SAND MOVEMENT BY WAVES AT THE SHALLOW SEA BOTTOM

Abstract

Many experimental studies concerning sand movement caused by waves have been made in laboratories using water tanks. However, only a very limited number of field studies were made, because of the observational difficulties and complicated factors affecting sand movement caused by waves, rip currents and others. Considering the results of the experimental studies in laboratories, the auther tried to make clear the actual process of sand movement by sea waves. The study area is situated at the center of the offshore of Tatado coast in Shimoda-shi, Izu Peninsula (Fig. 1). Ten field surveys at the sea bottom were made selecting the various condition of wave intensity (Table 1). Main results obtained are summarized as follows: 1. With the increasing intensity of waves, the ripple patterns in an offshore station changes from parallel to diagonal, lunate ripples and sand waves (Table 3). This sequence is also observed between the offshore and breaker zone. 2. The process of sand movement revealed by our observation differs from that of expe-rimental results in that the sand movement of traction type occurs in the same extent when the crest and trough of the wave passes over the minor topographies at the sea bottom (Figs. 6-1, 2, 3, and 4). 3. Correlation exists between the wave intensity and the transported amount of sediments, and as Manohar described the rate of the transported amount, G1 (g•cm-1 sec-1) and G2 (g• cm-2•sec-1), are expressed as a function of the intensity of flow of the fluid near the sea bottom, φ1', (Figs. 7 and 8).