On the Sediment Dynamics in a Tidally Energetic Channel: The Inner Sound, Northern Scotland

Jason Mcilvenny,Lonneke Goddijn-Murphy,Duncan Tamsett,Philip Gillibrand

doi:10.3390/jmse4020031

Jason Mcilvenny, Lonneke Goddijn-Murphy + Show 2 more

Open Access

https://doi.org/10.3390/jmse4020031

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Abstract

Sediment banks within a fast-flowing tidal channel, the Inner Sound in the Pentland Firth, were mapped using multi-frequency side-scan sonar. This novel technique provides a new tool for seabed sediment and benthic habitat mapping. The sonar data are supplemented by sediment grab and ROV videos. The combined data provide detailed maps of persistent sand and shell banks present in the Sound despite the high energy environment. Acoustic Doppler Current Profiler (ADCP) data and numerical model predictions were used to understand the hydrodynamics of the system. By combining the hydrodynamics and sediment distribution data, we explain the sediment dynamics in the area. Sediment particle shape and density, coupled with persistent features of the hydrodynamics, are the key factors in the distribution of sediment within the channel. Implications for tidal energy development planned for the Sound are discussed.

Highlights

The strong tidal flows of the Pentland Firth have been a focus of attention for tidal energy developers, with a number of sites identified and leases granted for tidal energy extraction using tidal turbines
We provide more detailed information on sediment deposits in the Inner Sound to the south of Stroma, where the first tidal turbine array is about to be deployed, and, by analysing measurements and numerical model simulations of local velocity fields, we infer the local sediment dynamics
From the merged colour mosaic image, Figure 3iv; clear distinctions can be made between material types

Summary

Introduction

The strong tidal flows of the Pentland Firth have been a focus of attention for tidal energy developers, with a number of sites identified and leases granted for tidal energy extraction using tidal turbines. Government consent to deploy tidal turbines and marine energy generation devices in general, is subject to environmental impact assessment, demonstrating little or acceptable environmental effect. These assessments typically focus on collision risk for marine mammals and seabirds, which present the highest impact risks. Other, more subtle, environmental impacts arising from the deployment of large numbers of tidal turbines can be envisaged. These have been outlined by a number of authors, with the focus being mainly on ecological and socio-economic impacts (e.g., [4,5])

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