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河流係一動態系統，其河床演變受集水區來水來砂及河道附近之人為活動所影響。台灣地區河川坡陡流急、豐枯流量懸殊，其河性與國外常流型河川迥異，颱洪豪雨期間河床常劇烈變動，加上近年來氣候變遷引發極端降雨事件，造成河川堤防、路堤等之損壞頻傳，危及人民之生命財產安全。例如，93年敏督利颱風造成大安溪、大甲溪沿岸多處堤防損壞、98年莫拉克颱風中部濁水溪台16線集集水里段路堤7車15人落河、數間房屋毀損，以及南部曾文溪、高屏溪流域多處堤防遭水流沖刷損壞等。 破堤的原因頗多，其中河道短期一般沖刷扮演極為重要的角色。臺灣河道單場颱洪變量流期間所造成的短期一般沖刷，於洪水前後之河床高程差異可能不大，惟洪峰附近河床之沖刷深度可能相當可觀。例如，經濟部水利署水利規劃試驗所（以下簡稱本所）(2008)以沖刷磚柱法，量測辛樂克颱風台1線大甲溪公路橋下游河道深槽之颱洪最大一般沖刷深度高達4.5公尺，然退水回淤高程卻較颱洪前為高。因此，如何掌握颱洪河床之沖淤變動情形，提出適合本土河川一般沖刷深度之推估方法，供災後復建或新建工程之設計參考，誠為河川治理必須面對之一大課題。本計畫主要目的，乃針對颱洪期間河道之一般沖刷，研擬適當觀測技術，配合現場水理調查，獲致更充足實測資料，據以修正既有推估方式，提出適用於本土河川之經驗公式，俾利於現場工程實務之參考。

An understanding of the extreme riverbed scouring and filling characteristics for the typhoon-induced floods is always a major research topic for the riverbed regulation in the civil and hydraulic engineering. In particular, both general and bend scours for gravel-bed reaches have frequently induced bridge and levee failures, and caused loss of lives and severe property damages. Field observations were performed at meandering river reaches at Fongchou Levee, Dajia River, and Shuideliaw Levee, Choshui River. The riverbed scour observation techniques, basic hydrological and geotechnical data in the watersheds were reviewed and collected. Both numbered-brick column and wireless tracer techniques were used to measure the maximum general scour and the real-time scouring, respectively. Totally field data for four typhoon events (Soulik, Trami, Kong-Rey and Usagi) were collected during typhoon-season this year. Among them the flood peak for Soulik (6,692 m3/s) was the hightest, which had broke the 50-yr flood record in Dajia River. The maximum scour depth at the levee toe for Fongchou levee(attack angle 37°) was greater than 5.23 m, and the ratio of bend scour to general scour (dbs/dgs ) was greater than 3. The flood peak at Shuideliaw Levee was about 7,285 m3/s, and the corresponding dbs/dgs ratio was about 2. The general scour depths collected at Fongchou Station for the Typhoon Soulik and Shuideliaw Station for the Typhoons Soulik and Trami were used to compare with the empirical general scour depth formula developed based on the field data collected previously(Lu and WRPI,WRA 2003~2005; 2008~2010). In addition, data monitored by the wireless tracer during the typhoons were found to be consistent with the results of the numbered-brick column technique. The maximum general scour depth for Typhoon Soulik was found to occur near the flood peak. The field scouring and filling observation data collected during the four typhoon events will be beneficial to the verification of the laboratory bend scour study currently conducting by WRPI, WRA, the river regulation, and the disaster prevention applications.