Urban drainage

Question 1

How is an urban hydrological cycle different to a rural one?

Answer 1

• increased evaporation - more surface detention due to more impermeable surfaces that water cannot infiltrate, so more availability of water to be evaporated, hotter due to UHI effect so increased evaporation
• less natural interception from vegetation eg. trees, grass, but increased interception from impermeable structures eg. buildings
• increased precipitation so input into water cycle is greater - air can hold more moisture so cloud formation increases
• increased surface runoff - more impermeable surfaces that water cannot infiltrate, leading to a shorter lag time
• more management in urban areas - more at risk due to economic value of property and businesses

Question 2

How is an urban hydrographic different to a rural one?

Answer 2

• increased peak rainfall - less interception and infiltration of rainfall leads to water reaching river more quickly, so lag time is shorter. Peak discharge will increase and rising/falling limb will be steeper

Question 3

What are the issues associated with urban river catchment management (SUDs)?

Answer 3

Increased river flow leads to flooding and erosion of river bank. During dry periods, flow decreases which can harm aquatic wildlife. Higher water temperatures can disturb ecosystems and pollution issues:

• sediment from building sites
• oil, grease and toxic chemicals from cars
• pesticides and nutrients from parks and gardens

Question 4

How did LA deal with flooding?

Answer 4

-hard engineering approach

• bank made from concrete to reduce friction meaning the river flows at a faster speed
• embankments which decrease the risk of flash flooding

Question 5

What were the problems with LA’s approach to dealing with flooding?

Answer 5

• unsustainable and expensive
• no vegetation or ecosystems so no biodiversity
• risk of earthquakes which could easily make concrete crack

Question 6

What are SUDs?

Answer 6

sustainable urban drainage systems

• a new approach to managing rainfall by using natural processes in the landscape to reduce and control flooding, and provide amenity for the community

Question 7

What are swales?

Answer 7

Shallow, vegetated channels designed to store and convey runoff and remove pollutants

• vegetation has a cooling effect which can reduce the UHI

Question 8

What is permeable paving?

Answer 8

Paving which allows water to filter through it rather than running off it, and then infiltrates directly into subsoil

Question 9

What are infiltration basins?

Answer 9

Shallow features where stormwater is stored which gradually infiltrates the soil of the basin floor.

• increase amenity value for community and vegetation reduced UHI through evapotranspiration

Question 10

What are green roofs?

Answer 10

eg. Cardiff university

• roofs which are partially/completely covered with vegetation, which can absorb and store rainfall, filter pollutants from rain, provide insulation, create habitats and reduce UHI through evapotranspiration

Question 11

What are soakaways?

Answer 11

Empty underground chambers which store water, and disperse surface and storm water into the ground

Question 12

What is river restoration?

Answer 12

the process of managing previously damaged rivers to reinstate natural processes and restore biodiversity. It is a part of river conservation, which aims protect, preserve, manage and restore

Question 13

Example of a river restoration project outside of the UK?

Answer 13

Cheonggyecheon stream restoration project:

• vegetation planted which reduces flow of water by encouraging infiltration and decreases flood risk, provides habitats and reduces UHI
• bridges and footpaths installed to make the area more accessible - cycle paths/walkways reduce emissions from traffic

potential problems:
- increased congestion and transport issues eg. rerouting roads
- expensive (money from taxpayers) causing political dispute
- no passing traffic = no passing trade for local businesses

Question 14

Example of a river restoration project in London?

Answer 14

River Lea - olympic park (2005-2012)

• aimed to restore biodiversity, provide access and amenity, and reduce flood risk
• 8kms river restored
• 2 million tons soil decontaminated
• 280 hectares brownfield sites cleared
• 20 million gallons contaminated groundwater treated
• 4000 homes with reduced flood risk
• walkways/cycle paths/bridges built to improve access and leisure

Question 15

How can river restoration projects affect urban drainage?

Answer 15

• vegetation - increases infiltration and decreases surface runoff so decreased flood risk
• embankments - made from permeable surfaces so water can infiltrate

Question 16

What are the benefits of SUD’s?

Answer 16

• enhanced biodiversity
• flood risk management
• improved air quality
• improved water quality

Question 17

What SUD’s are used in Olympic Park Stratford?

Answer 17

• porous asphalt strips (permeable paving) through pedestrian concourses - act as collection points for runoff and collect and convey water into tranches containing perforated pipes. The pipes divert the water back to the river course
• Swales - slow the flow devices
• Green roofs
• increased green space/grassland - encourage infiltration and acts as a leisure area

Question 18

What were the positives and negatives of SUD’s in Olympic Park?

Answer 18

positives
- enhanced biodiversity and new habitats created
- appropriate, carbon neutral and recycled materials used
- leisure areas for community
- reduced sources of water contamination

disadvantages
- increased use of nitrogenous fertiliser has led to widespread eutrophication (soil overly enriched with nutrients)