A partial coastal retreat has been proposed as the best way to protect St Clair and St Kilda Beaches and what lies behind them.
Associate Prof Mike Hilton, of the University of Otago geography department, presented a summary of his recent report on beach protection research at a community meeting at the St Clair Surf Life Saving Club last night.
His report, ''The Ocean Beach Coastal System'', was commissioned by the Dunedin City Council after representations to the council by the St Clair Action Group (SCAG).
He said that over the next 20 to 50 years, strong efforts would be needed to protect assets at St Clair, including the Esplanade.
But a better approach for other assets, including playing fields, would be to manage some coastal retreat. That would give the beach more room to replenish storm-related sand loss naturally.
He suggested moving some of the coastal defences further back from the sea along parts of Ocean Beach. A gradually rising slope before reaching the defences would allow dunes to regenerate more more naturally.
This would also allow more room for the beach itself, given the prospect of rising sea levels.
Addressing about 20 people at the meeting, called by the SCAG, Prof Hilton said present management problems ''had their origin in management decisions made over a century ago'', when the beach and much of the hinterland were ''reclaimed''.
That was when the sports fields, John Wilson Ocean Dr, Chisholm Park Golf Club, the Esplanade and other amenities of the Ocean Beach Domain were formed.
''Dunedin needs a long-term strategy that should aim to protect the beach, to maximise amenity values, and accommodate coastal processes.''
Prof Hilton also said the time was right for further collaborative approaches and more public discussion.
In the report, he said protecting the domain from the sea with structures, hard or soft or with beach nourishment, was ''expensive and runs the risk of unintended consequences and loss of amenity values''.
The current approach involved cleaning up after storm-forced erosion, repairing structural damage and maintaining access to the beach. The annual cost of this was already significant ''and this cost will rise with global sea level rise''.
The city needed to develop a coastal management plan for Ocean Beach and the Esplanade, and the report sought to contribute to that by examining findings of ''various coastal agencies and consultancies'' over the past 50 years, he said.