标题: 丁坝局部冲刷与挂淤保护机制之研究
Study on Local Scour and Sediment Exchange around Spur Dikes
作者: 钟仁凯
叶克家
Jhong, Ren-Kai
Yeh, Keh-Chia
土木工程系所
关键字: 丁坝;局部冲刷;挂淤机制;河岸保护;坝高-水深比;spur dike;local scour;sediment exchange;riverbank protection;overtopping rate
公开日期: 2017
摘要: 丁坝为河川常见之横向水工建造物。藉由丁坝传递适宜之人为扰动,可改变水流冲刷势能在河床上之分布,进而达到保护岸壁边界之目的。不过目前相关丁坝研究,仍多着墨于单座丁坝坝头之局部冲刷及束缩冲刷,鲜少从丁坝群角度切入,探讨河道主流泥砂进入丁坝坝田落淤之运移路径、及分析不同水流条件下丁坝坝田泥砂流失机制等课题。因此,本研究以台湾浊水溪流域为研究对象,透过现场调查取得实际丁坝局部深度变化、透过数值模式分析现场丁坝坝田可能之挂淤深度、透过实验水槽分析丁坝坝田泥砂运移路径等,随后整合相关分析内容,厘清现场丁坝坝头局部冲刷与坝田泥砂挂淤机制之运行规则。根据研究成果,相同入流条件下,丁坝在未浸没时保持坝田完整之能力优于浸没时;而浸没时各坝田泥砂之流失情形,可透过首座丁坝坝头局部冲刷深度、往下游距离及坝高-水深比等参数,加以估算。此外,利用现场观测资料提出局部冲刷公式,用以预测研究范围内丁坝局部冲刷变化,并提出相关丁坝设计改善建议供参。
Spur dikes are hydraulic structures that extend from a river bank into the river channel, and in on-site applications, they are present in groups. In river engineering, spur dikes have diverse functions. When applied to erodible banks, spur dikes can deflect near-bank currents to the river center. In addition, the recirculation zones behind spur dikes have a slow flow velocity, which increases sedimentation at the riverbank footing and reduces riverbank erosion. Although spur dikes serve multiple river management functions, their inherent structure hampers water flow from upstream to downstream. Thus, when water flows approach a group of spur dikes, the potential energy of the flows is increased to overcome the resistance engendered by the spur dikes. This increase in potential energy indicates that water flows passing through spur dikes demonstrate increasing turbulence intensity of flow, resulting in complex bed change near spur dikes. The local scour issue of a single spur dike has been studied by many researches, but fewer studies analyzed local scour of spur dikes. In addition, less study discussed the relationship between local scour mechanism and sediment exchange around spur dike field. Based on the field investigation, numerical simulation and flume experiment, this study explained the mechanism of spur dike scour and sediment loss in the spur dike fields. In the submerged case, the sediment loss in the spur dike fields caused by upward vortex and the scour zone development of first spur dike. The thickness of sediment loss in the spur dike fields can be calculated by local scour depth of first spur dike, the distances from upstream and overtopping rate. In the emerged case, the sediment loss in spur dike field is less than the submerged case. Moreover, an empirical formula was developed to estimate the maximum scour depth around the on-site spur dike group.
URI: http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT079716817
http://hdl.handle.net/11536/140320
显示于类别:Thesis