2.14. Urban Drainage

Question 1

How does urbanisation affect water movement?

Answer 1

• Urban areas are designed to shed water quickly -> sloping roofs, smooth rounded guttering and cambered roads contribute to rapid movement of water away from the surface
• Soil moisture storage will vary according to ground conditions
• Reservoirs, lakes, ponds, swimming pools are permanent stores but vulnerable to evaporation
• Pollutants from urban areas are being washed into rivers or into the ground and once polluted, groundwater is extremely difficult to clean up
• Warmer air in cities can hold more moisture
• Dust and pollution makes more condensation nuclei
• Interception storage is reduced owing to replacement of vegetation by impermeable structures such as building, roads and pavements engineered to drain water rapidly into the nearest river.
• In winter, grit is sprayed on roads and washed into water systems
• Central urban is 75-100% impermeable surface and 30% evapotranspiration

Question 2

Location of Lamb Drove

Answer 2

• Cambourne, west of Cambridge
• Cambridgeshire is a relatively low lying country where flooding is a concern

Question 3

What are the aims of the SuDs in Lamb Drove?

Answer 3

• To showcase practical and innovative sustainable water management techniques within new residential developments
• Demonstrate that SuDs are a viable and attractive alternative to more traditional forms of drainage and to deliver practical solutions for new housing areas

Question 4

How are SuDs am example of a “management train”

Answer 4

This uses simple, natural and visible drainage components in series to improve the water quality.
A management train also controls the quantity of runoff incrementally by reducing flow rates and volumes -> water management was considered from the point at which it falls on land and building to the point at which it leaves the site so mimicking natural patterns as best it can

Question 5

Green roof

Answer 5

Super insulating wildflower habitats with minimal runoff to gutters

Question 6

Detention basin:

Answer 6

Excavated basins increase water storage during flood events
Slow down run off rate and store water on a temporary short term basis during extreme events

Question 7

Filter strips

Answer 7

An additional layer that filters out pollutants

Question 8

Water butt

Answer 8

To collect water for garden irrigation

Question 9

Permeable paving

Answer 9

Allowing water to enter porous storage zones and to filter out pollutants

Question 10

Swale

Answer 10

Collect all excess water from the site, further slowing the flow continuing the water treatment process
Wide shallow drainage channels that are normally dry

Question 11

Retention pond

Answer 11

For final storage of water before being released to a drainage ditch beyond the development site

Question 12

Benefits of SuDs

Answer 12

• Slowing down surface water runoff and reducing the risk of flooding
• Reducing the risk of sewer flooding during heavy rain
• Preventing water pollution
• Recharging groundwater to help prevent drought
• Providing valuable habitats for wildlife in urban areas

Question 13

Limitations of SuDs

Answer 13

• They can be dangerous and people (especially young children) could fall into them and drown

Question 14

Which strategies increase storage?

Answer 14

• Detention basin
• Water butt
• Permeable paving
• Swales
• Retention ponds

Question 15

Which strategies slow down runoff?

Answer 15

• Swales
• Green roofs

Question 16

Which strategies filter/ treat?

Answer 16

• Swales
• Filter strips
• Permeable paving