| Summary: | 博士 === 國立中興大學 === 土木工程學系 === 90 === During the rainy season in Taiwan, mud slides and heavy floods often occur. Steep mountains and hillsides aid this dangerous phenomenon. The hillslope development is necessary to protect the growing population and the amount of livable land that is reducing. As land cover decreases and impervious area increases, the infiltration rate will reduce and add to the overland flow rate. An extremely high amount of sediment runoff comes from earthwork and bare land. Using detention facilities to control storm water runoff and the sediment outflow rate will avoid such adverse downstream effects. The purpose of this study is to analyze the detention pond design problem, and to propose a complete design method.
This study collected many simplified models for a start. By using inductive reasoning and complete comparisons, a method for calculating the detention pond was concluded. Detention volume was found to be the biggest for trapezoidal inflow and triangular outflow. A special design, such as pumping water after runoff beginning, can reduce detention volume. Moreover, a numerical hydrological model is developed after considering the hydraulic phenomena of the detention pond in which the inflow/outflow hydrograph and the storage-elevation relationship is analyzed carefully. This hydrological model also uses many steady/unsteady flow tests of detention pond experiments to verify this model can make a good simulation. By utilizing numerical calculation and experimentation, the detention volume of the rectangular orifice was determined to be smaller than the volume of the rectangular spillway; therefore the large ratio between recession time dividing peak time of the triangular inflow, and longer peak inflow time duration of trapezoidal inflow makes the delay time longer.
The second aim of this study was to propose easy calculation methods that can fit the above hydrological model. The graphical and perturbation methods were developed. After concluding the experiments and using the intersection method from established correlated graphs, the detention volume can be calculated. The perturbation method can calculate the approximate solutions for the hydrological continuity equation. The curve fitting method is adopted to reduce the error of calculation. The above methods were checked by the numerical solution, and can give some suggestions and applications for designers.
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