| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 99 === Check dam is one of the most common hydraulic facilities for the upper river reach in Taiwan. Its main functions include storing debris, adjusting sediment transport, preventing erosion, controlling stream flow and inhibiting debris. The number of check dam in Taiwan exceeds one thousand, but its lifetime is usually very short. Both safety and practicality were over emphasized on the construction of check dams in the past, and filled the original natural environment was destroyed. When the upstream of a check dam is gradually filled by sediment, it induces a drop height between the upstream and downstream, and causes a serious impact of ecological environment. In recent years, to enhance the concept of ecology conservation, the check dam improvement or removal becomes an important issue.
The hypotheses of this research include that upstream of check dam is full of sediment, the ratio of dam wing is 1: 0.5, and the check dam wing is not removed during the dam improvement. The hydraulic experiments were conducted under the follow conditions: a geometric standard deviation σg = 1.2, two ways of dam removal (the vertical and horizontal), four remove widths (1/4, 1/2, 3/4 and the demolition of all), three bed slopes (1%, 3% and 5%) and three relatively flow intensities (V/Vc = 0.6, 0.75 and 0.9) etc. The main objectives are to understand the impact of riverbed stability, river flow diversity and the increasing rate of dissolve oxygen after the check dam removal.
Based on the criteria of riverbed longitudinal stability, river flow diversity and the increasing rate of dissolve oxygen, the check dam improvement with vertical removal of b/2 is the best choice, which can offer both river safety and ecological advantages. The secondary choice of dam improvement is the vertical removal of 3b/4 dam or the complete removed.
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