MERGE: modelling erosion resistance for gully erosion - a process-based model of erosion from an idealised linear gully

Gullies are responsible for as much as 40% of the accelerated erosion impacting the Great Barrier Reef lagoon. Consequently, to protect the reef from the impacts of poor water quality associated with eroded sediment, the remediation of gullied landscapes is important. The geographic location and geomorphic characteristics of gullies affects their erosion characteristics and the extent to which eroded sediments may be transported to the reef. Existing models of gully erosion are predominantly empirical in nature, and are poorly suited to represent the potential benefits of different interventions in the data scarce environment that exists. The Queensland Government, through the Queensland Water Modelling Network, identified the development of process-based models of gully erosion as necessary to support efforts to protect the reef. MERGE (modelling erosion resistance for gully erosion) was developed to address this need. MERGE exhibits the expected characteristics for gully erosion including achieving a steady concentration under constant conditions, the development of a depositional layer, as well as first flush effects and hysteresis in the dynamic case. Analytical steady-state solutions are found to be excellent approximations to the full dynamic solutions. The suitability of the model to represent interventions is demonstrated for the example cases of porous check dams and improved ground cover.