Measurements of Hydraulic Data and the Mechanism of the Dispersivity in the Tidal Reach of Wu-Shi River

• Main Authors: Chen Yu-Jung, 陳毓嶸
• Other Authors: 鄭仙偉
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/25634741745145964505

碩士 === 逢甲大學 === 土木及水利工程研究所 === 89 === The wetland of Wu-Shi river estuary, an important natural resource of central area of western Taiwan, is one of four largest wetlands in Asia. In this thesis, the hydrological data, dispersion coefficient (K) and the tidal exchange ratio (R) of Wu-Shi river are studied through field measurements. The measurements were performed in six stations set along the tidal reach, especially the cross-sectional velocity and salinity distributions at different times during a tidal period. The dispersion coefficients of the Shi-Bin bridge, which is 3 km from the river mouth, are 240~400 which is direct proportional to the tidal elevation difference. The K values of the tidal reach of Wu-Shi river are 50~500 , which decreases gradually from the river mouth to upstream. From the salt transport analysis, the effects of tidal pumping, vertical shear dispersion and transverse shear dispersion cause the dispersion of the Shi-Bin bridge. The effects of wind, topography and coriolis force are insignificant. The main mechanism of the dispersion is caused by tidal pumping effect, which is about 98% in spring tide and about 60% in neap tide. The effect caused by vertical shear dispersion will decrease from 35% in neap tide to 0.4% in spring tide, therefore the density difference between upper to lower layer has great influence in neap tide. The effect caused by transverse shear dispersion is from about 11% in neap tide to about 2% in spring tide. The value of the tidal exchange ratio is not large. This phenomenon may be due to the blockage of the longshore current by the Tai-Chung power plant. In addition, the measured longitudinal salinity distributions can be use to calculate the concentration distribution, which are essential for the outfall design, caused by a waste water outfall in the tidal reach.