• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.761-770
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• 2014

In september 2004 and 2006, topographical and sedimentological survey were carried out using multibeam echosounder, which were to investigate shape characteristics, temporal changes and control factors of the subaqueous dunes in the southern Gyeonggi Bay. The present tidal current and sedimentary characteristics of study area make conditions that the sizes (length and height) of large subaqueous dunes are developed and maintained sufficiently. The change of sedimentary characteristics over time, the decrease in grain size causes reduction in the height of very large subaqueous dunes. Therefore it shows that the grain size of surface sediments is a primary control factor in defining subaqueous dune sizes in the study area.

• Journal of the Korean earth science society
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• v.31 no.6
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• pp.608-624
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• 2010

Morphological surveys of southern Gyeonggi Bay in the Yellow Sea were conducted for2 years (2006 and 2007) by using multibeam echosounder for investigating the morphological features of bedforms. The subaqueous dunes are shown in various shapes (A~F type) and continuous spectrum of heights and lengths of transverse-to-current dunes on the wide range of sedimentary types. The height-length power-law correlation of dunes is $H_{mean}=0.0393L^{0.8984}$ (r=0.66). The comparison between Flemming (1988)'s correlation and height-length correlation of this study indicates that the subaqueous dunes in the study area are equilibrated in the present hydrological and sedimentary environment. The major controlling factors to thedevelopment and maintenance of subaqueous dunes are both strong tidal currents and the abundant availability of sand. Marine sand mining, artificial impact, changes from the original shape to an irregular shape of the subaqueous dunes with a shorter wavelength and lower height, which has influence on the development and maintenance of bedform because it causes a decrease of the availability of sediment. Water depth and sedimentary characteristics, and othercontrolling factors seem to play limited roles in the development and maintenance of subaqueous dunes.

• Ocean and Polar Research
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• v.32 no.4
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• pp.337-350
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• 2010

This study conducted sedimentological and geophysical surveys for 3 years (2006-2008) in southern Gyeonggi Bay, Korea to elucidate temporal changes in subaqueous dune morphology on a sand ridge trending northeast to southwest that has been excavated by marine sand mining. The sand ridge (~20 m in height, ~2 km in width and 3~4 km in length) has a steep slope on the NW side and a gentle slope on the SE side, creating an asymmetric profile. Large (10~100 m in length) and very large (>100 m in length) dunes occurring on the SE side of the ridge show a northeastward asymmetrical shape, whereas dunes on the NW side destroyed by marine sand mining display a southwestward asymmetry. The comparison between Flemming (1988)'s correlation and the height-length correlation of this study indicates that tidal current and availability of sand sediment are major controlling factors to the development and maintenance of dunes. Depth and sedimentary characteristics (grain size) are not likely to be major controlling factors, but indirectly influence dune growth by hydrological and sedimentary processes. The length and the height of dunes decrease toward the southeastern trough away from the crest of the ridge. These features result from the decrease of tidal current and sediment availability. The length and the height of dunes on the southeast side decrease gradually over time. This is a result of the interaction between tidal current and the decrease in sediment availability due to sediment extraction by marine sand mining. Marine sand mining has destroyed the dunes directly, causing irregular shapes of shorter length and lower height. The coarse fraction of suspended sediments is transported and deposited very close to the sand pit. By contrast, relatively fine sediments are transported by the tidal current and deposited over a wide range by the settling-lag effect, resulting in a decrease of sediment grain size in the area where suspended sediments are deposited. In addition, marine sand mining, decreases the height of dunes. Therefore, morphological and sedimentological characteristics of dunes around the sand pits will be significantly changed by future sand mining activities.

• Journal of the Korean Geographical Society
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• v.39 no.2
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• pp.269-282
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• 2004

Luminescence dating of a coastal dune from the Shindu dunefield on the T'aean Peninsula shows that deposition of the dune structure began about 500-600 years ago. The lower section of the dune has remained stable since then but the upper part yields an age of about 30 years, suggesting reactivation or additional deposition since the 1970's. The two samples that were collected from the lower part of the dune at depths of 3.5 m and 2.0 m below the surface differ by an age interval of about 50-70 years. This indicates a net depositional rate of around 2.5 cm a year which is relatively slow for a coastal dune. Whilst only one dune structure has been dated for the time being and even though the dunefield was probably established much earlier in the Holocene, the OSL ages obtained demonstrate that some dunes in the area could be younger than 1000 years. Such chronologies point to a dynamic environment where the dune structures are not permanently fixed. Sedimentological properties of the dune sands are consistent with those of particles initially deposited under subaqueous conditions and then later transported by wind.