General situation of Bala hydropower station basin

Dadu River is the largest tributary of the Minjiang River system in the Yangtze River basin. It originates from the southern foot of Guoluo Mountain in Qinghai Province and is divided into Jiaomuzu River in the east and Chusijia River in the west. The east is the main source, and the two sources are called Dadu River after they meet at Shuangjiangkou. The main stream runs from north to south, passing through Jinchuan, Danba and Luding counties, flowing eastward, passing through Hanyuan, Ebian, Fulu and Shawan, receiving Qingyi River at Caoxiedu, joining Minjiang River in the south of Leshan City and passing through Aba, Ganzi and Ya 'an in Sichuan Province. The total length of the main stream is 1062km, including 852km in Sichuan, and 203km in Jiaomuzu reach (Shuangjiangkou to Ruomogou). The whole basin covers an area of 77,400 square kilometers (excluding Qingyi River) with an annual runoff of 47 billion cubic meters. The basin area in Sichuan is 7082 1 km2, of which the Jiaomu Formation River controls the basin area of about 25,000 km2, accounting for 32.2% of the total basin area.

There are many tributaries in the Dadu River basin, with the tributaries on both sides of the upper reaches quite symmetrical and the tributaries in the middle reaches on the right bank. The larger tributaries of the right bank basin with an area greater than 1000 square kilometers are: Geshizha River, Donggu River, Wasi River, Tianwan River, Songlin River, Nanya River, Niri River and Guanliao River. Left Bank: Xiaojinchuan, Jintang River and Liusha River. Vegetation in the basin is still good, and there are large grasslands and alpine meadows in the upper reaches of the river, and animal husbandry is relatively developed. Forests are mainly distributed in the main stream above Shuangjiangkou and tributaries of Jinchuan, Danba, Kangding and Luding counties, with an altitude of 2300 ~ 3700 m, dominated by coniferous trees such as fir and spruce. The Dadu River basin spans five latitudes and four longitudes, and the altitude difference is huge. In addition, the complex terrain changes lead to huge climate differences in the basin.

According to climate zoning, the upper reaches of the basin belong to the western Sichuan Plateau climate zone, and the middle and lower reaches belong to the subtropical humid climate zone of the Sichuan Basin. The basin involves four counties (cities, districts) in Qinghai and Sichuan provinces, and is mainly under the jurisdiction of Sichuan Province, accounting for 9 1.5% of the total basin area. According to the statistics of 200 1, the population of the basin is about 23 1.8 million, with an average of 30 people /km2. The population distribution in this area is uneven. Affected by natural conditions such as climate and land, the population basically increased from upstream to downstream, and the economy gradually became active from west to east. The upper reaches of banma county in Qinghai Province and Aba and Rangtang counties in Sichuan Province are sparsely populated, with an average of only 3-6 people per square kilometer. The traffic in the basin is convenient, mainly by road, and the main stream along the river is basically connected by road. The Niri estuary to the middle and lower reaches of Shawan passes through chengdu-kunming railway, with a total length of about 190km. The downstream section from Shawan to Leshan is a five-class waterway with a navigation mileage of 35 kilometers. The reach above Tongjiezi does not have navigation conditions.