The City of Wanneroo is calling on the McGowan Government to build a new desalination plant in Alkimos by 2028 saying the Water Corporation’s reliance on the Gnangara Mound to supply water for Perth and Peel is unsustainable.

The city’s call, which also includes a request for a wastewater recycling plant, is in response to the government’s release of the draft Gnangara groundwater allocation plan (GGAP).

In its submission on the plan – supported by councillors at their February 15 meeting – the city said the Water Corporation used 110.8GL of the total 274.2GL of water taken from the Gnangara Mound per annum while growers currently used 61.6GL a year.

If the proposed 10 per cent water reduction for the agriculture and horticulture sectors came into effect in 2028 the city said those sectors would be required to reduce their usage to 56.5GL per annum.

This meant North Wanneroo growers would need to reduce on average 6.9 million litres per annum for each license and Gingin agriculture users would lose access to 14.6m litres of water per annum per licence while Swan Valley users would need to reduce by 1.4m litres per annum per licence.

The city said the Water Corporation had the scale to develop alternative supplies and infrastructure whereas any reduction for the agricultural and horticulture sectors would affect productivity and profitability and a 10 per cent cut would likely result in a big number of growers needing to relocate to areas with an adequate water supply.

The draft GGAP already proposes that the Water Corporation be allocated a 27 per cent reduction but the city recommends it face a bigger cut to ensure other users are not unfairly affected by reductions to their capacity to use water for commercial agricultural purposes.

“The city recommends construction of the Alkimos desalination plant by 2028, construction of a wastewater recycling plant and the gradual decommissioning of WaterCorp bores located in the Gnangara Mound to maintain and increase groundwater levels in North Wanneroo,’’ the submission says.

When the draft GAPP was released last year the Department of Water and Environmental Regulation (DWER) said Gnangara groundwater supplied up to 40 per cent of Perth’s drinking water as well as water for horticulture and industry, garden bores, parks and other green spaces north of the Swan River.

It also supports wetlands, caves and bushland with lowered water levels now evident through the visible drying of wetlands such as Loch McNess and the loss of the Yanchep cave ecosystems.

Since 1980 the water table across the Gnangara Mound has fallen by up to 10m – a 1000GL loss of aquifer storage, equivalent to 1000 Optus Stadiums full of water.

The water cuts outlined in the draft GGAP and a proposal to align garden bore sprinkler rosters with the scheme sprinkler roster have been put forward as ways to redress the imbalance – the combined saving is expected to be 70GL of water each year.

In 2015-16 City of Wanneroo growers supplied $85.7 million of agricultural produce including strawberries, cabbages, peas, sweet corn and capsicums.

At the February 15 council meeting Cr Glynis Parker said agribusiness in the city should be supported and that Covid-19 had highlighted the importance of local produce while Cr Linda Aitken said if the plan was adopted it would mean relying on the eastern states or oversees for produce.

Technical studies on the north Yeal wetlands and Lake Nowergup have supported the development of the draft GGAP, which DWER said had been developed over five years of consultation with stakeholders.

The Yeal nature reserve in the Gnangara system’s north has wetlands with high regional ecological and cultural significance, including Yeal Lake, Quin Swamp and wetlands associated with upper Quin Brook.

Lake Nowergup is positioned upon the Swan coastal plain at the western margin of the Gnangara Mound, in the northern metropolitan area east of Pinjar Lake, about 37 km north of the Perth CBD.

Since 1973, the watertable in the superficial aquifer below Lake Nowergup has declined by around 3.5m.

Lake Nowergup is a conservation category wetland and Ministerial criteria site under the Environment Protection Act 1986 and a registered site of significance for Aboriginal heritage.

If adopted the proposal to align the domestic garden bore sprinkler roster with the two-days-a-week sprinkler roster for scheme water users in Perth and Mandurah would start on September 1 this year.

Public comment on the draft GGAP and proposed changes to the domestic garden bore sprinkler roster is open until February 28.

This article appeared on Yanchep News Online on 18 February 2022.