Three-dimentional Laser and X-ray Computed Tomography (CT) Scanners have been applied to investigate a time-space evolutions of wave-generated ripple geometry and vertical sediment structures of intertidal mudflat with non-destructive conditions at Shirakawa River mouth. Field observations were conducted in two places where there are many Ruditapes philippinarums (clam-dominant area) or not (calm non-dominant area). Time-space evolutions of wave-generated ripple geometry at non-dominant area

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... e found to be larger than those of calm-dominant area. Reconstructing threedimensional images using CT value, retention water in the intertidal sediment at calm-dominant area existed up to 6cm below the sediment surface during dry cycle of tide motions.