Coulee
Encyclopedia
Coulee is 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
word couler meaning "to flow".
The term is often used interchangeably in the Great Plains
for any number of water features, from pond
s to creek
s.
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 stream
s, generally smaller than bayou
s. The term is also used for small ditches or canals in the swamp.
In some parts of Louisiana coulees are not concreted but rather sheer sided large ditches that collect smaller ditch runoff.
and southwestern Canada
. In the American west, rapid melting of glacier
s 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 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). 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 habitat
s along streams in coulees and at the base of their walls.
The word coulee comes from the Canadian French
Canadian French
Canadian French is an umbrella term referring to the varieties of French spoken in Canada. French is the mother tongue of nearly seven million Canadians, a figure constituting roughly 22% of the national population. At the federal level it has co-official status alongside English...
coulée, from French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
word couler meaning "to flow".
The term is often used interchangeably in the Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
for any number of water features, from pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...
s to creek
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s.
In southern Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
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 stream
Perennial stream
A perennial stream or perennial river is a stream or river that has continuous flow in parts of its bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral"...
s, generally smaller than bayou
Bayou
A bayou is an American term for a body of water typically found in flat, low-lying areas, and can refer either to an extremely slow-moving stream or river , or to a marshy lake or wetland. The name "bayou" can also refer to creeks that see level changes due to tides and hold brackish water which...
s. The term is also used for small ditches or canals in the swamp.
Types and examples
- The dry, braided channels formed by glacial drainage of the Scablands of eastern Washington, such as Grand CouleeGrand CouleeThe Grand Coulee is an ancient river bed in the U.S. state of Washington. This National Natural Landmark stretches for about sixty miles southwest from Grand Coulee Dam to Soap Lake, being bisected by Dry Falls into the Upper and Lower Grand Coulee....
and Moses CouleeMoses CouleeMoses Coulee cuts into the Waterville plateau in Douglas County, Washington. It is to the west of and roughly parallel to the more famous Grand Coulee...
. - The furrowed moraineMoraineA moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
s channeling rain runoff in the area east of the Coteau du MissouriCoteau du MissouriThe Coteau du Missouri, or Missouri Plateau, is a large plateau that stretches along the eastern side of the valley of the Missouri River in central North Dakota and north-central South Dakota in the United States...
in the western United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and western CanadaCanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
at the base of the Rocky MountainsRocky MountainsThe Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
. - In the western United States, tongue-like protrusions of solidified lava, forming a sort of canyon.
- In Wisconsin, it is applied to smaller sometimes intermittent tributary streams in the watershed of the Upper Mississippi RiverUpper Mississippi RiverThe Upper Mississippi River is the portion of the Mississippi River upstream of Cairo, Illinois, United States. From the headwaters at Lake Itasca, Minnesota, the river flows approximately 2000 kilometers to Cairo, where it is joined by the Ohio River to form the Lower Mississippi...
, north of the Wisconsin RiverWisconsin River-External links:* * * , Wisconsin Historical Society* * * *...
and as far up as the Saint Croix River. 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 greater La Crosse, WisconsinLa Crosse, WisconsinLa Crosse is a city in and the county seat of La Crosse County, Wisconsin, United States. The city lies alongside the Mississippi River.The 2011 Census Bureau estimates the city had a population of 52,485...
metropolitan area, rather much like "Twin Cities" is applied to Minneapolis-Saint Paul. The term has also been incorrectly applied to the whole of the Driftless Area, when in fact the Coulee Region excludes portions of the Driftless, while including portions which are outside of it.
In some parts of Louisiana coulees are not concreted but rather sheer sided large ditches that collect smaller ditch runoff.
Geomorphology
Aside from those formed by volcanic eruptions, they are commonly canyons characterized by steep walls that have been shaped by erosion. These types of coulees are generally found in the northwestern United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and southwestern Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. In the American west, rapid melting of glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s at the end of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
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 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). The loose rocks at the base of the wall form what are called scree
Scree
Scree, also called talus, is a term given to an accumulation of broken rock fragments at the base of crags, mountain cliffs, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles...
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
Tallgrass prairie
The tallgrass prairie is an ecosystem native to central North America, with fire as its primary periodic disturbance. In the past, tallgrass prairies covered a large portion of the American Midwest, just east of the Great Plains, and portions of the Canadian Prairies. They flourished in areas with...
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
Sagebrush steppe
The sagebrush steppe is a type of shrub-steppe, which is a dry-xeric environment and plant community found in the Western United States and western Canada...
. Trees are often found in riparian habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s along streams in coulees and at the base of their walls.