Flood, levee, and erosion control glossary - S
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Sacrificial Berm
A nearshore berm, usually constructed with dredged sand, for the purpose of protecting an adjacent shoreline from erosive flow velocities by intercepting and dissipating hydrodynamic energy. See Berm.
Saffir/Simpson Hurricane Scale
Scale, adopted for use by
the National Hurricane Center, that relates hurricane intensity to damage
potential.
Salinity
A measurement of the amount of salt in water.
Generally reported as "parts per thousand" (i.e., grams of salt per
1,000 grams of water) and abbreviated as "ppt" or ä. Salinity also is
reported as "practical salinity units" and abbreviated as
"psu."
Salt Marsh
Class of wetlands consisting of salt-tolerant
grasses and other plants that are periodically exposed to salt water flooding.
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Photo of Salt Marsh. |
Salt-Water
Intrusion
Process by which an aquifer is over drafted creating a flow
imbalance within an area that results in salt water encroaching into
fresh-water supply.
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Photo of Salt-Water Intrusion. |
Sand
Soil particles ranging from 0.05 to 2.0 mm in
diameter; individual particles are visible to the unaided human eye.
Sand Boil
A sand boil occurs when the upward pressure of water flowing through soil pores under the levee (underseepage) exceeds the downward pressure from the weight of the soil above it. The underseepage resurfaces on the landside, in the form of a volcano-like cone of sand. Boils signal a condition of incipient instability that may lead to erosion of the levee toe or foundation or result in sinking of the levee into the liquefied foundation below. Complete breach of the levee may quickly follow.
Sand Dike
(EM 1110-2-5026) A retaining dike constructed with hydraulically dredged sand. See also dike.
Sand Lens
Lenticular band of sand in sedimentary banded
material.
Sandbags
A burlap or plastic bag that can be filled with
sand or native soil, which can be stacked or placed to redirect storm and debris
flows away from homes or property improvements.
Satellite Imagery
Information collected in the field by
surveyors, or from aerial photographs, satellite images, or by using the Global
Positioning System that is almost always represented on some type of map.
Saturation
A condition in soil in which all space between soil
particles is filled with water. Such conditions occur after prolonged periods
of rainfall or snowmelt, and force any additional rainfall to runoff into
streams. Saturation also occurs in earthen levees during floods, a condition
that can cause the levees to weaken.
Saturation Zone
A layer of rock through which water cannot
easily move.
Scale
A ratio between distance measured on a map (or other
representation) to the same distance measured on the earth.
Scarp, Beach
An almost vertical slope along the beach caused by erosion by wave action. It may vary in height from a few cm to a meter or so, depending on wave action and the nature and composition of the beach. See also Escarpment.
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. The erosion
of a stream bank caused by water moving at a velocity higher than equilibrium.
When water moves slower than equilibrium, deposition of sediment occurs. River
restoration projects often seek to achieve a sediment level and water velocity
that prevents scouring of the banks (or deposition). The localized erosion
around floodflow obstructions caused by the movement of soil or sediment by
high-velocity water.
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Photo of Scoured Floodplain. |
Scour Pockets
The erosive action of flowing water in streams that removes and carries away
material from the bed and banks in a particular area or pocket.
Scour Pool
An area of deeper water created by the scouring action of water. These generally occur downstream of obstructions or along the outside of a meander bend.
Sea Level
The ocean height at mean lower low tide (The
lower of the two low tides per day).
Sea
Wall or Seawall
A structure separating land and water areas, primarily
designed to prevent flooding and erosion caused by wave action. . 2. A structure, often concrete or stone, built along a portion of a coast to prevent erosion and other damage by wave action. Often it retains earth against its shoreward face. 3. A structure separating land and water areas to alleviate the risk of flooding by the sea. Generally shore-parallel, although some reclamation seawalls may include lengths that are normal or oblique to the (original) shoreline. a seawall is typically more massive and capable of resisting greater wave forces than a Bulkhead. A structure separating land and water areas, primarily designed to prevent flooding and erosion caused by wave action. A wall built
parallel to the shore, designed to halt shoreline erosion by absorbing the
impact of waves.
Secondary Aquifer
Any aquifer that is not the main source
of water to wells in a given area, includes shallow and perched aquifers.
Secondary Levee
A levee that is landward of the main or principal levee. The level of protection of a secondary levee is always less than the level of protection provided by the main levee.
Section (401)(a) Certification
A requirement of Section
401(a) of the Clean Water Act that all federally issued permits be certified by
the state in which the discharge occurs. The state certifies that the proposed
permit will comply with state water quality standards and other state
requirements.
Section 10 and 404 Regulatory Programs
The principal
federal regulatory programs, carried out by the U.S. Army Corps of Engineers,
affecting structures and other work below mean high water. The Corps, under
Section 10 of the River and Harbor Act of 1899, regulates structures in, or
affecting, navigable waters of the U.S. as well as excavation or deposition of
materials (e.g., dredging or filling) in navigable waters. Under Section 404 of
the Federal Water Pollution Control Act Amendments (Clean Water Act of 1977),
the Corps is also responsible for evaluating application for Department of the
Army permits for any activities that involve the placement of dredged or fill
material into waters of the United States, including adjacent wetlands.
Section 409 Hazard Mitigation Plan
A plan prepared as
required by Section 409 of the Robert T. Stafford Disaster Relief and Emergency
Assistance Act of 1988 by any jurisdiction that receives federal disaster
assistance.
Sediment
Solid material, both mineral and organic such as mud, sand, silt, clay, shell
debris, and other particles, that is in suspension, is being transported, or
has been moved from its site of origin by air, water, gravity, or ice, and has
come to rest on the earth's surface, either above or below sea level.
Eventually, sediment settles to the bottom of channels, canals, percolation
ponds, or behind dams
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Photo of Sediment Runoff. |
Sediment Basin
A pond created to retain runoff long enough
to allow excess sediment to settle out.
Sediment
Contamination
Informal guidelines for interpreting sediment
contamination based on many field and laboratory studies have been developed.
These guidelines attempt to relate observed chemical concentrations to those
known to either cause biological effects in laboratory spiked-sediments or
spiked-water experiments, or be associated with biological effects in field
studies.
Sediment Deposition
The accumulation of soil particles on
the channel bed and banks.
Sediment Load
The soil particles transported through a channel by streamflow.
Sediment Loading
The solid material transported by a
stream, expressed as the dry weight of all sediment that passes a given point
within a specific period of time.
Sediment Removal
The act of removing sediment deposited
within a stream. Typically, sediment is removed when it reduces capacity.
Sediment Transport
The main agencies by which sedimentary materials are moved are: gravity (gravity transport); running water (rivers and streams); ice (glaciers); wind; the sea (currents and longshore drift). Running water and wind are the most widespread transporting agents. In both cases, three mechanisms operate, although the particle size of the transported material involved is very different, owing to the differences in density and viscosity of air and water. The three processes are: rolling or traction, in which the particle moves along the bed but is too heavy to be lifted from it; saltation; and suspension, in which particles remain permanently above the bed, sustained there by the turbulent flow of the air or water.
Sediment Yield
The quantity of sediment arriving at a
specific location.
Sedimentation
Is defined as the settling out of soil particles transported by water.
Sedimentation occurs when the velocity of water in which soil particles are
suspended is slowed sufficiently to allow particles to settle out. Larger
particles, such as gravel and sand, settle more rapidly than fine particles
such as silt and clay. Sedimentation occurs after erosion has taken place.
Effective construction site management first minimizes excessive soil erosion
by keeping the soil stabilized as long as possible, and second directs runoff
from remaining disturbed areas to locations where sediments are removed prior
to discharge to water courses.
Photo courtesy of USDA NRCS. |
Photo of Sedimentation. |
Sedimentation Rate
The amount of sediment accumulated in an aquatic environment over a given period of time, usually expressed as thickness of accumulation per unit time.
Sediments
Soil, sand, and minerals washed from land into
water, usually after rain. They pile up in reservoirs, rivers and harbors,
destroying fish and wildlife habitat, and clouding the water so that sunlight
can- not reach aquatic plants. Careless farming, mining, and building
activities will expose sediment materials, allowing them to wash off the land
after rainfall.
Seed
The fertilized and ripened ovule of a seed plant that
is capable, under suitable conditions, of independently developing into a plant
similar to the one that produced it. Types of seeds include:
-
Certified seed
The progeny of foundation or registered seed that is so handled as to
maintain satisfactory genetic identity and purity and that has been approved
and certified by the certifying agency.
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Commercial seed
A term used to
designate other than recognized varieties of seed in commercial trade.
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Dormant seed
An internal condition of the chemistry or stage of development
of a viable seed that prevents its germination, although good growing
temperatures and moisture are provided.
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Firm seed
Dormant seeds, other
than hard seeds, that neither germinate nor decay during the prescribed test
period under the prescribed conditions. Firm, ungerminated seeds may be alive
or dead.
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Hard seed
A physiological condition of seed in which some seeds
do not absorb water or oxygen and germinate when a favorable environment is
provided.
Seed Purity
The percentage of the desired species in
relation to the total quantity of other species, weed seeds, and foreign
matter.
Seedbed
The soil prepared by natural or artificial means
to promote the germination of seed and the growth of seedlings.
Seeding, Direct
In broadcast seeding, seed is sown over
the entire area. Partial seeding may be done in strips, furrow rows, surface
roughened area, or for spot seeding.
Seepage
1. Groundwater emerging on the face of a streambank. Percolation of water
through the soil from unlined canals, ditches, laterals, watercourses, or water
storage facilities. Water escaping through, or emerging from, the ground along
an extensive line or surface, as contrasted with a spring where the water
emerges from a localized spot. Water that leaks through or under a flood
proofing measure such as a levee or floodwall. 2. Where levees or their foundations are not watertight, seepage occurs through or under the levee. Excessive seepage can weaken the structure’s stability or physically erode the structure from the inside out.
Seiche
A cyclic oscillation or "sloshing" of a
lake due to the effect of winds, seismic forces and/or atmospheric pressures.
Seine Survey
A fish capturing procedure where fish are
enclosed and drawn to shore using a large net with sinkers on one edge and
floats on the other.
Set-Back Levee
Levees that are constructed at a distance from the river channel in order to allow the river to occupy a portion of its floodplain; these levees are usually smaller in size than levees placed immediately adjacent to the river channel.
Setback Standards
Minimum distances established by
regulation that structures must be set back from river channels and coastal
shorelines.
Settleable Solids
Those suspended solids in stormwater
that separate by settling when the stormwater is held in a quiescent condition
for a specified time.
Settlement Analysis
Core sampling and other tests help engineers determine how much the soil and other materials in a levee have settled or can be anticipated to settle.
SFHA
Abbreviation for Special Flood Hazard Area. An area of land that would be inundated by a flood having a 1 percent chance of occurring in any given year (also referred to as the base flood or 100-yearflood).
SFHDF
Abbreviation for Standard Flood Hazard Determination Form.
Shaft Spillway
A vertical shaft having a funnel-shaped entrance and ending in an outlet tunnel that Provides an outflow from a reservoir. Also known as a morning glory or glory hole spillway.
Shale
Sedimentary or stratified rock structure generally
formed by the consolidation of clay or claylike material.
Shallow Flooding
A designated AO, AH, or VO zone of an
individual community's Flood Insurance Rate Map with 1% or greater annual
chance of flooding to an average depth of 1 to 3 feet where a clearly defined channel
does not exist, the path of the flooding is unpredictable, and velocity flow
may be evident. Such flooding is characterized by ponding or sheet slow.
Shear
Force parallel to a surface as opposed to directly
on the surface. An example of shear would be the tractive force that removes
particles from a streambank as flow moves over the surface of the slope; on the
other hand, a floating log that directly strikes the bank would not be a shear
force.
Sheet Erosion
The removal by surface runoff water of a fairly uniform layer of soil from a
bank slope.
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Photo of Sheet Erosion. |
Sheet Piling
Piling with a slender flat cross section to
be driven into the ground or seabed and meshed or interlocked with similar
sheets to form a bulkhead; may be aluminum, fiberglass, steel, vinyl, wood or
other suitable material.
Sheetflooding
A shallow (less than a foot) flooding caused
by inadequate drainage systems.
Sheetflow
Runoff which flows over the ground surface as a
thin, even layer, not concentrated in a channel.
Shellfish
An aquatic animal, such as a mollusk (e.g.,
clams, oysters, and snails) or crustacean (e.g., crabs and shrimp), having a
shell or shell-like external skeleton (exoskeleton).
Shore
The narrow strip of land in immediate contact with
the sea, or other body of water, including the zone between high and low water
lines. A shore of unconsolidated material is usually called a beach.
Shoreline Stabilization
(EM 1110-2-5026) The erosion protection of shorelines by engineering structures such as riprap or by biological features such as salt marshes or willow banks.
Short-Crested Wave
A wave, the crest length of which is of the same order of magnitude as the wave length. A system of short-crested waves has the appearance of hills being separated by troughs.
Shrub
A woody perennial plant differing from a tree by its
low stature and generally producing several basal shoots.
Shrub Wetlands
Wetlands, including shrub swamps and bogs,
that are represented by medium-height (less than 20 feet tall) woody plants.
Sigma-t
A measure used in physical oceanography to
describe water density, calculated by subtracting one from the specific gravity
of seawater and multiplying by 1000. The degree of water column stratification
is determined from the difference in sigma-t between surface and bottom waters.
Significant Wave Height
The average height of the one-third highest waves of a given wave group. Note that the composition of the highest waves depends upon the extent to which the lower waves are considered. In wave record analysis, the average height of the highest one-third of a selected number of waves, this number being determined by dividing the time of record by the significant period.
Silt
Noncohesive soil whose individual particles are not
visible to the unaided human eye (0.002 to 0.05 mm). Silt will crumble when
rolled into a ball. Sedimentary materials composed of fine or
intermediate-sized mineral particles suspended in water.
Silt Fence
Temporary sediment barrier consisting of filter
fabric, sometimes backed with wire mesh, attached to supporting posts and
partially buried.
Siltation
The process by which a river, lake, or other water body becomes clogged with
sediment. Silt can clog gravel beds and prevent successful salmon spawning.
Skimming
Using a machine to remove oil or scum from the
surface of the water.
Slab-on-Grade
A structural design where the first floor is
located on a poured concrete slab that sits directly on the ground.
Slash
Logs, branches, tree tops, or brush created as a
result of logging.
Slope (Energy)
The rate of the energy loss of a
watercourse.
Slope (Ground)
The change in vertical ground elevation
over a horizontal distance, usually based on the change in the vertical
elevation of the stream bottom.
Slope 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". ("Same as a Bench
Drain")
Sloughing
Movement of a mass of soil down a bank into the channel,
similar to a landslide; also slumping.
Slurry Wall
Barriers used to contain the flow of
contaminated groundwater or subsurface liquids.
Small Stream Flooding
Nuisance flooding of very small creeks and streams due to excessive rainfall over small drainage areas. Should not be confused with flash flooding. Usually 0.5-1.0 inch (1.3-2.5 cm) of rainfall in an hour is sufficient to cause some small stream flooding.
Smog
Smog forms when volatile organic compounds (VOCs) and
oxides of nitrogen (NOx) combine in the presence of sunlight on warm days. VOCs
come from solvent and paint evaporation, along with car, truck, boat, and plane
emissions. NOx comes predominantly from car and truck exhaust as well as the
smokestack emissions of industries and utilities. Also called ground-level
ozone.
Social Sciences
The study of human society and individual
relationships in and to society. Social sciences include sociology, psychology,
anthropology, economics, and political science.
Sod
A closely-knit ground cover growth, primarily of
grasses. Plugs, squares, or strips of turf with the adhering soil.
Soil
Soil finer than sand but coarser than clay, but not
so fine that it can remain suspended in water for long periods. The grain size
is considered to be less than 0.0625 mm.
Soil and Water Conservation Practices
Control measures
consisting of managerial, vegetative, and structural practices to reduce the
loss of soil and water.
Soil Conditioner
An organic material like humus or compost
that helps soil absorb water, build a bacterial community, and take up mineral
nutrients.
Soil Conditioning
Those essential treatment measures of a
physical, chemical, and/or biological nature that are applied to critical areas
1 to 6 months in advance of the establishment of vegetation.
Soil Erodibility
An indicator of a soil's susceptibility
to raindrop impact, runoff, and other erosive processes.
Soil Erosion
Soil erosion is the process by which soil particles are removed from the land
surface, by wind, water or gravity. Most natural erosion occurs at slow rates;
however, the rate of erosion increases when land is cleared or altered and left
disturbed.
Photo courtesy of USDA NRCS. |
Photo of Soil Erosion. |
Soil Group
A classification of soils by the Soil
Conservation Service into four runoff potential groups. The groups range from A
soils, which are very permeable and produce little or no runoff, to D soils,
which are not very permeable and produce much more runoff.
Soil Horizon
A layer of soil, approximately parallel to
the soil surface, with distinct characteristics produced by soil-forming
processes.
Soil Material
Any drastically disturbed portion of the
earth's surface that could consist of one or more of the soil horizons.
Soil Permeability
The ease with which gases, liquids, or
plant roots penetrate or pass through a layer of soil.
Soil Stabilization
The use of measures such as rock
lining, vegetation or other engineering structures to prevent the movement of
soil when loads are applied to the soil.
Soil Structure
The combination or arrangement of primary
soil particles into secondary particles or units. The secondary particles are
classified on the basis of size, shape, and degree of distinctness into
classes, types, and grades.
Soil Survey
A general term for the examination of soils in
the field and laboratories. This includes the mapping of different kinds of
soils. The adaptability of the different kinds of soil is also noted.
Soil Texture
Soil texture class names of soil are based on
the relative percentages of sand, silt, and clay.
Sole Source Aquifer
Designated under the Safe Drinking
Water Amendments (1986), an aquifer of critical value as the main or only
supplier of drinking water for a specific area.
Sorb
To take up and hold either by absorption or
adsorption.
Spatial Database
A collection of information that contains
data on the phenomenon of interest, such as forest condition or stream
pollution, and the location of the phenomenon on the Earth's surface.
Spatial Extent
The total area (water and land) where a
condition (e.g., shellfish diseases) or populations of plants and animals are
found.
Spatial Pattern
Generally, the way things are arranged on
a map. For example, the pattern of forest patches can be described by their
number, size, shape, distance between patches, etc. The spatial pattern
exhibited by a map can also be described in terms of its overall texture,
complexity, and other indicators.
Spatial Scale
For example, a landscape, forest ecosystem,
community, etc.
Spawning
Sexual reproduction in fish.
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Photo of Spawning Habitat. |
Special Flood Hazard Areas (SFHA)
An area having special flood, mudslide, or flood-related erosion hazards, and shown on a Flood Boundary Floodway Map (FBFM), Floodway Hazard Boundary Map (FHBM), or a Flood Insurance Rate Map (FIRM). SFHAs are further subdivided into Flood Hazard Zones A, AO, A1, A30, AE, A99, AH, E, or M. The lands adjoining the channel
of a river, stream, or watercourse which would be covered by flood water during
a base flood (100-year flood).
Special Hazards
Hazards that accompany flooding and cause
greater damage than the usual forces of flowing water. Special hazard areas
include areas below dams, areas behind levees, alluvial fans, and areas subject
to mudfloods.
Species
The species is the fundamental unit of biological
organization. Members of a species are genetically similar and normally mate
only with other members of the same species, thus preserving that genetic
similarity.
Spiking
A method of cultivation in which a solid tine or
pointed blade penetrates the turf and soil.
Spillway
A passage such as a paved apron or channel for surplus water over or around a
dam or similar obstruction. An open or closed channel, or both, used to convey
excess water from a reservoir. It may contain gates, either manually or
automatically controlled, to regulate the discharge of excess water. Usually
the spillway functions only in large floods.
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Photo of Spillway. |
Spillway Chute
The outlet channel for the spillway discharge.
Splash Zone
Portion of a streambank between the average
normal river stage and the high-water stage.
Sponsor
A non-federal government entity (e.g. a State,
county or municipal government) with whom the Federal government has agreed to
build a flood control project. Under the Water Resource Development Act of 1986
(See http://www.fws.gov/laws/laws_digest/WAT1986.HTML),
the sponsor normally provides 25% of the project's construction cost, and
agrees to operate and maintain the completed project.
Spread Footing
See Footings.
Spring
A place where ground water naturally comes to the
surface resulting from the water table meeting the land surface.
Spring
Melt/Thaw
The process whereby warm temperatures melt winter snow and
ice. Because various forms of acid deposition may have been stored in the
frozen water, the melt can result in abnormally large amounts of acidity
entering streams and rivers, sometimes causing fish kills.
Stable Channel
A channel with no net erosion or deposition over a period of several years; a graded stream.
Stage
Height of water above a given level, as measured by
a gage.
Stakeholder
Any organization, governmental entity, or
individual that has a stake in or may be impacted by a given approach to
environmental regulation, pollution prevention, energy conservation, etc.
Standard
Project Flood
A very large (low frequency) design flood standard
applied to the design of major flood control structures and representing the
most severe combination of meteorological and hydrological conditions
considered reasonably characteristic of a particular region.
Standards
Floodplain regulatory and design standards,
including prescriptive and performance standards, that provide a means for
uniform application of floodplain management practices and for the review and
evaluation of flood loss reduction and natural values protection projects.
State Coordinating Agency
The agency of a state government
or other office designated by a state governor or by state statute at the
request of the NFIP Administrator to assist in the implementation of the National
Flood Insurance Program in that state.
Station
Station is a standard channel location system used
by the SCVWD that gives the distance from the downstream limit of jurisdiction
(usually San Francisco Bay), or, for a tributary creek, from where it branches
off of the main channel. Distance is measured in feet, with each
"station" representing 100 feet. For example, station 43+56 would be
a point 4,356 feet upstream from the mouth of the channel.
Steady Flow
The state of flow where the depth of flow does
not change with time.
Steep Slope
Slopes of 40 percent gradient or steeper.
Step-Backwater Analysis
The most widely used method for
calculating river hydraulics.
Still-Water Elevation
The estimated height of the water
surface during a coastal storm as generated by the storm surge and the
astronomical tide. Measured in relation to NOVD, the estimated still-water elevation
does not include the added effects of waves on the water surface elevation. The
still-water elevation associated with the one-percent flood is referred to on
maps prepared by the Federal Emergency Management Agency as the Base Flood
Elevation.
Stolon
An above-ground stem capable of growing a new
plant.
Storage
The volume of a reservoir, usually measured in
acre-feet.
Storage Capacity, Exclusive Flood Control
The space in reservoirs reserved for the sole purpose of regulating flood inflows to abate flood damage.
Storage Reservoir
1. The volume of a reservoir, usually measured in acre-feet. (USACE) 2. The available volume behind a dam used to store water.
Storm Drain
A drainage system to collect stormwater
runoff, separate from the sanitary sewer or wastewater system for transporting
storm water to streams or outfalls for flood control purposes.
Storm Frequency
The time interval between major storms of
predetermined intensity and volumes of runoff for which storm sewers and other
structures are designed and constructed to handle hydraulically without
surcharging and backflooding, e.g., a 2-year, 10-year or 100-year storm.
Storm
Surge
The increase in water surface elevation above normal tide levels
due primarily to atmospheric pressure reduction and the piling up of water in
coastal areas due to the cumulative effects of wind stress acting in
essentially a constant direction across an open expanse of water. The maximum
water surface elevation in coastal areas resulting from hurricane force winds
driving ocean water upward over areas above mean sea level.
Photo courtesy of USACE. |
Photo of Storm Surge Effects. |
Storm Water Pollution Prevention Plan (SWPPP)
Is a report
that includes site map(s), an identification of construction/contractor
activities that could cause pollutants in the storm water, and a description of
measures or practices to control these pollutants. The SWPPP must be prepared
and implemented before construction begins.
Stormwater
Runoff, snow melt runoff, and surface runoff and drainage. It excludes
infiltration and runoff from agricultural land. Runoff from streets, parking
lots, parks, as well as agricultural and urban areas into a water body.
Stormwater Drainage System
Constructed and natural
features which function together as a system to collect, convey, channel, hold,
inhibit, retain, detain, infiltrate, divert, treat or filter stormwater.
Stormwater Facility
A constructed component of a stormwater
drainage system, designed or constructed to perform a particular function or
multiple functions. Stormwater facilities include, but are not limited to,
pipes, swales, ditches, culverts, street gutters, detention basins, retention
basins, constructed wetlands, infiltration devices, catchbasins, oil/water
separators, sediment basins and modular pavement.
Stormwater Quality
A term used to describe the chemical, physical,
and biological characteristics of stormwater.
Stormwater Quantity
A term used to describe the volume
characteristics of stormwater.
Stormwater Site Plan
A plan which shows the measures that
will be taken during and after project construction to provide erosion and
sediment control and stormwater control.
Strategies and Tools
The management strategies and
implementing tools established in House Document 465 to guide federal, state
and local decision-makers in implementing a national program for floodplain
management.
Stratification
The formation, accumulation, or deposition
of materials in layers, such as layers of fresh water overlying higher salinity
water (salt water) in estuaries. See Sigma-t.
Straw Bale
Temporary barriers made of straw bales are
sometimes installed across a slope or around the perimeter of a construction
site to intercept and detain sediment transported by runoff.
Stream
A body of water flowing in a natural surface channel. Flow may be continuous
or only during wet periods. Streams which flow only during wet periods are
termed "intermittent streams". A natural body of flowing water that
is a complex ecosystem in which biological, chemical, or physical changes may
affect other characteristics. A stream begins at its headwaters and gathers
water from runoff, rain, snowmelt, or from underground springs. Streams hold
great importance regardless of size or flow. They provide water supplies, a
variety of aesthetic values, and are also important wildlife habitats.
Stream Acidification
See Acid Deposition.
Stream Crossings
Stream crossings are defined as the area
of disturbed soil from break in grade on opposing banks.
Stream Gaging
The quantitative determination of stream
flow using gages, current meters, weirs, or other measuring instruments at
selected locations. See Gaging Station.
Stream Maintenance Program
The Stream Maintenance Program
will provide long-term guidance to the District to effectively implement
routine stream maintenance projects in a cost-effective and
environmentally-sensitive manner. The Stream Maintenance Program is to be
codified in a process and policy document that can be adopted by the District
and utilized in obtaining long-term permits from regulatory agencies. The
Stream Maintenance Program includes specific measures, protocols, and
monitoring and reporting requirements to ensure that routine stream maintenance
projects are implemented in an effective, cost-sensitive, and
environmentally-sensitive manner.
Stream Order
An important indicator of plants and animals
present in streams. First order, small streams often have distinct
characteristics. They are typically very clear and dominated by aquatic insects
and algae in the stream bottom, and often have small fish that feed on these bottom
organisms. Higher order streams (large streams) are often muddy and dominated
by larger fish. The joining of two
first order streams creates a second order stream. In turn, the joining of two
second order streams create a third order stream.
Streambank
The side slopes of a channel between which the
streamflow is normally confined.
Streambank
Erosion
Removal of soil particles from a bank slope primarily caused
by water action but also by climatic conditions, ice and debris, chemical
reactions, and changes in land and stream use.
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Photo of Streambank Erosion. |
Streambank Failure
Collapse or slippage of a large mass of
bank material into the channel.
Streambed
The part of a stream over which a column of
water moves.
Streamflow
The movement of water through a channel.
Streams
Those areas where surface waters flow sufficiently
to produce a defined channel or bed. A defined channel or bed is indicated by
hydraulically sorted sediments or the removal of vegetative litter or loosely
rooted vegetation by the action of moving water. The channel or bed need not
contain water year-round.
Streamside Management Zone (SMZ)
Land adjacent to
perennial, intermittent, and ephemeral streams, ponds, or lakes requiring
special attention during forestry operations. They are to be treated in a way
that meets water quality standards for nonpoint source pollution.
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Perennial stream
Identified by well-defined banks and
natural channels, and have continuously flowing water most years. They are
usually shown on a topographic map as a solid blue line.
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Intermittent stream
Has well-defined banks and natural
channels, but typically has flowing water from a headwater source for only a
portion of the year. They are usually shown on a topographic map as broken blue
lines.
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Ephemeral stream
A flow as a result of wet weather
conditions when the ground is saturated. The channel is characterized by being
free of leaf litter showing bare rock soil that has been exposed by flowing
water. Not shown on topographic maps.
Stressor
Any physical, chemical, or biological entity that
can induce an adverse response (or stress).
Structural Measures
Measures such as dams, reservoirs, dikes,
levees, floodwalls, channel alterations, high flow diversions and spillways,
and land treatment measures designed to modify floods.
Stubble
The basal portion of plants remaining after the
top portion has been harvested.
Subbasin
A drainage area which drains to a water course or
waterbody named and noted on common maps and which is contained within a basin.
Subcritical Flow
State of flow where the gravitational
forces are more pronounced than the inertial forces. The flow tends to have a
low velocity. In general, in this flow regime, the hydraulic depth is more than
twice the velocity head.
Subdivision
The partitioning or dividing of a parcel or
tract of land.
Subdivision Regulations
Regulations and standards
established by a local unit of government with authority granted under a state
enabling law, for the subdivision of land in order to secure coordinated land
development, including adequate building sites and land for vital community
services and facilities such as streets, utilities, schools, and parks.
Submerged Aquatic Vegetation (SAV)
Rooted aquatic
vegetation, such as seagrasses, that cannot withstand excessive drying and
therefore live with their leaves at or below the water surface in shallow areas
of estuaries where light can penetrate to the bottom sediments. SAV provides an
important habitat for young fish and other aquatic organisms.
Subsidence
A type of ground failure that can lower the
ground surface, causing or increasing flood damage in areas of high ground
water, tides, storm surges, or overbank stream flow. The tracts in the
California Delta, as an example, are experiencing subsidence at rates of
several inches per year. As the land subsides the levees must be raised and
reinforced to prevent flooding.
Subsoil
In soils with weak profile development, the
subsoil can be defined as the soil below the normal tilled area.
Subsoiling
The tillage of subsurface soil for the purpose
of breaking up dense layers that restrict water movement and root penetration.
Substantial Damage
The amount of damage to a structure
caused by flooding that may be sustained before certain regulatory and flood
insurance requirements are triggered. As defined in NFIP regulations, a
building is considered substantially damaged when the cost of restoring the
building would exceed 50% of the market value of the structure.
Substantial Improvement
Any repair, reconstruction or
improvement of a structure, the cost of which equals or exceeds 50% of the
market value of the structure either a) before the improvement or repair is
started, or b) if the structure has been damaged, and is being restored, before
the damage occurred.
Substrate
A surface on which a plant or animal grows or is
attached.
Sump
A low-lying area with no drainage outlet.
Sump Pump
A pump designed to pump water out of a sump or
basement.
Surface Runoff
Precipitation, snow melt, or irrigation
water in excess of what can infiltrate the soil surface and be stored in small
surface depressions; a major transporter of non-point source pollutants in
rivers, streams, and lakes.
Surface Water
Water found over the land surface in rivers,
streams, creeks, lakes, ponds, marshes, or oceans whose surface is exposed to
the atmosphere.
Suspended Solids/Suspended Sediments
Particles of soil,
sediment, living material, or detritus suspended in the water column.
Swale
A shallow drainage conveyance with relatively gentle sideslopes, generally with
flow depths less than one foot.
Photo courtesy of USACE. |
Photo of Swale. |
Swamp
A type of wetland dominated by woody vegetation but
without appreciable peat deposits. Swamps may be fresh or salt water and tidal
or non-tidal. See Wetlands.
SWMP
Abbreviation for stormwater management plan.
System
A combination of flood proofing measures.
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
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A Division of Infrastructure Defense Technologies
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