"كتيّب بلاد الرافدين. المجلد I. ١٩١٨" [‎٢‎٧] (٥٦٨/٣٦)

BOUNDARIES AND PHYSICAL FEATURES 27
century; at present it is dry during the low-water season (from
about July to about February). Below Kut el-Amara more and
more flood-water drains southwards into swamps, and from just
above Amara to Qal'at Salih an enormous amount of water is taken
off from the river by large canals, and it has been feared that, unless
preventive measures were taken, the Tigris might altogether leave
its present bed below Amara. Great permanent marshes are formed
on both sides of the river, and between Qal'at Salih and Ezra's Tomb
the Tigris is reduced to a narrow, winding channel. Part of the
water spilt from the right bank of the Tigris drains down into the
Euphrates between Nasirlyeh and Kurna; much water in the marshes
E. and W. of the Tigris is lost there by evaporation ; much returns
through many channels into the Tigris between Ezra's Tomb and
Kurna.
Conditions affecting Navigation. —In upper Mesopotamia the general
physical conditions affecting navigation on the Tigris and the
Euphrates are the swiftness of the current, due to a comparatively
steep fall, and the presence in the river-beds of rocks and ledges of
shingle, causing rapids and shallows. As waterways therefore the
middle Euphrates and middle Tigris have been used almost entirely
for down-stream traffic by flat-bottomed boats or rafts (see further
pp. 286-7, 290-2).
In lower Mesopotamia the inferiority of the Euphrates to the
Tigris as a waterway is due to the greater dispersion of the Euphrates
water in branches, canals, and broads. This dispersion has left the
lower Euphrates very shallow in parts during the low-water season,
with a slack current, which has enabled the silt to form here and
there in bars, over which there is very little water. The Tigris loses
much of its water in spills, and has its banks of silt, which give
trouble in a low river, and its narrows in its lower reaches, which
are difficult at all seasons, but it keeps a greater proportion of water
in one bed than does the Euphrates, and flows more strongly, and
therefore has better depths in the months of low river. The Tigris,
as a waterway, is capable of improvement by a thorough training of
its channel and by the limitation of the amount of water distributed
through canals so far as may be consistent with the needs of irrigation.
Measures have already been taken to preserve and improve the river
in the narrows between Amara and Qal'at Salih. As regards the
Euphrates, a scheme has been proposed for the restoration of the old
channel between Kurna and Suq esh-Shuyukh, For the obstacles
to navigation formed by the old and new Hindiyeh Barrages and
by the Hilla Regulator see pp. 283-4.