낙동강 하구 사주의 생성/발달 메카니즘에 관한 연구

Abstract

Nakdong river estuary located at the south-eastern coast of the Korea shows very unstable topographical changes due to the various uses of the wet-land area, and/or changes of interactions between enviroments: such as sediments, wave and current. A lot of studies have been carried out on the development of shoal and topographical changes under the base of long-term changes; Geology․geography and short-term changes; coastal process as sediment transport and topographical changes. No one ,however, discussed clearly the generation and development mechanism of the shoal and wet-land development behind the shoal. The aim of the study is designated to clarify the mechanism of the generation and the development of the shoal in front of the beach face in relating with the new temporal scales. To get the goal, this study was carried out mainly by the field measurements on the changes of bottom topography and wave conditions around Jinudo where shoals is actively generating and developing in Nakdong River Estuary. To examine initial bar generation/development, We calculated beach profile change of plane slope(1/300) with numerical simulation. Finally, We analyzed to mechanism of bar generation/development with sediment volumes calculated by topography and depth survey, wave characteristics measured in the estuary. We compared with analyzed historical charts. Also, it would like to be discussed with initial generation condition and development process of the shoal. Main results obtained are summarized as follows by the step of study: 1) For using the SBEACH(Storm-induced BEAch CHange) model, beach change model, We estimated higher wave that can be propagated in Nakdong River Estuary at Geoje buoy between 1999 to 2009. The results of investigated past record are that wave direction to shore is mainly S, SW. Significant wave heights estimated Maximum wave is 2.21, 1.87, 1.82, 1.67 m and wave period is 10, 9, 8, 6 sec, respectively. 2) As grading analysis for sampled surface sediments in front of Jinudo and Sinjado, Median grain size() was distributed at 0.253∼0.276 mm in swash zone, 0.203∼0.256 mm from bar to inshore and 0.177∼0.190 mm from bar to offshore. 3) Wave measurements in April and May, 2007 was analyzed and showed the Maximum singnificant wave height and period is 1.40 m, 8.10 sec on April, 1.72 m, 7.42 sec respectively. 4) The results of surveyed topography change for seaward Jinudo and Sinjado show that averaged total volume change is 364.5 m3/m and maximum sediment transport rate is 0.507 m3/m/hr. In addition, We confirmed that new shoal in front of Jinudo generated and developed about 800～1200 m from coastline. 5) We are carried out of numerical simulation using SBEACH(Storm-induced beach change) model for examination of bar generation and development in Nakdong River Estuary. Comparison between Numerical model and observation, we confirmed that bar generated between 800 and 1200 m from coastline. 6) The calculation results of numerical simulation obtained that breaking wave height is 1.2 times of incident wave height and 1.5 times of breaking water depth for 1/300 plane slope.