Frequently used terms

A

As built

A revised set of drawings submitted by a contractor upon completion of a project or a particular job. They reflect all changes made in the specifications and working drawings during the construction process, and show the exact dimensions, geometry and location of all elements of the work completed under the contract.

C

Catchment area

Also see drainage district and watershed. This term refers to the geography of an area of land from which water flows into a common outlet, such as a river, lake, or reservoir: in regards to stormwater, it is an area where stormwater may collect and flow into a river or drain.

D

Detention

Storage designed to eliminate or reduce the frequency of subsequent surface discharge. A detention, or dry, pond has a connection at the bottom of the basin and does not have a permanent pool of water. All the water runs out between storms and it usually remains dry.  Dry detention ponds are best used in areas where there is ten or more acres of land. On smaller sites, it is difficult to control water quality and other options may be more appropriate. The water then slowly drains out through the outlet at the bottom of the structure. Outlet structure is smaller than inlet. Detention volumes in retention ponds, dry detention ponds. Retention ponds with a detention value.

Drain

Drains come in various forms, including natural or artificial creeks or ditches, as well as pipes that carry stormwater.

Drainage district

Also see catchment area and watershed. Drainage districts according to the Michigan Drain Code (Public Act 40) are special purpose districts formed to manage drainage of land. Special purpose districts are units of government created to provide specialized services within the respective district. These districts can tax residents of the district for services. Geographically, special purpose districts may cross city, town and village boundaries. School districts, sewerage districts and drainage districts are all examples of special purpose districts.

F

Freeboard

A factor of safety usually expressed in feet above a flood level for purposes of floodplain management. The vertical distance between the upper design water level (flood level) and the crest of a waterway bank, dam or embankment, the underside of a bridge, or floor of a building.  For stormwater management, detention is freeboard.  A term used that describes how much air space that you have to put the water in.  Fills in where air was.

G

Green Infrastructure (GI)

The management of wet weather flows that use these processes, and to refer to the patchwork of natural areas that provide habitat, flood protection, cleaner air and cleaner water. At both the site and regional scale, Low Impact Design (LID)/GI practices aim to preserve, restore and create green space using soils, vegetation, and rainwater harvest techniques. LID is an approach to land development (or re-development) that works with nature to manage stormwater as close to its source as possible. LID employs principles such as preserving and recreating natural landscape features, minimizing effective imperviousness to create functional and appealing site drainage that treat stormwater as a resource rather than a waste product. As opposed to traditional engineering structures as curb and gutter projects and catch basins.

I

Illicit Discharge Elimination Program (IDEP)

In general, illicit discharges include any discharge into a storm drain system that is not entirely composed of stormwater. An illicit discharge is defined as any discharge to the municipal separate storm sewer system that is not composed entirely of storm water, except for discharges allowed under an NPDES permit or waters used for firefighting operations. These non-stormwater discharges can occur due to illegal connections to the storm drain system from any residential, commercial, or other establishments.

As a result of these illicit connections, contaminated wastewater can enter into storm drains or directly into local water ways without receiving treatment from a wastewater treatment plant. Illicit connections may be intentional or unknown to the business owner. These connections are most often due to the floor drains connected to the storm drainage system. Additional sources of illicit discharges are failing septic systems, illegal dumping practices, and the improper disposal of sewage from recreational practices such as boating or camping. Illicit discharges also can be generated by persons using antiquated methods for tasks such as cleaning pool filters, cleaning paint brushes, car washing and other common activities.

Read more information prepared by the Michigan Department of Environment, Great Lakes, and Energy (formerly Michigan Department of Environmental Quality, or DEQ) here.

L

Low-impact design (LID)

Low-impact design infrastructure used in developments is a term to describe a land planning and engineering design approach to manage stormwater runoff as part of green infrastructure. LID emphasizes conservation and use of on-site natural features to protect water quality. LID refers to systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat. The philosophy of LID is for post-project drainage conditions to mimic pre-project conditions. Before development occurs, rainwater infiltrates into the ground in the spaces between soil particles. The ground acts like a sponge, soaking up water and reducing runoff into streams and rivers.

M

Michigan Drain Code (Public Act 40)

Any drainage activities performed in the State of Michigan are generally governed by the Michigan Drain Code which provides guidelines and rules and administered by the County Drain Commissioner, the elected official in charge. The Drain Commissioner has jurisdiction over the established county drains and performs the duties set forth in the State of Michigan Drain Code. Basically, the Drain Commissioner administers the construction, maintenance, and improvement of county drains, and is responsible for the assessment of the costs incurred.

Municipal Separate Storm Sewer System (MS4)

The word municipal refers to a unit of local government, like a borough or a township, but may also refer to an organization responsible for the administration of a developed area. An MS4 is a system of drainage (including roads, storm drains, pipes, and ditches, etc.) that is not a combined sewer or part of a sewage treatment plant. During wet weather, pollutants are transported through MS4s to local water bodies.

N

Non-point source pollution

Non-point source pollution refers to diffuse contamination of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area.

National Pollutant Discharge Elimination System (NPDES)

The National Pollutant Discharge Elimination System (NPDES) is a program established by the Federal Clean Water Act and the Environment, Great Lakes and Energy Department of the State of Michigan. It is a permitting system that regulates point sources of water pollution, with the goal of improving water quality.

O

Orphan drain

Drains that were created or were put in to allow for drainage as subdivisions built in the 1980s and 1990s in rural areas. They are not managed by either the drain commissioner, water resources commissioner, the road commission, or the municipality. They were built as part of a development. A township, by state law, cannot manage drains.

An orphan drain has no legal mechanism set in place to perform and/or fund maintenance and improvement projects. The process to establish the orphan drains as part of a county system requires a board of determination.

P

Park

A large, public green area in a town used for recreation. This differs from a drain.

Point source pollution

Point source pollution has a single identifiable source of air, water, thermal, noise or light pollution. A point source has negligible extent, distinguishing it from other pollution source geometries.

R

Retention

Storage designed to eliminate or reduce the frequency of subsequent surface discharge. Wet ponds are the most common type of retention storage. Wet retention ponds are a stormwater control structure that provides retention and treatment of contaminated stormwater runoff. By capturing and retaining stormwater runoff, wet retention ponds control stormwater quantity and quality. The ponds natural processes then work to remove pollutants. Retention ponds should be surrounded by natural vegetation to improve bank stability and improve aesthetic benefits. Less effective than rain gardens and low-impact design toolbox.

Water is diverted to a wet retention pond by a network of underground pipes connecting storm drains to the pond. The system allows for large amounts of water to enter the pond, and the outlet lets out small amounts of water as needed to maintain the desired water level. Retention is often considered a component of green or low-impact development.

T

Treatment train

A sequence of stormwater treatments designed to meet the needs of a particular environment.

W

Watershed

Also see catchment area and drainage district. As defined by Patrick Lindemann in 1996: A system of many complex and interrelated sets of an ecosystem (layers) that are interdependent on a common flow of energy, material transport (waste removal), and nutrient input and output as a result of water collection, storage and movement. Learn more about Patrick’s definition and approach.