Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/33511
標題: 梳子型防砂壩之水理特性試驗
Experiment on the Hydraulic Characteristics of Slit-Type Check Dam
作者: 林永欣
Lin, Yung-Hsin
關鍵字: 梳子型防砂壩
slit-type check dam
收縮效應
斷面轉換係數
淘刷坑
constrictive effect
coefficient of transformed section
scoured pit
出版社: 水土保持學類
摘要: 摘要 本研究以梳子型防砂壩之開口寬度為主題,利用模型試驗,配合三種渠床 坡 度(3°、6°、9°)、三種流量(50l/min、60l/min、70l/min)及 二種試 料(粗:2mm、 細:0.84mm),於21cm寬之渠槽進行水理試驗, 並嘗試將多 開口斷面轉換成單一開口斷面,以探討總開口面積相同而開 口數不同之梳子 壩開口效應對上游土砂之攔阻效果,茲將研究結果分述 如下: 1.由試驗觀察得知,水流通過傳統防砂壩體前後,福祿數之變動不大,顯 示 此種壩型之溢洪道對於水流之束縮效應並不顯著。 2.由於本試驗供水條件所產生之流況不足以將傳統壩上游之堆積土砂沖刷 至 下游,因此傳統壩將完全阻擋上游之土砂,而梳子型防砂壩因開口較 傳統壩 低,因此,壩之上游面部份土砂將被水流經開口沖刷至下游,使 壩體上游產 生淘刷坑,顯示梳子壩不至於完全阻斷下游之供砂來源。 3.由於淘刷坑形成後之渠底較原堆積面降低,因此上游水流至此將受到緩 衝 作用,使流速減緩,而水流通過壩體時,因受開口之束縮效應使流速 增加, 相對應亦使開口處之水深較壩體上游之水深減小。 4.在本試驗條件下,當坡度或流量增大至足以使水流越流壩頂時,則開口 處 之流速將較淘刷坑未形成時之流速為緩,此則有助於淤砂之效果。 5.本文推導多開口斷面轉換成單一開口斷面之轉換係數與開口處之流速為 負 相關且經試驗證明之,而轉換係數愈大,表示梳子壩對上游淤砂之安 定效應 愈高,根據斷面轉換之結果,開口數愈多之開口壩,經轉換後斷 面之相對開 口效應愈大,表示其束縮效應愈小,則能量損失愈小,因此 ,其上游所產生 之淘刷坑規模較開口數少者為小。
Abstract The purpose of this study is to investigate the relationship between the width of opening and the hydraulic parameters for slit-type check dam.Three channel slopes (3°、6°、9°),three flow rate and two size of sediments(gravel:2mm、sand:0.84mm) were used to conduct the channel experiments in the channel with 21cm width.To realize the effect of the interception of the slit-type check dam,the multiple opening slit dam was transformed to single opening slit dam in this study.The result are obtained as follow: 1. The variation of Froude number is not distinguished when the flow through the traditional check dam.This is expressed that the constrictive effect of the check dam is not distinguished. 2. Because the flow can''t scoure out the sediments at the upstream of the traditional check dam under the condition of the water supplied,the dam will almost intercept sediments.But the height of opening in slit dam is lower than the traditional dam,so the sediments will transport through the opening to the downstream with the flow and there is a pit to scoured out at the upstreamof dam. 3. The scoured pit where is formed between the dam and the original deposited sediments has a cushioning effect for the flow,the velocity will be decreasedat the scoured pit.When the flow through the opening of slit dam,the velocity was increased with the contrictive effect. Then,the water depth at the opening of dam is lower than that at the upstream. 4. Under the condition of this experiment,if channel slope or discharge is large enough to maybe the flow water over the top of dam,the velocity at the opening of dam was slower than that before the pit being formed. 5. It is derived that the velocity at the opening of dam is a negative relation with the coefficient of transformed section, and it is proved to be correct by the experiments.A larger of the coefficient of transformed section means that the slit dam has a higher effect for stabilized the deposited sediments.And the more the opening numbers is,the higher opening opening effect is.It is meanning that the constrictive effect is not significant with a more number of opening,and the energy loss also is not significant.Therefore,the scoured pit at the upstream is smaller than that with the less opening numbers.
URI: http://hdl.handle.net/11455/33511
Appears in Collections:水土保持學系

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