Abstract:The hydrodynamic circulation in estuaries is primarily driven by tides, river inflows and surface winds. While tidal and river data can be quite easily obtained for input to hydrodynamic models, sourcing accurate surface wind data is problematic. Inaccurate wind data can lead to inaccuracies in the surface currents computed by three-dimensional hydrodynamic models. In this research, a high-resolution wind model was coupled with a three-dimensional hydrodynamic model of Galway Bay, a semi-enclosed estuary on the west coast of Ireland, to investigate the effect of wind forcing on model accuracy. Two wind-forcing conditions were investigated: (1) using wind data measured onshore on the NUI Galway campus (NUIG) and (2) using offshore wind data provided by a high resolution wind model (HR). A scenario with no wind forcing (NW) was also assessed. The onshore wind data varied with time but the speed and direction were applied across the full model domain. The modeled offshore wind fields varied with both time and space. The effect of wind forcing on modeled hydrodynamics was assessed via comparison of modeled surface currents with surface current measurements obtained from a High-Frequency (HF) radar Coastal Ocean Dynamics Applications Radar (CODAR) observation system. Results indicated that winds were most significant in simulating the north-south surface velocity component. The model using high resolution temporally-and spatially-varying wind data achieved better agreement with the CODAR surface currents than the model using the onshore wind measurements and the model without any wind forcing.

Abstract-Hydrodynamic circulation in estuaries is primarily driven by tides, surface wind and river inflows. While tidal and river data can be quite easily obtained for input to hydrodynamic models, sourcing accurate surface wind data are problematic. Firstly, the wind data used in hydrodynamic models are usually measured on land and can be quite different in magnitude and direction from real offshore wind. Secondly, surface wind is spatially-varying but due to a lack of data, usually a non-varying wind speed and direction are specified across the full extents of a model domain. These problems can lead to inaccuracies in the surface currents computed by two-dimensional or three-dimensional hydrodynamic models. In the present research, a wind forecast model was used to generate a high resolution wind field at a marine renewable energy test site, Galway Bay. These predicted high resolution wind date can be used to investigate the effect of surface wind data resolution on model accuracy.Index Terms-Wind field, high resolution, Galway bay, ARIMA.

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