'IRAQ AND THE PERSIAN GULF' [‎26r] (56/862)

DESCRIPTION OF THE LAND 23
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even in the low-water season, there is a channel into the Shatt al Arab
at Qarmat Ali, immediately above the airport of Basra.
The other great river, the Tigris, has a shorter, swifter course and
a greater fall as it passes through Iraq. Rising near the Golciik lake
north-west of Diyarbekir, it collects all the drainage south of the
Kurdish Taurus and eastwards to the Persian frontier. It enters
Iraq just above Pesh Khabur, 136 miles north of Mosul, still at
1,000 feet above sea-level. Between Mosul and Fat-ha it is joined
by its two greatest tributaries, the Great and the Little Zab, which
have drained the Kurdish mountains, and contribute a great volume
of silt-laden water during the season of the melting snows (March-
May). In flood time the Tigris below the confluence of the Great
Zab has almost double the volume which it has above (p. 42).
Below this confluence it meets the Qaiyara, Hibbara, and then the
Mak-hul hills and is deflected by them south-eastwards. Before
finding a passage through, it is reinforced by the Little Zab. Below
the Fat-ha gorge two other perennial tributaries reach the Tigris—the
Shatt al Adhaim, between Samarra and Baghdad, which collects
the drainage of a wide area behind the Jabal Hamrin from Kirkuk to
Tuz Khurmatli (p. 86) and is particularly susceptible to sudden
rises from heavy rain in winter, and the Diyala, which, as the Ab-i-
Sirwan, drains a large snow-fed basin in the Kermanshah district of
Persia. The Diyala is strongly affected both by winter rainfall and
by the melting snows of spring and early summer, but in the low-
water season its waters are all used for irrigation.
Near Baghdad the Tigris with the aid of its tributaries has so
built its course above the level of the land on either side that some
of the waters of the Diyala which leave the river above and below
Shahraban, and all those of the lesser perennial streams that break
through the foothills near Mandali, Badra, and Ziarat Kaka Ali, are
dissipated in the low marshlands between the hills and the Tigris;
only some of this marshland water seeps into the Tigris through the
subsoil at low water. From Baghdad downwards the Tigris has
more and more to be harnessed to its course by earthern bunds.
A break in the bund near the site of ancient Ctesiphon was responsible
for the flooding of great tracts of land between the Tigris and the
Euphrates; the canals down-river of Aziziya keep the great Haur
Dalmaj almost perennially supplied with water; the Abbasid course
of the Tigris, now known as the Shatt al Gharraf or Shatt al Hai,
annually floods great tracts of land on either side of its course, and its
waters in flood time merge with those of the Euphrates near Nasiriya.