圖書典藏及影音數位平台

澎湖為離島且附屬島嶼甚多，民國七、八十年代興建海堤甚多，為了解海堤興建對當地居之影響有必要作深入了解，對於海堤降低是否對地方安全之適合性尤甚；又澎湖尚有許多海岸線相關之海岸地形資料附之闕如，亦有必要建立相關資料以供國土資源規劃參考。

One, Origin and purpose This project will focus on general seawall around Tie-sian, Wu-dei, Si-we and An-jhai in Magong city in Peng-hu to reduce the feasibility study of seawall height. In order to achieve the purpose of the coastal protection and water-loving space, reduce the negative effect on the coast of the natural environment protection facilities. In addition, we conducted in Shan-shuei offshore breakwaters of topography changes before the construction of the comparison to evaluate the protective effectiveness of breakwaters. Plan scope Project area is coast of west of about 1 km in Shan-shuei, another coast is about 4 km from Tie-sian to Wu-dei. Two,Field investigate and data collection The topography measurement: Tie-sian to Wu-dei: Due to the coastal terrain for reef rocks, the overall topography is little change. The sea, topography in the depth of 0 to 5 m presents erode-sediment alternately, but is within 0.5 meters. Topo in Shan-shuei: Two survey in front of the beach in Shan-shuei wetland presents a 2 to 3 m erosion, zero-meter curve to retreat within 20 ~ 30 m, the depth between 0 ~ 5 m presented slight sediment. Tidal, wave, current measurement: Long-term tidal station (2015/6/1~2015/10/27): Long-men fishing port during long-term tide station observation of maximum tide level is 1.59 m, the lowest tide level is 1.42 m, and the largest tidal range of 2.54 m. Spring average high tide level is 1.02 m. Spring average high tide level is + 1.02 m. Tides are semidiurnal tide and main constituents for the M2 and K1. The twice survey of current (2015/6 and 2015/9):The direction of current in ESE at flood tide and ebb tide is WNW to give priority to, its range of 0 ~ 12.5 cm/s, surface current speed difference is not big, so middle and bottom is. Wave (2015/6/2 ~ 2015/7/6) for the first time during observing in wave height (H1/3) is 13.6 cm, in period (T1/3) is 3.42s, and direction is the NW and WNW. The second (2015/9/1 ~ 2015/10/7) wave height (H1/3) is 16.6cm, in period(T1/3) is 3.20s, wave direction is WNW, S, and NW. Sea bottom sediment: There two surveys in this year, 104/6 and 104/9. Sea area sampling includes three sections, a total of 9 points. High and low tide sampling contains 7 station, a total of 14 point. Sea area sampling: In Tie-Sian and Wu-dei bay is roughly silt, distribution trend is not obvious, with coarser size in the west of the surveyed area. Beach sampling: Particle size distribution is non-uniform and the coast by the wave filtering behavior is unobvious. Third,Shoreline change One-dimensional shoreline change for a long time Shan-shuei coast in the 12 years from 2003 to 2015, according to the results of the sedimental effect of the long-term analysis behind offshore submerged breakwater is obvious. Without influence of on- and off-shore under the abnormal climate, the coast of the can be maintain its function of the tourism and recreation. Tie-sian to Wu-dei coast is less affected by the wave, long-term results coast shoreline is no obvious change. Two-dimensional numerical simulation In the winter, NE and SE in summer under the wind waves, Tie-Sian and Wu-dei nearshore wave height is less than 0.1 m, current is lower than 0.01 m/s, the coastline is roughly stable. By 50-year-period, NNE and SSE of typhoon waves, only near Ma-gong current and wave is larger, the coastline is roughly stable also. Forth, Proposing of seawall improvement Safety assessment of overtopping The coast protections in Tie-Sian and Wu-dei under 50-year-period typhoon wave acting is no more overtopping, however, protections and excess seawall elevation is between 0.57 ~ 0.84 m, so the feasibility of the seawall elevation is not indeed have lower. Feasibility evaluation of seawall elevation reduced From Tie-Sian to Wu-dei coast, elevations of three seawalls deducted the overtopping under 50-year-period waves, the excess amount of the elevations respectively are 0.63, 0.57, 0.84 m. Because of excess is not large, and the slope type known that Tie-Sian and Wu-dei seawalls is belong to the smoothing surface, it’s less able to stop the overtopping. Under the consideration of long-term safety, it is suggested that maintain the current state of the seawall elevation, not be reduced. Fifth, Embankment Landscape Improvement Master Plan Environmental improvement concept and Landscaping strategies： (1) Integrate the landscape design; plant design and ecological engineering to rebuilt the coastal environment. (2) Using natural material and local elements to reduce the visual impact of the bare concrete embankment. (3) Through the overall creation of coastal environment to strengthen the connection of landscape and humanities.