Agricultural fields in the middle Shira River basin play an important role as a source of groundwater recharge; however, the water balance between the agricultural water and river water is unclear. This study was conducted to investigate the water balance in the fields by measuring the stream flow of agricultural water channels, which draw water from the Shira River. The flow rate of water channels was found to increase in the beginning of May, which corresponded to the cultivation of paddy rice fields. During summer, the total agricultural intake was comparable to the river flow observed in the middle Shira River Basin. Determination of the water budget for the targeted area revealed that most of the recharged water was dependent on agricultural irrigation from the river. The annual recharge of the overall target area was estimated to be as high as 15,300 mm. In addition, the infiltration rate was as high as 170 mm/day in the paddy fields during summer, and as high as 30 mm/day in the upland fields during winter. In order to recover the groundwater recharge in this region, it is necessary to extend the submerged period to include periods in which the stream water in the Shira River is not subject to heavy rainfall as well.

Three-dimentionalLaser 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 were found to be larger than those of calm-dominant area. Reconstructing three-dimensional 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.

X-ray Computed Tomography (CT) has been applied to investigate a time-space evolutions of sediment density profile due to beach profile changes in the laboratory wave flume conditions. The sediment density and pore profiles in the collecting sediment cores were measured using X-ray CT scanning. The sediment density profiles in the erosional conditions are different from these of deposional conditions. The depth of disturbance was found to be few centimeter orders of magnitude. Reconstructing three-dimensional images using CT value, the evolutions of low bulk density region and porosity structure were examined.

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