Study of River Bed Variation Measuring Techniques and Estimation Methods

Abstract

The real-time riverbed scour and deposit monitoring instruments (water and soil inter-facer) for field observations relating to the maximum general scour depth were improved. In addition, a series of experiments were conducted in the laboratory and field for the “water and soil inter-facer” in order to assess the feasibility of the real time dynamic general scour measurements. There are four major tasks in this test, including elevation of water level, riverbed elevation, water-proof ability, and wireless data transmission. The results show that the “water and soil inter-facer” is suitable for measuring the dynamic general scour in all the tests. Also, it is an effective field measuring technique that gives riverbed variation measurements with good precision. The water level obtained from the “water and soil interface monitoring system” is consistent with that measured by the Fourth River Management Bureau (WRA) for typhoon Matmo (2014).Also the riverbed level of the water and soil inter facer is consistent with that measured by using wireless tracer for typhoon Matmo (2014). Measuring errors of riverbed variation are within the allowable error for typhoon Matmo (2014). Overall, the system is feasible to measure the real-time dynamic general scour depth of riverbed during the flood event. The remaining problems to be overcome include the protection and improvement of the stability for the system. A general scour depth estimation formula is developed by using traditional nonlinear regression analysis method with the observed data from the Cho-Shui River. The accuracy of the results from the formula developed in this project is the best among all of the estimation formulas compared. As the observed data is still limited, more data should be collected during typhoons in the future for further verification.

為改進現有之河道最大一般沖刷深度量測技術，本文研發即時動態河床沖淤之量測儀器-水土介面儀， 進行水土介面儀之室內、外各項測試，包含水位、砂位、防水功能、無線傳輸等功能。結果顯示水土介 面儀具有明確水位、砂位鑑別度，各項測試量測精度頗高。水土介面儀之防水功能與無線傳輸功能頗佳， 已能有效且精確的應用於河床沖淤動態變化之量測。 應用於麥德姆颱風(2014)時，發現水土介面儀量測所得水位與第四河川局量測值具有一致性。砂位則 與無線追蹤粒子測得之沖刷深度約略相當，其水砂位誤差均在合理範圍內。整體而言，水土介面儀應用 於洪水時期量測河川即時動態河床沖淤變化深具可行性，惟如何確保儀器安全與穩定為待克服之問題。 本研究針對濁水溪現場實測資料利用 SPSS 進行非線性迴歸分析，並與國內外各家公式進行比較分析，發 現本計畫研提之推估公式，其推估之河道一般沖刷深度吻合度最佳。惟因目前實測資料有限，未來應蒐 集更多天然河川之颱洪觀測資料，以供進一步之驗證。