Longest Rivers of the World

Longest Rivers of the World

Rank	River	Location	Approximate Length—miles
1.	Nile	Africa	4,180
2.	Amazon	South America	3,912
3.	Mississippi-Missouri-Red Rock	United States	3,710
4.	Chang Jiang (Yangtze)	China	3,602
5.	Ob	Russia	3,459
6.	Huang Ho (Yellow)	China	2,900
7.	Yenisei	Russia	2,800
8.	Parana	South America	2,795
9.	Irtish	Russia	2,758
10.	Zaire (Congo)	Congo	2,716

1.Nile River

The Nile River is Regarded as the longest river in Africa, but only few knows it’s also the longest River in the world, spanning 10 different African countries. The popularity of the  Nile River easily dwarfs other longest Rivers in Africa.Either ways , all the longest  rivers  in Africa have their special peculiarities.  This list hope to lessen the gap in knowledge about other longest rivers in Africa.

Regarded as the father of African Rivers by the Britannica Encyclopedia, and the longest river  in  Africa and the World in general. it spans a total of 11 countries namely Ethiopia, Eritrea, Sudan, Uganda, Tanzania, Kenya, Rwanda, Burundi, Egypt, Democratic Republic of the Congo, South Sudan It arises from two main source namely the Blue Nile and The White Nile. The Blue Nile begins at Lake Tana, Ethiopia, and joins the White Nile south of Egypt in Khartoum, Sudan. Together, they make up the longest river in the world, The Nile River is the main source of Water in Egypt and Sudan. Its home for some large creatures like the hippopotamus,black Rhinoceros and the Nile Crocodile. most now almost extinct.

2. Amazon rivers

Amazon rivers, major pathways for wildlife, people and water

Sometimes they rush, sometimes they just creep along, and in some places they may almost die out. At other times of the year, they will suddenly overflow with water.

Rivers are unpredictable, and nowhere is this truer than in the Amazon River Basin, which is subject to radical seasonal changes throughout the year.
Amazon rivers provide a range of habitats, including swamps, marshes and streams, each hosting different types of wildlife. These waterways are subject to major annual flood cycles, affecting the ecology and the landscape of the region.

The Amazon River

Coming a close second after the Nile as the world’s longest river, the Amazon River sets the record in terms of the sheer volume of water that it carries – a mind-boggling average discharge of 219,000 m^₃/sec of water.
It is estimated that approximately one-sixth of all fresh water that drains into the world's oceans goes through the 320-km-wide delt  of the Amazon, where it meets the Atlantic Ocean.
As the seasons change, so does the river. During the dry season, the width of the Amazon River can be 4 km to 5 km in places – and in the wet season, this can increase to 50 km! At the height of the wet season, the current can reach a speed of 7 km/hr.
Major roles of the Amazon River
As the drainage system of the Amazon Basin, the Amazon River and its approximately 1,100 tributaries play major roles in the ecology of the basin.
Before roads and airstrips started appearing in the basin, these waterways were the major access routes to the interior areas of Brazil and the northern half of South America.
For example, the only way you can get to Iquitos, Peru, which is right on the Amazon River, is to board a plane or a boat. There are no roads to get there.

Origins and course of the river
The Amazon River has its source high in the Peruvian Andes, at an elevation of 5,598 m. There, at a mere 192 km from the Pacific Ocean where it once flowed into, the Amazon River begins as a small tributary called the Carhuasanta.
As it heads east, it flows into and becomes the Hornillos, which merges into the Apurimac, a major tributary that eventually joins the Ene, the Tambo and then the Ucayali.
After an initial drop in elevation, the Amazon River steadies its descent towards the Atlantic Ocean at a rate of 1.5 cm for every kilometre over a distance of over 6,400 km. In some places, the river reaches a width of 10 km, as far as 1,600 km upriver, and large ships can dock all the way up to Iquitos, Peru.
Sighting the river before the land
The brown waters of the Amazon River can be seen as far as 100 km out to sea from the mainland, well before the continent is in sight.
In the early days of colonization, this phenomenon would help ships sailing from Europe to South America ensure they were on good course before sighting the land.

3. MISSISSIPPI RIVER

MISSISSIPPI RIVER. One of the major rivers of North America, the Mississippi River has been a focal point in American history, commerce, agriculture, literature, and environmental awareness. The length of the Mississippi River from its source in Lake Itasca in northwestern Minnesota to its mouth in the Gulf of Mexico flows 2,348 miles; it is the second longest river in the United States behind the Missouri (2,466 miles). The Mississippi River system drains the agricultural plains between the Appalachian Mountains to the east and the Rocky Mountains to the west. This drainage basin (approximately 1,234,700 square miles) covers about 40 percent of the United States and ranks as the fifth largest in the world.

Mississippi River's Course

The Mississippi River actually begins as a small stream flowing from Lake Itasca, Minnesota. The river initially flows north and then east as the means of connecting several lakes in northern Minnesota. The river begins to flow southward near Grand Rapids, Minnesota, and is joined with the Minnesota River between the cities of Minneapolis and Saint Paul. The muddy waters of the Missouri River flow into the clear waters of the Mississippi River just north of St. Louis, Missouri. At this point, the Mississippi
becomes brown and muddy for the rest of the journey south.
At Cairo, Illinois, the Ohio River flows into the Mississippi, doubling its volume and creating the point that divides the Upper Mississippi from the Lower Mississippi. The Lower Mississippi Valley is a wide and fertile region. In this area, the river meanders its way south and over time has continuously changed its course, leaving behind numerous oxbow lakes as remnants of its past. As it flows in this southern region, the Mississippi deposits rich silt along its banks. In many areas, the silt builds up to create natural levees. South of Memphis, Tennessee, the Arkansas River junctions with the Mississippi River. Near Fort Adams, Mississippi, the Red River joins with the Mississippi, diverting with it about a quarter of the flow of the Mississippi into the Atchafalaya River.
As the Mississippi River nears the Gulf of Mexico it creates a large delta with its silt. The Mississippi River delta covers approximately 13,000 square miles. South of the city of New Orleans, the Mississippi creates several channels, known as distributaries, which then flow separately into the Gulf of Mexico. The most prominent of these are known as the North Pass, South Pass, Southwest Pass, and Main Pass. Annually, the Mississippi River discharges about 133 cubic miles of water (approximately 640,000 cubic feet per second).

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History

The Mississippi River played an important role in the lives of many Native Americans who lived in the Upper Mississippi Valley, such as the Santee Dakota, the Illinois, the Kickapoo, and the Ojibwe, as well as those tribes in the southern valley, such as the Chicksaw, the Choctaw, the Tunica, and the Natchez. The name "Mississippi," meaning "great river" or "gathering of water," is attributed to the Ojibwe (Chippewa).
The first known European to travel on the Mississippi River was the Spaniard Hernando de Soto, who crossed the river near present-day Memphis in May 1541. Over a century later, in 1673, the French explorers Louis Jolliet and Father Jacques Marquette entered the Mississippi River from the Wisconsin River and traveled by canoe downriver to a point near the mouth of the Arkansas River. Less than a decade later, another Frenchman, René-Robert Cavelier, Sieur de La Salle, explored the Mississippi River from the Illinois River to the Gulf of Mexico. La Salle declared on 9 April 1682 that the Mississippi Valley belonged to France, and he named the region Louisiana. It was not until 1718 that the French were actually established at New Orleans. They maintained control over the lower Mississippi until the end of the French and Indian War (1754–1763). In 1762 and 1763, the French made cessions that established the Mississippi River as an international boundary with Spanish territory to the west and British territory to the east.
During the American Revolution (1775–1783), the river served as the supply line for George Rogers Clark, allowing him to maintain control of the Illinois country. The Peace of Paris of 1783 outlined the new country of the United States as extending to the Mississippi River between Spanish Florida and the Canadian border. Additionally, the United States was entitled to free navigation of the Mississippi River. Spain, though not party to the treaty, controlled the mouth of the Mississippi and, through high duties, maintained actual power over the river and, in essence, over the entire Mississippi Valley. Not until Pinckney's Treaty with Spain in 1795 was the river truly free to American navigation. This freedom was short-lived, however, for when Spain ceded Louisiana back to France in 1800, the French again closed the Mississippi to American river traffic. Finally, the Louisiana Purchase (1803) made the Mississippi an American river, and it rapidly became a major route of trade and commerce for the entire Mississippi Valley.
Western settlers and traders traversed the Mississippi in flatboats (on which farmers floated their produce downstream to market) and keelboats (which could be pushed upstream with great effort). Certainly the most significant change in river transportation on the Mississippi came in 1811 when the steamboat New Orleans made its legendary trip from Pittsburgh to New Orleans. This event opened the Mississippi River to two-way traffic, essentially doubling the carrying capacity of the river. By 1860, more than 1,000 steamboats were actively engaged in transport along the Mississippi River system, and the cities of Cincinnati (Ohio), Louisville, (Kentucky), St. Louis, Memphis, and New Orleans became important cities in the movement west.
During the Civil War (1861–1865) both the Union and the Confederacy recognized the importance of the Mississippi River, and the fight over its control was a major part of the war. A decisive victory for the Union came with the fall of Vicksburg, Mississippi (1863), which essentially gave the Union full possession of the river, reopening the trade routes down the Mississippi from the Ohio Valley and splitting the Confederacy.
Following the war, life on the Mississippi did not return to the golden years so richly described in Mark Twain's writings. The faster and more convenient railroads replaced much of the commercial traffic on the Mississippi. In 1879, the U.S. Congress established the Mississippi River Commission as a means of maintaining and improving the river as a commercial waterway. In the years that followed, the commission deepened and widened several channels along the river, making it more navigable for larger boats and barges. These changes promoted increased transport on the Mississippi, particularly of heavy and bulky freight.
At the turn of the twenty-first century, the Mississippi River carried more than half of the freight transported on American inland water. Nearly 460 million short tons of freight were transported on the Mississippi River each year. Most of this freight was carried on large barges pushed by tugboats. The upper Mississippi traffic was predominantly composed of agricultural products such as wheat, corn, and soybeans. Coal and steel freight traveled down the Ohio River and onto the lower Mississippi River. At Baton Rouge, Louisiana, petroleum, petrochemical products, and aluminum joined the freight being moved south. It is at this point that the depth of the Mississippi River increases, allowing for larger ships to traverse upriver to this point.

Flooding

People living along the Mississippi River are well aware of the flooding potential of the river. During de Soto's exploration of the Mississippi, he noted much flooding. Evidence from Native American Mississippi Valley settlement locations (on higher land) and the creation of mounds on which they placed their dwellings indicate Native American awareness of and adaptation to flooding of the Mississippi. Significant flooding of the Mississippi Valley in 1927 prompted national discussion of flood control along the Mississippi. Other severe flooding events occurred in 1937, 1965, 1973, 1982, and 1993. The severe flooding in 1993 is considered to be the most devastating in recorded U.S. history. It affected the upper and middle Mississippi Valley from late June until mid-August 1993 with record levels on the Mississippi River and most of its tributaries from Minnesota to Missouri. At St. Louis, the river remained above flood stage for over two months and crested at 49.6 feet (19 feet above flood stage). Industry and transportation along the Mississippi were virtually at a standstill during the summer months of 1993. In all, over 1,000 of the 1,300 levees in the Mississippi River system failed, over 70,000 people were displaced, nearly 50,000 homes were either destroyed or damaged, 12,000 square miles of agricultural land was unable to be farmed, and 52 people died. Fortunately, larger cities along the Mississippi remained protected by floodwalls. The cost of the flood was enormous. Most estimates of total flood damage run to nearly $20 billion. Flood events are certain to remain a part of life along the Mississippi River.

Human Influence

Humans have influenced the flow of the Mississippi and the quality of its water. Historically, the river and its tributaries meandered across the floodplain, and erosion, sedimentation, and flooding were natural processes. During the twentieth century, however, humans interrupted these processes. In the 1930s, twenty-nine navigation dams were built between St. Louis and Minneapolis. These dams impound the water to improve navigation. One cost of damming, however, is increased retention of sediment in the river. Flood-control levees have been built in order to manage the seasonal flooding. Much of the Mississippi floodplain has been converted to agriculture. This change has two serious consequences for the Mississippi River. First, the loss of prairie wetlands and floodplain forest decreases the biodiversity of the region. Second, conversion of land to agriculture often leads to increased run off of fertilizers and pesticides. The presence of high rates of nitrogen and phosphorus can be directly attributed to farming practices in the Mississippi Valley. At the end of the twentieth century, many experts suggested that agricultural pollution in the Mississippi River was directly responsible for the creation of the "dead zone," an area in the Gulf of Mexico where there is little aquatic life due to abnormally low levels of oxygen.
Industrial pollution is also a concern along the Mississippi River. Industries have contributed significant amounts of oil, aluminum, lead, and other industrial wastes such as sulfur dioxide, hydrogen sulfide, and benzene to the flow of the Mississippi. A study in 2000 estimated that 58 million pounds of toxic discharge travels down the Mississippi annually. At the turn of the twenty-first century, much of the river remained unswimmable and unfishable, despite the fact that it serves as the primary source of drinking water for 18 million people. Growing awareness of environmental processes and increased concern for the state of the Mississippi River system that began during the last decade of the twentieth century may prove to have a positive influence in the life of the great river.

4. CHANG JIANG RIVER

Yangtze River, Chinese (Pinyin) Chang Jiang or (Wade-Giles romanization) Ch’ang Chiang , longest river in both China and Asia and the third longest river in the world, with a length of 3,915 miles (6,300 kilometres). Its basin, extending for some 2,000 miles (3,200 km) from west to east and for more than 600 miles (1,000 km) from north to south, drains an area of 698,265 square miles (1,808,500 square km). From its source on the Plateau of Tibet to its mouth on the East China Sea, the river traverses or serves as the border between 10 provinces or regions. More than three-fourths of the river’s course runs through mountains. The Yangtze has eight principal tributaries. On its left bank, from source to mouth, these are the Yalung, Min, Jialing, and Han rivers; those on the right bank include the Wu, Yuan, Xiang, and Gan rivers.

The name Yangtze—derived from the name of the ancient fiefdom of Yang—has been applied to the river mainly by those in the West. Chang Jiang (“Long River”) is the name used in China, although it also is called Da Jiang (“Great River”) or, simply, Jiang (“[The] River”). The Yangtze is the most important river of China. It is the country’s principal waterway, and its basin is China’s great granary and contains nearly one-third of the national population.

Physical features

The upper course

The upper course of the Yangtze flows across the Plateau of Tibet and descends through deep valleys in the mountains east of the plateau, emerging onto the Yunnan-Guizhou (Yungui) Plateau. Summers there are warm, and the winters are cold. The source of the Yangtze is the Ulan Moron (Wulanmulun) River, which originates in glacial meltwaters on the slopes of the Tanggula Mountains in southern Qinghai province on the border with the Tibet Autonomous Region. From the confluence of this stream with several others, the river flows generally easterly through a shallow, spacious valley, the bottom of which is studded with lakes and small reservoirs. This part of its course lies in the higher regions of the Tibetan highlands.
The river’s character changes sharply upon reaching the eastern limits of the highlands. There the river—which in this stretch is called the Jinsha—descends from a high elevation, winding its way south of the high Bayan Har Mountains and forming a narrow valley up to 2 miles (3 km) in depth. Individual mountain peaks exceed elevations of 16,000 feet (4,900 metres) above sea level and are crowned with glaciers and perpetual snow. The steep, rocky slopes are cut with gorges and deep valleys. For several hundred miles the Yangtze flows in a southeasterly direction, before turning south to flow downward in rushing rapids. For a considerable distance the river flows through passes that are so steep that no room is left even for a narrow path. Villages, which are rarely found, are located high above the river. In this region the Yangtze runs close and parallel to both the Mekong and Salween rivers; all three rivers are within 15 to 30 miles (25 to 50 km) of one another and continue to flow in mutual proximity for a distance of more than 250 miles (400 km).
North of latitude 26° N these great rivers diverge, and the Yangtze turns east to pass through a winding valley with steep slopes. The river receives the waters of many tributaries, among which the Yalong River is the largest and contributes the most water. The Yangtze then widens to between 1,000 and 1,300 feet (300 and 400 metres), reaching depths often exceeding 30 feet (9 metres). In narrower gorges the water width decreases by almost half, but the depth increases sharply.
Near the end of the upstream part of its course, the Yangtze descends to an elevation of 1,000 feet above sea level. Thus, over the first 1,600 miles (2,600 km) of its length, the river has fallen more than 17,000 feet (5,200 metres), or an average of more than 10 feet per mile (2 metres per km) of its course. In the mountains, however, there is a substantial stretch where the fall of the river is considerably greater.

The middle course

The middle course of the Yangtze stretches for about 630 miles (1,010 km) between the cities of Yibin in Sichuan province and Yichang in Hubei province. The climate is characterized by hot summers and relatively mild winters, as the high mountains to the west protect the region from the cold north and west winds. Annual precipitation measures between 40 and 60 inches (1,000 to 1,500 mm), a large part of it occurring in summer; the growing season lasts for more than six months. In most of this segment, the river crosses hilly Sichuan province, where the lower mountains and plateaus connect the highlands of southwestern China with the Qin (Tsinling) Mountains lying between the Yangtze and Huang He (Yellow River) basins. Located in this area is Chongqing, a major industrial centre and river port. The river’s width there is from about 1,000 to 1,600 feet (300 to 500 metres), and the depth in places exceeds 30 feet. The current is swift; the banks often are high and steep. The river falls some 820 feet (250 metres) in Sichuan, more than a foot per mile (0.2 metre per km) of flow.
As the Yangtze flows through eastern Sichuan and into western Hubei, it traverses for a distance of 125 miles (200 km) the famous Three Gorges region before debouching onto the plains to the east. The gorges have steep, sheer slopes composed mainly of thick limestone rocks. Prior to the completion of the Three Gorges Dam in 2006, they rose some 1,300 to 2,000 feet (400 to 600 metres) above the river, although with the creation of the reservoir behind the dam their height has been diminished fairly significantly. Nonetheless, they still present the appearance of fantastic towers, pillars, or spears. Qutang, the first gorge—about 5 miles (8 km) long—is the shortest; prior to its inundation, the river there was considered the most dangerous for navigation, being extremely narrow with many rapids and eddies. Wu, the second gorge, stretches for about 30 miles (50 km); it is a narrow, steep corridor with almost vertical walls of heights up to 1,600 or even 2,000 feet above the river. The last gorge, Xiling, is located upstream of Yichang and extends for a distance of 21 miles; in places limestone cliffs rise directly out of the water, although with the rise of the reservoir to much lower heights than before. The gorges are rocky, and the walls are speckled with cracks, niches, and indentations. Even before the river was inundated, its depth in the gorges was considerable, increasing to between 500 and 600 feet (150 and 180 metres) and giving the Yangtze the greatest depths of any river in the world.

The lower course

The lower part of the Yangtze basin is centred on the extensive lowland plains of east-central China. The region experiences a temperate climate with warm springs, hot summers, cool autumns, and relatively cold winters for the latitude. Monsoons (seasonally changing winds) dominate the weather of the region, and in the summer and autumn typhoons occur periodically. As the Yangtze exits from the Three Gorges Dam, near Yichang, it enters a complex system of lakes, marshes, and multiple river channels developed on the plains of Hunan and Hubei provinces. This vast region, lying at elevations below 165 feet (50 metres), has served as a natural flood-regulation basin in recent geologic history. Three main tributaries (the Yuan, Xiang, and Han rivers) and many smaller ones join the Yangtze in this region, which also is where the current slows as the river reaches the plain. Water levels fluctuate considerably between the flood and low-flow seasons. In addition, the presence of a number of large lakes, including Dongting Lake and Lakes Hong and Liangzi, also causes considerable fluctuations in water volume. The total area of the lakes, at average water levels, is some 6,600 square miles (17,100 square km). The lakes are of national economic significance, mainly as fisheries.
At the edge of the Lake Liangzi plain the Yangtze widens markedly, the course of its stream wandering in the form of a large loop. The width of the river is up to 2,600 feet (800 metres), the depth is more than 100 feet (30 metres), and the water current flows at a rate of about 3.5 feet (1 metre) per second. The banks are built up for protection from floods. In the southern part of the plain lies Dongting Lake, which once was the largest freshwater lake in China but now has been reduced in area by silting and land reclamation; it shares four tributaries and two canals with the Yangtze, whose flow it serves to regulate. The surrounding area, agricultural and studded with lakes, is China’s most important rice-producing region.
At the centre of the lakes region is the large metropolis of Wuhan. Situated on the Yangtze near the mouth of the Han River, it was formed in 1950 by the merger of the cities of Hanyang and Hankou on the left bank and Wuchang on the right bank and has become one of China’s most important metallurgical-industry centres and river ports. Farther east the Yangtze flows into a narrowing, picturesque valley and then passes onto the plain of Jiangxi province, which contains Lake Poyang, China’s largest natural freshwater lake. The lake, with an average area of about 1,385 square miles (3,585 square km), receives the Kan River tributary and, in turn, is linked to the Yangtze by a wide tributary. The river then turns to the northeast, passes through a widening valley, and flows out onto the southern North China Plain. The width of the river increases at this point to between 3,000 and 6,000 feet (900 and 1,800 metres), and the depth in places approaches 100 feet. In this region there are a number of large cities, including Anqing, Wuhu, and Nanjing. The Grand Canal (Da Yunhe), which, with a length of nearly 1,100 miles (1,800 km), is one of the longest canals in the world; it crosses the Yangtze in the vicinity of the city of Zhenjiang.

The Yangtze delta

The Yangtze delta, which begins beyond Zhenjiang, consists of a large number of branches, tributaries, lakes, ancient riverbeds, and marshes that are connected with the main channel. During major floods the delta area is completely submerged. Lake Tai, with an area of about 930 square miles (2,410 square km), is notable as the largest of the many lakes in the delta. The width of the Yangtze in the delta, as far as the city of Jiangyin, ranges from less than 1 mile to almost 2 miles (1.6 to 3.2 km); farther downstream the channel gradually widens and becomes a large estuary, the width of which exceeds 50 miles (80 km) near the mouth of the river. Major cities in the delta include Wuxi, Suzhou, and, at the river’s mouth, Shanghai.
Before emptying into the sea, the Yangtze divides into two arms that drain independently into the East China Sea. The left branch has a width of about 3 to 6 miles (5 to 10 km), the right branch of 6 to 15 miles (10 to 25 km). Between the branches is situated Chongming Island, which was formed over the centuries by the deposit of alluvium at the mouth of the Yangtze. The depth of the river in places approaches 100 to 130 feet (30 to 40 metres) but decreases to only several feet near the sea at the mouth of the river because of the presence of sandbars.
The section of river from the mouth to 250 miles (400 km) upstream is subject to the influence of tides. The maximum range of the tides near the mouth is 13 to 15 feet (4 to 5 metres). The Yangtze delta is rich in mud and silt and is dominated by fluvial and tidal processes.
The present-day bed of the Yangtze in this area is somewhat above the elevation of the plain. Thus, to protect the surrounding region from floodwaters, the banks of the main and other rivers are built up; the total length of banks on the Yangtze on which levees have been constructed is about 1,700 miles (2,740 km). Dams also have been built for flood protection on the shores of several lakes; the Qingjiang Reservoir, for example, built for this purpose near Dongting Lake, has a design capacity of 194 million cubic feet (5.5 million cubic metres). The delta is protected from the sea by two gigantic parallel banks that are faced with stone in most parts.

Geology

In its upper reaches the Yangtze River drains across the Plateau of Tibet, which is still uplifting as the Indian and Eurasian tectonic plates collide. The bedrock comprises an assemblage of marine sedimentary, igneous, and metamorphic rocks. Within intermontane basins, thick deposits of sediments of Cenozoic age—i.e., less than about 65 million years old—overlie the bedrock. The Yangtze descends abruptly from the Tibetan Plateau to flow across deeply eroded mountain plateaus consisting of Paleozoic and Mesozoic rocks roughly 350 to 150 million years old. In its lower reaches, the Yangtze River flows across basin fills of Cenozoic material that is about 65 to 25 million years old. These are the result of fluvial sedimentation as the Yangtze has migrated across its lower basin throughout its Cenozoic history.

Hydrology

The Yangtze basin is comparatively well irrigated; the average yearly rainfall amounts to about 43 inches (1,100 mm). Most of the precipitation is brought by the monsoon winds and falls primarily as rain in the summer months. In the mountainous part of the basin the precipitation is mainly snow. Floods, which result from the monsoon rains in the middle and lower parts of the basin, usually begin in March or April and can occur at any time during the next eight months. In May the water level decreases somewhat but then sharply increases again, continuing to rise until August, when it reaches its highest level. After that the water level gradually falls to the premonsoon levels, the decrease continuing through the autumn and most of the winter until February, when the lowest annual level is reached.
The annual range of water-level fluctuations is considerable—an average of about 65 feet (20 metres)—with 26 to 35 feet (8 to 11 metres) during years of low water. Downstream from the Three Gorges Dam the impact of the water-level variation is lessened by the dam itself and by the regulating effect of the lakes. In the delta tides exert the greatest influence on the water level. Near the city of Wusong the daily tidal range is 15 feet (4.5 metres), and the yearly range is 20 feet (6 metres).
A breakdown of the water volume delivered to the mouth of the Yangtze shows that the highland part of the basin contributes 10 percent of the flow, while the remainder of the water in the river is contributed by the middle and downstream parts of the basin, with runoff from the basins of Dongting Lake and Lake Poyang being responsible for about two-fifths of the volume.
The Yangtze carries a tremendous volume of water. In the upstream areas the average flow exceeds 70,000 cubic feet (1,980 cubic metres) per second, which is more than the discharge rate of the second longest river in China, the Huang He, at its mouth. After the inflow from the first large tributary—the Yalong River—the volume in the Yangtze increases sharply, approaching an average of 194,000 cubic feet (5,500 cubic metres) per second. Farther downstream the Yangtze admits many tributaries, and the volume gradually increases. Prior to the completion of the Three Gorges Dam, it reached 529,000 cubic feet (15,000 cubic metres) per second at the end of the Three Gorges area, 847,000 cubic feet (24,000 cubic metres) per second at Wuhan, and some 1,100,000 cubic feet (31,100 cubic metres) per second at its mouth; the total volume entering the sea annually was roughly 235 cubic miles (979 cubic km), ranking it third in volume of flow behind the Amazon and Congo rivers. Those numbers have decreased somewhat since the completion of the dam in 2006. The suspended sediment load at the mouth of the Yangtze is some 478 million tons per year, one of the highest sediment loads of any river in the world.
During the seasonal rains the Yangtze widely floods the lower areas, and the maximum volume of water entering the sea can be more than double the average flow. Likewise, the flow decreases during the dry season, sometimes to about one-fourth the average flow. In spite of the fact that the discharge volume of the Yangtze vastly exceeds that of the Huang He, the Yangtze is significantly less silty than the Huang He. This is because much of the Huang He’s course is over the Loess Plateau with its easily erodible loess (wind-deposited soil), whereas the Yangtze flows over little loess, and its floodplains are more vegetated and less erodible. In the mountainous part of the basin, particularly in the Plateau of Tibet, the waters of the Yangtze contain little silt.
Downstream, however, the waters become muddy and acquire a coffee colour. It is estimated that the Yangtze annually carries between 280 million and 300 million tons of alluvium to its mouth, depositing an estimated 150 million to 200 million tons on the river bottom in addition. Thus, the total amount of suspended material carried or deposited is between 430 million and 500 million tons per year, one of the highest sediment loads of any river in the world. As a result of the depositing of alluvium at the river’s mouth, the delta extends into the sea an average of one mile every hundred years.
During the period of monsoon rains, the Yangtze and its tributaries formerly spilled over, creating extensive floods. If the floods in the main channel coincided with flooding in one or more of the major tributaries, powerful, destructive flood waves could result, an occurrence that happened repeatedly in the history of China. One of the major objectives of the Three Gorges project is to control such flooding by the river.
When flooding occurs, it frequently results from the deposit of silt in the bed of the Yangtze. Upon leaving the mountains and entering the plain, the current in the Yangtze sharply decreases, and thus the flow cannot continue to carry the entire amount of silt. As a result, a significant portion is deposited in the bed, causing the bottom to rise. A similar situation occurs in many of the Yangtze’s tributaries. Flooding thus presents a great danger to the inhabitants of the adjacent plains.
Human adaptation to and utilization of the plains of the Yangtze valley have evolved in the context of such floods. Among the legends and myths handed down from the earliest historical times are accounts of floods that submerged vast areas. These are said to have turned the plains into inland seas, with water remaining in the lowest places for many years at a time. Catastrophic floods have occurred throughout recorded history. During the period from 206 bce to 1960 ce, China experienced more than 1,030 major floods. Especially extensive flooding has occurred on the Yangtze more than 50 times and on the tributary Han River more than 30 times. On the average, the Yangtze basin has been the scene of catastrophic flooding every 50 to 55 years.
Widespread flooding also may take place at shorter intervals. This has been the case since the mid-19th century, as the Yangtze basin has flooded in 1870, 1896, 1931, 1949, and 1954. Of these, the 1931 and 1954 floods were national disasters. The 1931 flood resulted from heavy, continuous monsoon rains that covered most of the middle and lower parts of the basin. During May and June, six huge flood waves swept down the river, destroying the protecting dams and levees in two dozen places and flooding more than 35,000 square miles (90,000 square km) of land; 40 million people were rendered homeless or otherwise suffered. Many population centres, including Nanjing and the Wuhan conurbation, were underwater. In Wuhan the water remained for more than four months, the depth exceeding 6 feet (1.8 metres) and in places more than 20 feet (6 metres). In the summer of 1954 another powerful flood occurred, again the result of continued monsoon rains. The water level sharply increased and at times exceeded the 1931 flood levels by almost 5 feet (1.5 metres). Effective flood-control measures developed since the 1930s, however, averted many of the potential consequences of the flood.

5. OB RIVER

Ob River, river of central Russia. One of the greatest rivers of Asia, the Ob flows north and west across western Siberia in a twisting diagonal from its sources in the Altai Mountains to its outlet through the Gulf of Ob into the Kara Sea of the Arctic Ocean. It is a major transportation artery, crossing territory at the heart of Russia that is extraordinarily varied in its physical environment and population. Even allowing for the barrenness of much of the region surrounding the lower course of the river and the ice-clogged waters into which it discharges, the Ob drains a region of great economic potential.
The Ob proper is formed by the junction of the Biya and Katun rivers, in the foothills of the Siberian sector of the Altai, from which it has a course of 2,268 miles (3,650 km). If, however, the Irtysh River is regarded as part of the main course rather than as the Ob’s major tributary, the maximum length, from the source of the Black (Chorny) Irtysh in China’s sector of the Altai, is 3,362 miles (5,410 km), making the Ob the seventh longest river in the world. The catchment area is approximately 1,150,000 square miles (2,975,000 square km). Constituting about half of the drainage basin of the Kara Sea, the Ob’s catchment area is the sixth largest in the world.

Physical features

Physiography

The West Siberian Plain covers about 85 percent of the Ob basin. The rest of the basin comprises the terraced plains of Turgay (Kazakhstan) and the small hills of northernmost Kazakhstan in the south and the Kuznetsk Alatau range, the Salair Ridge, the Altai Mountains and their foothills and outliers in the southeast.
There are more than 1,900 rivers within the basin, with an aggregate length of about 112,000 miles (180,000 km). The Irtysh, a left-bank tributary 2,640 miles (4,250 km) long, itself drains about 615,000 square miles (1,593,000 square km; a somewhat larger area than that drained by the upper and middle Ob above the Irtysh confluence); and some 70 percent of the whole basin is drained by left-bank tributaries.
The huge basin of the Ob stretches across a number of natural zones. Semidesert prevails in the far south around Lake Zaysan (recipient of the Black Irtysh and source of the Irtysh proper), bordered on the north by steppe grassland. The central regions of the West Siberian Plain—i.e., more than half of the basin—consist of taiga (swampy coniferous forest), with great expanses of marshland. In the north there are vast stretches of tundra (low-lying, cold-tolerant vegetation).
The upper Ob runs from the junction of the Biya and Katun to the confluence of the Tom River, the middle Ob from the junction with the Tom to the Irtysh confluence, and the lower Ob from the junction with the Irtysh to the Gulf of Ob.
The Biya and the Katun both rise in the Altai Mountains: the former in Lake Telets, the latter to the south among the glaciers of Mount Belukha. From their junction near Biysk the upper Ob at first flows westward, receiving the Peschanaya, Anuy, and Charysh rivers from the left; in this reach, the river has low banks of alluvium, a bed studded with islands and shoals, and an average gradient of 1 foot per mile (20 cm per km). From the Charysh confluence the upper Ob flows northward on its way to Barnaul, receiving another left-bank tributary, the Aley River, and widening its floodplain as the valley widens. Turning westward again at Barnaul, the river receives a right-bank tributary, the Chumysh River, from the Salair Ridge. The valley there is 3 to 6 miles (5 to 10 km) wide, with steeper ground on the left than on the right; the floodplain is extensive and characterized by diversionary branches of the river and by lakes; the bed is still full of shoals; and the gradient is reduced, but the depth increases markedly. At Kamen-na-Obi, however, where the river begins to bend northeastward, the width of the valley shrinks to 2 to 3 miles (3 to 5 km). Just above Novosibirsk another right-bank tributary, the Inya River, joins the upper Ob; and a dam at Novosibirsk forms the huge Novosibirsk Reservoir. Below Novosibirsk, where the river leaves the region of forest steppe to enter a zone of aspen and birch forest, both valley and floodplain broaden notably until, at the confluence with the Tom River, they are, respectively, 12 and 3 or more miles (19 and 5 or more km) wide. The depth of the upper Ob (at low water) varies between 6.5 and 20 feet (2 and 6 metres).
The middle Ob begins where the Tom flows into the main stream, from the right. Taking at first a northwesterly course, the river thereafter becomes much deeper and wider, especially after receiving its mightiest right-bank tributary, the Chulym, shortly below the confluence of the Shegarka River from the left. Successive tributaries along the northwesterly course, after the Chulym, include the Chaya and the Parabel (both left), the Ket (right), the Vasyugan (left), and the Tym and Vakh rivers (both right). Down to the Vasyugan confluence the river passes through the southern belt of the taiga, thereafter entering the middle belt. Below the Vakh confluence the middle Ob changes its course from northwesterly to westerly and receives more tributaries: the Tromyegan (right), the Great (Bolshoy) Yugan (left), the Lyamin (right), the Great Salym (left), the Nazym (right), and finally, at Khanty-Mansiysk, the Irtysh (left). In its course through the taiga, the middle Ob has a minimal gradient, a valley broadening to 18 to 30 miles (29 to 48 km) wide, and a correspondingly broadening floodplain—12 to 18 miles (19 to 29 km) wide. In this part of its course, the Ob flows in a complex network of channels, with the main bed widening from less than 1 mile (about 1 km) on the higher reaches to nearly 2 miles (3 km) at the confluence with the Irtysh and becoming progressively free of shoals. Low-water depths vary between 13 and 26 feet (4 and 8 metres). At high water there are great floods every year, sometimes spreading 15 or even 50 miles (24 to 80 km) across the valley and lasting from two to three months.
From its start at the confluence of the Irtysh, the lower Ob flows to the northwest as far as Peregrebnoye and thereafter to the north, crossing the northern belt of the taiga until it enters the zone of forest tundra in the vicinity of its delta. The valley is wide, with slopes steeper on the right than on the left, and the vast floodplain—12 to 18 miles (19 to 29 km) wide—is crisscrossed by the braided channels of the river and dotted with lakes. Below Peregrebnoye the river divides itself into two main channels: the Great (Bolshaya) Ob, which receives the Kazym and Kunovat rivers from the right, and the Little (Malaya) Ob, which receives the Northern (Severnaya) Sosva, the Vogulka, and the Synya rivers from the left. These main channels are reunited below Shuryshkary into a single stream that is up to 12 miles (19 km) wide and 130 feet (40 metres) deep; but after the confluence of the Poluy (from the right) the river branches out again to form a delta, the two principal arms of which are the Khamanelsk Ob, which receives the Shchuchya from the left, and the Nadym Ob, which is the more considerable of the pair. At the base of the delta lies the Gulf of Ob, which is some 500 miles (800 km) long and has a width reaching 50 miles (80 km); the gulf’s own catchment area (forest tundra and tundra proper) is more than 40,000 square miles (105,000 square km).

Climate and hydrology

The Ob basin has short, warm summers and long, cold winters. Average January temperatures range from −18 °F (−28 °C) on the shores of the Kara Sea to 3 °F (−16 °C) in the upper reaches of the Irtysh. July temperatures for the same locations, respectively, range from 40 °F (4 °C) to above 68 °F (20 °C). The absolute maximum temperature, in the arid south, is 104 °F (40 °C), and the minimum, in the Altai Mountains, is −76 °F (−60 °C). Rainfall, which occurs mainly in the summer, averages less than 16 inches (400 mm) per year in the north, 20 to 24 inches (500–600 mm) in the taiga zone, and 12 to 16 inches (300–400 mm) on the steppes. The western slopes of the Altai receive as much as 62 inches (1,575 mm) per year. Snow cover lasts for 240 to 270 days in the north and for 160 to 170 days in the south. It is deepest in the forest zone, where it ranges from 24 to 36 inches (60–90 cm), and in the mountains, where it averages 80 inches (200 cm) per year. It is much shallower on the tundra, ranging from 12 to 20 inches (30–50 cm), and very thin on the steppe, where 8 to 16 inches (20–40 cm) fall.
On the upper Ob the spring floods begin early in April, when the snow on the plains is melting; and they have a second phase, ensuing from the melting of snow on the Altai Mountains. The middle Ob, scarcely affected by the upper Ob’s phases, has one continuous spring-summer period of high water, which begins in mid April. For the lower Ob, high water begins in late April or early May. Levels, in fact, begin to rise when the watercourse is still obstructed by ice; and maximum levels, which occur by May on the upper Ob, may not be reached until June, July, or even August on the lower reaches. For the upper Ob, the spring floods end by July, but autumn rains bring high water again in September and October; in the middle and lower Ob, the spring and summer floodwaters gradually recede until freezing sets in. On the lower reaches, flooding may last four months. Flooding of the Ob proper and of the Irtysh obstructs the minor tributaries’ drainage.
Ice forms on the Ob from the end of October to the second week of November, after which the lower reaches begin to freeze solid. By the last week of November the entire river is frozen; the upper reaches remain frozen for some 150 days, the lower for 220. The thawing of the ice—which takes longer than the freezing—lasts from the end of April (upstream) to the end of May, and the spring drift (about five days in duration) produces considerable ice jams. The difference in level between high water and low is 25 feet (8 metres) at Novosibirsk on the upper Ob; it reaches 43 feet (13 metres) at Aleksandrovskoye on the middle Ob but decreases to no more than 20 feet (6 metres) at Salekhard near the mouth. The water is warmest in July, reaching a maximum of 82 °F (28 °C) in the vicinity of Barnaul.
The Ob has the third greatest discharge of Siberia’s rivers, after the Yenisey and the Lena. On average, it pours some 95 cubic miles (400 cubic km) of water annually into the Arctic Ocean—about 12 percent of that ocean’s total intake from drainage.
The volume of flow at Salekhard, just above the delta, is about 1,500,000 cubic feet (42,000 cubic metres) per second at its maximum and 70,000 cubic feet (2,000 cubic metres) per second at its minimum, while for Barnaul, on the upper Ob, the corresponding figures are 340,000 and 5,700 cubic feet (9,600 and 200 cubic metres) per second. The average annual discharge rate at the river’s mouth is about 448,500 cubic feet (12,700 cubic metres) per second. Most of the water comes from the melting of seasonal snow and from rainfall; much less of it comes from groundwater, mountain snow, and glaciers.
The waters of the Ob are only slightly mineralized: dissolved substances account for an annual outpouring of 30.2 million tons into the Kara Sea. The average amount of solid matter discharged annually by the Ob totals only about 50 million tons.

Plant and animal life

Rich meadows extend in bands 1 to 2 miles (2 to 3 km) wide for great distances along the banks of the Ob and cover many of the numerous islands. Pine, cedar, silver fir, aspen, and birch also grow on the banks and occasionally constitute isolated forests on the higher ground of the floodplain. Large areas near the river are covered with willow, snowball trees (Viburnum), bird cherry (Prunus padus), buckthorn (Hippophaë), currant bushes, and wild roses.
Of some 50 species of fish found in the river or in the gulf, the most valuable economically are several varieties of sturgeon and such “whitefish” as nelma (Stenodus leucichthys nelma), muksun (Coregonus muksun), tschirr (C. nasus), and peled (C. pelea); pike, burbot, Siberian dace, carp, and perch are also caught. The seasonal ice cover, however, causes depletion of oxygen in the water, killing many fish every winter in the reaches between the Tym confluence and the delta.
Fur-bearing mammals of the Ob valley include European and Siberian mole, Siberian and American mink, ermine, fox, wolf (in the taiga), elk, white hare, water rat, muskrat, otter, and beaver. Among more than 170 species of birds breeding in the floodplain are grouse, partridge, goose, and duck.

People

Politically, most of the Ob basin is within Russia, but its southern portion forms the northernmost part of Kazakhstan. Russians and other Slavs constitute the majority of the population, but there also are numerous non-Slavic peoples. These include the Kazakhs in the south, the Altay and Shor peoples of the mountains, the Tatars of the Irtysh basin, the Khanty (Ostyak) and the Mansi (Vogul)—whose autonomous district (Khanty-Mansi) occupies part of the taiga—and the Nenets, Nganasan, Enets, and Selkup peoples of the north. The valleys of the river are more densely populated than other parts of the basin.

Economy

The Ob, one of western Siberia’s principal means of transportation, is navigable for about 190 days of the year on its upper reaches and for 150 on its lower. Both imports and exports are shipped along the river. Most goods are transported to and from it along the northern sea route, which stretches across the Arctic. The Trans-Siberian Railway crosses the Irtysh at Omsk and the upper Ob at Novosibirsk. Railways to Kazakhstan from Novosibirsk and from the foothills of the mountains cross the upper Ob at Barnaul.
The Ob’s immense hydroelectric potential is estimated at some 250 billion kilowatts. Three main stations have been built: one on the Ob proper, at Novosibirsk, and the other two on the mountainous reaches of the Irtysh, at Bukhtarma and Öskemen.
Both industry and agriculture have been intensively developed in the Ob basin. Cities such as Omsk, Novosibirsk, and Barnaul are major industrial and manufacturing centres. The steppe zone, in the southern Ob basin, is the major producer of spring wheat in Russia. The west Siberian oil and gas fields, located in the taiga and tundra zones of the middle and lower Ob, are the most important in Russia, contributing about two-thirds of the country’s crude oil and natural gas output.

Study and exploration

Although paleo-Asiatic peoples have inhabited the Ob basin for millennia, Russian explorers and adventurers first penetrated the area only toward the end of the 16th century. During the reign of Ivan IV (the Terrible), the Cossack folk hero Yermak led an expedition into the Ob basin (1581–84/85) that claimed vast expanses for the tsar. Settlements and forts were established at Tyumen (1586), Tobolsk (1587), Obdorsk (now Salekhard; 1595), and Tomsk (1604). The lower Ob was explored in the first half of the 17th century, and a navigation chart of that section was published in 1667. Russian scientists investigated the lower Ob during the Great Northern Expedition (1733–42). For the next 150 years the river system was explored chiefly to foster the development of transportation. Detailed hydrologic observations and studies were initiated by the end of the 19th century and were pursued intensively during the 20th. During the 20th century Soviet scientists studied long-term climate change and the landscape evolution of this region and the adjacent Kara Sea.

 6. HUANG HE RIVER

Huang He, Wade-Giles romanization Huang Ho, also spelled Hwang Ho, English Yellow River , principal river of northern China, east-central and eastern Asia. The Huang He is often called the cradle of Chinese civilization. With a length of 3,395 miles (5,464 km), it is the country’s second longest river—surpassed only by the Yangtze River (Chang Jiang)—and its drainage basin is the third largest in China, with an area of some 290,000 square miles (750,000 square km).
The river rises in southern Qinghai province on the Plateau of Tibet and crosses six other provinces and two autonomous regions in its course to the Bo Hai (Gulf of Chihli), an embayment of the Yellow Sea of the North Pacific Ocean. In its lower reaches it is a shifting, turbulent, silt-laden stream that often overflows its banks and sends floodwaters across the North China Plain. For that reason, it has been given such names as “China’s Sorrow” and “The Ungovernable.” The Mandarin Chinese word huang (“yellow”) is a reference to the fine loess sediments that the river carries to the sea. The Huang He basin has an enormous population—exceeded by only a small number of countries—and the river and its tributaries flow past some of China’s oldest cities, including Lanzhou, Baotou, Xi’an (Sian), Taiyuan, Luoyang, Zhengzhou, Kaifeng, and Jinan.

Physical features

The Huang He is divided into three distinct parts: the mountainous upper course, the middle course across a plateau, and the lower course across a low plain.

The upper course

The Huang He originates at an elevation above 15,000 feet (4,600 metres) in the Bayan Har Mountains, in the eastern Plateau of Tibet. In its upper reaches the river crosses two large bodies of water, Lakes Ngoring and Gyaring. Those shallow lakes, each covering an area of about 400 square miles (1,000 square km), are rich in fish and freeze over in winter. The Huang He in that region flows generally from west to east. The broad highlands of the upper course rise 1,000 to 1,700 feet (300 to 500 metres) above the river and its tributaries. The highlands consist of crystalline rocks that are sometimes visible as eroded outcroppings on the surface. The river enters a region of deep gorges, winding its way first southeast, then northwest around the A’nyêmaqên (Amne Machin) Mountains, where its fall exceeds 10 feet per mile (2 metres per km), and then east again between the Xiqing and Laji mountains.
Past the gorges, near the city of Lanzhou in southeastern Gansu province, it leaves the Plateau of Tibet. That transition marks the end of the upper Huang He, which is some 725 miles (1,165 km) from its source. The upper course drains a basin covering about 48,000 square miles (124,000 square km), consisting chiefly of inaccessible, highly mountainous, sparsely populated terrain with a cold climate.

The middle course

The middle course of the Huang He, extending more than 1,800 miles (2,900 km), consists of a great loop and drains an area of about 23,000 square miles (60,000 square km). The river at first flows northeast for about 550 miles (880 km) through the sandy soils of the northern Hui Autonomous Region of Ningxia and of the western Ordos Plateau. It has many rapids there, and in a number of places it narrows. The river then turns eastward and flows for another 500 miles (800 km) through alluvial plains in the Inner Mongolia Autonomous Region, in places branching into numerous distributary channels. In that stretch its fall is less than half a foot per mile (9 cm per km), and many of the channels have been developed over the millennia for irrigated agriculture.
The Huang He then turns sharply to the south and flows for about 445 miles (715 km), forming the border between Shaanxi and Shanxi provinces. The river’s width usually does not exceed 150 to 200 feet (45 to 60 metres) in that section, as it cuts through narrow gorges with steep slopes several hundred feet (above 100 metres) in height. The river then gradually widens, notably after receiving the waters of its two longest tributaries—first the Fen River of Shanxi province and then the Wei River of Shaanxi. At the confluence with the Wei, the Huang He turns sharply to the east for another 300 miles (480 km) as it flows through inaccessible gorges between the Zhongtiao and eastern Qin (Tsinling) mountains. The average fall in that stretch is slightly more than 1 foot per mile (20 cm per km) and becomes increasingly rapid in the last 100 miles (160 km) before the river reaches the North China Plain at the city of Zhengzhou in Henan province.
Most of the middle course is cut through the Loess Plateau, which extends eastward from the Plateau of Tibet to the North China Plain at elevations ranging between 3,000 and 7,000 feet (900 and 2,100 metres). The plateau contains terraced slopes as well as alluvial plains and a scattering of peaks sometimes rising more than 1,500 feet (450 metres) above the plateau. The river has cut at least six terraces across the plateau, which rise to more than 1,600 feet (500 metres) above the present river level. The terraces, formed over the past 2.5 million years, provide an important record of landscape evolution and ancient environmental change in the region. The underlying rock systems are covered with thick layers of loose soils, consisting mainly of wind-deposited sand and loess. The loess strata reach thicknesses of 160 to 200 feet (50 to 60 metres) and in some places as much as 500 feet (150 metres). Through those loose deposits the river has cut deep valleys, carrying away with it huge quantities of surface material, making that region one of the most highly eroded landscapes in the world. The easily eroded loess soil accounts for the instability of the riverbed both in the middle basin, where the erosion is considerable, and on the plain, where deposition builds up the channel bed.

The lower course

Downstream from Zhengzhou the Huang He broadens out to flow through Henan and Shandong provinces across the North China Plain. The plain is a great, nearly featureless alluvial fan broken only by the low hills of central Shandong; it was formed over some 25 million years as the Huang He and other rivers deposited enormous quantities of silt, sand, and gravel into the shallow sea that once covered the region. The plain has been densely inhabited for millennia and long has been one of China’s principal agricultural regions. The river has changed its course across the plain several times, and the region’s inhabitants have built extensive systems of levees and irrigation works in an attempt to control the river’s flow. The area illustrates perhaps better than any other place on Earth how human activity has combined with natural forces to shape the landscape.
The lower Huang He is about 435 miles (700 km) long with an average fall of about 3 inches per mile (5 cm per km). Along the river are found occasional areas of sand dunes 15 to 30 feet (5 to 9 metres) high. In general, however, the plain is an area of great floods because the riverbed, built up gradually by sediment deposits, lies above the surrounding land in many places. In the section north of the city of Kaifeng in northern Henan, the low-water level is some 15 feet (5 metres) above the surrounding countryside, the mid-water level between 19 and 23 feet (6 and 7 metres), and the high-water level sometimes as much as 30 to 35 feet (9 to 11 metres) above the land. From Kaifeng to the Grand Canal (Da Yunhe), the levees are lower than farther upstream, rarely exceeding 3 to 6 feet (1 to 2 metres) in height. Marshes are common. Below the Grand Canal the height of the levees increases to between 13 and 16 feet (4 and 5 metres) and in some places to 25 feet (8 metres).
The delta of the Huang He begins approximately 50 miles (80 km) from its mouth and spreads out over an area of about 2,100 square miles (5,400 square km). The delta land is marshy, composed of mud and silt, and is covered with reeds. A sandbar at the river’s mouth impedes navigation at low tide by boats drawing more than 4 feet (1.2 metres) of water; at high tide the depth on the bar is 8 or 9 feet (2.4 or 2.7 metres).
Until the late 20th century the Huang He delta was one of the most actively growing deltas in the world, as the North China Plain continued to extend farther into the Bo Hai (the remnant of the ancient sea now covered by the plain). In the century from 1870 to 1970 the delta grew an average of more than 12 miles (19 km). Some outlying parts expanded even more rapidly: one area grew 6 miles (10 km) during the period 1949–51, and another grew more than 15 miles (24 km) in 1949–52. However, beginning in the 1950s, dam construction upstream—notably the Sanmen Gorge installation in Henan province—began to reduce the silt load that the river could carry to its mouth. By the 1990s the delta was continuing to expand seaward, but it was also eroding. The Chinese government subsequently took measures to divert the final part of the main stream, so that deposits built up on the north side of the delta.

Hydrology

The lower Huang He has changed course radically throughout its geologic history. The river’s decreased gradient and velocity on the plain cause its suspended load of silt to settle. As the riverbed builds up, the stream shifts course to occupy a lower level. In the past four millennia the river has entered the Yellow Sea at points as much as 500 miles (800 km) apart. From the 3rd millennium bce to 602 bce, when it occupied its northernmost course, it flowed near the present-day city of Tianjin and entered the nearby Bo Hai. From 602 bce to 70 ce both the river and its mouth shifted to a point on the Yellow Sea south of the Shandong Peninsula. From 70 to 1048 the Huang He again shifted to the north, taking up a course near its present bed.
From 1048 to 1194 changes in the course of the river occurred farther inland, where the river enters the North China Plain. In 1194 the river occupied a course running to the southern edge of the delta. In that year, after protecting dikes had been ruptured, a second arm of the Huang He began flowing south of the Shandong Peninsula. From 1289 to 1324 the river took over the bed of the Guo River and a large part of the Huai River, entering the Yellow Sea well to the south of Shandong. It was stable for more than 500 years, until the 1850s, when it again shifted to the north of the Shandong Peninsula, finally settling into its present course.
As the Chinese developed agriculture on the plain, they became more adept at building levees to stabilize the channel and thereby protect the inhabitants against the floods brought by shifts in the channel. Tens of thousands of miles of levees have been constructed through the centuries. The overall effect of those structures has been to delay flooding, but, because the riverbed has been elevated and confined artificially, levee breaching and channel shifts have become more dramatic and destructive than they otherwise would have been. The few hydraulic engineers who succeeded in decreasing rather than increasing the flood hazard have gained legendary status in Chinese history.
Breaks in the levees have been more frequent than course changes throughout history. Such events have triggered cataclysmic floods, notably during the 18th and 20th centuries. Between 960 and 1048 there were 38 major breaks, and 29 more were recorded from 1048 to 1194. In later years such breaches were less frequent as a result of systematic improvements to the levee system. The slackening of those efforts during the Taiping Rebellion (1850–64) led to the major change in the course of the river that occurred from 1852 to 1854. In 1887 the Huang He burst the levees near Kaifeng and began to flow into the Huai River, but engineering efforts succeeded in returning it to its former course in 1889. The flood of 1887 covered thousands of square miles, completely burying many villages under silt. In 1889 another flood destroyed 1,500 villages. The next major flood, in 1921, wiped out hundreds of populated places, mainly near the river’s mouth. In the flood of 1933 more than 3,000 populated places were submerged and 18,000 people killed. Other floods occurred in 1938—when the levees were purposely broken near Zhengzhou to delay the advance of Japanese troops—and in 1949.
The Huang He carries an average annual volume of about 13.4 cubic miles (56 cubic km) of water down to the sea, a rate of about 62,500 cubic feet (1,770 cubic metres) per second. The rate can be as much as 78,000 cubic feet (2,200 cubic metres) per second in high-volume years and as little as 22,000–28,000 cubic feet (600–800 cubic metres) per second in low-volume years. There also is considerable seasonal variation in its volume. The river has a low discharge rate—eight other Chinese rivers exceed that of the Huang He—because its basin encompasses large areas of arid or semiarid land, where considerable quantities of water evaporate or are diverted for irrigation. More than half of the basin’s annual precipitation falls during the rainy season (July to October). The average annual precipitation for the entire basin is about 18.5 inches (470 mm), but its distribution is highly uneven. In some years the bulk of the river’s volume comes from its tributaries. In the upstream areas the main source is snowfall in the mountains, with the high-water level occurring in the spring. The highest water levels in the middle and lower parts of the river occur in July and August. Seasonal maximum flows can be considerable: 188,900 to 216,200 cubic feet (5,350 to 6,120 cubic metres) per second near Lanzhou, 350,000 cubic feet (10,000 cubic metres) near Longmen, and 1,270,000 cubic feet (36,000 cubic metres; recorded in 1943) in the lower parts of the river.
The Huang He carries along the highest concentration of sediment load of any river in the world, amounting to about 57 pounds of silt per cubic yard (34 kg per cubic metre) of water, as compared with 2 pounds (1 kg) for the Nile River, 9 pounds (5 kg) for the Amu Darya (the ancient Oxus River), and 22 pounds (13 kg) for the Colorado River. Floodwaters may contain up to 1,200 pounds of silt per cubic yard (710 kg per cubic metre) of water (70 percent by volume). The river, unimpeded, carried down to the sea about 1.52 billion tons of silt per year, a large part of it loess, which was loose and easily washed away. Other factors contributing to the high volume of silt included the steepness of the slopes, the rapidity of the current, and a lack of forested areas to check erosion. The reservoirs created by dams have allowed increasing quantities of silt to settle out.
The Huang He freezes over in parts of its middle section for several months each winter. On the North China Plain near Kaifeng there are 15 to 20 icebound days per year, but farther downstream there are none at all. Ice jams are broken up with the help of aerial bombardment or sometimes by artillery shelling.
Igor Vladimirovich PopovCharles E. GreerThe Editors of Encyclopædia Britannica

Plant and animal life

The floral and faunal communities of the Huang He basin vary widely, depending on location. Vegetation in the high upper-course region is sparse and tundralike, with some grassland areas at lower elevations suitable for grazing livestock. Likewise, the harsh dry climate and shifting sands of the Ordos Plateau section of the river basin support little plant life other than drought-resistant grasses and shrubs. There are only remnants of the original forest cover in the river’s lower basin, although higher elevations, such as on the Shandong Peninsula, still have stands of oaks and other hardwoods along with conifers, notably Japanese red pines (Pinus densiflora). Generally, however, the bulk of arable land in the Huang He basin has been given over to agriculture, notably wheat farming.
Wildlife is likewise limited by both natural conditions and the intense human occupation of the land. There are small populations of various ungulates in the higher reaches of the river, including rare species such as the chiru (Tibetan antelope) and wild yak, as well as populations of Chinese forest musk deer (Moschus berezovskii) and sikas lower in the basin. Aquatic species in the river include the Chinese paddlefish (Psephurus gladius) and the Yellow River scaleless carp (Gymnocypris eckloni). Low-lying wetlands, especially in the delta area, are important stopover points for migrating waterfowl and other bird species, including scaly-sided (Chinese) mergansers (Mergus squamatus) and rare red-crowned cranes (Grus japonensis)—both species endangered, particularly by loss of habitat.
The Editors of Encyclopædia Britannica

Economic development

Water resources in the Huang He basin have been managed by irrigation and flood-control works of significant size since the 3rd century bce. Modern hydraulic engineering techniques have been applied since the 1920s, while basinwide multipurpose development efforts have been under way since the mid-1950s. The major accomplishments of that program have included giant hydroelectric dams at the Liujia Gorge and other gorges near Lanzhou and major irrigation projects—some with smaller hydroelectric stations—at several locations farther downstream. On the plain, levees have been strengthened and the flood-control system rationalized and integrated with reservoirs and with the Grand Canal (which crosses the Huang He in western Shandong province). Erosion-control measures on the Loess Plateau have reduced the silt load carried downstream. The key project has been the huge dam at the Sanmen Gorge upstream of Luoyang and the reservoir impounded behind it. The project has augmented flood control on the plain and has also provided water for irrigation and hydroelectric power generation, although silt deposition in the reservoir has reduced its functional capabilities.
As modern economic development has increased throughout the basin, however, pollution from industrial sources and agricultural runoff has also increased. In addition, the greater demand for limited water resources has caused shortages, which have been severe at times and have included instances when river water did not flow to the Bo Hai.

Study and exploration

The Huang He and its floods have been central to the legend, folklore, and written history of Chinese civilization for more than three millennia. Regular records of major floods and of changes in the river’s course have been kept since the 6th century bce, and water levels have been studied since 1736. The first European to explore the upper reaches of the Huang He was a Russian traveler, Nikolay Mikhaylovich Przhevalsky, in 1879 and 1884. Systematic study of the river basin was first undertaken in the 1950s by Chinese and Soviet scientists. That work subsequently was carried on by Chinese scientists in cooperation with specialists from numerous other countries.

7.YENISEI  RIVER

Yenisei River

2007 Schools Wikipedia Selection. Related subjects: Geography of Asia

Yenisei River
The Yenisei basin, including Lake Baikal
Origin	Mongolia
Mouth	Arctic Ocean
Basin countries	Russia
Length	5,550 km (3,449 mi)
Avg. discharge	19,600 m³/s (692,272 ft³/s)
Basin area	2,580,000 km² (996,138 mi²)

The Yenisei (Енисе́й) is the greatest river system flowing to the Arctic Ocean, and the fifth longest river in the world. It is slightly shorter but with 1.5 times the flow of the Mississippi-Missouri. Rising in Mongolia, it follows a northerly course to the Kara Sea, draining a large part of central Siberia, the longest stream following the Yenisei-Angara-Selenga-Ider being about 5500 km. Its watershed, which includes the world's largest (by volume) lake, Lake Baikal, holds more water than any other river system.
The upper reaches, subject to rapids and flooding, pass through sparsely populated areas. The middle section is controlled by a series of massive hydroelectric dams fuelling significant Russian primary industry. Partly built by gulag labor in Soviet times, industrial contamination remains a serious problem in an area hard to police. Moving on through sparsely-populated taiga, the Yenisei swells with numerous tributaries and finally reaches the Kara Sea in desolate tundra where it is icebound for more than half the year. As with other Siberian rivers, the flow has increased recently, believed to be related to global warming. A concern is that altered salinity in the Arctic may have a global impact on ocean currents.

Upper Yenisei

The Yenisei rises in two major headstreams: the Bolshoi (greater) Yenisei also known as the Bii-Khem (Бии-Хем) rises in the Tuva region on the S flank of the Eastern Sayan Mountains and north of the Tannu-Ola Mountains at 52°20′N 97°30′E; the Malyy (lesser) Yenisei also known as the Kaa-Khem (Каа-Хем) rises in the Darhat ( rift) valley in Mongolia. Recent research has shown that the narrow exit to the Darhat Valley has regularly been blocked by ice producing a lake as large as neighbouring Lake Khuvsgul. When the glaciers retreated (the last time 9300 years BP) as much as 500 km³ of water would have escaped, possibly catastrophically.
These two headstreams flow west converging at Kyzyl, and on meeting the east-flowing Khemchik River head north through a canyon in the Western Sayan mountains. The Yenisei emerges from the mountains onto an area of steppe where its first control is the 30m dam at Mayna. This section is around 700 km.

Lake Baikal Headwaters

The 320 km (partly navigable) Upper Angara feeds into the northern end of Lake Baikal from the Buryat Republic but the largest inflow is from the Selenga which forms a delta on the south-eastern side. The longest tributaries rise on the eastern slopes of central Mongolia's Khangay mountains. Another tributary, the Tuul passes through the Mongolian capital, Ulaanbaatar while the Egiin drains Lake Khuvsgul.

This satellite image is 800 km across. The green area towards the top-left, containing several small lakes and bordered by the snow-capped Eastern Sayan Mountains to the north, is the source of the Bolshoi Yenisei in Tuva. The dry Darhat Valley just west of Lake Khuvsgul in the centre of the image is the source of the Malyy Yenisei. These two streams can be followed to their confluence at Kyzyl at the left of the image. Lake Baikal is at the right of the image and the Angara flowing north from Irkutsk can clearly be made out. It is already widening due to the dam at Bratsk 200 km further north. The Selenga, whose headwaters include Lake Khuvsgul, flows into Lake Baikal in a delta at the extreme edge of the image. The Lena River has its source in the top right of the image.

Just downstream from Mayna, the 242m Sayano-Shushenskaya dam at Sayansk powers Russia's largest hydroelectric plant completed in 1989 and producing 6400 MW for aluminium production. This is the same height and five times the power of the Hoover Dam. About 100 km downstream the Yenisei is swollen by the Abakan river and passes Abakan, capital of the Khakassia region, on the west bank and Minusinsk on the east bank. It passes within 10 km of the Chulym, a tributary of the Ob before reaching Krasnoyarsk after 300 km. This halt on the Trans-Siberian railway is the Yenisei's largest city. Krasnoyarsk is a major port. Not far away from Krasnoyarsk is Krasnoyarsk hydroelectric dam.
The closed city of Zheleznogorsk, 70km downstream, is a secret Soviet nuclear weapons and satellite facility missing from most maps. The exact state of the enormous nuclear waste dump is unclear, but some discharges continue to pollute the Yenisei. A further 200 km downstream comes the confluence with the Angara (whose final section is also known as the Upper [Verkhnyaya] Tunguska).

Angara River

The Angara (Ангара́) river drains Lake Baikal and runs 1840 km from the regional capital Irkutsk to converge with the Yenisei at Strelka ( 58.101° N 92.998° E). It is dammed in four places to power local industry. The 44m dam at Irkutsk produces 650 MW. Bratsk lies 500 km downstream, where the 124 m dam built in the 1960s produces 4500 MW. The resultant reservoir is nicknamed Dragon Lake because of its outline. The tributary Oka and Iya rivers, which rise on the north slopes of the Eastern Sayan Mountains, form the 'jaws' and 400 km of the Angara form the 'tail'. There are newer dams almost as large at Ust-Ilimsk 250 km downstream (also damming the tributary Ilim river) and Boguchany a further 400 km downstream (not operational). Further dams are planned but the environmental consequences of completely taming the Angara are leading to protests which may prevent funding.
Angarsk, the centre of the expanding Eastern Siberian oil industry and site of a huge Yukos-owned refinery, lies 50 km downstream of Irkutsk. A major pipeline takes oil west, and a new one is being built to carry oil east for supply to Japan from the Sea of Japan port of Nakhodka. The exact potential of Eastern Siberia is unknown, but two new major fields are the Kovyktinskoye field near Zhigalovo 200 km north of Irkutsk and the extremely remote Verkhnechonskoye field 500 km north of Irkutsk on the Central Siberian Plateau.

Yenisei River - As seen from the trans-Siberian railway near Krasnoyarsk

Lower Yenisei

The Great Kaz joins the Yenisei 300 km downstream of the Strelka. It is noteworthy for its connection to the Ob via Ob-Yenisei canal and Ket River. The river starts to widen, its bed being littered with islands as numerous rivers augment its flow, in particular 1800 km Stony (Podkamennaya) Tunguska, and the 3000 km Lower (Nizhnyaya) Tunguska at Turukhansk draining the desolate central Siberian Plateau from the east. The remote Tunguska (Тунгуска) region is most famous for the 1908 meteorite impact, but is now being explored for oil. Beyond Turukhansk, the river enters tundra.
The river is icebound for more than half the year, and if unchecked ice could dam the river causing major flooding. Explosives are used to keep the water flowing. The final town is Dudinka which is connected to Krasnoyarsk by regular passenger boat. The river widens to a 50 km estuary for its final 250 km and the shipping lanes are kept open by icebreaker.
During the ice age, the route to the arctic was blocked by ice. Though the exact details are unclear, the Yenisei is believed to have flowed into a huge lake filling much of western Siberia, eventually flowing into the Black Sea. (See West Siberian Glacial Lake of the early Weichselian Glaciation)

Navigation

The first team to navigate the Yenisei's entire length, including its violent upper tributary in Mongolia, was an Australian-Canadian effort completed in September 2001. Ben Kozel, Tim Cope, Colin Angus and Remy Quinter were on this team. Both Kozel and Angus wrote books detailing this expedition, and a documentary was produced for National Geographic Television.

History

Ancient nomatic tribes such as the Ket people and the Yugh people lived along its banks. The Ket, numbering about 1000, are the only survivors today of those who originally lived throughout central southern Siberia near the river banks. Their extinct relatives included the Kotts, Assans, Arins, Baikots, and Pumpokols who lived further upriver to the south. The modern Ket lived in the eastern middle areas of the river before being assimilated politically into the Russia or Siberia during the 17th through 19th centuries.

8. Paraná River

The Paraná River in south central South America, runs through Brazil, Paraguay and Argentina over a course of some 2,570 kilometers. It is second in size only to the Amazon River among South American rivers.
The Paraná along with its tributaries creates a massive watershed that spreads throughout much of the south central part of the continent, essentially encompassing all of Paraguay, much of southern Brazil, northern Argentina, and even reaching into Bolivia.
The Parana River delta is a huge forested marshland about 32 kilometres  northeast of Buenos Aires, Argentina.
Much of the length of the Paraná is navigable and is used as an important waterway linking inland cities in Argentina and Paraguay to the ocean, providing deep water ports in many of these cities.
The construction of massive hydroelectric dams along the river's length has blocked its use as a shipping corridor to cities further upstream, but the economic impact of those dams is considered to offset this.
Current threats
some fish species (such as the surubí and the sábalo) are commercially important and exploited for massive internal consumption or for export.
More than 90 percent of the energy used by Brazil comes from hydropower, the greater part of which is generated by dams on the Paraná River and its tributaries.¹
The Itaipu Dam, on the Paraná River, is the largest in the world and flooded approximately 100,000 ha of land, and destroyed significant aquatic habitat including the Guaíra Falls.

9. Irtysh River

Irtysh River, Kazakh Ertis, Chinese (Pinyin) Ertix He or (Wade-Giles romanization) O-erh-ch’i-ssu Ho, major river of west-central and western Asia. With a length of 2,640 miles (4,248 km), it is one of the continent’s longest rivers. The Irtysh and the Ob River, of which the Irtysh is the principal tributary, together constitute the world’s seventh longest river system.
The Irtysh rises from the glaciers on the southwestern slopes of the Altai Mountains in the Uygur Autonomous Region of Xinjiang in far northwestern China. It flows west across the Chinese border through Lake Zaysan (Zhaysang) and then ... (100 of 273 words)

10. AFRICA FACTS

Congo River

Congo River Facts

On this page we list interesting facts about Africa's Congo River. This information, written for kids and adults, includes how long it is, where in Africa it is located, and when the first European explorer saw the river. Out of all the amazing Africa landforms, lakes, and rivers, the Congo River stands out as one of the most important to the people of Africa. To understand this river's importance, consider the first list of facts listed below.

Congo River's Importance to Africa

• The Congo River is the main transportation source in Central Africa. The river along with all the streams that lead into it provide over nine thousand miles (14,500 kilometers) of navigable shipping routes in Central Africa. A tremendous amount of goods are transported on the river every day.
• The Congo River is an extremely powerful river; in fact it is the most powerful river in Africa. On average one million four hundred thousand cubic feet of water (41,000 cubic meters) flows into the Atlantic Ocean every second from the river. There are approximately forty hydropower plants along the river that utilize this power to provide energy for the African continent.

Interesting Congo River Facts

• It is the second longest river in Africa (the Nile is the longest).
• It is the ninth longest river in the world.
• The Congo River is the deepest river in the world. It reaches depths of over 750 feet (230 meters).
• The river gets its name from the ancient Kongo Kingdom which existed near the mouth of the river.
• The river runs through the Congo rainforest which is the second largest rain forest in the world.
• It is also called the Zaire River.
• The rivers sources are in the mountains and highlands of the East African Rift, as well as Lake Tanganyika and Lake Mweru.
• The Congo River is so powerful that if has the potential to supply all of sub-Saharan Africa's electricity needs.
• In 1482 Diego Cao was the first European known to sight and enter the Congo River.
• The main tributaries are the Ubangi, Sangha, and Kasai.
• There are more than 4,000 islands in the river; over fifty are at least ten miles long.
• The river crosses the equator twice.
• The river discharges a volume of water that is second only to the Amazon River.
• Numerous cataracts (large or high waterfalls), dangerous rapids, and numerous islands make navigation difficult or impossible in certain areas of the river.
• Two countries are named after the river, they are The Democratic Republic of the Congo and the Republic of the Congo.
• The amount of water flowing out of the river is fairly constant year round due to the fact that some part of the river is always in a rainy season.
• Approximately seven hundred fish species have been recorded living in the Congo River. The total is probably much larger.
• The Congo River formed approximately 1.5 - 2 million years ago during the Pleistocene period.