The Barron basin has an area of 2189 km2 with Mareeba and Atherton as the main population centres.
The basin consists of 29% natural/minimal use lands, 31% grazing, 18% forestry, 8% other crops (including bananas), 3% sugarcane, 3% dairy, 5% urban and 4% other land uses.
The Barron River is the most modified river in the Wet Tropics region and is heavily regulated by water supply infrastructure.
The basin has a large upper catchment on the Tablelands and a smaller lower catchment north of Cairns where it discharges into Trinity Bay.
A major dam is situated at Tinaroo Falls at the northern end of Lake Tinaroo. The Barron River is a strong story place for Aboriginal custodians.
The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.
Water quality for the Barron basin in 2016-17 has remained ‘very good’ with the score decreasing slightly from 82 in 2015-16 to 81.
The sediment score, comprised of the total suspended solids (TSS) indicator, scored the lowest with 76 (‘good’) with monthly median concentrations of TSS often meeting the guideline values.
Nutrients were ‘very good’ scoring 87, with dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP) monthly median concentrations mostly meeting guideline values.
Pesticides are not monitored in the Barron basin, therefore a score and grade cannot be provided.
Water quality grades are based on aquatic ecosystem guidelines for protection of freshwater systems, and are not based on load reduction targets for the marine environment. The results are derived from the end of catchment monitoring site at Myola, capturing 89% of the basin.
Habitat and hydrology
The habitat and hydrology index is comprised of four longer-term indicator categories that are updated every four years: wetland extent, riparian extent (both to be updated for 2017-18), invasive weeds (to be updated for 2019-20), habitat modification (impoundment length (to be updated for 2018-19) and fish barrier indicators (in development)).
The flow indicator for the Barron basin (reported annually) was introduced in 2016-17.
The annual habitat and hydrology index scores for 2014-15, 2015-16 and 2016-17 represent the changes resulting from the addition of indicators and not changes in the indicator scores themselves.
The habitat and hydrology index remained ‘moderate’ in 2016-17 with the score increasing from 43 to 47 due to the addition of the flow indicator.
The habitat modification score of 36 (‘poor’) is comprised of the impoundment length indicator showing 7.7% of the total length of the waterways with a stream order of 3 or higher are impounded by artificial structures. Tinaroo Dam is the largest impoundment in the basin.
The fish barrier indicator method is still being developed and will be available in future report cards.
Riparian extent for the Barron basin scored 68 (‘good’) with 11.1% loss from pre-clear extent to 2013. It is expected that the majority of loss is due to development and land use.
Wetland extent scored 11 (‘very poor’) with 72.2% loss of palustrine (freshwater) wetlands from pre-clear to 2013. These results reflect a high level of historic loss due to development. Wetland losses in future reporting periods will be minimal.
The invasive weeds indicator scored 56 (‘moderate’) in the Barron basin and represents some impacts of aquatic weeds within the Barron freshwater system including hymenachne (Hymenachne amplexicaulis), salvinia (Salvinia molesta), water hyacinth (Eichornia crassipes) and pond apple (Annona glabra).
The Barron basin was graded ‘good’ for flows during 2016-17. Flows in the Barron basin were not substantially different to predevelopment flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production. However, the flow indicator provides scores for each flow assessment site and this can be used to assess flows at more local scales.
Freshwater Creek, which is a sub-catchment within the Barron basin, had flows substantially altered from predevelopment conditions and included changes in the duration and the frequency of medium flows and the duration of low flows. These changes to flow can adversely affect riffle habitats, macrophyte beds, low flow spawning fish, critical hydraulic habitat, longitudinal connectivity and water quality (Stewart-Koster et al. 2018).
The altered flows are likely to result from the water resource development of Freshwater Creek which serves as a water supply for the Cairns area, with Copperlode Dam and water extraction infrastructure located upstream of the flow assessment site. More information on the results of the flow indicator is available in the results technical report.
The fish index is currently under development and will be available in future report cards.
Further information on the methods used to produce the scores and grades and detailed results can be found here.