coulee

Coulee is a geographic term used primarily in North America to describe a broad, steep-sided valley or drainage channel. In the Canadian Prairies and the western United States, a coulee often refers to a long, narrow valley that is usually dry for much of the year, with water present only after heavy rains or during snowmelt.

Origin of term: The word comes from the French coulée, meaning a flowing channel, and was adopted into English to describe such valleys.

Formation and appearance: Coulees are formed by erosion from streams, rivers, or glacial meltwater. They may start as broad, flat upland channels that become deeply incised, producing high, cliff-like walls. In arid regions, episodic streams cut and re-cut the sides, creating terraces and gullies. Some large coulees are remnants of ancient spillways created by glacial or flood events, such as Missoula Floods in the western United States.

Geography and notable examples: Grand Coulee in Washington is among the best-known, a massive valley later dammed to form the Grand Coulee Dam. In Canadian landscapes, coulees are common in southern Alberta and Saskatchewan, and appear in badlands regions and river valleys.

Ecology and land use: The steep walls and sheltered benches support grasses, shrubs, and riparian species distinct from surrounding plains. Coulees can be prone to erosion and are often less suitable for cultivation, though they can be used for grazing in some settings. They influence drainage patterns, microclimates, and wildlife habitat.