'IRAQ AND THE PERSIAN GULF' [‎281v] (565/862)

436 IRRIGATION, AGRICULTURE, AND MINOR INDUSTRY
channels and cuts, or by lifting water by various methods from rivers
and canals into the channels and cuts, or by direct area inundation. 1
The first two systems serve large areas, although the second is limited
to lands relatively close to rivers and canals; and the third is only
useful for rice cultivation (p. 456). The relative importance of the
three methods is shown by the estimate that in 1942 out of the total
area then cropped by irrigation 1,700,000 acres were irrigated by
lift, 1,500,000 by canals, and 250,000 by direct inundation. Canals
are of two kinds, either controlled or uncontrolled; a controlled canal
receives its water through a regulator at its mouth on the main river
and provides water at all seasons. An uncontrolled canal receives
water directly the river rises above the level of the canal-head and
is usually full in flood season and empty in low-water season, which
in Iraq is generally the very time when it is most wanted (figs. 3, 4).
The principal complication in Iraq is the fact that the rivers are high
at the wrong time of year for most crops, except rice, and thus
cannot be used generally for cultivation by direct inundation. Hence
their water-level must be raised in order to be available at the neces
sary times. This is the function of the major works on the rivers:
the Hindiya barrage on the Euphrates, the Kut barrage on the Tigris,
and the weir on the Diyala. These serve to hold up enough water
primarily to feed the controlled canals after the flood season, and also
to ensure a greater flow for the uncontrolled canals. The flood-waters
themselves are a danger to growing crops, and have to be retained
in the river-beds by great bunds along their courses. If the level rises
dangerously, the bunds may have to be breached and the waters
dispersed in areas where least harm is done.
Controlled Canal Zones of Southern Iraq
There are five areas dependent upon large canals controlled by
barrages and sluice gates at the canal-heads.
(1) The five left-bank Euphrates canals running generally eastwards
from the Euphrates between Ramadi and Musaiyib. The canals are
perennial, and irrigation is by free flow; they benefit to a certain extent
by the existence of the Hindiya barrage, but are not directly dependent
on it. The principal works on these canals are the regulators at their
heads; the number of regulating culverts for the control of the dis
tributing channels is being constantly increased. The canals are out
lined on pp. 30, 32 and shown in figs. 6, 7,13; details for 1936-1937
are summarized in the table below.
1 The areas so irrigated are shown on figs. 16, 18, 19, 20, and 21.