An urban stream is a formerly natural

waterway A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary ...

that flows through a heavily populated area. Urban streams are often polluted by

urban runoff Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain , storms and other precip ...

and

combined sewer A combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the sewage gets dil ...

outflows.

Water scarcity Water scarcity (closely related to water stress or water crisis) is the lack of fresh water resources to meet the standard water demand. There are two types of water scarcity: physical or economic water scarcity. Physical water scarcity is whe ...

makes flow management in the rehabilitation of urban streams problematic.

Description

Governments may alter the flow or course of an urban stream to prevent localized

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

river engineering River engineering is a discipline of civil engineering which studies 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 be ...

: lining

stream bed A stream bed or streambed is the bottom of a stream or river ( bathymetry) or the physical confine of the normal water flow ( channel). The lateral confines or channel margins are known as the stream banks or river banks, during all but fl ...

s with

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

or other hardscape materials, diverting the stream into

culvert A culvert is a structure that channels water past an obstacle or to a subterranean waterway. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. In the United Kingdo ...

s and

storm sewer A storm drain, storm sewer ( United Kingdom, U.S. and Canada), surface water drain/sewer ( United Kingdom), or stormwater drain ( Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious su ...

s, or other means. Some urban streams, such as the

subterranean rivers of London The subterranean or underground rivers of London are or were the direct or indirect tributaries of the upper estuary of the Thames (the Tideway), that were built over during the growth of the metropolis of London. They now flow through culver ...

, run completely underground. These modifications have often reduced habitat for

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

and other species, caused downstream flooding due to alterations of

flood plain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

s, and worsened

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

Restoration efforts

Some communities have begun

stream restoration Stream restoration or river restoration, also sometimes referred to as river reclamation, is work conducted to improve the environmental health of a river or stream, in support of biodiversity, recreation, flood management and/or landscape developm ...

projects in an attempt to correct the problems caused by alteration, using techniques such as

daylighting Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting. Particular attention is given to daylighting while designing a b ...

and fixing stream bank

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

caused by heavy

stormwater Stormwater, also spelled storm water, is water that originates from precipitation ( storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed l ...

runoff. Streamflow augmentation to restore habitat and aesthetics is also an option, and recycled water can be used for this purpose.

Urban stream syndrome

Urban stream syndrome (USS) is defined as a consistent observed ecological degradation of streams caused by urbanization. This kind of stream degradation is commonly found in areas near or in urban areas. USS also considers hydrogeomorphology changes which are characterized by a deeper, wider catchment, reduced living space for biota, and altered sediment transport rates. This could be from mining and deforestation, but the main cause can be attributed to urban and suburban development. This is because such land use has a domino effect that can be felt tens of kilometers away. Consistent decrease to ecological health of streams can be from many things, but most can be directly or indirectly attributed to human infrastructure and action. Urban streams tend to be “flashier” meaning they have more frequent and larger high flow events. Urban streams also suffer from chemical alterations due to pollutants and waste being uncleanly dumped back into rivers and lakes. An example of this is

Onondaga Lake Onondaga Lake is a lake in Central New York, immediately northwest of and adjacent to Syracuse, New York. The southeastern end of the lake and the southwestern shore abut industrial areas and expressways; the northeastern shore and northwestern e ...

. Historically one of the most polluted freshwater lakes in the world, its salinity and toxic constituents like mercury rose to unsafe levels as large corporations begun to set up shop around the lake. High levels of salinity would be disastrous for any native freshwater marine life and pollutants like mercury are dangerous to most organisms. Higher levels of urbanization typically mean a greater presence of Urban Stream Syndrome.

Treatment

Many water managers treat USS by directly addressing the symptoms, most commonly through channel reconfiguration that includes reshaping rock to address altered hydrology and sediment regimes. In spite of having ecological objectives, this approach has been criticized for addressing physical failures in the system without improving ecological conditions.

References

Bibliography

* {{cite book , last1=Riley , first1=Ann L. , last2=Leopold , first2=Luna B. , title=Restoring Streams in Cities: A Guide for Planners, Policymakers, and Citizens , url=https://books.google.com/books?id=2NyTJHrDYpkC&q=Ann+Riley+restoring+streams , year=1998 , publisher=Island Press , location=Washington, DC , isbn=978-1-55963-042-9

External links

Urban Waters Program
- U.S. Environmental Protection Agency (EPA)
Ecosystem Effects of Urban Stream Restoration
- EPA Hydrology and urban planning Water pollution Environmental engineering Water streams Rivers Hydrology Fluvial landforms