Water eductor
Encyclopedia
A water eductor or water dredge is a tool used by underwater archaeologists
to remove sediments from an underwater archaeological site. Airlift
s may be used for the same purpose.
It consists of a large bore straight tube to which is attached a hose pipe through which clean water is pump
ed. The Bernoulli effect
from the flow of pumped water causes suction at the mouth of the dredge. Water and sediment is sucked from the excavation site and released from the far end of the tube. The tube can be made of any rigid material such as steel
or plastic
. The diameter of the tube depends on the power available from the pump and whether delicate work is required.
In the hands of a trained archaeologist, the water dredge performs the same function as a wheelbarrow on land. It is used to carry away sediments, not to dig holes. The archaeologist dislodges the material using a trowel, brush or by making a fanning motion with the hand to cause a current to dislodge sediment. The archaeologist can also place overburden material directly into the mouth of the dredge. As the water dredge will remove particles held in suspension in the water, provided it is used correctly it will improve visibility in the immediate area of the excavation. Careful use of the water dredge ensures that artifacts can be recorded in context
and features
and stratigraphy
can be studied.
Using a water dredge or airlift, the underwater archaeologist has an advantage over terrestrial counterparts, as the spoil is removed without effort and without needing to be transported across other parts of the archaeological site.
Where there is a possibility of small artifacts
being missed because of poor visibility, a trap may be used at the outlet so that the lifted sediment can be filtered.
Water eductors are also used by marine treasure hunters to suck sediments for filtering for buried artifacts. Using the water dredge to directly suck sediments means that archaeological information on context and stratigraphy
is not recorded.
Underwater archaeology
Underwater archaeology is archaeology practised underwater. As with all other branches of archaeology it evolved from its roots in pre-history and in the classical era to include sites from the historical and industrial eras...
to remove sediments from an underwater archaeological site. Airlift
Airlift (dredging device)
An Airlift is device based on a pipe, used in nautical archaeology to suck small objects, sand and mud from the sea bed and to transport the resulting debris upwards and away from its source. It is sometimes called a suction dredge...
s may be used for the same purpose.
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
ed. The Bernoulli effect
Bernoulli's principle
In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy...
from the flow of pumped water causes suction at the mouth of the dredge. Water and sediment is sucked from the excavation site and released from the far end of the tube. The tube can be made of any rigid material such as steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
or plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
. The diameter of the tube depends on the power available from the pump and whether delicate work is required.
In the hands of a trained archaeologist, the water dredge performs the same function as a wheelbarrow on land. It is used to carry away sediments, not to dig holes. The archaeologist dislodges the material using a trowel, brush or by making a fanning motion with the hand to cause a current to dislodge sediment. The archaeologist can also place overburden material directly into the mouth of the dredge. As the water dredge will remove particles held in suspension in the water, provided it is used correctly it will improve visibility in the immediate area of the excavation. Careful use of the water dredge ensures that artifacts can be recorded in context
Archaeological context
In archaeology, not only the context of a discovery is a significant fact, but the formation of the context is as well. An archaeological context is an event in time which has been preserved in the archaeological record. The cutting of a pit or ditch in the past is a context, whilst the material...
and features
Feature (archaeology)
Feature in archaeology and especially excavation has several different but allied meanings. A feature is a collection of one or more contexts representing some human non-portable activity that generally has a vertical characteristic to it in relation to site stratigraphy. Examples of features are...
and stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
can be studied.
Using a water dredge or airlift, the underwater archaeologist has an advantage over terrestrial counterparts, as the spoil is removed without effort and without needing to be transported across other parts of the archaeological site.
Where there is a possibility of small artifacts
Artifact (archaeology)
An artifact or artefact is "something made or given shape by man, such as a tool or a work of art, esp an object of archaeological interest"...
being missed because of poor visibility, a trap may be used at the outlet so that the lifted sediment can be filtered.
Water eductors are also used by marine treasure hunters to suck sediments for filtering for buried artifacts. Using the water dredge to directly suck sediments means that archaeological information on context and stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
is not recorded.