NSW coastal ocean wave model: investigating spatial and temporal variability in coastal wave climates

The Office of Environment and Heritage (OEH), with the assistance of Cardno (NSW/ACT) and Baird Australia, have developed the NSW Coastal Ocean Wave Model – a coupled WAVEWATCH III/SWAN modelling system that has been designed to simulate historical and potential future coastal wave climates. The purpose of the model is to investigate latitudinal and temporal variability in NSW deep-water wave climates, and alongshore variability in nearshore wave conditions. This paper describes the wave modelling facility, discusses the evaluation of model performance to date, and describes the proposed wave data products, which will be useful for assessing coastal hazard risks in NSW. Measured wave records in NSW are enviable by global standards, with Waverider buoys (WRBs) deployed along the coastline since the mid-1970s. However, wave modelling provides an opportunity to address some limitations of the existing measurement records, including: the sampling frequency of earlier instruments; instrument failure (particularly during storms); the relatively recent capability to measure wave directions; and deployment durations at different locations – e.g. prior to 2011, directional buoys were only deployed at Sydney (1992), Byron Bay (1999) and Batemans Bay (2001). As measurements are not available for particularly stormy periods experienced during the 1950s, 1960s and early 1970s, extreme values derived from more recent data may under estimate storm-wave climates. Thus the directionality and extreme nature of NSW wave climates may not be fully resolved. Simulated wave climates generated by the NSW Coastal Ocean Wave Model have been evaluated against measurement records and other wave models. For example, comparison of CFSR-driven model predictions with WRB data for 1998-2009 suggest that predicted peak storm wave height and direction are overall very good, whilst mean wave period is typically under predicted. Although model-data agreement varies along the NSW coastline, the simulated wave climates are consistent with available measurement data, and improve on existing model data. Therefore the wave model products will address some limitations of WRB records, particularly wave directions and the definition of storm peaks.