Research On The Flow And Sediment Transport Of Dujiangyan Project

With consideration of its historical role, current state and future development of the Dujiangyan Project, this dissertation investigates the characteristics of the discharge diversion, sediment transportation and fluvial processes. The study is of great significance for better maintenance of the Dujiangyan Project and for sustainable development of the Irrigation District. The results also cast new light on the behavior of mountainous rivers.The study is based on measuring system development, database construction and field data analysis. The main results are summarized as follows:1. A new system is developed for measuring flow depth and velocity along cross-section. The GPS RTK positioning system, ultrasonic depth-sounding equipment, camera equipment, data acquisition and processing system are integrated in the measurement system. The system can obtain 3D coordinates of the measuring point, elevation of river bed and surface flow field, based on which the discharge of the section can be calculated. The new system can be easily operated, and it has been applied in the measurement of the Dujiangyan Reach with high measuring accuracy and efficiency.2. The hydrologic and sediment information analysis system for the Dujiangyan Project is developed based on relational database technology with full consideration of hydraulic standards and regulations. The system provides scientific storage and integrated analysis of hydrologic and sediment data.3. The important change of the Dujiangyan Project and the measured discharge data of 67 years are analyzed, and the rule of water-diversion of Fish-mouth and Precious-bottle-neck is investigated. It is revealed that the water-diversion of Fish-mouth is mainly controlled by the project layout and regulation. The water diversted into the Neijiang River is less than 50 percent in spring-time before 1949, but the ratio is increased to 75 percent with the regulation of the Waijiang Gate. The Sand-flying-weir Gate ensures the water income of Precious-bottle-neck without any digging in the Fengqiwo Reach. 4. Based on the measured river cross-section data of more than 20 years, the rule of scour and silt of the Neijiang Reach at Dujiangyan and the variation of the cross-section are systematic analyzed. The concept of total effect force of flow is proposed. Data analysis shows that the annual amount of scour and silt of the reach is negatively correlated with the total effect force.5. The rule of the digging load in the Fengqiwo Reach at Dujiangyan is systematicly studied from the view of river mechanics. The effect of discharge and sediment transport on the deposition of the Fengqiwo Reach is analyzed. The critical discharge of scour and silt in the Neijiang River is about 400m3/s. The basic condition of no-digging for a long term in the Fengqiwo Reach is the use of the Waijiang Gate and the Sand-flying-weir Gate.6. Three assumptions in the original derivation of the Einstein bed load formula are modified and a new formula is proposed. The modified version is tested with years of data of Cuntan Station of the Yangtze River and Neijiang Sation of the Dujiangyan Reach. The result shows the modified Einstein formula can be used to estimate bed load transport in mountainous rivers.