3.2.3.5 CUE urban drainage Flashcards
what is the traditional approach to urban drainage
using underground pipe systems to carry the water away as quickly as possible
what is the more modern approach to urban drainage
sustainable urban drainage systems which deliver a more holistic approach to managing surface water and wherever possible mimic natural drainage
what is urban hydrology like
precipitation falls in greater amounts and with greater intensity in towns and cities than in surrounding rural areas
what are the comparisons of infiltration and runoff for natural landscapes and urban areas
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
how are urban areas designed to shed water quickly
sloping roofs and smooth rounded guttering
what is a storm hydrograph like for urban areas
short lag time and high peak discharge with a fast return to base flow means a flashy hydrograph
what is the result of this type of hydrograph
more likely to have flooded rivers after heavy rainfall
why are more people at risk of flooding
population and urban growth, predicted increase in the occurrence of severe weather as a result of climate change
what is catchment management
a way of managing rivers and improving drainage systems by looking at the whole river catchment and the interactions between water and land
what are the two main methods to managing river catchments
hard engineering and soft engineering
examples of hard engineering strategies for managing river catchment
man made structures such as dams, flood walls, reservoirs to prevent flooding and ensure water supply
evaluation of hard engineering
generally expensive, can disrupt natural ecosystems and can alter wildlife habitats
examples of soft engineering strategies to manage catchments
land-use management e.g planting trees, preventing building on flood plains and can involve river restoration and conservation
evaluation for soft engineering
generally cheaper, use knowledge of the river basin and processes to work with nature
what is river straightening
cutting through meanders to create a straight channel, this increases the gradient and speed of flow which may increase flood risk further downstream
what are embankments
raised riverbanks using concrete walls, blocks of stone or material dredged from the river bed, the latter is arguably more sustainable
what are diversion spillways
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
what is river channelisation
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
what is afforestation
planting trees to establish woodland or forest, trees increase interception and reduce through flow and surface runoff because they take up water.
what is riverbank conservation
planting bushes and trees reduces lateral erosion and bank collapse
what is floodplain zoning
restricts different land uses to certain locations on the floodplain, natural floodplains act as a natural soak away
what is river restoration
returning the channel to its natural course and so reversal of artificial drainage management ‘solutions’ adopted in the past
what is a named example of catchment management
the river aire in Leeds
why did the river aire need managing
In Leeds city centre during heavy flooding there can be flooding
what attempts have been made to manage the river aire within the city
raised embankments and channelisation
why did they have to improve the management of the river aire and what did they do
severe flooding in 2015
Leeds city council and the environment agency set up the uks largest natural flood management scheme
what did the management scheme involve (river aire)
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.
what are SuDS
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
what do SuDS help to do
- 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
examples of SuDS techniques
Swales, vegetated trenches, rain gardens, balancing ponds vegetated/green roofs and permeable surfaces
what is a swale
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.
what are vegetated trenches
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
what is a rain garden
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
what is a vegetated roof
vegetation on a roof that intercepts rainfall and increases evapotranspiration which reduces flood risk
may be collected in water butts which reduces drought risk
what are permeable surfaces
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.
what is the case study for SuDS
Storm water Leeds
what did Leeds city council enforce in 2004
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
what did stormwater involve
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
what are examples of SuDS techniques used for storm water
- 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
other sustainable techniques used at stormwater
some parking is provided but residents must pay an extra fee to have a car park space along with their property
social benefits from stormwater
- provides a pleasant social community for residents
- visually improved the area
economic costs of stormwater
properties are very expensive - according to zoopla the average house cost is £376,222
project costs £250M
economic benefits of storm water
- 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
environmental benefits of stormwater
- mimics the natural environment
- slows down surface runoff and reduces flood risk
- meadows and green spaces have created space for ecosystems to flourish
what is the case study for river restoration
Einfield, north London
why does Enfield need river restoration and conservation
- 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
what were the aims of the restoration
- 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
which SuDS did they use to meet these aims - river aire
- vegetated trenches to absorb runoff and decrease flood risk
- rain planters have been installed in schools
- wetlands have been constructed to improve water quality
what groups were involved (Einfield)
- 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)
what are the project’s success (Einfield)
- 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
are there still some issues with Einfield
yes pollution and litter
