The large-scale influence of the Great Barrier Reef matrix on wave attenuation

Abstract

Offshore reef systems consist of individual reefs, with spaces in between, which together constitute the reef matrix. This is the first comprehensive, large-scale study, of the influence of an offshore reef system on wave climate and wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16-yr record of wave height from seven satellite altimeters. Within the GBR matrix, the wave climate is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, wave energy that penetrates the matrix has little depth modulation. There is no clear evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because individual reefs cast a wave shadow much larger than the reef itself; thus, a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the GBR matrix. Here, wave conditions appear to be dependent largely on local wind speed, rather than wave conditions either seaward, or within the reef matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.

The Influence of Carbonate Platforms on the Geomorphological Development of a Mixed Carbonate‐Siliciclastic Margin (Great Barrier Reef, Australia)

“…Based on output from a global hindcast model, which centers on the wind wave climate of Australia and the South Pacific (Durrant et al, 2014), we prescribe an easterly wave direction and a significant wave height of 2.0 m as boundary conditions for the wave module. The hindcast model predictions are in good agreement with measured wave heights from satellite altimetry (Gallop et al, 2014). While the late Pleistocene and Holocene wave climate for central Queensland is still poorly understood, major climatic phenomena such as El Niño–Southern Oscillation (ENSO) have likely experienced variability over this time (Shulmeister & Lees, 1995).…”

“…As a result of the variable rainfall regime and the topographic control imposed by the mountains to the west, modern rivers and their catchments are comparatively small (~500–2,000 km 2 ), seasonal in flow, and sometimes ephemeral, emptying their sediments in the nearshore (<20 m depth; Neil et al, 2002; Orpin et al, 2004). The region is macrotidal (Ryan, Brooke, et al, 2007), and offshore wave regime is moderately energetic, where both swell and locally generated waves are driven by east‐south‐easterly winds and power north‐westward longshore currents (Gallop et al, 2014; Larcombe et al, 1995; Orpin et al, 2004).…”

Natural hazards in Australia: sea level and coastal extremes

“…Introduction 36 Australia's coastal zone -defined herein as the region of low-elevation coastal land and 37 adjacent estuarine and marine ecosystems -is bisected by approximately 34,000 km of 38 coastline and encompasses tropical, sub-and extra-tropical climates. The arid nature of much 39 of Australia's interior means that approximately 80% of Australia's population lives in or near 40 the coastal zone together with a diversity of coastal and estuarine ecosystems, making it of 41 critical importance for a range of social, economic and environmental reasons. 42 In this review paper, our region of relevance extends from the continental shelf offshore, 43 where oceanic processes responsible for extreme sea levels occur, through to the low-lying 44 coastal land inshore where physical impacts are felt.…”

Extreme water levels, waves and coastal impacts during a severe tropical cyclone in northeastern Australia: a case study for cross-sector data sharing

“…During cyclone events, conditions greatly exceed this, with wave heights greater than 5 m not uncommon. The predominately low wave energy regime is a result of effective attenuation of ocean swells by the GBR matrix, which 2606 T. R. Mortlock et al: Extreme water levels, waves and coastal impacts means nearshore wave conditions are largely dependent on local wind speeds rather than far-field wave generation (Gallop et al, 2014).…”