A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Q | Y | Z


The adhesion of atoms, ions, or molecules to a surface.

A layer of earth containing groundwater that can be used for human purposes.

Back to top ↑


A barrier constructed of compacted earth, often used in stormwater management BMPs such as rain gardens.

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, or completely filled with water.

Best Management Practices. Best available practices or devices that, when used by themselves or together, eliminate or reduce the contamination of surface and/or ground waters.

A designated area adjacent to and/or a part of a steep slope or landslide hazard area which protects slope stability, softening 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.

Back to top ↑


Catch Basin
A container that catches debris, sediment, and other items that would not readily pass through a sewer. These are typically located where a street gutter opens into a sewer.

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

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

Combined Sewer
A type of sewer system that collects sanitary sewage and stormwater runoff in a combined, single pipe system. Howard County does not have a combined sewer system.

Combined Sewer Overflow. CSOs are caused by large differences in flow between dry and wet weather, and can cause serious pollution problems.

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.

Critical Drainage Area
An area with a high potential for stormwater quantity (flooding) or quality problems. This can be due to a number of factors, including cumululative impacts of urbanization and development.

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.

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

Back to top ↑


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

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

Dispersed Discharge
Release of surface and stormwater 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.

A constructed channel whose top width does not exceed 10 feet at design flow.

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

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 man-made feature that collects, conveys, stores, or treats surface and storm water runoff. Drainage man-made 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.

Back to top ↑


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

Environmental Protection Agency

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

Back to top ↑


Underground water usually found in aquifers. Groundwater usually originates from infiltration. Wells tap the groundwater for water supply uses.

Back to top ↑


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

Harmful Pollutant
A substance that has damages an organism and may cause 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.

Back to top ↑


Illicit Discharges
Discharges of non-stormwater to the storm drainage system. Examples are discharges from internal floor drains, appliances, industrial processes, sinks, and toilets that are connected to the nearby storm drainage system. These discharges should be going to the sanitary sewer system, a holding tank, an on-site process water treatment system, or a septic system.

Impervious Surface
A hard surface area which prevents or slows 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 speeds when compared to natural conditions. 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.

Back to top ↑


Municipal separate storm sewer systems. Polluted stormwater runoff is commonly transported through Municipal Separate Storm Sewer Systems (MS4s), from which it is often discharged untreated into local waterbodies. To prevent harmful pollutants from being washed or dumped into an MS4, jurisidictions must obtain a permit and develop an operations and maintenance management program to control stormwater pollution.  MS4 permits are issued on a five year cycle.  In Maryland, MS4 permits are issued and enforced by the Maryland Department of the Environment (MDE).   

Back to top ↑


Natural Conveyance System Elements
Swales and small drainage courses, streams, rivers, lakes, and wetlands.

Nonpoint Source (NPS) Pollution
NPS 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)

National Pollutant Discharge Elimination System. The part of the Clean Water Act which requires point source discharges to obtain permits. These permits, referred to as NPDES permits, are administered by the Washington State Department of Ecology.

Natural Onsite Drainage Feature
A natural swale, channel, stream, closed depression, wetland, or lake.

Back to top ↑


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

Back to top ↑


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

Point Source Pollutant
Stormwater 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.

Back to top ↑


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

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

The process of collecting and holding surface and stormwater runoff with no surface outflow. This can improve water quality by allowing sediment clearing and slows the velocity of runoff, decreasing negative ecosystem effects.

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

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.

Back to top ↑


Safe Drinking Water Act

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.

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.

Stormwater Management Program

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.

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

Stormwater Management Program

Back to top ↑


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.

Poisonous, carcinogenic, or otherwise directly harmful to life.


Everyone lives in a watershed. A watershed is the total area of land that drains to a specific point—usually a stream or river.  Watersheds are looked at in different sizes.  Small local watersheds are where all stormwater, rain, snowmelt, and ground water flow to a small stream section, for instance the Little Patuxent River Watershed. Medium sized watersheds are a group of a few small watersheds flowing to the same river, for instance the Patuxent River Watershed. Large watersheds are a grouping of smaller watersheds that flow to a large body of water, for instance, we all live in the Chesapeake Bay Watershed because eventually all of our streams (small watersheds) and rivers (medium watersheds) flow to the Bay (larger watershed).

Back to top ↑