'IRAQ AND THE PERSIAN GULF' [‎26v] (57/862)

24 GEOLOGY AND DESCRIPTION OF THE LAND
The Shatt Dujaila, probably a still more ancient course (pp. 49-50),
which now leaves the Tigris downstream of Kut, has however, so
built up its bed above the surrounding country that the Gharraf
marshlands on the west and those of the Haur Sanmya on the east
are both areas of lower ground. The present Tigris course below
Kut is already built higher than these low-lying marshlands in the
south and the dissipated waters of the mountain streams. Navigation
on the Tigris here is less difficult, and in flood time when the waters
are nearly level with the top of the bunds the river-vessels are actually
sailing many feet above the level of the surrounding country.
A difficulty which faces the administration of the country is the
conflict of interest between the settled Arab near the banks of the
Mesopotamian rivers and the nomad who pastures his flocks beyond
reach of the river. The training of the river within its banks and its
control for irrigation is important to the former. But flooding beyond
the settled land is equally desired by the nomad, for when the floods
subside, rich grass springs up on which he can graze his flocks.
(b) The Regimes of the Euphrates and Tigris
The climatic conditions governing the two rivers are alike, but
their effects in Iraq are rather different, because the mountain basin
of the Euphrates is far more distant than that of the Tigris. The
fluctuations of level of the Tigris are therefore much more marked
than those of the Euphrates, the rises caused by early winter rainfall
being more closely related to individual depressions and storms, and
those brought by melting of the snow being more directly related to
the temperatures in the hills. But the rainfall affects both rivers to a
different degree throughout the winter, until the rising temperature
melts the snow in March, April, and May, and brings high flood.
From June onwards both rivers subside until they reach their lowest
levels in September or October.
The Euphrates (fig. 3) is at its lowest in September or October.
Flow is almost steady until November, when the level normally
begins to rise, and the fluctuation of level and rate of rise tend to
increase. By December winter conditions have set in, and the rise
becomes more marked. There are occasional fluctuations from rain
fall, but they bring no danger. The lower snows melt in March, but
the river is not in full flood until April or May, when it begins to
decline steadily, drawing its supplies at first from the snow reservoirs
of the high mountains of Armenia and from springs lower down its
course. In the heat of summer the evaporation in the long course