Urban Drainage

Question 1

why is flood risk high in urban areas?

Answer 1

short lag time
impermeable surfaces - more surface runoff

high peak discharge
precipitation higher and storms more intense - UHI

Question 2

What is catchment management?

Answer 2

A way of managing drivers and improving drainage
Looks at the whole river catchment and interactions between water and land

• aims to minimise flooding, drought and water pollution

Question 3

Hard engineering for catchment management

Answer 3

• man made structures
• often expensive
• damaging to ecosystems
  Examples:
  River straightening
  dams
  Channel lining with concrete (reduces friction, flow more)

Question 4

Soft engineering for catchment management

Answer 4

• land use management, works with the environment
• cheaper
  Examples:
  Afforestation
  Conservation
  Flood pIain zoning
  River restoration

Question 5

Example of catchment management

Answer 5

River Aire, Leeds
- embankments and channelisation used in city
- vegetation planted upstream to decrease surface runoff and increase lag time
- decreases flood risk in city

Question 6

What do SUDS do?

Answer 6

Use natural processes to manage flooding, sustainably
They help to:
- slow surface runoff
- reduce flood risk
- prevent water pollution
- create habitats and green spaces

Question 7

SUDS techniques

Answer 7

Swales - shallow, sloping channel, increases infiltration, reduces pollution, slows runoff

Rain garden - sloped retention area, captured water, infiltration reduces flooding

Balancing pond - captures and stored water, reduces flooding, habitat

Vegetated roof - intercepts rainfall, increases evapotranspiration, reduce flood, collects water

Permeable paving - used on roads and paths, rain filtered and stored under

Question 8

SUDS example

Answer 8

Leeds CITU, Stormwater
Homes redeveloped to manage flooding
- vegetated roof
- permeable paving

+ protects homes by reducing flooding
+ visual improvements

• cost £250 million
• expensive to buy

Question 9

What is river restoration?

Answer 9

Aims to restore rivers to a more natural state

Question 10

River restoration example and aims

Answer 10

Enfield, London
Aims to:
- reduce flood risk
- reduce runoff and pollution
- increase biodiversity

Groups involved: Defra + Thames water, local people and schools
- 1000 students did litter picking

Question 11

Why did Enfield need restoring?

Answer 11

Urbanisation, increased impermeable surfaces and flood risk
- 9000 homes at risk

Increased levels of pollutants in river due to runoff from roads

Domestic pollution
10% of houses wastewater pipes go into river

Question 12

Evaluation of Enfield restoration

Answer 12

+ flood risk was reduced, no flooding after heavy rain in december 2013
+ 67% reduction in ammonia
+ 43% reduction in nitrogen
+ increase in some species eg eels

• pollution and litter still an issue

Question 13

methods they used

Answer 13

SUDS
- vegetated trenches - absorb runoff, decrease flood risk

• wetlands - improved filtration and water quality
• rain planters in schools, manage flow of water, reducing floods, allows for education on management