Incorporating Fine Sediment Pollution Impacts Into Unsealed Road Management: A Case Study from the Great Barrier Reef Catchment Area

Excess fine sediment is a significant contributor to ecological degradation in the Great Barrier Reef (GBR). Erosion of unsealed formed roads in Queensland, Australia, causes excess fine sediment to be delivered downstream to the GBR lagoon, negatively affecting the World Heritage-listed marine ecosystem (Waterhouse et al, 2024). This paper presents a Cost-Benefit Analysis (CBA) of alternative road management scenarios aimed at reducing fine sediment loads to the GBR, to assess the economic viability of these compared to current practices. The CBA used high-resolution erosion data and cost estimates from case study sites in Queensland. Four road management scenarios were assessed: (1) business-as-usual grading to bare earth, (2) alternative maintenance of drains and batters using vegetation management, (3) major erosion control to address erosion hotspots, and (4) full betterment using bitumen dust seal. Our results show that the alternative maintenance, major erosion control and full betterment road management scenarios were economically viable (i.e. yield positive net present values between AUD$2.9 to 7.8 million) when compared with the business-as-usual scenario. The management of roads in GBR catchments is publicly funded, as are most mitigation efforts aimed at reducing fine sediment delivery to the GBR, particularly through government programs and initiatives targeting improved land and catchment management. As such, cost savings from implementing changes to existing road management practices will have wider benefits through efficiencies in government spending. Our findings demonstrate the importance of considering indirect, off-site impacts of road erosion in road management decisions to achieve better long-term ecological outcomes.