本文旨在探討潛沒砂丘於斜坡上之演變過程。防止海岸侵蝕一直是海岸工程重要課題之一，傳統防止海岸侵蝕方法大多採用硬性工法，雖能有效防止海岸侵蝕，卻也衍生其他問題，例如加速海堤堤趾侵蝕、破壞海岸景觀等。基於自然保護原則，軟性工法漸漸成為海岸保護之主流，而潛沒砂丘則是軟性工法當中兼具養灘、防浪以及近自然等優點之工法。潛沒砂丘研究由來已久，然迄今吾人對其於近岸環境中之演變行為所知仍相當有限，因此本文乃嘗試以試驗探討潛沒砂丘於波浪作用下之演變過程及此一過程中之底質傳輸特性。
　　本文試驗在二維波浪水槽進行，水槽長25.0m、寬0.3m、高0.7m，實驗用砂為中值粒徑0.32mm，比重2.45之玻璃砂。試驗中觀測潛沒砂丘於1：10及1：40兩種底床坡度上之演變，而此兩種底床坡度則分別代表陡坡及緩坡。本試驗之底床質、砂丘形狀與Shields參數等皆與黃等人(2003)於平底床試驗者相同，只改變底床坡度，俾與黃等人(2003)二維水平底床潛沒砂丘演化之試驗作一比較。其中初始砂丘形狀乃選取兩組具有相同體績，但不同高度之砂丘進行試驗比較，而試驗條件之Shields參數介於0.038~0.095之間，每次試驗均以相鄰兩試驗之消失百分比差值小於0.01及修正之拋放點高程近趨於定值作為砂丘演變最終狀態之判斷標準。為減少波浪受砂丘及斜坡底床反射之影響，並選定試驗造波時間間隔為15分鐘，並於其間多次利用暫時停止造波時量測砂丘之形狀。砂丘地形量測乃是利用影像處理技巧獲得地形表面高程，其過程包括雷射光源定平校正、實際高程率定、影像擷取、分析及高程轉換等。
　　試驗結果顯示，潛沒砂丘置於斜坡上受到波浪作用時，砂丘之變遷過程係逐漸朝兩側拓展，但砂丘放置於較陡之斜坡上，底質受斜坡重力之影響較大，底質朝離岸移動之量相對較多，故潛沒砂丘並不適宜放置於陡坡上；反之，砂丘放置於緩坡上時，底質受斜坡重力影響較小，砂丘整體皆朝向岸移動。另者，砂丘於斜坡上之變形，略分為以下三階段 ：(1)於斜坡上形成小山丘狀(2)於斜坡上形成平台(3)沿底床攤平。
　　本文定義無因次累計輸砂率(消失百分比)探討砂丘演變與波浪條件之關係，並建立砂丘置於緩坡之輸砂率經驗式，而以臨界Shields參數(0.038)判定砂丘之穩定性。最後，本文整理數據分析砂丘消失百分比與砂丘拋放點高程、砂丘堤底寬之經驗式，以供工程實際之應用。

　　The present study depicts the evolution process of submerged berms on sloping bottoms. To protect beaches against erosion has been an important issue of coastal engineering design. Traditional coastal protection measures have been almost hard structures. However, they often cause other problems, such as corrosion on the toe of the sea-dike or unsightly scenery and so on. Standing on the point of view in harmonic with the natural, the construction method of coast protection has been led into soft-works gradually.
　　The experiments were conducted in a glass-side walled wave flume. The wave flume was 25m long, 0.3m wide and 0.7m deep. Grains of density, 2.45, and median grain diameter, 0.32mm, were used as the testing sediment. Two bottom slopes, 1:10 and 1:40 were simulated and they represented a steep and a gentle slope respectively. To compare with those completed under a constant water depth by Hwang et al. (2003), similar input conditions were used. Two initial submerged berm shapes with different berm heights were used under the same volume. The Shields parameter was between 0.038 and 0.095. The development of bottom geometry was measured by image processing method in every 15 minutes.
　　The result showed that when berm was placed on a sloping bottom, sediments would move offshore and onshore. As the berm was placed on the steeper slope, the influence of gravity became stronger and this caused more volume move offshore. It thus indicated that the berm was not suitable placing on a steeper slope.
　　In order to quantify the amounts of sediment transport from the berm, the percentage of disappearing, R, was defined. The percentage of disappearing increases with the Shields parameter. Since the berm is suggested to be applied on a gentle slope, an dimensionless averaged transport rate was formulated in terms of the Shields parameter. The critical Shields parameter, , was employed to distinguishing whether the berm is stable or movable. Finally, the result establishing the percentage of disappearing related to berm elevation, and percentage of disappearing related to berm width, which were applied on the engineering physically applied.

1 黃煌煇等，外傘頂洲保護措施進行數值分析及水工實驗研究計畫，成大水工所試驗報告第二七一號。(2002)

2 黃煌煇，黃志誠，黃國書“離岸潛堤在海灘侵蝕防治之最佳配置研究(Ⅱ)”，第二十六屆海洋工程研討會論文集。(2003)

3 Bagnold, R. A., 1963. “Mechanics of marine sedimentation,” in The Sea, Vol. 3, Interscience, New York, NY, pp.507-528.

4 Bagnold, J A., 1981. “An energetics total load sediment transport model for a plane sloping beach,”J. Geophys. Res. Vol 86,No. C11,pp.10938-10954.

5 Dean R. G.. and Dalrymple R. A., Coastal Processes with Engineering Application. Cambridge University Press. 2002.

6 Gunyakti, A., 1987. “Beach preservation by means of offshore submerged mound of dredged materials,”Proc. Coastal Zone ’87,American Society of Civil Engineering, New York, NY, pp.2461-2471.

7 Hallermeier,R. J., 1978 “Uses for a calculated limit depth to beach erosion.”Proc. Sixteenth Coastal Engineering Conference, American Society of Civil Engineering, NY,pp.1493-1512.

8 Hallermeier,R. J., 1980 “Sand motion ignition by water waves: Two asymptotes,” Journal of Waterway, Port, Coastal and Ocean Engineering, American Society of Civil Engineering, New York,NY,pp.229-318.

9 Hallermeier,R. J., 1981 “A profile zonation for season sand beaches from wave climate,” Coastal Engineering, Vol. 4,pp.253-277.

10 Hands, E.B., 1991. “Unprecedented migration of a submerged mound off Alabama coast,” Proc. Of the Twelfth Annual Conference of the Western Association and the Twenty-Fourth annual Texas A&M Dredging Seminar, Las Vegas, Nevada.

11 Larsen, M., and Kraus N.C., 1992. “Analysis of cross-shore movement of natural longshore bars and material placed to create longshore bars,” Technical Report DRP-92-5, US Army Engineering Waterways Experiment Station, Vicksburg, MS.

12 Mansard,E.P.D. and Funke E.R., 1980, “The measurement of incident and reflected spectra using a least squares method,” Proceeding of International Conference on Coastal Engineering,pp.154-172.

13 Meyer-Peter E.and Muller, 1948. “Formulas for bed-load transport,” Proc. Int. Ass. Hydr. Struct. Res.,Stockholm.

14 Emre N. Otay, 1994, “Long-term evolution of nearshore disposal berms,” Doctoral dissertation, University of Florida.

15 Sawaragi, T., Deguchi, I., and Park, S.K, 1988. “Experiment study on the function of submerged breakwater to control cross-shore sediment transport on artificial nourished beaches,” Coastal Engineering in Japan, Vol. 31,No. 1,pp.121-130.

16 Sleath, J.F.A., 1970. “Measurements of bed-load in oscillatory flow,”Proc.,ASCE, Vol. 104, No. WW4,291-307.

17 Vincent C.L.,and Briggs,M.J., 1989. “Refraction-diffraction of irregular waves over a mound,” Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 115, No.2, American Society of Civil Engineering,NY,pp.269-284.

18 Vera-Cruz, D., 1972. “Artificial nourishment of Copacabana Beach,” Proc. Thirteenth Coastal Engineering Conference,American Society of Civil Engineering, NY,pp.1451-1463.

19 Zwamborm, J.A., Fromme, G.. A. W., and Fitzpatrick, J. B., 1970. “Underwater mound for the protection of Durban’s beaches,” Proc. Twelfth Coastal Engineering Conference, American Society of civil Engineering, NY,pp.975-994.