Operational ocean and wave models are used to produce forecasts for navigation but also required for a wide range of services, most of them relying on particle tracking methods. Improving the forecast capabilities and accuracy of a model is then a constant necessity in order to deliver more reliable services. The Marine Institute in Ireland is running several coastal operational models, one of them focuses on the area of Galway Bay in the west coast. At the moment it consists of a stand-alone ocean application, it is the purpose of the work presented here to set-up a coupled application with a wave model. Coupled models are a recent development in ocean modelling, developer teams have included ocean and wave coupling by combining existing models each dedicated to a specific physics. Two theoretical formulations are mostly used for the implementation, both giving the same equations of evolution and interaction terms known as the vortex-force formalism. One approach is using a Lagrangian framework defining an exact averaged operator following the fluid particles, the other approach is Eulerian making use of a multi-scale expansion. In both cases the larger current components are found to be forced by gravity and infra-gravity waves. The Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modelling system is a widely used code, the vortex-force formalism has been implemented in 2012 coupling the Regional Ocean Modeling System (ROMS) with the Simulation Wave Nearshore wave model (SWAN). The implementation has been validated with academic cases and used in several real case studies in the last decade. The work presented here is making use of COAWST, a coupled model is set-up for Galway Bay running a 1-year hind-cast application for 2017 and preliminary results are shown here. The performance of the coupled model is compared with each stand-alone model, using in-situ data as a reference. In the last releases of COAWST the wave model WAVEWATCHIII has been added and can be used in the coupled system. This new feature is tested and the results are compared against SWAN, both wave codes are solving the same equations but different technical choices have been made resulting in different capabilities.

The authors implemented the Regional Ocean Modelling System (ROMS) to coastal waters on the west coast of Ireland. The Connemara model has c.200 m horizontal resolution and has 20 vertical sigma levels and stretches from 10.8oW to 8.9oW and from 52.95oN to 53.73oN. It has three open ocean boundary conditions in the north, south and west, and several rivers are included at the head of Galway Bay. Both 3D and 2D configurations have been set up; with the aim of the 2D configuration being the prediction of storm surges. The 3D configuration has been running in the operational forecasting mode for approximately the last decade and produce weekly hindcasts and 3-day forecasts. Details of the operational system will be presented. Most recent developments include the implementation of wetting/drying algorithm with a critical depth of 0.25 m. It has undergone a testing phase and the authors will report on the findings in terms of the computational efficiency and in terms of the changes to the model skill. Details of the set-up of each configuration, as regards the forcing functions, the choice of boundary conditions, atmospheric forcing, advection schemes, turbulence schemes, will be presented. The predictive skill of various configurations have been assessed by means of root mean square error (RMSE) differences and correlations with data collected from the Marine Institute’s observational network in Galway Bay. The observational platforms comprise of 5 tide gauges, 4 x ADCPs and temperature and salinity sensors. The harmonic analysis has been carried out on the data from the tide gauges and the corresponding model predictions in order to validate the tidal signal. The tidal signal in the Sea Surface Height (SSH) data is dominated by three semi-diurnal constituents (i.e. constituents with a period of approx. 12 to 12.5 hours), M2, S2 and N2, and three diurnal constituents, K1, O1 and Q1. At Galway Port tide gauge, the M2 magnitude error between the model and data is 0.07 m. The surge component is calculated for observed and modelled data at the locations of tide gauges. The authors will present the skill of the model as regards the prediction of storm surges to include the comparison between a 3D and 2D configuration.