From Roads to the Reef: Improving Water Quality

Abstract

Poor water quality is the second most serious threat to the Great Barrier Reef (GBR), behind climate change. Within the reef catchment, there are thousands of kilometers of state and local government unsealed roads. Local government manages over 38,000km of unsealed roads accounting for at least 53% of the public formed road network within the GBR catchment. Unsealed roads represent areas of exposed earth that are prone to erosion, particularly over the wet season and are also contributing to gully erosion and increased sediment loads in waterways.

The Australian and Queensland Governments continue to invest heavily in land-based programs to improve water quality runoff into the GBR lagoon, however funding arrangements for implementing road maintenance from these same governments is, in some instances, adding to the problem.

As part of the Reef Trust Partnership between the Australian Government and the Great Barrier Reef Foundation (GBRF), in 2021 GBRF awarded both the Local Government Association of Queensland (LGAQ) and South Cape York Catchments (SCYC) separate grants to investigate erosion from unsealed roads in several regions. Additionally, AECOM is also providing pro-bono support in the form of GIS and hydrologic modelling analysis to determine the total potential quantum of sediment from unsealed roads entering local stream and river networks and subsequently the GBR lagoon.

The results from both the LGAQ and SCYC projects indicate that erosion from roads and their drainage is a significant contributor of sediment to the Reef – compared to other catchment landuses. Modelling is continuing to quantify this at a GBR catchment scale. The LGAQ project data estimated that between 8 and 11 tonnes/ha/y of fine sediment (< 20 µm) per annum was exported from the unsealed road network.

Utilising on high resolution terrestrial laser scanning (TLS), the SCYC project data estimated 42 tonnes/ha/y (or 68 t/km/y) of fine sediment eroded from the combined disturbed area of road surfaces, cut slopes, table and cut-off drains, and bed level creek crossings, These rates were significantly reduced by applying erosion prevention and control measures. A recently completed cost-benefit analysis (CBA) provides evidence to support their long-term implementation.

Reef councils are significant partners in the success of fine sediment reduction through their important role in managing thousands of kilometres of unsealed roads. The solution is multi-faceted including adapting on-ground practices by maintenance contractors and updating road maintenance funding policies and guidance. Support from the Australian and Queensland Governments will be critical in facilitating long-term implementation and water quality outcomes for the Reef.

LGAQ and SCYC have commenced the process of developing erosion prevention and control guidance for unsealed roads. By working with the IPWEAQNT, local government, and relevant Australian and Queensland Government agencies, it is hoped that policies, funding arrangements and on-ground practices can be better aligned to existing programs to improve Reef water quality.