科研之友
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摘要
Intertidal flats are key elements in marine environments; they consist of regions with rich bioactivity and also contribute to water purification. Recently, it has been demonstrated that benthic activities in intertidal flats are closely related to geoenvironmental characteristics. The purpose of this study is to investigate the tidal flat stratigraphy which should be strongly affected by the geoenvironmental characteristics. We examined the shear wave velocity/stiffness structures of intertidal flats by a surface wave method called the multichannel analysis of surface waves (MASW) in order to identify and describe the cross-shore and alongshore tidal flat stratigraphy. Field surveys were carried out on a natural sandflat, natural mudflat, and artificial layered sand-mud flat during the spring tides in summer when these flats were exposed. The MASW has proved to be a very useful method to effectively survey the stratigraphy of various types of intertidal flats. This method is widely acceptable to nature because it does not have any harmful impacts. The tidal flat stratigraphy obtained by the MASW was consistent with the morphological soil structures that manifested themselves under relevant geoenvironmental dynamics. In the sandflat, the formation of stratigraphy obtained by the MASW (as distributions of the shear wave velocity/stiffness) and by soil sampling and physical soil tests (as distributions of the void ratio) can be attributed to the cyclic elastoplastic contraction of the soils that are subjected to various suction dynamics under tide-induced groundwater table fluctuations. In the mudflat, although a variation in the void structure was observed in association with grain size distributions, the soil stiffness was extremely homogeneous because suction did not occur in the soil. In the small-scale artificial layered sand-mud flat, which contained dredged muddy soil with a sand capping, the artificially layered tidal flat stratigraphy was clearly identified by the MASW. The groundwater table dynamics were equivalent to those in the natural large-scale sandflat, indicating that the geoenvironmental characteristics were successfully recreated, even though it had a layered sand-mud stratigraphy.
- 出版日期2008-7-7
