Northern Beaches Council will start work to replace the old timber retaining wall at Clontarf Reserve with a new sandstone seawall. The timber retaining wall was washed away during the severe East Coast Low storm event in June 2016.

Northern Beaches Council General Manager Mark Ferguson said the new seawall will better prevent erosion and add significantly to the amenity of Clontarf Reserve.

"In comparison to the older type timber wall constructed using timber sleepers the sandstone wall is far more permanent, requires less maintenance and will provide better public amenity at Clontarf Reserve.

"The new seawall will be built along the same alignment as the old wall and will sit at approximately the high tide line, which is high enough to prevent king tides from encroaching onto the Reserve. The wall will also have the stability required in the event of a storm or strong wave action.

"Having a larger better-resourced Council enables these types of projects to be delivered more quickly and efficiently, with funds available and experienced staff designing and constructing the seawall," Mr Ferguson said.

The new sandstone seawall will extend 56 metres from the north-west corner of Clontarf Reserve to the existing stone steps near the tidal pool.

It will be built one metre high on the beach side (depending on the seasonal movement of sand), be flush with the Reserve side and have a thickness of half a metre.

On the Reserve side, the area will be turfed to meet concrete capping that will be constructed along the top of the wall's sandstone blocks to match existing work.

The seawall will cost approximately $65,000 to construct and is scheduled to be completed in mid-March, subject to weather conditions.