'IRAQ AND THE PERSIAN GULF' [‎42v] (89/862)

48 GEOLOGY AND DESCRIPTION OF THE LAND
by the combined behaviour of the up-river tributaries, so that the
number of peaks is considerable. A comparison of the records of the
Tigris at Mosul, and of the Great and Little Zabs, shows that the last
generally reaches its maximum flood at the beginning of April, the
Tigris at Mosul in the third week of the month, and the Great Zab
at the end of the month; and that the mean monthly maximum dis
charges occur in the Little Zab in March, in the Tigris in April, and
in the Great Zab in May. These differences have the effect of pro
longing the danger at Baghdad and in the delta over a much longer
period than is the case of the Euphrates at Falluja (figs. 3, 4).
Baghdad to Kut al Imara (direct distance 103 miles; by river 213 miles)
The Diyala. Less than 5 miles from Hinaidi airfield on the southern
outskirts of Baghdad, the Tigris receives its last important affluent on
the left bank. The Diyala is unique among the Tigris tributaries in
that during the low-water season its entire discharge is now diverted
at its outlet from the Jabal Hamrin into irrigation canals (p. 439).
From there the course of the river is south-west over an alluvial plain
to the town of Baquba, and then southwards to meet the banks of the
ancient Nahrwan canal. It follows these closely for 22 miles to the
hamlet of Haujuna, close to the mound shown on earlier maps as
Sifwe or Safwah, which marks the Abbasid town of Jisr Nahrwan,
where the Khorasan road from Baghdad crossed the canal. Here the
old canal turned south-east, and it has been suggested that this may
have been an ancient course of the Diyala river before the canal was
constructed. At the present day the Diyala continues on a south-
south-westerly course to the Tigris, leaving the whole country to
the east of it a cemetery of dead cities and canals (p. 434). There
is no more promising region for detailed excavation and study than
here, but only a beginning has yet been made. Near its junction with
the d igris the banks of the Diyala are 10 feet high and form a con
siderable obstacle.
From Baghdad to Kut al Imara the d igris is extremely tortuous
(fig* ?)> 80 much so that while the distance by road is about 105
miles, it is 213 miles by river, a fact that was of considerable impor
tance during the advance to Baghdad in March 1917 (p. 283). Some
of the bends are so acute that river-boats on their passage down
river have difficulty in rounding them when the current is strong.
This section is indeed one of the most difficult of all for navigation
by river steamers. Some of the meanders have been cut off and the
‘ox-bow’ depressions thus formed are cultivated. About 15 miles