圖書典藏及影音數位平台

由於東港至林邊溪之間，因屬地層下陷區，自民國70年以來便陸續興建各項保護工程，並不斷加高海堤，且沿線興築離岸堤，預定進行塗家厝以南至林邊溪以北之海岸基本資料調查，以瞭解本段海岸變遷現況，提供未來擬定海岸防護對策參考之依據。

Origin and purpose Pingtung coast in the past, large farming fishery development, and the excessive use of groundwater has caused severe ground subsidence. With major rivers such as the Kaoping, Donggang and Linbian River, sediment can’t recharge near the coast effectively and it makes Pingtung coast erosion. Sea level reaches to in front of the seawall foundation during flood tide, whenever a typhoon waves overtopping the seawall and its impact caused the destruction of protections, road slope and houses. In light of this, since 1981 the construction of the coastal protection engineering, higher seawalls in the affected seawall, or build offshore breakwaters protection facilities, etc. In recent years, the Pingtung 7th River bureau actively handle landscape improvement and basic data monitoring survey and so on related work, proposing appropriate feasible coastal protection strategy, coastal environment in order to achieve sustainable utilization and management goals. South of Pingtung Tu-jia-cuo and Lin-bian River, the past lack of marine meteorology related data from field investigation and study, need to coastline change of for a long time for analysis. Plan for this year from south of Tu-jia-cuo to Lin-bian River coast of basic investigation understand coastal change, in order to provide the basis of future coast protection countermeasures. Project scope This project area from south of Tu-jia-cuo to Lin-bian River coastline length is about 5.2 kilometer Site survey and data collection A. Topography measurement This year in April and September twice measurement, suffered Soudelor and Lotus typhoon influence. From Nan-pin-li to Ci-fong seawalls all along the beach erosion, erosion rate is about 0.2 m to 2 m. Sea area, the back of the offshore breakwaters sedimentation trend, slightly, the breakwaters for side of the toe elevation - 5 m in slightly erosion. B. Tide, wave, current data Tide: Dong-gang station is located in Dong-gang fishing port, near Tu-jia-cuo, and observation time in Lin-bian station for a long time. Dong-gang station in September observed during 1998 to 2015, the highest high water level of 1.22 m, the lowest low of 0.81 m, the average tidal range of 0.59 m. Current: During the summer, near Dong-gang waters the current distribution between 10 to 60 cm/s, current for SE, SSE and NW direction. During the winter in the northeast monsoon, Dong-gang area current between 0 to 63 cm/s, the current to the distribution of a wide range. Wave: Da-peng-wan buoy data show that maximum probability 23% for cycle 4 ~ 6 seconds, wave range of 0.6 ~ 0.8 m high, and the main wave direction within the range of the wave height for W, WSW and WNW. Marine sediment: This year we are in April and August respectively to investigate, sea area sampling 6 sections, a total of 24 points, high and low tide level sampling 11 stations, a total of 22 points. The sea area size contour somewhat parallel to the shoreline, Shuei-li seawall north of particle size of 100 microns sediment distribution and - 10 m to 15 m water depth contour direction is roughly parallel. The beach particle size distribution of high and low tide level roughly from Ci-fong to Shuei-li near to the north-south degressive trend. Coastal landform change One-dimensional model of long-term change Analysis results showed that from 2007 to 2011, in the meantime, coastline is erosion trends, and from 2005 to 2007 and from 2011 to 2012, shows the tendency of sedimentation. Another this area during Morakot hit is affected by the typhoon waves, cause the erosion of the sand tongue behind the offshore breakwaters, the whole coastline of retreat. But in Morakot hit in April of next year, a total of eight months after the monsoon, according to this coastline back sedimentation phenomenon, some part of the coastline has back to state before it hit. Two-dimensional numerical simulation of coastal change Only in winter under the action of wind and waves, nearshore current speed at north of Lin-bian, offshore side of breakwaters, about 0.12 m/s, most of the remaining less than 0.1 m/s. Summer under wind and waves, the location of the nearshore current speed faster mostly located in offshore side of Shuei-li breakwaters, about 0.12 m/s, only parts in onshore of Tu-jia-cuo and Shuei-li faster. For 50 return period, according to the results of simulation analysis of SW direction under typhoon waves of coastal characteristic, nearshore wave height in offshore side of breakwaters mostly between 2.0 to 2.0 m, onshore side of breakwaters are all less than 2.0 m. Nearshore current of offshore side in Shui-li is about 0.9 to 1.2 m/s. By 50-years-period typhoon wave of SW direction, in ShuiLi offshore side all appear stability, offshore breakwaters show that to achieve the effect of damping wave. But Tujiacuo coast were erosion, and between coastal and breakwaters are sedimentation. Evaluation of seawall protection Under 50-year-period typhoon waves, project area at 11 sections has no possibility of overtopping. Testing analysis of coastal protections Seawall elevation In 2015,seawall set up a new control point TL03 230 m north, south to the Lin-bian river, about four seawall total length of about 620 to 700 m elevation less than + 5.00 m, with the forest north seawall of Lin-bian river lowest elevation is about 4.33 m. Specifications of offshore breakwaters Offshore breakwaters of original design height of 2.2 m, the measured water level Z 1/10 is between 0.9 to 2.63 m. 45 offshore breakwaters and the design elevation of the divide between 1.3 m and 0.43 m, according to most offshore breakwaters have obvious subsidence, which is most obvious between Tu-jia-cuo to Ci-fong. The original length of 80m, the results shows the breakwaters length more than 90m of a total of six (91to 95 m). There are 13 offshore breakwaters length is shorten, reduced the average is about 2.3 m, 32 more offshore breakwaters length increases. There are 27 offshore breakwaters widths narrow, 18 offshore breakwaters width increases.