【摘要】：水庫大壩具有防洪發(fā)電、灌溉供水、航運旅游等多種功能,我國已建有水壩約9.8萬座,多為小型水壩。受當時技術(shù)、經(jīng)濟等的制約,很多水壩在規(guī)劃、設計、施工和管理等方面存在一定欠缺,隨著使用壽命的臨近,其安全、經(jīng)濟和環(huán)境等方面的負面效應日益突出。針對一些安全性差、功能喪失嚴重、生態(tài)環(huán)境影響惡劣的小型水壩,實施降等或報廢拆除是一種必要管理措施。相對于水壩建設運行,其報廢拆除將再次打破河流的生態(tài)平衡,引起河流水動力和泥沙的劇烈變化,同時間接對河流生物棲息地產(chǎn)生影響。目前,拆壩后庫區(qū)及壩下河道泥沙情勢短期內(nèi)急劇變化及其長期生態(tài)河貌影響已成為拆壩工程的巨大挑戰(zhàn),研究拆壩后水動力泥沙情勢變化過程及其地貌響應具有重要意義,將為水壩報廢拆除提供理論參考和技術(shù)支撐。本文利用貴州省西河大壩拆除案例,通過實測地形數(shù)據(jù)和泥沙基本資料,推算了西河無資料流域降雨徑流過程和含沙量,利用Delft3D建立西河二維水沙模型,分別模擬了拆壩前庫區(qū)長期泥沙淤積情況、拆壩后河道短期和長期的水動力與泥沙變化以及河貌演變,同時研究了不同拆壩方式對庫區(qū)泥沙運動和地貌變化的影響,得到以下結(jié)論:(1)對于無資料地區(qū)小型河流,在對臨近水文站長序列數(shù)據(jù)分析后,利用水文比擬法和降水徑流頻率相應法推算得到的西河年徑流均值相一致,符合地區(qū)分布規(guī)律及下墊面特點。(2)通過模擬建壩后的水沙運動過程,表明大壩修建使大量泥沙在庫區(qū)淤積,其淤積形態(tài)為“錐形淤積”;壩后由于下泄流量變小河道整體流速降低。(3)通過模擬拆壩后短期和長期的水沙過程,表明拆壩后短期內(nèi),由于水庫瞬時大量排水,壩上壩下高水頭差使壩址流速很大,導致庫區(qū)泥沙發(fā)生下切侵蝕,主河道沖刷非常嚴重,產(chǎn)生裂點向上游遷移,侵蝕上游更多的泥沙;主河道兩側(cè)由于水位迅速下降導致兩側(cè)高程較大的地方流速小而發(fā)生淤積;下游因水量下泄流速太大泥沙基本不會淤積。長期來看,經(jīng)過枯水期和平水期泥沙沖淤變化不大,但經(jīng)過洪水期后大量泥沙向下游輸運同時落淤在河道兩側(cè);河道形態(tài)在上游變化劇烈,向窄深方向發(fā)展,下游變化不太顯著。(4)分階段拆壩和一次性拆壩相比,減小了壩上壩下水頭差,形成的正向與負向波都較小,流速相對較低,侵蝕不夠嚴重,溯源侵蝕距離較短,但長期來看,泥沙沖淤分布和一次性拆除類似。
[Abstract]:Reservoir dams have many functions, such as flood control and power generation, irrigation and water supply, shipping and tourism. There are about 98000 dams in China, most of which are small ones. Restricted by technology and economy at that time, many dams are deficient in planning, design, construction and management. With the approaching of service life, the negative effects of safety, economy and environment are becoming more and more prominent. For some small dams with poor safety, serious loss of function and bad ecological environment, it is a necessary management measure to carry out downgrade or scrap demolition. Compared with dam construction and operation, its scrapping and dismantling will once again upset the ecological balance of the river, cause dramatic changes in river hydrodynamic force and sediment, and indirectly affect the biological habitat of the river. At present, the rapid change of sediment situation in the reservoir area and the river channel under the dam after dam removal and its long-term ecological river profile have become a great challenge for the dam demolition project. It is of great significance to study the variation process of hydrodynamic sediment situation and its geomorphological response after dam removal. It will provide theoretical reference and technical support for dam scrapping and demolition. Based on the case of Xihe dam demolition in Guizhou Province, the process of rainfall runoff and sediment content in Xihe River basin without data are calculated through the measured topographic data and basic sediment data. A two-dimensional model of water and sediment in Xihe River is established by using Delft3D. The long-term siltation of the reservoir area before the dam removal, the short-term and long-term hydrodynamic and sediment changes of the river after the dam removal and the evolution of the river profile are simulated, respectively. At the same time, the effects of different ways of removing the dam on the sediment movement and geomorphologic change in the reservoir area are studied. The conclusions are as follows: (1) for small rivers without data, after analyzing the sequence data of adjacent hydrological stations, the average annual runoff of Xi River calculated by hydrological analogy method and the corresponding method of precipitation runoff frequency is consistent. In accordance with the regional distribution law and the characteristics of the underlying surface. (2) by simulating the process of water and sediment movement after the dam construction, it is shown that a large amount of sediment is silted in the reservoir area by the dam construction, and its siltation form is "conical siltation"; After the dam, the flow velocity of the river decreases because of the decrease of the flow rate. (3) by simulating the short-term and long-term water and sediment processes after the dam removal, it is shown that, in the short term after the dam removal, the flow velocity of the dam site is very large because of the instantaneous and massive drainage of the reservoir, and the high water head under the dam makes the flow rate of the dam very large. As a result, the sediment in the reservoir area is cut down, the main channel scour is very serious, the crack point moves to the upstream, more sediment is eroded in the upper reaches, and the two sides of the main river channel are silted up because of the rapid drop of the water level, which results in the low velocity of the high elevation on both sides of the main river. The sediment in the lower reaches will not be silted up because the discharge velocity is too large. In the long run, there is little change in scouring and silting during the period of low water and water, but after the flood period, a large amount of sediment is transported downstream at the same time and siltation falls on both sides of the river, and the shape of the channel changes sharply upstream and develops in a narrow and deep direction. (4) compared with one-off dam removal, the downstream change is not obvious. (4) compared with one-off dam dismantling, the head difference of dam bottom is reduced, the positive and negative waves are smaller, the velocity of velocity is relatively low, the erosion is not serious enough, the distance of traceability erosion is short, but in the long run, Sediment scouring and silting distribution is similar to one-time demolition.
【學位授予單位】：重慶交通大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TV147.5

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本文編號：2273790