Sichuan has very developed water systems. There are more than 1200 rivers, big or small. The area belonging to the Yangtze River system is 96.5%, while that belonging to the Yellow River system is 3.5%. The heads or upstreams of the rivers mostly run through the mountains and gorges; the midstreams flow through the peri-basin mountains; some midstreams and downstreams wind through the intra-basin hilly regions and eventually into the Yangtze River, belonging to the upstream system of the Yangtze River; the only rivers going into the Yellow River are the White River and the Black River. Sichuan has a potential hydropower resource of 150 million kw, only second to Tibet; its exploitation amount almost reaches 100 million kw, ranking 1st in China.
1. The karst regions in Sichuan are a part of the Yangtze River system, accommodating many rivers and therefore having abundant amount of water characterized by high water in summer and low water in winter as well as sudden high water and sudden low water. The underlaying surface has a good permeability; the underground hydrological activities are fierce; the groundwater level depth is usually greater than 100m; if the forests and vegetation are damaged, the water diversion and storage capacity may weaken and the utilization ratio of water resources may fall, easily leading to drought or flood.
2. Northwestern Sichuan has many rivers crossed each other with a runoff volume of 98.2 billion m3. The rivers belonging to the Yangtze River system include the Yalong River, Jinsha River, Xianshui River, Dadu River, Min River, etc.; those belonging to the Yellow River system include the White River, Black River and their tributaries, both originating from the Zoigê wetland. The plateau in northwestern Sichuan has a plateau surface with flat ground and blocked water flow, which may easily lead to formation of swamp and wetland of a large area amounting to 1.16 million hm2. The plateau swamp and wetland is one of the important features of the water system of northwestern Sichuan, not only having important ecological functions, but also providing a good habitat for aquatic lives, especially aquatic birds.