Lower Burdekin River Basin
Lower Burdekin subcatchments
The Lower Burdekin Basin is comprised of 7 sub-catchments, as follows:
SedNet Modelling of Water Quality
Model results for the Lower Burdekin River Basin are summarized as follows:
- Basin modelled area: 8,499 sq. km.
- Source contributions: Hillslope = 38%; Gully = 9%; Streambank = 52%
- Total suspended sediment (flow weighted) supply: 1,380 kt/yr
- Total suspended sediment supply (flow weighted; normalized to area): 1,624 kg/ha/yr
- Suspended sediment end-of-basin (flow weighted) yield: 2,567 kt/yr (for Burdekin River)
- Event Mean Concentration (flow weighted): 270 mg/L (for Burdekin River)
- Mean Annual Flow: 9,493,686 ML (for Burdekin River)
Streambank erosion is identified as the major source of sediment and particulate nutrients affecting water quality in the Lower Burdekin Basin (52%), while hillslope (38%) and to a lesser extent gully (9%) erosion are also predicted to be significant contributors. Loss of sediment and associated particulate nutrients from all sources (supply) is only moderate (1,380 kt/yr) when compared to other, larger basins. However, this loss equates to 1,645 kg/ha/yr, which is very high when compared to all subcatchments and other basins.
Modelled suspended sediment loads for the Burdekin River and subcatchments above the gauging station on at Home Hill/Inkerman were estimated to permit a more accurate and explicit comparison between modelled estimates and monitoring data. These loads are as follows:
- Catchment modelled area: 128,701 sq. km.
- Total suspended sediment (flow weighted) yield: 2,618 kt/yr (exported from Burdekin Catchment)
The Burdekin River (below dam) (2,990 kg/ha/yr), Burdekin Delta (1,906 kg/ha/yr), Haughton River (1,201 kg/ha/yr) & Stones Creek (1,182 kg/ha/yr) subcatchments are predicted to have relatively high rates of soil loss when compared to subcatchments across the Burdekin Dry Tropics region. Barratta Creek, Landers Creek and Upstart Bay subcatchments are predicted to have more moderate rates of soil loss that are below the Basin average. While streambank erosion is identified as the major source of sediment and particulate nutrients affecting water quality in the Lower Burdekin Basin, mostly this is sourced from the Burdekin River. Hillslope erosion dominates in the non-Burdekin River subcatchments.
Total soil loss from all sources is predicted to be greatest in the Burdekin River (below dam) subcatchment (772 kt/y) and much higher than from other subcatchment in the Lower Burdekin Basin. Most other subcatchments are predicted to contribute only very little to the end-of-subcatchment sediment loads. The Haughton River subcatchment contributes an intermediate quantity of sediment to the end-of-catchment load.
Water Quality Monitoring
Bainbridge et al. (2007b) report that the coastal catchments, including the lower Haughton River, Reid River and Barratta Creek sites all had low TSS concentrations compared to the other Burdekin subcatchments, with mean TSS concentrations between 20-160 mg/L for all sites. The two larger grazed catchments, including the upper Haughton River & Upstart Bay (Yellow Gin Creek) subcatchments both had higher mean TSS concentrations of 790 mg/L & 435 mg/L respectively. Disproportionately high mean NOx concentrations (ranging between 85-645 µg N/L) were measured in the Haughton River, Reid River and Barratta Creek coastal catchments when compared to typical mean concentrations from grazed subcatchments. The highest mean concentrations were measured at the three Barratta Creek sites (415- 440 µg N/L) and the upper Haughton River (645 µg N/L), although only limited sampling was conducted at this later site, and the elevated NOx concentration is most likely due to the high sediment concentrations in this subcatchment, where the particulate fraction of N and P were also high. Mean FRP concentrations were also elevated for Sheep Station Creek (150 µg P/L), Plantation Creek (110 µg P/L), west Barratta Creek (100) and the upper Haughton (95 µg P/L) sites, compared with typical mean FRP concentrations measured across the region (<60 µg P/L).
Total suspended sediment loads calculated from monitoring data for the Burdekin River at Inkerman Bridge over 8 wet seasons between 1995-6 and 2006-7 are reported to have averaged 3.31 million tons/yr. When adjusted to the mean annual flow based on records from 1921-2 to 2006-7 (87 years), this equates to an average of 4.58 million tons/yr. Both the measured and adjusted total suspended sediment loads are well in excess of the modelled predictions at the end-of-Burdekin River catchment. The data show that sediment load estimates were underestimated in the model by as much as 43%.
Although only limited pesticide monitoring was conducted directly through this project, a sub-project to investigate the presence of pesticide residues in the lower Burdekin canelands was established by ACTFR for the Burdekin WQIP before the on-set of the 2005/06 wet season. Pesticide samples were collected at the lower Burdekin sampling sites (along with sediment and nutrient samples for this project) during event flow conditions in the 2005/06 and 2006/07 wet seasons. A suite of herbicides (diuron, atrazine and ametryn) were commonly detected in the waterways of the lower Burdekin, as well as in the Haughton River and Barratta Creek freshwater plumes generated in 2007. No pesticides were detected in the Burdekin River plume. Ambient, “low flow” samples were also collected prior to each wet season, and a full description of this project is provided in Lewis et al. (2007).
Results of a Rapid Land Condition Assessment (adopted from Hassett et al. 2000) are presented below. The assessment has been devised to subjectively characterise condition while traversing the BDT region by vehicle. The data are based on a total of 4666 observations across the Burdekin region between 2004 and 2007.
The data were collected to provide independent information on land condition and provide a regional perspective. Resource assessment data are most useful when interpreted with other sources of data e.g. time-series remote sensing, modelling and water quality monitoring.
The estimated condition of the Lower Burdekin River Basin is proportioned as follows:
- A Condition: n/a
- B Condition: 8%
- C Condition: 84%
- D Condition: 8%
Data from the Lower Burdekin River Basin is based on 36 observations.
On the basis of the rapid assessment, the Lower Burdekin River Basin is estimated to have the largest proportion of land in poor (C) condition (84%), followed by fair (B) condition and very poor(D) condition land (8%). Data not available for good (A) condition land.
Ground Cover in the Lower Burdekin River Basin is proportioned as follows:
- ( BC) Bare Cover: 4%
- ( LC) Low Cover: 64%
- ( MC) Moderate Cover:21%
- ( HC) High Cover: 11%
- (VHC) Very High Cover: n/a
Data from the Lower Burdekin River Basin is based on 28 observations.
On the basis of the rapid assessment (2004-2007), the Lower Burdekin River Basin is estimated to have the highest proportion of land within the low (LC) ground cover category (64%), followed by moderate (MC) cover (21%) and high (HC) cover (11%) categories. 4% of land was estimated to fall into the bare cover (BC) category.
Resource Condition Summary
The Lower Burdekin Basin is relatively small (~ 9,292 sq. km.) and covers around 7% of the BWQIP region. Common to most of the BQWIP basins, land use is dominated by grazing on natural or modified pastures. However, in contrast to the other Basins, approximately 12% of the land area is used for intensive agriculture (mostly irrigated sugar production), while around 9% is set aside for conservation and minimal use. The condition of riparian habitat varies between subcatchments, from fair (B) to very poor (D), and there has been a general decline in condition over the last 30 years, principally due to clearing along streams and floodplains. The lower areas of the four coastal subcatchments represent a single floodplain which is considered to contain the single most important, healthy and productive wetland systems in the Burdekin region and, indeed, along the Queensland coast. It includes many large, permanent freshwater wetlands, long lengths of perennially-flowing creeks, and estuarine wetlands that are recognised internationally as Ramsar wetlands and listed in the National Directory of Important Wetlands (DOIW). However, the flow regime of much of the lower Burdekin floodplain has been altered from seasonal to perennial flow by the tailwater discharge from the development of extensive system of irrigation channels for agriculture. In contrast, the two non-coastal subcatchments (Burdekin (below dam), Landers Creek & Stones Creek) and upper parts of the Haughton River, Barratta Creek and Upstart Bay subcatchments are mostly dry, ephemeral creek systems.
Streambank erosion is identified as the major source of sediment and particulate nutrients affecting water quality in the Lower Burdekin Basin, mostly sourced from the Burdekin River. Hillslope erosion dominates in the non-Burdekin River subcatchments. The rate of soil erosion for the Basin overall is predicted to be high and well above the BWQIP region average, with some individual subcatchments predicted to lose from two to four times the BWQIP region average. The Burdekin River (below dam) subcatchment, in particular, is predicted to have a very high rate of soil erosion and to contribute substantially to the total sediment load at end-of-catchment. While coverage of rapid assessment data of grazing land condition is quite limited within the basin, analyses of ground cover from satellite imagery (reference) identify the Burdekin River (below dam) subcatchment to be in poorest condition and to have large areas that are vulnerable to further erosion.
Water quality in the Burdekin River is predicted by models to have only slightly elevated concentrations of suspended sediment and particulate nutrients at the end-of-basin during wet season flow events, notwithstanding the very large sediment and nutrient load that is derived from the entire Burdekin River catchment upstream. Water quality monitoring data over 8 wet seasons recorded sediment loads well in excess of the modelled predictions and show that the total sediment load is underestimated in the model by as much as 43%. In contrast, water quality monitoring data from the other coastal rivers and creeks of the Lower Burdekin Basin that drain the irrigated agricultural areas of the floodplain show that suspended sediment concentrations and loads are much lower than predicted by models. However, disproportionately high dissolved inorganic nitrogen concentrations and loads, which is attributed largely to fertilizer use in irrigated agriculture, have been recorded from the Haughton River, and Barratta, Sheep Station, Plantation and Iyah Creeks. Nevertheless, the measured total load of dissolved inorganic nitrogen (DIN) from the Burdekin River catchment rangelands greatly exceeds that delivered to the GBR through coastal streams draining the irrigated agricultural areas of the Lower Burdekin. Several herbicide residues have also regularly been detected in coastal rivers and creeks, including atrazine, diuron, ametryn and hexazinone. Elevated concentrations of tebuthiuron have been recorded from catchments draining grazing land, particularly the Burdekin and Haughton Rivers.
Water Quality Targets
The following water quality Resource Condition Targets were developed based on Best Management Practice Guidelines for Water Quality Improvement, extensive modelling of a range of management scenarios, preparation of a discussion paper (reference) and then, finally, a series of workshops. These preparatory activities were undertaken in collaboration with landholders (graziers and cane farmers), industry representatives, Government, the scientific community and BDTNRM staff.
- Attain a minimum 40% (to maximum 50%) reduction in mean annual sediment load at end of Burdekin Catchment (Inkerman Bridge/Claire Weir) from current (2008) by 2058 (i.e. reduction from approximately 3,700 kt/yr to 2,220 kt/yr)
- Attain a 60% (minimum) to 80% reduction in nitrogen (nitrate) load entering the GBR from Lower Burdekin sugar and other irrigated lands from current (2008) by 2058 (i.e. reduction from approximately 3,000 t/yr to 600 t/yr)
- Attain an 8% (minimum) to 25% reduction of nitrogen (nitrate) load entering the GBR from Lower Burdekin sugar lands from current (2008) by 2013 (i.e. reduction from approximately 3,000 t/yr to 2,250 t/yr)
- Attain a 25% (minimum) to 50% reduction of pesticide (atrazine, diuron, ametryn, hexazinone) load entering the GBR from Lower Burdekin sugar lands from current (2008) by 2013
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