Fairy Bower wave overtopping monitoring | Water Research Laboratory

Year: 2019-ongoing
Client: Northern Beaches Council

Located on Guringai land south of Manly Beach, Fairy Bower seawall fronts 750 m of high traffic pedestrian promenade (Marine Parade), and experiences several wave overtopping events each year that are hazardous to pedestrians and potentially damaging to infrastructure.

In 2019 WRL launched the wave overtopping early warning and monitoring system at Fairy Bower in Manly, with project partner Northern Beaches Council.

A typical Saturday in summer along Marine Parade, 2022.

A wave overtopping event captured by the monitoring system camera, 2019.

The early warning system developed by Coastal Engineers Ian Coghlan, James Carley and Dr Dan Howe comprises a fixed position Spectur video camera for real-time and post-event viewing of overtopping occurrences, coupled with an automated forecast tool for overtopping hazard.

Ordinarily Fairy Bower presents as a typically sheltered location; however, the overtopping hazard is very sensitive to the nuances of wave direction and period. Including variations in tide, tidal anomaly, wave height, period and direction, forecasting the risk to this stretch of coastline is particularly challenging.

The overtopping forecasts created by the system are based on offshore ocean conditions, coupled with site specific wave transformation modelling, which consider the characteristics of the nearshore zone close to the promenade. Forecast hazardous conditions above a threshold during the next 7 days trigger an automated warning alert via e-mail to Northern Beaches Council and WRL staff ahead of time. In addition to this, these staff can access the latest wave overtopping forecast via a website.

This complete monitoring and decision support system enables Northern Beaches Council staff to better manage overtopping hazard at the site by informing pedestrians to keep an eye on the water as the walk and, if necessary, limiting access to Marine Parade. The live camera system allows Council to monitor conditions remotely and provides the opportunity to fine tune the forecasts delivered by WRL to improve the reliability of the overtopping predictions.

Prior to the early warning system being installed, WRL captured this video at the beginning of the famous east coast low that impacted the Northern Beaches in June 2016.