Chapter 5: Opportunities for water resource development in the Mitchell catchment

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Petheram, Cuan ORCID ID icon; Barry, Karen ORCID ID icon; Davies, Phil ORCID ID icon; Doble, Rebecca; Gonzalez, Dennis ORCID ID icon; Hughes, Justin; Page, Declan ORCID ID icon; Rogers, Lee; Taylor, Andrew ORCID ID icon; Vanderzalm, Joanne ORCID ID icon; Yang, Ang


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Petheram C, Watson I, Bruce C and Chilcott C

Water can be sourced and stored for irrigation in the Mitchell catchment in a variety of ways. Major dams: Major instream dams could supply the largest quantities of reliable water of any of the storage options considered in the catchment. Four of the more promising major dams in the Mitchell catchment could supply about 2800 GL of water in 85% of years at the dam wall, or about 1540 GL to the crop after losses. This would provide sufficient water to irrigate about 140,000 ha of land throughout the year (e.g. a crop such as sugarcane), but this does not consider the current regulatory environment and the needs of other water users. Eight potential dam sites were selected for pre-feasibility analysis on the basis that these were the more cost-effective sites in distinct geographic areas in proximity to soils suitable for irrigated agriculture. The sites with the lowest cost per ML supplied were the Pinnacles dam site on the Mitchell River, the Rookwood dam site on the Walsh River and the Palmer dam site on the Palmer River. These had equivalent annual unit costs of 45, 84 and 92 $/year per ML/year respectively. For any of the options to advance to construction, far more comprehensive studies would be required. Groundwater extraction: Excluding the natural water bodies discussed later, groundwater extraction from the Bulimba Formation is the cheapest method of supplying water for irrigated agriculture in the Mitchell catchment (Table 5 1). However, the total groundwater resource in the Bulimba Formation is likely to be less than 5 GL/year, sufficient to irrigate a maximum of 350 ha throughout the year, with a maximum of 1–2 GL/year at each location. It is possible that up to an additional 5 GL/year of groundwater could potentially be extracted from the Gilbert River Formation within 50 km from the outcropping areas and up to another 5 GL/year could potentially be extracted from alluvial aquifers associated with the Gilbert River Fan Aggregation. At each location a maximum of about 1 GL could potentially be extracted, sufficient to support small-scale irrigation developments. Due to the steeply dipping nature of the Gilbert River Formation, groundwater extraction from this formation would need to be within 50 km from outcropping areas to be economically viable. Water harvesting and farm-scale offstream storage: Water harvesting and large farm-scale offstream storages such as ringtanks are comparable in cost (i.e. equivalent annual unit cost) to major dams, but more expensive than groundwater and gully dams, largely due to the costs of pumping water. They can, however, enable larger areas of irrigated agriculture in the Mitchell catchment than groundwater and gully dams. It is possible to pump or divert about 2000 GL of water in 85% of years into large farm-scale offstream storages such as ringtanks sited adjacent to major rivers. After evaporation, seepage, conveyance and field application losses this is sufficient water (1100 GL) to irrigate about 200,000 ha of a single dry-season crop. Below the confluence of the Mitchell and Palmer rivers where broad–scale flooding occurs adjacent to the major river channels, well-constructed ringtanks can withstand slow-moving floodwaters. However, rotations that seek to maximise the use of land developed for irrigation by also cropping during the wet season would carry considerable risk, unless flood control measures are implemented. Furthermore, accessing land during the wet season, below the confluence of the Mitchell and Palmer rivers in particular, would be very challenging without considerable upgrades to infrastructure such as roads and bridges. Large farm-scale gully dams: Large farm-scale gully dams are slightly more expensive than groundwater extraction, and are cheaper than other water supply options.



dam, groundwater, irrigation, regulation, managed aquifer recharge, ringtanks, water harvesting, farm dams; Northern Australia Water Resource Assessment; NAWRA

Water Resources Engineering

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Water resource assessment for the Mitchell catchment. A report to the Aust Govt from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund


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Petheram, Cuan; Barry, Karen; Davies, Phil; Doble, Rebecca; Gonzalez, Dennis; Hughes, Justin; Page, Declan; Rogers, Lee; Taylor, Andrew; Vanderzalm, Joanne; Yang, Ang. Chapter 5: Opportunities for water resource development in the Mitchell catchment, In: Petheram C, Watson I, Bruce C and Chilcott C, editors. Water resource assessment for the Mitchell catchme. Canberra: CSIRO; 2018. <a href="" target="_blank"></a>

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