沖洗載與懸浮載比例對河道沖淤之影響-以高屏溪下游河段為例

Abstract

台灣河道輸砂量之推估，不論在物理或數值模式皆有相當不錯之成果。河床與沖洗載泥砂之運動規律有所不同，而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，常假設占懸浮載濃度之70~90%作為推估各河川沖洗載含量，其界定粒徑與劃分方法往往無準確之標準，亦影響輸砂量高估或低估情形，因此如何界定沖洗載粒徑及所占之比例，為本研究之重要課題。 本研究主要推導沖洗載比例與河川中影響因子之相關式，其中影響濃度比例之因子區分為水理、地文、輸砂因子三種類型，以高屏溪下游河段為研究對象，並由實測資料進行複迴歸分析，建立一沖洗載濃度經驗公式。再以CCHE1D模式進行動床案例模擬，入砂量以一般經驗法與沖洗載濃度經驗公式之模擬比較，探討沖洗載比例對於河道沖淤之影響。 由模擬結果得知，本研究以經驗公式與一般經驗法模擬與實測之底床沖淤誤差平均值比較前者為0.53 m；後者為0.62 m，顯示沖洗載濃度比例推估優於一般經驗法推估結果。綜合上述，本研究推估公式可有效推估高屏溪主流河段之實際情形，對於推估沖洗載之含量亦提供一個創新的方法及後續應用。

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 since the mechanism of characteristic motion are different between wash load and bed material load. Lacking of fundamental data in the past, wash load has been generally assumed as composed of 70% to 90% suspend load in the river, so overestimation or underestimation of sediment transport occurs frequently with inaccurate wash load size and proportion. This study aims at developing a relationship of the proportion of wash load with the influential factors including the hydraulic, geometrical and sediment factors. The empirical formula of wash load is established by using the multivariate regression analysis with data collected from the lower Kao-Ping 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 the empirical formula of wash load. From the simulated results, the standard error of bed variation between the application of empirical formula and the observed values is 0.53m, which is superior to the result of 0.62m while applying general empirical method. In summary, the empirical formula of wash load is innovative and available for lower Kao-Ping River Reach and further application.