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IMPACT OF
THE BURDEKIN RIVER Rivers collect the freshwater runoff from the land and deliver it to the sea at the coast. The runoff collects and carries with it: nutrients, pollutants and sediments, as it makes its journey to the sea. Using the latest in 3-dimensional mathematical techniques, this project aims to use computer simulation to better understand the final fate of riverine water as it mixes and moves around with the currents and winds. In particular, the project is focussing on simulating all the floods of the Burdekin River for the 30 year period 1966-1995. This river has a very large discharge when in flood and these are known to impact the Central Great Barrier Reef (CGBR). The following database includes information on the duration of exposure to fresh water (exceedance), the minimum salinity and the return periods for the modelled domain shown below. Abstract A verified 3-dimensional hydrodynamic model, capable of simulating river plume dynamics, was employed to create computer simulations of the fate and mixing of a flood of freshwater from the Burdekin River. The model was used to simulate 30 years (1966 - 1995) of the Burdekin River in flood based on measured local winds and river discharge data. The computer simulations have produced a comprehensive time varying and 3-dimensional spatially varying database of the fate and mixing of plume waters from the Burdekin River during the flood events. This database has been analysed to determine the concentrations and residence times of plume waters in the Central Great Barrier Reef (CGBR).The 30 years of simulations showed that the Burdekin River plume regularly stretches over 400 km to the north in coastal waters due to the discharge and wind. Steering effects from the coastal topography, continental islands and the dense reef matrices created complex spatial patterns in the plume distribution. The model predicts that shelf edge reefs in the CGBR are unlikely to be affected by Burdekin River plumes, but that the inner shelf reefs are impacted when an offshore wind prevails following a flood event. A simulation of one extreme low salinity event of 26 ppt, shows that Burdekin River water can reach the inner reefs with a minimum dilution rate of 1 part river water to 3 parts coastal seawater. The simulations also showed that the plume would usually take at least a 2-3 week period, after discharge from the river mouth, to reach the inner reefs. Given the natural temporal and spatial variability that exists in the plume behaviour, the model simulations for all 30 years were compiled to examine the intensity, duration and frequency of different lower salinity events. Return periods were then calculated for such events over the entire model domain. This analysis reveals that close proximity to the river mouth does not necessarily increase the likelihood of impact. Indeed, the closest mid-shelf reefs to the mouth of the river are only 50 km away, yet the most frequently impacted region (Rib Reef, John Brewer Reef, Lodestone and Keeper) are over 120 km away. The 30-year historical simulation of the discharge and dilution of Burdekin River runoff was undertaken to broaden the understanding of the spatial extents of likely impacts on the reefs and coastal waters of the CGBR from catchment management practices. The simulations demonstrate a range of common spatial patterns and unusual events that can be expected from a dynamic process. A risk assessment using return period analysis of the frequency of different impact events was undertaken to identify 'high-risk' regions or reefs. Environmental managers can use the database to assess land use changes. For example, risk assessments can be performed on the expected dilutions and residence times of Burdekin river water and hence the implications for dilutions and residence times of dissolved and suspended material carried within catchment runoff into the CGBR. Further, Environmental Managers can also use the simulations to identify the potential plume pathways and travel times for the runoff and its contents to reach the reefs. See also - King, McAllister, Wolanski, Done and Spagnol, 2000 "River Plume Dynamics in the Central Great Barrier Reef" As Chapter 10 in: Coral Reef Processes; Physics-Biology Links in the Great Barrier Reef. E.Wolanski (Ed.).CRC Press, Boca Raton, Florida. (for full report, see CRC Reef Reports, Task 1.5.1/4, 1999)
Additionally MECCA was run to model plume behaviour for the Burdekin, Herbert, Tully and North and South Johnstone Rivers combined. These runs are referred to as the all rivers runs. Analysis of the model outputs for these runs can be viewed in a similar manner.
Permission to
use Citation
River Discharge |
Return Periods |
Exceedance Plots |
Minimum Salinity Plots |
Salinity Transect
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