Spatial extent of riverine flood plumes and exposure of marine ecosystems in the Tully coastal region, Great Barrier Reef

Tully River flood plume monitoring data for 11 events (1994–2008) were used to determine what physical characteristics of the floods (size of flood, direction of plume movement, shape of hydrograph) most influence the flood plume water quality and areal extent. During some events, the maximum area influenced by the Tully flood plumes extended into the Coral Sea. Areal extents depended on wind direction and discharge volume, with large extents more likely during light or northerly winds. Strong gradients in water quality existed away from the Tully mouth during the wet season and the adjacent marine ecosystems were regularly exposed to land-derived material. Flood plumes were grouped into three plume types: primary, secondary and tertiary plumes, based on water-quality characteristics (suspended solids, coloured dissolved organic matter and chlorophyll). The number of reefs and seagrasses exposed to plume waters varied from year to year, and was dependent on the characteristics of the event. Over the 11 years, out of the major 37 reefs and 13 seagrass meadows identified in the Tully marine area, between 11 (30%) and 37 coral reefs (100%) and most of the seagrass meadows were inundated by either a primary or secondary plume every year.