Urban Drainage

Question 1

How do urban areas impact the water cycle? - Urban Drainage

Answer 1

Urban areas have increased precipitation due to the urban heat island effect/presence of condensation nuclei, increased runoff and reduced infiltration due to presence of impermeable surfaces, reduced evapotranspiration due to lack of green spaces, less throughflow and groundwater flow.

Question 2

What is base flow? How is urban base flow different from rural base flow? - Urban Drainage

Answer 2

Base flow is the natural, residual volume of water that would be in a river had a flood NOT occurred. Urban base flow is lower than in rural areas due to reduced infiltration from impermeable surfaces.

Question 3

How do urban areas impact the storage of water? - Urban Drainage

Answer 3

Urban rivers are significant stores of water, temporary stores such as puddles and surface water are significant, interception storage reduced as a result of a loss of vegetation (replaced by urban structures designed to rapidly drain water), soil moisture storage reduced as soil is often covered with impermeable surfaces.

Question 4

How are precipitation levels affected by urban areas? - Urban Drainage

Answer 4

Precipitation levels are significantly increased as a result of the urban heat island effect, which generates warmer and more humid conditions, generating more frequent rain of greater intensity.

Question 5

What is catchment management? - Urban Drainage

Answer 5

Catchment management is a way of managing rivers and improving drainage systems by observing a whole catchment, as well as interactions between water and land.

Question 6

How are drainage systems valuable to cities and their populations? - Urban Drainage

Answer 6

Drainage systems provide important water resource management, sustain wildlife habitats, moderate urban climates, provide recreational areas/community facilities, regulate and monitor water quality.

Question 7

What 2 methods are used to manage river catchments? Give examples of each - Urban Drainage

Answer 7

Hard engineering: dredging, flood defences, river channelisation (straightening/deepening of the channel), overflow channels, dams, levees, etc.
Soft engineering: electronic warning systems, afforestation, flood plain zoning (managing land use), sandbag use, river restoration schemes, managed retreat.

Question 8

What urban issues do catchment management schemes aim to solve? - Urban Drainage

Answer 8

Catchment management schemes aim to avert urban issues such as flooding, drought, water pollution, erosion and ecosystem destruction.

Question 9

What are typical features of hard and soft management strategies respectively? - Urban Drainage

Answer 9

Hard - typically man made structures, control natural processes, require planning, costly, unsustainable, may have long term benefits.
Soft - doesn’t change or manage the environment, instead working with natural processes, cheaper, sustainable, less intrusive.

Question 10

Why was the LA Catchment Management Scheme introduced? What did this aim to produce? - Urban Drainage

Answer 10

The LA Catchment Management Scheme was introduced following flash floods in the 1930s, aiming to create a ‘fail safe’ strategy which could virtually never result in flooding.

Question 11

What were features of the LA Catchment Management Strategy? - Urban Drainage

Answer 11

The LA Catchment Management Strategy saw the revived channel reconstructed from cement, an impermeable surface, in order to ensure that the flow of water was controlled and that excessive meandering could not be created.

Question 12

What are advantages and disadvantages of the LA Catchment Management Scheme? - Urban Drainage

Answer 12

Advantages: heavily restricts possibility of any flooding, a highly regulated and managed river system.
Disadvantages: infrastructure may be vulnerable to earthquakes, destroying the management scheme. Has also seen the devastation of natural river habitats and ecosystems that previously existed here.

Question 13

Who decides on catchment management measures? On what basis are changes introduced? - Urban Drainage

Answer 13

Catchment management measures are introduced by experts separate from an affected region rather than residents who will be impacted. These changes are brought in based on benefits for a catchment as a whole rather than individual residents, meaning some may face disruption.

Question 14

What issues are involved with the management of drainage in urban areas? - Urban Drainage

Answer 14

Drainage management has to deal with water pollution, pesticide use (eutrophication), damage to wildlife, sewage management, balancing and regulation of water levels in the catchment to prevent flooding.

Question 15

What are SUDS? What are their aims? - Urban Drainage

Answer 15

SUDS are systems which aim to imitate natural drainage systems in urban areas rather than channelling water through pipes and drains.

Question 16

What do SUDS often result in? - Urban Drainage

Answer 16

SUDS frequently result in reduced flooding, less water pollution and less drought in urban areas. Can slow down runoff and allow natural processes to break down pollutants. Designed as being safe to fail.

Question 17

How do rain garden planters achieve the aims of SUDS? - Urban Drainage

Answer 17

Rain garden planters filter water through soil rather than placing it directly into drainage, prolonging the process of drainage to reduce runoff and risk of flooding. Also filter any pollutants out of water and into soils.

Question 18

How do water butts achieve the aims of SUDS? - Urban Drainage

Answer 18

Water butts help to achieve the aims of SUDS by storing water in a source for a prolonged period, meaning that runoff is regulated and therefore flooding prevented.

Question 19

How do tree pits help to achieve the aims of SUDS? - Urban Drainage

Answer 19

Tree pits help to achieve the aims of SUDS as slanted impermeable surfaces can be used to divert excess runoff water towards plants and trees with roots that are able to absorb it.

Question 20

How do swales help to achieve the aims of SUDS? - Urban Drainage

Answer 20

Swales create shallow channels with gently sloping sides, increasing the surface area of a permeable area and its capacity to hold water. This therefore means that infiltration is increased, runoff is managed and groundwater storage increased.

Question 21

How does permeable paving assist SUDS in achieving their aims? - Urban Drainage

Answer 21

Permeable paving helps SUDS achieve their aims as small gaps in the paving allows water to infiltrate into the ground, reducing runoff and therefore preventing flooding. Also filters water through the paving, meaning that pollutants are extracted.

Question 22

How do vegetated roofs help achieve the aims of SUDS? - Urban Drainage

Answer 22

Vegetated roofs are able to intercept rainfall and increase evapotranspiration, reducing flood risk.

Question 23

What are the benefits of SUDS? - Urban Drainage

Answer 23

SUDS slow down runoff, prevent pollution of river systems, create green spaces, reduce flooding and work with natural environmental processes to manage drainage rather than creating expensive and intrusive drainage systems.

Question 24

What is river restoration and conservation? What are its aims? - Urban Drainage

Answer 24

River restoration and conservation aims to restore river systems to a more natural state in order to reduce flood risk, decrease water pollution, create natural habitats and improve biodiversity.

Question 25

Where is Enfield located? What river is it located on? What reasons are there for the river restoration project here? - Urban Drainage

Answer 25

Enfield is located in North London on the River Lea. Regular flooding in 2006/7/8 and it’s urbanised catchment prompted efforts to combat issues with its drainage and water quality.

Question 26

How many houses in Enfield are at risk of flooding? What % of houses directly discharge waste into the river? - Urban Drainage

Answer 26

9000 houses in Enfield are at risk of flooding, with 10% of houses directly discharging waste into the River Lea.

Question 27

How has surface runoff contributed to significant levels of pollution in Enfield? - Urban Drainage

Answer 27

Surface runoff has increased pollution in the River Lea at Enfield due to the presence of oil in these systems. Oil is washed into the rivers, reducing and damaging the water quality severely.

Question 28

What were the aims of the Enfield river restoration project? (3) - Urban Drainage

Answer 28

Enfield’s river restoration project aims to reduce flood risk and its impacts, reduce pollutants in the river as a result of surface runoff, provide more habitats for wildlife and new recreational areas.

Question 29

What are the benefits of the Enfield river restoration scheme? - Urban Drainage

Answer 29

The Enfield scheme has seen reduced flood risk, with no floods on the scale of 2006/7/8 since the scheme was implemented, eel populations have increased (BIODIVERSITY), high community involvement, ammonia levels at Salmons Brook down by 67%

Question 30

What are the disadvantages of the Enfield river restoration scheme? - Urban Drainage

Answer 30

The Enfield river restoration scheme has not managed to completely tackle pollution and litter, with these issues persevering in some rivers.

Question 31

What SUDS measures were adopted in Enfield? - Urban Drainage

Answer 31

Enfield saw vegetated trenches used to absorb runoff and decrease flood risk, rain planters were introduced in schools to manage flow of water into drains, wetlands constructed as major water stores and to improve water quality due to filtration.

Question 32

What groups were involved in the Enfield river restoration scheme? - Urban Drainage

Answer 32

The Enfield river restoration scheme involved DEFRA (who granted £350,000 to the project), local residents and community groups and local schools.

Question 33

How much money did DEFRA offer to fund the Enfield scheme? How many students are involved in litter picking and wildlife schemes? - Urban Drainage

Answer 33

DEFRA funded £350,000 worth of the Enfield project. 1000 school children are involved in litter picking and wildlife monitoring as part of the scheme.

Question 34

Where is Stormwater located? What does it aim to achieve? - Urban Drainage

Answer 34

Stormwater is located in Leeds, adjacent to the Dock and built on a brownfield site. This aims to be a sustainable living development which is resilient to flooding and prevents runoff from reaching the city’s drains.

Question 35

Describe features of Stormwater’s design - Urban Drainage

Answer 35

Stormwater involves thick vegetation to increase interception and uptake of water. Permeable pavements used to decrease runoff. Houses have ‘rain gardens’ which store rainwater and regulate its drainage. Houses have green roofs which retain rainwater, promote evapotranspiration. Recycled plastic beneath grassy areas control infiltration and prevent floods during downpours.

Question 36

What % of the land at Stormwater is open green space? What are the impacts of this? - Urban Drainage

Answer 36

> 50% of land at Stormwater is open green space, meaning that interception is increased, reducing surface storage in puddles and increasing evapotranspiration.

Question 37

What are the social costs and benefits of Stormwater? - Urban Drainage

Answer 37

Costs - exclusionary community due to costs associated with living there.
Benefits - Stormwater creates a pleasant social community for residents, with the area being beautified to create an enjoyable and vibrant community. Homes significantly protected from flood risk.

Question 38

What are the economic costs and benefits of Stormwater? - Urban Drainage

Answer 38

Costs - properties are incredibly expensive (with average house prices £375,000), project cost £250m.
Benefits - houses built high enough to withstand 1/200 year flood event so economic damages reduced, site benefits from Leeds City Council £50m flood prevention scheme.

Question 39

What are the environmental benefits of Stormwater? - Urban Drainage

Answer 39

Strategies used mimic the natural environment, strategy slows down surface runoff generation, reduced urban flood risk, greenery has developed diverse ecosystems, hugely sustainable.