G. Masselink et B. Hegge, MORPHODYNAMICS OF MESOTIDAL AND MACROTIDAL BEACHES - EXAMPLES FROM CENTRAL QUEENSLAND, AUSTRALIA, Marine geology, 129(1-2), 1995, pp. 1-23
Detailed measurements of the morphology, waves, and longshore and cros
s-shore currents were conducted on two beaches on the low- to medium-e
nergy, macrotidal coastline of central Queensland (Australia). Nine Mi
le Beach is characterised by a relatively steep upper profile, a low-g
radient intertidal zone with one or two swash bars, transverse bar/rip
morphology at low-tide level and a very low-gradient, dissipative sub
tidal zone. The beach is composed of fine to medium sand and experienc
es a modal wave height of 0.75 m and a mean spring-tide range of 3.6 m
. Lambert's Beach possesses a steep, coarse-grained, reflective upper
profile, and a low-gradient dissipative low tide terrace composed of f
ine to medium sand. Subdued rip channels intersect the low tide terrac
e and the beach is subject to a modal wave height of 0.6 m and a mean
spring-tide range of 4.6 m. The two beaches are classified as Low Tide
Bar/Rip and Low Tide Terrace beaches, respectively, following the mod
el of Masselink and Short (1993). During the present investigation, th
e Low Tide Bar/Rip beach (Nine Mile Beach) exhibited a larger temporal
variability than the Low Tide Terrace beach (Lambert's Beach), despit
e similar hydrodynamic conditions over the survey period. This differe
nce is principally attributed to the differences in the beach morpholo
gies and the types of morphological changes that occurred. On Nine Mil
e Beach, morphologic changes were primarily associated with secondary
features (swash bars and low tide bar/rip system), whereas on Lambert'
s Beach the changes in morphology were largely the result of adjustmen
ts of the overall beach profile. A number of surf zone processes were
investigated, including incident-wave attenuation, infragravity-wave e
nergy, bed return flow and longshore currents. The influence of the ti
de on surf zone dynamics was found to be insignificant, except in the
case of longshore currents. On Nine Mile Beach, the longshore current
associated with the nearshore cell circulation was stronger during low
tide. On Lambert's Beach, the shore-parallel current on the low tide
terrace was largely driven by the tide. A beach profile zonation was d
efined for Nine Mile Beach and Lambert's Beach based on an examination
of the varying influence of swash, surf zone and shoaling wave proces
ses. The four-part tidal zonation consists of: (1) an upper intertidal
zone across which swash and aeolian processes are the major influence
; (2) a mid-intertidal zone dominated by swash and surf zone processes
; (3) a lower intertidal zone controlled by surf zone and shoaling wav
e processes; and (4) a subtidal zone largely influenced by shoaling wa
ve processes.