Study On Drainage Problems Of Haihe River Mainstream Under Conditions Of Water Function Zoning In Tianjin

Tianjin is the economical center of North China, occupying an important strategic position. The Haihe river mainstream, winding through the city center, is a comprehensive channel, which undertakes discharging flood, drainage, storing water, landscape and tourism. And it is also the backup water source in the Project of Diversion Yellow River water to Tianjin. Meanwhile, The Haihe river mainstream takes charge of drainage of city proper and regions around Tianjin during flood season, being very critical in ensuring the safety of draining off flood and drainage. With the acceleration of the urbanization process, and the increasing industry land around the city, the staunch areas expand, and the peak-volume and the corresponding time of drainage become greater and advanced, respectively, which put pressures on the drainage of city finally. However, Tianjin Municipal Government has authorized "Haihe River water function zoning in Tianjin" in 2008. Therefore, according to Tianjin water function zoning and city flood-control planning, and considering the requirements of the urban development, water storing and landscape, it's necessary to discuss the drainage problems in Haihe River mainstream under the new situation.According to the specifications of Haihe River water function zoning, the design storm was derived, and the rainfall-runoff was calculated by partition, then the flood discharge-drainage model of Haihe river trunk stream was established, to simulate the designing water-level of different drainage schemes under different return periods of design storm. Then by comparing different drainage schemes, it's available to getting the appropriate drainage scheme, to relieve drainage pressures of Haihe river mainstream under Tianjin water function zoning. The main research contents and innovative results are as follows:(1) The designed storm was derived. Through a frequency analysis by curve fitting method using the maximum yearly rainfall of Erzha at various time, the designed storm under different return periods was calculated. Simultaneously, based on the distribution table of rainfall patterns, the designed rainstorm process was also derived. Finally, with the point-area reduction coefficient, the designed areal rainfall rainstorm process was acquired by the designed point rainfall storm process.(2) The rainfall-runoff was calculated. According to the different underlying terrains, the runoff yield was estimated by partition using runoff coefficient method Otherwise, based on the features of conflux in Haihe River mainstream, the conflu time of the drainage networks each region was calculated, then a comprehensive conflux time derived. Finally, the waterlog was discharged based on the draining capability of pumping stations, falling into Haihe River mainstream according to the locations of pumping stations. Thus the drainage processes of each region were derived.(3) The flood discharge-drainage model of Haihe river trunk stream was established, then calibrated and validated through the discharge and water level records in 2011 and 2012. The calculated results agree well with the measured data, indicating that, the established model can be used to simulate and predict the variations of drainage water-level and discharge. And the model also provides the computational tools for further research.(4) Four kinds of drainage schemes were proposed. With using established flood discharge-drainage model, the water levels of different drainage schemes under different return periods of design storm were simulated. Based on the criteria of the requirements of water function zoning (there is no water on landscape platform), the different drainage schemes were compared to obtain the appropriate drainage scheme, to relieve the drainage pressure.