An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same...An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same time, seawater tempera- ture, conductivity and pressure were measured. Us- ing a data sampling rate of 4 Hz, the high-frequency pressure signals in response to water surface fluc- tuations were recorded and subsequently trans- formed into wave parameters. The analytical results show that the apparent bed roughness length has a magnitude close to the height of sand ripples, which is much larger than the grain size diameter. The bot- tom shear stress associated with current-wave in- teraction is higher than the tidally-induced stress and intensified turbulent mixing and resuspension. Fur- thermore, several suspended sediment concentration peaks occurred during a tidal cycle, which can be related to strong turbulence near the bed caused by frontal tidal currents and the enhanced resuspension; advection and extreme weather conditions (e. g. storms and strong winds) also played an important role. Finally, large net suspended sediment fluxes were observed to present when the flood or ebb currents prolonged, i.e. the flow became quasi-unid- irectional during a tidal cycle. In general, the MIDAS- 400 is a suitable tool for high-resolution data collec- tion for the situations of combined current-wave ac- tion over intertidal flats; the data obtained can be used to analyze the processes and mechanisms of material transport.展开更多
A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10,...A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which in- dicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30—150 kg·m?1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2×104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topog- raphy of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the cal- culated bedload transport, and the grain-size trend vectors for the spring tide are larger than those forthe neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40576040,40231010 and 40206006).
文摘An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same time, seawater tempera- ture, conductivity and pressure were measured. Us- ing a data sampling rate of 4 Hz, the high-frequency pressure signals in response to water surface fluc- tuations were recorded and subsequently trans- formed into wave parameters. The analytical results show that the apparent bed roughness length has a magnitude close to the height of sand ripples, which is much larger than the grain size diameter. The bot- tom shear stress associated with current-wave in- teraction is higher than the tidally-induced stress and intensified turbulent mixing and resuspension. Fur- thermore, several suspended sediment concentration peaks occurred during a tidal cycle, which can be related to strong turbulence near the bed caused by frontal tidal currents and the enhanced resuspension; advection and extreme weather conditions (e. g. storms and strong winds) also played an important role. Finally, large net suspended sediment fluxes were observed to present when the flood or ebb currents prolonged, i.e. the flow became quasi-unid- irectional during a tidal cycle. In general, the MIDAS- 400 is a suitable tool for high-resolution data collec- tion for the situations of combined current-wave ac- tion over intertidal flats; the data obtained can be used to analyze the processes and mechanisms of material transport.
基金The study was supported financially by the National Natural Science Foundation of China （Grant Nos. 40206006 and 40231010）.
文摘A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which in- dicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30—150 kg·m?1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2×104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topog- raphy of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the cal- culated bedload transport, and the grain-size trend vectors for the spring tide are larger than those forthe neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.
