国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ
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| 0459 |
Innermost Asia : vol.2 |
| 極奥アジア : vol.2 |
引用情報
OCR読み取り結果
weirs or barrages similar in type to the present Band-i-Sīstān. Like every terminal river-course
where it enters a deltaic area, the Helmand is periodically liable to great shifts of its channel. Such
shifts are marked by the abandoned dry beds of the Sana-rūd and Rūd-i-biyābān or Rūd-i-
Trākun. That the latter has carried water at widely different periods into the southern delta of
Sīstān, now wholly desert, is proved by the ruined sites which I shall have occasion to discuss below.¹
But whichever channel receives the fertilizing water of the river, the use of this for regular
cultivation over a wider area can be assured only if control is maintained over its discharge by means
of a barrage. The necessity for this arises from the fact that the drainage which the Helmand
brings down from the mountains greatly diminishes after the cessation of the spring rains and the
completion of the melting of the winter snow. At the same time heat and winds during the summer
and autumn cause excessive evaporation in the plain and thus reduce the water-supply still farther.
Hence whatever changes may take place at intervals in the direction of the main channel of the
river, owing to the gradual rise of the bed through silting and from concomitant causes, the distribu-
tion from it of the available volume of water over the cultivated area must always for a great
portion of the year depend entirely upon the maintenance of weirs.²
The Band-i-Sīstān is but the latest of a series of such works which at different periods and in
conformity to changing conditions served that purpose. Local tradition, supported from late
mediaeval times onwards by historical records, assigns to these earlier works positions higher up
on the present course of the river as far as the point known as Bandar-i-Kamāl-Khān.³ There
the river, after emerging from the well-marked trough that it has followed all the way below Kala-i-
Bīst, makes its great bend to the north, and there its delta may properly be considered to start.
The interrelation between these older barrages and the areas that were once cultivated on the Afghān
side of the river and now are all desert marked by extensive ruins is a subject of distinct historical
and archaeological interest. Its investigation must be left for some qualified student in the future
who is able to combine personal examination of those numerous ruined sites with the study of the
abundant materials collected by Sir Thomas Ward, the great irrigation expert of the Sīstān Mission.
It may, however, be stated with some confidence that those ancient works are not likely to have
differed in essential features from the present Band-i-Sīstān, upon the skilful construction of which
in each succeeding year the prosperity of Sīstān proper wholly depends.
As seen in the photograph, Fig. 476, the barrage consists of an earth embankment about 6 feet
across on the top, strengthened with fascines of tamarisk brushwood, a material as abundant along
Sīstān watercourses as it is on the banks of rivers in the Tārīm basin. Used also as a revetment
it enlarges the band to about 21 feet in width at the bottom. This has annually to be built in the
late summer or early autumn, when the water has fallen quite low. It is then thrown across almost
the whole width of the Helmand-i-Kalān or 'great Helmand', from which the two branches of the
Rūd-i-Pariūn and the river of Nād-ʿAlī take off some 10 miles lower down. Only a small channel
is left for the water to pass down the main bed, the rest being turned into the Rūd-i-Sīstān, which
irrigates the major portion of Persian Sīstān. By March or April the great spring flood of the river
sweeps away the whole dam, and the chief concern of the people is then to prevent the two eastern
river branches from breaking out of their channels, destroying the heads of local irrigation canals
and inundating the cultivated land towards the northern parts of the Hāmūn. The rebuilding of
the dam was said to keep about a thousand labourers hard at work for twenty to thirty days. Com-
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22
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32
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42
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52
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62
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73
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83
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93
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103
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114
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124
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135
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145
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155
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165
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175
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185
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195
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205
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216
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226
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237
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247
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257
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268
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278
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288
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298
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309
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319
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329
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339
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351
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361
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371
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381
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391
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403
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413
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424
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435
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445
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457
458
459
460
461
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467
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477
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487
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497
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507
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517
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527
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537
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547
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557
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567
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577
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587
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597
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607
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617
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627
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637
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647
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657
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667
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677
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687
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697
698
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