3.2.3.5 CUE urban drainage

Question 1

what is the traditional approach to urban drainage

Answer 1

using underground pipe systems to carry the water away as quickly as possible

Question 2

what is the more modern approach to urban drainage

Answer 2

sustainable urban drainage systems which deliver a more holistic approach to managing surface water and wherever possible mimic natural drainage

Question 3

what is urban hydrology like

Answer 3

precipitation falls in greater amounts and with greater intensity in towns and cities than in surrounding rural areas

Question 4

what are the comparisons of infiltration and runoff for natural landscapes and urban areas

Answer 4

natural landscapes have more interception of precipitation and therefore allow water to slowly infiltrate whereas urban areas have little interception and also more impermeable surfaces which cause increased runoff

Question 5

how are urban areas designed to shed water quickly

Answer 5

sloping roofs and smooth rounded guttering

Question 6

what is a storm hydrograph like for urban areas

Answer 6

short lag time and high peak discharge with a fast return to base flow means a flashy hydrograph

Question 7

what is the result of this type of hydrograph

Answer 7

more likely to have flooded rivers after heavy rainfall

Question 8

why are more people at risk of flooding

Answer 8

population and urban growth, predicted increase in the occurrence of severe weather as a result of climate change

Question 9

what is catchment management

Answer 9

a way of managing rivers and improving drainage systems by looking at the whole river catchment and the interactions between water and land

Question 10

what are the two main methods to managing river catchments

Answer 10

hard engineering and soft engineering

Question 11

examples of hard engineering strategies for managing river catchment

Answer 11

man made structures such as dams, flood walls, reservoirs to prevent flooding and ensure water supply

Question 12

evaluation of hard engineering

Answer 12

generally expensive, can disrupt natural ecosystems and can alter wildlife habitats

Question 13

examples of soft engineering strategies to manage catchments

Answer 13

land-use management e.g planting trees, preventing building on flood plains and can involve river restoration and conservation

Question 14

evaluation for soft engineering

Answer 14

generally cheaper, use knowledge of the river basin and processes to work with nature

Question 15

what is river straightening

Answer 15

cutting through meanders to create a straight channel, this increases the gradient and speed of flow which may increase flood risk further downstream

Question 16

what are embankments

Answer 16

raised riverbanks using concrete walls, blocks of stone or material dredged from the river bed, the latter is arguably more sustainable

Question 17

what are diversion spillways

Answer 17

flood relief channels, by-pass the main channel, they can be used for emergencies only when high flow levels threaten flooding or a permanent feature enhancing the environment by creating new wetlands and recreational opportunities

Question 18

what is river channelisation

Answer 18

involves lining straightened channels with concrete, this reduces friction, improves rate of flow and reduces the build up of silt because it prevents the banks from collapsing

Question 19

what is afforestation

Answer 19

planting trees to establish woodland or forest, trees increase interception and reduce through flow and surface runoff because they take up water.

Question 20

what is riverbank conservation

Answer 20

planting bushes and trees reduces lateral erosion and bank collapse

Question 21

what is floodplain zoning

Answer 21

restricts different land uses to certain locations on the floodplain, natural floodplains act as a natural soak away

Question 22

what is river restoration

Answer 22

returning the channel to its natural course and so reversal of artificial drainage management ‘solutions’ adopted in the past

Question 23

what is a named example of catchment management

Answer 23

the river aire in Leeds

Question 24

why did the river aire need managing

Answer 24

In Leeds city centre during heavy flooding there can be flooding

Question 25

what attempts have been made to manage the river aire within the city

Answer 25

raised embankments and channelisation

Question 26

why did they have to improve the management of the river aire and what did they do

Answer 26

severe flooding in 2015
Leeds city council and the environment agency set up the uks largest natural flood management scheme

Question 27

what did the management scheme involve (river aire)

Answer 27

increased vegetation along the river from the source in Malham down to Leeds city centre to use natural processes to slow the flow of surface water.

By increasing the vegetation more water is moved as throughflow and groundwater flow, and is therefore gently released into the river so that lower areas are not overwhelmed by flood water.

Question 28

what are SuDS

Answer 28

sustainable urban drainage systems, an alternative to using hard engineering and can be described as safe to fail

they use natural processes in the landscape to reduce flooding, control flooding and provide amenity for the community

they aim to imitate natural drainage systems rather than channelling water through pipes and drains

Question 29

what do SuDS help to do

Answer 29

• slow down surface runoff and reduce flood risk
• reduce risk of sewer flooding during heavy rain
• prevent water pollution
• recharge groundwater to help prevent drought
• provide valuable habitats for wildlife
• create green spaces for people in urban areas

Question 30

examples of SuDS techniques

Answer 30

Swales, vegetated trenches, rain gardens, balancing ponds vegetated/green roofs and permeable surfaces

Question 31

what is a swale

Answer 31

shallow channel with gently sloping sides.

may be either natural or man-made.

Artificial swales are often infiltration basins, designed to manage water runoff, filter pollutants, and increase rainwater infiltration.

Question 32

what are vegetated trenches

Answer 32

practically the same as Swales

they increase interception of rainfall to decrease runoff and channel flow which lowers flood risk

increased infiltration also decreases the amount of pollutants entering water courses

Question 33

what is a rain garden

Answer 33

sloped retention area designed to capture water while allowing it to infiltrate the ground

Some of the water is soaked up by the vegetation, therefore reducing flooding

they are usually at the end of a roof gutter and between 6 and 9 inches deep

Question 34

what is a vegetated roof

Answer 34

vegetation on a roof that intercepts rainfall and increases evapotranspiration which reduces flood risk

may be collected in water butts which reduces drought risk

Question 35

what are permeable surfaces

Answer 35

used on roads and paths – this means rain falling on these surfaces is filtered and stored in the stone below, or it flows into grass channels, which have a stone filter drain underneath, before it joins the rest of the SUDS system.

Question 36

what is the case study for SuDS

Answer 36

Storm water Leeds

Question 37

what did Leeds city council enforce in 2004

Answer 37

any new development which created buildings and or hard surfaces which create runoff had to show how they would deal with the drainage issues in order to obtain planning permission

Question 38

what did stormwater involve

Answer 38

800 terraced houses and apartments on the north banks of a former brownfield site using timber framed panels fabricated in Citus own factory on the other side of the river

Question 39

what are examples of SuDS techniques used for storm water

Answer 39

• houses have permeable paving
• wildflower meadows and beds of edible plants to help slow down surface water filtration
• every house has its own small rain garden
• houses have green roofs

Question 40

other sustainable techniques used at stormwater

Answer 40

some parking is provided but residents must pay an extra fee to have a car park space along with their property

Question 41

social benefits from stormwater

Answer 41

• provides a pleasant social community for residents
• visually improved the area

Question 42

economic costs of stormwater

Answer 42

properties are very expensive - according to zoopla the average house cost is £376,222

project costs £250M

Question 43

economic benefits of storm water

Answer 43

• citu claim the houses are built sufficiently high above the river to withstand a 1 in 200 year flood
• the site benefits from Leeds city councils £50M flood prevention scheme

Question 44

environmental benefits of stormwater

Answer 44

• mimics the natural environment
• slows down surface runoff and reduces flood risk
• meadows and green spaces have created space for ecosystems to flourish

Question 45

what is the case study for river restoration

Answer 45

Einfield, north London

Question 46

why does Enfield need river restoration and conservation

Answer 46

• major floods in 2006,2007 and 2008
• heavily urbanised area
• over 9,000 homes are at risk of flooding
• surface runoff has increased levels of pollutants such as oil and heavy metals in water courses

Question 47

what were the aims of the restoration

Answer 47

• reduce flood risk and limit impacts of flooding on habitats and homes
• reduce surface runoff from roads and pollutants entering rivers in order to improve water quality
• provide habitats for wildlife and new recreational areas for residents

Question 48

which SuDS did they use to meet these aims - river aire

Answer 48

• vegetated trenches to absorb runoff and decrease flood risk
• rain planters have been installed in schools
• wetlands have been constructed to improve water quality

Question 49

what groups were involved (Einfield)

Answer 49

• defra and Thames water provided funding (in 2012 they granted £340,000 to the project)
• local residents ( volunteers involved in water quality monitoring and litter pickups
• local schools (Thames 21 offers education sessions for local schools increase engagement. In 2015, 1 000 students were involved in litter picking and wildlife monitoring)

Question 50

what are the project’s success (Einfield)

Answer 50

• Flood risk seems to be reduced e.g. high rainfall in December 2013 and January 2014 did
  not cause significant flooding in Enfield.
• SUDS have reduced ammonia levels in Salmons Brook by 67% and nitrogen levels by 43%
• Population of eels and some species of insects, e.g. dragonflies, have increased

Question 51

are there still some issues with Einfield

Answer 51

yes pollution and litter