Acta Oceanol. Sin., 2011, Vol. 30, No. 5, P. 1-13 DOI: 10.1007/s13131-011-0142-3 http://www.hyxb.org.cn E-mail: hyxbe@263.net Numerical investigation of wave propagation in the Liverpool Bay, NW England LI Ming 1∗ , RAYMOND Ip 1 , WOLF Judith 2 , CHEN Xueen 3 , BURROWS Richard 1 1 School of Engineering, University of Liverpool, Liverpool L69 3GQ, UK 2 National Oceanography Centre, Joseph Proudman Building, Liverpool L3 5DA, UK 3 College of Physical and Environmental Oceanography, Ocean University of China, Qingdao 266100, China Received 23 January 2011; accepted 14 June 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011 Abstract The computer model for near shore wave propagation, SWAN, was used to study wave climates in Liverpool Bay, northwest England with various input parameters, including bottom friction factor, white capping, wind drag formulation and effects of tidal modulations. Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions. In particular, the model results were found very sensitive to different input formulations, and tend to underestimate the wave parameters under storm conditions in comparison with the observations. It is therefore important to further validate the model against detailed field measurements, particularly under large storms that are often of the primary concern. Key words: coastal engineering, flooding, wave model, near shore, tide 1 Introduction The study of wave climate is important since waves play a pivotal role in sediment transport in the nearshore zone, which is a major contributory fac- tor of coastal erosion. It also determines the possible extent of coastal flooding during storms which may cause catastrophic consequences if coastal defences are overtopped. Waves in shallow water are strongly con- trolled by the water level as well as the wind forcing. In particular, the wave propagation within Liverpool Bay has considerable impacts on the coastline of northwest England, with particular regard to the construction of sea defences, coastal flooding and sediment transport along the coast. Detailed knowledge of the prevailing wave climate is therefore regarded as an essential step for further assessment of shoreline behaviours. Thus far, National Oceanography Centre (Liverpool) has established several monitoring sites using the latest field measurement technology, including wave buoys, acoustic doppler current profiler (ADCP) and high fre- quency (HF) radar through coastal observatory pro- gramme (Fig. 1). These data provide valuable basis to verify computer models and reveal important physi- cal processes that can provide in-depth understanding of the wave climate within Liverpool Bay. By making use of these data and a nearshore wave model SWAN, the occurrence of typical and extreme wave conditions in Liverpool Bay and the adjacent estuaries could be investigated. It is instrumental in assessing the risks in areas which may be susceptible to flooding due to waves in combination with high water levels. In addi- tion, through studying the phenomenon of tidal mod- ulation, more thorough understanding could be gained on the actual physics and possible effects of tide and surge on the nearshore wave parameters so that engi- neers could review the adequacy of design of existing coastal structures. When the SWAN is applied to the UK coastal sites (Wolf, 2003), it is worth noting that varying the bottom friction formulation can have a significant ef- fect on the modelling results, with the Madsen for- mulation (Madsen et al., 1988) better than the JON- SWAP formulation (Hasselmann et al., 1973). With the SWAN model, it is possible to transform the statis- tical extreme events for extreme value analysis. How- ever, the interpretation of transformed event can be problematic. To study future climate scenarios, it is Foundation item: The Public Science and Technology Research Funds Projects of Ocean under contract Nos 200905001 and 201005019; this work is partially sponsored by Engineering and Physics Science Research Council (UK) through DTA training scheme. ∗ Corresponding author, E-mail: mingli@liv.ac.uk 1