The Nile´s watershed
The Nile (Arabic: النيل, an-Nīl; Ancient Egyptian: Iteru & Ḥ´pī; Coptic Egyptian: ⲫⲓⲁⲣⲱ, P(h)iaro; Amharic: ዓባይ?, ʿAbbai) is a major north-flowing river in northeastern Africa, generally regarded as the longest river in the world. It is 6,650 km (4,130 miles) long. The Nile is an "international" river as its water resources are shared by eleven countries, namely, Tanzania, Uganda, Rwanda, Burundi, Democratic Republic of the Congo, Kenya, Ethiopia, Eritrea, South Sudan, Sudan and Egypt. In particular, the Nile is the primary water resource and life artery for Egypt and Sudan.
The Nile has two major tributaries, the White Nile and Blue Nile. The White Nile is longer and rises in the Great Lakes region of central Africa, with the most distant source still undetermined but located in either Rwanda or Burundi. It flows north through Tanzania, Lake Victoria, Uganda and South Sudan. The Blue Nile is the source of most of the water and fertile soil. It begins at Lake Tana in Ethiopia at 12°02′09″N 037°15′53″E and flows into Sudan from the southeast. The two rivers meet near the Sudanese capital of Khartoum.
The northern section of the river flows almost entirely through desert, from Sudan into Egypt, a country whose civilization has depended on the river since ancient times. Most of the population and cities of Egypt lie along those parts of the Nile valley north of Aswan, and nearly all the cultural and historical sites of Ancient Egypt are found along riverbanks. The Nile ends in a large delta that empties into the Mediterranean Sea.
Flooding of the Nile
The flooding of the Nile (Arabic: عيد وفاء النيل) has been an important natural cycle in Egypt since ancient times. It is celebrated by Egyptians as an annual holiday for two weeks starting August 15, known as Wafaa El-Nil. It is also celebrated in the Coptic Church by ceremonially throwing a martyr´s relic into the river, hence the name, Esba` al-shahīd (´The Martyr´s Finger´). Ancient Egyptians believed that the Nile flooded every year because of Isis´s tears of sorrow for her dead husband, Osiris.
The flooding cycle
The four main stages of the Egyptian flood cycle were Akhet, the time of the season of emergence, and She mu, the season of drought. Without this cycle people would die from starvation. The flood cycle was so consistent that the Egyptians timed its onset using the heliacal rising of Sirius, the key astronomical event used to set their sidereal calendar. Retake was the first season of the year, between the months of Mid-June and Mid-September. Peret or the Egyptian Autumn season marked the time when their crops grew in the fields and were harvested, running from October to mid-February. Sh emu was the third and last season of the Egyptian year which ran from mid-February until the end of May; it essentially signalled the spring season of the Egyptian calendar.
The first indications of the rise of the river may be seen at the first of the cataracts of the Nile (at Aswan) as early as the beginning of June, and a steady increase goes on until the middle of July, when the increase of water becomes very great. The Nile continues to rise until the beginning of September, when the level that remains stationary for a period of about three weeks, sometimes a little less. In October it rises again, and reaches its highest level. From this period it begins to subside, and though it rises yet once more and reaches occasionally its former highest point, it sinks steadily until the month of June when it is again at its lowest level. Flooding reached Aswan about a week earlier than Cairo, and Luxor 5 – 6 days earlier than Cairo. Typical heights of flood were 45 feet (13.7 metres) at Aswan, 38 feet (11.6 metres) at Luxor (and Thebes) and 25 feet (7.6 metres) at Cairo. (This gives the picture before the construction of the lower and high Aswan dams.)
The main flooding was associated with observations of the first or heliacal rising of the star Sirius, related to the Sothic cycle.
Importance for Egypt
Were it not for the Nile River, Egyptian civilization could not have developed, as it is the only significant source of water in this desert region. Its other importance was the fact that it was their gateway to the unknown world. The Nile flows from south to north, to its delta on the Mediterranean Sea. It would flood each year, bringing in silt-laden waters; when the waters receded the silt would stay behind, fertilizing the land,the silt would be helpful for growing crops. If a flood was too large it would wash over mud dykes protecting a village. A small flood or no flood at all would mean famine. A flood must be of just the right intensity for a good season.
The ancient Egyptians did not realize that the flood in fact appeared due to rains on the mountains to the south, and it was seen as the annual coming of the god Hapi. The rains would swell the different tributaries and other rivers that joined to become the Nile River.
End of the flooding
In 1970, with the completion of the High Dam at Aswan, the annual flooding cycle in Egypt came to an end. Today, farmers must use fertilizers to keep their land productive, as the deposits of silt no longer occur each year. Flooding still occurs above the dam in modern-day Sudan.
FROM WIKIPEDIA