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Catchment Management and SUDS

Issues associated with catchment management in urban areas and the development of sustainable urban drainage systems (SUDS).

The need for sustainable drainage

Changes to drainage systems in urban areas occurred because of the need to channel water away from vital and expensive industry and housing. In the past little thought was given to the ecological impact of these changes and to the COST of taking such actions. Many rivers were straightened or channelised, or put into tunnels under the ground as culverts, or ponds and lakes drained without a thought for the longer-term consequences of those actions. Increased urban flooding as a result of using impermeable surfaces is also a major problem.

In the 20th Century hard engineering was used with the goal of drainage systems being FAIL SAFE, this is a design feature that in the event of flood failure, inherently responds in a way that will cause no or minimal harm to other equipment, the environment or to people. Many old concrete flood channels in urban areas were designed this way. Channelisation was often involved, a method of river engineering that widens or deepens rivers (and often uses concrete) to increase the capacity for flow volume at specific sections of the river. Used in urban areas to reduce flooding. An example of this is the Los Angeles River, which flows through a concrete channel on a fixed course, which was built after a series of devastating floods in the early 20th century. 1

The Los Angeles River receiving the Tujunga Wash (right) near Colfax Ave. in Studio City, California. View is to the west by Junkyardsparkle [CC BY-SA 3.0  (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons 2

The Los Angeles River receiving the Tujunga Wash (right) near Colfax Ave. in Studio City, California. View is to the west
by Junkyardsparkle [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons 2

The value of sustainable drainage

Drainage systems have an amenity value to people and cities, this means that they have value in terms of water resource management, provision of habitat for wildlife, recreational value for people, community facilities and even in moderating urban climates. Water quality is also regulated and moderated by drainage systems, and this is seen as an increasingly important aspect of urban drainage systems. Now, in the 21st century, urban planners are paying far closer attention to the environmental and sustainability aspects of any changes they make to natural drainage systems in urban areas.

There are 2 major areas to consider;

  1. Urban catchment management - the management of urban water and surface water runoff within a given urban drainage basin
  2. SUDS - Sustainable Urban Drainage Systems, designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges

Some of the major issues associated with the management of urban catchments include:

  • Water Pollution - the degradation of urban water due to the addition of unwanted materials. The major pollutants found in runoff from urban areas include, and viruses
  • Sources of water pollution in urban areas include sediment from construction, oxygen-demanding substances, road salts, heavy metals from cars and industrial processes, petroleum hydrocarbons, pathogenic bacteria, pesticides from parks and gardens
  • Controlling increased river flows in urban areas during wet periods leads to flooding and increased erosion
  • Decreased river flows in urban areas during dry periods causes extremely low flows and can damage fish spawning grounds and aquatic vegetation
  • Higher water temperatures from increased urban air temperatures and discharged waste water can disturb ecological balance 3

SUDS

To combat these issues urban planners are moving towards Sustainable Urban Drainage Systems (SUDS). The idea behind SUDS is to try to replicate the drainage patterns of natural systems by using cost-effective solutions with low environmental impact to drain away dirty and surface water run-off through collection, storage, and cleaning before allowing it to be released slowly back into the environment, such as into water courses. This is to counter the effects of conventional drainage systems that often allow for flooding, pollution of the environment – with the resultant harm to wildlife – and contamination of groundwater sources used to provide drinking water. These SUDS provide ecosystem services, which are benefits obtained from the regulation of ecosystem processes, in this case urban river systems, such as climate regulation, flood regulation, water purification and waste management, pollination or pest control.

Swale at NGP
 

Swale at Newcastle Great Park with reeds

The principles of SUDS solutions should be a drainage system;

  1. storing runoff and releasing it slowly (attenuation)
  2. harvesting and using the rain close to where it falls
  3. allowing water to soak into the ground (infiltration)
  4. Slowly transporting (conveying) water on the surface
  5. filtering out pollutants 6
  6. allowing sediments to settle out by controlling the flow of the water4

Examples of SUDS

 

  1. Green roofs/rain gardens – these cover the roof of a building with vegetation cover/landscaping. The roof is likely to consist of an impermeable layer, a substrate or growing medium and a drainage layer, designed to intercept and hold precipitation, reducing the volume of runoff and lowering peak flows.
  2. Paving which allows rainwater to soak through the cracks between slabs so is better than concrete and tarmac
  3. Swales, which are shallow, broad and vegetated channels designed to store and/or move runoff and remove pollutants. Can pass the runoff to the next stage of treatment and can be designed to promote infiltration where soil and groundwater conditions allow.
  4. Retention ponds - small lakes that store storm water and allow for its treatment. Support emergent and submerged aquatic vegetation along their shoreline. Sediments settle out in the pond and plants can uptake pollutants.
  5. Wetlands - can be built as part of SUDS to remove fine sediments, metals and particulates, and dissolved nutrients. Wetlands mainly treat polluted runoff, provide attenuation and deliver biodiversity and amenity. 5

NEXT TOPIC - River Restoration and Conservation

SOURCES

1- The River Project - The Los Angeles River. Accessed 12th January 2020 from https://www.theriverproject.org/learn/the-los-angeles-river-watershed

2- Junkyardsparkle [CC BY-SA (https://creativecommons.org/licenses/by- sa/3.0)] Accessed 12th January 2020 from https://commons.wikimedia.org/wiki/File:L.A._River_Tujunga_Wash_under_Colfax.jpg

3- Department for environment, food and rural affairs (2012) Tackling water pollution from the urban environment. Accessed 11th January 2020 from https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/82602/consult-udwp-doc-20121120.pdf

4- Susdrain (2020) – SUDS principles - Accessed 11th January 2020 from https://www.susdrain.org/delivering-suds/using-suds/suds-principles/suds-principals.html

5- Essex County Council (2020) What are sustainable drainage systems (SuDS)? Accessed 11th January 2020 from https://flood.essex.gov.uk/new-development-advice/what-are-sustainable-drainage-systems/

 

Posted by Rob Gamesby April 2020

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