South East Queensland
17.2 River outflow from the region
This line item consists of the end-of-system flow from rivers into estuaries, inlets and the sea. The following table details the end-of-system flow estimates for the South East Queensland (SEQ) region.
The volume of the end-of-system flow from rivers into estuaries was considerably greater during the 2010–11 year than the 2009–10 year (1,576,606 ML). This was due to the 2010–11 year being significantly wetter, with major flood events occurring in December 2010 and January 2011. Further information on the rainfall within the region can be found in the Climate overview.
|Water resource plan (WRP) area||River||Volume
|Gold Coast||Coomera River||319,876|
|Total Gold Coast WRP area||831,056|
|Logan Basin||Logan River Basin||1,339,979|
|Total Logan Basin WRP area||1,339,979|
|Total Moreton WRP area||9,872,364|
|Total SEQ region||12,043,399|
As there are no end-of-system gauges, regression relationships were developed between the historical recorded flow data at the most downstream gauging station and the modelled end-of-system flow for each river catchment. The modelled end-of-system flow was estimated using the DERM integrated quantity quality model for each catchment within the SEQ region.
The regression relationship was then applied to the 2010–11 year recorded flow data at the most downstream gauging station to estimate the annual flow at the outlet.
For example, for Logan River (Logan Basin WRP area), DERM added estimated ungauged catchment flows to recorded flows at the Logan River at Yarrahappini gauge (145014A) and the Albert River at Bromfleet gauge (145102B) to estimate the end-of-system flows using regression analysis.
For the Nerang River (Gold Coast WRP area), estimated ungauged catchment flows were added to recorded flows at the Mudgeeraba Creek at Springbrook Road gauge (146020A) and Nerang River at Glenhurst gauge (146002B) to estimate the end-of-system flows using regression analysis.
Assumptions, Limitations, Caveats and Approximations
In this analysis, it was assumed that the gauging station flow data are reliable and the regression relationships are valid. A comparison of alternative 'extrapolation' methods has not been undertaken.
Derived from modelled data. DERM reliability and accuracy rating is B3/B4.
This line item corresponds to line Item 14.2 Streamflow into downstream entity reported in the 2010 Account. In the 2010 Account Elanora, Merrimac and Coombabah wastewater treatment plant (WWTP) discharge volumes were added to the end-of-system flows. These WWTPs were considered to discharge to the surface water below the lowest gauge on the rivers. In the 2010 Account a volume of 39,284 ML was added to the end-of-system flow estimates to account for these discharges.
Further investigation into the discharge points indicate that the discharge is into the Southport Seaway. For the purpose of the 2011 Account this was considered a marine environment and not part of the SEQ region, resulting in Elanora, Merrimac and Coombabah WWTP discharges considered as line item 19.7 Wastewater discharge outside of region. These WWTP discharges were not added to the end-of-system flow estimates for the 2011 Account and were removed from the 2011 Account comparative year volume.
The following table compares the value at 30 June 2010 reported in the 2011 Account with the corresponding value reported in the 2010 Account.
|2011 Account line item||2010 Account line item||Description||Volume reported in the 2010 Account
|Prior period error correction
|Volume difference due to scope change
|Restated volume reported in the 2011 Account
|17.2 River outflow from the region||14.2 Streamflow into downstream entity||End-of-system flow estimates||1,576,606||0||0||1,576,606||No change required.|
|Wastewater discharge downstream of gauge||39,284||0||–39,284||0||Discharge now considered to Southport Seaway, outside SEQ region.|