自然地理の立場から見た長江上・中流の旅 (特集長江研究旅行)

概要

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Sichuan Intermountain Depression is a fault basin. The Min Jiang that is the important tributary of the upper reach of the Yantze River deposited sand and gravel and formed a fan. The fan consists of round gravel and black soil which were transported by the flooding caused by the melting snow. About 2, 300 years B.P., Dujiang Yan constructed. Due to the weir, the flood damage was de-creased and irrigation was developed in the Sichuan Intermountain Depression. After construction of the weir, improvement work had been done several tunes. But the basic idea is still remained to the present age. The Min Jiang is bifurcated to the outer river (natural river) and inner river (irri-gation canal) in this place. In flood time 60% of the discharge will be flow down to the outer river and 40%, inner river. On the other hand, in the period of water shortage, outer river is 40% and in-ner river, 60%. The Jianghan Plain situated between Wuhan and Yichan has rock fans or pediment at the foot of the mountain. The depth of the deposited layer is thin. The plain is erosional plain.