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O'Sullivan Dam facts for kids

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O'Sullivan Dam located near the bottom of Potholes Reservoir.

O'Sullivan Dam (National ID # WA00268), one of the largest earthfill dams in the United States (200 ft/61 m high; 19,000 ft/5,791 m long; completed 1949), is on Crab Creek in the U.S. state of Washington, about 45 km south of Ephrata and 25 km south of Moses Lake.

The 27,800-acre (113 km2) Potholes Reservoir formed by this dam collects return flows from all irrigation in the upper portion of the project for reuse in the southern portion. A system of wasteways has been built on both the West and East Low Canals to provide operational safety for the canals and a means of delivering water into Potholes Reservoir to supplement the natural and return flows.[1]

The dam was built as part of the Columbia Basin Project.


  • Active storage capacity: 332,200 acre feet (409,800,000 m3)
  • Structural height of dam: 200.0 ft (60 m)
  • Construction date: 1947-1949
  • Normal water surface elevation: 1052.0 ft (320.6 m)
  • Drainage area: 3,920.0 sq mi (10,153 km²)
  • Storm duration: 72 hr
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