濁水溪流域沖洗載推估對河道沖淤之影響研究

Abstract

台灣於河道輸砂量之推估，不論在物理或數值模式皆有相當不錯之成果。不過沖洗載輸砂量推估之相關研究相對較少。過去台灣許多學者對於沖洗載泥砂之探討，受限於基本資料之缺乏，常假設懸浮載中沖洗載佔70~90%作為推估各河川沖洗載含量，該界定標準在各個不同流域河道中往往不盡相同，高估或低估皆會影響輸砂量，因此如何界定沖洗載在懸浮載中所占之比例，為本研究之主要課題。 本研究建立沖洗載比例與河道、集水區、水文、地文因子之關係式，其中影響濃度比例之因子區分為水理、輸砂、降雨地文因子三種類型，以濁水溪下游河段為研究對象，並由實測資料進行迴歸分析，建立一沖洗載濃度經驗式，再以CCHE1D模式進行動床案例模擬。入砂量以一般經驗法、河道經驗式(劉庚翰(2015)所建立之經驗式)及降雨經驗式(本研究建立之經驗式)三者模擬結果做比較，探討沖洗載比例對於河道沖淤之影響。 本研究以一般經驗法、河道經驗式、降雨經驗式模擬與實測底床沖淤進行比較，模擬2008~2015年之洪水事件，底床誤差平均值分別為0.89m、0.76m、0.63m，顯示降雨經驗式優於一般經驗法及河道經驗式推估結果。綜合上述，本研究建立之經驗式可有效推估濁水溪主流河段沖洗載比例之實際情形，對於推估沖洗載之含量比例提出一個新的方法供後續應用。

Unlike the achievement of bed material load estimation in laws of physics and numerical models in river channels in Taiwan, wash load estimation is rarely mentioned. Lacking of fundamental data in the past, wash load has been generally assumed as composed of 70% to 90% suspend load in the river, there are no clear standard of specified particle size and division method in different river,so overestimation or underestimation of sediment transport occurs frequently with inaccurate wash load proportion. This study aims at developing a relationship of the proportion of wash load with the influential factors including the hydraulic, geometrical, sediment, rainfall and physiographical factors. The empirical formula of wash load is established by using the regression analysis with data collected from the lower Chou-Shui River Reach. CCHE1D, a one dimensional mobile-bed model developed by the Center for Computational Hydroscience and Engineering, was applied to simulate the effect of river deposition-erosion with the influence of the proportion of wash load by different inflow sediment concentrations established by general empirical method and river empirical formula (the empirical formula of wash load by river condition) and rainfall empirical formula (the empirical formula of wash load by river, rainfall, physiographical condition.) This study used CCHE1D to simulate bed variation of Chou-Shui River Reach for 2008 to 2015, the standard error of bed variation between the application of rainfall empirical formula and the observed values is 0.63m, which is superior to the result of 0.76m and 0.89m while applying river empirical formula and general empirical method. In summary, the rainfall empirical formula of wash load is innovative and available for lower Chou-Shui River Reach and further application.