Three days before Warragamba Dam could spill due to severe storms, the Baird government has committed to raising its wall to prevent a potential flood disaster in western Sydney, four years after being advised to review the options.

As a looming east coast low raised the possibility that the dam could spill on Sunday, the government said it will commit $58 million towards raising the wall by 14 metres to avoid a catastrophe that could place 43,000 western Sydney residents at risk.

Construction, at an estimated cost of about $690 million, is expected to be complete within three to four years after a business case is signed off in 2019, subject to planning approvals.

The Hawkesbury-Nepean Valley between Penrith and Sackville has the greatest flood risk of anywhere in NSW.