Analysis of Bayed Beaches in Static Equilibrium

Abstract

A bayed beach in equilibrium could be in a state of either dynamic or static equilibrium; the latter being a special case of the former when the absolute quantity of longshore transport is nil. As a bay approaches its equilibrium shape, the net sediment‐transport rate in the bay decreases and eventually ceases. The writers carried out a series of model beach studies to investigate the planform of crenulate‐shaped bays in static equilibrium. By adopting the method of measurement proposed by Hsu and Evans in 1989, the writers found that the effects of beach materials, wave characteristics (other than wave approach), and location and spacing of breakwaters need not be considered separately. In further consideration of the tangent of the bay planform at the downcoast control point, the writers found that a second‐order polynomial equation of R/R0 with (β/θ) as the parameter could be used to describe the crenulate‐shaped bay in static equilibrium for a wide range of wave obliquity, β; R is the shortest line between the upcoast breakwater to a point on the beach, and θ is the angle between this line and the incident wave crests; R=R0 when θ=β. This approach also leads to the simplification of the proposed equation and reduces the number of unknowns from three unknown coefficients to a single variable, α(α=α{β}), which had been determined using the results of the present study and indirect comparison with published data. A list of α for a wide range of wave obliquity is also presented.