Study On The Influence Of The Design Return Period On Urban Waterlogging

Urban waterlogging disasters occur frequently, exposing the problems existing in urban planning and construction. Urban drainage systems are important measures not only for the maintenance of the city's survival and sustainable development but also environmental protection. Design return period is an important part of rainstorm intensity formula, as well as the important parameter of the planning and designing rainwater drainage system. Whether the design return period is set reasonable that is related to the safety of the urban flood control and drainage. In order to explore the impact of the return period of urban waterloggi ng, the thesis mainly studied from the following aspects:Firstly, starting with design flow calculation method and design return period two aspects, the differences of design criteria between our country and foreign countries were compared. With drainage design method as the basic clue, this paper summarized the problems and disadvantages of our design approach. At the same time, comparative analysis for urban drainage system design criteria of the domestic part of the big city was performed. Besides, the impact of the return period on rainstorm intensity was studied.Secondly, several models which can be applied to the calculation of urba n waterlogging, such as SWMM Model, STORM Model and Wallingford Model were introduced. In addition, the thesis expounded the calculation principles, model construction and application processes of Digital Water Simulation which referred to as DS. Then, the flood analysis module design process of the model and the calculation method of water depth were introduced.Finally, in order to calculate the planning design return period of rainwater system in Changsha, this paper chose a method based on lowest total social investment to analyze it. Using Digital Water Simulation for simulating various road waterlogging conditions caused by different f requency rainstorms. A mathematical model was set up to make economic analysis. The appropriate rainwater system planning design return period is confirmed: general areas are recommended 3 years and important areas are recommended 5 years in Changsha.The study has guiding significance to improve the reliability and economy of urban rainwater system.