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。

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呱to 0.48呱，is interrupted by rapids of all sorts. Favourable sites for reservoirs are numerous.