Southern Tibet : vol.2 / 190 ページ（白黒高解像度画像）

0190	Southern Tibet : vol.2
南チベット : vol.2

months earlier Ryder had written:¹ »Following down the bed of the old outlet, Sven
Hedin found several springs, which probably are underground channels from the lake.
There was no sign of these when Rawling and I were there in December; but as
the Rakas Tal was then frozen over, doubtless the springs were also frozen. This,
however, proves that the lakes are still connected, though underground, with the
Sutlej system.« Henry Strachey observed some filtration of water in 1846. SHERRING,
in 1905, heard from the natives that an underground escape was believed to exist.
But from his definition of a source Rawling is forced to draw the conclusion that the
connection does not exist. The fact that the Rakas-tal is fresh means nothing, he
says, as it is »40 or 50 years ago« since the lake did regularly overflow and it would
take centuries for the Rakas-tal to become salt.² My own opinion is that the lakes
must be reckoned to the Satlej system so long as they remain fresh. Rawling be-
lieves the Rakas-tal is steadily diminishing in volume and that it will never again
overflow into the channel of the Satlej. I have expressed the same probability for
the future development, which seems necessary on account of the constant desicca-
tion going on during post-glacial time. But I have also pointed out the periodical
fluctuations of Tibetan rivers and lakes.³

Before I had had occasion to publish anything on the results of my visit to
the lakes, Colonel S. G. BURRARD explained the whole problem in a perfectly
correct way. None of all the travellers who have seen the region with their own
eyes has ever come nearer to the solution, and to the very soul and heart of its
hydrography than Burrard, who gives the single right key to the problem in the
following words:⁴

»If the water of the Manasarowar lakes overflows occasionally into the Sutlej, they must
be regarded as belonging to the basin of the latter. We define a basin as the whole tract of
country drained by a river and its tributaries: by the word 'drained' we do not imply any
perpetual flow, but refer only to times of rain and flood. All the small tributaries of the Him-
alayan rivers are dry at certain times of the year, but a dry tributary remains a branch of
the drainage. If the water from Rakas Tal flows into the Sutlej once a century, and then only
for such a short period as to be observed by no one, we shall still be justified in including
the lakes in the catchment area of the river.«

The word »century« is not to be taken in a literary meaning, nor is it of sign-
ificance that no surface water has flowed out of the Rakas-tal during the last half
century. The sole scientific boundary in time for including the lakes in the catch-
ment area of the Satlej can be given by the qualities of the lake-water itself. So

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