The NSW Government has released a long-term plan to mitigate flooding in the Hawkesbury-Nepean Valley.

It includes an initial allocation of $58 million to improve public awareness and flood forecasting and integrate flood risk management into regional planning.

More than 25,000 homes and 2 million square metres of commercial space are subject to flood risk, with the threat expected to increase significantly in the next decade.

Improvements on community engagement and evacuation route signage will start this year.

Next year the State Government will look to improve weather predictions and flood forecasting, and will begin road upgrades. Forty roads are earmarked as priorities for upgrading.

Up to 134,000 people who live and work on the floodplain could require evacuation, and this figure is expected to double over the next 30 years.

In 2019 the Government will implement a regional land use and road planning framework, and in 2020 it will make a full business case for raising the Warragamba Dam wall – which is expected to reduce flood damage by 75% on average.

A government report says while raising the dam wall would make a significant difference, no combination of infrastructure options will eliminate flood risk.