An urban stream is a formerly natural

waterway A waterway is any Navigability, 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 ways. A first distinction is ...

that flows through a heavily populated area. Often times, urban streams are low-lying points in the landscape that characterize catchment urbanization. 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 Precipitati ...

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 surface runoff, urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the se ...

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. One is ''physical.'' The other is ''economic water scarcity''. Physic ...

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

flood A flood is an overflow of water (list of non-water floods, 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 of significant con ...

ing by

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 b ...

: lining

stream bed A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...

s with

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

or other

hardscape Hardscape is hard landscape materials in the built environment structures that are incorporated into a landscape. This can include paved areas, driveways, retaining walls, sleeper walls, stairs, walkways, and any other landscaping made up of ...

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 (fluid conveyance), pipe, reinforced concrete or other materia ...

s and

storm sewer A storm drain, storm sewer (United Kingdom, United States, U.S. and Canada), highway drain, surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to Drainage, drain excess rain an ...

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 tributary, tributaries of the upper estuary of the River Thames, Thames (the Tideway) that were Subterranean river, built over during the growth of the metropo ...

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

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

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. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

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 ...

Stressors

Toxicant A toxicant is any toxic substance, whether artificial or naturally occurring. By contrast, a toxin is a poison produced naturally by an organism (e.g. plant, animal, insect, bacterium). The different types of toxicants can be found in the air, so ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

ic concentrations, available nutrients, temperature (and light), and

dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...

are key stressors to urban streams.

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 develop ...

projects in an attempt to correct the problems caused by alteration, using techniques such as daylighting and fixing stream bank

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

caused by heavy

stormwater Stormwater, also written 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 lan ...

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 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. Keep in mind the status of water quality is difficult to assess in urban areas because of the complexity of the pollutions sources. 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 located in Central New York, immediately northwest of and adjacent to Syracuse, New York. The southeastern end of the lake and the southwestern shore are industrial areas and expressways; the northeastern shore and northwestern ...

. 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. Hydrology plays a key role in urban stream syndrome. As urbanization of these streams continue, there is in turn a decrease in the perviousness of the catchment to precipitation, which leads to a decrease in the infiltration and an increase in the

surface runoff Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to ''channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

. This can cause problems during flood discharges. For example, flood discharges in urban catchments were at least 250% higher in urban catchments than in forested catchments in New York and Texas during similar storms.

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
Suspended Sediment and Discharge in a West London River
Hydrology and urban planning Water pollution Environmental engineering Water streams Rivers Hydrology Fluvial landforms