Tigris and the Euphrates peaks in April and May as a result of winter rainfall and spring
snowmelt on the mountains of Anatolia, Iran and Iraq (Adams 1981 : 3 – 6 ). This not
only threatens the ripening grain crops, but also requires that considerable efforts be
made to protect the fields from flooding (Hunt 1988 : 193 ). Thus Miguel Civil may be
correct to suggest that the Sumerians expended more effort on flood control than in
the distribution of water for irrigation (Civil 1994 : 110 ):Most Ur III texts dealing with earth moving refer to the construction of embank-
ments (ég). This is (i)n agreement with the water regime in the area. The need to
protect the crops, ready for harvest from the river’s high waters, and to prevent the
flooding of towns and fields, is clear in economic and literary texts.
(Civil 1994 : 134 )Of the two rivers, the Tigris had both a higher total annual water discharge and a
higher flood level, and this combined with the entrenched nature of part of its valley
means that it is conventionally regarded as being the more difficult of the two rivers for
irrigation.
The mismatch between the annual flood and the eventual development of large-
scale irrigation is perplexing because it makes it difficult to understand how the early
phases of irrigation developed. The Dutch soil scientist Buringh suggests that initial
irrigation was a form of flood recession agriculture that took place in the lower flood
basins following the retreat of the annual flood waters (Buringh 1960 : 152 ). Although
simple irrigation could subsequently have developed out of small natural overflows and
levee breaks, which provided the locus for more organised irrigation (Buringh 1960 ;
Wilkinson, T.J. 2003 : 89 ), these could only operate during the spring floods when the
water was at its peak, which was not the correct time for the irrigation of cereals.
Moreover, by discharging excess water at weak points on the river bank, these crevices
could be enlarged by the river thereby encouraging channel breaks and even channel
shifts or avulsions. On the other hand, spring and early summer floods would have
benefited the palm gardens that require copious water, especially during the hot
summer months and which must have been a very important crop during the third
millennium BC(Crawford 2004 : 52 ). Because date gardens occupy the levee crests, this
cycle of summer irrigation would have been in keeping with the natural ecology of the
region. This spring and early summer flood would also have provided the appropriate
soil water to initiate cereal crops’ growth in the autumn. As the need for cereals grew
during the later stages of the Ubaid and/or the Uruk period, irrigation channels could
have been extended down levee to more distant fields that would progressively
withdraw more water during the lower phases of the flood cycle. Such an evolutionary
model of progressive development away from a riverine belt of palm gardens would fit
the model of traditional palm garden agriculture in southeast Arabia where palm
garden oases formed the primary focus of cultivation together with lower storeys of
plants within the shade. In such cases, only excess flow from the irrigation systems
would have been guided to temporary cultivation downstream of the oasis. The levee-
crest garden agriculture of southern Mesopotamia would complement the wetland
resources to provide the formative stage of Sumerian agriculture.
–– Hydraulic landscapes and irrigation systems ––