The main body of the structure contains approximately 6,500,000 cubic yards (5,000,000 m Dworshak Reservoir is the name of the lake formed behind the dam.
During initial filling of the reservoir, the dam developed several large vertical cracks on the upstream side – some more than 400 feet (120 m) long – due to the rapid change of water pressure from the rising reservoir.
Workers had to drill 1.5 in (3.8 cm) diameter drain holes between the cracks and the dam's existing foundation drainage system, or "drainage gallery", at 5-foot (1.5 m) intervals, relieving the pressure on the dam's backside./s) of water spraying across the downstream side of the dam.
The project was authorized on October 23, 1962 as Bruce's Eddy Dam; the name was later changed to honor Senator Henry Dworshak (1894–1962), who was instrumental in gaining congressional approval for the However, proponents of the project held that the construction of a fish hatchery would maintain the river's steelhead runs, and that the construction of the dam would render other dam projects in the Clearwater River basin unnecessary.
While clearing and preparations at the dam site were underway as early as June 1965, actual construction did not begin until early 1966 with the excavation of a 40-foot (12 m) diameter diversion tunnel and the creation of a 110-foot (34 m) high cofferdam to divert the river around the dam site.
Discharge rates from the dam only increase significantly during high water summers, when flooding requires the opening of the spillways.
The power plant generates an average of 1.693 billion KWh each year.) of winter flood-storage space, and dam releases are operated so that water levels reach a maximum of 1,570 feet (480 m) in July.
However, the large annual drawdown of the reservoir causes boat ramps and marinas to be out of reach for months each year and an unsightly "bathtub ring" to be visible along the shoreline.
A study by the University of Idaho calculated that this mode of operation causes the loss of between .5–5.9 million of tourism revenues each year.
Excavation of keyways in the canyon walls to provide future foundations for the concrete commenced in 1966 and continued through 1968.
The first bucket of concrete was placed in early 1968, and by May 28, 1969, more than 1,000,000 cubic yards (760,000 m) had been poured in the dam.
Seventy drainage holes were drilled into the crack to relieve pressure before the crack was permanently sealed by an aggregate of cement, volcanic ash and sawdust. Dworshak Dam is a concrete gravity dam with a sloped downstream face and vertical upstream face, standing 717 feet (219 m) high from the foundations, 632 feet (193 m) above the riverbed and measuring 3,287 feet (1,002 m) long along its crest.