||Conditions of the inshore hydrometeor and floating sand were changed due to the excessive development along sea, resulted in the problems of sea shore erosion. The most serious problem is the gradual loss of the Waishanding sandbank island, the largest offshore sand shoal of Taiwan. It is a nature protective shield of Yunlin-Jiayi coast. Losing this protection will cause a heavy threat to the high development and densely population coast area. Therefore, well understanding the topography transition of Waishanding sandbank island could be helpful to the development of coastal area and the security of residents’ lives and properties.|
Purpose of this research is to investigate the relationships among the square measure’s variation of Waishanding Barrier Island and sediment content of Chuoshui River, Peigang River, as well as relationship between sandbank measures and the construction of Mailiao Harbor. We inquire the hydrological data, collect the recent 20 years’ sand quantities transported by Chuoshui River and Peigang River, using the data table with the annual tree diagram to show the differentiation of various time phases, then to analyze and find that the sediments of these two river basins were supplied stably. Therefore we continue to explore the next hypothesis, that is, if there were significant differences in sediment deposition before, during and after the construction of Mailiao Port. By using 3D graphics software, nesting coordinates of Mailiao Harbor seabed topography, and demonstrate the comparative difference by way of 3D simulation drawings. We illustrated the recent 20 years’ evolution of seabed sediment situation surrounding the Mailiao Industrial Zone to observe that if the construction of the harbor facilities resulted in reducing/intercept the basin sand source by harbor silt, and lead to the gradual loss of the body of the Waishanding Island. By this experimental observation, we found that the longtime deposit of Mailiao Harbor is a positively existent phenomenon. These sand and gravel discharged from Chuoshui River basin, which originally should be drifted to Waishanding island, but to be held up by the Harbor.
From the former researches and literatures, we collect the surface area data of the Waishanding island up to year 1994. Also we calculated the square measures of the island after 1994. And then make a diagram of curve according to these data. By this experimental observation, we could find that the longtime deposit of Mailiao Harbor is a positively existent phenomenon. These sand and gravel deposited should be from sediment discharge of Chuoshui River basin, originally should be transported to Waishanding Barrier Island, but to be held up by the Harbor.
We calculate and make a diagram according to these square measure data. It can be clearly judged that the Island measure is affected by the construction of Mailiao Harbor and lead to area diminution.