"كتيّب بلاد الرافدين. المجلد I. ١٩١٨" [‎٢‎٤] (٥٦٨/٣٣)

24 BOUNDARIES AND PHYSICAL FEATURES
agriculture, on navigation, on movement by land in Irak, &c. The
great increase in the volume of the rivers during certain months is
caused by rainfall and melting snow in the highlands of Armenia,
Kurdistan, and Persia.
The low-water season may be said to last from July to November,
the high-water season from December to June. The Tigris is at its
lowest in Irak in October, and throughout most of November.
Towards the end of the latter month and in December there may be
irregular rises due to rainstorms over a wide area, and the river may
even (exceptionally) touch overflow level. In January the regular
rise of the river begins, and in this month and in February it may
reach overflow levels for short periods. In the latter half of March
or at the beginning of April come the great floods of spring, when
the river is at its highest. Throughout May and June it is steadily
falling, and in July the low-water season may be considered to begin,
the river continuing to decrease. The rise and fall of the Euphrates
take a similar general course, but its spring floods are about a week
later than those of the Tigris. Both rivers, and especially the Tigris,
are liable to rise in sudden and violent spates. By far the greater
part of the water that passes Baghdad and Hindiyeh is spilt into
marshes farther downstream and lost by evaporation.
In the flood months of March, April, and May the average dis
charge of the Tigris at Baghdad is about 100,000 cusecs 1 , but fox-
short periods the river may discharge as much as 250,000 cusecs.
In the low-water months of August, September, and October the
average is about 10,600 cusecs. At Kut el-Amara, while the low-
water discharge is about the same as at Baghdad, the flood discharge
is greater (about 160,000 cusecs ?) owing to the contribution
received in high water from the Diyaleh, which in low water is dry.
Between Kut el-Amara and Qal'at Salih the volume of the Tigris
is enormously reduced by spills and distribution through canals.
As far as Amara the reduction occurs chiefly in the flood season:
thus at Amara above the Jehaleh (Chahala) canal the average flood
discharge is only 35,000 cusecs; the low-water discharge is about
10,100 cusecs. Between Amara and Qal'at Salih the great canals
have been taking off much water in the low season as well as in
flood j thus the flood discharge at Amara below the Jehaleh canal
was recently reported to be 20,000 cusecs, the low-water discharge
5,600 cusecs, while for Qal'at Salih the figures were 4,000 cusecs in
flood and 2,800 cusecs in a low river. Below Qal'at Salih there is
an increase in the volume of the river due to a return of water from
the marshes; at Ezra's Tomb the flood discharge is 13,400 cusecs,
1 Cusecs — cubic feet per second.