DESTRUCTIVEINVESTIGATIVE TECHNIQUES 147
Airlifts can be easier to handle than water-dredges, but
where water depth is particularly shallow, a water-dredge
may be the only option, particularly as it lies almost flat.
However, the airlift can work well in a depth of less
than 2 m (6.5 ft) provided a very large volume of air is
pumped through it. Additionally, the airlift will also
work with up to one-third of its length protruding above
the water surface. Both tools can be controlled easily by
the hand-operated valves, but can do untold damage if
used in an uncontrolled fashion. As in all archaeological
operations, it is in the best interests of the surviving
evidence if the work is carried out in a careful and dis-
ciplined manner.
Water-jet
Another power-tool occasionally used is the water-jet.
This is simply high-pressure water released through
various shaped nozzles at a volume and pressure appro-
priate for the task. The indiscriminate nature of a high-
volume and/or high-velocity jet of water, let alone its effect
on visibility, limits its application on archaeological sites.
Miniature versions, run off a water-dredge, however, can
be highly effective for delicate work. Alternatively, a sep-
arate water-jet can be used in conjunction with a dredge.
Small water-jets with a very low power are used in a sim-
ilar way to brushes and are effective on organic material.
As in all cases where delicate material is being excavated,
however, do not experiment with a new technique or a
new tool on the object itself.
Another use for water-jets is to induce an artificial
current where it is otherwise very difficult to maintain
visibility around the working area, such as in lakes. The
technique was developed in Switzerland for excavation
of prehistoric lakeside settlements. Water is pumped from
the surface and directed through rows of small nozzles
directed along and just above the bed.Advantage should be taken of the unique ability of the diver
to hover above the area under investigation. There are many
techniques that can be tried. One advantage of a solid
site-grid (chapter 14) is that it can offer additional diver
support, and one technique successfully applied on a
number of sites is to clasp the horizontal bar with the feet
(one over, one under) to hang inclined at 45 degrees
above the site (plate 15.1). Pressure applied alternately with
either foot will allow the excavator to move around the
area with complete control over his/her height above the
archaeological deposits. When using an airlift, height can
be adjusted by control of breathing or by slightly altering
the buoyancy of the airlift as described above. However,
the best means of control is to use the increase in the air-
lift’s buoyancy that occurs when the intake is partially
obstructed. The excavator simply holds the airlift by the
rim and extends or retracts their fingers into the water flow
making the airlift rise or fall respectively. This technique
can be tricky to learn but once acquired allows excava-
tors to lower or raise themselves into and out of sensitive
areas with ease.Further Information
Adams, J., 2002a, Excavation methods underwater, in C. Orser
(ed.), Encyclopaedia of Historical Archaeology, 192– 6. London.
Barker, P., 1993 (3rd edn), Techniques of Archaeological
Excavation. London.
Buglass, J. and Rackham, J., 1991, Environmental Sampling on
Wet Sites, in J. M. Coles and D. M. Goodburn (eds), Wet Site
Excavation and Survey. WARP Occasional Paper No. 5. Exeter.
English Heritage, 2004b, Dendrochronology: Guidelines on Pro-
ducing and Interpreting Dendrochronological Dates. London.
Harris, E. C., 1989 (2nd edn), Principles of Archaeological
Stratigraphy. London.
Institute of Field Archaeologists, 2001a (rev. edn), Standards and
Guidance for Archaeological Excavation.Reading.
Mook, W. G. and Waterbolk, H. T., 1985, Radiocarbon Dating,
Handbooks for Archaeologists No. 3. Strasbourg.
Nayling, N., 1991, Tree-ring dating: sampling, analysis and
results, in J. M. Coles and D. M. Goodburn (eds),Wet
Site Excavation and Survey. WARP Occasional Paper No. 5.
Exeter.
Oxley, I., 1991, Environmental Sampling Underwater, in J. M.
Coles and D. M. Goodburn (eds), Wet Site Excavation and
Survey. WARP Occasional Paper No. 5. Exeter.
Roskins, S., 2001, Excavation.Cambridge.
Tyers, I., 1989, Dating by tree-ring analysis, in P. Marsden
(ed.), A late Saxon logboat from Clapton, London Borough
of Hackney, International Journal of Nautical Archaeology
18 .2, 89 –111.
Watts G. P. Jr, 1976, Hydraulic Probing: One solution to over-
burden and environment, International Journal of Nautical
Archaeology 5 .4, 76 – 81.