Content area
Full text
ABSTRACT
T. Kakinoki, G. Tsujjimoto, D. Sakai and K. Uno, 2011. Beach Profile and Sediment Characteristics of a Mixed Sand Beach Under Diurnal Sea Level Variations. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 765 - 770. Szczecin, Poland, ISSN 0749-0208
The effects of tidal level fluctuations on low-energy beaches can become increasingly important and can affect the beach profile. Therefore, this paper investigates the mechanisms of sediment transport due to diurnal water level changes affected by wave actions. Measurements of bed profiles, sediment grain size and wave conditions have been carried out in the field and an experimental water flume. The size of the resulting berm increased under depositional waves on flooding tides, and the offshore bar moved further seaward on the eddy under erosive waves. With the rise and fall of the tide, sediment sorting develops horizontally and vertically; therefore, grain size and porosity inside the bed change accordingly.
ADDITIONAL INDEX WORDS: Morphological change, mixed sand, tide
INTRODUCTION
Studies of morphological and sedimentological changes on sandy ocean-facing beaches have been described for high-energy wave fields by many researchers. Davis (1964) describes low energy by relative energy and comparative location and includes "beaches in partially enclosed seas that are sheltered from swell" and "where wave action is minimal compared with exposed coasts". Jackson (2002) uses the term low energy for locations where there are (1) non-storm significant wave heights < 0.25 m, or (2) significant wave heights during strong onshore winds < 0.5 m.
Where the region around a low-energy beach has a high population density or an important economic role, the maintenance of such beaches can be a very important issue. However, there is less knowledge of low-energy beaches. Often, results from high-energy ocean-facing beaches are often scaled down to be applied to the problems of low-energy beaches. Nearshore bar/rip morphologies are not present on low-energy beaches and according to the high-energy beach nomenclature, low-energy beaches could be classified as either reflective or dissipative (Jackson, 2002).
Hegge et al. (1996) developed a profile classification based on 15 low-energy sites. Four low-energy morphotypes were identified from a cluster analysis of beach characteristics. The four beach morphotypes were distinguished by their dimensions, slope, curvature and grain size, and included:...