Mackenzie River
The Mackenzie River is a river in the Canadian boreal forest and tundra. It forms, along with the Slave, Peace, and Finlay, the longest river system in Canada, the second largest drainage basin of any North American river after the Mississippi.
The Mackenzie River flows through a vast, thinly populated region of forest and tundra entirely within the Northwest Territories in Canada, although its many tributaries reach into five other Canadian provinces and territories. The river's main stem is long, flowing north-northwest from Great Slave Lake into the Arctic Ocean, where it forms a large delta at its mouth. Its extensive watershed drains about 20 percent of Canada. It is the largest river flowing into the Arctic from North America, and including its tributaries has a total length of, registering the 13th longest river system and 12th largest drainage basin on Earth.
The ultimate source of the Mackenzie River is Thutade Lake, in the Northern Interior of British Columbia. The Mackenzie valley is believed to have been the path taken by prehistoric peoples during the initial human migration from Asia to North America over 10,000 years ago, despite sparse evidence. The Inuvialuit, Gwich'in and other Indigenous peoples lived along the river for thousands of years. The river provided the major route into Canada's northern interior for early European explorers.
Economic development remains limited along the river. During the 19th century, fur trading became a lucrative business, but this was affected by harsh weather conditions. The discovery of oil at Norman Wells in the 1920s began a period of industrialization in the Mackenzie valley. Metallic minerals have been found along the eastern and southern edges of the basin; these include uranium, gold, lead, and zinc. Agriculture remains prevalent along the south, particularly in the Peace River area. Various tributaries and headwaters of the river have been developed for hydroelectricity production, flood control and irrigation.
Geography
Headwaters
Through its many tributaries, the Mackenzie River basin covers portions of five Canadian provinces and territories — British Columbia, Alberta, Saskatchewan, Yukon, and the Northwest Territories. Thutade Lake, in the Northern Interior of BC, is the ultimate source of the Mackenzie River via the Finlay–Peace River system, which stretches through BC and Alberta. The Athabasca River originates further south, in Jasper National Park in southwest Alberta. Together, the Peace and Athabasca rivers drain a significant portion of the eastern slope of the Rocky Mountains and the central Alberta prairie. The Peace contributes the majority of the water, about 66 km3 per year, and the Athabasca contributes 25 km3.The Peace and Athabasca meet at the Peace-Athabasca Delta, a vast inland delta at the western end of Lake Athabasca, which also takes runoff from the northern third of Saskatchewan. The Slave River is formed by the confluence of the two rivers and flows due north into Great Slave Lake, at Fort Resolution, Northwest Territories. The Slave is by far the largest river flowing into the lake, with an annual flow of 108 km3. It contributes about 77% of the overall inflow, and forms a large delta where it enters the lake. Other rivers entering Great Slave Lake are the Taltson, Lockhart and Hay Rivers, the latter of which also extends into Alberta and BC.
Main stem
The Mackenzie River issues from the western end of Great Slave Lake about south-west of Yellowknife. The channel is initially several kilometres wide but narrows to about at Fort Providence, which was historically an important ferry crossing in the summer, and used as an ice bridge in the winter for traffic along the Yellowknife Highway. In 2012 the Deh Cho Bridge was completed at a point about upstream, providing a safer permanent crossing. It is the only bridge across the main stem of the Mackenzie. West of Fort Providence the Mackenzie widens considerably, resembling a shallow, swampy lake more than a river; one large widening here is known as Mills Lake.After heading west for about the Mackenzie narrows and turns northwest through a long stretch of fast water and rapids, past the village of Jean Marie River. At Fort Simpson it is joined by the Liard River, its biggest direct tributary, from the west. The Liard drains a large area in the southern Yukon and northern British Columbia and carries a large amount of sediment during the summer melt which does not fully mix with the clear water in the Mackenzie for almost downstream, resulting in a clear current on the east bank and muddy water on the west bank.
Image:Fish drying racks and Mackenzie River.JPG|thumb|left|Dene fishing camp on the Mackenzie River, north of the Arctic Circle
The river continues west-northwest until its confluence with the North Nahanni River, where it turns north towards the Arctic. It flows through open taiga with its wide valley bounded, on the west, by the Mackenzie Mountains and to the east by low hills of the Canadian Shield. This mostly uninhabited area is called the Mackenzie Lowlands; although partly forested, it is mostly covered by large areas of muskeg, swamps and many small lakes. A number of major tributaries join from the west, including the Root River, Redstone River and Keele River. Below the Keele River, the Mackenzie River flows north along the western base of the Franklin Mountains before turning northwest, and receives the Great Bear River, the outflow of Great Bear Lake at Tulita.
The Mackenzie widens considerably to about at Norman Wells, a major centre of oil production. There is a narrows at the Mountain River confluence called the Sans Sault Rapids, where the Mackenzie falls about. Below the Mountain River the Mackenzie flows due north until reaching The Ramparts, a limestone gorge barely wide and up to deep. Below The Ramparts is the village of Fort Good Hope, where the Mackenzie turns northwest again, soon crossing the Arctic Circle. The Mackenzie here flows slightly lower in elevation than the surrounding tundra, as a braided river between low bluffs about apart. It receives the Arctic Red River from the southwest at Tsiigehtchic, where traffic on the Dempster Highway crosses via ferry/ice bridge.
About northwest of Tsiigehtchic is Point Separation, the head of the vast Mackenzie River Delta, whose branching channels, ponds and wetlands spread across more than of the coastal plain. The delta is nearly from north to south, and ranges in width from. It is the second biggest Arctic delta in the world, after the Lena River delta in Russia. Most land in the Mackenzie delta consists of permafrost, which reaches as deep as the bedrock. A characteristic feature of the delta is its numerous pingos, or hills of earth-covered-ice – some 1,400 of them. The Peel River, carrying much of the runoff from the northern Yukon, joins in the delta at a point northeast of Fort McPherson. Below there, the Mackenzie diverges into several large channels with the largest heading north-northeast, emptying into the Beaufort Sea west of Tuktoyaktuk. The Mackenzie Delta contains a logjam with 400,000 caches of wood, which stores 3.4 million tons of carbon, equivalent to a year's emissions from 2.5 million cars.
Drainage basin
At, the Mackenzie River drainage basin encompasses nearly 20 percent of Canada. About, or 54 percent of the basin, lies above Great Slave Lake. Permafrost underlies about three-quarters of the watershed, reaching up to deep in the Mackenzie Delta. As a whole, the Mackenzie basin receives only meager to moderate rainfall, averaging over the entire basin, though mountain areas experience much higher precipitation, and areas near and north of the Arctic Circle receive much lower precipitation. Changes in climate and land cover of the basin are rapidly being reflected in its altered cryosphere and hydrology.The Mackenzie drainage basin is bordered by multiple major North American watersheds. Much of the western edge of the Mackenzie basin runs along the Continental Divide. The divide separates the Mackenzie watershed from that of the Yukon River, which flows to the Bering Strait; and the Fraser River and Columbia River systems, both of which empty into the Pacific Ocean. Lowland divides in the north separate the Mackenzie basin from the Arctic Ocean watersheds of the Anderson, Horton, Coppermine and Back Rivers. In the east, the Mackenzie borders on the Hudson Bay watersheds of the Thelon and Churchill Rivers, and to the south it is bordered by the Saskatchewan–Nelson River system, which also empties into Hudson Bay. The Mackenzie system is hydrologically connected to the Hudson Bay watershed via Wollaston Lake, which is not only the source of the Fond du Lac tributary of Lake Athabasca, but also of the Cochrane River, which flows east into the Churchill River.
The eastern portion of the Mackenzie basin is dominated by vast reaches of lake-studded boreal forest and includes many of the largest lakes in North America. By both volume and surface area, Great Bear Lake is the biggest in the watershed and third largest on the continent, with a surface area of and a volume of. Great Slave Lake is slightly smaller, with an area of and containing of water, although it is significantly deeper than Great Bear. The third major lake, Athabasca, is less than a third that size with an area of. Six other lakes in the watershed cover more than, including the Williston Lake reservoir, the second-largest artificial lake in North America, on the Peace River.
Flow characteristics
The river discharges more than of water each year, accounting for roughly 11% of the total river flow into the Arctic Ocean. The river is frozen for most of the year, with the ice typically breaking up by early to mid-May in the south, and late May-early June in the north. Ice breaks up earlier on the tributaries, sometimes causing ice jams and flooding where they meet the Mackenzie. In the middle of the larger lakes, such as Great Slave, ice can persist as late as mid-June. The river typically freezes by late October or November, starting in the north. Year round, the Mackenzie's outflow has a major stabilizing effect in the local climate above the Arctic Ocean with large amounts of warmer fresh water mixing with the cold seawater.Image:View over Churches and Shoreline - Hamlet of Tsiigehtchic - Near Inuvik - Northwest Territories - Canada.jpg|thumb|right|Mackenzie at Tsiigehtchic
The average flow rate at the mouth is, the second largest in Canada after the St Lawrence, and the fourteenth largest in the world. About 60 percent of the water comes from the western half of the basin, which includes the Rocky, Selwyn, and Mackenzie mountain ranges out of which spring major tributaries such as the Peace and Liard Rivers, which contribute 23 and 27 percent of the total flow, respectively. In contrast the eastern half, despite being dominated by marshland and large lakes, provides only about 25 percent of the Mackenzie's discharge.
During peak flow in the spring, the difference in discharge between the two halves of the watershed becomes even more marked. While large amounts of snow and glacial melt dramatically drive up water levels in the Mackenzie's western tributaries, large lakes to the east retard springtime discharges. Spring floods from the Peace-Athabasca system are significantly slowed by the delta area at the western end of Lake Athabasca causing the lake to rise, and the excess water can only flow out after the rivers have receded. The same phenomenon occurs at Great Slave Lake, which naturally regulates the flow from the Slave River into the Mackenzie.
There are river gauges at several upstream points along the Mackenzie River. The average flow rate at the outlet of Great Slave Lake is. At Fort Simpson, below the Liard River, it is. At Norman Wells it is, and at the Arctic Red confluence it is.
Mackenzie monthly mean discharge at Arctic Red River
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