Grand Coulee is an ancient river bed in the U.S. state of Washington. This National Natural Landmark stretches for about 60 miles (97 km) southwest from Grand Coulee Dam to Soap Lake, being bisected by Dry Falls into the Upper and Lower Grand Coulee.
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👉 Grand Coulee in the context of Grand Coulee Dam
Grand Coulee Dam is a concrete gravity dam on the Columbia River in the U.S. state of Washington, built to produce hydroelectric power and provide irrigation water. Constructed between 1933 and 1942, Grand Coulee originally had two powerhouses. The third powerhouse ("Nat"), completed in 1974 to increase energy production, makes Grand Coulee the largest power station in the United States by nameplate capacity at 6,809 MW.
The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups. One group wanted to irrigate the ancient Grand Coulee with a gravity canal while the other pursued a high dam and pumping scheme. The dam supporters won in 1933, but, although they fully intended otherwise, the initial proposal by the Bureau of Reclamation was for a "low dam" 290 feet (88 m) tall which would generate electricity without supporting irrigation. That year, the U.S. Bureau of Reclamation and a consortium of three companies called MWAK (Mason-Walsh-Atkinson Kier Company) began construction on a high dam, although they had received approval for a low dam. After visiting the construction site in August 1934, President Franklin Delano Roosevelt endorsed the "high dam" design, which at 550 ft (168 m) high would provide enough electricity to pump water into the Columbia basin for irrigation. Congress approved the high dam in 1935, and it was completed in 1942. The first waters overtopped Grand Coulee's spillway on June 1 of that year.
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Grand Coulee in the context of Moses Coulee
Moses Coulee is a canyon in the Waterville plateau region of Douglas County, Washington. Moses Coulee is the second-largest and westernmost canyon of the Channeled Scablands, located about 30 kilometres (19 mi) to the west of the larger Grand Coulee. This water channel is now dry, but during glacial periods, large outburst floods with discharges greater than 600,000 m/s (21,000,000 cu ft/s) carved the channel. While it's clear that glacial floodwaters passed through and contributed to the erosion of Moses Coulee, the age of those waters, thus the origins of the coulee are less clear. No clear connection between the head of the coulee and major flood routes to the north, east, or west is known. Some researchers propose that floods from glacial Lake Missoula formed Moses Coulee, while others suggest that subglacial floods from the Okanogan Lobe incised the canyon. The mouth of Moses Coulee discharges into the Columbia River.
Two National Natural Landmarks were established in 1986 for features, notable as the best examples of their kind, in and around Moses Coulee. The Great Gravel Bar of Moses Coulee, on the western edge of Moses Coulee where US Highway 2 crosses the coulee, is described as "the largest and best example of a pendant river bar formed by catastrophic glacial outburst floods that swept across the Columbia Plateau prior to the last Pleistocene glaciation." Withrow Moraine and Jameson Lake Drumlin Field "contains the best examples of drumlins and the most illustrative segment of the only Pleistocene terminal moraine in the Columbia Plateau biophysiographic province. ... They are also the only such glacial features in the world to show a clear geological relationship to catastrophic flooding." The canyon is named for Chief Moses (1829–99).