The main urban centre in the Tully Basin is the township of Tully, which is located inland and has a population of 2,436. Several localities, including Hull Heads, Tully Heads, and Mission Beach, are located on the coast.
The Tully Basin is steep in its upper areas which are primarily occupied by tropical rainforest and sclerophyll forests (largely in the Wet Tropics World Heritage Area), while the coastal floodplain has largely been cleared and drained for agricultural purposes.
Streams emerge from the coastal mountain range with high velocities and volumes resulting from rainfall events.
Koombooloomba Dam is located in the upper catchment and is used for power generation.
Wetlands listed in the Directory of (Nationally) Important Wetlands include Tully River-Murray River floodplains, Edmund Kennedy Wetlands and Licuala Palm Forest.
The Tully Basin has an area of 1,685 km2 and has a high proportion of natural/minimal use lands (75%). The remaining area is comprised of 12% sugarcane, 4% bananas, 5% grazing, 2% forestry, 1% other crops, 1% urban and 3% other land uses.
The Tully Basin grade has remained ‘good’ and the score decreased from 64 to 61 since the previous year.
The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.
The water quality grade in 2018-19 for the Tully Basin remained ‘good’ with the score increasing from 63 in 2017-18 to 68.
Dissolved inorganic nitrogen (DIN) scored the lowest (42) whilst the grade improved from ‘poor’ in 2017-18 to ‘moderate’, although monthly median concentrations were consistently not meeting guideline values. The filterable reactive phosphorus (FRP) indicator scored 90 and improved from ‘good’ in 2017-18 to ‘very good’, with monthly median concentrations mostly meeting guideline values.
Total suspended sediment (TSS), the indicator for sediment, scored 78, and remained ‘good’, with monthly median concentrations often meeting guideline values.
Pesticides for the Tully Basin improved from “moderate” in 2017-18 to ‘good’ and scored 63, equating to over 95 percent of species protected for the risk assessment metric.
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 Euramo, capturing 86% of the basin.
Habitat and hydrology
The habitat and hydrology index is comprised of the flow indicator category (updated annually) and four longer-term indicator categories that are updated every four years: wetland extent (updated for 2017-18), riparian extent (to be updated for 2019-20), instream habitat modification consisting of impoundment length (updated for 2018-19) and fish barrier indicators (in development), and invasive weeds (to be updated for 2019-20).
The annual scores for habitat and hydrology index for 2015-16 and 2016-17 represented changes due to the addition of the invasive weeds and flow indicators, respectively, and not changes in the indicator scores themselves. The index score for 2018-19 includes the third year of reporting for the flow indicator and the updated wetland extent indicator. The Tully Basin habitat and hydrology index scored 54 for 2018-19 and the grade declined from ‘good’ to ‘moderate’ dur to the poorer flow indicator score.
The habitat modification score of 57 (‘moderate’) is comprised of the impoundment length score of 57 (‘moderate’) with 4.6 per cent of the total length of the waterways with a stream order of 3 or higher impounded by artificial structures. Koombooloomba Dam is the largest impoundment in the basin. There was no change in impoundment length score for the 2018-19 assessment.
The fish barrier indicator method is still being developed and will be available in future report cards.
Riparian extent for the Tully Basin scored 72 (‘good’) with 9% loss from pre-clear extent to 2013. It is expected that the majority of loss is in the lowlands due to development and land use.
Wetland extent scored 17 (‘very poor’) with 57.8% loss of palustrine (freshwater) wetlands from pre-clear to 2017. Since 2013, an area of 6.6 hectares of palustrine wetlands has been lost. These results reflect a high level of historic loss due to development.
The invasive weeds indicator scored 81 (‘very good’) in the Tully Basin and represents low impacts of aquatic weeds within the Tully freshwater system. The Tully Basin was the highest scoring basin in the Wet Tropics for invasive weeds meaning that the impacts from aquatic weeds on waterway health is the lowest for the region.
The Tully Basin flow indicator declined from ‘very good’ in 2017-18 to ‘moderate’. Flows in the Tully Basin were altered from modelled pre-development flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production. The combination of very low rainfall from August to November and very high rainfall in December may have resulted in the flow scoring tool underestimating dry season flow scores. However, lower scores for high flow metrics may have resulted from flow attenuation at Koombooloomba Dam.
The fish index is currently being rolled out for the basins in the Wet Tropics and will be available for the Tully Basin next year.