Outdoor Glossary: D
dabbling ducks also referred to as puddle ducks. Ducks that feed on
surface or in shallow water and do not dive for their food- e.g., mallard,
American black duck, gadwall, American wigeon, northern pintail, northern
shoveler, and teal.
daily retardation of tides The amount of time by which
corresponding tidal phases grow later day by day (about 50 minutes).
dam Structure built in rivers or estuaries, basically to separate
water at both sides and/or to retain water at one side.
dapping The art of dangling rather than casting your fly
data collection platform (DCP A microprocessorbased system that
collects data from sensors, processes the data, stores the data in random access
memory (RAM), and provides communication links for the retrieval or transmission
of the data.
datum Any position or element in relation to which others are
determined, as datum point, datum line, datum plane.
datum (vertical) For marine applications, a base elevation used as
a reference from which to reckon heights or depths. It is called a tidal datum
when defined in terms of a certain phase of the tide. Tidal datums are local
datums and should not be extended into areas which have differing hydrographic
characteristics without substantiating measurements. In order that they may be
recovered when needed, such datums are referenced to fixed points known as bench
marks.
datum of tabulation A permanent base elevation at a tide station to
which all tide gauge measurements are referred. The datum is unique to each
station and is established at a lower elevation than the water is ever expected
to reach. It is referenced to the primary bench mark at the station and is held
constant regardless if changes to the tide gauge or tide staff. The datum of
tabulation is most often at the zero of the first tide staff installed.
datum plane A horizontal plane used as a reference from which to
determine heights or depths. The plane is called a tidal datum when defined by a
certain phase of the tide. Datum planes are referenced to fixed points known as
bench marks, so that they can be recovered when needed. See also reference
plane.
Davidson Current A North Pacific Ocean countercurrent setting
northward between the California Current and the coasts of California, Oregon,
and Washington during the winter months.
day The period of rotation of the Earth. There are several kinds of
days depending on whether the Sun, Moon, or other object or location is used as
the reference for the rotation. See constituent day, lunar day, sidereal day,
and solar day.
daylight saving time A time used during the summer months, in some
localities, in which clocks are advanced I hour from the usual standard time.
DBH (diameter at breast height) The diameter of a tree 4 and 1/2
feet above the ground on the uphill side of the tree.
debris line A line near the limit of storm wave UPRUSH marking the
landward limit of debris deposits.
decay area Area of relative calm through which waves travel after
emerging from the generating area.
decay distance The distance through which waves travel after
leaving the generating area.
decay of waves The change which occurs in waves when they leave a
generating area and pass through a calm(or region of lighter winds). In the
process of decay the significant wave length increases and the significant wave
height decreases.
decibar The practical unit for pressure in the ocean, equal to 10
centibars.
decision criteria The rules and standards used to evaluate
alternatives to a proposed action on National Forest land. Decision criteria are
designed to help a decisionmaker identify a preferred choice from the array of
alternatives.
decking area A site where logs are collected after they are cut and
before they are taken to the landing area where they are loaded for
transport.
declination Angular distance north or south of the celestial
equator, taken as positive when north of the equator and negative when south.
The Sun passes through its declinational cycle once a year, reaching its maximum
north declination of approximately 23- about June 21 and its maximum south
declination of approximately 23- about December 21. The Moon has an average
declinational cycle of 27-1/3 days which is called a tropical month. Tides or
tidal currents occurring near the times of maximum north or south declination of
the Moon are called tropic tides or tropic currents, and those occurring when
the Moon is over the Equator are called equatorial tides or equatorial currents.
The maximum declination reached by the Moon in successive months depends upon
the longitude of the Moon's node, and varies from 28- when the longitude of
the ascending node is 0, to 18- when the longitude of the node is 180. The
node cycle, or time required for the node to complete a circuit of 360 of
longitude, is approximately 18.6 years.
declinational inequality Same as diurnal inequality.
declinational reduction A processing of observed high and low
waters or flood and ebb tidal currents to obtain quantities depending upon
changes in the declination of the Moon; such as tropic ranges or speeds, height
or speed inequalities, and tropic intervals.
deep water In regard to waves, where depth is greater than one-half
the wave length. Deep-water conditions are said to exist when the surf waves are
not affected by conditions on the bottom.
deep water waves A wave in water the depth of which is greater than
one-half the wave length.
deflation The removal of loose material from a beach or other land
surface by wind action.
degradation The geologic process by means of which various parts of
the surface of the earth are worn away and their general level lowered, by the
action of wind and water.
DEIS (Draft Environmental Impact Statement) The draft version of
the Environmental Impact Statement that is released to the public and other
agencies for review and comment
delta (1) An alluvial deposit, usually triangular, at the mouth of
a river of other stream. It is normally built up only where there is no tidal or
current action capable of removing the sediment as fast as it is deposited, and
hence the delta builds forward from the coastline. (2) A tidal delta is a
similar deposit at the mouth of a tidal inlet, put there by tidal currents. (3)
A wave delta is a deposit made by large waves which run over the top of a spit
or bar beach and down the landward side.
density (1) a measure of animal abundance in which the number of
animals is given per unit area (i.e., 100 elk/km2). (2) independent factors- not
related to the density of animals, cause changes in population parameters
(primarily survival rates).
density A line's buoyancy, which is determined by the relationship
of its mass to that of water. If the density of line is greater than water the
line will sink; if it's less, it will float.
density stratification The lateral expansion of a sediment plume as
it moves out of the distributary mouth, where salt and fresh water mix. This is
most likely to occur where the speed of the river flow is moderate to low and
the distributary mouth is relatively deep.
density, in situ ( s,t,p) Mass per unit volume. The reciprocal of
specific volume. In oceanography, the density of sea water is numerically
equivalent to specific gravity and is a function of salinity, temperature, and
pressure. See specific volume anomaly, thermosteric anomaly, sigma-t, and
sigma-zero.
density-driven circulation Variations in salinity create variations
in density in estuaries. These variations in density create horizontal pressure
gradients, which drive estuarine circulation.
depression A general term signifying any depressed or lower area in
the ocean floor.
depth A vertical measurement, most often employed for the maximum
height of the body excluding the fins; also refers to the distance below the sea
surface in which the fish lives; also the vertical distance from a specified sea
level to the sea floor.
depth, controlling See contolling depth.
depthfinder - An electric device that is used to detect the
geography beneath the waters surface. Also used as a fishfinder.
design storm Coastal protection structures will often be designed
to withstand wave attack by the extreme design storm. The severity of the storm
(i.e. return period) is chosen in view of the acceptable level of risk of damage
or failure. A design storm consists of a design wave condition, a design water
level and a duration.
design wave In the design of harbors, harbor works, etc., the type
or types of waves selected as having the characteristics against which
protection is desired.
desired future condition Land or resource conditions that are
expected to result if goals and objectives are fully achieved.
detached breakwater A breakwater without any constructed connection
to the shore.
detritus Small fragments of rock which have been worn or broken
away from a mass by the action of water or waves.
developed recreation Recreation that requires facilities that, in
turn, result in concentrated use of the area. For example, skiiing requires ski
lifts, parking lots, buildings, and roads. Campgrounds require roads, picnic
tables, and toilet facilities.
deviation (of compass) The deflection of the needle of a magnetic
compass due to masses of magnetic metal within a ship on which the compass is
located. This deflection varies with different headings of the ship. The
deviation is called easterly and marked plus if the deflection is to the right
of magnetic north, and is called westerly and marked minus if it is to the left
of magnetic north. A deviation table is a tabular arrangement showing the amount
of deviation for different headings of the ship. Each compass requires a
separate deviation table.
diapositive A positive photograph on a transparent medium.
differential erosion / weathering These features develop in rocks
which have varying resistance to the agencies of EROSION and/or weathering so
that parts of the rock are removed at greater rates than others. A typical
example is the removal of soft beds from between harder beds in a series of
sedimentary rocks. The term may be applied to any size of feature, from
small-scale etching to the regional development of hills and valleys
controlled by hard and soft rocks.
diffraction The phenomenon occurring when water waves are
propagated into a sheltered region formed by a breakwater or similar barrier
that interrupts a portion of the otherwise regular train of waves, resulting in
the multi-directional spreading of the waves.
digital tide gauge See automatic tide gauge.
dihedral Wings of a flying bird held at an angle appearing to form
a "V". No picture yet.
dike Sometimes written as dyke; earth structure along a sea or
river in order to protect littoral lands from flooding by high water; dikes
along rivers are sometimes called levees.
dink A very small fish; also known as a "guppy" or "fry guy."
direction of current Direction toward which current is
flowing.
direction of waves Direction from which waves are coming.
direction of wind Direction from which the wind is blowing.
disc drag Allows for line to go out under pressure to avoid line
breaks
disorger An implement that removes hooks embedded in the throats
and mouths of fish
dispersal the movement of an animal from it natal area (place where
it was born) to a new area where it lives and reproduces (if it survives that
long).
disperse (1) To spread or distribute from a fixed or constant
source. (2) To cause to become widely separated.
dispersed recreation Recreation that does not occur in a developed
recreation site, such as hunting, backpacking, and scenic driving.
dispersion (1) Act of dispersing, or state of being dispersed. (2)
The separation of waves by virtue of their differing rates of travel.
disturbance Any event, such as forest fire or insect infestations
that alter the structure, composition, or functions of an ecosystem.
diurnal Having a period or cycle of approximately one tidal day.
Thus, the tide is said to be diurnal when only one high water and one low water
occur during a tidal day, and the tidal current is said to be diurnal when there
is a single flood and a single ebb period of a reversing current in the tidal
day. A rotary current is diurnal if it changes its direction through all points
of the compass once each tidal day. A diurnal constituent is one which has a
single period in the constituent day. The symbol for such a constituent is the
subscript 1. See stationary wave theory and type of tide.
diurnal current The type of tidal current having only one flood and
one ebb period in the tidal day. A rotary current is diurnal if it changes its
direction through all points of the compass once each tidal day.
diurnal inequality The difference in height of the two high waters
or of the two low waters of each tidal day; also, the difference in speed
between the two flood tidal currents or the two ebb currents of each tidal day.
The difference changes with the declination of the Moon and, to a lesser extent,
with the declination of the Sun. In general, the inequality tends to increase
with increasing declination, either north or south, and to diminish as the Moon
approaches the Equator. Mean diurnal high water inequality (DHQ) is one-half the
average difference between the two high waters of each tidal day observed over
the National Tidal Datum Epoch. It is obtained by subtracting the mean of all
the high waters from the mean of the higher high waters. Mean diurnal low water
inequality (DLQ) is one-half the average difference between the two low waters
of each tidal day observed over the National Tidal Datum Epoch. It is obtained
by subtracting the mean of the lower low waters from the mean of all the low
waters. Tropic high water inequality (HWQ) is the average difference between the
two high waters of each tidal day at the times of tropic tides. Tropic low water
inequality (LWQ) is the average difference between the two low waters of each
tidal day at the times of tropic tides. Mean and tropic inequalities, as defined
above, are applicable only when the type of tide is either semidiurnal or mixed.
Diurnal inequality is sometimes called declinational inequality.
diurnal range Same as great diurnal range.
diurnal tide level A tidal datum midway between mean higher high
water and mean lower low water.
diving ducks synonymous with bay-diving ducks.
dock The slip or waterway between two piers, or cut into the land,
for the reception of ships.
dorsal fin The top fin of a fish. A median fin along the back,
which is supported by rays. There may be two or more dorsal fins, in which case
the most anterior one is designated the first.
double ebb (tidal) An ebb current having two maxima of velocity
separated by a smaller ebb velocity.
double flood (tidal) A flood current having two maxima of velocity
separated by a smaller flood velocity.
double tide A double-headed tide; that is, a high water consisting
of two maxima of nearly the same height separated by a relatively small
depression, or a low water consisting of two minima separated by a relatively
small elevation.
downbound toward the Atlantic Ocean.
downdrift The direction of predominant movement of littoral
materials.
downrigger A mechanical device that uses larger weights to get
fishing lures or bait down to a specific depth and keep it there.
downwelling A downward movement (sinking) of surface water caused
by onshore Ekman transport, converging currents or when a water mass becomes
more dense than the surrounding water.
draft (or draught) depth of water needed to float a ship.
drag The mechanical system in a reel that applies friction to the
spool; also the force of water against a fly line or leader that causes the fly
to move in an unnatural manner.
drainage basin Total area drained by a stream and its
tributaries.
dredging Excavation or displacement of the bottom or shoreline of a
water body. Dredging can be accomplished with mechanical or hydraulic machines.
Most is done to maintain channel depths or berths for navigational purposes;
other dredging is for shellfish harvesting or for cleanup of polluted
sediments.
dressed fish Fish with viscera, head and tail removed (some fish
may have the tail on) but with skin and bone retained.
dressing weight The weight of a fish after the viscera and
sometimes the head and other body parts have been removed.
drift (of current) The speed of the current.
drift current A broad, shallow, slow-moving ocean or lake current.
Opposite of stream current.
drift sector A particular reach of marine shore in which littoral
drift may occur without significant interruption, and which contains any and all
natural sources of such drift, and also any accretion shoreforms accreted by
such drift.
dropline A deepwater fishing method involving the use of a vertical
line bearing rows of baited hooks.
dry fly An artificial fly that floats on the surface of the water;
designed to replicate the adult stage of an insect
drying beach That part of the beach uncovered by water (e.g. at low
tide). Sometimes referred to as subaerial beach.
dunes (1) Accumulations of windblown sand on the BACKSHORE, usually
in the form of small hills or ridges, stabilized by vegetation or control
structures. (2) A type of bed form indicating significant sediment transport
over a sandy seabed.
durable water-repellent finish (DWR) - Chemically treated fabrics
that are water-repellent
duration In forecasting waves, the length of time the wind blows in
essentially the same direction over the FETCH (GENERATING AREA).
duration of ebb The interval of time in which a tidal current is
ebbing, determined from the middle of the slack waters.
duration of fall The interval from high water to low water.
duration of flood The interval of time in which a tidal current is
flooding, determined from the middle of slack waters.
duration of flood and duration of ebb Duration of flood is the
interval of time in which a tidal current is flooding, and duration of ebb is
the interval in which it is ebbing, these intervals being reckoned from the
middle of the intervening slack waters or minimum currents. Together they cover,
on an average, a period of 12.42 hours for a semidiurnal tidal current or a
period of 24.84 hours for a diurnal current. In a normal semidiurnal tidal
current, the duration of flood and duration of ebb each will be approximately
equal to 6.21 hours, but the times may be modified greatly by the presence of
nontidal flow. In a river the duration of ebb is usually longer than the
duration of flood because of fresh water discharge, especially during spring
months when snow and ice melt are predominant influences.
duration of rise and duration of fall Duration of rise is the
interval from low water to high water, and duration of fall is the interval from
high water to low water. Together they cover, on an average, a period of 12.42
hours for a semidiurnal tide or a period of 24.84 hours for a diurnal tide. In a
normal semidiurnal tide, duration of rise and duration of fall each will be
approximately equal to 6.21 hours, but in shallow waters and in rivers there is
a tendency for a decrease in duration of rise and a corresponding increase in
duration of fall.
duration, minimum The time necessary for steady-state wave
conditions to develop for a given wind velocity over a fetch.
dynamic decimeter See geopotential as preferred term.
dynamic depth (height) See geopotential difference as preferred
term.
dynamic depth (height) anomaly See geopotential anomaly as
preferred term.
dynamic equilibrium Short term morphological changes that do not
affect the morphology over a long period.
dynamic meter (D) The former practical unit for geopotential
difference (dynamic depth), equal to 10 geopotentials (dynamic decimeters). See
geopotential (dynamic depth) anomaly.
dynamic topography See geopotential topography as preferred term.
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