'IRAQ AND THE PERSIAN GULF' [‎279v] (561/862)

434 IRRIGATION, agriculture, and minor industry
easy for local cultivators to maintain some head of water in their
distributaries by their own efforts and at the expense of weaker
neighbours, for when it becomes uneconomical to clear the silt from
the canal bed because of the increasing height of the banks, a new
channel can be cut alongside. But it needs a strong central govern
ment to co-ordinate these efforts, to ensure the economic use of water,
and, above all, to develop new schemes necessitated by changes in
the course of the rivers which supply the water. Thus the decline
of irrigation set in gradually during the last two centuries of the
Abbasid period: the Nahrwan canal between the Diyala and Kut
ceased to carry water in the time of the Seljuk Sultans; the upper
part of the Nahrwan system was probably destroyed when the Tigris
broke into it below Samarra in the thirteenth century (p. 46) just
before the Mongol invasion of Hulagu Khan in 1258 (p. 254); and
the Ottoman administration was never vital enough in Iraq to form
a strong central authority.
The notion, which has profoundly influenced modern policy, that
Iraq was continuously cultivated in Abbasid times, also needs some
modification. This was true for certain areas, as for instance in the
immediate neighbourhood of Baghdad, both above and below, and
in all areas commanded by the great canals. But shepherd tribes had
been endemic in Iraq since the Chaldean invasions of the thirteenth
century B.c., and though the pastoral zones in Abbasid times were
far more restricted than to-day, it is apparent from detailed Arabic
accounts that they existed, particularly east of the Nahrwan, where
cultivation seems to have been intensive around the numerous towns
which lined the canals, but intermittent between them. It is also
probable that despite the better system of drainage, land salination
could not be entirely avoided, particularly in the south where the
land was level, and that the tendency for cultivation to shift because
of this factor existed then as now. This factor certainly operated in
Sumerian and Babylonian times and, together with the change in the
courses of the rivers, accounts for the remarkable number of towns
which disappeared in the lower delta of the Euphrates between the
Babylonian and the Parthian period.
The recovery of the land began in the nineteenth century with the
cleaning of some of the Euphrates and Diyala canals, and was extended
by the building of the first great modern work, the Hindiya barrage,
in 1909-1913. During the War of 1914-1918 the modernization of
the Euphrates canals was first undertaken. Between 1918 and 1934
there was great activity on the Euphrates canals, and many new