possible when the dam was designed and constructed in the early 1900s. Raising the height of the dam by seventy-seven feet increased the storage capacity of Roosevelt Lake by twenty percent, for a total of more than 1.8 million acre-feet. An acre-foot is the amount of water needed to cover an acre of land to a depth of one foot, about three hundred twenty-five thousand eight hundred fifty-one gallons, roughly the amount of water used by a family of four in one year.