Sedimentation patterns in Repulse Bay, Hong Kong

Abstract

Comparative grain size analyses were made of sediments obtained from six zones at Repulse Bay, Hong Kong, in c. der to test the hypothesis that the onshoreoffshore migration of sediments would result in a sequential development of textural characteristics. Although similar depositional processes may occur in different bay environments some processes could be unique. If the textural responses of these latter processes are greater than the non-unique processes, characteristic grain size distributions could well develop. Earlier work on Hong Kong beaches has shown that such distributions do occur. SCUBA, tacheometry, dyed sands, sieving and statistical testing was used to investigate the above premise. Results showed that no significant difference could be observed between sediment samples obtained from either end of the bay. This is in accordance with a proposed sediment transport model. During inter-storm periods, six sedimentation zones were found normal to the beach trend. Offshore zones tended to be homogeneous in texture because their location in the hydraulic regime was seawards of the surf zone. Foreshore zones were heterogeneous because they were sited in the swash/surf zones. Backshore zones were affected by both eolian and hydraulic processes. Energy levels in this zone were usually low in marked contrast to foreshore areas. During tropical cyclonic conditions the various zones were not distinguishable and a characteristic homogeneous sediment distribution was found. In post-storm conditions, extensive re-working of the area quickly re-established the zones. Different processes and intensities of these processes were constantly at work in the bay. These processes gave rise to distinctive sediment patterns which inferred a to and fro transfer of sediment within the bay rather than along it.