Scottish Shelf Model. Part 4: East Coast of Lewis and Harris Sub-Domain

1 Introduction

1.1 Background

Halcrow Group Ltd. (a CH2M company) was commissioned by Scottish Ministers to develop a "Hydrodynamic model of Scottish Shelf waters" The contract was commissioned under the Scottish Government Framework Contract for the Provision of Strategic Environmental Assessment, Appropriate Assessment and Marine Planning Services and Advice to Support Sustainable Economic Development in Scottish Marine Waters (REF: 177895) - Call Off Number 11 - Provision of a Hydrodynamic Model of Scottish Shelf waters - 16 May 2012. The project is managed on behalf of the Scottish Ministers by Marine Scotland.

The Scottish Government is committed to the development of a successful marine renewable energy industry in Scotland, which is currently also the largest producer of farmed Atlantic salmon in the EU and third largest globally. To achieve the sustainable development of both the offshore renewable energy industry and the aquaculture sector, Marine Scotland has adopted a planning approach to identify potential developmental areas.

Both of these factors are drivers for the development of a regional hydrodynamic model of the Scottish Shelf Waters and four more localised models which will be used to inform their planning approach. Marine Scotland will take ownership of the hydrodynamic models at the end of the study enabling them and other community organisations they work with, to undertake simulations and further development to meet their planning and research needs.

This report forms part of a series of reports that were produced during the lifetime of the project.

1.2 Study areas

The overall study area includes all of the Scottish shelf waters out to the 200m depth contour at the edge of the continental shelf. A Scottish shelf waters model covering this study area was developed to simulate the hydrodynamic conditions in three-dimensions, including meteorological and tidal forcings. The model resolution is variable and matched to the processes and bathymetry that are required for the simulations.

Within this region-wide shelf waters model, four local three-dimensional models were setup providing higher resolution to resolve key bathymetry, coastline and physical processes over smaller more local areas. These four model areas have been defined as case studies and cover the following regions:-

Case Study 1: Pentland Firth and Orkney Waters

Case Study 2: Wider Loch Linnhe System

Case Study 3: East Coast of Lewis and Harris ( ECLH)

Case Study 4: Northwest Shetland mainland - St Magnus Bay area

The locations and approximate areas of these models are shown in Figure 1‑1, note that these model domains are not the final model domains but an approximation.

1.3 Aims and scope of numerical modelling works

The main aims of the project are to: 1) develop a validated three dimensional hydrodynamic model for the Scottish shelf waters; 2) develop a validated three dimensional hydrodynamic model for each of the four identified case studies. In addition, to develop a validated wave model for the Pentland Firth and Orkney Waters (Case Study 1); and 3) integrate the case study sub-models into the wider domain shelf model.

The modelling provides a quantitative description of marine currents and water properties for the whole of Scottish waters on a range of spatial scales. The outputs of this study are a validated hydrodynamic model capable of predicting tidal and non-tidal currents for the whole of the Scottish shelf and inshore waters and include a more accurate assessment of the connectivity of different regions, and the available energy resources (only in the Pentland Firth and Orkney Waters). It also includes description of methods for assessing the impact of extracting some of that energy upon the physical environment.

The modelling was undertaken using an open-source three-dimensional (3D) hydrodynamic model called FVCOM (Chen et al., 2013). One of the reasons behind the choice of this modelling software is that the models developed in this project will be freely available to others at the end of the Project. Marine Scotland have a vision that the models will be used and developed further by Marine Scotland staff and the marine modelling community as more data becomes available and/or other needs are identified.

1.4 Project Team

The project team for this study consists of:

• Halcrow Group Ltd as the main contractor, responsible for co-ordination of the team and development of the hydrodynamic models for the four case studies.
• National Oceanography Laboratory, Liverpool ( NOC-L) as subcontractor, responsible for development of the Scottish shelf model.
• Centre for Ecology and Hydrology ( CEH) responsible for delivering river outflow discharge data covering the entire Scottish waters and Northern Ireland using the Grid to Grid model.
• Prof. Chen of University of Massachusetts, USA, responsible for providing technical support on the application of the FVCOM software.
• Prof Christina Sommerville of University of Stirling, UK, responsible for providing technical support on sea lice and the development of connectivity indices.

1.5 This Report

This report documents the work carried out in developing the East Coast of Lewis and Harris ( ECLH) model. This work includes: data collated and/or identified for the numerical modelling, setup and calibration of the flow model, and the longer term simulations required for this study. It is noted that the data section in this report is a summary of the overall Data Review report (Halcrow, 2012) that is relevant to the ECLH area.

This report is Volume 1 of the ECLH model report. A companion volume (Volume 2 - Model Documentation Report for ECLH) contains additional details on model development (data preparation, mesh generation, preparation of model setup files, how to run the model, etc.) and lessons learnt.

1.6 Datums

Unless explicitly stated otherwise the following reference datums are used in this study:

• All horizontal co-ordinates are referenced to latitude and longitude.
• All vertical levels are relative to MSL.

1.7 Acknowledgments

We gratefully acknowledge with thanks the contributions of the following organisations and individuals to this project.

• Marine Scotland (Alejandro Gallego, Rory O'Hara Murray and George Slesser) for providing, requesting and collecting available data.
• UKHO for the bathymetry datasets
• BODC/ NOC-L for the wide range of oceanographic data and metadata; this is a great source of data. Thanks to Polly Hadziabdic at BODC for helping us with our enquiries.
• SEPA for providing tide gauge data, which was very useful for this study.
• CEH (Robert Moore and team) for their work towards providing river discharges data using the Grid-to-Grid model for this study.
• Professor Chen at the University of Massachusetts (Dartmouth) and his team for making the FVCOM software available for this project.

We also acknowledge with thanks the owners of the internet websites mentioned below for the valuable data downloaded from them for this study.

• Tide gauge data (class 'A') from the National Tide and Sea Level Facility ( NTSLF - available from www.pol.ac.uk/ntslf) was downloaded and used for calibration purposes.
• ICES database ( http://ocean.ices.dk/) which proved to be a good source of data.
• Bathymetric metadata and Digital Terrain Model data products have been derived from the EMODNet Hydrography portal - http://www.emodnet-hydrography.eu. This portal was initiated by the European Commission as part of developing the European Marine Observation and Data Network ( EMODNet).