Gully erosion is a critical contributing factor to water quality impacts on Australian marine environments, with alluvial gullies in the three largest catchments contributing 70% of sediment loads to the Great Barrier Reef lagoon.

Project 1.7, led by Dr Andrew Brooks at Griffith University, has re-examined more than 500 hectares of alluvial gully survey data in the Normanby catchment from 2013 to establish erosion patterns, taking advantage of the impact of Cyclone Ita in early 2014 as a ‘natural experiment’.

Project 1.7’s results, which are now available online, show that complex management efforts will be needed to demonstrably reduce sediment run-off levels.

Remediation efforts at just one part of the gully (such as building berms or fencing off cattle) can be negated by further erosion downstream, and Light Detection and Ranging (LiDAR) technology usually used to measure large-scale erosion can fail to detect fine-scale surface erosion that can contribute up to 70 per cent of total sediment load.

The results from Dr Brooks’ project show gully erosion may also be a far greater source of nutrient run-off into the Great Barrier Reef than first thought, additionally removing essential organic carbon and nutrients from grazing land.

Dr Brooks recommends a holistic approach to erosion and sediment management, including a hierarchical monitoring program to detect changes in all erosion processes simultaneously.

Although fencing off cattle from river frontage is a key management step in stopping the formation of new gullies, it can take up to twenty years for vegetation to recover on already-eroded areas even if cattle are excluded from grazing there.

The final report Reducing sediment sources to the Reef: managing alluvial gully erosion shows that there is still much room for research discovering the dynamics and long-term effects of alluvial gully erosion, which will be needed to inform effective management practices to limit both impacts on the health of the Great Barrier Reef and the loss of quality agricultural land.


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