A sheet pile barrier in front of the existing concrete structure is the recommended short-term option for addressing damage to the Prince Street seawall between North Cronulla and Elouera beaches.
The Wall, as it is known to surfers, has been severely undermined by a series of storm events in recent years and suffered further damage in this month's big seas.
The Bate Bay Coastal Management Program, which Sutherland Shire Council adopted in April, reported on the condition of the 350 metre hexagonal block structure and examined repair options.
The report said demolishing the seawall and starting again was "a permanent long-term solution, and is recommended for consideration by council as the existing structure nears the end of its design and practical life".
The estimated minimum cost of reconstruction is $15 million, whereas the short term option of sheet piling will cost just 1.45 million (2021 figure).
"The endorsed rectification option is the installation of sheet piling in front of the existing contiguous piling," the report said.
"This sheeting would be sufficiently embedded into the beach sand below a future scour level and fixed to the existing capping beam."
The report further recommended consideration be given to the use of vinyl sheet piling, rather than steel sheet piling from a durability and maintenance perspective.
Vinyl sheet piling was said to have a 50-year design life.
"This type of piling has seen recent advancements in terms of its strength, resistance to UV, and potential for leaching of any chemicals," the report said.
"Vinyl sheet piling can be up to 95 per cent recycled, which is a positive for sustainability."
The report included a summary of repairs to The Wall from when major rectification works were carried out in 2008-2010.
In 2015, a review of the structural condition of the seawall was undertaken after significant subsidence was observed on site.
A trial of rectification measures was undertaken in 2017, but a recommended further trial in 2018 was not carried out.
"Several storm events in October and November 2020 eroded additional sand and caused further washout of material from behind the seawall foundations," the report said.
"As a result, a large number of Seabee units subsided/dropped due to formation of large cavities underneath.
"In December 2020, large voids beneath the Seabees were filled with approximately 160 cubic metres of stabilised sand (low density concrete/sand mixture, with 4:1 ratio of sand to concrete)."