'IRAQ AND THE PERSIAN GULF' [‎46v] (97/862)

52 GEOLOGY AND DESCRIPTION OF THE LAND
channels, the Nahr Butaira, draws water from the right bank and
there are a number of smaller channels between it and the town
(hg 10). Immediately above the town on the left bank are the
heads of the nahr Mashara and Nahr Chahala. It is near Amara
that the Tigris begins to disperse.
From the records of discharge at various points on the river it is
calculated that the Tigris at Mosul in October contributes per
cent, of the volume discharged at Baghdad, the Great Zab 26 per
cent., and the Little Zab at Altun Kopru 13 per cent., a further
contribution of 22 per cent, being accounted for by springs and
seepage the whole suffering a loss of 6 per cent, through evaporation.
But unlike the Euphrates below Hit, the Tigris maintains a high
discharge right down to Amara in the low-water season, having a
net loss of only 4 per cent, between Baghdad and Kut, and regaining
it by the time the Nahr Butaira is reached because of the high rate of
subsoil infiltration back from the marshes when the river is low.
ut the effect of the Butaira, Mashara, and Chahala draw-offs is
very marked: the Butaira takes 26 per cent, of the discharge, and the
T, 3 , 5 betWCen them ’ leavin S onl y 39 Per cent, of
the Baghdad discharge in the river downstream of Amara. These
figures will doubtless be modified now that the Kut barrage is
completed and the Shatt al Gharraf has become perennial.
Amara t0 Q urna (direct distance 60 miles; by river 90 miles)
The three channels mentioned above are partly regulated, and
their waters are used for rice irrigation before being dispersed in
. mp " , e u r L dUCed discharge in the river channel is at once
noticeable both by the loss in velocity and by the reduction of the
width between the banks. Just as the flood-rises on the Euphrates are
smoothed out below Suq ash Shuyukh because of dispersal, so here
there is less difference between the peaks and between the monthly
averages The river-level in October is 18-2 feet (5-56 m.), and risel
to a maximum monthly mean of 23-8 feet (7-25 m.) in April The
peaks are rarely more than 1 or 2 feet higher, and the absolute maxi
mum ever recorded, 25-5 feet (776 m.), occurred in January 1926
and was caused by ram. ^ ^
A* 5 ; ee '? noted ? bove at Amara only 39 per cent, of the
aghdad discharge is left. Between Amara and Qala Salih 34 miles
down river, the Nahrs Tabar, Mijar al Kabir, and Michariya-t h e
zone^cem "ifs* bank ’ the laSt ° n thS left — draw off another
20 per cent. In all, 81 per cent, of the discharge at Baghdad is thus