Gray Creek

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Subcatchments

Smaller subcatchments within the Gray Creek Catchment include:

  • Gray Creek
  • Porphyry Creek

Vegetation

Riparian Habitat

iTRARC analysis of Riparian Habitat indicates that this subcatchment was in poor condition in the 1970s, and has not changed much since, with an increase in the number of gaps the only change. The field survey site supports this assessment showing very poor condition, however additional sites would be required to capture the variability of riparian conditions that may persist within the catchment.

iTRARC Scores

Catchment Class 3 E
Maximum iTRARC Score 12 (B+)
1970s Score 4 (C)
2004 Score 3 (C)
Reduction in Ecosystem Services Very Minor
Increase in Potential for Erosion No Change
Reasons for Change in Score
  • Increased number of gaps in the riparian corridor of the main channel

TRARC (field survey) scores

Survey SiteScoreRegenerationWeeds
Gray Ck47 (D)2 (B)1 sp: 20% cover (B)
Average 47 (D)

Reference:Assessing the condition of Riparian Vegetation in the Burdekin catchment

Wetlands

This sub-division is poorly known ecologically, hence the low degree of confidence. The creeks are generally dry with limited habitat availability. Condition is not well known though thought to be similar to adjoining sub-divisions and typical of the upper Burdekin grazing rangelands.

For more information see Gray Creek wetland condition summary

Reference: Assessing the condition of Wetlands in the Burdekin catchment

Water

SedNet Modelling of Water Quality

Model results for the Gray Creek subcatchment are summarized as follows:

  • Subcatchment modelled area: 1,667 sq. km.
  • Source contributions: Hillslope = 66%; Gully = 32%; Streambank = 2%
  • Area of subcatchment with <50% ground cover: 183 sq. km or 11% of subcatchment
  • Hillslope sediment supply: 301 kg/ha/yr
  • Total suspended sediment (flow weighted) supply: 76 kt/yr
  • Total suspended sediment supply (flow weighted; normalized to area): 516 kg/ha/yr
  • Total suspended sediment end-of-subcatchment (flow weighted) yield: 70 kt/yr
  • Event Mean Concentration (EMC - flow weighted): 546 mg/L
  • Mean Annual Flow: 128,613 ML

Reference: Improved SedNet Modelling of Grazing Land in the Burdekin Catchment

Both hillslope and gully erosion are identified as major sources of sediment and particulate nutrients affecting water quality within the Gray Creek sub-catchment (66% & 32% respectively). However, soil loss from hillslopes (301 kg/ha/yr) is relatively lower than many other sub-catchments. This is consistent with the relatively low proportion of the sub-catchment (11% with ground cover below 50%. The loss of sediment and particulate nutrients from all sources (supply) is at a moderate level (458 kg/ha/yr). The sub-catchment receives little rainfall, which drives up the predicted event mean concentration of sediments to a moderate level (546 mg/L).

Water Quality Monitoring

The monitoring site in the Gray Creek catchment is Gray Creek on the Gregory Developmental Road which has been sampled by a BDTNRM volunteer over 1 wet season (2006/07). The monitoring site drains a catchment area of 1006 sq km and the land use is predominately grazing (97.5%). The suspended sediment concentrations monitored in the 2006/07 wet season were relatively high (mean concentration of 2,737 mg/L) compared to other catchments in the Burdekin rangelands. While this concentration is considerably higher than the modelling data, additional monitoring is required to draw meaningful comparisons with the SedNet model.

Relevant information of Water Quality Monitoring in the Upper Burdekin River Basin:

Environmental Values

Aquatic Ecosystems

The aquatic ecosystem values of Gray Creek subcatchment are poorly known and, while considered to be Slightly to Moderately Disturbed (SMD) as a consequence of the surrounding land use for cattle grazing, the biological communities are thought to remain in a healthy condition and ecosystem integrity is likely to be largely retained. No High Ecological Value (HEV) waters are identified in the subcatchment.

Stock Watering

Water supply for production of healthy livestock.

Cultural and Spiritual

Custodial use of water by Gugu and Badhun traditional owners.

References:

Landuse

Principle land uses within the Gray Creek subcatchment as a proportion of total area:

  • Grazing: 90%
  • Conservation & minimal use: 9.6%
  • Water: limited water activity use identified.
  • Mining: Limited mining water activity use identified.
  • Irrigated horticulture & cropping: Limited irrigated horticulture water use identified.
  • Urban & semi urban: Limited urban & semi urban horticulture water use identified.

Grazing Land

Gray Creek is a relatively small subcatchment where land use is dominated by grazing on natural pastures.

Land Condition

Definition of ABCD land condition framework

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 Gray Creek sub-catchment is proportioned as follows:

  • A Condition: 30%
  • B Condition: 33%
  • C Condition: 34%
  • D Condition: 3%

Data from the Gray Creek sub-catchment is based on 64 observations.

On the basis of the rapid assessment, the Gray Creek sub-catchment is estimated to have the largest proportion of land in poor (C) condition (34%), followed by fair (B) condition (33%) and good (A) condition land (30%). 3% of observed land was in very poor (D) condition.

Ground Cover

Ground Cover in the Gray Creek sub-catchment is proportioned as follows:

  • ( BC) Bare Cover: 0%
  • ( LC) Low Cover: 23%
  • ( MC) Moderate Cover: 33%
  • ( HC) High Cover: 33%
  • (VHC) Very High Cover: 11%

Data from the Gray Creek sub-catchment are based on 57 observations.

On the basis of the rapid assessment (2004-2007), the Gray Creek sub-catchment is estimated to have the highest proportion of land within the high (HC) and moderate (MC) ground cover category (33%), followed by low (LC) cover (23%). 11% of land was estimated to fall into the very high cover (VHC) category.

Resource Condition Summary

Gray Creek is a relatively small subcatchment where land use is dominated by grazing on native pastures. Approximately 10% of the land area is set aside for conservation and minimal use as remnant native vegetation, while there are many abandoned and operational mines throughout the subcatchment. Riparian habitat in this subcatchment has changed little over the last 30 years, with only a slight increase in the number of gaps, and is currently assessed to be in poor (C) condition. The Gray Creek subcatchment is a largely sandy, dry seasonal creek system with limited habitat availability. The ecology and condition of water bodies in the subcatchment is poorly known.

Hillslope erosion is identified by models as the major source of sediment and particulate nutrients affecting water quality within the Gray Creek subcatchment, while gully erosion is also predicted to make a significant contribution. The rate of soil erosion is predicted to be moderate and only a little below the basin and BWQIP region average, while the total soil loss to waterways from the subcatchment is comparatively low due to its small area. Grazing land condition is assessed as having approximately equal proportions in good (A), fair (B) and poor (C) condition. This is also reflected in the ground cover assessment (2004-07). Analysis of satellite imagery (reference) identifies areas of more vulnerable 'D' condition land near the top and bottom of the subcatchment, while the mean ground cover over the entire subcatchment fluctuated relatively little between 1999 and 2006 (between 95% and 87%).

Water quality in the Gray Creek subcatchment is predicted by models to have moderately elevated sediment concentrations during wet season event flows. Water quality monitoring data, however, have recorded much higher concentrations of sediment than predicted by models. Comparisons are difficult to draw between the monitoring and modelling datasets due to the small number of samples collected over only one wet season. The high monitored concentrations are difficult to explain in light of quite good ground cover throughout most of the subcatchment and may reflect more extensive gullying than predicted. Additional water quality monitoring is warranted in order to verify model predictions.

Draft Environmental Values

The aquatic ecosystems values of the Gray Creek subcatchment are poorly known and, while considered to be Slightly to Moderately Disturbed (SMD) as a consequence of the surrounding land use for cattle grazing, the biological communities are thought to remain in a healthy condition and ecosystem integrity is likely to be largely retained. No High Ecological Value (HEV) waters are identified in the subcatchment. Little is known about the human use Environmental Values of water in the Gray Creek subcatchment, which are thought to be limited to use for stock watering and the cultural and spiritual values of the Gugu and Badhun traditional owners.

Maps

References

GrayCreek.jpg
Download Catchment Layer as *.kml (requires Google Earth)

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