A

Algae
Mostly aquatic, non-vascular plants that float in the water or attach to larger plants, rocks, and other substrates. Also called phytoplankton, these individuals are usually visible only with a microscope. They are a normal and necessary component of aquatic life, but excessive numbers can make the water appear cloudy and colored.

Alluvial fan

A fan-shaped accumulation of alluvium deposited at the mouth of a ravine or at the juncture of a tributary stream with the main stream.

Alkalinity
The acid-neutralizing capacity of water. It is primarily a function of the carbonate, bicarbonate, and hydroxide content in water. The lower the alkalinity, the less capacity the water has to absorb acids without becoming more acidic.

Anadromous fish

Fish that ascend rivers from the sea for breeding.

Aquifer

A geologic stratum containing groundwater that can be withdrawn and used for human purposes.

B

Basin

Any area draining to a point of interest.

Basin plan

A plan and all implementing regulations and procedures including but not limited to capital projects, public education activities, land use management regulations adopted by ordinance for managing surface and storm water management facilities, and features within individual sub-basins.

Bentho
The communities of aquatic life which dwell in or on the bottom sediments of a water body.

Best Management Practices (BMP)

Methods adopted by resource users designed to mitigate harm to the environment that might result from their activities.

Biodiversity

A measure of the distinct characteristics, qualities, or elements of plant and animal life in a defined area; a measure of biological differences.

Biofiltration swale or Bioswale

A long, gently sloped, vegetated ditch designed to filter pollutants from stormwater. Grass is the most common vegetation, but wetland vegetation can be used if the soil is saturated.

Buffer

A designated area adjacent to and a part of a steep slope or landslide hazard area which protects slope stability, attenuation of surface water flows, and landslide hazards reasonably necessary to minimize risk; or a designated area adjacent to or a part of a stream or wetland that is an integral part of the stream or wetland ecosystem.

C

Channel

A long, narrow excavation or surface feature that conveys surface water and is open to the air.

Channel, constructed

A channel or ditch constructed to convey surface water; also includes reconstructed natural channels.

Channel, natural

A channel which has occurred naturally due to the flow of surface waters; or a channel that, although originally constructed by human activity, has taken on the appearance of a natural channel including a stable route and biological community.

Closed depression

An area which is low-lying and either has no surface water outlet, or has such a limited outlet that during storm events the area acts as a retention basin, with more than 5000 square feet of water surface area at overflow elevation.

Collection site

A stream, lake, reservoir, or other body of water drained from a watershed.

Combined Sewer Overflow (CSO)

Discharges of combined sewage and stormwater into water bodies during very wet or storm weather. These discharges occur to relieve the sewer system as it becomes overloaded with normal sewer flow and increased storm run-off. The term is also used to denote a pipe that discharges those overflows.

Conductivity

A measure of water's capacity to convey an electric current. It is related to the total amount of dissolved charged substances in the water. Therefore, it can be used as a general indicator of the quality of the water and can also suggest presence of unidentified material in the water. It is often used as a surrogate for salinity measurements.

Confined aquifer

A water-saturated layer of soil or rock that is bounded above or below by impermeable layers.

Conflict resolution

The act of arbitrating differences of belief or opinion about a given set of conditions or circumstances.

Conservation

The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming, and industry, and thus increasing water supplies for optimum long-term economic and social benefits. 

Constructed conveyance system facilities

Gutters, ditches, pipes, channels, and most flow control and water quality treatment facilities.

Contaminant

Any substance that when added to water (or another substance) makes it impure and unfit for consumption or use.

Conveyance system

Drainage facilities and features that collect, contain, and provide for the flow of surface and storm water from the highest points on the land down to a receiving water. Conveyance systems are made up of natural elements and of constructed facilities.

Critical drainage area

An area with such severe flooding, drainage, and/or erosion/sedimentation conditions which have resulted or will result from the cumulative impacts of development and urbanization.

D

Depletion

The loss of water from surface water reservoirs of ground water aquifers at a rate greater than that of recharge.

Deposition

The process of laying down sediment or accumulating layers of material carried in suspension.

Detention

Release of surface and storm water runoff from the site at a slower rate than it is collected by the drainage facility system, the difference being held in temporary storage.

Detention facility

A facility that collects water from developed areas and releases it at a slower rate than it enters the collection system. The excess of inflow over outflow is temporarily stored in a pond or a vault and is typically released over a few hours or a few days.

Direct discharge

Un-detained discharge from a proposed project to a major receiving water.  

Discharge

Runoff, excluding offsite flows, leaving the proposed development through overland flow, built conveyance systems, or infiltration facilities.

Dispersed discharge

Release of surface and storm water runoff from a drainage facility system such that the flow spreads over a wide area and is located so as not to allow flow to concentrate anywhere upstream of a drainage channel with erodible underlying granular soils or the potential to flood downstream properties.

Ditch

A constructed channel with its top width less than 10 feet at design flow.

Diversion

A change in the natural discharge location or runoff flows onto or away from an adjacent downstream property.

Drainage

The collection, conveyance, containment, and/or discharge of surface and storm water runoff.

Drainage area or drainage basin

An area draining to a point of interest.

Drainage facility

A constructed or engineered feature that collects, conveys, stores or treats surface and storm water runoff. Drainage facilities shall include but not be limited to all constructed or engineered streams, pipelines, channels, ditches, gutters, lakes, wetlands, closed depressions, flow control or water quality treatment facilities, erosion and sedimentation control facilities, and other drainage structures and appurtenances that provide for drainage.

E

Easement

A legal document that makes it possible to give, sell, or take certain land and/or water rights without transfer of title (e.g. the passage of utility lines).

Effluent

Liquids discharged from sewage treatment plants, septic systems, or industrial sources to surface waters.

Embankment

A structure of earth, gravel, or similar material raised to form a pond bank or foundation for a road.

Epilimnion

The warmer, well-lit surface waters of a lake that are thermally separated from the colder (hence denser), water at the bottom of the lake when a lake is stratified.

Erosion

The detachment and transport of soil or rock fragments by water, wind, ice, etc.

Eutrophication

The acceleration of the loading of nutrients to a lake by natural or human-induced causes. The increased rate of delivery of nutrients results in increased production of algae and consequently, poor water transparency. Human-induced (cultural) eutrophication may be caused by input of treated sewage to a lake, deforestation of a watershed, or the urbanization of a watershed.

Eutrophic

A condition of a water body in which excess nutrients, particularly phosphorous, stimulates the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen. Thus, less dissolved oxygen is available to other aquatic life.

Evapotranspiration

The loss of water from the soil through both evaporation and transpiration from plants.

F

Fen

A type of wetland that forms peat deposits. Peat comes from the plants (especially Sphagnum moss) that grow, die, and accumulate in the fen. Bogs and fens are similar in that they both produce peat; however, bogs are essentially closed to water input other than rainwater, while fens generally have a surface water flow. Because of this hydrologic difference, fens are less acidic than bogs and may support different plants and animals.

Floodplain

Any normally dry land area that is susceptible to being inundated by water from any natural source; usually lowland adjacent to a stream or lake.

Flow control facility

A drainage facility designed to mitigate the impacts of increased surface and storm water runoff generated by site development. Flow control facilities are designed either to hold water for a considerable length of time and then release it by evaporation, plant transpiration, and/or infiltration into the ground, or to hold runoff a short period of time and then release it to the conveyance system.

G

Gradient

A measure of a degree of incline; the steepness of a slope.

Groundwater

Water stored beneath the surface of the earth. The water in the ground is supplied by the seepage of rainwater, snowmelt, and other surface water into the soil. Some groundwater may be found far beneath the earth surface, while other groundwater may be only a few inches from the surface. Groundwater discharges into lowland streams to maintain their baseflow. 

H

Habitat

The specific area or environment in which a particular type of plant or animal lives and grows.

Hardpan

A cemented or compacted and often clay-like layer of soil that is impenetrable by roots.

Headwaters

The source of a stream.

Hydrology

The science dealing with the properties, distribution and circulation of water. The term usually refers to the flow of water on or below the land surface before reaching a stream or man-made structure.

Hypolimnion

The dark, cold, bottom waters of a lake that are thermally separated from the warmer (hence less dense) surface waters when a lake is stratified.

I

Impervious surface

A hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development; and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development.

Infiltration facility

A drainage facility designed to use the hydrologic process of water soaking into the ground (commonly referred to as percolation) to dispose of surface and storm water runoff.

Instream flow

The minimum amount of water required in a stream to maintain the existing aquatic resources and associated wildlife and riparian habitat.

Invertebrates

Animals without internal skeletons. Some require magnification to be seen well, while others such as worms, insects, and crayfish are relatively large. Invertebrates living in stream and lake sediments are collected as samples to be identified and counted. In general, more varied invertebrate communities indicate healthier water bodies.

Isohyetal line

A line drawn on a map or chart connecting points that receive equal amounts of precipitation.

J

Joint problems

Problems that involve more than one jurisdiction or which impact the sustainability and functionality of the drainage basin.

L

Levee

An embankment or raised area that prevents water from moving from one place to another.

Limiting nutrient

The nutrient that is in lowest supply relative to the demand. The limiting nutrient will be exhausted first by algae which require many nutrients and light to grow. Inputs of the limiting nutrient will result in increased algal production, but as soon as the limiting nutrient is exhausted, growth stops. Phytoplankton growth in lake waters of temperate lowland areas is generally phosphorus limited.

Limnology

Scientific study of inland waters.

Littoral zone

Portion of a water body extending from the shoreline lakeward to the greatest depth occupied by rooted plants.

Loading rate
Addition of a substance to a water body; or the rate at which the addition occurs. For example, streams load nutrients to lakes at various rates as in "500 kilograms per year (500 kg/yr)" or "227 pounds per year (227 lb/yr)."

Local problems

Problems that impact only one jurisdiction and only a small isolated portion of the basin. Local problems also have relatively minor environmental impacts when viewed on a basin-wide scale, and are not expected to impact the overall sustainability and functionality of the drainage basin.

M

Macrophytes
Rooted and floating aquatic plants, larger (macro-) than the phytoplankton.

Mediation

The process of intervening between two or more parties in conflict to promote reconciliation, settlement, or compromise.

Mesotrophic
A condition of lakes that is characterized by moderate concentrations of nutrients, algae, and water transparency. A mesotrophic lake is not as rich in nutrients as a eutrophic lake, but richer in nutrients than an oligotrophic lake.

Monomictic
A lake which has one mixing and one stratification event per year. If a lake does not freeze over in the winter, the winter winds will mix the waters of the lake. In summer, the lake resists mixing and becomes stratified because the surface waters are warm (light) and the bottom waters are cold (dense).

N

Natural conveyance system elements

Swales and small drainage courses, streams, rivers, lakes, and wetlands.

Nonpoint source pollution

Pollution that originates from diffuse areas and unidentifiable sources, such as agriculture, the atmosphere, or ground water.

Nonstructural BMP

A preventative action to protect receiving water quality that does not require construction. Nonstructural BMPs rely predominantly on behavioral changes in order to be effective. Major categories of non-structural BMPs include education, recycling, maintenance practices and source controls.

O

Oligotrophic

A condition of lakes characterized by low concentrations of nutrients and algae and resulting good water transparency. An oligotrophic lake has fewer nutrients than a mesotrophic or eutrophic lake.

Outfall

A point where collected and concentrated surface and storm water runoff is discharged from a pipe system or culvert.

P

Pathogens

Microorganisms that can cause disease in other organisms or humans, animals, and plants. Pathogens include bacteria, viruses, fungi, or parasites found in sewage, in runoff from farms or city streets, and in water used for swimming. Pathogens can be present in municipal, industrial, and nonpoint source discharges.

Pelagic zone

Deep, open water area of a lake away from the edge of the littoral zone towards the center of the lake.

Peat

An unconsolidated deposit of semi carbonized plant remains, generally found in a watershed environment such as a bog or a fen. It generally has a moisture content of at least 75%, but when it is dried out, it burns very easily.

Peatland

An area of vegetated matter with extensive peat deposits.

Permeable

Capable of transmitting water (e.g. porous rock, sediment, or soil).

Permeable layer

A layer of porous material (rock, soil, unconsolidated sediment); in an aquifer, the layer through which water freely passes as it moves through the ground.

pH
Measure of the acidity of water on a scale of 0 to 14, with 7 representing neutral water. A pH less than 7 is considered acidic and above 7 is basic.

Physiographic subdivisions

Physiographic (or geomorphic) subdivisions are based on terrain texture, rock type, and geologic structure and history.

Photic zone

The lighted region of a lake where photosynthesis occurs.

Phytoplankton

Floating, mostly microscopic algae (plants) that live in water.

Point discharge

The release of collected and/or concentrated surface and storm water runoff from a pipe, culvert, or channel.

Point source pollution
An input of pollutants into a water body from discrete sources, such as municipal or industrial outfalls.

Primary treatment

The first stage of wastewater treatment involving removal of debris and solids by screening and settling.

Pump station

A structure used to move wastewater uphill, against gravity.

R 

Ravine

A small stream channel, narrow and steep-sided in cross section.

Reach

A length of channel with uniform characteristics.

Receiving waters

Bodies of water or surface water systems receiving water from upstream man-made or natural systems.

Regulator

A structure that controls the flow of wastewater from two or more input pipes to a single output. Regulators can be used to restrict or halt flow, thus causing wastewater to be stored in the conveyance system until it can be handled by the treatment plant.

Restoration

The act or process of bringing something back to a previous condition or position.

Retention

The process of collecting and holding surface and storm water runoff with no surface outflow.

Ridge lines

Points of higher ground that separate two adjacent streams or watersheds; also known as divides.

Riparian

Pertaining to the banks of rivers and streams, and sometimes also wetlands, lakes, or tidewater.

Riprap

A facing layer or protective mound of stones placed to prevent erosion or sloughing of a structure or embankment due to the flow of surface and storm water runoff.

Runoff

Water originating from rainfall and other precipitation that ultimately flows into drainage facilities, rivers, streams, springs, seeps, ponds, lakes, and wetlands as well as shallow groundwater.

S

Salinization

The condition in which the salt content of the soil accumulates over time to above the normal level. 

Salmonid

A member of the fish family Salmonidae. Salmonid species include Chinook, Coho, chum, sockeye, and pink salmon; cutthroat, rainbow, and brown trout and steelhead; Dolly Varden, brook trout, char, kokanee, and whitefish.

Secchi Depth

Measure of transparency of water obtained by lowering a 10 cm black and white disk into water until it is no longer visible.

Secondary treatment

Following primary treatment, bacteria are used to consume organic wastes. Wastewater is then disinfected and discharged through an outfall.

Sediment

Fragmented organic or inorganic material derived from the weathering of soil, alluvial, and rock materials; removed by erosion and transported by water, wind, ice, and gravity.

Separation

A method for controlling combined sewer overflow whereby the combined sewer is separated into both a sanitary sewer and a storm drain, as is the practice in new development.

Sewage

That portion of wastewater that is composed of human and industrial wastes from homes, businesses, and industries.

Standard

A legally established allowable limit for a substance or characteristic in the water, based on criteria. Enforcement actions by the appropriate agencies can be taken against parties who cause violations.

Stratification of lakes

A layering effect produced by the warming of the surface waters in many lakes during summer. Upper waters are progressively warmed by the sun and the deeper waters remain cold. Because of the difference in density (warmer water is lighter); the two layers remain separate from each other: upper waters “float” on deeper waters and wind induced mixing occur only in the upper waters. Oxygen in the bottom waters may become depleted. In autumn as the upper waters cool, the whole lake mixes again and remains mixed throughout the winter, or until it freezes over.

Storm drain system

The system of gutters, pipes, streams, or ditches used to carry surface and storm water from surrounding lands to streams, lakes, or Puget Sound. Also see Conveyance System.

Stormwater

Stormwater is the water that runs off surfaces such as rooftops, paved streets, highways, and parking lots. It can also come from hard grassy surfaces like lawns, play fields, and from graveled roads and parking lots.

Stormwater management

The application of site design principles and construction techniques to prevent sediments and other pollutants from entering surface or ground water; source controls; and treatment of runoff to reduce pollution.

Structural BMP

Constructed facilities or measures to help protect receiving water quality and control stormwater quantity. Examples include storage, vegetation, infiltration, and filtration.

Substrate

A layer of material beneath the surface soil.

Surface water

Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater, and runoff.

Swale

A shallow drainage conveyance with relatively gentle side slopes, generally with flow depths less than one foot.

T

Temporary wetland

A type of wetland in which water is present for only part of the year, usually during the wet or rainy seasons; also called vernal pools.

Tightline

Typically a continuous length of pipe used to convey flows down a steep or sensitive slope with appropriate energy dissipation at the discharge end.

Total maximum daily load (TMDL)

A calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. Water quality standards identify the uses for each waterbody, for example, drinking water supply, contact recreation (swimming), and aquatic life support (fishing), and the scientific criteria to support that use. The Clean Water Act, section 303, establishes the water quality standards and TMDL programs.

Total suspended solids (TSS)

Particles, both mineral (clay and sand) and organic (algae and small pieces of decomposed plant and animal material), that are suspended in water.

Transparency

A measure of the clarity of water in a lake, which is measured by lowering a standard black and white Secchi disk into the water and recording the depth at which it is no longer visible. Transparency of lakes is determined by the color of the water and the amount of material suspended in it. Generally in colorless waters of the Puget lowland, the transparency of the water in summer is determined by the amount of algae present in the water. Suspended silt particles may also have an effect, particularly in wet weather.

Tributary

A stream that contributes its water to another stream or body of water.

Trophic status
Rating of the condition of a lake on the scale of oligotrophic-mesotrophic-eutrophic (see definition of these terms).

Turbidity
Cloudiness of water caused by the suspension of minute particles, usually algae, silt, or clay.

U

Unconfined aquifer

An aquifer in which the upper boundary is the top of the water table.

Upland

An area of high or relatively high ground

W

Wastewater

Total flow within the sewage system. In combined systems, it includes sewage and stormwater.

Wastewater treatment

Any of the mechanical or chemical processes used to modify the quality of wastewater in order to make it more compatible or acceptable to humans and the environment.

Water allocation

In a hydrologic system in which there are multiple uses or demands for water, the process of measuring a specific amount of water devoted to a given purpose.

Water column

Water in a lake between the surface and sediments. Used in vertical measurements used to characterize lake water.

Water quality standard

Recommended or enforceable maximum contaminant levels of chemicals or materials (e.g. nitrate, iron, arsenic) in water. These levels are established for water used by municipalities, industries, agriculture, and recreationists.

Water quality treatment facility

A drainage facility designed to reduce pollutants once they are already contained in surface and storm water runoff. Water quality treatment facilities are the structural component of best management practices (BMPs); when used singly or in combination, WQ facilities reduce the potential for contamination of surface and/or ground waters.

Water resource management

The decision-making, manipulative, and nonmanipulative processes by which water is protected, allocated, or developed.

Water right

A legal right to use a specified amount of water for beneficial purposes.

Water table

The top of an unconfined water aquifer; indicates the level below which soil and rock are saturated with water.

Water use practices

Direct, indirect, consumptive, and nonconsumptive used of water. These include domestic practices, navigation, wildlife habitat management, irrigation practices, recreation activities, industrial uses, and hydroelectric power generation.

Watershed

The areas that drain to surface water bodies, including lakes, rivers, estuaries, wetlands, streams, and the surrounding landscape.

Wetland

An area inundated or saturated by ground or surface water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.

Wetpond

Drainage facilities for water quality treatment that contain a permanent pool of water. They are designed to optimize water quality by providing long retention times (on the order of a week or more) to settle out particles of fine sediment to which pollutants such as heavy metals adsorb, and to allow biologic activity to occur that metabolizes nutrients and organic pollutants. For wetvaults, the permanent pool of water is covered by a lid which blocks sunlight from entering the facility, limiting light-dependent biologic activity.

X

Xeriscaping

A form of landscaping that utilizes a variety of indigenous and drought-tolerant plants, shrubs, and ground cover.

Z

Zone of aeration

The unsaturated surface layer of the ground in which some of the spaces between soil particles are filled with water and others are filled with air.

Zone of saturation

The part of the ground water system in which all the spaces between soil and rock material are filled with water

Zooplankton

Small, free swimming or floating animals in water, many are microscopic