Nice Barrier Reef decline may influence Queensland’s coastal erosion

Diagrammatic illustration of sediment transport alongside the north (a), central (b) and south (c) coastlines of Queensland. Credit score: Cowley and Harris 2023.

Coastal wave motion happens as a result of intricate interaction between offshore ocean circumstances, the native panorama of the shoreline, currents, tides, and storms. This course of performs a vital position within the transport of sediment to and from the shoreline, together with seashores.

Sediment within the ocean is stirred up by each river runoff into the ocean and wave disturbances, making it vulnerable to heavy rainfall and storm occasions. In tropical and subtropical areas, the presence of reefs considerably influences wave vitality reaching the coast and gives some safety in opposition to erosion by altering the traits of the waves.

Dr. Dylan Cowley and Dr. Daniel Harris from the College of Queensland, Australia, carried out a examine on the influence of the Nice Barrier Reef on sediment transport to the northeast coast of Australia by a course of referred to as longshore drift. This course of entails waves bringing sediment to the coast at an angle, and because the water recedes, the backwash carries it away from the shoreline perpendicularly, leading to a zig-zag transportation sample alongside the shoreline. If the sediment just isn’t replenished adequately, it might probably result in erosion within the upstream space and accumulation of sediment downstream.

Utilizing pc modeling and actual measurements from buoys alongside the coast, Dr. Cowley and Dr. Harris estimated that the Nice Barrier Reef reduces offshore wave vitality because it strikes north alongside the coast. Their analysis, revealed in Marine Geology, revealed that waves within the south of Queensland can transport over 500,000 m3 of sediment to the shoreline, whereas this decreases to lower than 50,000 m3 when transferring north in direction of Fraser Island.

The scientists discovered that the median wave top reaching the north of the examine space is 1 m to 2 m, in comparison with lower than 0.5 m round Fraser Island. The wave interval additionally decreased from eight to 10 seconds to 3 to 5 seconds, indicating a shift in direction of decrease swells. Moreover, a change within the dominant wave course from east-southeast to east-northeast was noticed.

Great Barrier Reef decline could impact Queensland's coastal erosion
Imply volumes of sediment transported underneath totally different wave instructions (a, from the south, b from the east and c, from the north) within the north (i), heart (ii) and south (iii) of Queensland. Black arrows point out northward longshore drift and crimson arrows southward longshore drift. Credit score: Cowley and Harris 2023.

This variation in wave vitality resulted in considerably totally different estimates of sediment transport volumes alongside the coast. In southern Queensland, roughly 1,800,000 m3 of sediment are transported every year, whereas this decreases to 400,000 m3 within the Capricorn Channel previous the Nice Barrier Reef, and fewer than 40,000 m3 within the lagoon behind the reef.

The course of longshore drift is influenced by the offshore wave course, with waves from the south inflicting higher northward sediment transport alongside the south Queensland coast in direction of Fraser Island. Nonetheless, the consequences turn out to be extra variable because the shoreline transitions into the Capricorn Channel and Nice Barrier Reef lagoon, with southward transport even dominating within the latter.

When winds blow from the north, the situation described above is reversed, coinciding with a change in shoreline orientation from predominantly north-south to northwest-southeast. The extra uncovered nature of the shoreline south of Fraser Island, mixed with a steep slender shelf, makes it extra vulnerable to offshore wave vitality, leading to increased swells and higher sediment transport to the coast.

Total, the Queensland coast experiences a internet optimistic improve in sediment transport, which may be exacerbated by southeasterly commerce winds and excessive wave-generating occasions equivalent to tropical cyclones and El Niño. These occasions can alter the wave course and depth, resulting in modifications in sediment transport.

Throughout La Niña phases, elevated rainfall contributes to higher sediment runoff from land to the coast, additional affecting sediment transport. The researchers emphasize the significance of this discovering, as excessive climate occasions are predicted to turn out to be extra frequent and intense sooner or later, impacting sediment dynamics.

Because the Nice Barrier Reef continues to say no, its capacity to dissipate incoming wave vitality is prone to diminish. This can lead to waves with higher vitality reaching the shoreline, resulting in elevated erosion and sediment mobilization. Understanding the modifications in wave vitality and sediment transport is essential as a result of rising coastal populations and financial dependence on these areas.

As we anticipate vital coastal transformations within the coming a long time as a result of local weather change, it’s important to acknowledge the ability of our oceans in shaping our landscapes. We should attempt to seek out methods to assist the planet’s pure processes and mitigate the impacts of human actions.

Extra info:
Dylan Cowley et al, Wave-driven sediment transport potential on a tropical coast: Implications for the northeastern Australian sediment finances, Marine Geology (2023). DOI: 10.1016/j.margeo.2023.107104

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Nice Barrier Reef decline may influence Queensland’s coastal erosion (2023, August 7)
retrieved 7 August 2023
from https://phys.org/information/2023-08-great-barrier-

 

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