Comparison on downstream erosion between permeable and impermeable groundsill by flume tests

• Main Author: 孫崇育
• Other Authors: 許少華
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/8c3b4x

碩士 === 逢甲大學 === 水利工程與資源保育學系 === 104 === Due to the geographical features of Taiwan, steep slope and fast flow, river scouring and deposition are quite severe during flood peaks. In order to stabilize riverbed elevation, groundsill is a common use as a protective structure on riverbed. While flow passes through the interface between groundsill and riverbed, local scour usually occurs downstream of the groundsill. Hence the need to place energy-dissipation structures downstream of the groundsills as a protective measure is also common. Once damage occurs to this protective measure, the stability of the groundsill itself will be affected. As a consequence, the subject of downstream scouring at groundsill has been a major research topic in Taiwan. In this study, downstream scouring of permeable groundsill and traditional non-permeable groundsill were compared based mainly on erosion at the downstream basis point of groundsill. Site investigations were performed firstly in Dajia River Bridge, and a 1 to 100 scale of flume experiment in laboratory was designed according to the field data. Discussion was focused on the differences caused by permeable or not. Field investigation showed that severe local scour occurs downstream of a traditional groundsill, while deposition occurs downstream of a permeable groundsill. Laboratory experiments showed deeper down-cutting for traditional groundsill, while relatively minor for permeable one. The main cause is that a portion of flow penetrates through the permeable groundsill and reduces the drop flow over the top of groundsill, thereby reducing the drop impact on the downstream bed surface.