The Theoretical Research On Design Of Rainwater Tanks

Before stormwater management in China due to urban flooding and water shortage, the theory of stormwater detention is almost blank, and the storage volume calculation of stormwater detention tanks in urban drainage is with the use of the formula of the former Soviet Union. In recent years, urban rainwater utilization projects launched in many places, the design of rainwater tanks frequent involved in these projects, so researches on calculation methods of storage volume and related design contents carry out. However, research on the relevant theory of stormwater detention is very few. It will need further study, further enrichment and perfection. According to the current status of stormwater tanks design, studying the theory of design is the goal of this thesis. This study aims to contribute approaches to compute storage volume problems and on this basis to theoretical research on design of stormwater tanks.On the basis of previous studies, using the theories and basic principles of hydrology, hydraulics, mathematical statistics, and so on, the relevant theory of stormwater detention is considered, including design storm (rainfall data processing and analysis, temporal distribution), rainfall depth formula, rainfall losses, flow hydrograph, calculation methods of storage volume for different objectives, computer simulations, and so on. It is carried out by comprehensive analysis, theoretical study and example application. The main results and conclusions are as follows:(1) Rainfall data statistical method is discussed by using more easily available daily rainfall observed data. On the basis of the comparisons and estimation results, it can be concluded that, if the length of rainfall records is short or the small return period is needed, the annual multi-sampling series method is proposed, otherwise, the annual maximum series (AMS) method is proposed.(2) Based on Beijing rainfall data, research on the appropriate distributions for daily rainfall depth is carried out. The result shows that log normal, Pearson III, GEV etc may be used as the appropriate distributions for Beijing. This result gives a reference for selecting the distributions for daily rainfall depth.(3) The method and procedure of rainfall depth formula deduction is proposed. Based on Beijing rainfall data, after the proposed procedure of rainfall depth formula deduction, the rainfall depth formula is obtained as D= a₁ + a₂ (ln( P))^a3. The method of deriving rainfall depth formula may be employed to other city or region. Rainfall depth formula with determined parameters may use to generate daily rainfall depths with different recurrence intervals.(4) Instantaneous unit hydrograph method is recommended to flow routing after the comprehensive analysis of flow routing methods. The numerical algorithm of incomplete gamma function in instantaneous unit hydrograph is presented, and the instantaneous unit hydrograph procedure was programmed using Delphi language, then two examples (small catchment and large catchment) were given. The results show the proposed algorithms have good agreement with look-up table method and 34 points Gaussian integral method. The instantaneous unit hydrograph method with proposed algorithms may be used for calculating runoff from small or large catchment.(5) The Flow Hydrograph & Model method for detention storage volume calculation, based on the flow hydrograph concept and model, is discussed. The case study is conducted using EPA SWMM. Compared with current design methods, the proposed method not only gets storage volume, but obtains the inflow hydrograph of the tank and the hydraulic status of the whole system. It also can conduct risk analysis and flood computation.The Flow Hydrograph & Model method gives a new method for China's detention storage volume calculation and fixes the weaknesses of the design manual's formula. It lays the foundation for high design criteria check and risk analysis.(6) The Frequency Analysis & Model method is proposed for computing treatment volume for pollution control. Through EPA SWMM, a case study is carried out. Compared with the current methods in China, the proposed method can deal with different environmental protection objectives and consider different runoff pollution water quality. It also can do design check and high return periods risk analysis and obtain the inflow hydrograph of the tank.This method gives a new method for China, and fixes the problem of selecting rainfall depth by subjectivism and arbitrariness, and gives a basis for treatment volume calculation.(7) A method is proposed for rainfall depth determination. By introducing the concept of design frequency, a rainfall depth formula is deduced. The rainfall depth is obtained from rainfall depth formula with a given return period (frequency). This increases science and rationality of storage volume calculation of storage tank for rainwater reuse. Based on flow hydrograph concept, the method using model for storage volume calculation is discussed. The volume of the storage tank is computed through rainfall depth formula, SCS rainfall distributions and SWMM. Then the design check is conducted by model simulation. This improved the accuracy of the storage volume calculation. The introduction of the concept of design criteria lays the foundation of risk analysis for the storage tank.(8) The stormwater tanks design theory has been preliminarily established, which including design storm (rainfall data processing and analysis, temporal distribution), rainfall depth formula, rainfall losses, flow hydrograph, calculation methods of storage volume for different objectives, computer simulations, and so on.This study provides effective methods and theoretical references for stormwater tanks sizing, and lays the foundation for the scientific design of stormwater tanks. The achievements in the study will promote the research and development of stormwater tanks design theory, and lay the foundation for the further work of stormwater management in China. The research work is of great theoretical and practical value to our planning, design and management of new drainage system, urban disaster prevention and reduction, water pollution control and sustainable development.