If these three contributors, the White Nile, the Blue Nile, and the Atbara, all reached their maximum at the same time, the result in an ordinary year would be a discharge at Assouan of some 13,000 to 14,000 cubic metres per second, and in occasional years a very great deal more. But this is not the case. In an ordinary year the Nile is at its lowest at Assouan at the end of May, discharging no more than 410 cubic metres per second. After the arrival of the ‘green’ water it rises slowly till July 20. By that time the ‘red’ water is fairly on the move, and the rise goes on with increased rapidity till the maximum is reached, on September 5, of 10,000 cubic metres. But both date and amount are liable to variation. If the White Nile flood is a weak one, and the Atbara early, the maximum may be reached a day or two earlier; but if the White Nile is very strong it will not be attained until September 20. A late maximum, in other words, means a good supply of water in the White Nile, and as the White Nile is the principal source of supply after the flood is over, this fact is of inestimable importance to Egypt. But occasionally, as in 1878, this is carried to excess. In that year the White Nile flood was very late and very high. The maximum was not reached till September 30, when 13,200 cubic metres per second were passing Assouan, with very disastrous results in Egypt. All through the following summer the supply was very good, and at its lowest, in May, was more than three times as great as the average.[3] Curiously enough, the preceding year offered a startling contrast. It was the lowest Nile on record. The maximum was reached on August 20, and was some 3,500 cubic metres below the average, and in the following May the discharge at Assouan fell to 230 cubic metres per second, as against the average 410. By the end of October the Atbara has usually disappeared altogether, and the Blue Nile falls very quickly after the middle of September. The White Nile, however, owing to the regulating effect of its natural reservoirs and the slackness of its current, is very much more deliberate in its fall, and the results at Assouan are as follows in a normal year: By the end of September the discharge has fallen to 8,000 cubic metres per second; end of October to 5,000; end of November to 3,000; end of December to 2,000; end of January to 1,500; end of March to 650; and end of May to 410.