Coulee, orcoulée (/ˈkuːleɪ/ or/ˈkuːliː/),^[1] is any of various different landforms, all of which are kinds of valleys or drainage zones. The wordcoulee comes from theCanadian Frenchcoulée, fromFrenchcouler 'to flow'.

The term is often used interchangeably in theGreat Plains for any of a number of water features, fromponds tocreeks.

In southernLouisiana the wordcoulée (also spelledcoolie) originally meant a gully or ravine usually dry orintermittent but becoming sizable during rainy weather. As stream channels were dredged or canalized, the term was increasingly applied toperennial streams, generally smaller thanbayous. The term is also used for small ditches or canals in the swamp.^[2]

In the northwestern United States, coulee is defined as a large, steep-walled, trench-like trough, which also includespillways andflood channels incised into thebasalt plateau.^[3]

• The dry, braided channels formed by glacial drainage of theScablands of easternWashington, such asGrand Coulee andMoses Coulee. Moses Coulee andLenore Canyon, lower Grand Coulee, havehanging valleys, where pre-flood tributaries enter the coulees at least 100 m (330 ft) above the coulee floor.^[3]
• The furrowedmoraines channeling rain runoff in the area east of theMissouri Coteau in the westernUnited States and westernCanada at the base of theRocky Mountains.
• In the western United States, tongue-like protrusions of solidified lava, forming a sort of canyon.
• InWisconsin it is applied to valleys. These valleys tend to have high, steep walls. "Hollow" is used as a synonym, often for the smallest of such valleys. The term is also applied to the greaterLa Crosse, Wisconsin metropolitan area (i.e. the "Coulee Region").^[4]
• The Gassman Coulee inNorth Dakota may have been a contributing factor to the flooding of theSouris River in June 2011.^{[citation needed]}

Aside from those formed by volcanic eruptions, coulees are commonly canyons characterized by steep walls that have been shaped by erosion. These types of coulees are generally found in the northwesternUnited States and southwesternCanada. In the American west, rapid melting ofglaciers at the end of the lastice age caused catastrophic flooding which removed bedrock by massive down-cutting erosion, forming deep canyons. Some coulees may be seasonally dry or contain small streams, however these smallmisfit streams do not have the magnitude of force necessary to form such expansive erosion.

In Wisconsin, they are the product of nearly a half million years of erosion, unmodified by glaciation (seeDriftless Area^[5]). The loose rocks at the base of the wall form what are calledscree slopes. These are formed when chunks of the canyon wall give way in a rockslide. Left alone, the valleys are often woodland, with the ridgetops transitioning intotallgrass prairie when not turned into pasture or used for row crops.

Coulees provide shelter from wind and concentrated water supplies to plants which would otherwise struggle to survive in thexericsagebrush steppe. Trees are often found inriparianhabitats along streams in coulees and at the base of their walls.^[6]

• Channeled Scablands – Landscape in eastern Washington state scoured by cataclysmic floods during the Pleistocene epoch
• Grand Coulee – Ancient river bed in the U.S. state of Washington

• Fluvial landforms
• Erosion landforms

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