Cape Campaspe River Basin
Cape Campaspe subcatchments
Cape Campaspe Basin is comprised of 4 subcatchments, as follows:
- Campaspe River Subcatchment
- Cape River Subcatchment
- Lower River Subcatchment
- Rollston River Subcatchment
SedNet Modelling of Water Quality
Model results for the Cape Campaspe Basin are summarized as follows:
- Basin modelled area: 19,510 sq. km.
- Source contributions: Hillslope = 66%; Gully = 28%; Streambank = 6%
- Total suspended sediment (flow weighted) supply: 704 kt/yr
- Total suspended sediment supply (flow weighted; normalized to area): 361 kg/ha/yr
- Suspended sediment end-of-basin (flow weighted) yield: 488 kt/yr
- Event Mean Concentration (flow weighted): 495 mg/L
- Mean Annual Flow: 986,146 ML
Hillslope erosion is identified as the major source of sediment and particulate nutrients affecting water quality in the Cape Campaspe Basin (66%), while gully erosion (28%) is also predicted to be significant contributor. Loss of sediment and associated particulate nutrients from all sources (supply) is predicted to be relatively low (704 kt/yr) when compared to other basins. This loss equates to 361 kg/ha/yr, which is relatively low when compared to all sub catchments and other basins.
Modelled suspended sediment loads for the Cape Campaspe Basin above the gauging station on the Cape River at Taemas were estimated to permit a more accurate and explicit comparison between modelled estimates and monitoring data. These loads are as follows:
- Sub-basin modelled area: 15,679 sq. km.
- Total suspended sediment (flow weighted) yield: 419 kt/yr
The rate of soil erosion is predicted to vary relatively little between the four sub catchments of the Cape Campaspe Basin, from a high in the Campaspe River subcatchment of 452 kg/ha/yr to a low of 250 kg/ha/yr in the Cape River sub catchment. Overall, the rate of soil erosion is predicted to be relatively low at 361 kg/ha/yr.
The total loss of sediment from all sources to waterways is predicted to vary more substantially between sub catchments, and to be greatest in the Campaspe River subcatchment. This results from a combination of a more elevated rate of soil loss combined with the large area of the sub catchment. In contrast, the Lower Cape and Rollston River sub catchments, both of which are relatively small, are predicted to have low total sediment load losses. The Cape River sub catchment, which is also very large but with a low rate of soil erosion, is predicted to have an intermediate level of soil loss between the Campaspe and Lower Cape River subcatchments.
Comparison between modelled and monitored data from the Cape River at Taemas indicate that modelled predictions may be overestimating the total suspended sediment load leaving the Cape Campaspe Basin.
Water Quality Monitoring
Bainbridge et al. (2007) report that both the Cape River and its major tributary the Campaspe River yielded low TSS concentrations across the four years monitored (270 and 500 mg/L, respectively), with this major sub-Basin consisting of a flatter landscape that is dominated by regolith and tertiary sediments. The slightly higher mean for the Campaspe River is considered by the authors most likely to reflect the north-eastern region of this tributary which drains erodible granodiorite country. Tributaries in this north-eastern region of the Campaspe River such as Policeman, Yarraman and Oaky Creeks continually produced elevated TSS concentrations (means between 665-1,890 mg/L) throughout the monitoring project. However it should be noted that only limited “opportunistic” sampling has been conducted at these sites. Nutrient concentrations were also fairly similar for the Cape and Campaspe Rivers, and typical of a grazed Burdekin subcatchment.
Total suspended sediment loads calculated from monitoring data at Taemas during 2002-3, 2004-5, 2005-6 & 2006-7 wet seasons are reported to be 65 kt, 110 kt, 31 kt & 175 kt. When adjusted to the mean annual flow, these loads become 242 kt, 201 kt, 340 kt & 205 kt respectively. All four years had below average wet season flows. Monitoring data for all four years consistently show lower than predicted sediment loads leaving the Cape Campaspe Basin, including the flow adjusted loads which averaged 247 kt over the four years. It therefore appears that modelled predictions may be overestimating the total suspended sediment load leaving the Cape Campaspe Basin. Model results for nutrient loads show little relationship to monitoring data and are not considered to provide reliable predictions of nutrient loads.
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 Cape Campaspe Basin is proportioned as follows:
- A Condition: 14%
- B Condition: 33%
- C Condition: 48%
- D Condition: 5%
Data from the Cape Campaspe Basin is based on 811 observations.
On the basis of the rapid assessment, the Cape Campaspe Basin is estimated to have the largest proportion of land in poor (C) condition (48%), followed by fair (B) condition (33%) and good (A) condition land (14%). 5% of observed land was in very poor (D) condition.
Ground Cover in the Cape Campaspe Basin is proportioned as follows:
- ( BC) Bare Cover: 1%
- ( LC) Low Cover: 20%
- ( MC) Moderate Cover:38%
- ( HC) High Cover: 38%
- (VHC) Very High Cover: 3%
Data from the Cape Campaspe Basin is based on 788 observations.
On the basis of the rapid assessment (2004-2007), the Cape Campaspe Basin is estimated to have the highest proportion of land within the moderate (MC) ground cover category and the high (HC)(38%), followed by low (LC) cover (20%) categories. 1% of land was estimated to fall into the bare cover (BC) category.
Resource Condition Summary
The Cape Campaspe Basin is intermediate in size (~ 20,000 sq. km.) and covers around 15% of the BWQIP region. Common to most of the BQWIP basins, land use is dominated by grazing on natural pastures.
Approximately 18% of the land area is set aside for conservation and minimal use, mostly as remnant native vegetation. Riparian habitat is currently in similar condition throughout the basin and is assessed to be in fair (B) condition. Cape Campaspe Basin waterways are generally dry and sandy, with few permanent water bodies.
Hillslope erosion is identified by models as the major source of sediment and particulate nutrients affecting water quality within the Cape Campaspe Basin, while gully erosion is also identified as a significant contributor. The overall rate of soil loss is predicted to be comparatively low, without major differences between subcatchments, possibly due to a combination of low relief and rainfall. The Campaspe River subcatchment is predicted to have the highest rate of soil loss within the basin and to contribute the most sediment to the end-of-basin load, while the Cape River subcatchment is predicted to have the lowest rate of soil loss. Rapid assessment of grazing land condition rates nearly half of the land area as poor (C), with another one third of the basin in fair (B) condition. Analysis of ground cover from satellite imagery (reference) identifies substantial areas of vulnerable and marginal 'D' condition land, particularly along the lower reaches of the Campaspe River and Natal Creek.
Water quality in the Cape Campaspe Basin is predicted by models to have only slightly elevated loads and concentrations of suspended sediment at the end-of-basin. Modelled and monitored sediment concentrations are generally consistent; both identify the Campaspe River subcatchment as the major source of sediments and nutrients. However, monitoring data indicate that the models may be overestimating the total suspended sediment load leaving the Cape Campaspe Basin.
Water Quality Targets
The following water quality Resource Condition Target was 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 NQ Dry Tropics staff.
Attain a minimum 40% reduction in mean annual sediment load from the Cape Campaspe Basin (measured at Taemas) from current (2008) by 2058 (i.e. a reduction from approximately 325 kt/yr in 2008 to 195 kt/yr by 2058).
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