Page 45 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
The high energy environments within Alderney’s territorial waters suggest that those features
predominately recorded within Project 1 and 2 areas are also likely to be observed elsewhere.
Further detail on the hydrodynamic conditions is provided in Section 4.2.
In addition to seabed features with positive relief, those with a negative relief are also present.
An example would be Hurd Deep, which characterises the approach to the Casquets from the
north to north-east. The depth of this feature, in places, exceeds 90 m water depth and it has
been reported that it is characterised by black mud, in addition to coarser sediments (NGIA,
2004). The function of Hurd Deep as a fine sediment trap has also been observed at other
similar features, for example Silver Pit in the North Sea (Proctor et al., 2001).
4.1.1.3 Future baseline
Over the short to medium-term, the future baseline is not considered to be markedly different
from the present baseline and is anticipated to remain within the envelope of variability. This is
demonstrated by the manner in which the coastal and seabed features respond to inter-annual
variations in tides and the prevailing storm events. Therefore, in the absence of any other
known significant past, present or future marine development in Alderney and its territorial
waters, it is considered that there is unlikely to be any change in the character of the marine
geomorphology over these timescales.
It is over the medium to long-term that the effects of climate change may have the potential to
influence coastal and seabed morphological characteristics. Climate change is predicted to
lead to increases in mean sea level (see Section 4.2.1.3). Changes in storm surges are likely
to be small in comparison to natural variability and as such would not constitute a measurable
change. Along Alderney’s coast, changes in water levels have the potential to lead to changes
in the future baseline whereby any intertidal is reduced due to coastal squeeze. The predicted
rise in sea level is unlikely to result in significant modifications to the existing hydrodynamic or
sediment regime and therefore seabed features such as sandbanks are unlikely to be
significantly affected.
4.1.1.4 Limitations and data gaps
There are several areas of uncertainty associated with defining the present baseline which
relate to gaps in primary data. At the EIA project-level, it is recommended that developers
undertake a desk-based review and fieldwork designed to provide more detail on the following:
ƒ Superficial seabed sediments (at a minimum including composition and particle size,
geochemical properties and contaminants);
ƒ Morphodynamic features (small- to large-scale); and
ƒ Seabed geology.
These could be collected using the following methods:
ƒ Side scan sonar, video or photographic survey to identify the seabed sediments and
geomorphology;
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