Time filter

Source Type

Innaloo, Australia

Gallop S.L.,University of Southampton | Gallop S.L.,University of Western Australia | Bosserelle C.,University of Western Australia | Eliot I.,Damara WA Pty Ltd | Pattiaratchi C.B.,University of Western Australia
Marine Geology

The effect of coastal reefs on seasonal erosion and accretion was investigated on 2. km of sandy coast. The focus was on how reef topography drives alongshore variation in the mode and magnitude of seasonal beach erosion and accretion; and the effect of intra- and inter-annual variability in metocean conditions on seasonal sediment fluxes. This involved using monthly and 6-monthly surveys of the beach and coastal zone, and comparison with a range of metocean conditions including mean sea level, storm surges, wind, and wave power. Alongshore 'zones' were revealed with alternating modes of sediment transport in spring and summer compared to autumn and winter. Zone boundaries were determined by rock headlands and reefs interrupting littoral drift; the seasonal build up of sand over the reef in the south zone; and current jets generated by wave set-up over reefs. In spring and summer, constant sand resuspension and northerly littoral drift due to sea breezes allowed a sand ramp to form in the South Zone so that sand overtopped the reef to infill the lagoon. This blocked the main pathway for sand supply to downdrift zones which subsequently eroded. In autumn and winter, with the dominance of northwesterly storms and reversal in the direction of littoral drift, the South Zone eroded and sand travelled through the lagoon in the current jet to nourish the northern beaches. Inter-annual and seasonal variation in sea level, storm frequency and intensity, together with pulsational effects of local sand fluxes at Yanchep due to inter-seasonal switching in the direction of littoral drift determined marked differences in the volumes of seasonal sand transport. These seasonal 'sediment zones' highlighted interesting and unexplored parallels between coasts fronted seaward by coral reefs and rock formations. © 2013 Elsevier B.V. Source

Gallop S.L.,University of Western Australia | Bosserelle C.,University of Western Australia | Pattiaratchi C.B.,University of Western Australia | Eliot I.,Damara WA Pty Ltd
Journal of Coastal Research

Beaches associated with geological or engineered structures, recognised as perched beaches, are commonplace on many coastlines around the world and especially so in South West Western Australia (SWWA). Although it is accepted that hard coastal structures will affect beach behaviour, little is known about the mechanisms through which this occurs. The microtidal Perth coast in SWWA is influenced by one of the strongest and most persistent sea breeze cycles in the world. This, together with offshore limestone reefs attenuating swell means that locally generated sea breeze waves and currents dominate the hydrodynamics for half of the year. Field measurements were made of wave, current and beach morphology changes due to strong sea breeze forcing at the perched Yanchep Beach and Lagoon on the Perth Metropolitan coast. Spatial and temporal variation of waves and currents at the beach and in the lagoon were monitored throughout several sea breeze cycles and changes in beachface morphology surveyed at two beach profiles. A 50% reduction in sea breeze wind speed was found to weaken the lagoonal currents by 50% due to less wave overtopping of the limestone reef. Results show the influence of the limestone formations on waves and currents which affects the beachface response to sea breeze. Both beach profiles showed a clear cycle of erosion and accretion to sea breeze, with differences between the profiles even though they were spaced just 120 m apart. These results provide insights into the role of geological formations on the behaviour of a perched beach. Source

Gallop S.L.,University of Western Australia | Bosserelle C.,University of Western Australia | Eliot I.,Damara WA Pty Ltd | Pattiaratchi C.B.,University of Western Australia
Continental Shelf Research

Mechanisms through which naturally-occurring hard landforms, such as rock and coral reefs, influence coastal sediment transport are still poorly understood. Therefore, field investigations were undertaken during storm conditions on the sandy beaches of Yanchep Lagoon in southwestern Australia, which are perched on Quaternary limestone reefs. During two consecutive winter storms, the response of three subaerial beach profiles were quantified at: (a) an Exposed Profile which was fronted to seaward by a predominantly sandy substrate; (b) a Reef Profile that was fronted directly seaward by limestone outcrops submerged below mean sea level; and (c) a Bluff Profile where the dry beach was perched on a limestone bluff that reached above mean sea level and that contained a shallow coastal lagoon. The subaerial beach response to the storms had considerable spatial variation alongshore and was strongly dependent on the local rock topography. The Exposed Profile eroded most with a 2. m-high scarp cut into the dune while the dunes at the Reef and Bluff Profiles were stable. The Bluff Profile also eroded considerably and the coastal lagoon widened and deepened. The Reef Profile was the most stable overall because erosion was balanced by short periods of accretion during the storm period which was partly due to sediment supplied by longshore transport through the coastal lagoon from the Bluff Profile. During the month after the storms wave energy was relatively low and the beach at the Exposed Profile accreted almost to the pre-storm volume, although the scarp in the dune was still present. The Reef Profile accreted most in the month after the storms while recovery at the Bluff Profile was low. It appeared that the bluff inhibited onshore sediment transport during and after the storms and in addition, strong currents in the lagoon transported sediment alongshore to supply the other beach profiles. These observations indicated that rock topography, especially elevation relative to sea level determined if beach erosion was reduced during storms and whether accretion was dampened in the post-storm recovery phase. © 2012 Elsevier Ltd. Source

Eliot M.,Damara WA Pty Ltd | Travers A.,Coastal Zone Management Pty Ltd.
20th Australasian Coastal and Ocean Engineering Conference 2011 and the 13th Australasian Port and Harbour Conference 2011, COASTS and PORTS 2011

Investigation of historic beach and dune field evolution was undertaken, to develop a probabilistic model of future shoreline change, to be used for coastal vulnerability assessment of foreshore infrastructure at Scarborough Beach. The analysis compared long-term records with previous studies of beach width, to describe relationships with key climate variables. A major finding of the investigations was the significant role of annual alongshore wind anomalies in beach growth or recession. Source

Gallop S.L.,University of Western Australia | Bosserelle C.,University of Western Australia | Pattiaratchi C.,University of Western Australia | Eliot I.,Damara WA Pty Ltd
Marine Geology

We hypothesized that beach profiles that are perched on natural rock structures would be better protected from waves and currents than profiles that are not fronted by rock. In southwest Western Australia many beaches, such as at Yanchep, are perched on Quaternary limestone. Yanchep Lagoon is fronted by a low-crested limestone reef that partially encloses a coastal lagoon. The spatial variation of waves and currents around the rock structures were quantified during the sea breeze cycle at locations: (1) offshore; (2) 20 m seaward of the reef; (3) inside the lagoon; and (4) in the surf zone. The spatial variation in the beach profile response was measured at two beach profiles: (1) the Exposed Profile that was not fronted directly seaward by outcropping limestone; and (2) the Sheltered Profile which was fronted seaward by submerged limestone at 2. m water depth and that was near the lagoon exit at the end of the limestone reef. The Sheltered Profile had greater volume changes during the cycle of the sea breeze whilst the Exposed Profile recovered more by overnight accretion when wind decreased. The lagoonal current drove the strong response of the Sheltered Profile and may have contributed to the lack of overnight recovery of the beach together with the seaward rock formation impeding onshore sediment transport. The different direction and speed responses of bottom-currents in the surf zone fronting the two profiles reflected the local variation in geology, the influence of the jet exiting the lagoon, and wave refraction around the reef that was measured with GPS drifters and wave-ray tracing using XBeach. Major spatial variation in waves, currents and beachface behavior at this perched beach shows the importance of the local geological setting. © 2011 Elsevier B.V. Source

Discover hidden collaborations