| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系 === 88 === ABSTRACT
Previous in-bank flow studies showed that a main channel transitional section in front of and behind a bridge abutment in a compound channel could reduce abutment local scour. This study is interested in that how this transition affects the topography of the channel during over-bank flow conditions. Three experimental sets with or without this transition were thus conducted in a 20x1.1x0.3m movable bed compound channel that was constituted of a trapezoidal main channel and two horizontal floodplains. At each experiment, equilibrium local scour, water level and velocity profiles at various points near the bridge region were measured.
Due to large velocity profile measurement work and limit of time, the present study could not give a strong conclusion that inclusion of the transitions can reduce local scour depth around the bridge abutment. However, the following evidences give the light that the argument may be true. If there is a transition section, then in the main channel:
(1) Water level in front of the bridge abutment rises by 0.19%~0.57%,
(2) Velocities upstream the bridge reduce by 12%~20%, and
(3) Discharge through main channel reduces by 6.8﹪ and the measured maximum local scour depths reduce by 47.4%~61.5%.
In addition to the above evidences this study provided, it is thought that present velocity profile measurement and bed topography data are accurate. They can be used for the verification of further numerical studies.
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