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| Glossary of Terms |
Flooding can result from a shift in weather patterns, basin topography, channel changes, land use, flow restrictions (dams), or flood control structures (dikes, levees). When describing flood events, engineers, scientists, and others often use different terminology.
|
Channel
erosion |
Includes
the processes of
streambank erosion,
streambed scour, and
degradation. |
|
CFS
or cubic feet per
second |
A
rate of flow that
would fill a container
of one cubic foot
size, that is about
7-1/2 gallons, in one
second. |
|
Conditional
use |
A
land use which is not
allowed unless certain
conditions specified
in the zoning
ordinance are met and
a permit is granted by
the board of
adjustment or appeals
or, where appropriate
the zoning agency.
Synonymous with
special exception. |
|
County
Shoreland Zoning |
The
recognized authority
by the legislature of |
|
Confluence |
A
meeting of two or more
streams or rivers. |
|
Culvert |
Any
covered structure not
classified as a bridge
which conveys a
waterway under a road
or other paved area. |
|
Degradation |
Process
of a channel lowering
its elevation through
increased erosion,
channel bed scour, or
down-cutting. A type
of fluvial geomorphic
instability. |
|
Design
capacity |
An
engineering term used
to describe the amount
of water that a
modified channel was
designed to convey.
Generally, the design
capacity for improved
District facilities is
to accommodate the 1
percent or 100-year
flood. This is the
level of protection.
Capacity is in CFS or
Q. See "Flood
Capacity." |
|
Design
flow |
The
magnitude of stream
flow that is used in
design of channel
improvements and
structures across the
channels. |
|
Drainage
area |
Area
that drains into a
body of water such as
a stream or a
reservoir. |
|
Drop
structure |
A
structure designed to
convey flows over a
vertical distance from
a higher to a lower
elevation. |
|
Easement |
Right
of way granted by a
property owner to
another party for an
expressed purpose of
either constructing
flood and erosion
control improvements
or maintaining the
channel. The property
owner retains the
ownership rights on
the area under the
easement but his use
of the area is
restricted only by
those uses which are
compatible with the
other party uses. |
|
Erosion |
The
detachment and
movement of soil or
rock fragments by
water, wind, ice,
gravity, or extreme
sun or heat. |
|
FEMA |
Federal
Emergency Management
Agency. Has authority
over federal flood
insurance program and
publishes the 100-year
flood map. |
|
Fish
ladders |
Artificial,
stepped pools to
enable fish traveling
upstream, against the
flow of water, to span
a large vertical
distance in a series
of gradual steps. Used
at dams or other
in-stream barriers. |
|
Flood |
The
temporary inundation
of lands normally dry;
any waters escaping
from a creek or river. |
|
Flood
storage |
Those
floodplain areas where
storage of flood
waters has been taken
into account in
reducing the regional
flood discharge. |
|
Floodproofing |
Any
combination of
structural provisions,
changes or adjustments
to properties and
structures, water and
sanitary facilities
and contents of
buildings subject to
flooding, for the
purpose of reducing or
eliminating flood
damage. |
|
Flood
protection elevation |
An
elevation 2 feet above
the regional flood
elevation. |
|
Floodfringe |
That
portion of the
floodplain outside of
the floodway, which is
covered by flood water
during the regional
flood.
This term is
generally associated
with standing water
rather than flowing
water. |
|
Floodplain |
That
land which has been or
may be covered by
flood water during the
regional flood.
This includes
the floodway,
floodfringe, shallow
depth flooding, flood
storage, and coastal
plain areas. |
|
Floodwall |
A
wall constructed
adjoining channel to
prevent flooding of
the surroundings
areas. |
|
Floodway |
The
channel of a river or
stream, and those
portions of the
floodplain adjoining
the channel required
to carry the regional
flood discharge.
This term is
generally associated
with flowing water
rather than standing
water. |
|
Freeboard |
Vertical
distance between the
top of an embankment
adjoining a channel
and the water level in
the channel. |
|
Human
habitation |
A
human residence or
dwelling. |
|
Hard
structures |
A
type of bank
protection structure
incorporating rock,
riprap, sack concrete,
gabion baskets and
mattresses, or
concrete. These
structures are inert
and rigid. |
|
Hydrology |
The
science dealing with
the origin,
distribution and
circulation of waters
of the earth such as
rainfall, streamflow,
infiltration,
evaporation, and
groundwater storage. |
|
Invasive
species |
A
subcategory of
nonnative plants that
aggressively invade
natural plant
communities and
displace native plants
or less aggressive
weedy plants. Examples
of invasive species in
|
|
Invert |
A
creek or channel
bottom. |
|
Levee |
An
embankment constructed
to prevent a river or
stream from flooding
adjacent lands. |
|
Low
flow channel |
That
section of stream
which carries the more
frequent, periodic
streamflows. |
|
Modified
natural channel |
A
watercourse which has
had improvements such
as bank protection
(e.g., gabions, rip
rap, other revetments)
and selected areas of
historical
channelization (e.g.,
widening,
straightening) and/or
other capacity or
passage improvements. |
|
Natural
channel |
A
watercourse without
any significant
improvements or
modifications and very
little evidence of
historical
alterations. |
|
Non-native
vegetation |
Any
vegetation which,
under natural
conditions, does not
originate within the
ecosystem in which it
is found.
Synonymous with
invasive plant
species. |
|
Reach |
The
smallest subdivision
of a drainage system
consisting of a
uniform length of
channel or a discrete
portion of a channel. |
|
Regional
Flood |
A
flood determined to be
representative of
large floods known to
have occurred in |
|
|
|
|
Restoration |
The
reestablishment of the
structure and function
of ecosystems.
Ecological restoration
is the process of
returning an ecosystem
as closely as possible
to predisturbance
conditions and
functions. Implicit in
this definition is
that ecosystems are
naturally dynamic. It
is therefore not
possible to recreate a
system exactly. The
restoration process
reestablishes the
general structure,
function, and dynamic
but self-sustaining
behavior of the
ecosystem. |
|
Riparian |
Located
along the edge of a
channel, generally on
the floodplain.
Characterized by
access to and
influence of the
channel, but not in
it. |
|
Riprap |
Loose
rock or concrete of
varying size,
typically brought to a
site. Used to protect
channel banks from
scouring forces. |
|
Runoff
(surface) |
The
flow of water across
the land surface and
in stream channels.
Occurs only after the
local storage capacity
of the landscape has
been exceeded and
includes both overland
flow and streamflow. |
|
Scour |
The
clearing and digging
action of flowing air
or water, especially
the downward erosion
caused by stream water
in removing material
(e.g., soil, rocks)
from a channel bed or
bank or around
in-channel structures. |
|
Sediment |
Solid
material, both mineral
and organic, that
settles to the bottom
of channels, canals,
percolation ponds, or
behind dams. |
|
Sediment
removal |
The
act of removing
sediment deposited
within a stream.
Typically, sediment is
removed when it
reduces capacity. |
|
Sheetflooding |
A
shallow (less than a
foot) flooding caused
by inadequate drainage
systems. |
|
Shoreland
Zoning |
|
|
Stormwater
management |
Public
policy and action to
control stormwater
runoff associated with
development within a
rapidly urbanizing
watershed in order to
prevent the occurrence
of, or increase in,
flood damage
portential. |
|
Streambed |
The
part of a stream over
which a column of
water moves. |
|
Special
exception |
A
land use which is not
allowed unless certain
conditions specified
in the zoning
ordinance are met and
a permit is granted by
the board of
adjustment or appeals
or, where appropriate
the zoning agency.
Synonymous with
conditional use. |
|
Vegetation
management |
Removal
of vegetation in and
adjacent to creeks to
maintain the ability
of channels to
function as flood
protection facilities.
In addition,
vegetation is removed
to meet local fire
code requirements and
to reduce combustible
weeds and grasses on
property adjacent to
the streams within the
District's
jurisdiction. The
control of invasive
nonnative vegetation
is another purpose for
which the District
undertakes vegetation
control. Vegetation
management can be
accomplished through
mowing, discing, hand
clearing, or herbicide
applications
(depending on the
environmental
conditions of the
site). |
|
Velocity |
Speed
with which water
should flow in a
channel. It depends on
several factors, such
as slope, smoothness
and uniformity of
channel, area of flow
and wetted perimeter. |
|
Watershed |
A
geographic area from
which water is drained
by a river and its
tributaries to a
common outlet. A ridge
or drainage divide
separates a watershed
from adjacent
watersheds. |
|
100-Year
Flood |
Flood
of a magnitude with an
expected recurrence of
once in 100 years.
Synonymous with
regional flood. |