蘭陽溪上游流域降雨量、逕流量、輸砂量之趨勢分析

Abstract

河川為形塑地貌主要營力之一，透過侵蝕、搬運作用塑造大地的面貌，許多研究指出台灣河川的沉積物輸出高於世界之平均值，蘭陽溪為台灣北部主要的河之一，蘭陽溪的流域單位面積輸砂量較世界其他主要河川高，但蘭陽溪河口為目前的砂質海岸侵蝕熱點，而砂質海岸的變化與河川的沉積物輸出特性息息相關。而河川沉積物的運輸與逕流量、雨量關係密切，因此本文主要目的是應用趨勢分析來探討蘭陽溪上游集水區降雨量、逕流量與輸砂量的變化特性。本研究區域位於蘭陽溪上游流域。 本研究主要透過M-K（Mann-Kendall trend analysis）趨勢檢定及距平趨勢探討研究區域內降雨量、逕流量、輸砂量的變化趨勢，除此之外，並利用克利金（Kriging） 空間內插法計算整體流域之平均降雨。 本研究之結果均呈現降雨呈現增加的趨勢；整體流量結果顯示呈現減少的趨勢；輸砂方面整呈現減少的趨勢，而透過單位逕流所產出的輸砂量亦有逐年遞減的變化趨勢。River is one of major forces for shaping the earth’s surface through erosion and sediment transportation. Many studies have pointed out that rivers in Taiwan generate higher sediment than the world average. The Lanyang River is one of major rivers in northern Taiwan. The sediment yield from Lanyang River is more than other main rivers in the world. But the embouchure of Lanyang River is one of the erosional hot spots in Taiwan. The evolution of coastal geomorphology is closely related to river sediment yield. The sediment transportation is also related to river runoff and precipitation. This study aims to detect the trend of river runoff, precipitation and sediment yield of Lanyang river upstream watershed by Mann-Kendall trend analysis. Kriging spatial interpolation is used to calculate the average precipitation of whole study area. The results of this study have shown the trend of precipitation is increasing while the trend of river runoff and sediment yield are decreasing.