An urban stream is a formerly natural waterway

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 that flows through a heavily populated area

Urban area

An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets.Urban areas are created and further...

. Urban streams are often significantly polluted

Water pollution

Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

, due to urban runoff

Urban runoff

Urban runoff is surface runoff of rainwater created by urbanization. This runoff is a major source of water pollution in many parts of the United States and other urban communities worldwide.-Overview:...

 and combined sewer outflows.

Government agencies may alter the flow and/or course of an urban stream to prevent localized flooding

Flood

A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

, using a construction technique called channelization and a collection of related practices collectively known as river engineering

River engineering

River engineering is the process of planned human intervention in the course, characteristics or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and behaviour of rivers since before recorded history - to manage the water resources,...

. These techniques may include lining a stream bed

Stream bed

A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...

 with concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 or other hardscape

Hardscape

Hardscape, in the practice of landscaping, refers to the paved areas like streets & sidewalks, large business complexes & housing developments, and other industrial areas where the upper soil profile is no longer exposed to the actual surface of the Earth...

 materials, and/or diverting the stream into culvert

Culvert

A culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...

s and storm sewers. Some urban streams, such as the subterranean rivers of London

Subterranean rivers of London

The subterranean or underground rivers of London are the tributaries of the River Thames and River Lea that were built over during the growth of the metropolis of London...

, run completely underground. These modifications have often resulted in loss of habitat for fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and other species, downstream flooding due to alterations of flood plains, and further deterioration of water quality

Water quality

Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...

.
Some communities have initiated stream restoration

Stream restoration

Stream restoration or river restoration, sometimes called river reclamation in the UK, describes a set of activities that help improve the environmental health of a river or stream. Improved health may be indicated by expanded habitat for diverse species and reduced stream bank erosion...

 projects, using techniques such as daylighting

Daylighting (streams)

In urban design and urban planning, daylighting is the redirection of a stream into an above-ground channel. Typically, the goal is to restore a stream of water to a more natural state...

, in an attempt to correct the problems caused by previous stream alteration efforts, as well as to address stream bank erosion caused by heavy stormwater

Stormwater

Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

 runoff volumes.

See also

• Nationwide Urban Runoff Program (NURP) - U.S. research program
• Nonpoint source pollution
  Nonpoint source pollution
  Nonpoint source pollution refers to both water and air pollution from diffuse sources. Nonpoint source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Nonpoint source air pollution...
  
  
• Subterranean river
  Subterranean river
  A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth ....
  
  
• Water pollution
  Water pollution
  Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
  
  

External links

• Ecosystem Effects of Urban Stream Restoration (U.S. Environmental Protection Agency)