This side canyon of Grand Coulee in Washington was carved by the Missoula floods.
A view through a coulee in Alberta, with steep but lower sides, and water in the bottom.

Coulee, or coulée (/ˈkl/ or /ˈkl/)[1] is a term applied rather loosely to different landforms, all of which refer to a kind of valley or drainage zone. The word coulee comes from the Canadian French coulée, from French couler 'to flow'.

The term is often used interchangeably in the Great Plains for any number of water features, from ponds to creeks.

In southern Louisiana the word coulée (also spelled coolie) originally meant a gully or ravine usually dry or intermittent but becoming sizable during rainy weather. As stream channels were dredged or canalized, the term was increasingly applied to perennial streams, generally smaller than bayous. 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 include spillways and flood channels incised into the basalt plateau.[3]

Types and examples

Drumheller Channels in the Columbia Basin of Washington


A view upward into a coulee in the Oldman River valley in Lethbridge, Alberta

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 northwestern United States and southwestern Canada. In the American west, rapid melting of glaciers at the end of the last ice 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 small misfit 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 (see Driftless Area[5]). The loose rocks at the base of the wall form what are called scree 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 into tallgrass 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 the xeric sagebrush steppe. Trees are often found in riparian habitats along streams in coulees and at the base of their walls.[6]

See also


  1. ^ "coulee". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. ^ Edwards, Jay Dearborn; Nicolas Kariouk Pecquet du Bellay de Verton (2004). A Creole lexicon: architecture, landscape, people. Louisiana State University Press. p. 73. ISBN 978-0-8071-2764-3. Retrieved 15 July 2011.
  3. ^ a b Baker, Victor (2010). Migon, Piotr (ed.). Channeled Scablands: A Megaflood Landscape, in Geomorphological Landscapes of the World. Springer. pp. 21–28. ISBN 9789048130542.
  4. ^ "The Coulee Region - La Crosse, WI - Wisconsin Historical Markers on".
  5. ^ Cotton Mather, "Coulees and the coulee country of Wisconsin", pp. 22-25, Wisconsin Academy Review, September 1976 (James R. Batt, (ed.)), Retrieved July 26, 2007
  6. ^ Easterbrook, Don J. (1999). Surface Processes and Landforms. Prentice Hall, Upper Saddle River New Jersey. Pp. 381-385