| Summary: | 碩士 === 國立中興大學 === 土木工程學系 === 91 === Abstract
As the local land area is small and the density of population is high, the use of level ground become saturated thus increases the amount of hillside land''s developments. Excessive development could lead to a decrease of the ground infiltration rate and an increase of the surface run-off. When a heavy rainfall occurs in an area with a steep slope, the resulting rapid stream causes a disaster at the hillside. Accordingly, a detention pond is practically set to alleviate the amount of excess flood due to the hill development. In the study, a numerical hydrological routing model, base on the continuity equation, is proposed to investigate the characteristics of flood detention. Additional detention pond experiments are carried out in parallel to verify the results of the numerical model. The conclusions are as follows:
1.According to the theoretical and experimental results, the discharge formula for a rectangular orifice and a spillway outlets is suggested as Q0=k1(H**1.5*(1-(1-hc/H)**1.5*U(H-hc))-h0**1.5*(1-(1-hc/h0)**1.5*U(h0-hc))) , where Q0 is the outlet discharge; k1=2/3*Cd*bc*(2*g)**0.5 , being the discharge hydrograph characteristic parameter; Cd is the discharge coefficient; g is the acceleration of gravity; bc is the width of outlet; hc is the height of outlet; H is the outlet water height; h0 is the base flow water height; U(H-hc) and U(h0-hc) are the unit step functions.
2.By using the Runge-Kutta numerical method together with the verification of the results from the detention pond experiments, the numerical model provides a way for flow predictions with various inflow hydrographs and different sizes of outlets. The good agreement between the predicted and experimental result shows the applicability of the proposed numerical method, which allows for accurate evaluation of flow discharge as a flood passes through a detention pond.
3.Based on the regressed equations (5-1) and (5-3), a normalized peak reduction factor (κ), associated with a rectangular discharge outlet, is obtained for cases with a triangular and a trapezoidal inflow hydrograph. In terms of the peak lag time, when the characteristic parameter (βe) of the triangular inflow hydrograph increases (or when the ratio between the recession time and the peak time of the triangular inflow increases), the lag time increases. On the other hand, as the characteristic parameter (γe) of trapezoidal inflow hydrograph becomes large, it results in a longer lag time due to an increase of the peak sustained inflow time.
4.Regarding the design of the minimum volume of the detention pond, the theoretical formula (3-30) and the empirical formula (5-2) are valid for cases with a triangular inflow hydrograph. For cases with a trapezoidal inflow hydrograph, on the other hand, the resulting dimensionless detention volume based on the theoretical equation (3-31) is about 15 to 75% larger than that from the empirical formula (5-4).
|
|---|
