‘Persia – especially Seistan’ [‎129v] (257/949)

earthwork would no doubt come in freely from Afghanistan and Persia. Bricks
could be manufactured on the spot in flame kilns, as were the burnt bricks
used in the ancient ruins, the same kilns and size of bricks and method of
of construction being used at the present day at Nasratabad. The stone for
the weir works must come from the Koh-i-Malik Siah Mountains, about 70
miles away, but shingle for concrete can he got on the spot. Lime can be
made on the spot from limestone pebbles, or from limestone at Koh-i-Malik
Siah. On the whole, the cost should not be much greater per acre irrigated than
on the big Punjab perennial canals, whilst the profits should be as large, once a
railway has been made to remove the produce.
The land, both waste and cultivated, belongs to the State, and is very
fertile.
11. It is not evident why the Helmand cut back its bed and left the
channels toTarakun and Sar-o-Tar dry, but it is probable that, when the river
spread itself out by many channels as it fanned out over the deltaic plain,
the volume in each channel was not such as to cause a scour and conse
quent retrogression of levels; but when a larger and larger part of the water
was allowed to go down the one channel which had the most direct course to the
deep part of the valley, the large volume flowed with a much increased velocity,
due in part to the larger volume and in part to the greater bed slope. This
velocity set up a scour which for a time may have been checked at or above
Band-i-Kamal Khan by the weirs referred to in history and the traditional sites
of which are still pointed out by the people. Moreover, they probably forced
the silt-laden flood waters down the Tarakun channel, thus raising the level of
that tract more rapidly than the northern part of the delta to which only
water in canals under control went.
It should be noticed that the Tarakun channel is of full size, capable of
carrying the whole Helmand lliver in flood. The river must have left it
sudenly. Had the supply been gradually reduced through a long series of
years, the channel would have become reduced in size by silting, as we found
that the Nadali channel had done. Some 6 miles of old river bed exists at
a level of some 15 or 20 feet above present river bed on the left bank of the
Helmand between Madar-i-Padshah and Kala Jan Beg. It would seem that
in ancient times the Helmand flowed west pasr, Taiakun, and the present river
was then a canal, which, through neglect or bad management, developed into
the main river.
12. Whilst Mr. Tate and I rode down the old riverbed to Tarakun, some
sections were taken by Lala Thakur Das, Supervisor, and B. Ghulam Kadir
and Hari Singh Bhai at Band-i-Kamal Khan to ascertain the difference of
level between the old river, or Tarakun channel, and the present river. The plan
is given on a scale of 4 inches to a mile on plan No. I, the longitudinal section
is given on plan No. II, and two cross sections The shape revealed by cutting vertically through a land surface at right angles to the feature of interest. of the Tarakun channel on plans
Nos. Ill and IY. A detailed plan of the head of the small Tarakun canal,
made by Lala Thakur Das, Supervisor, while on the march down the valley, is
given on sheet No. V, whilst sheet No. VI is a detail section made by Lala
Thakur Das to show the position of a small canal on the high gravel plain
which must have irrigated some part of that plain when the Helmand Liver
flowed down the Tarakun channel.
Plans Nos. YII and VIII are Mr. Johns’ sections Nos. I and II of his
no t e —Appendix D—replotted to the scales usually employed in the Irrigation
Branch so as to be more easily compared wiih the other sections on plans
Nos. II, III, and IV. Mr. Johns’s note and sections are a very valuable addi
tion to our knowledge, which would otherwise have been very incomplete. The
surface slope of the river was levelled at Khwaja Ali, about 74 miles above
Band-i-Kamal Khan, and at Mirabad, about 8 miles below. A great reduction
in the steepness of the water slope takes place in this distance. At Khwaja
Ali the average surface fall, measured along the edge of the water as the river
winds, was 1 in 2,083, or 2,524 feet a mile. The slopes varied between 1 in
3,403 and 1 in 2,098 along short lengths of about 4,000 feet, with rapids about
1,000 feet long at one in 500 between each short length. At Mirabad, below
Band-i-Kamal Khan, the slope varied between 1 in 5,391 and 1 in 1,370 and