UNEXPLODED ORDNANCE - Wind Energy Network

SPONSORS OF Unexploded Ordnance
Unexploded ordnance
a recognised threat
The potential for UXO within proposed
offshore wind developments has become
a recognised threat in recent years. Risk
reduction to ‘As Low as Reasonably
Practicable’ (ALARP), is not only a legal
requirement, but is also a consenting,
insurance and project financing issue,
and as such can become a serious
obstacle to the overall development
of the site.
Data
Data was processed and interpreted using
Oasis Montaj with UX-Detect extension,
which allows accurate localisation and
analysis of UXO targets which were then
or interpreted by the company’s specialist
processing geophysicists.
In-depth profile-by-profile analysis of the
data, as opposed to automated target
picking algorithms, ensured that all
anomalies were analysed and that many
geological anomalies could be rejected
on the basis of their morphology, thus
narrowing the number of relevant targets
delivered to the UXO Consultants.
Seabed survey
An early stage in ensuring the consenting
area is free from UXO involves a detailed
seabed survey using a high-resolution
side scan sonar, and a magnetometer
positioned close to the seabed.
The magnetometer is used to detect
variations in the total magnetic field of the
underlying seafloor and sub-seabed geology
on the basis of anomalies in the Earth’s
magnetic field, caused by the presence of
ferrous iron on, or below, the seafloor.
Materials high in ferrous or ferric
compounds may include wreck debris,
pipelines, sites of archaeological interest,
volcanic rocks, and clearly, UXO.
Osiris Projects – a case study
Osiris Projects were commissioned to
perform such a survey for a major Round
2 development.
A WW2 50kg bomb was identified by
specialist UXO consultants to be the
smallest threat on-site, which required the
magnetometer data to have a maximum
lateral spacing of 5m, and a maximum
vertical height from seabed of 3m.
Specialist procedure
The company developed a simple but
effective tow configuration allowing
multiple magnetometers to be
deployed simultaneously whereby each
magnetometer is deployed in a ‘piggyback’
arrangement behind a side scan
sonar fish and controlled from separate
winches.
This allows the towing height of each
fish to be controlled independently and
equipment deployment and recovery
time is drastically reduced compared to a
towed array setup. Each magnetometer
is fitted with a USBL beacon for accurate
and independent positioning.
On this project, the magnetometer towing
configuration delivered a mean fish height
of 2m above seabed - exceeding the
client specification - and the accurate
positioning allowed areas of infill to be
quickly identified resulting in almost
complete coverage of the site.
Outcome
Dive investigations, conducted by
specialist commercial diving contractor,
corroborated potential targets identified
by Osiris Projects, and fortunately the site
was free from UXO.
Osiris Projects
www.osirisprojects.co.uk
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