應用整合位移偵測演算法於臺灣西部河道變化之研究

Abstract

傳統河道變遷偵測方法需要大量人工作業，隨著航空測量攝影及遙感探測技術發展，已可產製許多高精度之數值影像及高程模型，將之作為河道變遷分析之素材，提供河道變化量資訊，並可據此分析河道變遷歷程，說明河道變化之影響因子。本論文提出整合位移偵測方法，收集多時期數據，利用影像匹配加上DSM相減方法，首先比較影像匹配方法成果，確定使用之演算法後再獲得研究區域之真實三維變化情形。 臺灣西部地區河道屬於軟弱岩層分布，易遭受自然因素(如：斷層錯動、地體抬升)、及人為因素(砂石開採、興建人工構造物或人為束縮河道)之營力而導致河道地形劇烈改變。本論文利用整合位移偵測方法測試短時期劇烈變化之大安溪中游及長時期河道營力作用之八掌溪中游地區兩個研究區，將測試成果以實測資料及前人研究比對，驗證本論文之偵測方法之可行性，探討河道變遷情形。相較於傳統方法，可更為快速獲取研究區域之真實三維變化，而作為河道變遷研究之依據。 研究成果顯示，大安溪河段地形隆起後，從2001至2010年間共可分成3個階段，分別為2001至2003年、2004至2006年及2007至2010年。河道一開始並無固定流路，行水路徑逐年變化，在氾濫平原區域擺盪，至侵蝕到護甲層流失造成岩床裸露後，確定河道位置，接著河道開始下切，其下切最大值為15公尺。八掌溪河段由於人工構造物興建、砂石開採及河道限縮，其跨河人工構造物下游地區在1983至2013年間，因人工構造物改變侵蝕基準面加上河道限縮寬道，而導致河道下切作用旺盛，河道高程變化十分快速，其下切最大值為50公尺，主要發生在五虎寮橋及仁義潭攔河堰下游地區。整合位移偵測方法考量河道水平擺盪情形加上DSM相減成果，確實可擷取出河道之真實三維變化，並詳細描述河道變遷歷程。

The traditional method of river changing detection uses much times and manual operation. Along with the high quality of digital images and Digital Elevation Model (DEM) had been developed, the new products provide more information to describe the landform and the process and the factor of river changing. We propose the integration method that combinate the Particle Image Velocimetry (PIV) technique and DEM subtraction, are described to detect the active kinematics of the river morphology in this thesis. The PIV technique is applied to identify the horizontal movements from both orthoimages and digital surface models (DSMs). While PIV can provide estimates for the channel change direction and magnitude; vertical analysis such as river incision rate derivation could be performed using the height difference between multi-temporal surface models. The watersheds in western Taiwan are weak bedrock erosion, and affected by natural and human factors to change the river landform drastically. We use the integration method to identify the short period of the procedure of river changing in Taan River and the long period of the procedure of river changing in Bachang River. The result of the integration method was verified with cross-section profiles and previous studies. The integration method obtained the 3D movement of test site, and provided the evidence of river changing. It is observed that the proposed scheme is capable of identifying three river evolution stages from the extracted movements in the Taan case. These stages are: years 2001 to 2003, 2004 to 2006, and 2007 to 2010, respectively. The channel begins to have no stable path, and have regular path from 2001 to 2010. The total incision between 2001 and 2010 is about 12 m. The Bachang River is caused by the weir building and gravel mining changing the base level of erosion. The result shows that the river incision is main factor to cause height decrease up to 50 meters from 1983 to 2013. The extremely incision sites were happened in the downstream of Wuhuliao Bridge and Renyitan Dam. This study demonstrates that both PIV and DSM subtraction are effective in river geomorphological change identification. The integration of these two approaches could provide more information when observing the evolution of river morphology.