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Can Blue-Green Infrastructure decrease flood risk?

Society’s need to build more and more on undeveloped land is decreasing the amount of space available for surface water to drain naturally within our urban areas. This is a problem which will only increase in the future as approximately 83% of the UK population currently live in towns and cities, which is up from 80% in 2007.

The DEFRA 25 Year Plan which was released in early 2018, highlights the fact that we “build on approximately 17,000 hectares of undeveloped land each year”. To combat the effects of surface water flooding from new developments, the plan aims to “embed an ‘environmental net gain’ principle for developments including housing and infrastructure” and will action this by “producing stronger new standards for green infrastructure”.

Until relatively recently when a new development was planned, the standard option for drainage was typically grey – concrete, with systems such as surface water gullies, culverts and channel drains being the norm. All of these are designed to take water from a low point and feed it quickly into a sewer drainage network, stream, river or the sea. While this is an effective way to direct surface water away from our urban areas, in certain circumstances such as periods of extreme heavy rainfall, conventional drainage systems can quickly become overwhelmed. Using green space to manage surface water and implement a more natural approach to urban drainage, enables water to be controlled closer to the source. This reduces the chances of traditional drainage systems becoming overwhelmed.

 

Blue-Green infrastructure aims to manage the risk of flooding whilst reintroducing a more natural water cycle into urban environments and allowing multi-functional land use to generate benefits for the environment, society and the economy. The natural water cycle is characterised by high evaporation, high infiltration, and low surface water runoff.

Blue infrastructure includes features that retain water, such as detention basins, ponds and wetlands.  Green infrastructure applies to natural land or is plant based, including woodlands, domestic gardens, green open space and parks.

Both types of infrastructure are designed to attenuate flow before it enters a watercourse and provide areas where water can be stored, infiltrated and harvested for re-use. A benefit of blue-green infrastructure features is that they act as natural cleaning agents, reducing the amount of contaminants and sediment in surface water runoff through settlement or biological breakdown of pollutants.  New developments provide better opportunities to apply and utilize blue-green infrastructure, as old developments require retrofitting and may present less opportunities to apply it due to how the development was built. Blue-green infrastructure also fits within the scope of natural sustainable drainage systems (SuDS) and can help to reduce surface water runoff in the urban environment. Download our ‘An Introduction to SuDS’ booklet for more information on this.

 

Benefits of Blue-green infrastructure

Blue/green infrastructure can provide many benefits, such as:

  • Reducing the amount of surface water which is fed directly into traditional systems.
  • Reducing the risk of flooding.
  • Improving the amenity of an area, providing attractive, usable space for communities.
  • Improving air quality as trees and plants filter out air pollutants from industrial activity and motor vehicle emissions.
  • Improving water quality by removing pollutants and contaminants in runoff.
  • Providing habitats for wildlife.
  • Improving biodiversity.

 

 

As the climate changes and the population increases, blue/green infrastructure will be crucial to the wellbeing of the communities who live and work in our towns and cities.  They are an important measure in reducing the likelihood of traditional drainage systems becoming overwhelmed and flooding many properties. Through creating more open, green spaces, not only will this have positive effects for flood risk, but they will benefit the amenity of an area, providing attractive, useable space for communities. If we also factor in the natural flood management benefits that green spaces offer too, the value/environmental net gain increases even more.

Click here to download our Blue-green infrastructure resource

 

Sources: Statista.com

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