'Report on the Development of Mesopotamia with Special Reference to the Regeneration of the River Systems' [‎16] (22/50)

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(34) From my knowledge of the country and with the experience noted above,
1 make the following suggestions for regenerating the river between Amara and
Kurnah :—
{i) Retired bunds or levees should be constructed on both banks as surveys
and levels would indicate, in order to provide for the ultimate flow
of the bulk of the flood waters of the Tigris down the regenerated
channel.
(ii) The carrying capacities of the Baitiria, Chahala, Majar Kabir, Michiri-
yah, and other canals to be strictly limited to the water actually
required for existing agricultural and domestic purposes.
(m) All unimportant or useless channels to be closed.
(iv) The widening of the existing channel and easement of severe bends such
as,—the Devil's Elbow, by means of dredgers.
Besides these works, it will be most necessary to prevent Arab cultivators
from reclaiming any further lands from the river bed or, indeed, doing any agricul
tural work inside the bunds.
It will be as w T ell to point out how these measures, as between Kut and Kurnah
will affect existing cultivation. The existing embankments would be maintained
to protect cultivation, and new embankments built to protect land at present subject
to heavy flooding. The restriction of the carrying capacity of channels applies
to these such as the Chahala, which, having increased beyond the requisite size
merely serve as feeders to the marshes and to further the degeneration of the river
The question of the extent of the restriction will depend upon the result of t] e
surveys to ascertain the amount of irrigation proposed, and particular care would
be exercised to prevent any diminution of the irrigated tract.
(35) The question as to what extent, if any, it will be possible to eliminate some
of the existing bends between Baghdad and Kut, and bends such as the Peardrop
Bend near Kurnah, requires the very closest study, as in many cases much more
harm than good is done by interfering with the natural regime of the river.
The immediate result of a cut-off is to increase the slope through the cut-off
over that which previously existed around the bend ; whilst the energy which
had been expended in overcoming the friction of the bend and that resulting
from a steeper slope would be expended in largely increasing the velocity^
Increased velocity would produce scour, and the deepening of the river bed
above the cut-off; the eroded material being deposited on the gentler slope
below—thus raising the bed, and this action would continue until the slope
through the cut-off was less than formerly existed around the bend. The river
would be affected for long distances above and below the cut-off, whilst a consi
derable period would be required before the river again came to equilibrium :
and although ultimately a good channel with a gentle slope would be formed
through the cut-off, the slope, and the low-water navigation would be found to
have been seriously affected for several miles above and below. For these reasons
all engineers regard the short-circuiting of bends with great apprehension ; in
deed, on the Mississippi active measures are taken to prevent the river effecting
a cut-off in the ordinary course of nature.
The above remarks are not to be taken as meaning that no improvements
can be effected on the Tigris (because if all bends w'ere eliminated between Baghdad
and Kurnah, the high water slope would be only 4-4 inches per mile), but to
indicate the necessity for extreme caution.