Coastal Flooding by Extreme Events (CoFEE) model simulations information document
The Coastal Flooding by Extreme Events ( CoFEE ) project is a NERC Flood Risk for Extreme Events ( FREE ) Research Programme project (Round 1 - NE/E002471/1 - Duration April 2007 - May 2010). It was concerned with the possible increase in the intensity of extreme coastal flooding events, and their impact on the human and physical environment of the UK coastline. The broad aims of the project were to improve understanding of how the coastline responded to changes in climate, sea-level and storm and wave frequency. This understanding would then be used as the basis for informed decisions on management of the coastal zone, especially in relation to mitigation and amelioration of coastal flooding. The Liverpool Bay region, concentrated on the area between Liverpool and Southport, was used as a study area.
As part of CoFEE, hydrodynamic modelling of the study area was undertaken. The model simulations carried out looked at the changes in off-shore forcing factors such as waves, tidal currents and storm surges and how they affected observations of coastal changes. Three specific simulations were run, as follows:
Daily average east and northward velocity components (m s -1 ) for every model depth level across the model domain
Depth averaged east and northward velocity components (m s -1 ) across the model domain, every 30 minutes
- Significant wave height (m), second moment wave period (s), peak wave period (s) and wave to direction (°), every hour
The model simulations ran from 00:30 hours UTC 01 January 1996 to 00:00 hours UTC 01 January 2007.
The information presented here is compiled from sections of Brown et al. (2010) and has been confirmed by the Data Originator.
The CoFEE simulations used a parallel computer system applied with 1.85 km resolution to the Irish Sea. In order to accurately simulate the waves in the study area, the state of the art 3rd generation WAve Model ( WAM ), Komen et al. , 1994) was modified for shallow water, as described in Monbaliu et al. (2000). Following Osuna et al. (2007) WAM simulates the 2D wave spectral evolution considering the energy input by wind, energy dissipation by white-capping and bottom friction, and non-linear wave-wave interactions. Depth-limited wave-breaking has not been included in these simulations. Externally generated waves propagating into the Irish Sea are included by adopting a one-way nested model approach. A one degree northeast Atlantic model provides hourly boundary forcing for the 1.85 km Irish Sea model. This coarse grid model was driven by six-hourly, one degree resolution European Centre for Medium-range Weather Forecasting (ECMWF) (ERA-40, see Uppala et al. , 2005) wind data.
To simulate the tides and surge within the Irish Sea, the Proudman Oceanographic Laboratory Coastal Ocean Modelling System ( POLCOMS ) hydrodynamic model was used. This is a three dimensional model formulated in spherical polar coordinates on a B-grid with a terrain following (sigma) coordinate in the vertical (Holt and James, 2001). For the 11-year hindcast, hourly wind and pressure data were provided by the UK Meteorological Office (UKMO) northeast Atlantic (mesoscale) model, with a resolution of 0.11° (approximately 12 km). To capture the external surge generated outside of the Irish Sea, a one-way nested approach has been applied from the 1/9° by 1/6° (approximately 12 km) operational surge model (run at UKMO) to the 1.85 km POLCOMS Irish Sea model. The operational surge model (detailed in Flather, 1994) provided total (tide plus surge) hourly elevation and velocity boundary forcing.
For the Irish Sea model wave-tide-surge interaction has been taken into account by two-way coupling of POLCOMS and WAM (Osuna and Wolf, 2005). The coupled POLCOMS-WAM system has been under development at the Proudman Oceanographic Laboratory since 2002. The coupling is achieved through the surface and bottom stress and wave refraction due to the presence of time varying current and elevation fields (Wolf et al. , 2002). Presently, radiation stress is not included within the coupled model. The surface stress formulation allows waves to influence the surface roughness in the surge simulation using the method of Charnock (1955), with a wave dependent Charnock parameter (Janssen, 2004). The effect of waves on bottom friction is estimated using the method of Madsen (1994). In the standard POLCOMS-WAM model, the minimum water depth was set to 10 m, but for the CoFEE research, in which the focus is Liverpool Bay, improved bathymetric data (North West Shelf Operational Oceanographic System (NOOS) data set: Zijderveld and Verlaan, 2004) in the eastern Irish Sea has allowed a 5 m minimum water depth to be applied to this region only. This minimum depth allows resolution of the coastal bathymetric features, but prevents numerical instability due to drying areas occurring in the model domain as a consequence of the tidal variation. This gave improved surge prediction locally within the eastern Irish Sea (Brown and Wolf, 2009).
Please be aware that the data are stored by BODC in the state they were supplied by the Data Originator. No quality control or assessments of the data have been undertaken and any interested parties should use the data at their own risk.
Brown, J.M., Wolf, J., 2009. Coupled wave and surge modelling for the eastern Irish Sea and implications for model wind-stress. Continental Shelf Research, 29(10), 1329-1342
Brown, Jennifer M., Souza, Alejandro J., Wolf, Judith., 2010. An 11-year validation of wave-surge modelling in the Irish Sea, using a nested POLCOMS-WAM modelling system. Ocean Modelling, 33. 118-128.
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