‘WAR DIARY. ARMY HEADQUARTERS, INDIA. […] I.E.F. “D”. Volume 14. PART II. (From 16th to 30th September 1915.)’ [‎70r] (144/276)

*
area which must be taken up, which will be denoted by A, to bring in net annual
return of 5} per cent, is found from the expression :— 48+40+ 6Q,Q( ^ 00 — =104,
from which the area A is found to be 375,000 acres. The calculation just
given is a very rough one, but it serves to indicate the unpromising prospects of
a barrage scheme for the irrigation of the Basrah tract. It is not argued,
however, that it will be impossible to develop a large proportion of the area
available which amounts to some 500,000 acres by means of lift irrigation
from tide fed canals, but it is certainly considered that the development of
the tract should proceed cautiously from small beginnings, in the manner
suggested in this report until the necessity or advisability, from the economic or
administrative point of view, of embarking on a project of large scope and cost
is indicated.
14. Turning now to the swamped area lying to the north of the desert tract
Reclamation of marahe, above Gurmat Ali. treatcd of > a scheme for its partial
reclamation and cultivation will next be
discussed.
Sir W. Willcocks, on page 35 of his report, states that he at first entertain
ed the idea of draining these swamps but, after a two years’ study of the ques
tion abandoned it in favour of the Basrah barrage scheme. His argument was
that the drainage of the sw r amps into the Khor Abdulla would convert 800.000
hectares of land, worth something even to-day, into a desert, and the Shatt*el-
Arab deprived of this reserve of fresh w r ater would fill with sea w ater for many
months of the year to the detriment or even destruction of the enormous number
of date palms along its ban&s. The sw r amps effect a large control on the floods
in the Shatt-el-Arab by storage and evaporation and the conservation of the
greater part of them, for this purpose alone, will certainly be necessary for a long
{ time to come, but it is quite practicable to bring a part of the tract under the
benefits of cultivation without harm to other interests. Sir W. Willcocks an
ticipated that the people would themselves reclaim a part of the swamped area
embankments and erecting pumping plants to control the water level in the
reclaimed area, and estimated the cost at L. T. 8*5 per hectare or Bs. 46 per
acre {vide page 40 of his report). Reclamation carried out in this way, by the
people, would develop very slowly, however, and to obtain revenue for adminis
trative purposes it would be necessary to take up a definite area and bring it
under cultivation as a public work. For want of adequate maps and other data
it is not possible at this stage to give any reliable figures of cost but an attempt
will be made to arrive at a rough provisional estimate. To begin with let it be
assumed that an area of 100,000 acres w r ould be taken up, situated
approximately as shown on the accompanying tracing, scale 1:500,000. The
area wmuld first be enclosed by the embankment A. B G. which would be made
partly by dredging and partly by hand digging. A drain D. falling into the
west head of the Khor Abdulla, would be required to drain off excess irrigation
supplies and seepage water when cultivation was established and to effect the
initial reclamation A tidal sluice w r ould be necessary near the tail of the drain.
The supply for irrigation would be drawn through regulators constructed in the
enclosing embankment, the necessary supply channels would be small and could
be made by the cultivators. The public works would be confined to the con
struction of the embankment, regulators, and main drain. The question of the
capacity of the drain and its design would need very careful investigation but
for present purposes it will be assumed to require a bed width of 100 feet. Sir
W. Willocks states that the natural surface level of the swamps is 1 metre above
mean sea level, the fall from this level to low tide level at the head of the Khor
Abdulla would be about 2^ metres. The length of the drain would be about 32
kilometres and the maximum surface slope 1T3,000. At this surface slope a
drain running 6J feet deep with a bed width of 100 feet would discharge about
1,200 cusecs." With this design the discharge of the drain would practically be
unaffected by the rise of the tide until the rise exceeded feet, after which the
discharge would decrease to zero, when the tide had risen 2^ metres or 8’2 feet.
The mean discharge of the drain would exceed one half the maximum discharge
but allowing for the period when the sluices would be closed and the drain not
acting at all, the average discharge will be taken at 600 cusecs or about 1,200
feet acres per diem. The drain would thus be capable of lowering the water
level over 100,000 acres by l-7th of an inch in one day. The average daily
depth of watering required for the irrigation of summer crops may be put at
about J inch. The drain would therefore be capable of dealing effectively with
surplus supplies and seepage, and assisted, as it would be to a very large extent,