Dynamics of Cobbles in and Near the Surf Zone and Mine Movements in and Near the Surf Zone.

摘要

The long-range goals of this research are to develop, by laboratory experimentation, theoretical analyses and comparisons with field observations, a basic understanding and, eventually, a predictive capability of the behavior of large bottom particles (cobbles) in the shoaling, wave-breaking and swash zones. Here, the size classification of cobbles used by the American Geophysical Union as particles in the diameter range 6.4 to 25.6 cm is employed. Disk-shaped anti-tank mines are of similar size. The scientific objectives for this research are directed toward better understanding the motion and burial/scouring of cobbles on beaches which (a) are impermeable with various characteristic roughness and (b) are permeable with sand bedforms that are free to vary with time and with flow characteristics. The objectives for the impermeable floor case are to (1) develop proper parameterizations for the background velocity field in the shoaling, wave-breaking and swash zones; (2) use this parameterization to extend the models previously developed for time- dependent flows to include the space and time-dependent surf zone; (3) obtain data on the transport of cobbles in the entire wave-tank surf zone and test the model against the experimental data. The objectives for the permeable sandy floor case are directed to better understanding (1) the large time dynamics of sand ripples, formed in periodical flow, and (2) the process of burial/scouring of cobbles on a sandy beach with ripples in such periodical flow. In particular, we wish to study (1) the evolution of an initially flat sandy bottom; (2) the long-time behavior of the bottom topography and (3) the eventual long-time fate of the model cobbles.