宜蘭清水溪流域河道變化及輸砂行為分析
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2013
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台灣位於菲律賓海板塊與歐亞大陸板塊的斜向聚合碰撞帶上，由於板塊的擠壓作用，導致地震頻繁，地形陡峭，河川因而坡陡流急，沖刷嚴重。同時，台灣位於西太平洋颱風路徑上，大部分颱風帶來的豪雨常引起嚴重的災情。近年全球氣候異常，許多研究指出台灣地區年降雨日數有減少趨勢，但降雨強度增強，豪大雨發生頻率與規模亦有加大現象。由於地質、地形、氣候與人為的影響，使得臺灣地區崩塌、地滑、土石流等災害一再發生，造成生命財產損失。
台灣主要河川源頭多於高山地區，高山對於集水區的輸砂與水文有著重要的關係。中海拔以上地區，因地震與颱風的關係，容易造成許多崩積物運移而堆積於河道。以往欲了解河道的變化，常因交通不便、地形資料缺乏，造成研究無法進行。同時對於河道分析，需要長時間的監測，以取得輸砂量、降雨和河川流量等資料，以進行相關性的分析。針對輸砂量的評估，通常藉由河道中的懸浮顆粒，與河川流量、流速等資料進行計算。但是粒徑大的顆粒，如:礫石等，常以推移、跳動等方式搬運，因此難以進行分析
近年來因遙測技術之快速發展，數值地形模型(Digital Terrain Model; DTM)之建立日趨完備。因此，本研究運用航空照片建置不同時期之高精度數值地形模型，利用ArcGIS對於民國82年至97年宜蘭清水溪流域進行長時間的河道分析。首先對於河道位置的改變及沖積平原的變化作觀察，主河道隨著時間向兩側移動與侵蝕，沖積平原隨著時間有加大的趨勢，並配合各時期高程差變化對清水溪河道歷程作解釋，整體河道以堆積行為為主，河道兩側有大量堆積行為，於82至91年及95至97年期間河道有明顯的變化，推測可能為雨量事件造成之影響。接著，於河道中有變化位置及堆積行為明顯的兩側繪製多條橫剖面，觀察整個河谷變化的情形，其結果顯示，山坡崩塌為兩側大量堆積的主因，且於橫剖面確實看到河道側向侵蝕的行為。而沿著河道繪製縱剖面，觀察從中游至下游河道的變化情形，95年於中游區發生堆積事件使河道改變，整體河道高程於82年後變高，堆積約0.7m於河道。然後對河道中及兩側量體作估算，觀察了侵蝕與堆積的行為與地層岩性構造是相關的，最後藉由野外調查佐證了數值地形模型觀察的結果，映證了DTM之精確性。
Taiwan is located in the conjuncted belt of oblique convergence between the Philippine Sea plate and the Eurasian plates. Due to oblique collision between two plates, earthquakes take place frequently, and rugged topography has been developing. Also, steep slope causes river short and rapid and wash out strongly. At the same time, Taiwan is on the passage of typhoons come from western Pacific Ocean. Heavy rains brought by most of the typhoons often cause serious damage. Especially, in recent years, global climate changes dramatically. Many of studies further pointed out that not only the annual number of rainy days in Taiwan has decreased but also the rainfall intensity has increased and the frequency and magnitude of heavy rain has increased as well. Because conditions of geology, topography, climate and human impact, natural hazards, such as slump, landslide, and debris flow, in Taiwan occur repeatedly. It causes huge loss of life and property. Most of major rivers in Taiwan start in apline areas. Thus, topography in mountains has strong influences on sediment transport and catchment hydrology. Above medium elevations, because of frequent earthquake and typhoon, landslide is easy to be induced and thus sediments deposit in the river very often. In the past, the study of river channel migration usually cannot be completed due to inconvenient transportation and lack of detailed topographic data. At the same time for the analysis of river channel, a long term monitoring is needed to gather data, for example, the amount of sediment transport, rainfall and river flux. Assessment of sediment yield is estimated usually by the data of suspended loads, river flux, and velocity. But large particles, such as gravel, often transport by slating and translation. Thus, the bed load is difficult to estimate. In recent years, the rapid development of remote sensing technology establishes the digital terrain models into a better performance. This study uses aerial photographs to construct the high precision digital terrain models of different periods and analyzes the river migration of ChingShui River, Ilan from 1993 to 1997. The observations of river migration and flood plain change indicate that lateral erosion of ChingShui River and size of flood plain is increased. And Chingshui river course to explain the difference in elevation changes with each period, the overall river accumulation behavior, and the river on both sides of a large accumulation behavior. Significant changes in 82-91 years and 95-97 years during the river, presumably to cause the effect of rainfall events. The river, changes in location and accumulation behavior on both sides of drawing a number of cross-section to observe the situation of the entire valley change, the results show that both sides of the large accumulation of the main because of the hillside collapsed, and in cross-section do see the river lateral erosion behavior. Stream profile, midstream to downstream river changes, 1995, the accumulation of events occurred in the midstream area to the river to change the overall river elevation change after 82 years, the accumulation of about 0.7m in the river. River and on both sides of the amount of the estimates, Chingshui river sediment content compared to the the Lanyang statistics is consistent. Erosion and accumulation behavior and formation lithology constructed distribution is related by field survey, more evidence the results of a digital terrain model was observed, reflected, the accuracy of the DTM.
Taiwan is located in the conjuncted belt of oblique convergence between the Philippine Sea plate and the Eurasian plates. Due to oblique collision between two plates, earthquakes take place frequently, and rugged topography has been developing. Also, steep slope causes river short and rapid and wash out strongly. At the same time, Taiwan is on the passage of typhoons come from western Pacific Ocean. Heavy rains brought by most of the typhoons often cause serious damage. Especially, in recent years, global climate changes dramatically. Many of studies further pointed out that not only the annual number of rainy days in Taiwan has decreased but also the rainfall intensity has increased and the frequency and magnitude of heavy rain has increased as well. Because conditions of geology, topography, climate and human impact, natural hazards, such as slump, landslide, and debris flow, in Taiwan occur repeatedly. It causes huge loss of life and property. Most of major rivers in Taiwan start in apline areas. Thus, topography in mountains has strong influences on sediment transport and catchment hydrology. Above medium elevations, because of frequent earthquake and typhoon, landslide is easy to be induced and thus sediments deposit in the river very often. In the past, the study of river channel migration usually cannot be completed due to inconvenient transportation and lack of detailed topographic data. At the same time for the analysis of river channel, a long term monitoring is needed to gather data, for example, the amount of sediment transport, rainfall and river flux. Assessment of sediment yield is estimated usually by the data of suspended loads, river flux, and velocity. But large particles, such as gravel, often transport by slating and translation. Thus, the bed load is difficult to estimate. In recent years, the rapid development of remote sensing technology establishes the digital terrain models into a better performance. This study uses aerial photographs to construct the high precision digital terrain models of different periods and analyzes the river migration of ChingShui River, Ilan from 1993 to 1997. The observations of river migration and flood plain change indicate that lateral erosion of ChingShui River and size of flood plain is increased. And Chingshui river course to explain the difference in elevation changes with each period, the overall river accumulation behavior, and the river on both sides of a large accumulation behavior. Significant changes in 82-91 years and 95-97 years during the river, presumably to cause the effect of rainfall events. The river, changes in location and accumulation behavior on both sides of drawing a number of cross-section to observe the situation of the entire valley change, the results show that both sides of the large accumulation of the main because of the hillside collapsed, and in cross-section do see the river lateral erosion behavior. Stream profile, midstream to downstream river changes, 1995, the accumulation of events occurred in the midstream area to the river to change the overall river elevation change after 82 years, the accumulation of about 0.7m in the river. River and on both sides of the amount of the estimates, Chingshui river sediment content compared to the the Lanyang statistics is consistent. Erosion and accumulation behavior and formation lithology constructed distribution is related by field survey, more evidence the results of a digital terrain model was observed, reflected, the accuracy of the DTM.
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Keywords
數值地型模型, 河道變遷, 宜蘭, 清水溪, Digtial Terrain Model, River channel analysis, Ilan, Chinshui River