Why are there white Nile and blue Nile in the Nile?

Located in the northeast of Africa, the Nile is an international river. Originated in the highlands of Burundi in East Africa south of the equator, the mainstream flows through Burundi, Rwanda, Tanzania, Uganda, Sudan and Egypt, and finally flows into the Mediterranean Sea. The tributaries also flow through Kenya, Ethiopia, parts of the Democratic Republic of the Congo, Eritrea and other countries. With a total length of 6,670 kilometers, the main stream is the longest river in the world from the source of the Kagala River to the estuary. The basin covers an area of about 2.87 million square kilometers, accounting for more than one ninth of the African continent. The average annual runoff of the estuary is 8 1 100 million m3.

The word "Nile" first appeared more than 2000 years ago. There are two theories about its origin: one comes from the Latin "Nile", which means "impossible". Because the middle and lower reaches of the Nile have been inhabited for a long time, but because of the barrier of waterfalls, people in the middle and lower reaches think that they can't understand the source of this river, so they named it the Nile. The second is that the word "nilus" evolved from the name of the ancient Egyptian Pharaoh (king) Nyroos.

The Nile is formed by the confluence of three rivers: kagera river, White Nile and Blue Nile. The valley delta in the lower Nile is one of the earliest cradles of human civilization, where ancient Egypt was born. Up to now, 96% of Egypt's population and most of its agricultural production are concentrated here. Therefore, the Nile is regarded as the lifeline of Egypt. For thousands of years, the Nile River has flooded regularly from June to 10 every year. When the river reached its highest level in August, it flooded large fields on both sides of the river bank, and then people moved to high places to stay temporarily. After 10, the flood subsided, bringing fertile soil to the Nile. On these fertile land, people planted cotton, wheat, rice and jujube crops. A "green corridor" has been formed in the arid desert area. Egypt, an ancient civilization with a history of 5,000 years, has created splendid Egyptian culture here. Today, more than 90% of Egypt's population is distributed in the plains and deltas along the Nile. Egyptians call the Nile the mother of their lives.

The upper reaches of the Mueller River in Soltani are 1730km long, which are called kagera river, Victoria Nile and Albert Nile respectively from top to bottom. From Nimulai to Khartoum, the middle reaches of the Nile River are 65,438+930 km long, which is called the White Nile, among which Malakal is also called the Jebel River, and the largest tributary, the Blue Nile (B65,438+0 UC Nile), flows into the lower reaches of Khartoum. The White Nile meets the Blue Nile, which is called the Nile and belongs to the lower reaches, with a length of about 3000km. The Nile River crosses the Sahara desert and enters the estuary delta north of Cairo, where it divides into two tributaries and flows into the Mediterranean Sea.

Nile and ancient Egyptian culture

In order to irrigate all the year round, people built several dams on the Nile in the19th century. Aswan Dam was built in 1902, from 1959 to 1970, which took 1 1 year and cost 1 billion dollars, and the world-famous Aswan High Dam was built. Aswan Dam controls the annual flood of the Nile, protects residents and crops, and provides a lot of electricity. Aswan Dam is located near Aswan, Egypt. This is a rockfill dam. The dam height is11m, the crest length is 3830m, and the volume is 44.3 million cubic meters. The capacity of the formed reservoir (Nasser Reservoir) is16.89 million cubic meters. After the completion of the reservoir, the irrigation area will be increased by more than 320,000 hectares, and the flooded area of 280,000 hectares will be transformed into perennial irrigation areas. Egypt and Sudan agreed to distribute Nile water between the two countries (totaling about 74 billion cubic meters per year), of which 55.5 billion belongs to Egypt. In order to build the reservoir, the ancient temple of Abu Simbo was moved, and the population moved by 6,543,800+0.4 million. A new agricultural area has been formed. High dams have brought great benefits to Egypt. For the first time in history, human beings have controlled the annual flood of Nile water, irrigated tens of millions of acres of farmland, and improved the navigation capacity of the upstream and downstream. The power generation is as high as 2 1mw, and the water depth of the reservoir is 90 meters, with an average width of 22 kilometers. The development of aquaculture in the reservoir area can make up for the adverse impact of the dam on the fishing areas along the Mediterranean coast. However, the dam has also had a negative impact, mainly because the fertility of farmland on both sides of the Nile has gradually decreased, resulting in reduced crop production, because fertile silt remains in the reservoir. At present, Egypt uses 6,543,800 tons of chemical fertilizer every year, which is still not enough to replace the 40 million tons of river mud brought by river water every year. The Nile valley is one of the cradles of world civilization. People in this area have created splendid culture and made outstanding contributions in the long history of scientific development. The outstanding representative is ancient Egypt.

When it comes to the cultural heritage of ancient Egypt, people will first think of the pyramids standing on the banks of the Nile, the rich papyrus in the Nile, ancient ships sailing on the Nile and mysterious mummies. They marked the height of science and technology in ancient Egypt, and also recorded and carried forward the development of civilization for thousands of years.

Papyrus is a reed-like plant, which is abundant in the Nile Delta. The stem is triangular, about five meters high and six to eight centimeters in diameter near the root. When in use, the papyrus stems are peeled, cut into long strips along the growth direction with a knife, placed horizontally and vertically, and struck with a mallet to make the juice of the papyrus ooze. After drying, these strips are permanently glued together, and finally polished with pumice, which can be used. It became the most advanced writing carrier at that time-papyrus paper, which was more than 1000 years earlier than that of China and Cai Lun, and became an important document for later scholars to study ancient Egyptian civilization. However, because papyrus paper is not suitable for folding and cannot be made into books, it is necessary to stick many papyrus pieces into long strips and roll them into scrolls after writing.

An ancient ship unearthed in Egypt about 4700 BC, nearly 50 meters long and fully equipped, shows the original navigation technology and scale. Lighter boats are made of reeds. Don't underestimate this reed boat. The reed boat imitated by modern people has proved that this kind of boat can cross the Atlantic. These undoubtedly played a vital role in the social prosperity and civilization of ancient Egypt towards the world.

The Nile also gave the local people unparalleled artistic imagination. What a rough and magnificent temple is located in the arid land of East Africa, in stark contrast to the winding Nile next to it. Many works of art in ancient Egypt are both masculine and feminine.

According to legend, the goddess Izz and her husband loved each other. One day, her husband was killed. Izz was heartbroken and tears poured down the Nile, causing the river to surge and flood. Every June 17 or 18, Egyptians hold a grand celebration for this, which is called "the night of tears". From this fairy tale, we can easily see people's deep feelings for the Nile.

Water system composition

Nile is a very old river, which existed in Eocene about 65 million years ago. The river course has been changed many times, but it always flows north. In the Pleistocene, there used to be a big lake between Juba and Khartoum, which was supplemented by the existing blue and white Nile. Later, the lake rose above the edge of the basin, passed through the canyon north of Khartoum, and flowed northward into the Mediterranean along the ancient Nile, so the current Nile water system appeared.

The Nile River originates from the Ruwuwu River in Burundi and flows into the Nyavangu River in Nigeria, which is called kagera river. It flows through the border areas of Rwanda, Tanzania and Uganda and flows into Lake Victoria. After flowing out from the northern end of Lake Victoria, it is called Victoria Nile, which flows into the Nile basin water system and the schematic diagram of the dams built in Uganda, and soon flows into Lake Kioga. Then it flows westward into Lake Albert (Lake Mobutu), with a drop of 400 meters ... After leaving Lake Albert, it flows northward, named Albert Nile, which flows into the Pargur River from the right bank, passes through Nimule Canyon and enters the Sudan Plain. The river from Nimulai is called White Nile, and the section from Nimulai to Malakal is also called Jebel River. 900 kilometers below Juba flows through the Sude swamp. After leaving the swamp area, Sobat River was accepted from the right bank, and the river flow doubled. Since then, most of the river banks up to Khartoum are semi-desert areas. Nimulai to Kasmu is 930 kilometers long, with a drop of 80 meters ... In Khartoum, the Blue Nile flows into this river, and then this river is called the Nile. The flow from Khartoum to Aswan is about 65,438+850 km, with a drop of about 290m m m. The two banks are desert areas, and the atbara River is the main support. The flow from Aswan to Cairo is about 900km, and the drop is very small. The Nile River starts from 20 kilometers downstream of Cairo and enters the delta, covering an area of about 22,000 ~ 24,000km2. Branches and lakes are densely covered. The largest Han River is Dumat River and Lashide River, each of which is about 200 kilometers long.

The main tributaries of the Nile are A Qiu Wa River, Gazelle River, Sobat River, Blue Nile River and atbara river.

60% of all the water in the Nile comes from the Blue Nile, 32% from the White Nile and the remaining 8% from atbara river. But the flood season and dry season change greatly. During the flood, Blue Nile accounted for 68%, White Nile accounted for 10%, and atbara river accounted for 22%. In the dry season, the Nile water decreased to 65,438+07%, while the White Nile rose to 83%, while atbara river stopped flowing and no runoff flowed in. The size and change of the proportion of the above rivers in the Nile water volume are closely related to the precipitation and seasonal distribution characteristics of each basin.

White Nile River

The White Nile is the source of the Nile. We need to go all the way south, through the Gao Chuan Canyon and desert swamp, and all the way to Burundi in the East African Plateau. The upper reaches of the Nile River are kagera river, which originates in Burundi and flows downstream into Lake Victoria. The lake flows into Lake Keoha through Owen Falls, which is called Victoria Nile after leaving the lake, and then flows into Lake Abbott through Kabarega Falls. The lake flows from the northern end and is called Abbott Nile. Since Nimule, it has been named White Nile. Among the tributaries of the Nile, the White Nile and the Blue Nile are the best known. One is graceful and the other is unrestrained, and is often described as "lovers". The White Nile flows northward along the slope of the East African Plateau. The valley is deep and narrow with many steep beaches and waterfalls. From Bor to the north, the White Nile flows into the shallow swamp basin, with slow flow, and a large number of aquatic plants mainly papyrus grow in the river. After flowing out of the basin, the White Nile flows northward, and successively joins the Sobat River, the Blue Nile River and the atbara river, with no tributaries below.

Blue Nile

Blue Nile is the largest tributary of the Nile, with a total length of about 1700km and a drainage area of 325,000 km2. Originating in the Gojam Highland of the Ethiopian Plateau, it flows northward into Lake Tana, and is called Little Abayik.

The Blue Nile flows from the southern end of Lake Tana to the Sudanese border, which is called Abay River. Due to the blocking of lava, it bypasses Bilhan Peak (4 154m above sea level) to the south and turns to the northwest to enter Sudan. In the process of 860km, the riverbed descends 1320m, and the gradient 1:650. There are many waterfalls and rapids along the way, the most famous of which is Tisesat Waterfall. Located about 30 kilometers downstream of Bahadar on the south bank of Tana Lake, with a drop of 45.8 meters, and about 3 kilometers above the waterfall, there is Alafami Waterfall with a drop of about 6 meters ... The Abay River twists and turns in Ethiopia and accepts many tributaries along the way. These tributaries are mainly concentrated on the left bank, including Bashiro River, Jama River, Mugel River, Didesa River and Dabbous River, which have water all the year round. There are few and small rivers on the right bank, and the only tributary with water all the year round is the Burroughs River, with steep slope and rapid flow. Due to the rapid flow of water, the amount of water lost in this reach is not large.

Abai River flows into Sudan and is called Blue Nile. The flow from Khartoum is 740km, and the riverbed only drops 130m ... The Blue Nile deeply cuts into the clay plain, forming a series of meanders due to scouring and siltation, and the bank is several meters higher than the flood peak, so that the flood will not flood in the flood season, thus avoiding a lot of losses of the river. Sudan's blue Nile receiving plant originated from the Lahad River and Tindel River on the edge of Ethiopian plateau. Both rivers are seasonal rivers, which dry up in winter and rise rapidly in summer. In September, the flow of Tindal River is almost equal to that of White Nile (including Sobat River). The flow of the Rikhard River can also reach one third of that of the White Nile.

The average annual runoff of the Blue Nile is 52 billion m3, of which Tana Lake accounts for 6%, Abay River accounts for 90%, Tindal River accounts for 3% and Reinhard River accounts for 1%. Every year, July 7- 10/0 is the flood season, the flood peak appears at the end of S, and June is the dry season. The flow in flood season is 60 times that in dry season. According to hydrological data, the historical maximum discharge of this river is 10900m3/s, and the minimum discharge is only 50m3/s. ..

Because the Blue Nile originates from the Ethiopian Plateau, with distinct wet and dry seasons, abundant water and little loss along the way, its hydrological characteristics are completely opposite to those of the White Nile. These characteristics are: ① large runoff; ② The gap is large; (2) The seasonal variation and interannual variation of discharge are great.

kagera river

Kagera river, a river in eastern Africa. Originated in the southwest of Burundi, it is formed by the confluence of the Ruwuwu River and the Nyavalongu River. It flows through Tanzania, Rwanda and Uganda and flows into Lake Victoria, with a total length of 400 kilometers. Upstream flows through the mountains, with Rusumo Waterfall; The downstream water flow is stable and abundant and navigable. It is the oldest river that flows into Lake Victoria, and is generally regarded as the upstream source of the Nile.

Ghazal R.

Shuai Xile River system, which is composed of rivers and lakes (mostly seasonal rivers and lakes) such as Yei River, Jules River and Lor River, which originated in the southwest plateau of Sudan, flows into Jebel River from the left bank. The marshes in the Bahr el Ghazal Lake area cover an area of 40,000 square kilometers. Except the Jules River, all other tributaries have disappeared in the swamp, and the amount of water injected into the Nile is very small every year.

sobat river

The river flows northwest and joins the White Nile in the south of Malakal. It is a tributary of the right bank of the White Nile, which is formed by the confluence of the Barrow River and the Pibor River. From the source of the Barrow River, the total length is 730 kilometers and the drainage area is 250,000 square kilometers. June-65438+February is the rainy season every year, and the river flow is very large, and the maximum flow occurs in165438+1October. The average discharge of the estuary is 4 12m3/s, and the 300km from the estuary to Nasir can be navigable in rainy season.

atbara river

Atbara river is the last tributary of the Nile, which originates from Gondel area north of Lake Tana, with a total length of 1 120km. The main tributary is the Tekeze River, which originates from the northeast of the Ethiopian Plateau with latitude 12. , east longitude 39. Near 30', it flows into atbara river from Shuwok, Sudan, with a flow of about 864km and a riverbed gradient of 1: 800. After atbara river accepted the Tekeze River, it entered the Sudanese clay plain, and after about 500km, it merged into the Nile at Atbala, with a gradient of 1:4000.

Although atbara river, like the Blue Nile, originates from the Ethiopian Plateau, it lacks a natural reservoir like Lake Tana, so its hydrological characteristics are different from those of the Blue Nile: ① The average runoff for many years is 654.38+0.2 billion m3, which is one of the important tributaries of the Nile. ② It is a seasonal river, the riverbed dries up from June to May every year, and the flood season is concentrated in July to September, with the maximum discharge of 2037m3/s in August. The river rises and falls sharply, and the seasonal variation of flow is even greater than that of the Blue Nile. There is a lot of sediment in the river.

60% of all the water in the Nile comes from the Blue Nile, 32% from the White Nile and the remaining 8% from atbara river. But the flood season and dry season change greatly. During the flood, Blue Nile accounted for 68%, White Nile accounted for 10%, and atbara river accounted for 22%. In the dry season, the Nile water decreased to 65,438+07%, while the White Nile rose to 83%, while atbara river stopped flowing and no runoff flowed in. The size and change of the proportion of the above rivers in the Nile water volume are closely related to the precipitation and seasonal distribution characteristics of each basin.

Natural characteristics of river basin

topography

The Nile Valley starts from the East African Plateau in the south, reaches the Mediterranean coast in the north, borders the Ethiopian Plateau in the east, extends northwest along the Red Sea, borders the Congo Basin and Chad Basin in the west, and extends northward along the Mara Mountains, the Grand Gulef Plateau and the Libyan Desert. The latitude it spans ranges from 4 south latitude to 31north latitude, reaching 35. Tota.

The landform of the basin can be simply summarized as follows: the East African Plateau dominated by crystalline rocks and the Ethiopian Plateau dominated by lava are located in the south and southeast of the basin respectively; The whole Sudan is basically a huge tectonic basin slightly inclined from south to north, and the Nile runs through it. Below Khartoum, the east and west sides of the Nile are vast desert platforms.

Upstream section (1): The section from Heyuan to the exit of Lake Victoria has obvious mountain and river characteristics. From the exit of Victoria Lake to Nimulai, the river bed gradient reaches 1: 1200, and there is Kabarega Waterfall along the way. In addition to shallow lakes such as Victoria Lake and Jiaojia Lake, there are also fault lakes such as Mobutu Lake, Edward Lake and George Lake developed along the west branch of the rift.

(2) Middle Reach: The Nile River flows through the vast Sudan clay plain, with flat terrain and extremely gentle slope. The slope above Malakal is only 1: 13900, with dense swamps and overflowing river branches along the way. From Malakal to Khartoum, the river bed gradient is more gentle, only 1: 100000.

(3) Downstream section: The downstream section of the Nile can be subdivided into: ① the river valley section from Khartoum to Aswan, where the Nile flows down the river, with a gradient of 1: 6000. Due to the wide exposure of crystalline rocks and the alternation of soft and hard bed rocks, six famous waterfall groups have been formed; ② The section from Aswan to Cairo, crossing between the eastern and western deserts, has a wide and flat valley and a long and narrow floodplain along the coast with a slope of1; 13000; (3) At the estuary below Cairo, the river branches about 20km below Cairo and flows into the Mediterranean Sea, forming a huge Nile Delta with an area of 24,000km2. The average thickness of alluvial soil layer is above 18m, the surface is flat, the river network is vertical and horizontal, the rivers are densely covered, and there are many lagoons and sandbars along the coast.

Climate and hydrology

The Nile valley spans 35 latitude, and the climate between north and south is very different, showing obvious latitude zonality. At the same time, non-zonal factors (mainly topography) also affect the distribution of climatic zones to some extent.

The Ethiopian Plateau is located in the southeast of the basin. Due to the uplift of the terrain, it has a vertical climate zone with distinct wet and dry seasons. In summer, there is a low pressure area over North Africa and Arabian Peninsula. The southeast trade winds blowing from the South Indian Ocean cross the equator and turn into southwest winds, which merge with the hot and humid airflow from the Gulf of Guinea to form a strong southwest airflow and rise along the windward slope of the plateau, forming a "rainstorm period" from July to September. In winter, the dry northeast wind from the southwest Asian continent prevails in the plateau, forming a dry season from 10 to February of the following year. From March to April, Sudan was located in the center of low pressure, which attracted humid air from the Indian Ocean and formed a "light rain period" before the "heavy rain period" in most parts of the plateau. The plateau, with an average annual rainfall of 65,438+0,000-2,000 mm, is the most important rainfall center in the Nile Valley.

65438+1920s to early 20th century

The characteristic of this period is to continue to flood irrigation, at the same time, to build sluice backwater, to draw low water for irrigation and to improve the multiple cropping index of farmland.

Perennial irrigation began in the 1920s 1 9. 1826 improved the Nile bank, excavated deep canal system and increased the irrigation area. 1843, Egypt decided to build a sluice on the Nile to control and improve the low water level of perennial irrigation and flood discharge. 186 1 year, two sluices, namely delta sluices, were built on Rosetta and the tributary of du Mijat, 23km north of Cairo. This is the earliest large-scale backwater project on the Nile, marking a new period of irrigation in Egypt. At the beginning of the 20th century, Zifta (Zi{ta), Ashuyut, Isna (1sna) and other sluices were built one after another. With the completion and use of the backwater project, Egypt obtained irrigation water in dry season, and from then on, the traditional dike irrigation began to transition to perennial irrigation. The irrigated area in Egypt increased from 1.820 to/.26 million hm2 in 1.907, and the corresponding multiple cropping index also increased from 1 to 1.43.

From the early 20th century to the 1960s.

The characteristics of this period are the construction of annual regulation reservoir, regulation of annual runoff, improvement of annual runoff utilization rate and comprehensive utilization of rivers.

With the expansion of perennial irrigation, the improvement of multiple cropping index and the increase of water demand of multiple cropping crops, natural runoff is not enough for irrigation, and the goal of further development and utilization is mainly from a large number of flood season floods in seasonal water-rich areas. In order to store floods and help the poor, Egypt built the first dam on the Nile in Aswan in 1902, with a storage capacity of 1 100 million m3 and an irrigation area of168,000 hm2. This is the earliest modern water storage project on the Nile. The old dam was raised twice, 19 12 6m, the storage capacity increased to 2.5 billion m3, the irrigation area was increased by 80,000 hm2, 1932 ~ 1933 8m, the storage capacity was 5 billion m3, and the dam height was 83m, which increased the irrigation area. 10,000 hm2, the current irrigation area is 32.8hm2, there is a hydropower station on the left bank, and the dam is also equipped with a lock. 1937, Egypt built the JebelAulia Dam on the White Nile, 48km south of Khartoum, Sudan, with a storage capacity of 3.5 billion m3, and released water to Egypt in dry season, with an irrigation area of 337,000 hm2.

In addition to the above dams, hammadi Sluice (1930) and Edfina Sluice (1950) have been added, and other sluices have been strengthened, modified or rebuilt.

In this way, Egypt has a complete irrigation system, from under the old dam in Aswan along the Nile valley to the delta. The left bank of Isner Gate is the Asfon Canal, with a length of 125km, and the right bank is the Carabia Canal, with a length of 225km. Above the Naja Hamadi Gate, the Naja hammadi Canal is divided into two parts. There is an Ibrahim branch canal on the left bank of Ashyut sluice, which is 3 17km long, with a flow of 30 ~ 80m3/s in summer and 500 ~ 900 m3/s in flood season, making it one of the largest irrigation canals in the world. In addition, another Yusuf River leads water from the canal to Fayoum Oasis. These canals are roughly parallel to the Nile and irrigate the narrow strip on the west bank of the Nile. There are four main canals in the delta, namely Ismailia Canal, Taufik Canal, Minuf Canal and Bumela Canal. Among them, the Ismailia Canal is 123km long, with a flow of1100m3/s, which is connected to the Suez Canal in Egypt in the east and is navigable for irrigation. Ten canals are divided into many branches in turn, forming a tight irrigation network. The total length of irrigation canal at 1966 reaches 25500km.

The irrigation canal discharges water from February to June every year, stops water in February and June in 65438+,and carries out annual maintenance in April and April in 438+ 10. The irrigation method is rotation irrigation, and the rotation irrigation period varies with crops.

In addition, Egypt also attaches great importance to drainage. 1964 The total length of drainage channels in China is 22,000 km, of which the total length of pipeline drainage is12,000 km, and Pengshui main canal and branch canal have initially formed a system. At the same time, Egypt also vigorously develops lift irrigation and controls gravity irrigation.

Perennial irrigation in Sudan began in the 1920s. The wide Jezira Plain between the Blue Nile and the White Nile has favorable conditions for developing large-scale gravity irrigation agriculture. In 925, Sennar Dam was built on the Blue Nile with a storage capacity of 780 million cubic meters. Since then, gravity irrigation has replaced water pumping irrigation, and the cotton planting area has expanded rapidly. Sennar Dam was rebuilt and expanded in 195 1- 1952, with a storage capacity of 930 million m3. From 1988 to 1959, the area of Gejila irrigation area has reached 420,000 hm2.

After Sudan's independence, Mangil branch line was opened in the west of MainGezira irrigation area. It was built in five phases from 1957 to 1963, with a total irrigation area of 250,000 hm2. In order to meet the agricultural water demand of the newly-increased irrigation area, a larger earth-rock dam was built at the upstream of Sennar Dam 1960 ~ 1966. At the beginning, the dam height was 57 meters. , with a storage capacity of 2 billion m3. Later, it was raised to 68m, the storage capacity increased to 7.4 billion m3, and the irrigation area was 553hm2.

1964, Sudan also built the KhashannGirBa dam in atbara river, and opened a new gravity irrigation area to accommodate 50,000 Sudanese who were relocated due to the Aswan high dam. The storage capacity of the reservoir is 654.38+300 million m3, which can irrigate farmland by 265.438+00,000 hm2. The first stage was completed in 1960s, and the irrigation area has reached s million hm2.

All the above gravity irrigation areas have supporting irrigation systems, and the canal system is vertical and horizontal. For example, Gezira main irrigation area and Mangil sub-irrigation area each have a main canal with a flow of 4m168m3/s; The main canal of Mangil is 50m wide and 4m deep, and the flow rate is186m3/s. The two main canals supply water to several main canals respectively, and each main canal supplies water to a small canal. The total area of Gepula and Mangil irrigation areas is over 800,000 hm2. Because of strict management, stable output and low irrigation cost, it has become a model for developing large-scale gravity irrigation agriculture in Africa.

During this period, a series of projects were built in the countries of the Nile valley. Although they are mainly used for irrigation, some projects also have certain power generation benefits.

However, in order to prevent sediment deposition, the reservoirs built in this period generally adopt the method of discharging mud and storing clear water, and only part of the remaining water can be stored in the flood period of that year to supplement the shortage in the dry season of the following year. Nevertheless, the reservoir sediment is still increasing year by year, and the flood storage capacity is getting worse and worse. In case of dry season, the above reservoirs will be powerless.

In addition, due to the rise of modern irrigated agriculture in Sudan, the irrigation water consumption in Egypt in summer is affected. Therefore, in 1929, Egypt signed the Nile water agreement with Britain, which strictly restricted the water consumption of Gezira Farm in Sudan and the storage time of Sennar Reservoir. Egypt accounts for 48 billion cubic meters, and Sudan may account for 4 billion cubic meters (both calculated by Aswan). This shows that there has been a water conflict between Egypt and Sudan.

In order to make full use of Nile water resources, Egypt and Sudan signed a new Nile water agreement in June1959165438+1October. The agreement recognizes the vested interests of Egypt and Sudan; Agree to build Aswan High Dam in Egypt, with annual net income of 22 billion cubic meters, Egypt 7.5 billion cubic meters and Sudan 654.38+04.5 billion cubic meters, so the share of Egypt and Sudan will increase to 55.5 billion cubic meters and 654.38+08.5 billion cubic meters respectively; In addition, the two countries also agreed to build a swamp water diversion project in Sudan to increase the water volume of the Nile, with the costs and benefits shared equally by the two countries, and set up a permanent joint technical committee to supervise the implementation. The new agreement embodies the international cooperation in the development and utilization of Nile water resources.

From the sixties to the seventies.

The characteristic of this period is that the comprehensive utilization of rivers has begun to take shape. With the construction of Aswan high dam as a symbol, it began to adjust the runoff for many years, which improved the water guarantee rate in dry years.

As mentioned above, the water resources of the Nile change greatly from year to year, which can be divided into wet years and dry years. The maximum annual runoff reaches 1, 5 1 100 million m3, but the minimum is only 42 billion m3, which is quite different. In some years, a large amount of river water is discharged into the sea without being used, while in other years, it is far from enough for irrigation. The only way to solve the above contradiction is to build a multi-year regulating reservoir on the Nile to store the excess water in the wet year.

The countries in the Nile valley have studied the "century water storage plan" and plan to build a series of water storage projects in the upper reaches of the Nile. The plan mainly includes the following projects: (1) building a multi-year regulation reservoir of Mobutu Lake to jointly regulate runoff with Victoria Lake Reservoir; (2) Qionglai Canal should be built to bypass the Sude swamp area to reduce evaporation loss; ③ Building Tana Lake multi-year regulating reservoir; ④ Build an annual regulation reservoir (the fourth waterfall dam) on the main stream of the Nile between Atbala and Wadi Halfa. This scheme is compared with the scheme of building Aswan high dam. Because the former was not adopted because of its large scale and long implementation time, it was decided to build Aswan High Dam first.

Dabazi1960 65438+1October 9, the dam 1967 was basically completed, and the 1970 project was completely completed.

Aswan High Dam is built in Sadeaali Valley, 7 kilometers upstream of the old dam and 800 kilometers south of Cairo. The maximum dam height is11m, the total storage capacity is 65.438+0689 billion cubic meters, and the effective storage capacity is 90 billion cubic meters. The backwater of the reservoir is 500km long, about 300km in Egypt and 200km in Sudan, which is called Nubian Lake. The average width of the reservoir is 10km. There are 0/2 hydropower stations/kloc-0, with a total installed capacity of 265,438+10,000 kilowatts and an annual power generation of/kloc-0,000 million kilowatt hours. ..

After the completion of the high dam, the seasonal decline of the Nile water level was effectively eliminated. Excluding the average loss of evaporation and leakage of 654.38+00 billion m3, the Nile can provide 74 billion m3 of stable water for Egypt and Sudan every year, 22 billion m3 more than before the dam was built.

The economic benefits brought by the high dam to Egypt are various, which are as follows: ① Ensuring the irrigation water demand can expand the cultivated land by 550,000 hm2, and the remaining 380,000 hm2 of cultivated land in Upper Egypt can be changed from ridge irrigation to perennial irrigation. Increasing the summer sowing index of industrialized cultivated land can increase the agricultural production in Egypt by 25%, and save agriculture in extreme drought season 1 972 ~ 1 973, 1 980 ~ 1 987. ② Control and eliminate floods. After the completion of the dam, Egypt has overcome three major floods: 1964, 1967 and 1975. (3) Gaoba will be built into a large hydropower station in Africa, which will provide cheap electricity for Egypt, thus reducing the fuel consumption of thermal power plants. (4) Improve shipping conditions and increase the freight volume of the Nile (Egypt section) to100000 tons. ③ Reduce the dredging workload of the downstream irrigation canal and save the dredging cost. ⑥ Lake Nasser has developed into a large freshwater fishing ground, with the catch increasing year by year, and the fishery resources have great potential. ⑦ Aswan's tourism industry has been developed, increasing government revenue. (8) Promote urban prosperity and increase employment opportunities.