Flooding of the Nile

The flooding of the Nile (commonly referred to as the inundation) has been an important natural cycle in Nubia and Egypt since ancient times.

The flooding of the Nile was poetically described in myth as Isis's tears of sorrow for Osiris when killed by his brother Set.

The flooding of the Nile is the result of the yearly monsoon between May and August causing enormous precipitations on the Ethiopian Highlands whose summits reach heights of up to 4,550 m (14,930 ft).

The flooding as such was foreseeable, although its exact dates and levels could be forecast only on a short-term basis, by transmitting the gauge readings at Aswan to the lower parts of the kingdom where the data had to be converted to the local circumstances.

This cycle was so consistent that the Egyptians timed its onset using the heliacal rising of Sirius, the key event used to set their calendar.

[1] Whilst the earliest Egyptians simply laboured those areas which were inundated by the floods, some 7000 years ago, they started to develop the basin irrigation method.

Agricultural land was divided into large fields surrounded by dams and dykes and equipped with intake and exit canals.

He endeavoured to extend arable land and achieve additional revenue by introducing cotton cultivation, a crop with a longer growing season and requiring sufficient water at all times.

Although the British, during their first period in Egypt, improved and extended this system, it was not able to store large amounts of water and to fully retain the annual flooding.

During the 1920s, the Sennar Dam was constructed on the Blue Nile as a reservoir in order to supply water to the huge Gezira Scheme on a regular basis.

In order to overcome these problems, Harold Edwin Hurst, a British hydrologist in the Egyptian Public Works from 1906 until many years after his retirement age, studied the fluctuations of the water levels in the Nile, and already in 1946 submitted an elaborate plan for how a "century storage" could be achieved to cope with exceptional dry seasons occurring statistically once in a hundred years.