Modelling erosion and sediment delivery from unsealed roads in southeast Australia

Unsealed roads and tracks are potentially significant sources of diffuse pollutants, particularly sediment. This paper describes the application and development of a road erosion and sediment transport model in the Moruya-Deua and Tuross River catchments of southeast Australia. An empirical model based on the Washington Road Surface Erosion Model (WARSEM) is applied using typically widely available spatial data sets and field-collected data. The results suggest that approximately 21 kt and 35 kt of sediment respectively are produced annually from road erosion in the Moruya-Deua and Tuross River catchments, but that less than 10% of the sediment is delivered to streams. Surprisingly, about half of the delivered sediment is derived from only 4% of the total road network. Testing of the model shows that the model outputs are likely to overestimate road erosion rates. To address this problem, catchment-specific testing of the factors of the model and improving knowledge of the processes of road to stream sediment transport are required.