The data obtained in these observations will be useful for the estimation of an amount of sediment transport in the surf zone, and for the prediction of the sea bottom changes in coastal regions. However, there still exist some uncertainties about the accuracy of the LISST-25 in field observations. Therefore, it will be necessary (i) to calibrate the accuracy of LISST-25 in a laboratory and field site, (ii) to confirm the applicability of LISST-25 in field observations, and (iii) to obtain a large amount of data under the various sea conditions.

　

　

Filed observations of the vertical profiles of suspended sediment concentration, coastal currents and waves by employing LISST-25, ADCP and wave gauges were conducted in the surf zone under storm conditions using the T-shaped Observation Pier in the Ogata Coast. The main conclusions are summarized below.

(1) The vertical profiles of suspended sediment concentration and air bubble concentration, which may be entrained by wave breaking, were estimated using observed data by the LISST-25, the ADCP and wave gauges and employing Vanoni distribution.

(2) The offshore-going suspended loads in the surf zone under the storm conditions are estimated based on the derived suspended sediment concentration.

(3) The linear relationship between offshore-going suspended sediment flux and wave energy are shown. It will be possible to estimate offshore-going sediment flux based on wave conditions.

　

　

This research was financially supported by a Grant-in-Aid for Encouragement of Young Scientists, from the Japan Society for the Promotion of Science (contract No. 13750490).

　

Beach, R.A. and R.W. Sternberg. 1996. Suspended-sediment transport in the surf zone: response to breaking waves, Continental shelf Research, Vol. 16, No. 15, pp. 1989-2003.

Farmer, D.M., S. Vagle and A.D. Booth. 1998. A free-flooding acoustical resonator for measurement of bubble size distributions, J. Atmospheric and Ocean Tech., pp. 1132-1146.

Fredsoe, J. and R. Deigaard. 1992. Mechanics of coastal sediment transport, World Scientific, 369p.

Izumiya, T., T. Kunita, M. Izumi, H. Nagamatsu and K. Ishibashi. 1999. Field observation of temporal and spatial variation of concentration of silty fine sand estimated from ADCP data, Proc. of Coastal Eng., JSCE, Vol. 46, pp. 576-580. (in Japanese)

Katayama, H., A. Okayasu and T. Nagata. 1999. Field measurements of suspended sediment concentration and grain size distribution by high speed water sampling system, Proc. of Coastal Eng., JSCE, Vol. 46, pp. 571-575. (in Japanese)

Miller, H.C. 1999. field measurments of longshore sediment transport during storm, Coastal Eng., Vol. 36, pp. 301-321.

Rijn, L.C. 1984. Sediment transport, Part II: suspended load transport, J. Hydraulic Eng. Vol. 110, No. 11, pp. 1613-1641.

Rose, C.P. and P.D. Thorne. 2001. Measurements of suspended sediment transport parameters in a tidal estuary, Continental Shelf Research, Vol.21, pp.1551-1575.

Soulsby, R.L. 1983. The bottom boundary layer of shelf seas. In: Johns, B. (Ed.), Physical Oceanography of Coastal and Shelf Seas, pp.189-266.

Soulsby, R.L. and B.L.S.A. Wainwright. 1987. A criterion for the effect of suspended sediment on near-bottom velocity profiles, J. Hydraulic Res., 25(3) pp.341-356.

Vanoni, V.A. 1975. Sedimentation Engineering, ASCE Manuals and Reports of Engineering Practice No.54, New York, p.76.

Yamashita, T., H. Yoshioka, M. Lu and S. Kato. 1997. ADCP observation of nearshore current structure in the surf zone, Proc, of Coastal Eng., JSCE, Vol.44, pp.361-365. (in Japanese)

Yoshioka, H., S. Serizawa and T. Takayama. 1998. Acoustic observation of sea surface boundary layer (bubble entrainment at wind wave breaking), Proc, of Coastal Eng., JSCE, Vol.45, pp.71-75. (in Japanese)

Williams, J.J., C.P. Rose and L.C. Rijn. 1999a. Suspended sediment concentration profiles in wave-current flows, J. Hydraulic Eng., Vol.125, No.9, pp.906-911.

Williams, J.J., C.P. Rose, P.D. Thorne, B.A. O'Connor, J.D. Humphery, P.J. Hardcastle, S.P. Moores, J.A. Cooke and D.J. Wilson. 1999b. Field observations and predictions of bed shear stresses and vertical suspended sediment concentration profiles in wave-current conditions, Continental Shelf Research, Vol.19, pp.507-536.

Williams, J.J., C.P. Rose, P.D. Thorne, L.E. Coates, J.R. West, P.J. Hardcastle, J.D. Humphery, S.P. Moores and D.J. Wilson. 1996. Observed suspended sediments in storm conditions. Proc. 25th ICCE, pp.3257-3296.