Analysis And Forecast For River Blocking Caused By Debris Flow In Tiemiersu Hydroelectric Power Station

Debris flow is a kind of common natural calamity which happens in mountainous areas. In the last decades, debris flow seemed to have occurred more frequently owing to the human social economic activities, the overdevelopment of natural resources and the constant destruction of the environment. Debris flow brings about one billion costs of money and1000death each year in China. It has a severe damage on the water conservancy and hydropower constructions by striking the hydropower stations, diversion canals and other infrastructures, blocking reservoirs forming barrier lakes and abrasing the surface of dam. Researches on geologic hazards also indicate that those secondary disasters introduced above supposed to be more dangerous than debris flow itself.The thesis based on the investigation of several gullies, especially two typical ones near the Ⅱ grade dam site in Tiemiersu Ⅰ, Ⅱ, Ⅲ grade hydroelectric power station area. The study focuses on the formation conditions, basic features, flow velocity as well as the flow quantity of the debris flow in gullies. Akeqiayisu debris flow in the dam site proved to be a diluted flow, its previous and present flow velocity are2.89m/s and2.4m/s, addition with the flow quantity of108.0m3/s and192.62m3/s, and total impact force of0.512tf/m2and0.617tf/m2, respectively. Maximum impact force per rock in previous debris flow was6.77tf. Qiganbulake Gully debris flow also belongs to be a diluted flow, with its previous flow velocity, flow quantity, total impact force and impact force per rock of2.75m/s,37.125m3/s,0.57tf/m2and3.37tf, respectively. According to preceding studies, the main factors that affect river blocking are summarized as:flow quantity of debris flow and main channel; unite weight of debris flow; angle between tributary and main gullies; the width of river. Forecast is made referring to Zhou Bifan empirical equation and Zhang Jinshan empirical equation for river blocking.The research indicates that hundred-year debris flow in Akeqiayisu will lead to river blocking which threatens the power house, yet the debris flows happen in Qiganbulake won’t completely block rivers at any frequency of debris flows. Analysis and discussion about debris flow caused river blocking in Tiemiersu hydroelectric power station not only guarantees normal building and safe operation of the hydropower station, but also provides reference for forecast and treatment of other river blocking issues result from debris flow.