— 53 — 
1,300 and 250 cubic metres per second, with a mean of 500 cubic 
metres per second. October is the highest month and June the lowest. 
The mean low water level is at R. L. 12.25. 
Tables 41 to 52 refer to the Nile between Assuan and the Barrage 
at the head of the Delta proper. 
Table 46 gives the Reduced Level of the mean low water level of 
the Nile at various points between Assuan and Cairo. If, for example, 
it is known that the water surface at any time of the year at Assiout is 
R. L. 50.80; we know the mean low water by the Irrigation Department 
levels is 45.05. The gauge is therefore 5.75, and by turning to Table 37 
we know the discharge. 
Table 37 gives the discharges of the river for gauges referred to 
the mean low water level. Between Esna and Kena the table is in 
excess of the truth, and between Assiout and Beni-Suef it is slighty 
under. Taken all round the table is reliable, calculated from the 
means of hundreds of discharges and carefully prepared. 
Table 45 gives the slope of the water surface of the Nile in flood 
and in summer between Assuan and Cairo. Owing to the more 
winding track of the low supply than of the flood waters, the former 
is 948 kilometres and the flood 900. The slope in summer is and 
in high flood t^Too- 
The other tables need no explanation. 
23. The Rosetta and Damietta Branches. — Plates XVII and 
XVIII give longitudinal sections of the two branches of the Nile and 
their cross sections are given on Plate XI. 
During winter, summer, and low floods, regulation at the Barrage 
interferes with the natural discharges of the two branches. The 
Damietta branch is gradually silting up and decreasing in size, while 
the Rosetta branch scours in high floods. The mean width of the 
Rosetta branch is 500 metres, and the mean area of the section in 
flood is 4000 square metres. The mean width of the Damietta branch 
is 270 metres and the mean section 2700 square metres. The mean 
velocity of the floods range from 1.00 metre to 1.60 metres per second. 
In summer the branches are hermetically closed at their heads and 
receive only the water which filters into them from the subsoil. This 
in the Rosetta branch amounts to 20 cubic metres per second, and less 
in the Damietta branch. It may be noted here that at Cairo the girder 
bridge at Kasr-el-Nil is 403 metres between the abutments and the 
smaller bridge is 178 metres, making a total width of 581 metres. 
