The present study aims at exploring and elucidating the dynamics of tidal flat geoenvironments,and at clarifying their link with the burrowing activity of benthos. It also aims at developing rational performance index for conservation and restoration of intertidal sandy flats. For these purposes, we highlight the role of the dynamics of suction that represents the tension of moisture in soil. We performed field observations / surveys, laboratory experiments and theoretical / conceptual analyses,which developed in an interactive manner. The principal findings can be outlined as follows;
1) Our field observations captured closely for the first time the dynamics of suction and the relevant associated physics of geo-environments of an intertidal sandy flat. We made clear the mechanism of water retention, involving the coupled processes of evaporation, upward moisture movement and salinity accumulation. The difference in the water retention dynamics for sandy flats and beaches arose from the difference in pore water migrations around air entry suctions for both types of the soils. Two quantitative index were proposed for assessing and designing such water retention fields.
2) The suction dynamics associated with the tide-induced ground water level variations plays a substantial role in causing significant tempo-spatial evolutions of voids, stiffness, and surface shear strength in the cyclically exposed and submerged soil. The suction-induced void state changes are a consequence of cyclic
elastoplastic contraction of the soil and are accompanied by distinct morphological changes. Such soil behavior depends strongly on the way in which suction develops above the ground water level during low tides. Discussions are made on how these effects of suction dynamics could contribute, via feedback involved in surface
transport processes, to the overall morphological evolution of cross-shore intertidal flat soils.
3) The burrowing activity of typical sand-bubbler crabs Scopimera globosa was closely linked with the suction dynamics. Notably,suction produced an effective cohesion which enabled sand burrowing.The results of well-controlled laboratory burrowing experiments showed that there were threshold, optimum, and critical suction conditions and related geophysical environmental conditions which
governed the development of the burrows. This gave rise to a rational performance index. A conceptual model that consistently accounted for such burrowing performance was described,together with its application to geoenvironmental design for creating conditions favorable to burrowing activity.