圖書典藏及影音數位平台

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，如何掌握颱洪期間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。 本計畫屬颱洪河道現場觀測研究工作，前置及量測作業頗耗費人力，加上動床觀測技術與分析需求，須借重專家學者及實作經驗者，據以提昇計畫品質及其完整性。本所囿於既有專業人力和技術考量，擬採委託專業服務方式辦理。

Field data for four events were collected during the flood period, including 515 extremely heavy rain ( Qp = 1,763 m3/s; May 15, 2014 ) downstream of Shikang Dam in the Dajia River Basin, and 519 extremely heavy rain ( Qp = 1,446 m3/s; May 21 ), 67 heavy rain ( Qp = 2,008 m3/s; June 7 ), and Typhoon Matmo ( Qp = 4,980 m3/s; July 23 ), in the Choshui River. Accordingly, empirical formulas were derived. A training course was held at Water Resources Planning Institute in September for transferring the technology.The major accomplishments of this project are briefly summarized below:1. Collection of general scour data in the literature General scour data and formulas in the literature were reviewed. Among others, two maximum general scour depths data were collected by Wang ( 2011~2014 ) in the sand-bed river reach near the Chu-Chiang Bridge downstream of the Choshui River, including Typhoon Saola ( dgs = 3.08 m, Qp = 17,000 m3/s, tp = 6 hr, 2012 ), and Typhoon Matmo ( dgs = 1.24 m, Qp = 6,000 m3/s, tp = 9 hr ). These data are useful for the future revision of the general scour formula. 2. Collection of hydrological and physiographic data Both hydrological and physiographic data, including variations of river cross-section, bed material etc., near the study river reaches for the recent years were collected and analyzed. 3. Observations of general scour depths and hydraulic information Scour depth for both nearly straight and curved river reaches were observed. Hydraulic information including the average water surface slope in the curved river reach were measured, which can be used to compare with the results of the physical model conducted by the researchers in the WRPI. In addition, data related to critical flow discharge (incipient motion) for the top brick of the brick column, average water surface velocity and the dynamic scouring of the riverbed were also successfully collected for Typhoon Matmo (July 23, 2014).4. Development of the general scour depth formula With consideration of the parameters related to flow, sediment and effective time to peak, general scour formulas in both dimensionless and dimensional forms were derived. Data collected previously in both sand-bed and gravel-bed reaches in Dajia and Choshui Rivers were also included to widen their applicability.5. Educational training course and technology transfer A training course was held in WRPI on Sept. 30, 2014 to transfer the technology developed in this project. Professor Chiew from Nanyang Technological University, Singapore was invited to give a lecture on “The probability of sediment entrainment from a rectangular cavity.”