Saemangeum Dike Research Articles

Decoupling natural and man-made impacts on the morphologic and sedimentologic changes in the tidal flats, Saemangeum area, west coast of Korea: Implications for benthic ecosystem stability

The morphodynamics of tidal flats responds mainly to the nonlinear interaction between tides and seasonal wave activity. Man-made activities such as reclamation further complicate the morphodynamics by disturbing physical processes acting on the tidal flats. Decoupling the anthropogenic influence from the natural forcing on the tidal-flat morphodynamics is crucial in assessing the adverse effects of man-made activities. Still, it remains a challenge due to inherent difficulties in characterizing spatiotemporal variability of the tidal-flat morphology. A three-year-long field survey using unmanned aviation vehicle (UAV)-assisted photogrammetry, sedimentological and benthic fauna data was conducted on the Shinsi tidal flats near the Saemangeum dike, west coast of Korea, to evaluate the relative significance between natural and anthropogenic influence on the morphologic changes of the tidal flats and benthic community structures. The Shinsi tidal flats exhibited non-seasonal sedimentation patterns and experienced overall erosion despite their sheltered location from the offshore waves. The Saemangeum dike contributed to the sustained erosion by reflecting offshore waves toward the tidal flats during winter to spring. Heavy rainfalls also promoted erosion of the tidal flats in summer. The small-scale embankments complicated the spatial sedimentation trend by protecting tidal flats from offshore waves or promoting erosion with shoaling waves. Notable mud deposition occurred during winter, incompatible with the general hydrodynamic condition, resulting from intensive dredging activity inside and outside the Saemanguem dike. The proliferation of the opportunistic species followed the mud deposition for several months until the enhanced wave activity removed the muddy sediments from the flats. Overall erosion dominance and the temporary occurrence of opportunistic species imply that the Shinsi tidal flats are subject to non-seasonal changes in sedimentology and morphology due to artificial structures and man-made activity, leading to the instability of the benthic communities in the tidal flats.

새만금 방조제 외측 조간대 저서환경 변화에 따른 대형저서동물 군집반응

Since the Saemangeum dike was constructed, artificial disturbances continue to occur in the outer area of Saemangeum due to the influence of irregular discharged water. Therefore, in this study, changes in benthic environment and macrozoobenthos community were investigated to understand the effect of environmental changes near the Saemangeum dike in the intertidal area around Sinsi-do. The mean mud content (MC) and loss on ignition (LOI) of the intertidal flat of Sinsi-do were 34.5±2.3% and 2.2±0.1%. A total of 161 species of macrozoobenthos appeared and polychaetes, crustaceans, and mollusks were dominated for 93.9% of the total number of species. Heteromastus filiformis that appeared at 94.0% of all the stations, appeared at the highest density in regions with relatively high MC. Arcuatula senhousia appeared in the region with the highest LOI, and Sinocorophium sinensis took the extreme dominance in the lowest MC. The highly polluted indicator species Capitella capitata, appeared temporarily in May 2019 with a maximum density of 48,564 indiv./m2, which is expected to have occurred temporarily through the discharged water from the inside Saemangeum dike where is relatively highly polluted. The intertidal tidal area near the Saemangeum dike has been influenced in suspended matters and sediments due to the discharged water after the construction of the embankment. Therefore, in the case of the intertidal area at the southern region of Sinsi-do where is adjacent to the Saemangeum embankment, it is considered that the irregular environmental changes caused by artificial disturbances directly affect the macrozoobenthos community.

Long-term Temporal and Spatial Morphological Variability of a Nourished Beach Using the EOF Analysis

Choi, T.J.; Choi, J.Y.; Park, J.Y., and Yang, Y.J., 2020. Long-term temporal and spatial morphological variability of a nourished beach using the EOF analysis. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 428–432. Coconut Creek (Florida), ISSN 0749-0208.Byeonsan Beach located at the west coast of Korea has been eroded seriously since 2006 after the construction of the Saemangeum dike. For this reason beach nourishment has been conducted from 2011 until 2017, and the result was successful by turning the beach in erosional phase of -4.1 cm/yr (2006 to 2010) into depositional condition of +2.0 cm/yr (2011 to 2017). Based on the EOF analysis of sixty-nine beach surveys during 13-year period from 2006 to 2019, the first four modes accounted for nearly 83% of total variability, leading to the interpretations of beach-nourishment effect, artificial construction, the influence of beach ridges migration, and irrigation-channel effect, respectively.

Changes in Fish Assemblages after Dike Construction in the Saemangeum Area

In the Saemangeum area, construction of a dike began in 1991 and was completed in 2006; desalination is currently being conducted. In order to investigate the influence of dike construction on fish assemblages, we analyzed the changes in fish assemblages using fish monitoring data accumulated before, during, and after construction of the Saemangeum Dike. Analysis of changes in the salinity of the Saemangeum Reservoir between 1997 and 2014 revealed that the overall salinity decreased, and this pattern became evident after completion of the dike. Long-term changes in fish assemblages were also confirmed in freshwater areas (Mankyeong and Dongjin Rivers) and the Saemangeum Reservoir. In freshwater areas, different fish assemblages were collected before and after dike construction according to NMDS analysis, and the proportion of freshwater fish continuously increased during analysis of ecological types. In the Saemangeum Reservoir, differences in fish assemblages were observed before, during, and after dike construction (PERMANOVA, F = 2.5325, P = 0.017). Moreover, the numbers of families and species decreased during dike construction; in terms of species composition, the proportion of brackish water fish increased, while that of marine fish decreased. Currently, a salinity gradient exists in the Saemangeum area between the rivers and the dike, and the M1-3 and D1-3 sites were classified as freshwater sites. Desalination is expected to increase freshwater areas in the future; as the change will happen over a very long period of time, differentiated management plans for each site of the Saemangeum area should be implemented through continuous monitoring.

Influence of dike-induced morphologic and sedimentologic changes on the benthic ecosystem in the sheltered tidal flats, Saemangeum area, west coast of Korea

The effects of dike construction on the geomorphology and sedimentary processes of tidal flats were investigated using high-precision topographic profiling, short cores, and unmanned aviation vehicle (UAV)-assisted photogrammetry to understand their adverse consequences on the benthic ecosystem. Tidal flats at the south of Shinsi Island near one of the two sluice gates of the Saemangeum dike, display prominent morphologic features known as shelly sand ridges or cheniers (sensu Otvos, 2000) that have migrated landward about 5 m in a year. The tidal flats were dominated by erosion from winter to spring and by deposition during the remainder of the year except for the periods of heavy precipitation when tidal drainage channels became larger and deeper by headward erosion. With overall coarser-grained surface sediments, the presence of actively migrating wave-built cheniers are in stark contrast to muddy tidal flats with a monotonous morphology before the completion of the Saemangeum dike in 2006. Southeasterly waves reflected from the dike during winter to spring when north to northwesterly winds prevail account for the wave-induced onshore sediment transport and rapid morphologic changes in the tidal flats despite their location protected from offshore waves. The diversity and biomass of major macrofauna species tend to increase during rapid erosion and decrease during rapid deposition, highlighting the anthropogenic effect of dike-induced physical disturbance on the benthic ecosystem in the otherwise sheltered tidal flats.

The Effects of Nourishments Using the Grain-Size Trend Analysis on the Intertidal Zone at a Sandy Macrotidal Beach

ABSTRACT Choi, T.-J.; Choi, J.-Y.; Park, J.-Y.; Um, H.-Y., and Choi, J.-H., 2018. The Effects of Nourishments Using the Grain-Size Trend Analysis on the Intertidal Zone at a Sandy Macrotidal Beach. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 426–430. Coconut Creek (Florida), ISSN 0749-0208. Byeonsan Beach is a typical macrotidal beach located at the west coast of Korea, which has been eroded continuously over the past decade since the construction of Saemangeum Dike. Starting from 2011, beach nourishment has been conducted annually on the Beach, with about 8 × 103 m3 of well sorted medium sands over the intertidal flat area. Primary purposes of this study are to understand the pattern of sediment transport using the grain-size trend analysis (GSTA) proposed by Gao and Collins (1992), and to evaluate the effect of nourishment procedures. Because of the mons...

The historical process of dredge fishery according to the construction of the Saemangeum Dike in Jeollabuk-do, Korea

The historical process of dredge fishery according to the construction of the Saemangeum Dike in Jeollabuk-do, Korea

Spatio-temporal variability of tidal asymmetry due to multiple coastal constructions along the west coast of Korea

At least 19 remarkable dikes and land reclamations have been constructed since 1970 along the west coast of Korea, which resulted in a reduction in tidal flat area of almost 50%. Both the reduction in tidal flats and the artificially simplified coastal line have distorted the spatio-temporal tidal hydrodynamics; to quantify this, we analyzed and evaluated tidal asymmetry by phase differences of the principal semi-diurnal lunar constituent M2 and its first over-tide M4. Moreover, we applied the ADCIRC model to quantitatively investigate near- and far-field impacts on tidal variations using the gamma parameter, tidal energy flux, and dissipation rate. Through this study, we found that the tidal regime around the Incheon harbor area in Gyeonggi Bay has changed from ebb- to flood-dominant due to multiple nearby reclamations, in particular to the construction of the Siwha dike. The Saemangeum dike caused near-field de-amplification of M2 but far-field amplification in the Shandong area of China. In addition to allowing a traditional asymmetry approach using phase difference, analyses based on the gamma parameter and tidal energy variations could distinctly improve spatial understanding of anthropogenic impacts on coastal tidal hydrodynamics.

새만금 방조제 내측과 외측 조하대 대형저서동물의 생태학적 연구

새만금 방조제 내측과 외측 조하대 대형저서동물의 생태학적 연구

새만금 수역 식물플랑크톤 현존량의 경년(2001-2010) 변화

Phytoplankton standing stocks had been researched in Saemangeum water region from 2001 to 2010 belong to the construction period of Saemangeum dike. The big change of phytoplankton standing stocks was shown, reaching 57 - 85,219 cells/ml according to the sampling seasons and stations. Inside of Saemangeum lake, a flux of fresh water and sea water made the phytoplankton standing stocks changed spatiotemporally. Meanwhile, the water bloom was frequent with continuously high standing stocks of fresh water stations and the standing stocks outside of the dike have been normal. In the long-term point of view, the standing stock did not show a big change comparing to the before and after of closing the dike(April, 2006).

Changes of fish community in the Mankyeong and the Dongjin River after construction of Saemangeum Dike

To monitor changes of fish assemblage, we selected 5 study sites in lower-middle part of the Mankyeong (3 sites) and the Dongjin (2 sites) River, and conducted field sampling 2 to 4 times per year from 2007 to 2009. Total sampled fishes were 66 species in 16 families. Cyprinidae (RA, 73.25%; 33 species) was dominant family. Dominant species was Zacco platypus (RA, 19.96%), and subdominant species was Chelon haematocheilus (RA, 11.11%). There were 18 Korean endemic species (RA, 12.56%) and one endangered species, Liobagrus obesus, was only found in the Mankyeong River. Three exotic species were found: Carassius cuvieri, Micropterus salmoides and Lepomis macrochirus. Fish assemblages showed similar occurrence patterns around the sampling periods. As a result of species number comparison between before and after dike construction at MR1 and MR2, there was no huge difference. When fishes were classified into two types, primary freshwater and peripheral species, using habitat characteristics, number of primary freshwater species was increased from 14 to 21 after dike construction. Moreover, relative occurrence rate of primary freshwater species was increased to 53% compared with before construction (18%). On the other hand, number of peripheral freshwater species was decreased from 29 to 19 after dike construction. As a result of cluster analysis using Jaccard method, fish community before and after dike construction was distinguished each other.

Sand Transport offshore the Saemangeum Dike, Midwest Coast of Korea

Abstract Geological investigations conducted over a vast seabed offshore the giant Saemangeum Dike on the west coast of Korea indicate that the surface area of fine to very fine sands has rapidly expanded southward in recent years (2002–2008). To unravel the processes responsible for this phenomenon, two field campaigns of hydrodynamic measurements were carried out at the same station with an instrumented tripod during May 2007 and January 2008. The measurements show the definite occurrence of wind-generated residual currents that were more distinctive and consistent during winter compared with the relatively weak, inconsistent analogues of the late-spring season. The simple algebraic calculations for bedload transport based on a cubic relationship between the bedload transport rate and steady currents suggest that the southward movements of surface sands result from interplay of wintertime residual currents and macrotidal currents. In addition, numerical model experiments illuminate that the dike constru...

새만금 주변 해역에서 박테리아 개체수 및 생산력의 공간 분포

Distribution of bacterial abundance and production was investigated in seawater around Saemangeum dike 7 times during March, <TEX>$2007{\sim}July$</TEX>, 2008. In the inner area of the dike, salinity variation was great due to river runoff from Mangyung and Dongjin Rivers and high chlorophyll a (chl a) concentrations up to <TEX>$124.3{\mu}g\;l^{-1}$</TEX> was found. In the outer area of the dike, salinity was higher than in the inner area of the dike, and chl a was lower up to 10 times than in the inner area of the dike. Thus, the area of Saemangeum showed meso- to hypereutrophic conditions. Bacterial abundance and production ranged from 0.3 to <TEX>$4.3{\times}10^9\;cells\;l^{-1}$</TEX> and from 5.2 to <TEX>$570 pmol\;l^{-1}h^{-1}$</TEX> in outer area of the dike, respectively, while in the inner area of the dike bacterial abundance and production was 3 to 4 times higher (<TEX>$0.4{\sim}12.7{\times}10^9\;cells\;l^{-1}$</TEX> and <TEX>$12.3{\sim}1309\;pmol\;l^{-1}h^{-1}$</TEX>, respectively) than those in the outer area. In both areas, bacterial abudance and production was highest in summer and lowest in winter. However, the variations of bacterial parameters was very large in each season. These large variations seemed to be related with the supply of organic matter. Bacterial abundance and production showed significant negative correlations with salinity in the inner area, suggesting that allochthonous organic matter input by river runoff could be an important factor in regulating the distribution of bacterial abundance and production. In addition, bacterial production also correlated positively with chl a in the inner area, suggesting that autochthonous substrate might be another regulating factor of bacterial growth in the area. These results suggest that the supply of both allochthonous organic substrates introduced by river runoff and autochthonous substrates produced by phytoplankon could be important in regulating bacterial growth and utilization of organic matter in the area. Thus, to manage water quality in the inner area of dike, it seems to be important to lower the load of both organic and inorganic nutrients from adjacent rivers.

Tidal modification and its effect on sluice-gate outflow after completion of the Saemangeum dike, South Korea

This study examined tidal modification and change in tidal currents caused by the construction of the Saemangeum dike, based on field observations and a numerical model. The Saemangeum dike was completed in April 2006, enclosing an estuarine area along the mid-western coast of South Korea. After closure of the dike, the tidal range outside the dike decreased slightly but significantly, while the inside tidal range decreased drastically. The numerical model results show that the dike construction has influenced tidal energy propagation and the tidal system in the Yellow Sea. The tidal current speed near the dike decreased abruptly following closure of the dike, except in front of the sluice gates. Since completion of the dike, outflow water discharged from the sluice gates has longer residence times due to the weakened tidal current; the change in the tidal current field has also caused greater northward expansion of outflow water. The sluice gates release fresher water, which spreads over the sea surface mainly by inertial momentum near the gate; this water is then gradually mixed with sea water farther from the gate. The less saline, possibly more contaminated outflow impacts the marine environment near the Saemangeum dike. Controlling the discharge and gate-opening timing can partially mitigate these impacts on the marine environment.

새만금 방조제공사로 인한 조하대 환경과 저서동물 군집 변화

The Saemangeum project is one of the biggest reclamation efforts in Korea and may cause coastal ecosystem change due to altered environments and habitat loss. Since February 2002, benthic environment and community structure in the Saemangeum subtidal area were studied to assess the influence of the project on macrofaunal community. The result of seasonal study from February, 2002 to August, 2005 is reported here. Overall, changes of species numbers and dominant species of benthic animals in the periods before (1988) and after (2002~2005) the Saemangeum dike construction were not evident both inside and outside the dike. However, local environmental and community change were noted. The partial completion of Saemangeum dike (4 th dike) in June 2003 altered water circulation and sediment deposition patterns both inside and outside the dike. Fine sediment was accumulated inside and outside the 4 th dike while coarse sediment dominated near the main channel (Sinsi gate). Benthic community responded to the altered sediment type in these areas. Species number and diversity in both site was low compared to other sites. The dominant species in these areas were composed of the benthos that had not commonly occurred in the Saemangeum subtidal area.