Shire of Irwin
|Area||~2,374 square kilometres, located ~360 km north of Perth.|
|Towns||Arrowsmith, Dongara and Port Denison.|
|Average Temperature||Mean daily maximum temperature over 30 years 1990 – 2019
32.7°C (Jan) and 20.5°C (Jul).
|Annual Rainfall||Average annual rainfall over 30 years 1990 – 2019 357 mm (BoM 2020).|
|ABS Profile||Irwin ABS profile|
|Shire Website||Shire of Irwin|
Around 3,600 people live in the Shire of Irwin, most of whom (~2,780 people) live in the contiguous coastal towns of Dongara and Port Denison (ABS 2016).
The population in the Shire of Irwin remained stable between the last census in 2011 and the most recent census in 2016, but is projected to decrease by 12% by 2031 (DPLH 2016).
Approximately 14% of residents of the Shire of Irwin were born overseas and approximately 2.5% are of Aboriginal and / or Torres Strait Islander descent.
Estimates of the resident populations as at 30 June are released annually for Local Government Areas (LGAs) in Australia by the Australian Bureau of Statistics. The estimates are generally revised 12 months later and final estimates are available after the following census. Visit the ABS website for further details.
The Shire of Irwin area has a diverse economy which includes agriculture, fishing, construction, and mining (oil and gas, mineral sands). Local farming includes the production of cereal crops (wheat, canola, lupins, oats), fruit and vegetable crops (olives, mangoes, melons), and livestock (sheep and cattle). The fisheries sector is focused on a large and productive western Rock Lobster industry. The picturesque coastal towns are popular holiday destinations and tourism is an important part of the local economy.
The main land in the Shire of Irwin includes are agriculture, commercial, industrial, residential and nature conservation.
Yardanogo Nature Reserve
The Yardanogo Nature Reserve covers ~8 711 ha and is located south east of Dongara. The reserve forms part of the Yamatji conservation estate.
Dongara Nature Reserve
The Dongara Nature Reserve covers ~69 ha and is located on the northern boundary of Dongara.
Beekeepers Nature Reserve
Beekeepers Nature Reserve extends from Jurien Bay to just south of Dongara, covering ~88 000 ha. A great variety of wildflowers can be seen in the reserve during the season.
The majority of the shire lies on the Yarragadee formation, formed during the Jurassic period form volcanic and sedimentary rock and consisting of fine to coarse grained sandstone interbedded with shale. The geology underlying the southern coastal boundary between Coorow and Irwin is the Cattamarra Coal Measures. The Cattamarra was formed during the Jurassic period from volcanic and sedimentary rocks and consists of siltstone, shale, claystone, coal and sandstone. The geology underlying the northern coastal boundary between the Irwin and the City of Greater Geraldton is the Kockatea Shale. The Kockatea Shale formed during the Triassic period from volcanic and sedimentary rock and consists of shale, minor siltstone and sandstone.
Deep calcareous sands overlies a series of coastal dune systems and low hills, with relict dunes and limestone outcrops dominating coastal areas. Inland, the landscape is undulating and characterised by deep siliceous sandy soils.
The shire is located within the Geraldton Hills (GES01) and Lesueur Sandplains (GES02) IBRA sub-regions and is characterised by proteaceous scrub heath and low close acacia shrublands on alluvial plains. The only Threatened Ecological Community known to occur in the shire is the Clay Flats Assemblages of the Irwin River, which is presumed destroyed. One Priority Ecological Community, Coastal Sands dominated by Summer-scented Wattle Acacia rostellifera, Ooragmandee Eucalyptus oraria and Dongara Mallee E. obtusiflora, occurs in the shire.
The coastline of the Northern Agricultural Region consists mainly of sandy beaches backed by low dunes, valued for recreational, aesthetic and cultural reasons and as storm protection and habitat. Primary dunes, or foreshore dunes, refer to the first system of dunes shoreward of the low water mark. These dunes typically support little vegetation. Secondary dunes, or back dunes, are undulating, sandy ecosystems located further from the water.
7 Mile Beach
The 7 mile beach Rock Lobster monitoring site is accessible, shallow and located near the center of the Western Rock Lobster’s distribution. Long term monitoring studies conducted at the site provide much of the published data on Rock Lobster foraging and recruitment.
The Central West Coast limestone reef system extends from Kalbarri to Perth and supports an extremely high species diversity of seagrasses. Extensive seagrass meadows in protected, near-shore areas of the NAR, provide shelter and nursery habitat for many fish and other marine creatures including Western Rock Lobster. Seagrasses also provides services as primary biomass producers, sources of dissolved oxygen, sediment traps and nutrient cyclers.
Arrowsmith Groundwater Area
The Arrowsmith Groundwater Area covers approximately 10,300 km2 and produces ~151 million m3 of available groundwater per year. The largest aquifers occur in the Yarragadee and Parmelia formations and recharge primarily from rainfall recharge. The Superﬁcial formation is an important resource near the coast. Water quality is variable. The Allanooka borefield, 50km south of Geraldton, supplies the integrated water scheme for Geraldton and Dongara/Port Denison.
Drainage Basin Length (km) Catchment Area (km2) Average Stream Salinity (mg/L) Key Characteristics Greenough 160 6,072 3000-35000 Originates east of Mullewa, and has middle and lower reaches with perennial ﬂow due to discharge from the groundwater systems. The river enters the ocean at Dongara and the mouth of the river is a coastal lagoon system, which is blocked by a sandbar for most of the year.
Drainage Basin Length (km) Catchment Area (km2) Average Stream Salinity (mg/L) Key Characteristics Greenough 82 1,605 3000-35000 Commences near Arrino, north west of Three Springs. It has no clearly deﬁned ocean outlet, and drains into a subterranean cave system.