ชลศาสตร์การไหลในทางน้ำเปิดที่มีเขื่อนกั้นภายใต้อิทธิพลของน้ำขึ้นน้ำลง / ชัชชัย หอมสุด = Hydraulics of flow in an open channel with a closure dam under tidal effects / Chutchai Homsud
In salt intrusion mitigation of a river, tidal barriers are usually used to prevent saline intrusion to upstream. However, it may cause some effects in downstream reaches, especially at the structure toe. This investigation aimed at studying the hydraulics of flow in an open channel with a closure dam under tidal effects. A change of water level was studied using a hydraulic model at the hydraulic and coastal model laboratory, Department of Water Resources Engineering, Chulalongkorn University. In the experiment, the hydraulic parameters were discharge, roughness coefficient and gate opening while tidal wave height and tidal wave period were parameters of wave condition. The hydraulic model used in this study consist of a river model, a sea model or wave basin, a tidal wave generator, a discharge controller, wave height meters, and an IBM-PC computer with an analog to digital conversion card for measuring wave data. The river model was made of plastic with dimension 0.3 m x 19.5 m x 0.20 m The range of flowwas 0.30-1.20 l/s. The range of roughness coefficient was 0.0132-0.0211. The range of gate opening was 0-100%. For each experiment, wave height was varied between 0.5-2.0 cm and wave period was varied between 70-600 seconds. The study of the change of water level with a closure dam under the tidal effect was made from the total 270 experiment cases. It was concluded that the increasing wave height at the closure station compare to that at the river mouth depended on the closure distance from the river mouth compared to the wave length. The increasing wave height was defined by an exponential equation, Hr=1+ae -b(L/Lc). Attempt was made to relate the parameters a and b with the hydraulic parameters of flow (Froude number, gate opening, roughness coefficient). However, insignificant relationships were found probably due to inconsistency inthe experiments. The effect of gate closure upon the changes of water level was clearly identified. More closing of the gate resulted rising of the wave height. If the gatewas totally closed, the maximum wave height occurred at the gate toe. The study result had some conclusions to be considered for a closure dam project regarding the change of the water level.
