광안대교 인근 해역 표층퇴적물 입도조성 및 유기물의 시·공간적인 분포특성

Abstract

Sediment texture and organic content in Suyeoung Bay nearby Gwangan Bridge area were monitored from August 2009 through May 2010, in order to investigate its temporal and areal variation. And the general trend of sediment transport was examined using a numerical model (Gao and Collins, 1992) based on the surface sediment texture, in order to get some insight on the stability of the area in terms of sedimentation and/or erosion. Seasonal distribution of suspended sediment concentration was also determined. During the four times of observations, distribution pattern of mean grain size showed no remarkable seasonal difference, mostly ranging the coarsest (3∼5 phi) close to the Gwanganri beach while the finest (5∼6 phi) at the entrance of the Suyeoung River estuary and the center of the bay. A meager trend of sediment transport toward the coast was observed from the numerical model, which suggests that the study area was in a fairly stable condition without a significant erosion. It was noted that no major typoon passed through the Gwanganri area, which might also be responsible for the little seasonal variation. Organic contents in the sediment showed a highly correlated areal distribution with little seasonal variation. The average values of ignition loss and COD were in the range of 1.9∼13.1% and 2.7∼44.8 ㎎/g, respectively. Even though most COD measurements (137 out of 160) fall below the pollution limit (20 ㎎/g by Japanese standard), sustaining monitoring and control will be necessary because high values were observed in the estuarine mouth and adjacent bay area. Suspended particulate matter (SPM) were highly variable with no clear distribution pattern, seasonally and spacially. When compared with the previous studies (of 1979 and of 1992), the SPM and organic contents seemed to have a decreasing trend. Assumingly, the operation of the sewage treatment plant in Suyeoung River, the renovation project of the riverside and the recent dredgings between Wondong Bridge to the Suyeoung 2nd Bridge could be, at least partially, attributable to the reduction of the values. Also, by comnparing with two previous studies (of 1990 and of 1998), it was noted that the mean grain size of the surface sediment increased slightly, which might suggest that the role of Suyeoung River as a source of fine grained sediment has been decreasing. From the observations that there were no significant seasonal variation in term of sediment texture and no evident sediment transport trend, it can be suggested that Suyeoung Bay and Gwanganri areas will be in a stable sedimentary condition, if no artifical disrupt (such as construction of Gwangan Grand Bridge) and/or natural disturbance (such as typoon). Still, further quantitative studies on the sediment budget in the Bay area are required to clarify the suggestions from this study.