G. Masselink et C. Pattiaratchi, MORPHODYNAMIC IMPACT OF SEA-BREEZE ACTIVITY ON A BEACH WITH BEACH CUSP MORPHOLOGY, Journal of coastal research, 14(2), 1998, pp. 393-406
Beach morphology and nearshore hydrodynamics were monitored over a num
ber of sea breeze cycles on a beach with pronounced beach cusp morphol
ogy in southwestern Australia. The action of the sea breeze resulted i
n consistent changes to the incident wave field and beach cusp morphol
ogy, and induced a diurnal cycle of beach change. The morphological ch
anges were accomplished without an apparent sediment gain or loss, but
involved a redistribution of sediment within the cusp morphological s
ystem. During the sea breeze, the addition of locally-generated, short
-period mind waves to the background swell resulted in an increase in
wave height, a decrease in wave period and an intensification of the n
earshore currents. The cusp morphology became increasingly subdued due
to accretion in the embayment and, to a lesser extent, erosion of the
horns. After the cessation of the sea breeze, the wind-wave energy le
vel gradually decreased and the associated wind-wave period increased.
Accretion on the cusp horns was accompanied by minor erosion of the e
mbayment and resulted in an accentuation of the cusp morphology. The b
uild-up of the cusp morphology was a consequence of the morpho dynamic
feedback between the antecedent cusp morphology and the wave runup ch
aracteristics. The wave runup was diverted from the horn into the emba
yment, resulting in decreased backwash volumes and hence build-up of t
he horn. In the cusp embayment, increased backwash volumes resulted in
scouring and the suppression of potential swash events at the base of
the beachface. Consequently, the proportion of infragravity-wave ener
gy in the runup record was larger in the embayment than on the horn. T
en hours after the sea breeze had stopped blowing, significant amounts
of wind-wave energy were still present. It is suggested that these wi
nd waves were generated a distance of almost 200 km south of the study
area, implying that the presence of the local sea breeze may have reg
ional implications for coastal processes.