Large and stormy surf overnight has ripped away large chunks of Sydney sandy beaches. 

Image: Large surf overnight caused significant beach loss across Sydney, coming close to properties at South Narrabeen. 

The deep feed of easterly flow that has led to significant rainfall and flooding over eastern New South Wales over the past two days pointed gale force winds towards the greater Sydney region overnight. These winds generated very large waves from the east, reaching significant wave heights of 4.5-5m and a maximum wave height of 9m overnight into this morning. 

Image: Modelled significant wave heights early on Saturday April 6, with wave heights reaching 4-5m over the region. 

In New South Wales, the largest and most powerful swells usually come from the south, with south-facing beaches benefiting from large sand dunes and offshore sand bars to protect them. When big waves come from the east (or northeast), beaches usually sheltered from the prevailing southerly swells are exposed to the full grunt of the waves, leading to more significant erosion with less protection available. 

Image: Comparison of the pre-and-post-storm beach state at South Narrabeen, with a significant 1-2m drop off, or berm, having formed along the beach. 

Image: Formation of a 1-2m berm along Narrabeen Beach as a result of large waves overnight, with fringing coastal properties less than 30m from the lapping waves. 

The Collaroy-Narrabeen stretch of Sydney’s Northern Beaches is a notorious erosion hot-spot due to poor urban planning in the last century, leading to houses and apartments replacing the sand dunes. Without this natural sand buffer, significant erosion events have plagued this stretch of the coastline, including the collapse of a backyard pool into the ocean back in 2016. An assessment of the beach conditions before last night's storm revealed a 40-60m wide beach. This morning the beach was 20-30m wide, and in some places the waves were lapping into people’s yards. 

Image: Comparison of the pre and post storm beach state in front of the Collaroy-Narrabeen sea wall, with a significant width of the beach being taken to sea. 

The past year has featured a general lack of large swells affecting east facing stretches of beach, which has allowed a healthy build up of sand, protecting the beach and nearby properties from damaging erosion. A shift away from El Niño in the coming months, with the possibility of other large easterly swell event will have residents and local beach goers concerned of future possible significant erosion events. 

Image: Waves lapping along the fringe of coastal properties on Collaroy Beach on Saturday April 6. 

A Severe Weather Warning for Damaging Surf is currently in place for coastal parts of New South Wales south from Sydney, with a Hazardous Surf Warning in place for coasts from the Hunter to Eden. Please refer to the latest warnings at: https://www.weatherzone.com.au/warnings