On the i oth December we began our march along the northern shore of the long Panggong-tso. With the view of exploring the river I paddled down it in the skiff, and intended to continue the trip by boat along the lake, but in this I was as usual prevented by the wind. The river hugs closely the southern mountains the whole way; hence we paddled in the shade and it was cold. The banks consist of level, or very slightly undulating, grassy, sandy ground. We passed on the left bank first a frozen spring, then an unfrozen one. Below the latter was the beginning of a long strip of alluvium, which contracts the river, and as this is also shallow, the current is quickened. It was here that we measured the spot in which the maximum depth was 0.94 m., and here too that the road crosses the river. A drop of only one meter in the level of the lake would cause the Tso-ngombo to be entirely cut off from the lower lake. The sounding 0.94 m. is the shallowest place in the deep bed of the stream but, as the velocity there is greatest, erosion is consequently most active at that spot, and it is uninterruptedly operative excavating the bed deeper. Pl. 54 shows the configuration of the river-bank at Camp CXLIV. At the spot where we measured the river the banks have a very different appearance, being far more energetically excavated, not indeed very high, barely a meter, but they are vertical, and bear distinctive marks of a water-level 0.44 m. higher than the existing level. Although the Tibetans tried to make me believe, that the river always maintains the same level, this water-mark proves conclusively that it does sometimes reach a higher level. At first it did occur to me, that the lake might exercise a moderating effect upon the outgoing volume in the same way as the Baghrasch-köl does upon the Kontsche-darja, by distributing it evenly throughout the year. Yet such is evidently not the case. The copious inflow in the summer must cause the lake to swell, giving rise to a considerable augmentation of volume in the outgoing stream in the late summer or autumn. At the time of our visit the river carried, as we have seen, a volume of 3.14 cub.m. and was I I m. broad. When the water rises 0.44 m. higher, the breadth increases to 2 2.5 m., and the velocity will then of course be considerably greater (fig. 2 2 3). A provisional calculation suggests that the volume will then be about 10 cub.m. In consequence
He d i n, Tourney in Central Asia. IV. 40
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