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〕 | length_imperial = 1243 | length_note = | width_imperial = | depth_imperial = | watershed_imperial = 258000 | watershed_round = -3 | discharge_imperial = 265000 | discharge_round = -2 | discharge_note = 〔〔Identical data in: 〕 | discharge_location = mouth (average); max and min at The Dalles, Oregon, from the mouth | discharge_max_imperial = 1240000 | discharge_min_imperial = 12100 | free = | map = Columbiarivermap.png | map_caption = Columbia River drainage basin | map_alt = Three-color map of the Columbia River watershed. The watershed is shaped roughly like a funnel with its wide end to the east and its narrow end along the border between Washington and Oregon as it nears the Pacific Ocean. The watershed extends into the western U.S. states of Washington, Oregon, Idaho, Nevada, Utah, Wyoming, and Montana, and the western Canadian province of British Columbia as far east as its border with Alberta. The river itself makes a hairpin turn from north-west to south in British Columbia and another sharp turn from south to west as it nears Oregon. | map_size = 300 | map_locator = | commons = Columbia River | statistics = | website = | footnotes = }} The Columbia River is the largest river in the Pacific Northwest region of North America.〔According to the United States Geological Survey fact sheet, ("Largest Rivers in the United States" ), "Rivers are considered large on the basis of one or more of three characteristics: total length from source to mouth, area of basin (watershed) drained by the stream, and average rate of flow (discharge) at the mouth." The Columbia is the largest river of the Pacific Northwest in all three senses.〕 The river rises in the Rocky Mountains of British Columbia, Canada. It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven U.S. states and a Canadian province. By volume, the Columbia is the fourth-largest river in the United States; it has the greatest flow of any North American river draining into the Pacific. The river's heavy flow and its relatively steep gradient gives it tremendous potential for the generation of electricity. The 14 hydroelectric dams on the Columbia's main stem and many more on its tributaries produce more hydroelectric power than those of any other North American river. The Columbia and its tributaries have been central to the region's culture and economy for thousands of years. They have been used for transportation since ancient times, linking the many cultural groups of the region. The river system hosts many species of anadromous fish, which migrate between freshwater habitats and the saline Pacific Ocean. These fish—especially the salmon species—provided the core subsistence for native peoples; in past centuries, Indigenous peoples traveled across western North America to the Columbia to trade for fish. In the late 18th century, a private American ship became the first non-indigenous vessel to enter the river; it was followed by a British explorer, who navigated past the Oregon Coast Range into the Willamette Valley. In the following decades, fur trading companies used the Columbia as a key transportation route. Overland explorers entered the Willamette Valley through the scenic but treacherous Columbia River Gorge, and pioneers began to settle the valley in increasing numbers, following both routes to enter it. Steamships along the river linked communities and facilitated trade; the arrival of railroads in the late 19th century, many running along the river, supplemented these links. Since the late 19th century, public and private sectors have heavily developed the river. The development, commonly referred to as taming or harnessing of the river, has been massive and multi-faceted. To aid ship and barge navigation, locks have been built along the lower Columbia and its tributaries, and dredging has opened, maintained, and enlarged shipping channels. Since the early 20th century, dams have been built across the river for the purposes of power generation, navigation, irrigation, and flood control. Today, a dam-impounded reservoir lies along nearly every U.S. mile of the once free-flowing river, and much of the Canadian stretch has been impounded as well. Production of nuclear power has taken place at two sites along the river. Plutonium for nuclear weapons was produced for decades at the Hanford Site, which is now the most contaminated nuclear site in the U.S. All these developments have had a tremendous impact on river environments, mainly through industrial pollution and barriers to fish migration. ==Course== The Columbia begins its journey in the southern Rocky Mountain Trench in British Columbia (BC). Columbia Lake – above sea level – and the adjoining Columbia Wetlands form the river's headwaters. The trench is a broad, deep, and long glacial valley between the Canadian Rockies and the Columbia Mountains in BC. For its first , the Columbia flows northwest along the trench through Windermere Lake and the town of Invermere, a region known in British Columbia as the Columbia Valley, then northwest to Golden and into Kinbasket Lake. Rounding the northern end of the Selkirk Mountains, the river turns sharply south through a region known as the Big Bend Country, passing through Revelstoke Lake and the Arrow Lakes. Revelstoke, the Big Bend, and the Columbia Valley combined are referred to in BC parlance as the Columbia Country. Below the Arrow Lakes, the Columbia passes the cities of Castlegar, located at the Columbia's confluence with the Kootenay River, and Trail, two major population centers of the West Kootenay region. The Pend Oreille River joins the Columbia about north of the U.S.–Canada border. The Columbia enters eastern Washington flowing south and turning to the west at the Spokane River confluence. It marks the southern and eastern borders of the Colville Indian Reservation and the western border of the Spokane Indian Reservation. The river turns south after the Okanogan River confluence, then southeasterly near the confluence with the Wenatchee River in central Washington. This C‑shaped segment of the river is also known as the "Big Bend". During the Missoula Floods 10,000 to 15,000 years ago, much of the floodwater took a more direct route south, forming the ancient river bed known as the Grand Coulee. After the floods, the river found its present course, and the Grand Coulee was left dry. The construction of the Grand Coulee Dam in the mid-20th century impounded the river, forming Lake Roosevelt, from which water was pumped into the dry coulee, forming the reservoir of Banks Lake. The river flows past The Gorge Amphitheatre, a prominent concert venue in the Northwest, then through Priest Rapids Dam, and then through the Hanford Nuclear Reservation. Entirely within the reservation is Hanford Reach, the only U.S. stretch of the river that is completely free-flowing, unimpeded by dams and not a tidal estuary. The Snake River and Yakima River join the Columbia in the Tri‑Cities population center. The Columbia makes a sharp bend to the west at the Washington–Oregon border. The river defines that border for the final of its journey. The Deschutes River joins the Columbia near The Dalles. Between The Dalles and Portland, the river cuts through the Cascade Range, forming the dramatic Columbia River Gorge. No other river except for the Klamath completely breaches the Cascades—the other rivers that flow through the range also originate in or very near the mountains. The headwaters and upper course of the Pit River flows through much of the Cascades; in contrast the Columbia cuts through the range nearly a thousand miles from its source in the Rocky Mountains. The gorge is known for its strong and steady winds, scenic beauty, and its role as an important transportation link. The river continues west, bending sharply to the north-northwest near Portland and Vancouver, Washington, at the Willamette River confluence. Here the river slows considerably, dropping sediment that might otherwise form a river delta. Near Longview, Washington and the Cowlitz River confluence, the river turns west again. The Columbia empties into the Pacific Ocean just west of Astoria, Oregon, over the Columbia Bar, a shifting sandbar that makes the river's mouth one of the most hazardous stretches of water to navigate in the world. Because of the danger and the many shipwrecks near the mouth, it acquired a reputation as the "Graveyard of Ships". The Columbia drains an area of about .〔 Its drainage basin covers nearly all of Idaho, large portions of British Columbia, Oregon, and Washington, ultimately all of Montana west of the Continental Divide, and small portions of Wyoming, Utah, and Nevada; the total area is similar to the size of France. Roughly of the river's length and 85 percent of its drainage basin are in the U.S. The Columbia is the twelfth-longest river and has the sixth-largest drainage basin in the United States.〔 In Canada, where the Columbia flows for and drains , the river ranks 23rd in length,〔This number was derived from the (rivers list ) published in ''The Atlas of Canada'' by Natural Resources Canada.〕 and the Canadian part of its basin ranks 13th in size among Canadian basins. The Columbia shares its name with nearby places, such as British Columbia, as well as with landforms and bodies of water. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Columbia River」の詳細全文を読む スポンサード リンク
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