Missouri River
The Missouri River is a river in the Central and Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Mountains of southwestern Montana, then flows east and south for before entering the Mississippi River north of St. Louis, Missouri. The river drains semi-arid watershed of more than 500,000 square miles, which includes parts of ten U.S. states and two Canadian provinces. Although a tributary of the Mississippi, the Missouri River is slightly longer and carries a comparable volume of water, though a fellow tributary carries more water. When combined with the lower Mississippi River, it forms the world's fourth-longest river system.
For over 12,000 years, people have depended on the Missouri River and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, with most leading a nomadic lifestyle and dependent on enormous bison herds that roamed through the Great Plains. The first Europeans encountered the river in the late seventeenth century, and the region passed through Spanish and French hands before becoming part of the United States through the Louisiana Purchase.
The Missouri River was one of the main routes for the westward expansion of the United States during the 19th century. The growth of the fur trade in the early 19th century laid much of the groundwork as trappers explored the region and blazed trails. Pioneers headed west en masse beginning in the 1830s, first by covered wagon, then by the growing numbers of steamboats that entered service on the river. Conflict between settlers and Native Americans in the watershed led to some of the most longstanding violence of the American Indian Wars.
During the 20th century, the Missouri River basin was extensively developed for irrigation, flood control, and the generation of hydroelectric power. Fifteen dams impound the main stem of the river, with hundreds more on tributaries. The Missouri River's reservoirs include the largest, second-largest, and fourth-largest artificial lakes in the United States by surface area: Lake Sakakawea, Lake Oahe, and Fort Peck Lake. Meanders have been cut off and the river channelized to improve navigation, reducing its length by almost from pre-development times. Although the lower Missouri valley is now a populous and highly productive agricultural and industrial region, heavy development has taken its toll on wildlife and fish populations as well as water quality.
Course
From the Rocky Mountains, three streams rise to form the headwaters of the Missouri River:- The longest source stream begins near Brower's Spring in southwest Montana, above sea level on the southeastern slopes of Mount Jefferson in the Centennial Mountains. From there it flows west then north; runs first in Hell Roaring Creek then west into the Red Rock; swings northeast to become the Beaverhead River; and finally joins with the Big Hole to form the Jefferson River.
- The Firehole River, which originates in northwest Wyoming at Yellowstone National Park's Madison Lake, joins with the Gibbon River to form the Madison River.
- The Gallatin River flows out of Gallatin Lake which is also in Yellowstone National Park.
Flowing eastward through the plains of eastern Montana, the Missouri receives the Poplar River from the north before crossing into North Dakota where the Yellowstone River, its greatest tributary by volume, joins from the southwest. At the confluence, the Yellowstone is actually the larger river.
The Missouri then meanders east past Williston and into Lake Sakakawea, the reservoir formed by Garrison Dam. Below the dam the Missouri receives the Knife River from the west and flows south to Bismarck, the capital of North Dakota, where the Heart River joins from the west. It slows into the Lake Oahe reservoir just before the Cannonball River confluence. While it continues south, eventually reaching Oahe Dam in South Dakota, the Grand, Moreau and Cheyenne Rivers all join the Missouri from the west.
The Missouri makes a bend to the southeast as it winds through the Great Plains, receiving the Niobrara River and many smaller tributaries from the southwest. It then proceeds to form the boundary of South Dakota and Nebraska and is joined by the James River from the north. At Sioux City the Big Sioux River comes in from the north, after which the Missouri forms the Iowa–Nebraska boundary. It flows south to the city of Omaha where it receives its longest tributary, the Platte River, from the west. Downstream, it begins to define the border between the states of Nebraska and Missouri, then flows between the states of Missouri and Kansas. The Missouri swings east at Kansas City, where the Kansas River enters from the west, and so on into north-central Missouri. To the east of Kansas City, the Missouri receives, on the left side, the Grand River. It passes south of Columbia and receives the Osage and Gasconade Rivers from the south downstream of Jefferson City. The river then rounds the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois.
Watershed
The Missouri River's drainage basin spans,encompassing nearly one-sixth of the area of the United States or just over five percent of the continent of North America. Comparable to the size of the Canadian province of Quebec, the watershed covers most of the central Great Plains, stretching from the Rocky Mountains in the west to the Mississippi River Valley in the east and from the southern extreme of western Canada to the border of the Arkansas River watershed. Compared with the Mississippi River above their confluence, the Missouri is twice as long
and drains an area three times as large.
The Missouri accounts for 45 percent of the annual flow of the Mississippi past St. Louis, and as much as 70 percent in certain droughts.
In 1990, the Missouri River watershed was home to about 12 million people. This included the entire population of the U.S. state of Nebraska, parts of the U.S. states of Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wyoming, and small southern portions of the Canadian provinces of Alberta and Saskatchewan. The watershed's largest city is Denver, Colorado, with a population of more than six hundred thousand. Denver is the main city of the Front Range Urban Corridor whose cities had a combined population of over four million in 2005, making it the largest metropolitan area in the Missouri River basin. Other major population centers – mostly in the watershed's southeastern portion – include Omaha, Nebraska, north of the confluence of the Missouri and Platte Rivers; Kansas City, Missouri – Kansas City, Kansas, at the confluence of the Missouri with the Kansas River; and the St. Louis metropolitan area, south of the Missouri River just below the latter's mouth, on the Mississippi. In contrast, the northwestern part of the watershed is sparsely populated. However, many northwestern cities, such as Billings, Montana, are among the fastest growing in the Missouri basin.
With more than under the plow, the Missouri River watershed includes roughly one-fourth of all the agricultural land in the United States, providing more than a third of the country's wheat, flax, barley, and oats. However, only of farmland in the basin is irrigated. A further of the basin is devoted to the raising of livestock, mainly cattle. Forested areas of the watershed, mostly second-growth, total about. Urban areas, on the other hand, comprise less than of land. Most built-up areas are along the main stem and a few major tributaries, including the Platte and Yellowstone Rivers.
Elevation in the watershed varies from just over at the Missouri's mouth to the summit of Mount Lincoln in central Colorado. The river drops from Brower's Spring, the farthest source. Although the plains of the watershed have extremely little local vertical relief, the land rises about 10 feet per mile from east to west. The elevation is less than at the eastern border of the watershed, but is over above sea level in many places at the base of the Rockies.
The Missouri's drainage basin has highly variable weather and rainfall patterns, Overall, the watershed is defined by a continental climate with warm, wet summers and harsh, cold winters. Most of the watershed receives an average of of precipitation each year. However, the westernmost portions of the basin in the Rockies as well as southeastern regions in Missouri may receive as much as. The vast majority of precipitation occurs in summer in most of the lower and middle basin, although the upper basin is known for short-lived but intense summer thunderstorms such as the one which produced the 1972 Black Hills flood through Rapid City, South Dakota. Winter temperatures in the northern and western portions of the basin typically drop to or lower every winter with extremes as low as, while summer highs occasionally exceed in all areas except the higher elevations of Montana, Wyoming and Colorado. Extreme maxima — almost all prior to 1960 — have exceeded in all US states in the basin.
As one of the continent's most significant river systems, the Missouri's drainage basin borders on many other major watersheds of the United States and Canada. The Continental Divide, running along the spine of the Rocky Mountains, forms most of the western border of the Missouri watershed. The Clark Fork and Snake River, both part of the Columbia River basin, drain the area west of the Rockies in Montana, Idaho and western Wyoming. The Columbia, Missouri and Colorado River watersheds meet at Three Waters Mountain in Wyoming's Wind River Range. South of there, the Missouri basin is bordered on the west by the drainage of the Green River, a tributary of the Colorado, then on the south by the mainstem of the Colorado. Both the Colorado and Columbia Rivers flow to the Pacific Ocean. However, a large endorheic drainage called the Great Divide Basin exists between the Missouri and Green watersheds in western Wyoming. This area is sometimes counted as part of the Missouri River watershed, even though its waters do not flow to either side of the Continental Divide.
To the north, the much lower Laurentian Divide separates the Missouri River watershed from those of the Oldman River, a tributary of the South Saskatchewan River, as well as the Souris, Sheyenne, and smaller tributaries of the Red River of the North. All of these streams are part of Canada's Nelson River drainage basin, which empties into Hudson Bay. There are also several large endorheic basins between the Missouri and Nelson watersheds in southern Alberta and Saskatchewan. The Minnesota and Des Moines Rivers, tributaries of the upper Mississippi, drain most of the area bordering the eastern side of the Missouri River basin. Finally, on the south, the Ozark Mountains and other low divides through central Missouri, Kansas and Colorado separate the Missouri watershed from those of the White River and Arkansas River, also tributaries of the Mississippi River.