Sewers and storms glossary

You can get definitions for the sewer and storms terms we use.

Definitions of terms and acronyms 

10-year 1-hour design

This design criteria is used for determining storm sewer size, and assumes 1.25" falling in 1 hour in a SCS Type II storm event.

100-year 24-hour design

This design criteria is used for determining storm sewer size, and assumes 5.9" falling in 24 hours in a SCS Type II storm event.

100-year flood

A flood so large, it has a 1% chance of occurring in any given year. The term 100-year is a measure of the size of the flood, not how often it occurs. Several 100-year floods can occur within the same year. Also called the base flood.

100-year storm

A precipitation event used for stormwater drainage system design, based on a frequency analysis of historical data. A 100-year storm means that there is a 1% probability of such a storm occurring at that location that year. Likewise,

  • A 10-year storm has a 10% probability of occurring.
  • A 2-year storm has a 50% probability of occurring.

Backwater valve

A backwater valve is a backflow prevention valve designed to prevent sanitary sewage from backing up through your floor drain from the sanitary system into a building.


Bassett Creek Watershed Management Commission.


Best Management Practice. These are structural, non-structural and managerial techniques that are recognized to be the most effective and practical means to prevent and/or reduce point source and non-point source pollution, in order to promote stormwater quality and protection of the environment.

Combined sewage

Wastewater and storm drainage carried in the same pipe.


Combined Sewer Overflows occurs when heavy rain or melting snow causes sanitary sewers to overflow into stormwater drainpipes. This allows sewage to mix with runoff from buildings, parking lots and streets and flow, untreated, into the Mississippi River.


Environmental Protection Agency

Erosion control

Anything that will keep soil on site and out of streets and storm drains. This includes silt fencing, berms (barriers), properly placed hay bales, grass and swales.

Federal disaster area

Before a community is eligible for disaster assistance from the federal government, it must be declared a Federal Disaster Area. These declarations are issued in fewer than 50% of flood occurrences.


Federal Emergency Management Agency

FEMA- designated flood zone

FEMA designates flood zones, which are zones where water overflows from a river or stream during extreme storm events. Homes in these zones require special flood insurance.

First flush

The first portion of a rain event washed out approximately 90% of the pollutants in the first part of a rain event.

Flood insurance

There are two types of Flood Insurance that compensate for physical property damage resulting from flooding:

  • Required Insurance, for properties located in FEMA designated flood zones (Zone A or B)
  • Optional Insurance, that is recommended for homes in areas that have been prone to past flooding (Zone C)

Flood plain

A natural area adjacent to a stream or river where water overflows during extreme storm events. (same as flood zone)


Floodproofing is making efforts to prevent moisture from forming, or preventing water from entering, your home.

Flood zone

A natural area adjacent to a stream or river where water overflows during extreme storm events. (same as flood plain)

Grit chamber

A concrete basin that allows larger grit particles (sand, dust, seeds, etc.) to settle out, while lighter materials pass through to the treatment process.


Water that flows below the ground surface through saturated soil, glacial deposits or rock.

Holding pond

A pond or basin, usually built in a depression in the ground, built to store excess stormwater runoff for a limited time. Holding pond types are either dry or wet.

I & I

Inflow and Infiltration

Inflow & infiltration

I & I occurs when groundwater and stormwater enters the sanitary sewer system.

Inflow is water that is dumped into the sanitary sewer system through improper connections, such as rainleaders, sump pumps & area drains.

Infiltration is groundwater that enters the sanitary sewer system through leaks or breaks in the pipe.


Integrated Pest Management. Develops and promotes the use of integrated, ecologically sound pest management programs.

Impervious surface

A constructed hard surface that cannot be penetrated by water, which causes water to run off in greater quantities. Examples include roadways, rooftops, sidewalks, driveways and parking lots.

Interceptor tunnels

Any large volume pipe or conduit having a deeper invert elevation to accept or intercept the sewer flow of smaller sanitary sewers. Interceptors are mostly owned by MCES and serve a number of regional areas.


Metropolitan Council Environmental Services


Minnehaha Creek Watershed District.


Vertical openings that serve as access holes for maintenance in sanitary or storm drain infrastructure. Manholes run from the sewer below the street up to street level, where they are covered by manhole covers.


Minnesota Department of Transportation


Minnesota Pollution Control Agency


Minneapolis Park & Recreation Board


Mississippi Watershed Management Organization.


National Flood Insurance Program


National Pollutant Discharge Elimination System

Created in Section 402 of the Clean Water Act in 1972 by the Environmental Protection Agency (EPA) to protect water quality by regulating the discharge of pollutants to lakes, streams, wetlands and other surface waters. The NPDES program gave the EPA the authority to regulate discharges into the nation's waters by setting limits on the water mixed with waste matter that can be introduced into a body of water from an operating and permitted facility.


Nitrogen and phosphorus occur naturally in water, soil and air. These nutrients are both present in fertilizer, which aids the growth of agricultural crops. Both nutrients are vital to the growth of plants within area lakes and rivers. Nutrients can also contribute to alga blooms and odors in standing bodies of water, such as lakes and ponds, in the spring.


The point where wastewater or drainage discharges from a sewer pipe, emptying into a receiving body of water.

Overflow regulator

A device in combined sewer systems for diverting wet weather flows that exceed downstream capacity to an overflow.

Peak flow

The maximum flow that occurs over a specific length of time. (i.e.: daily, hourly, instantaneous)

Pumping station /lift station

A mechanical device in a sewer or water system that moves liquids to a higher level via a pump and a forcemain.

Rain barrel

Rain barrels collect rainwater, which can be used in gardens and lawns, as well as preventing excessive runoff.

Rain garden

Rain gardens are native plant gardens that are designed to reduce the amount of stormwater and pollutants from entering our streams, lakes and rivers, as well as to aesthetically improve properties.


Rooftop drains are also called rainleaders. Rainleaders that are connected to the sanitary sewer system are one of the major causes of CSO’s. Rainleaders may be internally or externally connected to the sanitary system.

Rate control

Rate control refers to controlling the rate of runoff using structures to simulate pre-construction conditions.

Receiving waters

A lake, river, pond or creek that receives stormwater runoff from storm drainpipe.


Run-by occurs when a high magnitude storm occurs and the flow in the street is going too fast to enter the storm drain inlet, usually a catch basin, and ‘runs by’.


Water from rainfall or snowmelt, which flows across the ground surface into drainage facilities, rivers, streams, ponds, lakes and wetlands or shallow groundwater.

Sanitary sewer

A sanitary sewer is a pipe located in a street or easement that is designed to transport wastewater away from sanitary fixtures inside your house or place of business.


Shingle Creek Watershed Management Commission


Sediment is material suspended in water, that consists mostly of soil, but can also contain cigarette butts, litter, etc., which is carried by stormwater into the city's storm drain system and eventually into a body of water.


The waste and wastewater discharged into sewers from homes and industry.

Site plan review

Site Plan Review is a regulatory process in which the City seeks to ensure that land being developed for commercial, industrial, or residential use is developed, or redeveloped, and operated in a way that complies with City codes and is compatible with the surrounding community.


Standard Operating Procedure


Sanitary Sewer Overflow: Untreated or partially treated sewage overflows from a sanitary sewer collection system.

Storm drain

Any underground pipe or conduit designed to carry only stormwater to a known outfall. Same as storm sewer.

Storm drain outfall

A storm drain outfall is the point where a storm system discharges into a body of water. Road sand, salt, trash and lawn fertilizer can also be carried along with this water, although grit chambers may remove a portion of these suspended solids.

Storm sewer

Any underground pipe or conduit designed to carry only stormwater to a known outfall. Same as storm drain.


Stormwater is rainwater, snowmelt runoff or precipitation that accumulates in stormwater storage systems during and immediately following a storm event, that enters the storm drain system and empties into lakes, rivers and streams.

Surface runoff

The portion of rainfall that moves over the ground toward a lower elevation and does not infiltrate into the soil.

Surface water

Water that remains on the surface of the ground, including rivers, lakes, ponds, reservoirs, streams and wetlands, whether natural or artificial, public or private.


Total Suspended Solids


To become a developed city, or changing from rural to an urban state.


Watershed Management Organization


Wastewater (mostly water, with a small portion of dissolved and suspended solids) is water that has been used and discharged by homes, businesses and industries. Wastewater comes from sinks, bathtubs, floor drains and toilets.

Waters of the state

All streams, lakes, ponds, marshes, watercourses, waterways, wells, springs, reservoirs, aquifers, irrigation systems, drainage systems and all other bodies or accumulations of water, surface or underground, natural or artificial, public or private, which are contained within, flow through, or border upon the state or any portion thereof. (as defined in Minnesota Stat. § 115.01, subd. 22)


A watershed, also known as drainage area or catchment, is the specific land area that drains water into a lake, river or other body of water.

Watershed management organization

Watershed Management Organizations are creations of the state, and are appointed by the cities in which they are located. They may or may not have permitting authority. Also known as a WMO.


An area where the ground is temporarily, seasonally, or permanently saturated by surface water or groundwater, and that, under normal circumstances, is occupied by water-loving or water-tolerant vegetation.


A regulating device in a sewer that permits dry weather flow in a combined sewer to enter an interceptor, but causes the storm flow to leap over for a controlled overflow.

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Surface Water & Sewers

Public Works




Public Service Center
250 South 4th St, Room 300
Minneapolis, MN 55415

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