Historically, broadacre agriculture dominated the Midlands area; mainly cereal cropping and pastures for sheep and cattle. More recently, it is being recognised for its potential to support horticultural production, particularly annual vegetable crops, such as carrots, onions, potatoes and leafy vegetables, with perennial tree crops such as citrus, nuts, mangos and olives also being established.
Besides meeting the expansion needs of vegetable growers, the State Government has also received investor inquiries regarding large-scale fruit tree production, beef feed lots and feed-on dairy facilities.The Midlands project sought to provide information on water availability and land suitability for irrigated horticultural growth, through the identification of one or more 2000 to 3000 hectare focus areas suitable for intensive horticulture in the coastal Midwest of Western Australia. The project area covers approximately 17 000 square kilometres, is 120 kilometres north of Perth and stretches along the coast from Dongara in the north to Lancelin in the south, and inland from Mingenew in the north to Moora in the south.
Due to the extensive project area, a Community Reference Group was established to assist in identifying two key focus areas. From this two focus areas were identified, Irwin and Dinner Hill.
Irwin is in the north of the project area approximately 15 km east of Dongara and is underlain by the Yarragadee aquifer. The area is aligned with the Irwin River valley alluvial soils, straddling the Twin Hills, Allanooka and Eneabba Plains groundwater sub-areas of the Arrowsmith Groundwater Area.
Water investigation results within the Irwin focus found, shallow groundwater occurs primarily near the Irwin River and its tributaries. However, this water is relatively saline, and is more suited to stock water than irrigated agriculture.
Soil studies in the Irwin area have generally concluded that, due to the relatively high salt levels of the underlying water sources and the saline and poor draining subsoils, the area is more suitable for broadacre agriculture rather than irrigated agriculture. Irrigation would require careful site selection and substantial soil management in order to be undertaken.
Dinner Hill is in the south of the study area on the Leederville - Parmelia aquifer. It covers 502 square kilometres between Moora, Dandaragan and Badgingarra. Established irrigated horticulture producers are found across the area.
Groundwater investigations identified additional water available across the northern and western parts of the Dinner Hill focus area. However, the volume is insufficient to support significant expansion of land under intensive horticulture.
Investigations also found, existing groundwater allocations in the Dinner Hill area are currently under utilised. Studies have shown that water abstraction in the South East corner of the focus area closest to Moora, has resulted in a reduction in groundwater levels since 2000. The work highlights the need to manage local scale abstraction to avoid adverse effects on water quality, water supply and groundwater-dependent ecosystems.
The Dinner Hill groundwater allocation statement defines the water availability and the rules to access it. The Department of Water and Environmental Regulation website has relevant reports, more information on water allocations and the water register.