Nottingham SciBar: Flooding and Blue-Green Cities

The Great Notts Flood - 2009
 

Flooding is the UK's most serious natural hazard, with 1 in 6 properties are at risk of flooding. Climate change is set to make flooding even worse. The 2007 floods cost £3.2 billion, and the 2014 floods have already cost more than £1 billion. These led to the government announcing a £540million boost in funding in the 2016 budget, and £160million to be spent on the maintenance of flood defences over the next five years.

Nottingham isn't immune to flooding, having been swamped numerous times in the 1930's and 1940's. In fact, the city centre had floods as recently as 2014 and Southwell suffered major flooding in 2013. There is a huge clean-up operation involved, with sediment as big an issue as water.

Most cities have grey infrastructure, a traditional drainage system designed to remove rainwater as quickly as possible. The water flows into combined sewers where the surface water meets foul water. But grey infrastructure isn't designed for sustainability, managing water quality, biodiversity or amenities.

So, how do we deal with flood risk in our impermeable cities?

In Philadelphia, they have a greener vision. Instead of grey infrastructure, they are looking at blue-green infrastructure which slows water down, controls water at the source and offers storage. The idea is to look at the whole catchment area, not just the downstream areas that are at a direct risk of flooding.

A blue-green city will work with nature to introduce a natural water cycle – to create a multi-functional landscape, where there is connectivity between the blue-green spaces that not only deal with water better, but also look much nicer.

There are many blue-green options available to a city. Bioswales are areas of greenery in cities that act as source control, intercepting rainwater. On a similar vein, eco-roofs with plants on top of buildings, such as the Orchard hotel in Nottingham absorb heavy rain water, while helping to insulate the building. These are an effective way of reducing flood risks, and plans are underway to install an eco-roof on Vic Centre, but there are draw backs. You cannot put them onto listed buildings, or on particularly sloped roofs. Green walls are practically the same thing, only vertical. Both of these options improve bio-diversity, as they provide a suitable home for bees.

Downspout disconnectors help rainwater flow from gutters into gardens rather than sewers. Treatment trains are linked areas that help deal with sediment; there are three stages ending in a detention pond. A further option would be to re-meander rivers to slow down the flow of water.

Water butts and permeable paving also help, but are not quite as blue-green.

In China, they are looking at building ‘sponge-cities’, featuring greenery that would absorb rainwater so that it could be used in the dry season. Closer to home, Ribblesdale Road in Sherwood uses rain gardens to help remove pollutants from the water flowing into the river. Rainscape in Wales are even building a blue-green school.

At the minute, blue-green infrastructure is very ad-hoc. There is nothing to bring it all together to create a true blue-green city. There are also a number of uncertainties and barriers to creating such an infrastructure:

Physical science uncertainty:

• Asset management and performance
• Do the models reflect reality?
• Impacts of climate change

Socio-political uncertainty:

• Capital cost
• Public preferences (such as choice of plants in swales)
• Stewardship of blue-green infrastructure
• How do we quantify and monetise the benefits?

However, there are, of course, a number of benefits to blue-green infrastructure:

• Water quality
• ater quantity management
• Society – aesthetics, physical & mental health
• Economy – it's cheaper than traditional grey infrastructure
• Future adaptability

Among the general public, there is a low awareness and understanding of the purpose and function of blue-green infrastructure. There is also some discontent over having to pay for green streets, especially when your taxes are paying for greenery on other people's streets, or if it causes a loss of parking spaces. In general, people are either for or against blue-green infrastructure and there is little evidence of opinions changing over time.

We still need grey infrastructure, but we can supplement with blue-green infrastructure. Most of the time, we're not under flood conditions so why not have multi-functional benefits?

SciBar returns to The Vat & Fiddle on the 27th of April at 7:30pm where Professor Stephen Coombes from the University of Nottingham will be discussing ‘Mathematical Neuroscience: A new discipline for understanding the brain’.

Nottingham SciBar website