Detecting the intertidal morphologic change using satellite data

The objectives of this study were: (a) to generate an intertidal digital elevation model (DEM) using waterlines extracted from Landsat TM and in situ ground levelling data; (b) to quantitatively estimate morphologic change from the generated DEMs for the years 1991 and 2000; and (c) to evaluate the chenier migration in the tidal flats of Gomso Bay, Korea. On extracting the waterlines, we considered the tidal flat environments, such as tidal conditions, remnant surface water, suspended sediment, and exposure time. Ground levelling was carried out along one line in 1991, and two lines in 2000. From the extracted waterlines and ground levelling data, we succeeded in generating intertidal DEMs with an accuracy of 10.9 cm r.m.s. overall, and 7.3 cm r.m.s. in the lower tidal flats. The morphologic changes estimated by subtracting the two DEMs showed an erosion rate of −9.0 cm over 9 yr that corresponds to an annual mean morphologic change budget of −309,865 m3/yr. Overall, the Gomso tidal flats can be defined as an erosion-dominant environment. The changes with respect to the sedimentary facies were also evaluated as: (a) the sandy silt flat had a sedimentation rate of −3.4 cm over 9 yr that corresponds to an annual mean budget of −52,552 m3/yr; (b) the silty sand flat had a sedimentation rate of −14.3 cm over 9 yr that corresponds to a mean erosion of −197,927 m3/yr; and (c) the sand flat had a sedimentation rate of −11.8 cm over 9 yr that corresponds to a mean change of −58,808 m3/yr. The results comply with the general rules of sedimentology. We also investigated the chenier migration, which is the most dynamic geomorphologic change in the tidal flats. Chenier is usually composed by sand and shell as a result of coastal progradation in sand, and it is dominantly fed by sediments transported by long-shore currents. The chenier was found to have migrated about 148 m landward over 6 yr. The results demonstrate that satellite remote sensing is an efficient and effective tool for a long-term morphologic change estimation in tidal flats.