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  • 學位論文

花蓮和平溪流域山崩作用與河川化性之相關性

The relationship between landslide and river chemistry in Heping River, Hualien

指導教授 : 陳宏宇
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摘要


本研究藉由分析花蓮和平溪流域2007年至2012年的四個山崩事件,探討崩塌地、河川化性,以及輸砂量間的相互對應關係。研究結果顯示,崩塌率與颱風的累積雨量及降雨強度有明顯正相關性,蘇拉颱風造成之山崩有最高的崩塌率、新生率與重現率,分別為2.1%、71.4%,以及58.2%。此外,岩體強度較低的廬山層和畢祿山層,占全區80%以上的崩塌率,顯示各地層之崩塌率與岩體強度有著負相關的趨勢。從崩塌地在坡體上的分布發現,大約有30%的崩塌地面積集中在靠近河道的位置,這些崩塌地在蘇拉颱風之後向上擴大,變成從河道延伸至山嶺的大型崩塌地,使得更多地質材料與碳酸鹽礦物等物質進入河川,除了提供颱風期間輸砂量增加的來源,也導致K+、Ca2+、溶解無機碳濃度,以及δ13CDIC急遽地上升。 由近30年的輸砂量計算結果顯示,本研究區之平均年輸砂量為14.45Mt,其中,颱風暴雨的沖刷與山崩事件為年輸砂量主要的供應來源,颱風期間的累積雨量越大,輸砂量占該年度輸砂量的比例也越大。而濕季的平均輸砂量為乾季的12.1倍,也顯示由於濕季雨量較充沛,造成乾濕季輸砂量的差異性。 從河水Gibbs圖得知,和平溪之河水離子濃度受到岩性影響,屬於「岩性控制」類型,約有40%至80%來自於碳酸鹽礦物。河川化性與流量的關係指出,Na+和Mg2+濃度和流量間屬於稀釋作用的關係,濕季時的濃度較低;Cl-濃度和流量間屬於水文常數平衡的關係,乾濕兩季的濃度沒有明顯之差異;Ca2+和K+濃度和流量間屬於潤濕作用的關係,在濕季時的濃度分別為乾季時的1.13倍和1.07倍;溶解無機碳濃度則是在流量大於20m3/sec時,和流量有明顯正相關的趨勢。

並列摘要


This research concerned the relationship among four typhoon-induced landslide events, river chemistry and sediment discharge in the catchment of the Heping River during 2007 to 2012. The analyzed results point out that higher rainfall intensity and cumulative rainfall would cause higher landslide ratios. Therefore, typhoon Saola triggered a highest landslide ratio of 2.1%, new generation ratio of 71.4%, and reactivated ratio of 58.2% among four typhoons. In addition, More than 80% landslides occurred in Lushan and Pilushan Formations because of the weak rock strength. About 30% of landslides located near the river and expanded to hilltop after typhoon Saola. Consequently, more deposits and carbonate minerals were transported into the river, causing the concentration of K+, Ca2+, dissolved inorganic carbon and δ13CDIC raised abruptly. The average annual sediment discharge is 14.45 Mt and mainly resulted from the contribution of typhoon events. In comparison with sediment discharge and rainfall, the greater the cumulative rainfall during typhoon, the higher the proportion of typhoon-triggered sediment discharge to annual sediment discharge. The results also show that the average sediment discharge in wet season is 13.35 Mt, which is 12.1 times of dry season due to the difference of rainfall. The plot of the total dissolved salts versus Na+/ (Na++Ca2+) reflected that the chemical properties of Heping river belonged to rock-dominated type. Moreover, the relationship between water discharge and ionic concentrations indicate that the concentrations of Na+ and Mg2+ decreased with increasing discharge, the ionic concentrations were lower in wet season. In contrast, the concentrations of Ca2+ and K+ increased with increasing discharge, the concentrations in wet season were 1.13 and 1.07 times of the dry season, respectively. The concentrations of dissolved inorganic have apparently positive correlation with discharge when discharge is higher than 20 m3/sec.

參考文獻


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