_Measurement along the right bank_] [Illustration: PLATE XVIII. LONGITUDINAL SECTION OF THE DAMIETTA BRANCH _Longitudinal Scale 1 : 100,000_ _Vertical Scale 1 : 1,000_ _Measurement along the left bank_] The maximum, minimum and mean floods in the Rosetta branch are 6,500, 2,600 and 4,000 cubic metres per second. In the Damietta branch they are 4,600, 1,300 and 2,300 cubic metres per second respectively. CHAPTER III. The utilisation of the Nile. 24. =The Nile in flood.=--We are now in a position to apply our knowledge of the Nile and its tributaries to an examination of the behaviour of the rivers in flood and in time of low supply. Lake Victoria, the Victoria Nile, and Lake Albert may all be considered as the great equatorial regulators of the Nile. The river, as a river, begins at the outlet of Lake Albert, i.e., at the head of the Albert Nile. Generally at its lowest in April, it rises gradually and reaches its maximum in November. The mean minimum of 600 cubic metres per second is gradually increased to its mean maximum of 900 cubic metres. The regulating effect of the lakes is very evident. Between Lake Albert and Gondokoro the heavier rains begin late in April and with a break in June and July continue to November. The mean minimum discharge of 600 cubic metres per second in April is increased by alternating rises and falls to the mean maximum of 1600 cubic metres per second in September, which has disappeared by the end of November, when the water of Lake Albert alone remains in the river. The Gazelle river in no way affects the flood or the low supply. Its great function is to maintain the levels of the great swamps between latitudes 7° and 9°, saturate the soil, and prevent the complete disappearance of the waters of the Albert Nile between January and May. The functions this river performs are humble ones, but deprived of its aid, the Nile north of Khartoum would frequently be dry in April and May.