Nearshore wave environments around a sandy cay on a platform reef, Torres Strait, Australia

Abstract

Waves are the primary factor affecting reef-island morphology. This study examines spatial and temporal variations of wave characteristics in the nearshore around Warraber Island, a sandy cay on a platform reef in Torres Strait Australia, based on field measurements during the predominant southeasterly wind season. Water pressure was recorded simultaneously, and transformed to water surface wave spectra, at a location close to the reef edge and across the nearshore at different locations around the island. Wave environments off the reef were estimated based on wave characteristics measured at the reef-edge location and found to be primarily dominated by sea. Low and high wave-energy events were identified, based on wave energy level at the reef-edge location. Analysis of measured data at locations around the island shows that in general, waves on the windward side were larger and shorter in comparison with those on the leeward side. This spatial pattern was found to be more evident during high wave-energy events. The spatial variation of wave characteristics is influenced by relative energy contribution from three main spectral components (incident short-period waves <2.5 s, incident wind waves <8 s and infragravity waves, the principal component >8 s). During low wave-energy conditions, incident short-period waves are dominant. During high wave-energy conditions, wave spectra clearly show triple peaks on the windward side, but have only two peaks at infragravity and incident wind wave components on the leeward side. Incident wind wave components around the island are primarily a function of incident waves in seas off the reef. Development of infragravity waves is directly related to that of the incident wind waves. Incident short-period waves are generated locally on the reef flat and increase towards the island, particularly on the broad windward reef flat, and their characteristics can be estimated using fetch-limited and depth-limited wave models. Strong influence of water depth on wave characteristics was observed. Wave height and energy of the three wave components at all locations varied directly with changing water level on the reef, whereas wave periods show no clear trends, depending on location around the island. Wave conditions around the island during the northwesterly wind season were also estimated and are likely to be dominated by incident wind wave components.

Analytical modelling of wave refraction and convergence on coral reef platforms: Implications for island formation and stability

“…There are numerous field studies of wave interaction with coral reefs, the majority of which have examined wave transformation processes across reef edges and adjacent lagoon environments (Roberts et al, 1977;Lee and Black, 1978;Roberts and Suhayda, 1983;Young, 1989;Hardy and Young, 1996;Lugo-Fernández et al, 1998a, 1998b. A number of studies have also examined the characteristics of waves across reef surfaces and the generation of wave setup-driven currents (Roberts et al, 1992;Gourlay, 1994Gourlay, , 1996Symonds et al, 1995;Brander et al, 2004;Kench and Brander, 2006a;Jago et al, 2007;Samosorn and Woodroffe, 2008;Kench et al, 2009). The majority of these studies use the approach of reducing platforms to a two dimensional cross-reef profile which does not account for the three dimensional complexity of reef surfaces and directional propagation behaviour of waves on reefs.…”

Monsoonally influenced circulation around coral reef islands and seasonal dynamics of reef island shorelines

“…Fourth, few studies have attempted to document spatial and temporal variations in wave and current energy with a specific focus on their importance for the development and change to sedimentary deposits such as reef islands. Recently a number of studies have begun to examine such interactions, such as the potential role of wave energy in driving geomorphic processes in the nearshore of reef islands (Brander et al, 2004;Kench and Brander, 2006b;Kench et al, 2006;Samosorn and Woodroffe, 2008;Kench et al, 2009). …”

Assessing Long-Term Changes in the Beach Width of Reef Islands Based on Temporally Fragmented Remote Sensing Data

“…A shift in these parameters will cause a change in position of the nodal point and ultimately induce a rearrangement of the sediments [11,12]. Atoll islands thus are inherently dynamic and shoreline movement is controlled by a number of additional natural and anthropogenic influences that can result in erosion and/or accretion over different temporal and spatial scales ( [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], Table 1). …”