圖書典藏及影音數位平台

本計畫旨在對本海岸段離岸堤群的建構成效進行探討，透過資料蒐集分析，以探討水深變遷特性分析及離岸堤群現況探討，並依據所提出之改善對策進行斷面水工模型試驗，以驗證改善方案之可行性，以作為未來離岸堤群改善工程之參考。

This plan aims to study the effects of offshore breakwaters to improve the Wenfeng coastal zone, including this seawall for two-dimensional hydraulic test and benefit evaluation of protection of offshore breakwater. Monitoring and investigation are from Linbian river south to Wunfong seawall. The area was selected for four cross-section topography of hydraulic test. Works Including: (1) basic data collection analysis, (2) topography survey and analysis, (3) characteristic of topography change, (4) the causes of subsidence of offshore breakwaters, (5) Two-Dimension hydraulic test, (6) numerical model analysis. Based on the image analysis by Multibeam Echo Sounding (MBES) survey at offshore breakwaters toe, there is mostly sand deposition in front of Wunfong submergeds. The depth near offshore breakwaters at Huluwei is deeper, the topography around the toe of offshore breakwaters is present sinking. The water deep in front of the breakwater at Dajhuang is deeper, there are armor blocks scattering in front of the submergeds. It’s deeper around the offshore breakwaters at Fanzihlun, armors near toes are stacking completely. Presently, there are five offshore breakwaters near Wunfong seawall and the known elevation (+ 2.2 m) difference are more than 1.20 m. The rest from the Sialiao and Dajhuang to Fanzihlun seawalls of offshore breakwaters and the known elevation (+ 2.2 m) are less than 1.20 m. Offshore breakwater near Sialiao seawall under the number # 40 is higher than the known design (about 0.22 m + 2.2 m). The causes of subsidence of offshore breakwaters are: (1) Near coastal area the long-term over-pumping groundwater formed the ground subsidence and cause beach retreat between Linbian river and Sialiao and subsidence. (2) The instantaneous subsidence of the breakwater body weight: In the results of hydraulic model test and numerical simulation can display wave action began, there is phenomenon of scouring around the offshore breakwaters and subsidence. (3) Under the long-term action of wave it due to scour at toe and trigger the subsidence: By image analysis of the MBES at toe we can see more. Characteristics of topography change, coastline in 1975 and a maximum distance of current Wunfong seawall is up to 120 meters, in 1982 coastline (green) back to the present Wunfong and Huluwei seawall. Offshore breakwaters have been completed in 1987 ~ 1996, in 1996 there were a few sedimentations from behind the breakwaters. In 2011 near Linbian river have been desilted and there was artificial beach at Wunfong coast. In 2014 shoreline and NO.5 ~ 9 offshore breakwaters are linked together. Improvement suggestions are given by hydraulic test: (1) The No. 10 offshore breakwaters section can be used in the proposal I. (Seven-river bureau recommended inner-layer offshore breakwaters to offshoring). And desilting sand from the Linbian river can be banked up in the lining of the original offshore breakwaters. (2) The offshore No. 15 breakwaters can be use section No. 10 of the proposal I. (recommended inner-layer offshore breakwaters to offshoring). (3) The No. 48 offshore breakwaters, need to strengthen the new covering layer, and adding 5T-basing protecting around offshore breakwaters. (4) No.52 offshore breakwater in accordance with the hydraulic test results can be maintain current status. The numerical model analysis: Lengthening and heightening the offshore breakwaters in the sea-side, can reach the effect of damping the incident wave, causes the incident wave damping effect and smaller scouring near the blocks in front of the seawall. When waves act, topography change and scour phenomenon is obvious Waves act. after the terrain changes has eased, a stable situation gradually. Then the topography changes have been gradually slow and steady. Considering on improvement of Wunfong offshore breakwaters: First, offshoring the inner No. 14 breakwaters with concrete blocks locating about 134 m and 2 m depth, body length of about 70 m, elevation of about 0 m. Again from the outer breakwaters No. 2 and seawalls or outer No. 2 offshore breakwaters offshoring 100 m, elevating about 0 ~ + 2 m, dredging the earthwork about 5000 m3. By dredging earthwork in 20-ton truck loading to the inner offshore No. 14 breakwaters dumping, raise beach area by the first beach contour 30 m + 2 m in width at the laid of the platform. An area of beach nourishment is contour + 2 m and 30 m platform off the coast. With 1/16 slope topography laying to No. 10 and No. 11 offshore breakwaters, the alongshore width of about 120 m, keep beach earthwork about 5000 m3.