| Four step-hydropower stations have been planned to be constructed on the lower reaches of the Jinsha River, from Panzhihua to Yibing, which are essential to electricity transmission from west to east, and also to the development of the west China. Baihetan hydropower station will be constructed within Baihetan valley which links Qiaojia County of Yunan Province and Ningnan County of Sichuan Province. Debris flow, however, is active in this valley, a great threat to the construction of hydropower station there. Among the 130 debris flow valleys, Dazhai Gully suspends high on the up range of Baihetan hydropower station, with an altitude over 970 m and a drop more than 350 m. Gravels, mud and flood in this valley brings the construction site in great danger. 3 kilometers upriver from the mouth of Dazhai Gully, lies the Haizi Gully, which is also frequented by debris flows, but will be taken as the dumping site for the construction. It is therefore imperative to carry out the research on the formation, growth and discharge of the debris flows in these two gullies so as to safely put into construction the hydropower station and the sites needed.Experts agree that debris flow forms and grows upon three basic conditions, i.e., inducible landform, abundant material supply and adequate water flow. Research in this paper is thus concentrated upon the environment from the geology and the three conditions. Then based on the research ,the debris flow discharge is calculated by the Mate Method.The Dazhai Gully and the Haizi Gully are complex geology with many fracture zones and varied surface layers. The Xiaojiang fracture zone and the Qiaojia fracture zonejoin each other there. According to the distribution of the fracture zones and the surface layers, The Dazhaigou-Haizigou valley can be divided into two first-grade and three second-grade tectonic areas, which greatly affect the landform pattern and surface material movement, and thus influence profoundly the formation and growth of debris flow. In addition, the seismic magnitude up to 9 degree in this valley is favourable for the formation of debris flow. Quaternary incompact deposit in the Dazhaigou valley and the Haizigou valley is mainly slope wash and proluvium, and is 501.938 million m3, among which 45.63 million m3 is distributed in the former with an averages 1.5883 million m3 per m2 and 456.305 million m3 in the latter with an average distribution of , 4. 3044 million m3. The Quaternary incompact deposit provides the material basis for the formation and activities of mud-rock flowWith its special geology structure, Dazhaigou-Haizigou valley has a landform consists mainly of rising middle mountains and monoclinical middle mountains. Rising middle mountains abounds with steep slops and cliffs and monoclinical middle mountains high slants. This make them easy to collapse in high slants and slope failure usually happens in acclinal slopes. Regional geology structure exerts an obvious constraints on the water system of the Dazhaigou-Haizigou valley. The Dazhai Gully's basin length measures 9.73km, with an average breadth is 2.94 km and a drainage area of 28.37 km2. The average slope length is 2.43 km, the average falling gradient counts 0.339, the valley shape coefficient 0.367 and the average falling gradient of the main course reaches 205% |
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