National Network of Regional Coastal Monitoring Programmes

POLCOMS

Introduction

POLCOMS is the Proudman Oceanographic Laboratory Coastal Ocean Modelling System. It comprises a baroclinic three-dimensional model with the ability to run in regions which include both the deep ocean and the continental shelf, together with linked sediment, turbulence, wave and ecosystem models. The model is based on a regular grid with terrain following vertical coordinates. It requires model nesting to achieve high resolution coastal simulations. At the highest resolution wetting and drying of intertidal banks and beaches can be incorporated.

The iCOASST project has made use of several coupled models within the POLCOMS system:

  • POLCOMS, is formulated on a B-grid following Cartesian coordinates in the horizontal and solves Boussinesq, hydrostatic equation of motion separated into depth varying and depth independent parts to allow time splitting between barotropic and baroclinic components. The water depth (or free surface elevation), horizontal velocity components, temperature and salinity fields are calculated at each node of the computational mesh. The model also has an inbuilt sediment transport routine and particle tracking routine.
  • WAM, is a 3rd generation spectral WAve Model that has been modified for shallow water application (Monbaliuetal., 2000). WAM simulates wave propagation across the domain providing wave height, period and direction integrated at each node of the computational mesh. It is coupled to POLCOMS to enable wave-circulation interaction in both model simulations.
  • GOTM, is the General Ocean Turbulence Model (GOTM, Umlauf et al. 2005) coupled to POLCOMS to enable greater choice of parameter settings and turbulence schemes within the simulation. This allows for more sophisticated turbulence modelling, such as accounting for turbulent mixing with TKE injection at the surface to represent wave white-capping.

Model development

POLCOMS was originally developed by the Proudman Oceanography Laboratory, now the National Oceanography Centre. The software is no longer under development and is available on-line. To obtain access please email dataproducts@noc.ac.uk and join the user group polcoms-users@mailman.nerc-liv.ac.uk, which is used to communicate information about POLCOMS. To be kept up to date please register at: http://livintweb.nerc-liv.ac.uk:1801/polcoms-gnu

Application of POLCOMS within iCOASST

POLCOMS has been used by the National Oceanography Centre within the iCOASST project at two key scales for a typical year (2008):

  1. At the regional scale the model has been applied to Liverpool Bay at 180 m horizontal resolution to determine the processes that influence residual circulation within a hypertidal region of freshwater influence. The modelled velocities have been analysed to determine the monthly mean bedload transport pathways to inform the boundaries of the coastal evolution models developed within the iCOASST project for the Formby to Blackpool composition.
  2. At the national scale the model is used to assess the residual circulation around the UK coastline. Mapping the transport pathways to identify potential sources and sinks for sediment transport to inform coastal managers of the sediment trajectories between coastal management cells within the shoreline management plans. The model can also be used to identify regions where 2D modelling is adequate and 3D modelling is required to identify the appropriate modelling complexity to request when tendering scoping studies to consultancies.

Evaluation for end-users

As part of the Environment Agency project "Embedding iCOASST into practice", HR Wallingford have undertaken an independent evaluation of the usability of the iCOASST models. Each of the models have been downloaded from this website, compiled and run using (i) the documentation and (ii) the site-specific data sets on which they have been developed (also provided on this website). The outcome of this evaluation for this model can be found here and should be referenced by anyone interested in using or developing the model further.