For millennia, the Nile River has been both a blessing and a curse for the Egyptian people. Without the Nile, agriculture would be unthinkable in this desert country. On the other hand, the river’s seasonal flooding has often brought destruction and loss of human lives. To control these floods, the Aswan Dam was completed in 1970.

Asswan dam.jpg

The Aswan Dam, photo by Terje Tvedt

The Aswan Dam led to the formation of Lake Nasser, a reservoir that accumulates water from the upper parts of the Nile. The seasonal flood coming from the Ethiopian highlands vastly exceeds irrigation demand during the rainy season. The rest of the year, the water stored in Lake Nasser is needed for irrigation and allows for greater water supplies than were possible with the natural flow of the river before the dam was built. The release of water is almost exclusively managed for irrigation purposes although the dam is also used to produce electricity,

As a manager of the dam, it is important to be able to read graphs and analyze how the amount of water in Lake Nasser will develop over the year. Unexpected developments may call for increased or reduced outflows. As a constructor of the dam, it is important to find out how large the dam must be to be able to smooth the outflow of water over the seasons.

The figure below shows monthly inflows to and outflows from lake Nasser. Circles and squares show data for the flows in each month. Try to answer all the questions below.