Flood, levee, and erosion control glossary
To help site visitors understand flood fighting, flood control, flood protection, and erosion terms and terms associated with coastal and inland waters, Infrastructure Defense Technologies has included this one-of-a-kind glossary. The glossary is organized as an alpha listing to enable visitors to quickly find the term being looked for.
Numeric | A | B | C | D | E | F | G | H | I | J | K
L | M | N | O | P | Q | R | S | T | U | V | W | XYZ
Numeric
1% Flood
Refers to a flood of a magnitude that has an
estimated probability of 1 in 100 of occurring in any given year. Technically
more precise way of referring to the "100-year
flood". Generally, 1%, 2%, 10% events refer to levels of flood
flows with an expected recurrence of 100, 50, and 10 years respectively.
1-Percent-Annual-Chance Floodplain
An area that has at least a 1% annual chance of flooding and is designated as a Special Flood Hazard Area (SFHA) on the Flood Insurance Rate Map.
100-Year
Flood
A term
commonly used to refer to the one percent annual chance flood. The
"100-year" flood is the flood that is equaled or exceeded once in 100
years on the average, but the term should not be taken literally as there is no
guarantee that the "100-year" flood will occur at all within the
100-year period or that it will not recur.
100-Year Frequency Flood
A flood having an average
frequency of occurrence on the order of once in 100 years although the flood
may occur in any year (a one percent chance of being exceeded in any year). It
is based on statistical analyses of streamflow records available for the
watershed and analyses of rainfall and runoff characteristics in the general
region of the watershed and is a statistical means of estimating the
probability of flooding for insurance and land use planning. Over the life of a
30-year mortgage, there is approximately a 25- percent chance that this flood
or one of a greater magnitude will occur. For these and NFIP regulations the base flood is the 100-year frequency flood.
A
A Unified National Program for Floodplain Management
A
concept (and document of the same name) establishing the foundation of a
coordinated national effort to manage the Nation's floodplains.
The Unified National Program recommends a continuing unified program for
planning and action at all levels of government to reduce the risk of flood
losses and to protect floodplain values. The document was originally prepared
by the U.S. Water Resources Council in 1976 in response to a directive of the
1968 National Flood Insurance Act, and subsequently revised and updated in 1979
and 1986.
A-zone
That portion of the coastal floodplain as marked on maps prepared by the Federal
Emergency management Agency that is likely to be inundated by the one-percent
("100-year") flood and not subject to wave action. The A-zone, however, may be subject to residual forward
momentum of breaking waves. The A-zone and the V-zone
together form the Coastal Special Flood Hazard Area.
Abandoned Well
A well that has been permanently
disconnected and filled. Most States have regulations or guidelines for
abandoned wells to ensure that contamination cannot move from the surface into
the aquifer.
Abrasion
Removal of streambank
soil as a result of sediment-laden water, ice, or debris rubbing against the
bank.
Abutment
The foundation along the sides of the valley or gorge against which the dam is constructed.
Accelerated
Erosion
Erosion much more rapid than
normal, natural, or geologic erosion, primarily as a result of the influence of
the activities of man or in some cases, of other animals or natural KD that
expose base surfaces, for example, fires or flooding.
Photo courtesy of USDA NRCS.
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Accelerated erosion along a river bank. |
Accredited Levee
A levee that has been documented to provide protection from the 1%-annual-chance flood. Areas landward of accredited levees are shown on FEMA’s flood map as Zone X (shaded), which denotes an area of moderate flood risk. Exceptions are areas of residual flooding, which are shown as Special Flood Hazard Area - SFHAs.
Acid Deposition
A complex chemical and atmospheric
phenomenon that occurs when emissions of sulfur and nitrogen compounds and
other substances are transformed by chemical processes in the atmosphere, often
far from the original sources, and then deposited on earth in either wet or dry
form. The wet forms, popularly called "acid rain," can fall as rain,
snow, or fog. The dry forms are acidic gases or particulates.
Acid Neutralization Sump
A basin in which wastewater containing acids is neutralized prior to
being discharged to a sewer.
Acid Soil
Soil with a low pH (below 7.0).
Acre-foot
A volume of water equal to one acre covered to a
depth of one foot; often used to describe the volume of a reservoir. One acre
foot equals 43,560 cubic feet, or 326,700 gallons.
Active Floodplain
The level area adjacent to a stream channel that is subject to frequent overflow.
Actuarial Rates
Insurance rates determined on the basis of
a statistical calculation of the probability that a certain event will occur.
Actuarial rates are also called "risk premium rates." They are
established by the Federal Insurance Administration
pursuant to individual community Flood Insurance Studies and investigations
that are undertaken to provide flood insurance in accordance with the National
Flood Insurance Act and with accepted actuarial principles, including
provisions for operating costs and allowances.
Acute Toxicity
Any poisonous effect produced within a
short time after exposure to a toxic compound, usually within 24 to 96 hours.
Adjacent Steep Slope
A slope with a gradient of 15 percent or steeper within 500 feet of
the site.
Adjustable Groin
A groin whose permeability can be changed, usually with gates or removable sections.
Adsorption
Removal of a pollutant from air or water by collecting the pollutant on the
surface of a solid material; e.g., an advanced method of treating waste in
which activated carbon removes organic matter from waste-water
Advisory Level
A level of chemical concentration in fish
or shellfish whereby consumption of the fish would pose a human health risk.
Levels may be determined by various federal or state agencies and may lead to
advisories such as restricted consumption or consumption bans. Typical
chemicals for which advisories exist include PCBs, chlordane, and dioxins.
Aeration
A process that promotes breakdown of contaminants
in soil or water by exposing them to air.
Aerification
A mechanical process used to cultivate the
soil without destruction of the turf
Aesthetics
The appeal or
beauty of objects, animals, plants, scenes, and natural or improved areas to
the viewer and the appreciation for such items
Affected Public
1.The people who live and/or work near a
hazardous waste site. 2. The human population adversely impacted following
exposure to a toxic pollutant in food, water, air, or soil.
Age, Wave
The ratio of wave velocity to wind velocity (in wave forecasting theory).
Aggregate
Crushed rock or gravel screened to different
sizes for various uses in construction projects.
Agricultural Lands
Fields, pastures, and orchards that are
managed to produce food and fiber for people. Agricultural lands provide a
source of income and employment, open space for recreational activities, and
important habitat for wildlife. Agricultural
lands can also be a source of negative environmental impacts (e.g., water
pollution from nutrients, eroded soils, and pesticides).
Agroecosystem
A dynamic association of crops, pastures,
livestock, other flora and fauna, atmosphere, soils, and water. Agroecosystems
are contained within larger landscapes that include uncultivated land, drainage
networks, rural communities, and wildlife.
Agronomic Systems
See Agricultural
Lands.
Airshed
In recent years, the term "airshed" has
been used to describe those areas where significant portions of emissions
result in deposition of the various air pollutants to a region. Many types of
air pollution are carried by the wind from state to state, and are harmful to
people and the environment, even in rural areas.
Algae
Simple rootless plants that grow in bodies of water (e.g., estuaries) at rates
in relative proportion to the amounts of nutrients (e.g., nitrogen and phosphorus)
available in the water.
Photo courtesy of USDA NRCS.
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Algae in a pond. |
Alkaline Soil
Soil with a pH above 7.0.
Alkalinity
The total measurable bases (OH, HCO3,
CO3) in a volume of water; a measure of a material's capacity to
neutralize acids; pH > 7.
An area of sand, clay or
other similar material that has been gradually deposited by moving water.
Alluvial Channel
See Alluvial Stream.
Alluvial Deposits
Detrital material which is transported by a river and deposited - usually temporarily - at points along the flood plain of a river. Commonly composed of sands and gravels.
Alluvial Fan
Deposits of rock and soil that have eroded from mountainsides and accumulated
on valley floors in a fan-shaped pattern and which occur mainly in dry
mountainous areas. Erosion patterns and stream beds often shift erratically on
an alluvial fan.
Photo courtesy of USDA NRCS.
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Photo of alluvial fan. |
Alluvial Fan Flooding
Flooding occurring on the surface of an Alluvial Fan or similar landform which originates at the apex and is characterized by high-velocity flows: active processes of erosion, sediment transport, deposition, and unpredictable flow paths.
Alluvial Sediments
Relating to mud and/or sand deposited
by flowing water. Alluvial deposits may occur after a heavy rain storm.
Alluvial Stream
A stream that has formed its channel by the process of aggradation.
The sediment in the stream is similar to the material in the bed and banks.
Alluvium
A general term for all material (clay, silt,
sand, gravel, or similar unconsolidated material) deposited or in transit by
streams, including gravel, sand, silt, clay, and all variations and mixtures of
these materials.
Ambient Water-Quality Criteria for the Protection of Aquatic
Organisms
Non-enforceable guidelines for short-term (acute) and long-term
(chronic) exposures to some pesticides. These guidelines provide the basis for
state standards.
American Public Works Association (APWA)
Is an
international educational and professional association of public agencies,
private sector companies, and individuals dedicated to providing high quality
public works goods and services. APWA is the largest and oldest organization of
its kind in the world, with headquarters in Kansas City, MO., an office in
Washington D.C., and 67 chapters throughout North America. APWA provides a
forum in which public works professionals can exchange ideas, improve
professional competency, increase the performance of agencies and companies,
and bring important public works-related topics to public attention in local,
state and federal arenas. APWA has 26,000 members.
American Water Resources Association (AWRA)
Founded in
1964, the American Water Resources Association is a non-profit professional
association dedicated to the advancement of men and women in water resources
management, research, and education. AWRA's membership is multidisciplinary;
its diversity is its hallmark. It is the professional home of a wide variety of
water resources experts including engineers, educators, foresters, biologists,
ecologists, geographers, managers, regulators, hydrologists and attorneys.
Anadromous Fish
Fish that spend their adult lives in the
sea but swim upriver into fresh water to spawn (e.g., salmon, striped bass, American
shad).
Angle of Repose
Angle between the horizontal and the
maximum slope that soil assumes bynatural process.
ANI
Abbreviation for area not included.
Annual Flood
The highest peak discharge of a stream in a Water Year.
Annual Flood Series
A list of annual floods for a given period of time.
Annual Plant
A plant that completes its life cycle and
dies in one year or less.
Anoxic (Anoxia)
A condition where very little or no oxygen
is present in the water body.
Anthropogenic
Originating from man, not naturally
occurring.
Anthropogenic Cover
Land cover associated with human
activities, such as agricultural fields, rock quarries, and urban areas.
Literally, "land cover created by humans."
Antiscour Protection Apron
An apron in front of a revetment to help protect the revetment against underscour.
Anti-seep Collar
A device constructed around a pipe or
other conduit and placed through a dam, levee, or dike for
the purpose of reducing seepage losses and piping failures.
Apron
A floor or lining to protect a surface from erosion.
Aqueous
Water based liquid.
Aquifer
A geologic formation or structure that transmits water in sufficient quantity
to supply the needs for a water development; usually saturated sands, gravel,
fractures, and cavernous rock. The term "water-bearing" is sometimes
used synonymously with aquifer when a stratum furnished water for a special
use. A water-bearing soil layer, under the surface of the earth. This zone is
often the source of drinking or irrigation water. Aquifers can be classified as
confined or unconfined.
Aquitard
Underground geological formation that is slightly
permeable and yields insignificant amounts of water when compared to an aquifer.
Area Flooded
Area of a floodplain that is flooded in a specific stream reach, watershed, or river basin; may be for a single flood event, but is usually expressed as an average, annual value based on the sum of areas from all individual flood events over a long period of time, such as 50 to 100 years, and adjusted to an average value.
Area of Shallow Flooding
Designated Flood Zones AO and AH on a community's Flood Insurance Rate Map (FIRM) with a one percent or greater annual chance of flooding to an average depth of one to three feet where a clearly defined channel does not exist, where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow. Also referred to as Sheet Flow Area.
Area Of Special Flood-Related Erosion Hazard
The land within a community which is most likely to be subject to experience flood-related erosion losses. The area may be designated as Zone E on the Flood Insurance Rate Map (FIRM). See Flood Zones.
Armor
To protect; protective covering; shield. To use
other hardened materials to reinforce an earthen levee.
Artesian Aquifer
An aquifer
that contains water under pressure as a result of hydrostatic head. For artesian
conditions to exist, an aquifer must be overlain by a confining material and
receive a supply of water. The free water surface stands at a higher elevation
than the top of the confining layer, thus if the aquifer is tapped by a well,
the water in the well will raise above the level of the aquifer.
Artesian Well
Groundwater that is able to flow to the
Earth's surface under its own pressure.
Artificial Obstruction
Artificial obstruction shall mean
any obstruction which is not a natural obstruction.
Assessment
Interpretation and evaluation of results for
the purpose of answering policy-relevant questions about ecological resources,
including: 1) determination of the fraction of the population that meets a
socially defined value and 2) association among indicators of ecological
condition and stressors. See Ecological Risk
Assessment.
Assessment Endpoints
Detailed expressions of those values
that have been identified as environmental or societal values associated with
forests studied under the Forest Health Monitoring Program (FHP). See Ecological Risk Assessment.
Association of State Dam Safety Officials (ASDSO)
A national non-profit organization of
state and federal dam safety regulators, dam owners and operators, engineering
consultants, manufacturers and suppliers, academia, contractors and others
interested in dams safety. See www.damsafety.org.
Association of State Floodplain Managers (ASFPM)
An
organization of professionals involved in floodplain
management, flood hazard mitigation, the National
Flood Insurance Program, and flood preparedness, warning and recovery.
ASFPM has become a respected voice in floodplain management practice and policy
in the United States because it represents the flood hazard specialists of
local, state and federal government, the research community, the insurance
industry, and the fields of engineering, hydrologic forecasting, emergency
response, water resources, and others. See www.floods.org.
Atmosphere
The blanket of gases, vapor, and aerosol
particles encasing the Earth.
Atmospheric Deposition
The flux (flow) of chemicals and
materials from the atmosphere to the Earth's surface. Depending on the chemical
or material, "dry" deposition (e.g., by particles) can be less than,
equal to, or greater than "wet" deposition (e.g., precipitation).
Attenuation
The process by which a compound is reduced in
concentration over time, through absorption,
adsorption, degradation, dilution, and/or transformation. An also be the
decrease with distance of sight caused by attenuation of light by particulate
pollution.
Available Nutrient
That portion of any element or compound
in the soil that readily can be absorbed and assimilated by growing plants.
Available Soil Moisture
The portion of water in a soil
that can be readily absorbed by plant roots. It is the amount of water released
between in situ field capacity and the permanent wilting point.
Average Annual Flood Damages
The weighted average of all flood damages that would be expected to occur yearly under specified economic conditions and development. Such damages are computed on the basis of the expectancy in any one year of the amounts of damage that would result from floods throughout the full range of potential magnitude.
Average Annual Flow
The rate at which water flows through a channel, determined by averaging daily measurements of the flow during one entire year.
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L | M | N | O | P | Q | R | S | T | U | V | W | XYZ
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