King et al., 2001:

Departures from normal ocean salinity

"Rivers collect much of the freshwater runoff from the land and deliver it to the sea at the coast. The runoff also collects and carries sediment, nutrients, and contaminants depending on the catchment characteristics and land uses. Once discharged from the river, the runoff drives a buoyant plume into coastal and shelf waters. The plume eventually spreads and mixes and moves around with the winds and currents (Furnas 2003). This mixing with ambient coastal waters will ultimately dilute the runoff plume as well as any concentrations of sediments, nutrients and contaminants carried within the plume. In the wet and dry tropical catchments adjoining the Great Barrier Reef (GBR), river discharges are highly seasonal and usually event-driven in nature and result from rain-fall events associated with evolving monsoon troughs or passing tropical cyclones (Wolanski, 1994).

The unpredictable nature of rainfall and runoff events, and the unsteadiness and patchiness of the resulting plume intrusions in a complex region such as the GBR have traditionally made data logistically difficult to collect. Direct rainfall inputs onto the shelf can also lower surface salinity significantly (Wolanski 1994) and at a time when river discharges are also significant. Thus large spatial mapping of salinities is needed to determine the origin of lower salinity events (<34 ppt) within the reef matrix of the GBR. Further, understanding the possible fates of river plumes is a key question for management of the GBR because of their ability to transport pollutants from human activities on land into the GBR Marine Park.

Evidence of significant plume intrusion into the GBR has been observed and measured. Wolanski and Ruddick (1981) and Wolanski et al. (1997) showed that under favorable wind conditions, the plume waters from the Fly River do intrude into the northern GBR Marine Park at times. O'Neill et al. (1992) measured the flood plume from the Fitzroy river after the passage of Cyclone Joy in 1991. Using a combination of salinity measurements and aerial observations of water colour, O'Neill et al. (1992) mapped the 12-day travel of the Fitzroy River Plume from Keppel Bay into the Capricorn Bunker Group of reefs in the Southern GBR. Ayukai et al. (1997) mapped the salinity and nutrient distributions of the Daintree River plume into GBR waters after the passage of Cyclone Sadie. Wolanski and Van Senden (1983) reported the most detailed survey to date, which covered the 1981 flood events from the Burdekin, Herbert, Tully, Johnstone and Barron Rivers. King et al. (1998) utilized this survey to calibrate and verify a three-dimensional hydrodynamic model of the Burdekin River in flood. The model was used to produce a comprehensive long-term and three-dimensional spatially varying database of the fate and mixing of plume waters from the Burdekin, Herbert, Tully and South Johnstone Rivers (King et al., 2000; McAllister et al., 2000)." 

Summary distributions of the minimum surface predicted for each grid cell for 1977 and 1983

Salinity profiles through the water column along the transects shown in the insert from the coast into reef waters offshore of Cairns following the passage of Cyclone 'Steve" in February 2000

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Citation and/or URL

King, B., McAllister, F., Wolanski, E., Done, T. and Spagnol, S., 2001, River plume dynamics in the central Great Barrier Ree', In: Oceanographic processes of coral reefs: physical and biological links in the Great Barrrier Reef, ed. E. Wolanski, CRC Press LLC, p. 145-159  

Spatial Coverage

Central GBR

Temporal Coverage

 Modelling of past flood events back to 1977

Update Frequency

 Not appicable 

Other Information

 None