As for the high lands lying immediately between the river and the basin dyke, only eight or nine times in a century does the Nile rise high enough to flood them. They are called ‘berms,’ and are ingeniously irrigated by means of special high-level canals, which, starting from a point above the head of the basin system, or perhaps leading down from an upper system, pass by means of a siphon under the feeder canal. The berms are, of course, also irrigated by lifting water directly from the Nile itself. There are forty-five systems of basins in Upper Egypt, most of which, and those the largest, are on the left bank. Some of the feeder canals are insignificant, and feed only two or three basins. Others, like the Sohagia Canal, south of Assiout, feed an extensive system, and are real rivers when full. The basins themselves are 5,000 to 15,000 acres in extent, and it can easily be understood that when they are taking in they have an enormous effect in diminishing the pressure of the flood, and, on the other hand, their discharge lengthens it out in the lower reaches of the river, when the level has already fallen very much at Assouan. While the basins are filling in August and September, they absorb about 2,000 cubic metres per second. Besides this, a considerable amount is employed in filling the channel of the Nile itself and its branches. Evaporation, absorption, and direct irrigation, also play their part, and the result is that the discharge of the Nile at Cairo is some 2,500 cubic metres less than it is at Assouan. But during October and November the basins are discharging. The southernmost ones are empty by October 15, those in the neighbourhood of Cairo not till about November 30, or even later. The consequence is that the Nile at Cairo in October is discharging 900 cubic metres per second more than at Assouan, and in November 500 more.