A Regional Operational and Storm Surge Model for the Bay :Model Configuration and Validation Paper Number: CP44E-1381 Hazem Nagy 1,2 , Kieran Lyons1 , Tomasz Dabrowski 1 1 Marine Institute , Rinville , , Galway , Ireland 2 Oceanography Department, Faculty of Science, Alexandria University, Egypt

1- Background

The Regional Ocean Modelling System (ROMS) as described in Shchepetkin and McWilliams, (2005) is implemented for coastal waters Tide Gauges on the west coast of Ireland. The Connemara model has c.200 m horizontal resolution and has 20 vertical sigma levels and stretches ADCPs from 10.8oW to 8.9oW and from 52.95oN to 53.73oN Figure (1). It has three open ocean boundary conditions in the north, south and west, and several rivers are included at the head of . It is nested within a regional-scale ROMS model of the northeast Atlantic, Dabrowski et al. (2014). Both 3D and 2D configurations have been set up; with the aim of assessing differences in the prediction of storm surges. More recent developments include the implementation of a wetting/drying algorithm with a critical depth of 0.25 m.

We have validated the models using observed sea level time series from tide gauges for Inishmore Island and Galway Bay as shown in Galway Port Figure (1). The surge component is calculated, for observed and modelled data at the locations of Galway Bay tide gauge covering the period from December 2013 until January 2014. The Marine Institute’s observational network in Galway Bay contains 3 x ADCPs located Galway Bay at Bay as shown in Figure (1). Data collected in June 2018 is used to assess the impact on the modelled velocities by including Inishmore Island Kinvara Bay wetting/drying in the 3D model.

Figure (1) Bathymetry of the Connemara model in meters with main tide gauges sites and ADCP locations.

2. RESULTS  Models Validation against tide gauges

 Winter Storms (12 Dec 2013 – 12 Jan 2014) The tidal harmonic analysis for tide gauges and both models (wet/dry & operational) demonstrated that the tidal signal in the Figure (2) The 2D storm surge Connemara model has successfully reproduced the five storm surges while Sea Surface Height (SSH) data was dominated by three semi-diurnal constituents (M2, S2, N2,) and three diurnal constituents the 3D one has just missed the first surge (A). The 2D storm surge model has been forced with a high (K1 O1 and Q1) as presented in Table 1. Good agreement have been found between tide gauges and both models in terms of temporal and spatial resolution atmospheric product called MÉRA (Met Éireann Re-Analysis – Climate Re- amplitudes and phase angles as described in Table (1). analysis). It is of 2.5 km horizontal resolution and provides atmospheric variables at 1 hour temporal resolution; further details are available in Gleeson et al. (2017). The 3D Connemara uses ECMWF Galway Port Gauge Connemara_operational Connemara_Wet/Dry atmospheric forecast at 0.125o horizontal resolution and 3 hrs frequency. Tidal Constituent Amp (m) Phase (deg) Amp (m) Phase (deg) Amp (m) Phase (deg) M2 1.52 139 1.59 136 1.59 136 S2 0.58 175 0.61 170 0.6 170 Salthill Waterfront (Storm D) N2 0.32 114 0.33 117 0.33 116 Galway O1 0.07 322 0.06 323 0.06 320 Q1 0.02 245 0.02 245 0.02 242 K1 0.01 69 0.01 72 0.01 72 M2 1.47 140 1.49 136 1.49 136 S2 0.58 175 0.57 170 0.56 170 N2 0.30 113 0.31 117 0.32 116 Inishmore O1 0.07 321 0.06 322 0.06 320 Q1 0.02 248 0.02 249 0.02 245 K1 0.01 67 0.01 74 0.01 73 Figure (2) 2D & 3D Modelled Surges vs Galway Port Gauge Table (1) The amplitudes and phases for six of the principal tidal constituents calculated, for the measured and modelled data.  Models Validation against ADCPs ADCP Name Connemara_operational Connemara_Wet/Dry  The validation of models against ADCPs barotropic velocity components have shown a very good agreement as shown in Table (2). RMSE (m/s) Multiple R RMSE (m/s) Multiple R  The highest correlation coefficient was approximately 0.96 recorded for Berth A U_Bar 0.09 0.95 0.09 0.96 Table (2) RMSE and Multiple R, between the east barotropic component between wet/dry model and Berth_A ADCP V_Bar 0.03 0.68 0.02 0.72 Connemara operational and wet/dry models with the  The lowest correlation was 0.65 for north component between Berth B U_Bar 0.09 0.94 0.09 0.94 ADCPs Barotropic components during June 2018. operational model and Berth_B ADCP V_Bar 0.06 0.65 0.03 0.73  The smallest RMSE was 0.02 meters recorded for north barotropic Berth C U_Bar 0.11 0.92 0.1 0.92 component between wet/dry model and Berth A ADCP. V_Bar 0.02 0.67 0.015 0.71

3- Conclusions

 The spatial and temporal resolution of the atmospheric forcing plays an important role in improving storm surge models (e.g. forcing Connemara 2D model with MÉRA data)

 Inclusion of wetting/drying means the model implements a more realistic bathymetry in intertidal zones leading to improvement in model skill in those zones.

References Dabrowski, T., Lyons, K., Berry, A., Cusack, C., and Nolan, G., 2014. An operational biogeochemical model of the North-East Atlantic: Model description and skill assessment. Journal of Marine System. doi:10.1016/j.jmarsys.2013.08.001.

Gleeson, E., Whelan, E., Hanley, J., 2017. Met Éireann high resolution reanalysis for Ireland. Advances in Science & Research 14, 49-61.

Shchepetkin, A. F., and J. C. McWilliams, 2005. The Regional Ocean Modeling System: A split-explicit, free-surface, topography following coordinates ocean model, Ocean Modelling, 9, 347-404.