Cle Elum Dam, on the Cle Elum River 10 miles northwest of Cle Elum, is an earthfill dam constructed at the end of a natural lake that forms a reservoir with an active capacity of 436,900 acre-feet. The dam is 165 feet high and, including the dikes, contains 1,411,000 cubic yards of material.
The outlet works of Cle Elum Dam were modified in 1977-1979 under the Bureau of Reclamation’s Safety of Dams Program.
Cle Elum Dam and Lake Cle Elum lie within the U-shaped glacial valley of the Cle Elum River. Successive multiple advances of alpine glaciers during the Pleistocene have formed this U-shaped valley. The terminal moraine/outwash complex, which was deposited during the most recent Pleistocene glacial advance, essentially blocked drainage of the valley forming a natural dam. Following deglaciation, a lake was formed behind the terminal moraine. The moraine was subsequently breached, and a deep channel was incised through the moraine and outwash deposits, forming the outlet of the glacial lake currently known as Lake Cle Elum. The high-stand water level of the glacial lake was very close to the maximum water surface of the existing Lake Cle Elum. Cle Elum Dam, main dike, and three smaller saddle dikes are sited along the crest of the youngest terminal moraine described above. This glacial moraine received its name, Domerie, after the Domerie Flats, an extensive outwash terrace immediately downstream from the dam. The moraine, which is about 60,000 to 65,000 years old, consists of unconsolidated sediments ranging in size from rock flour to boulders. Its thickness is estimated from drill hole investigations downstream of the dam. Investigations at the dam site have never penetrated the glacial moraine to bedrock. Bedrock in the vicinity of Cle Elum Dam includes various volcanic and sedimentary units.