Beach response to Australian East Coast Lows: A comparison between the 2007 and 2015 events, Narrabeen-Collaroy Beach

East Coast Lows (ECLs) are intense extratropical cyclones that form off the east Australian coastline and are known to cause significant beach erosion. This study presents analysis of the beach response to two severe ECLs that occurred in the Sydney region in June 2007 and April 2015 based on a three-dimensional coastal monitoring program undertaken at Narrabeen-Collaroy Beach. The results indicate considerable reductions in the subaerial sand volume for both storms, with an average (maximum) reduction of 78 m(3) (124 m(3)) per alongshore meter for the 2007 event and 58 m(3) (104 m(3)) per alongshore meter for the 2015 event. The overwhelming majority (93%) of subaerial beach erosion for both storms was observed to be within the berm section of the beach profile. Further analysis into the alongshore variability of cross-shore beach response reveals that the enhanced erosion during the 2007 event was mainly concentrated in the mid to northern sections of the embayment. It was found that this enhanced erosion was predominantly a result of a greater berm volume in this section of the embayment prior to storm arrival and that berm response to these two events was very similar (R-2 = 0.81) when considering erosion as a percentage of the pre-storm berm volume. It is concluded that the berm reduction as a percentage of the pre-storm berm volume can potentially provide a suitable predictor for the beach response to severe ECLs within littoral cells along this coastline.