Glossary U – Z

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Unconfined aquifer

"An unconfined aquifer is an aquifer in which the water table forms the upper boundary." [1]

  1. [1] Freeze, R.A., and Cherry, J.A. 1979. Groundwater. Prentice-Hall, Inc., Eaglewood Cliffs, N.J., pp. 48.
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Undifferentiated ('Undiff')

Not divided into sub-types or sub-classes. For example, an ‘undifferentiated sedimentary rock’ is one which has only been identified as some type of sedimentary rock, but the specific type (e.g., sandstone, mudstone, conglomerate, etc) has not been determined.


The rise of sea water from depths to the surface, typically bringing nutrients to the surface.

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The worth we assign to an estuary or attributes of an estuary. These are reflected in the management objectives for the estuary.

Vector borne diseases

Vector borne diseases are diseases which are commonly transmitted through vectors.More information

Vertical Accretion

Accumulation of sediments or other material resulting in the building-up or infilling of an area in a vertical direction.


a photo of vibracoring technique The vibracoring technique provides a reliable means to sample unconsolidated and semi-consolidated sediment sequences by means of a submersible, electrically powered, vibrating head attached to a rigid core barrel (normally aluminium, 76mm ID, 80mm OD) that by its agitation forces the core barrel to be driven into the seabed. Vibrocorers are used wherever soil/sediment conditions are unsuited to gravity corers or where greater penetration of the seabed is necessary. Vibrocorers are used widely throughout the geotechnical investigation industry and can be deployed in water depths up to 1,000m.There are a number of types, such as the Quaternary Resources SEAS* (*Submersible Equipment and Services) vibracorers and the Aimers McLean type, which are standard industry designs for use in sands and denser/stronger soils.

Video Fishing

Underwater stereo-video is a research tool that is capable of making accurate, precise, non-invasive measurements of fish length or biomass [1-8] and may have many benefits for managers of wild stock and for aquaculturalists. Comparisons of the accuracy and precision of length estimates of plastic silhouettes of fish [6,7] and real fish [8] by experienced scientific divers and stereo-video cameras have demonstrated the measurement accuracy, precision and advantages of stereo-video measurements for both length and distance estimates.

Underwater stereo-video systems consist of two or more video cameras with known, fixed focal lengths, and known distances of separation and angles of convergence of the cameras [9]. Video imagery is imported in a stereo photo comparator [10] along with camera calibration and relative orientation information. The stereo photo comparator facilitates the location of objects in three dimensional coordinates (x, y, z) relative to the position and orientation of the camera pair. These data can be used to measure distance and angle, accurately defining the extent of a sampling unit (e.g. a 25 m x 5 m transect used for censusing reef fish), the swimming speed of a fish, the length of a fish or other morphometric measures. Research is now focusing on measuring the shape and volume of a fish and in incrementally automating the measurement process.

Stereo-video systems can be modified for use by divers, on Remote Operated Vehicles and sleds and in trawl nets. More recently they have been modified to sample fish assemblages using a remote baited camera station [11,12].

  1. Naiberg, A., Petrell, R. J., Savage, C. R. and Neufeld, T. 1993. Non-invasive fish size assessment method for tanks and sea cages using stereo-video. In: Techniques for Modern Aquaculture (Editor J.K Wang) pp. 372-381. American Society of Agricultural Engineers.
  2. Harvey, E.S., Shortis, M.R., Stadler, M. and M. Cappo. 2002. A comparison of the accuracy and precision of digital and analogue stereo-video systems. Marine Technology Society Journal, 36(2): 38-49.
  3. Li, R., Li, H., Zou, W., Smith, R. G. and Curran, T. A. 1996. An underwater digital photogrammetric system for fishery goematics. International Archives of Photogrammetry and Remote Sensing 31(B5): 524-529.
  4. Petrell, R. J., Shi, X., Ward, R. K., Naiberg, A. and Savage, C. R. 1997. Determining fish size an swimming speed in cages and tanks using simple video techniques. Aquacult. Eng.16: 63-84.
  5. Steeves, G., Peterson, R. and Clark, L. 1998. A quantitative stereoscopic video system for visually measuring the linear dimensions of free-swimming fish. In: Oceans 98 Engineering for sustainable use of the oceans. 28 September-1 October 1998, Nice, France Piscataway. NJ USA IEEE. OES, 3: 1405-1408.
  6. Harvey, E. S., Fletcher, D. and Shortis, M. 2001 a. A comparison of the precision and accuracy of estimates of reef-fish lengths made by divers and a stereo-video system. Fish. Bull. 99(1): 63-71.
  7. Harvey, E. S., Fletcher, D. and Shortis, M. 2001 b. Improving the statistical power of visual length estimates of reef fish: A comparison of estimates determined visually by divers with estimates produced by a stereo-video system. Fish. Bull. 99(1): 72-80.
  8. Harvey, E.S, Fletcher, D., and Shortis, M.R. 2002. Estimation of reef fish length by divers and by stereo-video. A first comparison of the accuracy and precision in the field on living fish under operational conditions. Fisheries Research, 57/3: 257-267
  9. Harvey, E. S. and Shortis, M. 1996. A system for stereo-video measurement of subtidal organisms. MTS J. 29(4): 10-22.
  10. Shortis, M. R. and Robson, S. 2001. VMS Reference and User Guide.
  11. Cappo, M., Speare, P., Wassenberg, T.J., Harvey, E., Rees, M., Heyward, A., and Pitcher, R. Use of Baited Remote Underwater Video Stations (BRUVS) to survey demersal fish: how deep and meaningful? In: Harvey, E.S. and M. Cappo (Eds). Direct sensing of the size frequency and abundance of target and non-target fauna in Australian Fisheries. 4-7 September 2000, Rottnest Island, Western Australia. Fisheries Research and Development Corporation. p 63-71, ISBN 1 74052 057 2.
  12. Cappo. M., Harvey. E., Malcom. H. and P. Speare. 2002 World Congress on Marine Protected Areas. Cairns, August, 2002. Advantages and applications of novel “video fishing” techniques to design and monitor marine protected areas. In Review.


Euan Harvey, University of Western Australia

Virtual Reality Modelling Language (VRML)

Virtual Reality Modelling Language (VRML) is an open source language, developed by the Web3D Consortium. It is a common export format from many 3D graphics software applications and provides a versatile tool that can be easily customised for different projects. VRML browsers allow versatile visual manipulation of 3D space through various navigation settings, as well as providing the flexibility for allowing limited data interrogation.

Vulnerability, coastal

"Vulnerability is a function of exposure to climatic factors, sensitivity to change and the capacity to adapt to that change. Systems that are highly exposed, sensitive and less able to adapt are vulnerable". [1]

Vulnerability, coastal

  1. Allen Consulting, 2005: 'Climate Change Risk and Vulnerability'; Final report to the Australian Greenhouse Office by The Allen Consulting Group, March 2005, 159pp

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Washover/Back barrier Deposit

Deposit of marine-derived sediment landward of a barrier system, often formed during large storm events.

Water Hardness

Water ‘hardness' is defined as the content of metallic ions in waters which react with sodium in soaps. Most water hardness is attributable to calcium (Ca2+) and magnesium (Mg2+) ions. A general expression used to calculate water hardness is:

hardness = 2.5(Ca2+) + 4.1(Mg2+)

in which calcium and magnesium are measured in milligrams per litre (mg L-1) [1]. Water is considered very hard if hardness values exceed 150 mg L-1 [1]. In comparison, hardness values of < 60 mg L-1 are indicative of soft waters [1]. Seawater has a hardness level of 500 mg L-1. Water hardness increases with salinity in a mixing system between seawater and rainwater/river water (Figure 1).

Some important mineral sources of calcium and magnesium ions are calcium carbonate (CaCO3) and dolomite (CaMg(CO3)2) dissolved from limestones.

Changes in water hardness with log salinity in a mixing system between seawater and rainwater.

Figure 1. Changes in water hardness with log salinity in a mixing system between seawater and rainwater.

  1. Freeze, R.A. and Cherry, J.A. 1979. Groundwater, Prentice-Hall Inc., Englewood Cliffs, N.J., pp. 604.

Water quality guideline(s)

"A water quality guideline is a recommended numerical value of an indicator (e.g. of a contaminant) or a descriptive statement (e.g. visual appearance of a water body) that will support and maintain the designated environmental values (EVs) of a particular water type. (Note that water quality guidelines are nowadays taken to encompass not only the physical and chemical characteristics of waters but also biological and even habitat characteristics)." --- ANZECC/ARMCANZ (October 2000) Australian Guidelines for Water Quality Monitoring and Reporting. More information

Water quality objectives

Water quality objectives are measurable yardsticks that need to be achieved to maintain or restore the community's initial choice for environmental values of waterways in the study area and the water quality guidelines to protect them. More information

Water Quality Targets

'Water Quality Targets' are numerical values or descriptive statements that must be met within a specified period of time to protect a set of environmental values (i.e. aquatic ecosystem protection, recreation and aquaculture/human consumption) [1]. Water Quality Targets are available on a bioregional basis on the the Department of Environment, Water, Heritage and the Arts website. Customising of targets to local conditions following procedures outlined in the guidelines is also highly encouraged [1].

  1. the Department of Environment, Water, Heritage and the Arts. Water Quality Targets: A Handbook, Commonwealth of Australia, 2002 (see also Water Quality Targets OnLine).


There are two main types of wastewater:

  • domestic wastewater i.e. waterborne wastes from households (e.g. faecal matter, urine, and waste from bathroom basins); and
  • industrial wastewater i.e. waterborne waste that is generated in industrial processes (including sewage treatment plants).


A periodic and repeating disturbance that travels through water (or other medium) from one location to another location.

Wave-dominated Delta

Coastal waterway in which waves are the principal factor that shape the overall geomorphology, and river input is sufficient to have filled in the basin so that there is limited space for continued sediment accumulation. They are characterised by a sandy barrier and a river channel that has a direct connection with the sea. See more information.

Wave-dominated Estuary

Coastal waterway in which waves are the principal factor in shaping the overall geomorphology. Characterised by a sandy barrier (partially constricting the entrance) that is backed a broad central basin and a fluvial delta, where the river enters the basin. See more information.

Water temperature

Water temperature is a measure of the degree of hotness or coldness of water (or the kinetic energy). More information


Wetlands are "areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres and may incorporate riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six metres at low tide lying within the wetlands" [1].

  1. [1] The RAMSAR Convention on Wetland website.
More information

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Zooxanthellae are unicellular dinoflagellate algae belonging to the genus Symbiodinium that live in the tissues of many tropical marine animals including corals, sea anemones, tridacnid clams and some foraminiferans and sponges.


Non-photosynthetic, heterotrophic planktonic organisms, including protists, small animals, and larvae, which exist within the water column.

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