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  • 學位論文

序率水文條件下壩體移除後河川形貌變遷之模擬分析

The Analysis of Channel Evolution after Dam Removal based on Stochastic Hydrology

指導教授 : 李鴻源

摘要


壩體移除會造成一連串的河道地形改變,包括在原淤積區之侵蝕深槽重現、下刷、側向擴展以及導致泥砂的運移等造成河川形貌之變化。但是以往分析上多以定率性(deterministic)之觀點來檢視評估此一現象做為決策之參考,其存在之不確定性多未進一步序率(stochastic)之分析討論。根據過去之研究發現,壩體移除造成河川形貌影響之主要控制因素為水文條件、尤其是高流量事件,其為不確定主要原因,將進一步分析其影響。 本文研究以七家灣溪一號壩拆壩案例作探討,利用合成水文序列的概念,從歷史流量資料找出七家灣溪降雨的水文特性,接著透過日流量生成模式(Shot noise model)產生新的流量序列,然後利用一維模式NETSTARS來作拆壩後動床輸砂模擬演算,藉由量化輸入模式的流量不確定性,以序率方法描述河川形貌變化之行為。研究結果顯示壩體上游變動性隨時間慢慢變小而趨於穩定;壩體下游變動性隨著時間慢慢增加,模擬三年後底床沖淤變化之機率情形大致與現場量測資料趨勢相符,並探討拆壩後泥砂沖淤是否影響到一號壩上、下游之構造物,經初步評估目前無立即性危險。以序率方法彌補在定率討論上的不足,在未來拆壩管理決策上能夠加入序率的方法做探討,始能擬定彈性且多方向之治理決策。

並列摘要


Dam removal will result in a series of river terrain changes, migration of sediment and other changes in river morphology. On the previous, most decision-making of dam removal rely on deterministic view as reference, and the uncertainties of it without further discussed in stochastic analysis. Based on past studies have found that the major factors of dam removal effects on river morphology is hydrological conditions, especially in high flow events. In this paper, we will further analyze its impact from hydrological uncertainty. This study takes the removal of the Chichiawan NO.1 dam as a case. AT First, with the concept of synthetic hydrologic sequences to identify Chichiawan hydrological properties of rainfall from historical flow data, and then applies a daily flow generation model (Shot noise model) to generate new flow sequences. Utilizing one-dimensional model NETSTARS to simulate channel evolution after dam removal, and then quantifying flow uncertainty inputted into the model. The changes in river morphology of the output from NETSTARS will describe in stochastic method. Simulation results show that magnitude of changes slowly become smaller with time in the upstream, but bigger in the downstream. Upstream gradually becomes stable. The probability of riverbed erosion and deposition conditions is consistent with field measurement data trends after three years. After preliminary assessment, it shows that no immediate danger currently. Analysis of stochastic method could make up for the lack of discussion in deterministic method. In the future, management decisions of dam removal may take the concept of risk into consideration, it will develop flexible and multi-direction governance decisions.

參考文獻


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