166 SITEMONITORING ANDPROTECTION
continue. Work that might take a diving team weeks or
even months can now be achieved in a few hours using
geophysical equipment. As a result, this type of survey is
likely to be used increasingly for monitoring in both gov-
ernment- and developer-funded projects. Nevertheless,
it should not be regarded as a complete solution or one
that works equally well on all sites. It is therefore unlikely
that the need for ground-truthing will be eliminated
in the foreseeable future.
The effectiveness of this technique for monitoring
largely depends on the detection of changes between sur-
veys. Therefore, more than one survey, separated by an
appropriate period of time, is required (plates 13.7 and
13.8). The high cost, particularly of multibeam equipment,
and the specialized knowledge required to operate it and
interpret the results, means that its application to projects
with modest funds is likely to be limited. Nevertheless the
possibility of its use should always be considered.
Other, readily available equipment can be used for
monitoring work and require less specialist skills (e.g. echo-
sounders). When combined with suitable differential
global positioning system (see chapter 11) equipment,
echo-sounders can provide detailed information about
changes in sea-bed profile around and within a site.
Hydrodynamic environment: Water temperature, pH
and salinity measurements can be taken relatively easily
for a modest cost. If sufficient funds are available, data-
loggers can be deployed to measure current-strength,
direction, suspended solids and other factors likely to
influence site stability (plate 17.2). Alternatively, informa-
tion on the hydrodynamic environment can be gained
from the type and distribution of marine growth and often
from other public or private sources such as hydro-
graphic agencies. Liaison with other groups or organiza-
tions studying this environment can provide valuable
information and technical input and is therefore always
advised.
Other techniques: Experimental techniques can be
very useful. Projects such as MOSS (Cederlund, 2004) have
demonstrated that valuable information on the degrada-
tion of wood can be derived from experimenting with
buried and exposed sacrificial test objects on site (plate
17.3). Such research can reveal much about site forma-
tion and stability. Other projects, such as recent invest-
igations on the wreck of the late seventeenth-century
warship Hazardousin the UK (Holland, 2005; 2006) have
shown how the use of ‘tracer’ objects can provide infor-
mation on burial processes and on the mobility of arte-
facts on the sea-bed. These techniques can be relatively
cheap to use and many do not require specialist techni-
cal knowledge. They do, however, usually require multi-
ple visits to the site.
Specialist knowledge may be required to understand the
biological environment of a site and to devise a method
for monitoring it, but advice is often available at little or
no cost. It is unlikely to be beyond the resources of a
reasonably committed project, particularly if it involves
a multidisciplinary approach.Many of the techniques described above rely on the
comparison of data gathered during more than one visit
to a site. The initial work will provide the ‘baseline’ data
against which subsequent data sets will be compared. It
is therefore essential that the way in which the baseline
data is obtained is very carefully recorded and that sub-
sequent data is obtained in the same way or in a way
that is comparable. Careful thought should be given at
the project-planning stage to ensure that this repeat-
ability can be achieved.
Careful thought should also be given to ensuring
that the work is repeated at an appropriate time. For
example, if it is suspected that the profile of the sea-
bed is affected by seasonal storms, then the site must
be visited before, during and after the appropriate season.
By way of contrast, if it is thought that the site is only
subject to very slow long-term or negligible change, then
it may only be necessary to repeat the work every year or
perhaps even less frequently.
The requirement to repeat monitoring work at inter-
vals emphasizes the need to keep the work as simple
as possible, particularly if resources are limited. If the
work is to be shared by a number of groups or indi-
viduals, then repeatability is even more essential. Pro-
forma style recording is a sensible way to approach
such situations.
It is not possible to give comprehensive advice on inter-
preting monitoring data in a book such as this because
of the limitless permutations of processes affecting indi-
vidual sites. However, the following are examples of what
might be considered:- Surface distribution of material:The movement or
disappearance of artefacts on a site can indicate
many processes. Missing non-ferrous metal artefacts
are usually taken as good indications of human
interference. However, the movement or disappear-
ance of artefacts can be due to a wide range of
factors, including erosion or natural burial and
care should be taken in interpretation. - Changes in the shape of the sea-bed:A sea-bed that
changes shape is probably being affected by erosion
and the site may, therefore, not be stable. Analysis
of the monitoring data may help to determine
whether this is a natural repeating cycle or a single
event and whether active intervention is required to
stabilize and protect the site. Changes in the shape