Salinity risk for in the Cattle Creek sub-catchment of the Mitchell River, Queensland

Webb, Ian, Hateley, Louise, Nelson, Paul, and Dwyer, Mike (2005) Salinity risk for in the Cattle Creek sub-catchment of the Mitchell River, Queensland. Report. Qld Department of Natural Resources, Mines and Water, Mareeba, QLD, Australia.

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Abstract

In Queensland’s Northern Gulf Region, irrigation salinity risk factors occur in many areas, including parts of the Mareeba-Dimbulah Water Supply Scheme (MDWSS). A specific risk of salinity arising from irrigation has been identified by the Department of Natural Resources, Mines and Water for Cattle Creek, a subcatchment in the headwaters of the Mitchell River. This sub-catchment was selected by the Northern Gulf Resource Management Group (NGRMG) for further investigation as an example of irrigation salinity risk. Cattle Creek covers an area of 16,700 ha, which represents roughly 20% of the MDWSS.

Groundwater monitoring in the Cattle Creek catchment began in 1987. Concern was raised shortly after this when groundwater levels in many of the observation bores were found to be rising up to 0.5 m per year in some parts of the catchment. Some of the consistently rising bores are extremely saline, with electrical conductivity (EC) up to 28,000 μS/m. Due to the watertable rise in some areas, there is a concern of major degradation of the natural resources with impact on primary production, downstream water quality and ecosystem health.

Investigations in the mid-1990s included the development of a groundwater model, but irrigation salinity risk assessments and maps were not developed. With changes in land use and irrigation practices since the mid- 1990s, plus the availability of updated groundwater records, it was considered timely to conduct new research to provide scientific information on the current salinity status and future salinity risk in the catchment.

The aims of this study are to inform the Queensland Government, Natural Resource Management (NRM), catchment and local groundwater management planning groups. The Cattle Creek Land Care members, Mitchell River Watershed Management Group representatives, landholders and the NRMW Land and Water Science team, used the action learning framework of “Plan, Act, Observe and Reflect” as the core process for collaboration in this project. The main objectives were to collate and review existing information, conduct detailed work required as input for modelling irrigation salinity and to provide information, tools and recommendations.

The area under irrigated agriculture doubled from 1,400 to 3,100 ha between 1992 and 1996 and has further increased to at least 5,400 ha by 2004/5. The total area under sugar cane increased from 3,862 ha in 1996 to 5,998 ha in 2001, but then decreased to 4,390 ha in 2004/05. In the period 1996-2000 there was an expansion in the use of overhead irrigation systems (centre pivot or linear move) for sugar cane to 860 ha, with the balance as furrow irrigation. Most of the irrigated cane is grown in the Arriga flats, a relict floodplain with dominantly clay soils, but which also has bands of sandier soils of higher permeability.

Recharge has changed in some areas due to changing land use and irrigation practices. Furrow irrigated sugar cane on permeable, light to medium textured soils is estimated to have the highest recharge rate. Over the 1997-2003 period water tables fell in the Paddy’s Green area. This is thought to be due to the cessation of irrigating tobacco and to the installation of interception drains. During the same period water tables rose in the Arriga Flats area. The streams in the Arriga flats part of the catchment are expected to discharge saline groundwater more frequently and in more places as water tables rise.

The total salt load to 20 m depth is moderate to high in the Arriga Flats section and reaches a maximum near the junction of Cattle Creek and Dingo Creek. Of the total salt load to 20 m depth, most is in the groundwater.

EMI surveys and deep soil sampling showed that there are two main hotspots of soil salinity: the larger one near the junction of Dingo Creek and Cattle Creek and the other at the junction of Chettle Road and the railway line. Chloride profiles show that these are salt discharge areas and that discharge to the soil surface occurs at least intermittently. There have been several incidents of crops in the Arriga flats being affected by soil salinity.

The project used simple spatial models to assess salinity risk. The surfaces for current depth to water table and total salt load were combined to produce the current salinity risk map (Appendix G - Map 19). This shows that approximately 466 ha have depth to water table of less than 4m and moderate (10-20 kg Cl/m2) or high (>20 kg Cl/m2) salt load. A second spatial model combined the distribution of salt load with trends in groundwater levels to assess future salinity risk. The Future Salinity Risk map (Appendix G - Map 20) shows the areas most susceptible to salinisation impact. A total of approximately 372 ha has moderate (10-20 kg Cl/m2) or high (>20 kg Cl/m2) salt load combined with the prediction that the water table will rise to within 2 m of the soil surface in the period 2004-2010. Flats are likely to become waterlogged and eventually saline. However, this may be avoided if suitable management options are identified and are successfully implemented. Management solutions will be required for recharge as well as discharge areas.

Further research is required on recharge under different soils, vegetation types and crop irrigation practices, with a view to improving water use efficiency and reducing deep drainage to the aquifer. The recharge estimation in this study used the SALF model, but the future work should use current best available methods. Continued monitoring of land use changes and irrigation practices is also required to help quantify recharge in the catchment. In areas with complex soil patterns, for example on the relict floodplains of the Arriga flats, this work should be supported by more detailed soils mapping and measurement of soil physical attributes. This data will be essential for future groundwater and salinity risk modelling and the matching of irrigation practices to soil and crop types to improve irrigation efficiency.

Groundwater monitoring must be continued in the catchment. It may be possible to gain insights into the relative contributions to groundwater rises from different water sources if electronic data loggers are installed on selected bores. The streams in the Arriga flats part of the catchment need to be closely monitored for discharge of saline groundwater.

A better understanding of the aquifers is needed, for example, the 1996 groundwater model in MODFLOW had to assess a large number of alternate scenarios, in part because of lack of knowledge of groundwater behaviour in the southeast of the catchment.

On-going monitoring of irrigation water inputs into the catchment is required. This should be compiled annually to ensure that this data is available for future modelling and improved water management.

As result of catchment studies in the mid-1990s some management actions were put into place to help reduce the risk of salinisation in Cattle Creek. It is recommended that a review of the effectiveness of these measures be conducted and alternatives considered, with a view to optimizing future management options.

Salinity risk assessments need to be conducted in other irrigated areas in the Northern Gulf catchments. Nelson and Webb (2004) reviewed the main needs and identified the Biboohra section of the MDWSS as a priority area. Recent local outbreaks of surface salinity and periodically high water tables in the southern part of this section reinforce this priority.

Community awareness of the risks from water-logging and salinity needs to be updated. As a first step an information leaflet is planned, which will make the findings of this study more widely available. Ongoing technical support should be provided for landholders making decisions regarding investment in improved irrigation and drainage practices.

Item ID: 11718
Item Type: Report (Report)
ISBN: 978-1-74172-187-4
Date Deposited: 14 Sep 2010 00:12
FoR Codes: 04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040603 Hydrogeology @ 20%
05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050302 Land Capability and Soil Degradation @ 40%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0701 Agriculture, Land and Farm Management > 070101 Agricultural Land Management @ 40%
SEO Codes: 82 PLANT PRODUCTION AND PLANT PRIMARY PRODUCTS > 8298 Environmentally Sustainable Plant Production > 829805 Management of Water Consumption by Plant Production @ 100%
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