【摘要】 <正>汉江全长1,497公里,流域面积174,000平方公里,包括陕西南部、四川东北一小部、河南西南部以及湖北大部:是长江中游最大的支流。作者於1953年4—6月随同中国科学院地理研究所的调查队在湖北西北、河南西南一带(图1)工作,注意该地区地更多还原

【Abstract】 The Han river above Tan-chiang-kou flows in a W-E direction, cutting obli-quely the NW-trending strata composed mainly of Sinian schists and limestones and tertiary red beds. The alternation of resistant and soft rocks allows the development of basin and gorge in this stretch of the valley, so that it may narrow at places to about 100 m and broaden at others 18 times as wide. The gradient, varying from 0.13%, to 0.48%,, is interrupted by rapids of all sorts. Favourable sites for reservoirs are numerous.Bordering the river are 4 steps of terraces, viz., the 10-15 m, 30-40m, 60-70 m, and the 90-110 m. The lowest, still subject to flooding, is composed of inter-bedding gravel and clay, and the upper three are of the different strata covered by deposits 10 to 15 m thick.According to morphological characteristics, 3 types of valley forms are reco-gnized in this stretch. They are:-1. Gorge of metamorphic rocks, including the most part of this stretch of the main river,2. Gorge of limestones, occupying the lower Tan-chiang (a river which enters the Han River at Tan-chiang-kou),3. Basin of red beds, existing between two gorges.In general, entrenched meanders are seen in the gorges of both types. Those of limestones are bordered by mountains over 150 m high with lapie landscape on the slopes; the gorge bottom may reach 200-400 m wide. Those of metamorphic rocks are either between mountains 300 m high or hills 100 m high; in the former case the bottom measures narrower than 350 m, and in the latter, wider than 400 m. with well preserved gravel terraces. The red bed basins may be as broad as 4.5 km. Above the bottom, hills 40 to 80 m high are flat-topped, when protected by conglomerate, or sulsta-shaped, when composed of inclined beds.The flat-topped ones may stand as pyramids, or as mesas.The basins are sites of economic centres, and hence, when selected for reser-voirs, bring considerable damage. While leakage on the sides of the reservoirs may be neglected as they are mostly impermeable; solution of limestones and of the gypsum layers in the red beds must be taken into consideration.更多还原