SAND from a Gippsland quarry being used to replenish eroded Portsea beach is being washed out into Port Phillip Bay by high tides.

Local are aghast at the actions of Department of Sustainability and Environment contractors, with a Sorrento-based mariner claiming a huge pile of sand dumped on the beach ready for spreading was washed away by one high tide last Wednesday.

"This occurred due to a flood tide and a northerly wind, and higher tides are predicted for next week," he said.

Last week, world renowned coastal engineer Gerry Byrne of Sorrento told The Mail the erosion had been caused by extra swell generated in Bass Strait or the Southern Ocean and called for detailed mathematical modelling of refraction and diffraction of waves as they travel from outside The Heads to Portsea.

"As a general principle, if we don't know what is causing a problem, we are unlikely to be able to fix it. The government, through DSE, is spending $1million on 'fixing' Portsea and will be monitoring it for the next two years. I think they should be doing proper studies and doing them quickly."

Peter Watkinson of DSE said: "We are confident that the works we are doing are best practice."

The government is spending $1million to repair the pier, replenish the beach with 10,000tonnes of sand and install 1000 huge sandbags to protected eroding dunes.