Spatial and temporal variations of suspended sediment responses from the subtropical Richmond River catchment, NSW, Australia

Suspended sediment exports from the Richmond River catchment were examined during 2 hydrological years (1994–96). On a yearly basis, the Richmond River catchment produced <2% suspended sediment load during dry seasons, whereas about 75–91% of the yearly suspended sediments were exported during floods which occurred <5% of the year. Annual suspended sediment exports from the Richmond River catchment varied more than 7-fold from dry year to wet year. Among the 3 major subcatchments, Richmond and Wilsons River subcatchments generated >93% of the suspended sediment load, while sediment exports from the Bungawalbin Creek subcatchment always remained low due to its flat topography and extensive forest coverage. Suspended sediment hysteresis patterns exhibited a clockwise response for 2 steep and less forested subcatchments and an anti-clockwise response for relatively low gradient and more forested subcatchment during all flood events. Land use changes in the Richmond River subcatchments indicate a possible increase of suspended sediment load of about 6-fold from their pristine condition.