220 Fourth Avenue South, Kent WA 98032 - (253) 856-5200

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The Official Website of the City of Kent

       STORMWATER       PugetSoundStartsHere

Lake Meridian Photo for Web

Stormwater... is the rain and melted snow/ice that falls onto our landscape and flows off of rooftops, streets, bare soils, and all other exposed surfaces. These surfaces can have pollutants on them (such as pet waste, dirt, litter, yard waste, chemicals, and auto fluids like oil and gas to name just a few) that will hitchhike with the stormwater as it travels, and then sadly if the stormwater is not treated, the pollutants end up in our ponds, creeks, lakes, rivers and eventually Puget Sound. Basic anatomy of a storm drainage system

Pollution in stormwater effects... You!

Stormwater is part of the water cycle, and as you know everything needs water, and good quality water. Polluted water is not drinkable, it can make us and other animals sick or worse, it smells bad, it looks bad, and we can't use it.

This is why all of us must to do our part to keep pollutants stored, used, and dispose of properly so they don't end up in our water resources and environment.

 

Check out a 5 minute video What is stormwater and why is it important? by King County that explains stormwater and its effect on the area. 

Report Spills and Water Pollution  Oil Spill

  • For emergency and hazardous spills call 911   

  • For urgent spills and discharges call the 24 hour Spill Hotline at 253-856-5600

  • For low-risk spills and discharges call the spill hotline or submit an online Spill Reporting Form.

 

reportspills (2)

 

 

Flooding or Drainage Problems?Click to access customer support center

 

Cleaning_Out_SD

 

 

 

Your storm drainage utility fee goes toward minimizing and eliminating flooding and water pollution in Kent. 

010 Utilities Storm Drainage - Mark traing Jason 2The utility fee is collected and utilized by the City to operate and maintain the public storm drainage system that we all benefit from which includes:
  • 18,000+ catch basins 
  • 350+ detention/retention ponds and bio-retention swales
  • 50 stormwater flow control and treatment facilities (vaults and filter vaults)
  • 300+ miles of pipes and roadside ditches
  • Stormwater pump stations
  • Dams
  • Culverts and channels
  • Creeks
  • Wetlands
  • Lakes
  • Green River in Kent

Drainage Utility Rates:  

  • Commercial storm drainage rates are based on property size, percentage of impervious surface, and the basin or basins in which the property is located.
  • Residential customers are billed a flat rate of $12.22. For property owners within the city limits, not receiving water and/or sewer service from the city,  storm drainage will be billed quarterly. Property owners who are outside of Kent's city limits will be billed with their property tax from King County.

Link to Kent Utility Billing Webpage

Most cities and counties in Western Washington collect a storm drainage utility fee to help minimize flooding of streets and private properties, and assure the safe collection and discharge of stormwater in their jurisdiction.

 

 

Stormwater Best Management Practices (BMPs)

BMPs_DoingRightDoingWrong(1)  

 

BMPs are a schedule of activities, prohibition of practices, maintenance procedures, and structural and/or managerial practices, that when used singly or in combination, prevent or reduce the release of pollutants and other adverse impacts to water-ways and water-bodies.

Click on each of the 3 types of BMPs to learn more.  

Source Control BMPs

Prevent pollution at the source through planning and good housekeeping

Flow Control BMPs

Stop or reduce erosion through collection, dispersion, and/or infiltration of stormwater runoff

Treatment BMPs

Remove pollutants in stormwater runoff to improve water quality

 

BMP Photo Example

 External Links:

Private Stormwater DrainagePrivateDrainInGutter

Property owners in Kent are responsible for managing stormwater and private drainage systems on their property, including regular inspections and maintenance. 

 

The City requires all private stormwater drainage systems comply with all city codes and standards. The City does not provide maintenance on privately operated and maintained stormwater drainage systems. 

 

The private management of private drainage systems is overseen by city of Kent's Public Works Department, Environmental Engineering NPDES work group.

 

For further information... click here to continue to the private drainage webpage. 

Public Stormwater DrainageMatt_1_12_15_10

Kent's publically operated and maintained stormwater drainage system is managed by the City's Public Works Department, and is an effective assembly of conveyance, collection, flow control, and treatment facilities including:

  • 18,000+ catch basins 
  • 350+ detention/retention ponds and bio-retention swales
  • 50 stormwater flow control and treatment facilities (vaults and filter vaults)
  • 300+ miles of pipes and roadside ditches
  • Stormwater pump stations
  • Dams
  • Culverts and channels
  • Creeks
  • Wetlands
  • Lakes
  • Green River in Kent

 

StormMapIconTo view a map of Kent's public drainage system, click here and select the storm drainage map.

 

 

 

 

More information regarding management of the public drainage system is available on the NPDES webpage.  

Questions? and Maintenance RequestsCustomerSupportCenterImage

We welcome your input and want to hear from you!

 

Please get in touch if you have any questions, concerns or comments about stormwater management in Kent, or if you notice an area where the public drainage system may be in need of attention or maintenance. 

 

NPDES Programonlyraindownthedrain(alone)

Kent's National Pollutant Discharge Elimination System (NPDES) Program is overseen by the Public Works Department Environmental Engineering work group.

 

The two primary goals for all stormwater managers is to minimize and prevent water pollution and flooding. With effort toward success of these goals, Kent maintains a NPDES Western Washington Municipal Stormwater Permit (Phase II) with the Washington State Department of Ecology.

 

Visit Kent's NPDES webpage to learn more about the permit and what Kent is doing to improve water quality and reduce and eliminate flooding in the city.

 

Glossary of Stormwater Words, Terms, and Abreviations

If you notice a stormwater related word not on this list that should be, please get in touch by emailing us at npdes@kentwa.gov. 

 

Aquifer

Generally, any water bearing soil unit or geologic formation. Specifically, a body of soil unit or geologic formation that contains sufficient saturated permeable material to conduct groundwater and yield economically significant quantities of groundwater to wells or springs.

 

Baffle 

A device to deflect, check or regulate flow.

 

Berm

A constructed barrier of compacted earth.

 

Biofiltration

The use of plants and other biological materials to enhance infiltration of water into the soil.

 

Bioretention

The process of collecting stormwater in a treatment area consisting of soil and plant materials to facilitate infiltration and remove sediment and other contaminants through physical, chemical, and biological processes. (Sketch PDF 171KB)

 

Bioswale

A long, gently sloped, vegetated ditch designed to filter pollutants from stormwater. (Sketch PDF 171KB)

 

BMPs or Best Management Practices

Schedules of activities, prohibitions of practices, general good housekeeping practices, pollution prevention and educational practices, maintenance procedures, and other management practices to prevent or reduce the discharge of pollutants directly or indirectly to the MS4 or waters of the state. BMPs also include treatment practices, structural methods, and operating procedures and practices to control site runoff, spillage or leaks, sludge or water disposal, or drainage from raw materials storage. BMPs are determined by reference to standard industry practice or applicable state, county, and local government design and pollution prevention manuals.

 

BSBL or Building Setback Line

An area in which structures, including but not limited to sheds, homes (including overhangs), buildings, and awnings shall not be permitted within, or allowed to project into, a critical area buffer. Roads, parking areas, uncovered at-grade decks, patios, lawns, and landscaping are permitted within the BSBL.

 

Buffer or Buffer Area

A vegetated zone contiguous to and surrounding a critical area that protects the critical area from adverse impacts to its integrity and value. Buffers are necessary for the continued maintenance, function, and/or structural stability of a critical area, and are an integral part of the resource’s ecosystem. Buffers may be enhanced and/or revegetated where they are degraded or as part of a mitigation program.

 

Catch Basin, Type I (Kent Standard Plan 5-1 (PDF, 255KB))

An underground rectangular-shaped concrete structure with a grated or solid cover, that allows for collection and conveyance of stormwater. The catch basin is designed with a bottom depression, called a sump, where stormwater collects and is contained to allow sediment (a pollutant) to settle out for later removal. The structure may also contain a Flow Restrictor/Oil Pollution control device, called a Control Structure.

 

Catch Basin, Type II (Kent Standard Plan 5-2 (PDF, 360KB))

An underground barrel-shaped concrete structure with a grated or solid cover, that allows for collection and conveyance of stormwater. The catch basin is designed with a bottom depression, called a sump, where stormwater collects and is contained to allow sediment (a pollutant) to settle out for later removal. The structure may also contain a Flow Restrictor/Oil Pollution control device, called a Control Structure.

 

Catch Basin Insert

A device installed at a catch basin inlet to treat stormwater through filtration, settling, absorption, adsorption, or a combination of these mechanisms. There are a number of shapes, sizes, and configurations of inserts available. 

 

Channel

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

 

Check Dam

A small dam constructed across a channel, swale, or ditch that slows runoff velocity, reduces channel erosion, promotes sediment deposition, and increases infiltration.

 

Cistern or Rain Barrel

An above ground container used to collect and capture rain water for later use.

 

Control Structure or Control Device

A facility and/or device designed to capture, store, and then slowly release stormwater runoff downstream.

 

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 may be a combination of constructed and natural facilities and features.

 

Critical Area or Environmentally Sensitive Area

An area that possesses important natural functions and embodies a variety of important natural and community values. Such areas include wetlands, streams, fish, and wildlife habitat, geologic hazard areas, critical aquifer recharge areas, and flood hazard areas. If not conducted properly, development or alteration of such areas may cause significant impacts to the valuable functions and values of these areas and/or may generate risks to the public health and general welfare, and/or to public and private property.

 

Culvert

Pipe or concrete box structure which drains open channels, swales, or ditches under a roadway or embankment typically with no catch basins or manholes along its length.

 

CWA = Clean Water Act.

The federal environmental law that includes the management of stormwater. (See EPA resources and the text of the law).

 

Dead Storage

The volume available in a depression in the ground below any conveyance system, or surface drainage pathway, or outlet invert elevation that could allow the discharge of surface and storm water runoff.

  

Dedication

Conveyance of land to the city or other not-for-profit entity by deed, easement, or other instrument of conveyance.

 

Depression Storage

The amount of precipitation that is trapped in depressions on the surface of the ground.

 

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

Facility designed to hold surface water run-off while gradually releasing it at a predetermined maximum rate.

 

Detention Pond King County sketch (PDF, 400-800kb)

A type of detention facility that is open-air with vegetated ground cover, and usually fenced for safety and water quality protection.

 

Detention Tank/Pipe King County sketch (PDF, 400-800kb)

A type of detention facility that is a large underground structure or pipe.

 

Detention Vault King County sketch (PDF, 400-800kb)

A type of detention facility that is a large underground concrete structure square or rectangular-shaped, and may be open to the air through vents or grates.

 

Discharge

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

 

Discharge, Direct

Undetained discharge from a proposed project to a major receiving water.

 

Discharge, Dispersed

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, usually lined with grass and found along roadsides.

 

Diversion

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

 

DOE = Washington State Department of Ecology

 

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.

 

Dry Season

May 1 to September 30.

 

EIS = Environmental Impact Statement.

A document that discusses the likely significant adverse impacts of a proposal, ways to lessen the impacts, and alternatives to the proposal. It is required by the national and state environmental policy acts when projects are determined to have the potential for significant environmental impact.

 

Embankment

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

 

EPA = Environmental Protection Agency

 

ESA = Endangered Species Act

 

Energy Dissipater

A rock pad constructed at inlets/outlets to prevent erosion, or a constructed percolation trench to disperse outletting flows over a large area, or a catch basin used to slow fast flowing runoff. Catch basins may be a part of the dispersion trench.

 

Erosion

A process whereby gravity, wind, rain, water, freeze-thaw, and other natural agents mobilize and transport soil particles.

 

ESC (aka TESC) = Erosion and Sediment Control (aka Temporary Erosion and Sediment Control)

Temporary or permanent controls used to reduce and hopefully prevent polluted runoff from leaving a site.

 

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.

 

Exotic Species

Any species of plant or animal that is foreign and not indigenous to the Kent area.

 

Facilities or Stormwater Facilities

Facilities that control the discharge of stormwater and that remove pollutants make up the bulk of the structural solutions applied to surface water problems in Kent. Stormwater facilities included storage facilities (ponds, vaults, underground tanks, and infiltration systems); water quality facilities (wetponds, biofiltration swales, constructed wetlands, sand filters, and oil/water separators); and conveyance systems (ditches, pipes, and catch basins).

Fen

A peat-accumulating wetland that receives some drainage from surrounding mineral soil and usually supports marsh-like vegetation.

 

FEMA = Federal Emergency Management Agency

 

Flow Control Facility

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.

 

Flow Restrictor or Flow Control Device (Sketch PDF 400-800KB)

A flow control device designed to capture, store, and then slowly release stormwater runoff downstream at a designated rate. Also see FROP.

 

Forested wetland

A wetland defined by the Cowardin system with at least thirty (30) percent of the surface area covered by woody vegetation greater than twenty (20) feet in height that is at least partially rooted in the wetland.

 

Freeboard

The vertical distance between the design water surface elevation and the elevation of the structure or facility which contains the water.

 

FROP = Flow Restrictor Oil Pollution (Sketch PDF 400-800KB)

A flow and pollution control device designed to capture and store stormwater runoff and pollutants, and then slowly release the less polluted runoff downstream at a designated rate. Also known as a FROP-T.

 

Grade

A gradient or slope.

 

Grading

Any excavating, filling, clearing, leveling, or contouring of the ground surface by human or mechanical means.

 

Groundwater

Water in a saturated zone or stratum beneath the surface of the land or below a surface water body.

Habitat

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

 

Habitat, Essential

Habitat necessary for the survival of federally listed threatened, endangered, and sensitive species and state-listed priority species.

 

Habitat, Wildlife

Areas that provide food, protective cover, nesting, loafing, breeding or movement for fish and wildlife and with which individual species have a primary association. Wildlife habitat includes naturally occurring ponds under twenty (20) acres in area.

 

Hardpan

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

 

Harmful Pollutant

A substance that has adverse effects to a living organism including death, chronic poisoning, impaired reproduction, cancer, or other effects.

 

Hydrologic Cycle

The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transpiration.

 

Illicit Discharges

Any direct or indirect nonstormwater discharge, not expressly allowed by KCC 7.14, to the MS4, waters of the state, or any other location within the city where the discharge has a reasonable likelihood of being washed into the MS4 or waters of the state. 

Illicit Connection

Any conveyance that is connected to the MS4 or waters of the state without a permit, excluding roof drains and foundation drains. Examples include sanitary sewer connections, floor drains, channels, pipelines, conduits, inlets, or outlets. Illicit connections include, but are not limited to, any conveyances that allow any nonstormwater discharge, including sewage, process wastewater, and wash water, to enter the MS4 or waters of the state; any connections from indoor drains and sinks, regardless of whether such drain or connection was previously allowed or approved by an authorized enforcement agency; or any drain or conveyance connected from a commercial or industrial land use to the MS4 or waters of the state that has not been documented in plans, maps, or equivalent records and approved by the city or another agency of government duly authorized to give such approvals.  

 

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.
Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam, or other surfaces which similarly impede the natural infiltration of surface and storm water runoff. Open, uncovered flow control or water quality treatment facilities shall not be considered impervious surfaces for determinations of thresholds. For the purpose of modeling though, onsite flow control and water quality ponds are modeled as impervious surface per Chapter 3 of the King County Surface Water Design Manual.

 

 

Infiltration or Percolation

The process of water moving through the soil from the soil surface.

 

Infiltration Basin sketch (PDF, 400-800kb)

A type of infiltration facility

 

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.

 

Infiltration Pond 

A type of infiltration facility. sketch (PDF, 400-800kb)

 

Infiltration Tank 

A type of infiltration facility. sketch (PDF, 400-800kb)

Inlet

An underground constructed basin that receives water to be conveyed, and does not have a basin sump to collect sediment.

 

Lake

An area permanently inundated by water.

Landslide

Means episodic downslope movement of a mass of soil or rock.

 

Manhole (Kent Standard Plan 4-1 (PDF, 365KB))

An underground constructed basin, usually barrel-shaped, that serves as access point into a channeled storm line or storm pipe.

 

MS4 = Municipal Separate Storm Sewer System

A conveyance, or system of conveyances; including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, manmade channels, flow controls, treatment facilities, or storm drains; operated and maintained by a municipality.

 

Natural Conveyance System Elements

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

 

Native Vegetation  

Plant species indigenous to the Puget Sound region that could occur or could have occurred naturally on the site, which are or were indigenous to the area in question. 

 

Nonpoint Source Pollution

Occurs when rainfall, snowmelt, or irrigation runs over land or through the ground, picks up pollutants, and deposits them into rivers, lakes, and coastal waters or introduces them into ground water. (See USEPA Factsheet) 

 

Nonstormwater Discharge

Any discharge to the MS4 or waters of the state that is not composed entirely of stormwater. 

 

NPDES = National Pollutant Discharge Elimination System

The part of the Clean Water Act which requires point source discharges to obtain permits. In Washington State, these permits, referred to as NPDES permits, are administered by the Washington State Department of Ecology.

 

Oil/Water Separator

A type of vault designed to provide a quiescent environment to separate oil from water.

 

Outfall

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

Point Discharge

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

 

Point Source Pollutant

Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events that often contain pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by an NPDES permit. The primary method to control storm water discharges is through the use of best management practices.

 

Pollutant or Contaminant

Anything that causes or contributes to pollution. Pollutants may include, but are not limited to: paints, varnishes, and solvents; oil and other automotive fluids; nonhazardous liquid and solid wastes and yard wastes; refuse, rubbish, garbage, litter, or other discarded or abandoned objects, and accumulations, so that the same may cause or contribute to pollution; floatables; pesticides, herbicides, and fertilizers; hazardous materials and wastes; sewage, fecal coliform and pathogens; dissolved and particulate metals; animal wastes; wastes and residues that result from constructing a building or structure; and noxious or offensive matter of any kind. 

 

Pollution Elbow (Sketch PDF 400-800KB)

A flow and pollution control device designed to capture and store stormwater runoff and pollutants, and then slowly release the less polluted runoff downstream at a slower rate. Also see FROP.

 

Pollution-generating impervious surface

An impervious surface considered to be a significant source of pollutants in surface and storm water runoff.. Such surfaces include those subject to vehicular use or storage of erodible or leachable materials, wastes, or chemicals, and which receive direct rainfall or the run-on or blow-in of rainfall. Thus, a covered parking area would be included if runoff from uphill could regularly run through it or if rainfall could regularly blow in and wet the pavement surface. Metal roofs are also considered pollution-generating impervious surface unless they are treated to prevent leaching.

 

Pollution-generating pervious surface

A non-impervious surface with vegetative ground cover subject to use of pesticides and fertilizers. Such surfaces include, but are not limited to, the lawn and landscaped areas of residential or commercial sites, golf courses, parks, and sports fields.

 

Pond (deepwater aquatic habitat)

Areas of open surface water that are less than twenty (20) acres in size that are either permanently inundated at mean annual water depths greater than six and six-tenths (6.6) feet, or permanently inundated at less than six and six-tenths (6.6) feet in depths that do not support rooted-emergent or woody plant species. (Sketch PDF 254KB)

 

Rain Barrel or Cistern

An above ground container used to collect and capture rain water for later use.

 

Receiving waters

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

 

Recharge

The flow to groundwater from the infiltration of surface and stormwater runoff.

 

Retention

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

 

Retention Facility

Facility designed to hold water for a considerable length of time and then consume it by evaporation, plant transpiration, or infiltration into the soil.

 

R/D Facility or Retention and Detention Facility

A type of drainage facility 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 surface and storm water runoff for a short period of time and then release it to the surface and storm water conveyance system.

 

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.

 

Sanitary sewer system

A conveyance, or system of conveyances, that is designed to convey domestic and commercial wastewater.

 

Sensitive Area or Critical Area

An area that possesses important natural functions and embodies a variety of important natural and community values. Such areas include wetlands, streams, fish, and wildlife habitat, geologic hazard areas, critical aquifer recharge areas, and flood hazard areas. If not conducted properly, development or alteration of such areas may cause significant impacts to the valuable functions and values of these areas and/or may generate risks to the public health and general welfare, and/or to public and private property. 

 

Sensitive Area Tract

A separate tract that is created to protect the sensitive area and its buffer.

 

Septic System

An onsite wastewater collection system.

 

Sewer System

The system of pipes and pump stations that collect and transport wastewater from homes and businesses to a wastewater treatment plant.

 

Slope

An inclined earth surface, the inclination of which is expressed as the ratio of horizontal distance to vertical distance.   

 

Source Control BMP or Source Control Best Management Practice

Source control tackles potential causes of pollution at their source. These potential sources exist inside and outside buildings. There are many pollution-prevention techniques and best management practices that serve to prevent, control, and treat contaminants before they enter the environment.

 

Stormwater 

Any surface flow, runoff, and drainage consisting of water from any form of natural precipitation, and resulting from such precipitation.

 

Stormwater Facility

Facilities that control the discharge of stormwater and remove pollutants. Stormwater facilities in Kent included storage facilities (ponds, vaults, underground tanks, and infiltration systems); water quality facilities (wetponds, biofiltration swales, constructed wetlands, sand filters, and oil/water separators); and conveyance systems (ditches, pipes, and catch basins).

   

Stormwater Management

The application of site design principles, construction techniques, procedures, activities and best practices to prevent flooding and to also prevent sediments and other pollutants from entering surface or ground water.

 

Stormwater System 

Facilities through which stormwater is collected, conveyed, or treated, including but not limited to inlets, conveyance pipes, pumping facilities, retention and detention basins, bioinfiltration facilities, drainage channels, and other drainage structures.

 

SWPP or Stormwater Pollution Prevention Plan

A document that describes the BMPs and activities to be implemented by an owner/operator to identify sources of pollution or contamination at a site, and the actions to eliminate or reduce pollutant discharges to stormwater, the MS4, and/or waters of the state.

 

Storm Drain System

An assembly of conveyance, collection, flow control, and treatment facilities used to collect and carry surface and stormwater to waters of the state. Link to Kent's public drainage map.

 

Stream

Areas where surface waters produce a defined channel or bed. A defined channel or bed is an area which demonstrates clear evidence of the passage of water and includes, but is not limited to, bedrock channels, gravel beds, sand and silt beds, and defined-channel swales. The channel or bed need not contain water year-round.

 

Structural BMP or Structural Best Management Practices

Constructed facilities or measures to help protect receiving water quality and control stormwater quantity.

 

Surface Water Design Manual 

The manual (and supporting documents as appropriate) describing surface and storm water design and analysis requirements, procedures, and guidance which has been formally adopted by rule.

 

Sump

A depression in the floor of a basement or Catch Basin where water collects. In a Catch Basin, stormwater is collected and any sediment (which is considered a pollutant) mixed with the water is allowed to settle in the sump for later removal.

 

Swale

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

 

SWMP or Stormwater Management Program

A set of actions and activities planned and implemented to meet the requirements of the Western Washington Municipal Stormwater NPDES Permit. In Kent, the Stormwater Management Program plan is updated annually, view the document pdf here.

 

TESC = Temporary Erosion and Sediment Control

Temporary plan, usually used for site development or demolition, to reduce and hopefully prevent polluted runoff from leaving a site. Erosion and sediment controls may be temporary or permanent.

 

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.

 

TMDL

A TMDL or Total Maximum Daily Load is 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.

 

Toxic

Poisonous, carcinogenic, or otherwise directly harmful to life.

 

Tract

A defined area of land.

 

Vault

An underground concrete structure designed to manage excess stormwater runoff on a developed site.

 

Vault, Filter

An underground concrete structure designed to manage and reduce pollutants from stormwater runoff on a developed site.

 

Waters of the state

Those waters as defined as “waters of the United States” in 40 CFR 122.2, within the geographic boundaries of the state of Washington, and those “waters of the state” as defined in Chapter 90.48 RCW, which includes lakes, rivers, ponds, streams, inland waters, groundwater, salt waters, and all other surface waters and water courses within the jurisdiction of the state of Washington.

 

Water Quality Treatment Facility

A drainage facility designed to reduce pollutants once they are already contained in surface and storm water runoff.

 

WDOE = Washington State Department of Ecology

 

WDOH = Washington State Department of Health

 

Wet Season

October 1 to April 30.

 

Wetland(s)

Areas that are inundated or saturated by surface water or groundwater 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. Wetlands do not include those artificial wetlands intentionally created from nonwetland sites, including, but not limited to, irrigation and drainage ditches, grass-lined swales, canals, detention facilities, wastewater treatment facilities, farm ponds, and landscape amenities, or those wetlands created after July 1, 1990, that were unintentionally created as a result of a road, street, or highway. However, wetlands include those artificial wetlands intentionally created to mitigate conversion of wetlands. For identifying and delineating wetlands, the Washington State Wetland Identification and Delineation Manual (Ecology, 1997) shall be used. Wetlands determined prior converted cropland (PCC) by federal agencies may still be considered wetlands by the city of Kent.