A water eductor or water dredge is an

eductor-jet pump A vacuum ejector, or simply ejector is a type of vacuum pump, which produces vacuum by means of the Venturi effect. In an ejector, a working fluid (liquid or gaseous) flows through a jet nozzle into a tube that first narrows and then expands in ...

-based tool used by underwater archaeologists to remove sediments from an underwater archaeological site.

Airlift An airlift is the organized delivery of supplies or personnel primarily via military transport aircraft. Airlifting consists of two distinct types: strategic and tactical. Typically, strategic airlifting involves moving material long distanc ...

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 A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...

ed. The

Bernoulli effect In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. The principle is named after the Swiss mathemat ...

from the flow of pumped water causes suction at the mouth of the dredge. Water and sediment are 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 is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

. 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 Context may refer to: * Context (language use), the relevant constraints of the communicative situation that influence language use, language variation, and discourse summary Computing * Context (computing), the virtual environment required to su ...

and

features Feature may refer to: Computing * Feature (CAD), could be a hole, pocket, or notch * Feature (computer vision), could be an edge, corner or blob * Feature (software design) is an intentional distinguishing characteristic of a software item ...

and

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...

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

is not recorded. An eductor can also form part of a

wet scrubber The term wet scrubber describes a variety of devices that remove pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the l ...

system which are designed to remove soluble gases and particulate by inducing a gas flow using high pressure liquid focused into a venturi throat. Additionally, eductor scrubbers can be used for direct-contact condensation.

References

* ''Nuestra Señora de la Concepción'' by William M. Mathers.

National Geographic Magazine ''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...

, Vol. 178, No. 3, page 47. * ''Maritime Archaeology'' by Keith Muckelroy. Cambridge University Press, 1978 pp 28–31 and pp49–50.
Eductor Wet Scrubbers
by Sly Filters Maritime archaeology Methods in archaeology Dredging

See also

References