OBJECTIVE

This paper has evaluated the influence of projected water level rise from climate change on overtopping and safety on the Coffs Harbour northern breakwater crest and compares these values with the latest internationally accepted standards of overtopping (PIANC 2003, EAUK 2007). These methods will be extrapolated to two other breakwaters in NSW much used by the public, namely the South Ballina and Forster breakwater crests.

BACKGROUND

From 1990 to date there have been six storms that have resulted in very severe overtopping of the Coffs North breakwater crest. The MHL wave data base has detailed hourly records of these storms. These storms have resulted in damage to boats and finger wharfs, lighting, handrails and fittings on and inside the Coffs Harbour boat harbour. One child was injured.

METHOD AND PRELIMINARY RESULTS

Recorded storm data and previous physical modelling and numerical modelling (REF/DIFF) results will be utilised to estimate the increased overtopping rates expected at the breakwater associated with the NSW projected sea level rise values of 40 cm and 90 cm for the years 2050 and 2100 respectively (DECCW, 2010). The paper provides examples of average overtopping values for depth limited waves at the breakwater at surveyed chainages. (table 1-Ch 585, Slope1:1.4 Tp12s Crest Level 5.2 m AHD). These values exceed allowable overtopping rates for pedestrians (EAUKR 2007).

CONCLUSION

This paper uses the well accepted numerical model REF/DIF and irregular wave flume physical modelling results for the Coffs North breakwater. The estimates of wave heights and overtopping rates from these models are utilised to evaluate the influence of projected water level rise associated with climate change on overtopping and safety on the Coffs Harbour northern breakwater crest. The estimated overtopping rates are compared with the latest internationally accepted standards of overtopping (PIANC 2003, EAUKR 2007).