The effect of sea breeze on beach morphology, surf zone hydrodynamics and sediment resuspension

G. Masselink, Charitha Pattiaratchi

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    88 Citations (Scopus)


    Beach morphodynamic processes were investigated over part of a sea breeze cycle on a microtidal, low wave energy sandy beach in southwestern Australia. Prior to the onset of the sea breeze, offshore winds with speeds less than 5 m/s prevailed. During the sea breeze, alongshore winds with speeds higher than 10 m/s were experienced. The sea breeze induced pronounced changes to the nearshore morphodynamics which were similar to that of a storm event: (1) root mean square wave height increased from 0.3 to 0.5 m; (2) zero-upcrossing wave period decreased from 8 to 4 s; (3) mean cross-shore flows reached velocities of 0.2 m/s directed offshore; and (4) the longshore current increased in strength from 0.05 to 1.0 m/s. Before the sea breeze, sediment resuspension typically occurred during isolated high-wave events associated with the passage of wave groups. Flux coupling between the wave-oscillatory currents and the suspended sediment (Jaffe, B.E., Sternberg, R.W., Sallenger, A.H., 1984. The role of suspended sediment in shore-normal beach profile changes. Proc. 19th Int. Conf. Coastal Engineering, ASCE, pp. 1983-1996) induced net onshore suspended sediment transport, resulting in beachface accretion and a steepening of the foreshore profile. In contrast, during the sea breeze, sediment resuspension was almost continuous. The suspended sediment load increased six-fold and, as a consequence, the longshore suspended sediment transport rate increased by a factor of 100. During the sea breeze, cross-shore transport was directed offshore and primarily associated with mean offshore flows. This resulted in erosion of the beachface and deposition in the surf zone and, consequently, a flattening of the beach profile. The suspended sediment load was strongly related to the Shields parameter defined for the combined action of waves and currents. Investigation of the suspended sediment profiles indicated that the degree of vertical mixing, parameterised by the sediment diffusion coefficient, increased with distance from the bed. In addition, the sediment diffusion coefficient exhibited a large temporal variation, ranging between 0.005 and 0.018 m(2)/s. The variability in the sediment diffusion coefficient is possibly due to changes in the sea bed morphology. (C) 1998 Elsevier Science B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)115-135
    JournalMarine Geology
    Issue number1-4
    Publication statusPublished - 1998


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