WATER RESOURCES DATA FOR WASHINGTON 2003 41
Acid neutralizing capacity (ANC) is the equivalent sum of
all bases or base-producing materials, solutes plus
particulates, in an aqueous system that can be titrated with
acid to an equivalence point. This term designates titration
of an “unfiltered” sample (formerly reported as
alkalinity).
Acre-foot (AC-FT, acre-ft) is a unit of volume, commonly
used to measure quantities of water used or stored,
equivalent to the volume of water required to cover 1 acre
to a depth of 1 foot and equivalent to 43,560 cubic feet,
325,851 gallons, or 1,233 cubic meters. (See also “Annual
runoff”)
Adenosine triphosphate (ATP) is an organic, phosphate-
rich compound important in the transfer of energy in
organisms. Its central role in living cells makes ATP an
excellent indicator of the presence of living material in
water. A measurement of ATP therefore provides a
sensitive and rapid estimate of biomass. ATP is reported in
micrograms per liter.
Adjusted discharge is discharge data that have been
mathematically adjusted (for example, to remove the
effects of a daily tide cycle or reservoir storage).
Algal growth potential (AGP) is the maximum algal dry
weight biomass that can be produced in a natural water
sample under standardized laboratory conditions. The
growth potential is the algal biomass present at stationary
phase and is expressed as milligrams dry weight of algae
produced per liter of sample. (See also “Biomass” and
“Dry weight”)
Alkalinity is the capacity of solutes in an aqueous system to
neutralize acid. This term designates titration of a
“filtered” sample.
Annual runoff is the total quantity of water that is
discharged (“runs off”) from a drainage basin in a year.
Data reports may present annual runoff data as volumes in
acre-feet, as discharges per unit of drainage area in cubic
feet per second per square mile, or as depths of water on
the drainage basin in inches.
Annual 7-day minimum is the lowest mean value for any
7-consecutive-day period in a year. Annual 7-day
minimum values are reported herein for the calendar year
and the water year (October 1 through September 30).
Most low-flow frequency analyses use a climatic year
(April 1-March 31), which tends to prevent the low-flow
period from being artificially split between adjacent years.
The date shown in the summary statistics table is the
initial date of the 7-day period. (This value should not be
confused with the 7-day, 10-year low-flow statistic.)
Aroclor is the registered trademark for a group of poly-
chlorinated biphenyls that were manufactured by the
Monsanto Company prior to 1976. Aroclors are assigned
specific 4-digit reference numbers dependent upon
molecular type and degree of substitution of the biphenyl
ring hydrogen atoms by chlorine atoms. The first two
digits of a numbered aroclor represent the molecular type,
and the last two digits represent the percentage weight of
the hydrogen-substituted chlorine.
Artificial substrate is a device that purposely is placed in a
stream or lake for colonization of organisms. The artificial
substrate simplifies the community structure by
standardizing the substrate from which each sample is
collected. Examples of artificial substrates are basket
samplers (made of wire cages filled with clean streamside
rocks) and multiplate samplers (made of hardboard) for
benthic organism collection, and plexiglass strips for
periphyton collection. (See also “Substrate”)
Ash mass is the mass or amount of residue present after the
residue from a dry-mass determination has been ashed in a
muffle furnace at a temperature of 500°C for 1 hour. Ash
mass of zooplankton and phytoplankton is expressed in
grams per cubic meter (g/m
3
), and periphyton and benthic
organisms in grams per square meter (g/m
2
). (See also
“Biomass” and “Dry mass”)
Aspect is the direction toward which a slope faces with
respect to the compass.
DEFINITION OF TERMS
Specialized technical terms related to streamflow, water-quality, and other hydrologic data, as used in this
report, are defined below. Terms such as algae, water level, and precipitation are used in their common everyday
meanings, definitions of which are given in standard dictionaries. Not all terms defined in this alphabetical list apply
to every State. See also table for converting English units to International System (SI) Units. Other glossaries that
also define water-related terms are accessible from
http://water.usgs.gov/glossaries.html.
42 WATER RESOURCES DATA FOR WASHINGTON 2003
Bacteria are microscopic unicellular organisms, typically
spherical, rodlike, or spiral and threadlike in shape, often
clumped into colonies. Some bacteria cause disease,
whereas others perform an essential role in nature in the
recycling of materials; for example, by decomposing
organic matter into a form available for reuse by plants.
Bankfull stage, as used in this report, is the stage at which a
stream first overflows its natural banks formed by floods
with 1- to 3-year recurrence intervals.
Base discharge (for peak discharge) is a discharge value,
determined for selected stations, above which peak
discharge data are published. The base discharge at each
station is selected so that an average of about three peak
flows per year will be published. (See also “Peak flow.”)
Base flow is sustained flow of a stream in the absence of
direct runoff. It includes natural and human-induced
streamflows. Natural base flow is sustained largely by
ground-water discharge.
Bed material is the sediment mixture of which a stream-
bed, lake, pond, reservoir, or estuary bottom is composed.
(See also “Bedload” and “Sediment.”)
Bedload is material in transport that primarily is supported
by the streambed. In this report, bedload is considered to
consist of particles in transit from the bed to the top of the
bedload sampler nozzle (an elevation ranging from 0.25 to
0.5 foot). These particles are retained in the bedload
sampler. A sample collected with a pressure-differential
bedload sampler also may contain a component of the
suspended load.
Bedload discharge (tons per day) is the rate of sediment
moving as bedload, reported as dry weight, that passes
through a cross section in a given time. NOTE: Bedload
discharge values in this report may include a component
of the suspended-sediment discharge. A correction may
be necessary when computing the total sediment
discharge by summing the bedload discharge and the
suspended-sediment discharge. (See also “Bedload,” “Dry
weight,” “Sediment,” and “Suspended-sediment
discharge.”)
Benthic organisms are the group of organisms inhabiting
the bottom of an aquatic environment. They include a
number of types of organisms, such as bacteria, fungi,
insect larvae and nymphs, snails, clams, and crayfish.
They are useful as indicators of water quality.
Biochemical oxygen demand (BOD) is a measure of the
quantity of dissolved oxygen, in milligrams per liter,
necessary for the decomposition of organic matter by
microorganisms, such as bacteria.
Biomass is the amount of living matter present at any given
time, expressed as mass per unit area or volume of habitat.
Biomass pigment ratio is an indicator of the total
proportion of periphyton that are autotrophic (plants).
This also is called the Autotrophic Index.
Blue-green algae (Cyanophyta) are a group of
phytoplankton and periphyton organisms with a blue
pigment in addition to a green pigment called chlorophyll.
Blue-green algae can cause nuisance water-quality
conditions in lakes and slow-flowing rivers; however, they
are found commonly in streams throughout the year. The
abundance of blue-green algae in phytoplankton samples
is expressed as the number of cells per milliliter
(cells/mL) or biovolume in cubic micrometers per
milliliter (µm
3
/mL). The abundance of blue-green algae in
periphyton samples is given in cells per square centimeter
(cells/cm
2
) or biovolume per square centimeter
(µm
3
/cm
2
). (See also “Phytoplankton”and “Periphyton.”)
Bottom material (See “Bed material”)
Bulk electrical conductivity is the combined electrical
conductivity of all material within a doughnut-shaped
volume surrounding an induction probe. Bulk
conductivity is affected by different physical and chemical
properties of the material including the dissolved-solids
content of the pore water, and the lithology and porosity
of the rock.
Canadian Geodetic Vertical Datum 1928 is a geodetic
datum derived from a general adjustment of Canada’s first
order level network in 1928.
Cell volume (biovolume) determination is one of several
common methods used to estimate biomass of algae in
aquatic systems. Cell members of algae are used
frequently in aquatic surveys as an indicator of algal
production. However, cell numbers alone cannot represent
true biomass because of considerable cell-size variation
among the algal species. Cell volume (µm
3
) is determined
by obtaining critical cell measurements or cell dimensions
(for example, length, width, height, or radius) for 20 to 50
cells of each important species to obtain an average
biovolume per cell. Cells are categorized according to the
correspondence of their cellular shape to the nearest
geometric solid or combinations of simple solids (for
example, spheres, cones, or cylinders). Representative
formulae used to compute biovolume are as follows:
sphere 4/3 πr
3
cone 1/3 πr
2
h cylinder πr
2
h.
pi (π) is the ratio of the circumference to the diameter of a
circle; pi = 3.14159….
From cell volume, total algal biomass expressed as
biovolume (µm
3
/mL) is thus determined by multiplying
the number of cells of a given species by its average cell
volume and then summing these volumes for all species.
WATER RESOURCES DATA FOR WASHINGTON 2003 43
Cells/volume refers to the number of cells of any organism
that is counted by using a microscope and grid or counting
cell. Many planktonic organisms are multicelled and are
counted according to the number of contained cells per
sample volume, and generally are reported as cells or units
per milliliter (mL) or liter (L).
Cfs-day (See “Cubic foot per second-day”)
Channel bars, as used in this report, are the lowest
prominent geomorphic features higher than the channel
bed.
Chemical oxygen demand (COD) is a measure of the
chemically oxidizable material in the water and furnishes
an approximation of the amount of organic and reducing
material present. The determined value may correlate with
BOD or with carbonaceous organic pollution from sewage
or industrial wastes. [See also “Biochemical oxygen
demand (BOD)”]
Clostridium perfringens (C. perfringens) is a spore-
forming bacterium that is common in the feces of human
and other warmblooded animals. Clostridial spores are
being used experimentally as an indicator of past fecal
contamination and the presence of microorganisms that
are resistant to disinfection and environmental stresses.
(See also “Bacteria”)
Coliphages are viruses that infect and replicate in coliform
bacteria. They are indicative of sewage contamination of
water and of the survival and transport of viruses in the
environment.
Color unit is produced by 1 milligram per liter of platinum
in the form of the chloroplatinate ion. Color is expressed
in units of the platinum-cobalt scale.
Confined aquifer is a term used to describe an aquifer
containing water between two relatively impermeable
bound-aries. The water level in a well tapping a confined
aquifer stands above the top of the confined aquifer and
can be higher or lower than the water table that may be
present in the material above it. In some cases, the water
level can rise above the ground surface, yielding a flowing
well.
Contents is the volume of water in a reservoir or lake.
Unless otherwise indicated, volume is computed on the
basis of a level pool and does not include bank storage.
Continuous-record station is a site where data are
collected with sufficient frequency to define daily mean
values and variations within a day.
Control designates a feature in the channel that physically
affects the water-surface elevation and thereby determines
the stage-discharge relation at the gage. This feature may
be a constriction of the channel, a bedrock outcrop, a
gravel bar, an artificial structure, or a uniform cross
section over a long reach of the channel.
Control structure, as used in this report, is a structure on a
stream or canal that is used to regulate the flow or stage of
the stream or to prevent the intrusion of saltwater.
Cubic foot per second (CFS, ft
3
/s) is the rate of discharge
representing a volume of 1 cubic foot passing a given
point in 1 second. It is equivalent to approximately
7.48 gallons per second or approximately 449 gallons per
minute, or 0.02832 cubic meters per second. The term
“second-foot” sometimes is used synonymously with
“cubic foot per second” but is now obsolete.
Cubic foot per second-day (CFS-DAY, Cfs-day,
[(ft
3
/s)/d]) is the volume of water represented by a flow of
1 cubic foot per second for 24 hours. It is equivalent to
86,400 cubic feet, 1.98347 acre-feet, 646,317 gallons, or
2,446.6 cubic meters. The daily mean discharges reported
in the daily value data tables numerically are equal to the
daily volumes in cfs-days, and the totals also represent
volumes in cfs-days.
Cubic foot per second per square mile [CFSM,
(ft
3
/s)/mi
2
] is the average number of cubic feet of water
flowing per second from each square mile of area drained,
assuming the runoff is distributed uniformly in time and
area. (See also “Annual runoff”)
Daily mean suspended-sediment concentration is the
time-weighted mean concentration of suspended sediment
passing a stream cross section during a 24-hour day.
(See also “Sediment” and “Suspended-sediment
concentration”)
Daily record station is a site where data are collected with
sufficient frequency to develop a record of one or more
data values per day. The frequency of data collection can
range from continuous recording to data collection on a
daily or near-daily basis.
Data collection platform (DCP) is an electronic instrument
that collects, processes, and stores data from various
sensors, and transmits the data by satellite data relay, line-
of-sight radio, and/or landline telemetry.
Data logger is a microprocessor-based data acquisition
system designed specifically to acquire, process, and store
data. Data usually are downloaded from onsite data
loggers for entry into office data systems.
44 WATER RESOURCES DATA FOR WASHINGTON 2003
Datum is a surface or point relative to which measurements
of height and/or horizontal position are reported. A
vertical datum is a horizontal surface used as the zero
point for measurements of gage height, stage, or elevation;
a horizontal datum is a reference for positions given in
terms of latitude-longitude, State Plane coordinates, or
Universal Transverse Mercator (UTM) coordinates. (See
also “Gage datum,” “Land-surface datum,” “National
Geodetic Vertical Datum of 1929,” and “North American
Vertical Datum of 1988”)
Diatoms (Bacillariophyta) are unicellular or colonial algae
with a siliceous cell wall. The abundance of diatoms in
phytoplankton samples is expressed as the number of cells
per milliliter (cells/mL) or biovolume in cubic
micrometers per milliliter (µm
3
/mL). The abundance of
diatoms in periphyton samples is given in cells per square
centimeter (cells/cm
2
) or biovolume per square centimeter
(µm
3
/cm
2
). (See also “Phytoplankton” and “Periphyton”)
Diel is of or pertaining to a 24-hour period of time; a regular
daily cycle.
Discharge, or flow, is the rate that matter passes through a
cross section of a stream channel or other water body per
unit of time. The term commonly refers to the volume of
water (including, unless otherwise stated, any sediment or
other constituents suspended or dissolved in the water)
that passes a cross section in a stream channel, canal,
pipeline, and so forth, within a given period of time (cubic
feet per second). Discharge also can apply to the rate at
which constituents, such as suspended sediment, bedload,
and dissolved or suspended chemicals, pass through a
cross section, in which cases the quantity is expressed as
the mass of constituent that passes the cross section in a
given period of time (tons per day).
Dissolved refers to that material in a representative water
sample that passes through a 0.45-micrometer membrane
filter. This is a convenient operational definition used by
Federal and State agencies that collect water-quality data.
Determinations of “dissolved” constituent concentrations
are made on sample water that has been filtered.
Dissolved oxygen (DO) is the molecular oxygen (oxygen
gas) dissolved in water. The concentration in water is a
function of atmospheric pressure, temperature, and
dissolved-solids concentration of the water. The ability of
water to retain oxygen decreases with increasing
temperature or dissolved-solids concentration.
Photosynthesis and respiration by plants commonly cause
diurnal variations in dissolved-oxygen concentration in
water from some streams.
Dissolved solids concentration in water is the quantity of
dissolved material in a sample of water. It is determined
either analytically by the “residue-on-evaporation”
method, or mathematically by totaling the concentrations
of individual constituents reported in a comprehensive
chemical analysis. During the analytical determination,
the bicarbonate (generally a major dissolved component
of water) is converted to carbonate. In the mathematical
calculation, the bicarbonate value, in milligrams per liter,
is multiplied by 0.4926 to convert it to carbonate.
Alternatively, alkalinity concentration (as mg/L CaCO
3
)
can be converted to carbonate concentration by
multiplying by 0.60.
Diversity index (H) (Shannon index) is a numerical
expression of evenness of distribution of aquatic
organisms. The formula for diversity index is:
,
where n
i
is the number of individuals per taxon, n is the
total number of individuals, and s is the total number of
taxa in the sample of the community. Index values range
from zero, when all the organisms in the sample are the
same, to some positive number, when some or all of the
organisms in the sample are different.
Drainage area of a stream at a specific location is that area
upstream from the location, measured in a horizontal
plane, that has a common outlet at the site for its surface
runoff from precipitation that normally drains by gravity
into a stream. Drainage areas given herein include all
closed basins, or noncontributing areas, within the area
unless otherwise specified.
Drainage basin is a part of the Earth’s surface that contains
a drainage system with a common outlet for its surface
runoff. (See “Drainage area”)
Dry mass refers to the mass of residue present after drying
in an oven at 105°C, until the mass remains unchanged.
This mass represents the total organic matter, ash and
sediment, in the sample. Dry-mass values are expressed in
the same units as ash mass. (See also “Ash mass,”
“Biomass,” and “Wet mass”)
Dry weight refers to the weight of animal tissue after it has
been dried in an oven at 65°C until a constant weight is
achieved. Dry weight represents total organic and
inorganic matter in the tissue. (See also “Wet weight”).
Embeddedness is the degree to which gravel-sized and
larger particles are surrounded or enclosed by finer-sized
particles. (See also “Substrate embeddedness class”)
d
n
i
n
----
log
2
n
i
n
----
i1≈
s
∑
–=
WATER RESOURCES DATA FOR WASHINGTON 2003 45
Enterococcus bacteria commonly are found in the feces of
humans and other warmblooded animals. Although some
strains are ubiquitous and not related to fecal pollution,
the presence of enterococci in water is an indication of
fecal pollution and the possible presence of enteric
pathogens. Enterococcus bacteria are those bacteria that
produce pink to red colonies with black or reddish-brown
precipitate after incubation at 41°C on mE agar (nutrient
medium for bacterial growth) and subsequent transfer to
EIA medium. Enterococci include Streptococcus feacalis,
Streptococcus feacium, Streptococcus avium, and their
variants. (See also “Bacteria”)
EPT Index is the total number of distinct taxa within the
insect orders Ephemeroptera, Plecoptera, and Trichoptera.
This index summarizes the taxa richness within the
aquatic insects that generally are considered pollution
sensitive; the index usually decreases with pollution.
Escherichia coli (E. coli) are bacteria present in the
intestine and feces of warmblooded animals. E. coli are a
member species of the fecal coliform group of indicator
bacteria. In the laboratory, they are defined as those
bacteria that produce yellow or yellow-brown colonies on
a filter pad saturated with urea substrate broth after
primary culturing for 22 to 24 hours at 44.5°C on mTEC
medium (nutrient medium for bacterial growth). Their
concentrations are expressed as number of colonies per
100 mL of sample. (See also “Bacteria”)
Estimated (E) value of a concentration is reported when an
analyte is detected and all criteria for a positive result are
met. If the concentration is less than the method detection
limit (MDL), an E code will be reported with the value. If
the analyte is identified qualitatively as present, but the
quantitative determination is substantially more uncertain,
the National Water Quality Laboratory will identify the
result with an E code even though the measured value is
greater than the MDL. A value reported with an E code
should be used with caution. When no analyte is detected
in a sample, the default reporting value is the MDL
preceded by a less than sign (<). For bacteriological data,
concentrations are reported as estimated when results are
based on non-ideal colony counts.
Euglenoids (Euglenophyta) are a group of algae that
usually are free-swimming and rarely creeping. They have
the ability to grow either photosynthetically in the light or
heterotrophically in the dark. (See also “Phytoplankton”)
Extractable organic halides (EOX) are organic
compounds that contain halogen atoms such as chlorine.
These organic compounds are semivolatile and extractable
by ethyl acetate from air-dried streambed sediment. The
ethyl acetate extract is combusted, and the concentration
is determined by microcoulometric determination of the
halides formed. The concentration is reported as
micrograms of chlorine per gram of the dry weight of the
streambed sediment.
Fecal coliform bacteria are present in the intestines or
feces of warmblooded animals. They often are used as
indicators of the sanitary quality of the water. In the
laboratory, they are defined as all organisms that produce
blue colonies within 24 hours when incubated at 44.5°C
plus or minus 0.2°C on M-FC medium (nutrient medium
for bacterial growth). Their concentrations are expressed
as number of colonies per 100 mL of sample. (See also
“Bacteria”)
Fecal streptococcal bacteria are present in the intestines of
warmblooded animals and are ubiquitous in the
environment. They are characterized as gram-positive,
cocci bacteria that are capable of growth in brain-heart
infusion broth. In the laboratory, they are defined as all the
organisms that produce red or pink colonies within 48
hours at 35°C plus or minus 1.0°C on KF-streptococcus
medium (nutrient medium for bacterial growth). Their
concentrations are expressed as number of colonies per
100 mL of sample. (See also “Bacteria”)
Fire algae (Pyrrhophyta) are free-swimming unicells
characterized by a red pigment spot. (See also
“Phytoplankton”)
Flow-duration percentiles are values on a scale of 100 that
indicate the percentage of time for which a flow is not
exceeded. For example, the 90th percentile of river flow is
greater than or equal to 90 percent of all recorded flow
rates.
Gage datum is a horizontal surface used as a zero point for
measurement of stage or gage height. This surface usually
is located slightly below the lowest point of the stream
bottom such that the gage height is usually slightly greater
than the maximum depth of water. Because the gage
datum is not an actual physical object, the datum is
usually defined by specifying the elevations of permanent
reference marks such as bridge abutments and survey
monuments, and the gage is set to agree with the reference
marks. Gage datum is a local datum that is maintained
independently of any national geodetic datum. However,
if the elevation of the gage datum relative to the national
datum (North American Vertical Datum of 1988 or
National Geodetic Vertical Datum of 1929) has been
determined, then the gage readings can be converted to
elevations above the national datum by adding the
elevation of the gage datum to the gage reading.
46 WATER RESOURCES DATA FOR WASHINGTON 2003
Gage height (G.H.) is the water-surface elevation, in feet
above the gage datum. If the water surface is below the
gage datum, the gage height is negative. Gage height often
is used interchangeably with the more general term
“stage,” although gage height is more appropriate when
used in reference to a reading on a gage.
Gage values are values that are recorded, transmitted, and/
or computed from a gaging station. Gage values typically
are collected at 5-, 15-, or 30-minute intervals.
Gaging station is a site on a stream, canal, lake, or reservoir
where systematic observations of stage, discharge, or
other hydrologic data are obtained.
Gas chromatography/flame ionization detector
(GC/FID) is a laboratory analytical method used as a
screening technique for semivolatile organic compounds
that are extractable from water in methylene chloride.
Geomorphic channel units, as used in this report, are
fluvial geomorphic descriptors of channel shape and
stream velocity. Pools, riffles, and runs are types of
geomorphic channel units considered for National Water-
Quality Assessment (NAWQA) Program habitat sampling.
Green algae (Chlorophyta) are unicellular or colonial algae
with chlorophyll pigments similar to those in terrestrial
green plants. Some forms of green algae produce mats or
floating “moss” in lakes. The abundance of green algae in
phytoplankton samples is expressed as the number of cells
per milliliter (cells/mL) or biovolume in cubic
micrometers per milliliter (µm
3
/mL). The abundance of
green algae in periphyton samples is given in cells per
square centimeter (cells/cm
2
) or biovolume per square
centimeter (µm
3
/cm
2
). (See also “Phytoplankton” and
“Periphyton”)
Habitat, as used in this report, includes all nonliving
(physical) aspects of the aquatic ecosystem, although
living components like aquatic macrophytes and riparian
vegetation also are usually included. Measurements of
habitat typically are made over a wider geographic scale
than are measurements of species distribution.
Habitat quality index is the qualitative description (level 1)
of instream habitat and riparian conditions surrounding
the reach sampled. Scores range from 0 to 100 percent
with higher scores indicative of desirable habitat
conditions for aquatic life. Index only applicable to
wadable streams.
Hardness of water is a physical-chemical characteristic that
commonly is recognized by the increased quantity of soap
required to produce lather. It is computed as the sum of
equivalents of polyvalent cations (primarily calcium and
magnesium) and is expressed as the equivalent
concentration of calcium carbonate (CaCO
3
).
High tide is the maximum height reached by each rising
tide. The high-high and low-high tides are the higher and
lower of the two high tides, respectively, of each tidal day.
See NOAA Web site:
http://www.co-ops.nos.noaa.gov/tideglos.html
Hilsenhoff’s Biotic Index (HBI) is an indicator of organic
pollution that uses tolerance values to weight taxa
abundances; usually increases with pollution. It is
calculated as follows:
,
where n is the number of individuals of each taxon, a is
the tolerance value of each taxon, and N is the total
number of organisms in the sample.
Horizontal datum (See “Datum”)
Hydrologic index stations referred to in this report are
continuous-record gaging stations that have been selected
as representative of streamflow patterns for their
respective regions. Station locations are shown on index
maps.
Hydrologic unit is a geographic area representing part or
all of a surface drainage basin or distinct hydrologic
feature as defined by the former Office of Water Data
Coordination and delineated on the State Hydrologic Unit
Maps by the USGS. Each hydrologic unit is identified by
an 8-digit number.
Inch (IN., in.), in reference to streamflow, as used in this
report, refers to the depth to which the drainage area
would be covered with water if all of the runoff for a given
time period were distributed uniformly on it. (See also
“Annual runoff”)
Instantaneous discharge is the discharge at a particular
instant of time. (See also “Discharge”)
International Boundary Commission Survey Datum
refers to a geodetic datum established at numerous
monuments along the United States-Canada boundary by
the International Boundary Commission.
Island, as used in this report, is a mid-channel bar that has
permanent woody vegetation, is flooded once a year, on
average, and remains stable except during large flood
events.
HBI sum
n()a()
N
----------------
=
WATER RESOURCES DATA FOR WASHINGTON 2003 47
Laboratory reporting level (LRL) generally is equal to
twice the yearly determined long-term method detection
level (LT-MDL). The LRL controls false negative error.
The probability of falsely reporting a nondetection for a
sample that contained an analyte at a concentration equal
to or greater than the LRL is predicted to be less than or
equal to 1 percent. The value of the LRL will be reported
with a “less than” (<) remark code for samples in which
the analyte was not detected. The National Water Quality
Laboratory (NWQL) collects quality-control data from
selected analytical methods on a continuing basis to
determine LT-MDLs and to establish LRLs. These values
are reevaluated annually on the basis of the most current
quality-control data and, therefore, may change. The LRL
replaces the term ‘non-detection value’ (NDV).
Land-surface datum (lsd) is a datum plane that is
approximately at land surface at each ground-water
observation well.
Latent heat flux (often used interchangeably with latent
heat-flux density) is the amount of heat energy that
converts water from liquid to vapor (evaporation) or from
vapor to liquid (condensation) across a specified cross-
sectional area per unit time. Usually expressed in watts
per square meter.
Light-attenuation coefficient, also known as the extinction
coefficient, is a measure of water clarity. Light is
attenuated according to the Lambert-Beer equation:
,
where I
ο
is the source light intensity, I is the light intensity
at length L (in meters) from the source, l is the light-
attenuation coefficient, and e is the base of the natural
logarithm. The light-attenuation coefficient is defined as
.
Lipid is any one of a family of compounds that are
insoluble in water and that make up one of the principal
components of living cells. Lipids include fats, oils,
waxes, and steroids. Many environmental contaminants
such as organochlorine pesticides are lipophilic.
Long-term method detection level (LT-MDL) is a
detection level derived by determining the standard
deviation of a minimum of 24 method detection limit
(MDL) spike-sample measurements over an extended
period of time. LT-MDL data are collected on a
continuous basis to assess year-to-year variations in the
LT-MDL. The LT-MDL controls false positive error. The
chance of falsely reporting a concentration at or greater
than the LT-MDL for a sample that did not contain the
analyte is predicted to be less than or equal to 1 percent.
Low tide is the minimum height reached by each falling
tide. The high-low and low-low tides are the higher and
lower of the two low tides, respectively, of each tidal day.
See NOAA Web site:
http://www.co-ops.nos.noaa.gov/tideglos.html
Macrophytes are the macroscopic plants in the aquatic
environment. The most common macrophytes are the
rooted vascular plants that usually are arranged in zones in
aquatic ecosystems and restricted in the area by the extent
of illumination through the water and sediment deposition
along the shoreline.
Mean concentration of suspended sediment (Daily mean
suspended-sediment concentration) is the time-weighted
concentration of suspended sediment passing a stream
cross section during a given time period. (See also “Daily
mean suspended-sediment concentration” and
“Suspended-sediment concentration”)
Mean discharge (MEAN) is the arithmetic mean of
individual daily mean discharges during a specific period.
(See also “Discharge”)
Mean high or low tide is the average of all high or low
tides, respectively, over a specific period.
Mean sea level is a local tidal datum. It is the arithmetic
mean of hourly heights observed over the National Tidal
Datum Epoch. Shorter series are specified in the name; for
example, monthly mean sea level and yearly mean sea
level. In order that they may be recovered when needed,
such datums are referenced to fixed points known as
benchmarks. (See also “Datum”)
Measuring point (MP) is an arbitrary permanent reference
point from which the distance to water surface in a well is
measured to obtain water level.
Megahertz is a unit of frequency. One megahertz equals
one million cycles per second.
Membrane filter is a thin microporous material of specific
pore size used to filter bacteria, algae, and other very
small particles from water.
Metamorphic stage refers to the stage of development that
an organism exhibits during its transformation from an
immature form to an adult form. This developmental
process exists for most insects, and the degree of
difference from the immature stage to the adult form
varies from relatively slight to pronounced, with many
intermediates. Examples of metamorphic stages of insects
are egg-larva-adult or egg-nymph-adult.
II
o
e
λ
L–
=
λ
1
L
---
log
e
I
I
o
----
–=
48 WATER RESOURCES DATA FOR WASHINGTON 2003
Method detection limit (MDL) is the minimum
concentration of a substance that can be measured and
reported with 99-percent confidence that the analyte
concentration is greater than zero. It is determined from
the analysis of a sample in a given matrix containing the
analyte. At the MDL concentration, the risk of a false
positive is predicted to be less than or equal to 1 percent.
Method of Cubatures is a method of computing discharge
in tidal estuaries based on the conservation of mass
equation.
Methylene blue active substances (MBAS) indicate the
presence of detergents (anionic surfactants). The
determination depends on the formation of a blue color
when methylene blue dye reacts with synthetic anionic
detergent compounds.
Micrograms per gram (UG/G, µg/g) is a unit expressing
the concentration of a chemical constituent as the mass
(micrograms) of the element per unit mass (gram) of
material analyzed.
Micrograms per kilogram (UG/KG, µg/kg) is a unit
expressing the concentration of a chemical constituent as
the mass (micrograms) of the constituent per unit mass
(kilogram) of the material analyzed. One microgram per
kilogram is equivalent to 1 part per billion.
Micrograms per liter (UG/L, µg/L) is a unit expressing the
concentration of chemical constituents in water as mass
(micrograms) of constituent per unit volume (liter) of
water. One thousand micrograms per liter is equivalent to
1 milligram per liter. One microgram per liter is equivalent
to 1 part per billion.
Microsiemens per centimeter (US/CM, µS/cm) is a unit
expressing the amount of electrical conductivity of a
solution as measured between opposite faces of a
centimeter cube of solution at a specified temperature.
Siemens is the International System of Units
nomenclature. It is synonymous with mhos and is the
reciprocal of resistance in ohms.
Milligrams per liter (MG/L, mg/L) is a unit for expressing
the concentration of chemical constituents in water as the
mass (milligrams) of constituent per unit volume (liter) of
water. Concentration of suspended sediment also is
expressed in milligrams per liter and is based on the mass
of dry sediment per liter of water-sediment mixture.
Minimum reporting level (MRL) is the smallest measured
concentration of a constituent that may be reliably
reported by using a given analytical method.
Miscellaneous site, miscellaneous station, or miscellaneous
sampling site is a site where streamflow, sediment, and/or
water-quality data or water-quality or sediment samples
are collected once, or more often on a random or
discontinuous basis to provide better areal coverage for
defining hydrologic and water-quality conditions over a
broad area in a river basin.
Most probable number (MPN) is an index of the number
of coliform bacteria that, more probably than any other
number, would give the results shown by the laboratory
examination; it is not an actual enumeration. MPN is
determined from the distribution of gas-positive cultures
among multiple inoculated tubes.
Multiple-plate samplers are artificial substrates of known
surface area used for obtaining benthic invertebrate
samples. They consist of a series of spaced, hardboard
plates on an eyebolt.
Nanograms per liter (NG/L, ng/L) is a unit expressing the
concentration of chemical constituents in solution as mass
(nanograms) of solute per unit volume (liter) of water. One
million nanograms per liter is equivalent to 1 milligram
per liter.
National Geodetic Vertical Datum of 1929 (NGVD 29) is
a fixed reference adopted as a standard geodetic datum for
elevations determined by leveling. It formerly was called
“Sea Level Datum of 1929” or “mean sea level.” Although
the datum was derived from the mean sea level at 26 tide
stations, it does not necessarily represent local mean sea
level at any particular place. See NOAA Web site:
http://www.ngs.noaa.gov/faq.shtml#WhatVD29VD88
(See “North American Vertical Datum of 1988”)
Natural substrate refers to any naturally occurring
immersed or submersed solid surface, such as a rock or
tree, upon which an organism lives. (See also “Substrate”)
Nekton are the consumers in the aquatic environment and
consist of large, free-swimming organisms that are
capable of sustained, directed mobility.
Nephelometric turbidity unit (NTU) is the measurement
for reporting turbidity that is based on use of a standard
suspension of formazin. Turbidity measured in NTU uses
nephelometric methods that depend on passing specific
light of a specific wavelength through the sample.
North American Datum of 1927 (NAD 27) is the
horizontal control datum for the United States that was
defined by a location and azimuth on the Clarke spheroid
of 1866.
WATER RESOURCES DATA FOR WASHINGTON 2003 49
North American Datum of 1983 (NAD 83) is the
horizontal control datum for the United States, Canada,
Mexico, and Central America that is based on the
adjustment of 250,000 points including 600 satellite
Doppler stations that constrain the system to a geocentric
origin. NAD 83 has been officially adopted as the legal
horizontal datum for the United States by the Federal
government.
North American Vertical Datum of 1988 (NAVD 88) is a
fixed reference adopted as the official civilian vertical
datum for elevations determined by Federal surveying and
mapping activities in the United States. This datum was
established in 1991 by minimum-constraint adjustment of
the Canadian, Mexican, and United States first-order
terrestrial leveling networks.
Open or screened interval is the length of unscreened
opening or of well screen through which water enters a
well, in feet below land surface.
Organic carbon (OC) is a measure of organic matter
present in aqueous solution, suspension, or bottom
sediment. May be reported as dissolved organic carbon
(DOC), particulate organic carbon (POC), or total organic
carbon (TOC).
Organic mass or volatile mass of a living substance is the
difference between the dry mass and ash mass and
represents the actual mass of the living matter. Organic
mass is expressed in the same units as for ash mass and
dry mass. (See also “Ash mass,” “Biomass,” and “Dry
mass”)
Organism count/area refers to the number of organisms
collected and enumerated in a sample and adjusted to the
number per area habitat, usually square meter (m
2
), acre,
or hectare. Periphyton, benthic organisms, and
macrophytes are expressed in these terms.
Organism count/volume refers to the number of organisms
collected and enumerated in a sample and adjusted to the
number per sample volume, usually milliliter (mL) or liter
(L). Numbers of planktonic organisms can be expressed in
these terms.
Organochlorine compounds are any chemicals that
contain carbon and chlorine. Organochlorine compounds
that are important in investigations of water, sediment, and
biological quality include certain pesticides and industrial
compounds.
Parameter code is a 5-digit number used in the USGS
computerized data system, National Water Information
System (NWIS), to uniquely identify a specific
constituent or property.
Partial-record station is a site where discrete
measurements of one or more hydrologic parameters are
obtained over a period of time without continuous data
being recorded or computed. A common example is a
crest-stage gage partial-record station at which only peak
stages and flows are recorded.
Particle size is the diameter, in millimeters (mm), of a
particle determined by sieve or sedimentation methods.
The sedimentation method uses the principle of Stokes
Law to calculate sediment particle sizes. Sedimentation
methods (pipet, bottom-withdrawal tube, visual-
accumulation tube, sedigraph) determine fall diameter of
particles in either distilled water (chemically dispersed) or
in native water (the river water at the time and point of
sampling).
Particle-size classification, as used in this report, agrees
with the recommendation made by the American
Geophysical Union Subcommittee on Sediment
Terminology. The classification is as follows:
The particle-size distributions given in this report are not
necessarily representative of all particles in transport in
the stream. For the sedimentation method, most of the
organic matter is removed, and the sample is subjected to
mechanical and chemical dispersion before analysis in
distilled water. Chemical dispersion is not used for native
water analysis.
Peak flow (peak stage) is an instantaneous local maximum
value in the continuous time series of streamflows or
stages, preceded by a period of increasing values and
followed by a period of decreasing values. Several peak
values ordinarily occur in a year. The maximum peak
value in a year is called the annual peak; peaks lower than
the annual peak are called secondary peaks. Occasionally,
the annual peak may not be the maximum value for the
year; in such cases, the maximum value occurs at
midnight at the beginning or end of the year, on the
recession from or rise toward a higher peak in the
adjoining year. If values are recorded at a discrete series of
times, the peak recorded value may be taken as an
approximation of the true peak, which may occur between
the recording instants. If the values are recorded with
finite precision, a sequence of equal recorded values may
occur at the peak; in this case, the first value is taken as
the peak.
Classification Size (mm) Method of analysis
Clay >0.00024 - 0.004 Sedimentation
Silt >0.004 - 0.062 Sedimentation
Sand >0.062 - 2.0 Sedimentation/sieve
Gravel >2.0 - 64.0 Sieve
Cobble >64 - 256 Manual measurement
Boulder >256 Manual measurement
50 WATER RESOURCES DATA FOR WASHINGTON 2003
Percent composition or percent of total is a unit for
expressing the ratio of a particular part of a sample or
population to the total sample or population, in terms of
types, numbers, weight, mass, or volume.
Percent shading is a measure of the amount of sunlight
potentially reaching the stream. A clinometer is used to
measure left and right bank canopy angles. These values
are added together, divided by 180, and multiplied by 100
to compute percentage of shade.
Periodic-record station is a site where stage, discharge,
sediment, chemical, physical, or other hydrologic
measurements are made one or more times during a year
but at a frequency insufficient to develop a daily record.
Periphyton is the assemblage of microorganisms attached
to and living upon submerged solid surfaces. Although
primarily consisting of algae, they also include bacteria,
fungi, protozoa, rotifers, and other small organisms.
Periphyton are useful indicators of water quality.
Pesticides are chemical compounds used to control
undesirable organisms. Major categories of pesticides
include insecticides, miticides, fungicides, herbicides, and
rodenticides.
pH of water is the negative logarithm of the hydrogen-ion
activity. Solutions with pH less than 7.0 standard units are
termed “acidic,” and solutions with a pH greater than 7.0
are termed “basic.” Solutions with a pH of 7.0 are neutral.
The presence and concentration of many dissolved
chemical constituents found in water are affected, in part,
by the hydrogen-ion activity of water. Biological
processes including growth, distribution of organisms, and
toxicity of the water to organisms also are affected, in
part, by the hydrogen-ion activity of water.
Phytoplankton is the plant part of the plankton. They
usually are microscopic, and their movement is subject to
the water currents. Phytoplankton growth is dependent
upon solar radiation and nutrient substances. Because they
are able to incorporate as well as release materials to the
surrounding water, the phytoplankton have a profound
effect upon the quality of the water. They are the primary
food producers in the aquatic environment and commonly
are known as algae. (See also “Plankton”)
Picocurie (PC, pCi) is one-trillionth (1 x 10
-12
) of the
amount of radioactive nuclide represented by a curie (Ci).
A curie is the quantity of radioactive nuclide that yields
3.7 x 10
10
radioactive disintegrations per second (dps). A
picocurie yields 0.037 dps, or 2.22 dpm (disintegrations
per minute).
Plankton is the community of suspended, floating, or
weakly swimming organisms that live in the open water of
lakes and rivers. Concentrations are expressed as a
number of cells per milliliter (cells/mL) of sample.
Polychlorinated biphenyls (PCBs) are industrial chemicals
that are mixtures of chlorinated biphenyl compounds
having various percentages of chlorine. They are similar
in structure to organochlorine insecticides.
Polychlorinated naphthalenes (PCNs) are industrial
chemicals that are mixtures of chlorinated naphthalene
compounds. They have properties and applications similar
to polychlorinated biphenyls (PCBs) and have been
identified in commercial PCB preparations.
Pool, as used in this report, is a small part of a stream reach
with little velocity, commonly with water deeper than
surrounding areas.
Primary productivity is a measure of the rate at which new
organic matter is formed and accumulated through photo-
synthetic and chemosynthetic activity of producer
organisms (chiefly, green plants). The rate of primary
production is estimated by measuring the amount of
oxygen released (oxygen method) or the amount of carbon
assimilated (carbon method) by the plants.
Primary productivity (carbon method) is expressed
as milligrams of carbon per area per unit time
[mg C/(m
2
/time)] for periphyton and macrophytes or per
volume [mg C/(m
3
/time)] for phytoplankton. The carbon
method defines the amount of carbon dioxide consumed
as measured by radioactive carbon (carbon-14). The
carbon-14 method is of greater sensitivity than the oxygen
light- and dark-bottle method and is preferred for use with
unenriched water samples. Unit time may be either the
hour or day, depending on the incubation period. (See also
“Primary productivity”)
Primary productivity (oxygen method) is expressed as
milligrams of oxygen per area per unit time
[mg O/(m
2
/time)] for periphyton and macrophytes or per
volume [mg O/(m
3
/time)] for phytoplankton. The oxygen
method defines production and respiration rates as
estimated from changes in the measured dissolved-oxygen
concentration. The oxygen light- and dark-bottle method
is preferred if the rate of primary production is sufficient
for accurate measurements to be made within 24 hours.
Unit time may be either the hour or day, depending on the
incubation period. (See also “Primary productivity”)
WATER RESOURCES DATA FOR WASHINGTON 2003 51
Radioisotopes are isotopic forms of elements that exhibit
radioactivity. Isotopes are varieties of a chemical element
that differ in atomic weight but are very nearly alike in
chemical properties. The difference arises because the
atoms of the isotopic forms of an element differ in the
number of neutrons in the nucleus; for example, ordinary
chlorine is a mixture of isotopes having atomic weights of
35 and 37, and the natural mixture has an atomic weight
of about 35.453. Many of the elements similarly exist as
mixtures of isotopes, and a great many new isotopes have
been produced in the operation of nuclear devices such as
the cyclotron. There are 275 isotopes of the 81 stable
elements, in addition to more than 800 radioactive
isotopes.
Reach, as used in this report, is a length of stream that is
chosen to represent a uniform set of physical, chemical,
and biological conditions within a segment. It is the
principal sampling unit for collecting physical, chemical,
and biological data.
Recoverable from bed (bottom) material is the amount of
a given constituent that is in solution after a representative
sample of bottom material has been digested by a method
(usually using an acid or mixture of acids) that results in
dissolution of readily soluble substances. Complete
dissolution of all bottom material is not achieved by the
digestion treatment and thus the determination represents
less than the total amount (that is, less than 95 percent) of
the constituent in the sample. To achieve comparability of
analytical data, equivalent digestion procedures would be
required of all laboratories performing such analyses
because different digestion procedures are likely to
produce different analytical results. (See also “Bed
material”)
Recurrence interval, also referred to as return period, is the
average time, usually expressed in years, between
occurrences of hydrologic events of a specified type (such
as exceedances of a specified high flow or nonexceedance
of a specified low flow). The terms “return period” and
“recurrence interval” do not imply regular cyclic
occurrence. The actual times between occurrences vary
randomly, with most of the times being less than the
average and a few being substantially greater than the
average. For example, the 100-year flood is the flow rate
that is exceeded by the annual maximum peak flow at
intervals whose average length is 100 years (that is, once
in 100 years, on average); almost two-thirds of all
exceedances of the 100-year flood occur less than 100
years after the previous exceedance, half occur less than
70 years after the previous exceedance, and about one-
eighth occur more than 200 years after the previous
exceedance. Similarly, the 7-day, 10-year low flow (7Q
10
)
is the flow rate below which the annual minimum
7-day-mean flow dips at intervals whose average length is
10 years (that is, once in 10 years, on average); almost
two-thirds of the nonexceedances of the 7Q
10
occur less
than 10 years after the previous nonexceedance, half occur
less than 7 years after, and about one-eighth occur more
than 20 years after the previous nonexceedance. The
recurrence interval for annual events is the reciprocal of
the annual probability of occurrence. Thus, the 100-year
flood has a 1-percent chance of being exceeded by the
maximum peak flow in any year, and there is a
10-percent chance in any year that the annual minimum
7-day-mean flow will be less than the 7Q
10
.
Replicate samples are a group of samples collected in a
manner such that the samples are thought to be essentially
identical in composition.
Return period (See “Recurrence interval”)
Riffle, as used in this report, is a shallow part of the stream
where water flows swiftly over completely or partially
submerged obstructions to produce surface agitation.
River mileage is the curvilinear distance, in miles,
measured upstream from the mouth along the meandering
path of a stream channel in accordance with Bulletin No.
14 (October 1968) of the Water Resources Council and
typically is used to denote location along a river.
Run, as used in this report, is a relatively shallow part of a
stream with moderate velocity and little or no surface
turbulence.
Runoff is the quantity of water that is discharged (“runs
off”) from a drainage basin during a given time period.
Runoff data may be presented as volumes in acre-feet, as
mean discharges per unit of drainage area in cubic feet per
second per square mile, or as depths of water on the
drainage basin in inches. (See also “Annual runoff”)
Sea level, as used in this report, refers to one of the two
commonly used national vertical datums (NGVD 1929 or
NAVD 1988). See separate entries for definitions of these
datums.
Sediment is solid material that originates mostly from
disintegrated rocks; when transported by, suspended in, or
deposited from water, it is referred to as “fluvial
sediment.” Sediment includes chemical and biochemical
precipitates and decomposed organic material, such as
humus. The quantity, characteristics, and cause of the
occurrence of sediment in streams are affected by
environmental and land-use factors. Some major factors
are topography, soil characteristics, land cover, and depth
and intensity of precipitation.
52 WATER RESOURCES DATA FOR WASHINGTON 2003
Sensible heat flux (often used interchangeably with latent
sensible heat-flux density) is the amount of heat energy
that moves by turbulent transport through the air across a
specified cross-sectional area per unit time and goes to
heating (cooling) the air. Usually expressed in watts per
square meter.
Seven-day, 10-year low flow (7Q
10
) is the discharge below
which the annual 7-day minimum flow falls in
1 year out of 10 on the long-term average. The recurrence
interval of the 7Q
10
is 10 years; the chance that the annual
7-day minimum flow will be less than the 7Q
10
is 10
percent in any given year. (See also “Annual 7-day
minimum” and “Recurrence interval”)
Shelves, as used in this report, are streambank features
extending nearly horizontally from the flood plain to the
lower limit of persistent woody vegetation.
Sodium adsorption ratio (SAR) is the expression of
relative activity of sodium ions in exchange reactions
within soil and is an index of sodium or alkali hazard to
the soil. Sodium hazard in water is an index that can be
used to evaluate the suitability of water for irrigating
crops.
Soil heat flux (often used interchangeably with soil heat-
flux density) is the amount of heat energy that moves by
conduction across a specified cross-sectional area of soil
per unit time and goes to heating (or cooling) the soil.
Usually expressed in watts per square meter.
Soil-water content is the water lost from the soil upon
drying to constant mass at 105°C; expressed either as
mass of water per unit mass of dry soil or as the volume of
water per unit bulk volume of soil.
Specific electrical conductance (conductivity) is a
measure of the capacity of water (or other media) to
conduct an electrical current. It is expressed in
microsiemens per centimeter at 25°C. Specific electrical
conductance is a function of the types and quantity of
dissolved substances in water and can be used for
approximating the dissolved-solids content of the water.
Commonly, the concentration of dissolved solids (in
milligrams per liter) is from 55 to 75 percent of the
specific conductance (in microsiemens). This relation is
not constant from stream to stream, and it may vary in the
same source with changes in the composition of the water.
Stable isotope ratio (per MIL) is a unit expressing the ratio
of the abundance of two radioactive isotopes. Isotope
ratios are used in hydrologic studies to determine the age
or source of specific water, to evaluate mixing of different
water, as an aid in determining reaction rates, and other
chemical or hydrologic processes.
Stage (See “Gage height”)
Stage-discharge relation is the relation between the water-
surface elevation, termed stage (gage height), and the
volume of water flowing in a channel per unit time.
Streamflow is the discharge that occurs in a natural
channel. Although the term “discharge” can be applied to
the flow of a canal, the word “streamflow” uniquely
describes the discharge in a surface stream course. The
term “streamflow” is more general than “runoff” as
streamflow may be applied to discharge whether or not it
is affected by diversion or regulation.
Substrate is the physical surface upon which an organism
lives.
Substrate embeddedness class is a visual estimate of riffle
streambed substrate larger than gravel that is surrounded
or covered by fine sediment (<2 mm, sand or finer). Below
are the class categories expressed as the percentage
covered by fine sediment:
Surface area of a lake is that area (acres) encompassed by
the boundary of the lake as shown on USGS topographic
maps, or other available maps or photographs. Because
surface area changes with lake stage, surface areas listed
in this report represent those determined for the stage at
the time the maps or photographs were obtained.
Surficial bed material is the upper surface (0.1 to
0.2 foot) of the bed material that is sampled using U.S.
Series Bed-Material Samplers.
Surrogate is an analyte that behaves similarly to a target
analyte, but that is highly unlikely to occur in a sample. A
surrogate is added to a sample in known amounts before
extraction and is measured with the same laboratory
procedures used to measure the target analyte. Its purpose
is to monitor method performance for an individual
sample.
Suspended (as used in tables of chemical analyses) refers to
the amount (concentration) of undissolved material in a
water-sediment mixture. It is defined operationally as the
material retained on a 0.45-micrometer filter.
0 no gravel or larger substrate 3 26-50 percent
1 > 75 percent 4 5-25 percent
2 51-75 percent 5 < 5 percent
WATER RESOURCES DATA FOR WASHINGTON 2003 53
Suspended, recoverable is the amount of a given
constituent that is in solution after the part of a
representative suspended water-sediment sample that is
retained on a 0.45-micrometer membrane filter has been
digested by a method (usually using a dilute acid solution)
that results in dissolution of only readily soluble
substances. Complete dissolution of all the particulate
matter is not achieved by the digestion treatment, and,
thus, the determination represents something less than the
“total” amount (that is, less than 95 percent) of the
constituent present in the sample. To achieve
comparability of analytical data, equivalent digestion
procedures are required of all laboratories performing
such analyses because different digestion procedures are
likely to produce different analytical results.
Determinations of “suspended, recoverable” constituents
are made either by directly analyzing the suspended mate-
rial collected on the filter or, more commonly, by
difference, on the basis of determinations of (1) dissolved
and (2) total recoverable concentrations of the constituent.
(See also “Suspended”)
Suspended sediment is the sediment maintained in
suspension by the upward components of turbulent
currents or that exists in suspension as a colloid. (See also
“Sediment”)
Suspended-sediment concentration is the velocity-
weighted concentration of suspended sediment in the
sampled zone (from the water surface to a point
approximately 0.3 foot above the bed) expressed as
milligrams of dry sediment per liter of water-sediment
mixture (mg/L). The analytical technique uses the mass of
all of the sediment and the net weight of the water-
sediment mixture in a sample to compute the suspended-
sediment concentration. (See also “Sediment” and
“Suspended sediment”)
Suspended-sediment discharge (tons/d) is the rate of
sediment transport, as measured by dry mass or volume,
that passes a cross section in a given time. It is calculated
in units of tons per day as follows: concentration (mg/L) x
discharge (ft
3
/s) x 0.0027. (See also “Sediment,”
“Suspended sediment,” and “Suspended-sediment
concentration”)
Suspended-sediment load is a general term that refers to a
given characteristic of the material in suspension that
passes a point during a specified period of time. The term
needs to be qualified, such as “annual suspended-sediment
load” or “sand-size suspended-sediment load,” and so on.
It is not synonymous with either suspended-sediment
discharge or concentration. (See also “Sediment”)
Suspended solids, total residue at 105°C concentration is
the concentration of inorganic and organic material
retained on a filter, expressed as milligrams of dry
material per liter of water (mg/L). An aliquot of the
sample is used for this analysis.
Suspended, total is the total amount of a given constituent
in the part of a water-sediment sample that is retained on a
0.45-micrometer membrane filter. This term is used only
when the analytical procedure assures measurement of at
least 95 percent of the constituent determined. Knowledge
of the expected form of the constituent in the sample, as
well as the analytical methodology used, is required to
determine when the results should be reported as
“suspended, total.” Determinations of “suspended, total”
constituents are made either by directly analyzing portions
of the suspended material collected on the filter or, more
commonly, by difference, on the basis of determinations
of (1) dissolved and (2) total concentrations of the
constituent. (See also “Suspended”)
Synoptic studies are short-term investigations of specific
water-quality conditions during selected seasonal or
hydro-logic periods to provide improved spatial resolution
for critical water-quality conditions. For the period and
conditions sampled, they assess the spatial distribution of
selected water-quality conditions in relation to causative
factors, such as land use and contaminant sources.
Taxa (Species) richness is the number of species (taxa)
present in a defined area or sampling unit.
Taxonomy is the division of biology concerned with the
classification and naming of organisms. The classification
of organisms is based upon a hierarchial scheme
beginning with Kingdom and ending with Species at the
base. The higher the classification level, the fewer features
the organisms have in common. For example, the
taxonomy of a particular mayfly, Hexagenia limbata, is
the following:
Thalweg is the line formed by connecting points of
minimum streambed elevation (deepest part of the
channel).
Kingdom: Animal
Phylum: Arthropeda
Class: Insecta
Order: Ephemeroptera
Family: Ephemeridae
Genus: Hexagenia
Species: Hexagenia limbata
54 WATER RESOURCES DATA FOR WASHINGTON 2003
Thermograph is an instrument that continuously records
variations of temperature on a chart. The more general
term “temperature recorder” is used in the table
descriptions and refers to any instrument that records
temperature whether on a chart, a tape, or any other
medium.
Time-weighted average is computed by multiplying the
number of days in the sampling period by the
concentrations of individual constituents for the
corresponding period and dividing the sum of the products
by the total number of days. A time-weighted average
represents the composition of water resulting from the
mixing of flow proportionally to the duration of the
concentration.
Tons p er a cre - foo t (T/acre-ft) is the dry mass (tons) of a
constituent per unit volume (acre-foot) of water. It is
computed by multiplying the concentration of the
constituent, in milligrams per liter, by 0.00136.
Tons per day (T/DAY, tons/d) is a common chemical or
sediment discharge unit. It is the quantity of a substance in
solution, in suspension, or as bedload that passes a stream
section during a 24-hour period. It is equivalent to 2,000
pounds per day, or 0.9072 metric ton per day.
Tota l is the amount of a given constituent in a representative
whole-water (unfiltered) sample, regardless of the
constituent’s physical or chemical form. This term is used
only when the analytical procedure assures measurement
of at least 95 percent of the constituent present in both the
dissolved and suspended phases of the sample. A
knowledge of the expected form of the constituent in the
sample, as well as the analytical methodology used, is
required to judge when the results should be reported as
“total.” (Note that the word “total” does double duty here,
indicating both that the sample consists of a water-
suspended sediment mixture and that the analytical
method determined at least 95 percent of the constituent in
the sample.)
Total coliform bacteria are a particular group of bacteria
that are used as indicators of possible sewage pollution.
This group includes coliforms that inhabit the intestine of
warmblooded animals and those that inhabit soils. They
are characterized as aerobic or facultative anaerobic,
gram-negative, nonspore-forming, rod-shaped bacteria
that ferment lactose with gas formation within 48 hours at
35°C. In the laboratory, these bacteria are defined as all
the organisms that produce colonies with a golden-green
metallic sheen within 24 hours when incubated at
35°C plus or minus 1.0°C on M-Endo medium (nutrient
medium for bacterial growth). Their concentrations are
expressed as number of colonies per 100 milliliters of
sample. (See also “Bacteria”)
Total d ischarge is the quantity of a given constituent,
measured as dry mass or volume, that passes a stream
cross section per unit of time. When referring to
constituents other than water, this term needs to be
qualified, such as “total sediment discharge,” “total
chloride discharge,” and so on.
Total in bottom material is the amount of a given
constituent in a representative sample of bottom material.
This term is used only when the analytical procedure
assures measurement of at least 95 percent of the
constituent determined. A knowledge of the expected
form of the constituent in the sample, as well as the
analytical methodology used, is required to judge when
the results should be reported as “total in bottom
material.”
Total length (fish) is the straight-line distance from the
anterior point of a fish specimen’s snout, with the mouth
closed, to the posterior end of the caudal (tail) fin, with the
lobes of the caudal fin squeezed together.
Total load refers to all of a constituent in transport. When
referring to sediment, it includes suspended load plus bed
load.
Total organism count is the number of organisms collected
and enumerated in any particular sample. (See also
“Organism count/volume”)
Total recoverable is the amount of a given constituent in a
whole-water sample after a sample has been digested by a
method (usually using a dilute acid solution) that results in
dissolution of only readily soluble substances. Complete
dissolution of all particulate matter is not achieved by the
digestion treatment, and thus the determination represents
something less than the “total” amount (that is, less than
95 percent) of the constituent present in the dissolved and
suspended phases of the sample. To achieve comparability
of analytical data for whole-water samples, equivalent
digestion procedures are required of all laboratories
performing such analyses because different digestion
procedures may produce different analytical results.
Total sediment discharge is the mass of suspended-
sediment plus bed-load transport, measured as dry weight,
that passes a cross section in a given time. It is a rate and
is reported as tons per day. (See also “Bedload,” “Bedload
discharge,” “Sediment,” “Suspended sediment,” and
“Suspended-sediment concentration”)
Total s ediment load or total load is the sediment in
transport as bedload and suspended-sediment load. The
term may be qualified, such as “annual suspended-
sediment load” or “sand-size suspended-sediment load,”
and so on. It differs from total sediment discharge in that
WATER RESOURCES DATA FOR WASHINGTON 2003 55
load refers to the material, whereas discharge refers to the
quantity of material, expressed in units of mass per unit
time. (See also “Sediment,” “Suspended-sediment load,”
and “Total load”)
Transect, as used in this report, is a line across a stream
perpendicular to the flow and along which measurements
are taken, so that morphological and flow characteristics
along the line are described from bank to bank. Unlike a
cross section, no attempt is made to determine known
elevation points along the line.
Turbidity is the reduction in the transparency of a solution
because of the presence of suspended and some dissolved
substances. The measurement technique records the
collective optical properties of the solution that cause light
to be scattered and attenuated rather than transmitted in
straight lines; the higher the intensity of scattered or
attenuated light, the higher the value of the turbidity.
Turbidity is expressed in nephelometric turbidity units
(NTU). Depending on the method used, the turbidity units
as NTU can be defined as the intensity of light of a
specified wavelength scattered or attenuated by suspended
particles or absorbed at a method specified angle, usually
90 degrees, from the path of the incident light. Currently
approved methods for the measurement of turbidity in the
USGS include those that conform to USEPA Method
180.1, ASTM D1889-00, and ISO 7027. Measurements of
turbidity by these different methods and different
instruments are unlikely to yield equivalent values.
Ultraviolet (UV) absorbance (absorption) at 254 or 280
nanometers is a measure of the aggregate concentration of
the mixture of UV absorbing organic materials dissolved
in the analyzed water, such as lignin, tannin, humic
substances, and various aromatic compounds. UV
absorbance (absorption) at 254 or 280 nanometers is
measured in UV absorption units per centimeter of path
length of UV light through a sample.
Unconfined aquifer is an aquifer whose upper surface is a
water table free to fluctuate under atmospheric pressure.
(See “Water-table aquifer")
Vertical dat um (See “Datum”)
Volatile organic compounds (VOCs) are organic
compounds that can be isolated from the water phase of a
sample by purging the water sample with inert gas, such as
helium, and, subsequently, analyzed by gas
chromatography. Many VOCs are human-made chemicals
that are used and produced in the manufacture of paints,
adhesives, petroleum products, pharmaceuticals, and
refrigerants. They often are components of fuels, solvents,
hydraulic fluids, paint thinners, and dry-cleaning agents
commonly used in urban settings. VOC contamination of
drinking-water supplies is a human-health concern
because many are toxic and are known or suspected
human carcinogens.
Water table is that surface in a ground-water body at which
the water pressure is equal to the atmospheric pressure.
Water-table aquifer is an unconfined aquifer within which
the water table is found.
Water year in USGS reports dealing with surface-water
supply is the 12-month period October 1 through
September 30. The water year is designated by the
calendar year in which it ends and which includes 9 of the
12 months. Thus, the year ending September 30, 2002, is
called the “2002 water year.”
Watershed (See “Drainage basin”)
WDR is used as an abbreviation for “Water-Data Report” in
the REVISED RECORDS paragraph to refer to State
annual hydrologic-data reports. (WRD was used as an
abbreviation for “Water-Resources Data” in reports
published prior to 1976.)
Weighted average is used in this report to indicate
discharge-weighted average. It is computed by
multiplying the discharge for a sampling period by the
concentrations of individual constituents for the
corresponding period and dividing the sum of the products
by the sum of the discharges. A discharge-weighted
average approximates the composition of water that would
be found in a reservoir containing all the water passing a
given location during the water year after thorough mixing
in the reservoir.
Wet mass is the mass of living matter plus contained water.
(See also “Biomass” and “Dry mass”)
Wet weight refers to the weight of animal tissue or other
substance including its contained water. (See also “Dry
weight”)
WSP is used as an acronym for “Water-Supply Paper” in
reference to previously published reports.
Zooplankton is the animal part of the plankton.
Zooplankton are capable of extensive movements within
the water column and often are large enough to be seen
with the unaided eye. Zooplankton are secondary
consumers feeding upon bacteria, phytoplankton, and
detritus. Because they are the grazers in the aquatic
environment, the zooplankton are a vital part of the
aquatic food web. The zooplankton community is
dominated by small crustaceans and rotifers. (See also
“Plankton”)
