Page 83 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
potential exposure to change as a result of a single array and associated infrastructure is
considered to be low, resulting in an insignificant to minor adverse impact.
A full build out of the Draft Plan, however, will result in the potential installation of up to 4000
tidal devices in Alderney’s territorial waters (see Section 2.2.2). Assuming the OpenHydro
turbine is exclusively used (see Section 1.2.2), this would result in approximately 3.1km2 of new
artificial substrate being introduced into the marine environment with the potential to be
colonised by non-native species. In terms of intra- and inter-array cabling, if cable protection
(i.e. concrete mattressing) were required along their entire length, approximately 1.8km2 of new
substrate would be introduced to the seabed. The cable protection associated with the export
cable between Alderney and France would result in an additional 0.15km2 of new substrate for
each cable that needs to be layed (Section 2.2.2). Overall, the full build out of the Draft Plan is
therefore considered to result in a moderate level of exposure to change and an insignificant
to moderate adverse impact.
5.1.2.6 Introduction of new structures
In designing the bases for devices and substations, or the armouring for cable, the potential
exists for the structures themselves to become suitable surfaces for the settlement of reef
forming species and thus there could be impacts during both the initial installation and at the
decommissioning phase. In addition, cables may be allowed to ‘self-bury’ over time in soft
sediments, thus changing the amount of available hard substrate through time. Wilson et al.
(2010) noted in reviewing offshore windfarms that the marine system is able to adjust to new
structures in the sea, and that these devices may even have the potential to act as a benefit to
their receiving environment. Work has shown how scour protection and towers may create
hard substrata and thus act as artificial reefs, thereby increasing primary production and
creating organic material and enrichment of the local marine environment. However, this
potential benefit will need to be studied in greater detail as part of project-level impact
assessments. Overall, the sensitivity of benthic species to this impact pathway is considered to
be low to moderate and the level of exposure to change is considered to be low, resulting in an
insignificant to minor adverse impact.
5.1.2.7 Mitigation
The following mitigation works should be considered by the developer, as appropriate, to
minimise any potentially significant impacts (i.e. moderate or major) on benthic ecology that
have been identified in this REA:
ƒ Reduction in the number of tidal devices and associated cables in order to minimise
the area of substratum loss and/or damage; and
ƒ Avoid any sensitive habitats (e.g. eelgrass beds) at the project planning and design
phase. With a potential full build out of the Draft Plan, there will still be approximately
97% of the seabed across all the licence blocks available for micro-routeing (see
Section 5.1.2.2). Such micro-routeing may need to be considered further at the EIA
project-level by the developer.
R/4001/7 59 R.2129