168 SITEMONITORING ANDPROTECTION
moderate extent, the force of waves. Sandbags can be
successfully used to fill in scours or excavation trenches
and to ‘weigh down’ artefacts, such as small fragments
of wooden hull that may be prone to disturbance. They
are best positioned so that each bag is touching or pre-
ferably overlapping, so that the gaps between them fill
with sand or other mobile sea-bed material (figure 17.1).
They are less effective when used individually or in small
groups and should not be regarded as a permanent or
‘fit and forget’ means of protection because the fabric,
whether man-made or natural, will decay. Unless the
sandbags are subsequently buried under overburden,
they will also require regular inspection.
Sandbags should be laid so that they promote the
smooth flow of the current across the site. This will re-
duce the risk of the sandbags themselves causing erosion
by creating current eddies in the immediate vicinity or
elsewhere on the site. It will also increase their useful
lifespan. If sandbags are to be laid across a whole site, they
should be closely packed and have a profile that is as low
and smooth as possible. Examples of sites where sandbags
have been laid to prevent erosion include the fifteenth-
century Studland Bay site off the Dorset coast of England
and the Duart Point site in Scotland. At Duart Point,
sandbagging has been used, after partial excavation, to
encourage reinstatement of the original sea-bed surface
(Martin, 1995b).
Deployment of sandbags can be a time-consuming
process and planning should ensure that it is carried out
as quickly as possible. Slow or partial deployment could
actually promote erosion rather than reduce it. It is also
a common mistake to underestimate the number of
sandbags that will be required.
Geotextiles: Membranes of artificial textiles can also be
used to cover a site and promote stability. A wide variety
of materials are available and the choice ranges from
rolls of weed-inhibiting textiles, available from gardening
suppliers, to more complicated textiles used by the civil
engineering industry for stabilizing vulnerable surfaces,
both under water and on shore. These textiles work by
providing a smooth, continuous barrier across the sea-
bed, which promotes a stable, often anaerobic, environ-
ment beneath it. Textiles manufactured specifically for
a sea-bed environment are often also designed to pro-
mote the re-deposition of sediment where they are laid.
For example, they may be manufactured with a layer
of ‘fronds’ designed to slow the current that comes into
contact with them, causing sand or silt in suspension to
fall to the sea-bed.
Geotextile sheets are often large and cumbersome and
can be very difficult to lay. Securing a geotextile cover to
the sea-bed takes care and thought and it is likely to require
regular monitoring. This is particularly significant in
busy areas for shipping or recreational use, as the geotextile
is likely to represent a significant hazard if it becomes loose.
Geotextile sheets can be expensive, particularly for large
sites. Nevertheless they can be very effective and their use
is therefore likely to increase. Although Terram is usually
cited as the example of a geotextile, there are many dif-
ferent types available. The possibility of setting up an experi-
ment to determine which is likely to be most suitable, either
close to a site or in a similar environment, should there-
fore be considered.Anodes: Work at sites such as Duart Point has shown
that anodes can be used to help stabilize metal artefacts,
such as iron guns, on the sea-bed (MacLeod, 1995). An
added benefit is that if it is anticipated that the artefact
concerned will eventually be recovered, then the use of
anodes may allow part of the usual conservation treatment
to be undertaken while the artefact is still on the sea-bed
(plate 17.4). However, the use of anodes requires some
specialist knowledge, involves a long-term fieldwork
commitment and can be fairly expensive. It is therefore
only likely to be attractive if the artefact concerned is con-
sidered to be exceptionally important, or if it is planned
to recover it subsequently.In certain circumstances in situ protection may be
impracticable or ultimately prove unsuccessful. In such
circumstances, the recovery of vulnerable artefacts may
be the only practicable means of ensuring their survival,
even if recovery runs counter to the prevailing heritage-
management policy. The possibility of this situation
arising should therefore be considered in the project plan
and contingency arrangements allowed for. This should
always be done in consultation with the relevant curator
and conservator. If an owner of the material concerned
has been identified, then that person or body should, of
course, be involved at an early stage.Figure 17.1 A covering of sandbags placed over a fragile
area on the Duart Point wreck. (Photo: Colin Martin)