Abstract

State-of-the-art beach profile data sets including field measurements and laboratory experiments are applied to investigate the predictions of beach-face slope. Field measurements of beach profile and sediment characters yield a logarithmic-type of model to link beach-face slope and sediment grain size, while a series of laboratory experiments data sets which contains hydrodynamic forcing are compared with formula suggested by Sunamura (1984), and certain discussions and improvements are proposed regarding to the quantitative predictions of beach-face slope.

Introduction

Coastal areas have become a major issue among both the researchers and government during the last century due to its predominant importance in scientific regimes and economic reasons. But since the coastal regions usually subject to a highly dynamic processes, our understanding of the whole processes is still limited, especially in the swash zone where sediment experiencing uprush and backwash periodically. Besides, there are several factors that are responsible for the swash zone sediment transport, including beach materials and hydraulic factors, like wave height, wave period and wave direction. During the last century, researchers are paying more and more attention to the sandy beach protections not only because sandy beach accounting for a large part of tourism economic growth among coastal countries but also due to the prevailing of the engineering work such as beach nourishment. And one of the most important issues involved is the property of the sandy beach especially the swash zone slope, i.e. beach-face slope, which determines the scale of the available areas that can be used for recreation by human.

Since the 1930s, a variety of scientific studies have been carried out by many researchers concerning the slope of the beach-face by means of both field measurements conducted by Bascom (1951), Emery and Gale (1951) King (1953) and laboratory experiments like Meyers (1933), Bagnold (1940). Since the swash zone is a complicated area affected by various factors, it is essential to select major controlling factors that are responsible for the variations of the beach. According to Sunamura (1984), controlling factors that are responsible for affecting beach-face slope are:

  • beach sediment characteristics such as grain size, degree of sorting, size distribution, and specific gravity;

  • wave properties such as wave height and wave period;

  • ground-water-level;

  • tidal stage;

  • longshore current.

And the first two factors are most crucial, although, our capacity of predicting beach-face slope is still limited. For example, Mclean (1968) analyzed two sand-shingle beaches and suggested that size verse slope curves for the studies beaches seems to contain two "plateaus" of almost constant slope angles and two areas of almost linear increase in slope with size. Dean (1977) hypothesized that equilibrium beach profile is directly related to the sediment size and proposed an equation of exponential type by the analysis of more than 500 beaches along the America and Gulf coasts, which is not available in the swash zone due to its exponential type of equation. King (1972) analyzed 27 beaches of different conditions and revealed the relation between beach slope and sediment size and wave energy, which did not take wave steepness into consideration.

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