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 Ubiquitous
Hydrophytes Plant species that grow
either in wetland or on upland areas e.g., red maple (Acer rubrum)
as opposed to Obligate Hydrophytes, which are plant species that
are found only in wetlands e.g., cattail (Typha latifolia).
Ubiquitous Organisms Organisms
that can tolerate a wide range of environmental conditions or variations.
Also, organisms that are so active or so numerous as to seem to be
present or existent in all types of environments.
Udometer A Rain Gauge.
Ultrafiltration Filtration through a medium (as a semipermeable
capillary wall) which allows small molecules (as of water) to pass
but holds back larger ones (as of protein).
Ultraviolet Radiation (UV) Light waves shorter than the visible
blue-violet waves of the spectrum, i.e., below 3900 Angstroms (D).
UV can be used for the disinfection of water.
Unbiased Sample (Statistics) A sample is said to be unbiased
if its behavior and characteristics are representative of the total
Population.
Unconfined Conditions in which the upper surface of the Zone
of Saturation forms a water table under atmospheric pressure.
Unconfined Aquifer An aquifer containing water that is not
under pressure; the water level in a well is the same as the water
table outside the well. An unconfined aquifer made up of loose material,
such as sand or gravel, that has not undergone lithification (settling).
In an unconfined aquifer the upper boundary is the top of the Zone
of Saturation (water table).
Unconsolidated Deposits (Sediment) Sediment not cemented
together; may consist of sand, silt, clay, and organic material.
Unconsolidated Formation Natural earth formations that have
not been turned to stone, such as alluvium, soil, gravel, clay, sand
and overburden.
Undercurrent A current, as of air or water, below another
current or beneath the surface.
Underflow (1) (Surface and Groundwater) The downstream flow
of water through the permeable deposits underlying a stream. (2) (Water
Quality) The slurry of concentrated solids or Sludge that is removed
from the bottom of a Settling Tank, Clarifier, or Thickener. (3) Submerged
gravity-driven flows which occur when inflows to a water body are
denser than the ambient water. The inflow subsequently plunges and
continues as a distinct flow which can be envisioned as a submerged
stream. Underflows, also called Density Current, are known to form
intermittently on coastal continental shelves, in reservoirs and at
effluent discharge sites.
Underdrain A drain that carries away water from prepared beds
or agricultural fields to which water or wastewater has been applied.
Underground Injection Control (UIC) A program required in each
state by a provision of the Safe Drinking Water Act (SDWA) for the
regulation of Injection Wells, including a permit system. An applicant
must demonstrate that the well has no reasonable chance of adversely
affecting the quality of an underground source of drinking water before
a permit is issued.
Underground Source of Drinking Water (USDW) An aquifer that
is currently being used as a source of drinking water or those potentially
capable of supplying a public water system. They have a total dissolved
solids content of 10,000 milligrams per liter or less, and are not
Exempted Aquifers.
Underground Storage Tank (Water Quality) (1) Any one or combination
of underground tanks and any connecting underground pipes used to
contain an accumulation of regulated substances. (2) A tank located
at least partially underground and designed to hold gasoline or other
petroleum products or chemicals.
Underground Water Water below the surface of the ground. Also
referred to as Groundwater, Ground Water, Subsurface Water, and Subterranean
Water.
Understory Plants growing beneath the canopy of other plants.
Usually refers to grasses, forbs, and low shrubs under a tree or shrub
overstory.
Unimpaired Flow The flow past a specified point on a natural
stream that is unaffected by stream diversion, storage, import, export,
return flow, or change in use caused by modifications in land use.
Unit Density A density of one gram per cubic centimeter or one
gram per milliliter; the density of water at 4EC (39.2EF).
Unit Hydrograph
(1) The Hydrograph of direct runoff from a storm uniformly distributed
over the drainage basin during a specified unit of time; the hydrograph
is reduced in vertical scale to correspond to a volume of runoff from
the drainage basin of one inch.
(2) The hydrograph of surface runoff (not including groundwater runoff)
on a given basin due to an effective rain falling for a unit of time.
Unit Period The time duration of a unit storm. See Unit Storm,
below.
Unit Storm A net rainfall one-inch deep which occurs over all
parts of a drainage area at a uniform rate during a specified unit
period of time.
Unmeasured Sediment Discharge The difference between Total Sediment
Discharge and measured Suspended-Sediment Discharge.
Unravel To loosen material from the edges of a revetment.
Unsaturated Flow Movement of water in a porous medium in which
the pore spaces are not filled with water and the direction of flow
is from the wetter zone of higher potential to one of lower potential.
Unsaturated Zone
(1) The portion of the soil profile which contains both air and water.
Water in this zone cannot enter a well.
(2) The subsurface zone between the water table (Zone of Saturation)
and the land surface where some of the spaces between the soil particles
are filled with air. It includes the root zone, intermediate zone,
and capillary fringe. The pore spaces contain water, as well as air
and other gases at less than atmospheric pressure. Saturated bodies,
such as Perched Ground Water, may exist in the unsaturated zone, and
water pressure within these bodies may be greater than atmospheric.
Also referred to as the Vadose Zone or, less frequently, the Zone
of Aeration.
Unsteady Flow Flow that is changing with respect to time.
Upgradient Well A groundwater monitoring well, such as those
required at facilities that treat, store, or dispose of hazardous
waste using surface impoundments or landfills, that allows sampling
and analysis of groundwater that is upstream from the facility, before
the groundwater is possibly affected by any escaping contaminants.
The results of the analyses are used for comparison to the results
of groundwater sampled from Downgradient Wells.
Uplands
(1) The ground above a floodplain; that zone sufficiently above and/or
away from transported waters as to be dependent upon local precipitation
for its water supplies.
(2) Land which is neither a Wetland nor covered with water.
Uplift (Hydraulics) The upward pressure of water on the base
of a structure or the upward pressure in the pores of a material,
i.e., Interstitial Pressure.
Upstream Toward the source or upper part of a stream; against
the current. In relation to water rights, the term refers to water
uses or locations that affect water quality or quantity of downstream
water uses or locations.
Upstream Blanket An impervious layer placed on the reservoir
floor upstream of a dam. In the case of an Embankment Dam, the blanket
may be connected to the impermeable element of the dam.
Upstream Control Control structure adjustments based on information
from upstream. The required information is measured by a sensing device
located upstream, or based on the upstream water schedule established
by the watermaster.
Upstream Slope (of a Dam) The part of the dam that is in contact
with the reservoir water. On Earthen Dams the upstream slope must
be protected from the erosive action of waves by rock Rip Rap, concrete,
or some other material.
Uptime (Irrigation) The total time that a system is available
for service.
Upwelling
(1) The appearance of water from the deep ocean at the surface. This
usually occurs along the coasts of continents (such as the coast of
Peru along the west coast of South America) where the prevailing winds
tend to push the surface waters away from the land area, allowing
waters from the deep ocean to rise to the surface. The deep waters
carry a significant input of plant nutrients to the surface, causing
an elevated level of primary production and abundant fish populations.
(2) The process or an instance of rising or appearing to rise to the
surface and flowing outward; especially the process of upward movement
to the surface of marine often nutrientrich lower waters particularly
along some shores due to the offshore drift of surface water (as from
the action of winds and the Coriolis Effect).
Urban Equilibrium (of a Channel) A term used to describe a channel
that has changed from its natural or original shape but has finished
adjusting to the urban influences affecting it so that it is relatively
stable in its planform and meander and has achieved a new balanced
in its bankfull width and depth, so that it is neither excessively
eroding nor depositing and has healthy riparian growth.
Urban Flooding Nuisance flooding of streets, underpasses, basements
and other low-lying urban areas. Should not be confused with flash
flooding. Usually due to poor drainage, or limited drainage capacity
of urban systems. The amount and rate of precipitation that causes
urban or Small Stream Flooding is usually constant for a specific
community. In general, 0.51.0 inch (1.32.5 cm) of precipitation
in one hour will cause at least minor urban/small stream flooding
in most urbanized areas. Over one inch of rainfall in an hour will
cause general urban flood problems, and may cause flash flooding.
Urban Runoff Storm water from city streets and gutters that
usually contains a great deal of litter and organic and bacterial
wastes into the sewer systems and receiving waters.
Urban Water Use The use of water for urban purposes, including
residential, commercial, industrial, recreation, military, and institutional
classes. The term is applied in the sense that it is a kind of use
rather than a place of use.
Urban Water Use per Capita A unit of water use which encompasses
all urban uses of water in a service area. Generally measured in gallons
per capita per day (gpcd).
Usable Storage Capacity The available storage capacity plus
the remaining ground water storage within a reasonable pump lift.
Specific yield of the sediments is used in calculating estimates of
usable storage capacity.
Use (Water) This term, when referring specifically to water
use, is normally preceded by one of the following descriptive terms:
[1] Conjunction Water The integrated use of surface and subsurface
water supplies and facilities, normally involving storage of surplus
waters when available, for use during periods when water supplies
are deficient.
[2] Consumptive Water The quantity of water discharged to the atmosphere
or incorporated in the products in the process of vegetative growth,
food processing, industrial processes, or other uses.
[3] Consumption Irrigation The quantity of water that is absorbed
by the crop and transpired or used directly in the building of plant
tissue together with that evaporated from the cropped area.
[4] Multiple The conscientious management of the various renewable
resources such as water, wood, forage, wildlife, and recreation resources,
to obtain sustained yield of products and services in the combination
that will best meet the needs of the public now and in the future.
USGS (Test-Well) Site Identification The standard U.S. Geological
Survey (USGS) site identification is based on the grid system of latitude
and longitude. The number consists of 15 digits. The first six digits
denote the degrees, minutes, and seconds of latitude; the next seven
digits denote degrees, minutes, and seconds of longitude; and the
last two digits (assigned sequentially) identify the sites within
a 1second grid. For example, site 365227114554401 is at 36E52N27O
latitude and 114E55N44O longitude, and it is the first site recorded
in that 1second grid. The assigned number is retained as a permanent
identifier even if a more precise latitude and longitude are later
determined.
U-Shaped Valleys U-shaped valleys are characteristic of glacial
erosion; valleys eroded by stream action are typically V-Shaped. Also
referred to as Glaciated Valleys.
Usufruct, also Usufructuary (LegalCivil Law) The right of
enjoying a thing, the property of which is vested in another, and
to draw from the same all the profit, utility, and advantage which
it may produce, provided it be without altering the substance of the
thing. For example, in Nevada, the states water belongs to the people,
but is permitted, through the water rights permitting process, to
be used beneficially by other individuals or entities.
Usufructuary (Water) Right
(1) A right to use rather than own the property of another, such as
the states water.
(2) A water right holders authority to divert and use a certain amount
of water. See Usufruct.
Utility Water Use Water supplied from a Public Water Supply
System and used for such purposes as firefighting, street washing,
and municipal parks and swimming pools. Public water use also includes
system water losses (water lost to leakage) and brine water discharged
from desalination facilities. Also referred to as Public Water Use.
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