A method of standard syntaxis of the flood control and drainage based on the theory of water level safety margin is constructed, and the northern part of the Taihu Lake Basin is used as the study area to analyze the cohesion between the sub-basin flood and urban drainage standards. Through the trial calculation of different simulation schemes, the effect of changes of sub-basin flood and urban drainage standards on the inflow and outflow volume in key sections is analyzed, and the design combination of sub-basin flood and urban drainage standards is proposed based on the evaluation method of water level safety margin. The results indicate that the current sub-basin flood and urban drainage standards of the northern part of the Taihu Lake Basin basically can resist the flood with a return period of 50-year. However, the capacity and demand of flood control and drainage at the sub-basin and urban are incohesion, which shows that the water level in the urban is far lower than the flood control design water level, while the sub-basin water level is close to or even higher than the flood control design water level and even slightly higher than its flood control capacity. There are significant differences in the characteristics of changes in the flood discharge pattern caused by the improvement of flood control standards in different sub-basins. The flood control capacity of Wuchengxiyu District and Yangchengdianmao District is improved by expanding the flood discharge to the Yangtze River, while the Huxi District is profited by expanding flood discharge to the Taihu. Limiting the discharge volume of polder of urban has limited effect on alleviating the flood control pressure in the external area of urban. Finally, the sub-basin flood standard with a return period of 50-year and the urban drainage standard with a return period of 20-year in the north of Taihu Lake Basin are the design combination of standard syntaxis.

This paper conducted systematic research on the mute feed effect caused by the change of project scheduling conditions of flood and waterlogging between three levels of basin, sub-basin and urban in the Taihu Basin. Taking the Taihu Basin and its internal water conservancy districts and towns as an example, different simulation conditions and scheduling scenarios were designed based on the idea of control variables, and the flood movement process in the basin under different flood control project conditions and scheduling schemes at various levels was quantitatively simulated. The mute feed effect of flood and waterlogging was analyzed from the aspect of water level variation at various levels. The results indicate that properly raising the drainage control water level of urban flood protection and waterlogging drainage project can relieve the flood control pressure of basin and sub-basin while ensuring the safety of urban internal flood control and drainage, but with limited effect. Modestly reducing the control water level of sub-basin drainage project along the Yangtze River and Hangzhou Bay can significantly reduce the water level of the Taihu Lake and sub-basins, and can also have a certain effect on the internal water level drop of urban. The capacity of flood discharge of the basin has highly increased with implementation of the flood releasing projects such as the Wusong River, and can also substantially reduce the water level of the Taihu Lake and sub-basins. However, further implementation of the sub-basin flood protection and waterlogging drainage project could only lower the internal water level of sub-basins, with almost no impact on the basin and the urban.