Flood, levee, and erosion control glossary - B
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Backfill
To refill an excavated area with uncontaminated
soil, gravel, rock, or other material; or, the material itself that is used to
refill an excavated area.
Backshore
The zone of the shore or beach including the
berms that lie between the foreshore and the dunes or bluffs. The backshore is
acted upon by waves only during severe storms, especially when combined with
exceptionally high water.
Backwater
A flood upstream caused by obstructions downstream, such as ice jams or
debris.
Photo courtesy of USDA NRCS.
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Backwater along a river bank. |
Backwater Area
The low-lying lands adjacent to a stream
that become flooded during periods of high water.
Backwater Effect
The rise in water surface elevation
caused by some obstruction such as a narrow bridge opening, buildings or fill
material that limits the area through which the water must flow. Also referred
to as "heading up".
Backwater Flooding
Flooding caused by a restriction or blocking of flow downstream. Examples include a narrowing of the channel, logjam, ice jam, high flow in a downstream confluence stream, or high tide blocking high river flows from entering estuaries.
Baffle
A flat board or plate, deflector, guide, or similar
device constructed or placed in flowing water or slurry systems to cause more
uniform flow velocities to absorb energy and to divert, guide, or agitate
liquids.
Bank
The part of the soil next to a stream, lake, or body
of water where the soil elevation adjacent to the water is higher than the
water level; also embankment.
Bank Migration
Lateral or horizontal movement of the banks of a streamcourse.
Bank Protection / Bank Erosion Protection
Bank protection involves any action by
the District to streambanks that are eroding (repair) as well as preventative
erosion protection. The District implements streambank protection when the
problem (1) causes or could cause significant damage to a property or adjacent
property, (2) is a public safety concern, (3) negatively affects transportation
or recreational use, (4) negatively affects water quality, or (5) negatively
affects riparian habitat. Bank protection stabilizes a channel bank using rock,
riprap, concrete, soft materials, vegetation, or a combination of materials or
methods. Bank protection can also include preventative maintenance to ensure
that banks do not erode in the future. This new work is considered routine
maintenance because it is either restoring the flood protection function of a
modified channel or it is repairing a natural bank to its approximate condition
prior to becoming an erosion problem.
Photo courtesy of USDA NRCS.
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Photo of bank erosion protection. |
Bank Repair
Maintenance of existing bank protection
structures with in-kind, in-place materials. This type of maintenance occurs
when such structures fail.
Bank Slip
Downward slippage of the bank of a stream or
body of water caused by erosion and stress
Bankfull Stage
At a given location, the maximum elevation
to which a river can rise without overflowing its banks or causing significant
damage.
Bar
A sand or gravel deposit in a streambed that is often
exposed only during low water periods. A submerged or emerged embankment of sand, gravel, or other unconsolidated material built on the sea floor in shallow water by waves and currents. See Cuspate Bar.
Barriers, Coastal
Elongated, shore-parallel, usually sandy features that parallel coasts in many places and are separated from the mainland by bodies of water of various sizes, and/or salt marshes, lagoons, mud, or sand flats, and tidal creeks.
Base Flood
A flood which is
representative of large floods known to have occurred generally in the area or
reasonably characteristic of what can be expected to occur on a particular
stream or other body of water. This flood is generally being recognized and
accepted nationally by Federal and non-Federal interests as one with an average
frequency of occurrence on the order of once in 100 years (see 100-Year
Frequency Flood). A flood having a 1 percent chance of being equaled or
exceeded in any given cross-section or in a given reach. The selected flood
frequency for regulatory purposes. The NFIP has adopted the
"100-year" flood as the base flood to indicate the minimum level of
flooding to be used by a community in its floodplain management regulations.
Base Flood Elevation
The water surface elevation of the base
flood. It shall be referenced to the National Geodetic Vertical Datum of 1929
(NGVD).
Base Floodplain
The floodplain that would be inundated by
a 100-year (one-percent chance) flood.
Baseflow
The part of stream discharge that originates from groundwater seeping into the stream.
Basin
The total area from which surface runoff is carried
away by a drainage system. Other comparable terms are "drainage area",
"catchment area", and "watershed".
Bastion
A massive groin, or projecting section of seawall normally constructed with its crest above water level.
Beach
A deposit of unconsolidated sand along the edge of a
sea that extends landward to the base of the dunes or bluff. The zone of
sedimentary material that extends landward from the low water line to the place
where there is marked change in material or form, or to the line of permanent
vegetation (usually the effective limit of storm waves). The seaward limit of a
beach is the mean low water line. A beach includes foreshore and backshore.
Beach Nourishment
The process of replenishing a beach,
either naturally through accretion due to the longshore transport, or
artificially through the deposition of dredged materials.
Bed
The bottom of a channel, creek, river, stream, or
other body of water.
Bed Forms
Any deviation from a flat bed that is readily detectable by eye and higher than the largest sediment size present in the parent bed material; generated on the bed of an alluvial channel by the flow.
Bed Load
Sediment particles resting on or near the channel
bottom that are pushed or rolled along by the flow of water.
Bed Slope
The inclination of the channel bottom.
Bedrock
The solid rock underlying soils and in depths
ranging from zero (where exposed by erosion) to several hundred feet. See Alluvial
Sediments.
Bench Drain
Typically a gunite or concrete V-ditch located
horizontally and vertically along residential hillside areas. This device
assists in draining the slope to protect against hillside erosion. Typical
width is 3-5 feet and typical depth is 12". This is also referred to as a
"Slope Drain".
Benthos
Plants or animals that live in or on the bottom of
an aquatic environment such as an estuary.
Berm
A nearly horizontal part of the beach or backshore
formed at the high water line by waves depositing material. Some beaches have
no berms, others have one or several. An area that breaks the continuity of a
slope used to prevent the migration of contaminants.
Photo courtesy of USDA NRCS.
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Photo of berm rehabilitation. |
Best
Management Practices (BMPs)
Means schedule of activities, prohibitions
of practices, maintenance procedures, and other management practices to prevent
or reduce the pollution of waters of the United States. BMPs also include
treatment requirements, operating procedures, and practices to control site
runoff, spillage, or or drainage from raw material storage.
BFE
Stands for Base Flood Elevation, and refers to the elevated water level expected in that once-in-100-years flood event.
Bioaccumulation
A process where chemicals (e.g., DDTs,
PCBs) are retained by plants and animals and increase in concentration over
time. Uptake can occur through feeding or direct absorption from water or
sediments.
Bioconcentration
Entails the uptake and accumulation of
chemical substances in the tissues of an organism through the food chain.
Biodegradable
Able to decompose when exposed to biological
agents and soil chemicals.
Biodiversity
The variety and variability among living
organisms and the ecosystems in which they occur. Biodiversity includes the
number of different items and their relative frequencies; these items are
organized at many levels, ranging from complete ecosystems to the biochemical
structures that are the molecular basis of heredity. Thus, biodiversity
encompasses expressions of the relative abundances of different ecosystems,
species, and genes.
Bioengineering
Combination of vegetative and structural
practices to prevent erosion or stabilize slopes or streambanks.
Biofiltration
The simultaneous process of filtration,
infiltration, adsorption, and biological uptake of pollutants in stormwater
that takes place when runoff flows over and through vegetated areas.
Biofiltration Swale
A sloped, vegetated channel or ditch
that provides both conveyance and water quality treatment to stormwater runoff.
It does not provide stormwater quantity control but can convey runoff to BMPs
designed for that purpose.
Biomagnification
The progressive increase in the
concentration of chemical contaminants (e.g., DDTs, PCBs, methyl mercury) from
the bottom (e.g., phytoplankton, benthic animals) to the top of the food web
(e.g., striped bass) as contaminated food species are consumed.
Biosphere
The envelope of Earth (including all organic
matter, both living and nonliving) and its atmosphere that can support life.
Black Water
Water containing liquid and solid human body
waste generated through toilet use.
Blanket
Material placed on soil or a streambank to cover
eroding soil.
Blowout
A depression on the land surface caused by wind erosion.
Blowout Plug
A designed "weak" spot in a basement wall or
floor that will fail first due to hydrostatic force, thus preventing total
failure of the wall or floor.
Bluff
A high, steep bank or cliff.
Boardwalk
A path constructed along a beach for walking and
cycling. In the west boardwalks are usually paved instead of the classic board
planking often seen in the east.
Bog
A type of wetland that accumulates appreciable peat
deposits. Bogs depend primarily on precipitation for their water source, and
are usually acidic and rich in plant residue with a conspicuous mat of living
green moss.
Bored Well
A well drilled with a large truck-mounted
boring auger, usually 12 inches or more in diameter and seldom deeper than 100
feet.
Borrow
Surface excavated area. Material has been removed
to facilitate construction.
Borrow Area
An area where material has been excavated for
use as fill at another location.
Borrow Pit
An excavated area where soil, sand or gravel
has been dug up for use elsewhere.
Bottomland Hardwoods
Tree species that occur on
water-saturated or regularly inundated soils. Classified as wetlands, these
areas contain both trees and woody shrubs.
Brackish
Having a salinity between that of fresh and sea
water or salt water.
Breach
1. A new opening in a narrow landmass, such as a barrier spit or a barrier island, that allows flow between water bodies on either side of the landmass. 2. A rupture, break or gap in a levee whose cause has not been determined.
Breaching
1. Formation of a channel through a barrier spit or island by storm waves, tidal action, or river flow. Usually occurs after a greater than normal flow, such as during a hurricane. 2. Failure of a dike allowing flooding.
Breakthrough
A crack or break in a filter bed that allows
the passage of floc or particulate matter through a filter; will cause an
increase in filter effluent turbidity.
Breakwater
A structure protecting a shore area, harbor,
anchorage, or basin from waves.
Breakwaters
Structures, usually built offshore, to protect
a shore area, harbor, anchorage or basin by intercepting the energy of
approaching waves.
Brownfields
Abandoned, idled, or under-used industrial and
commercial facilities where expansion or redevelopment is complicated by real
or perceived environmental contamination.
Brush Layering
Use of live branch cuttings laid crisscross
fashion on benches between successive lifts of soil.
Buffer
A small area of permanent vegetation bordering a field, stream, or lake or
running through cropland, protecting the soil from wind and rain erosion,
slowing water runoff, and trapping sediment and other pollutants.
Buffer Zone
An undisturbed area of vegetation used for screening roads or other sensitive
areas.
Photos courtesy of USDA NRCS. |
 |
Photos of buffer zones. |
Building Code
Regulations adopted by a local governing
body setting forth standards for the construction, addition, modification, and
repair of buildings and other structures for the purpose of protecting the
health, safety, and general welfare of the public.
Building Official
The officer charged with the
administration and enforcement of the Building Code and these Flood Proofing
Regulations or a regularly authorized deputy.
Bulkhead
A vertical wall of wood, steel or concrete, built
parallel to the shoreline and designed to deflect waves and control erosion.
See sea wall, retaining wall, revetment, or armor.
Bunchgrass
A grass that does not have rhizomes or stolons
and forms a bunch or tuft.
Buoyancy
Forces that cause a structure to float.
Bypass Channel
A flood protection facility through which a
portion of a stream's flow is diverted from one point and reintroduced into the
stream at the downstream end of the bypass channel. Bypass channels can be used
during the construction or maintenance process. Permanent bypass channels can
also be designed to accommodate flood flows.
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