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|
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 uses as shown in the Local Planning Scheme for the Shire of Irwin includes reserves, agriculture, residential, commercial and industrial.
For more information about land use in the region, visit the Land Use theme page.
The Yarragadee formation underlies the majority of the Shire of Irwin. The Yarragadee formation was formed during the Jurassic period form volcanic and sedimentary rock. The Yarragadee formation consists of fine to coarse grained sandstone with thin interbeds of shale. The geology underlying the southern coastal boundary of Shire of Coorow and Irwin the Cattamarra Coal Measures. The Cattamarra was formed during the Jurassic period from volcanic and sedimentary rocks. The formation comprises of siltstone, shale, claystone, coal and sandstone. The geology underlying the coastal boundary between the CGG and Shire of Irwin is the Kockatea Shale, which was formed during the triassic period from volcanic and sedimentary rock. The Kockatea Shale consists of shale, minor siltstone, sandstone with deposits of calcareous sandstone.
Deep calcareous sands overlies a series of coastal dune systems and low hills with relict dunes and limestone outcrops along the coastal area of Shire of Irwin. The eastern portion of the Shire consists of deep siliceous sandy soils overlying a complex undulating landscape.
Please go to the below link for more information on soil and geology in the region
Priority Fauna Species
Lesueur Sandplains (Geraldton Sandplains 2)
The Geraldton Hills is located in the LGAs in the middle portion of the region. This subregion is characterised by Proteaceous scrub heath dominates the undulating sandplain lying over the Permian and Cretaceous strata. Outwash plains associated with the drainage lines are dominated by York Gum and Jam woodlands. The lateritic mesas, sandplains, coastal sandplains and limestone are rich in shrub-heaths (Desmond and Chant, 2001c).
Geraldton Hills subregion (Geraldton Sandplains 1)
The Geraldton Hills is located in the LGAs in the middle portion of the region. This subregion is characterised by sand heaths of emergent Banksia and Cypresses, York Gum woodlands on alluvial plains. Areas of limestone are dominated by proteaceous heath and Acacia scrubs. Low closed Acacia shrublands occupies much of the alluvial plains associated with the Greenough and Irwin Rivers (Desmond and Chant, 2001b).
Threatened Ecological Communities
Priority Ecological Communities
Coastal sands dominated by Acacia rostellifera, Eucalyptus oraria and Eucalyptus obtusiflora
Floristically, this community is similar to other Acacia rostellifera communities but is differentiated on structure, being dominated by mallee eucalypts. The community occurs on limestone ridges, in some swales in the coastal dunes between Cape Burney and Dongara, on the Greenough Alluvial Flats on limestone soil and near Tarcoola Beach. Some very small occurrences have also been recorded on the limestone scarp north of the Buller River.
Category (WA) – Priority 1
For more information visit the DPaW website.
Primary and Secondary Coastal Dunes
Primary dunes (from low water mark) and secondary dunes. Valued for recreational, aesthetic and cultural reasons, along with the services provided for storm protection and habitat.
Seven Mile Beach Rock Lobster Monitoring Site
This shallow water site is located near the centre of the western rock lobster’s range of distribution. Studies conducted at the site provide much of the published data on rock lobster foraging and recruitment.
Seagrasses are flowering plants that complete their life cycle submerged in seawater. Western Australia has the world’s highest diversity of seagrasses, with 27 species occurring in shallow waters off the coast. Seagrasses form a vital component of marine ecosystems through their services as primary biomass producers, sources of habitat (including breeding and nursery areas) and dissolved oxygen, sediment traps, and nutrient cycling. Seagrass distribution is determined by a combination of shelter, sediment, turbidity, nutrient, temperature, current and tidal influences.
Extensive seagrass meadows occur in protected near-shore areas of the NAR, where clear water, low nutrients and sandy sea floors prevail, and are dominated by the long strap-like Ribbonweed or Strapweed (Posidonia spp) and the thin-stemmed Wireweed (Amphibolis spp).
Seagrass habitats are fragile and susceptible to damage and can take many years to recover from disturbance, such as physical damage/removal and shading due to algal blooms (as a result of increased nutrients), and sedimentation (due to dredging activities and erosion in catchment areas).
More information on seagrasses in Western Australia can be found in the following publications: Flowers of the Ocean: WA’s Expansive Seagrass Meadows; The Wonders of Weed Information Sheet; Fisheries Fact Sheet: Seagrasses; Establishing Reference and Monitoring Sites to Assess a Key Indicator of Ecosystem Health (Seagrass Health) on the central west Coast of Western Australia (see references).
Gascoyne Groundwater Area
The Gascoyne Groundwater Area extends north to Kalbarri and bounds the Arrowsmith Groundwater Area east to pastoral country. The largest groundwater aquifer occurs in the Yarragadee Formation, which has an estimated yield of 22.5 million m³/year (NACC, 2005). Groundwater from fractured rock aquifers in the eastern, inland part of the region is predominantly saline and poor yielding. This region of the Gascoyne Groundwater Area falls under the Carnarvon Artesian Basin Allocation Plan.
Located 50 km south of Geraldton in the Arrowsmith groundwater area, the Allanooka Borefield houses the bores and summit reservoir that provide an integrated scheme water supply for the area between and including the City of Greater Geraldton and the towns of Dongara/Port Denison in the Shire of Irwin.
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.