Sediment Trapping Efficiency Resulted from Detention Pond Sediment Basin Combined Design

• Main Authors: Lee Ying Fu, 李英福
• Other Authors: Wu Chia-Chun
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/96199773890711915441

碩士 === 國立屏東科技大學 === 水土保持系 === 92 === Limited land resources and high population density has restricted land development in Taiwan. The limitation further reduces land use efficiency form the viewpoint of economy; especially for small landholders provided that both sediment basin and detention pond are implemented. Hence, combined design of sediment basin and detention pond is suggested in the 2003 version of Soil and Water Conservation Technical Guideline. Lacking of research support with respect to sediment outflow from the combined design, it is necessarily to conduct scientific-sounded research. Scale model of sediment basin and detention pond combined design in 1:15 scale was used in this study to quantify the sediment trapping efficiency. Total of three peak inflows, four sediment inflow rates, three basin depths, and three sediment sizes were used in combination in this study. The laboratory experiments indicated that (1). Large volume of coarse sediment outflow occurred at the tail end of the hydrograph due to collapse of trapped sediment, (2). Large volume of mid- and fine sediment outflows occurred during the arrival of peak flow, and (3). Sediment trapping efficiency of the combined design was greatly affected by the sediment settling velocity. Results of this study can be additional summarized as follows: (1). The collapse of trapped sediment inside the combined design; due to the removal of hydrostatic pressure, produces high sediment outflow at the recession of the hydrograph. The flush of sediment outflow seldom occurs when sediment basin and detention pond are built separately. (2). The sediment settling velocity, volume of the sediment basin, and the longitudinal dimension of the basin controls sediment trapping efficiency. Higher the preceding parameters, higher the trapping efficiency. The trapping efficiency is greatly affected by the sediment settling velocity. However, the trapping efficiency is reduced when both inflow velocity and sediment inflow rate increase. (3). The advantage of the combined design has been demonstrated in this study, of which, the sediment trapping efficiency decline as compared to that of the separated design. However, the trapping efficiency remains 80% without offsetting the flood detention. Nevertheless, the major drawback of the combined design is the outflow discharge quality fails to meet the suspended-solid discharge standards set by Environmental Protection Agency. Further research is needed to improve the sediment trapping efficiency of the sediment basin and detention pond combined design, so that both aspects of economic development and disaster mitigation can be converged.