Urban precipitation and drainage management Flashcards
On average what percentage more precipitation does urban areas experience compared to rural areas?
5-15% more
Why is there more precipitation in urban areas compared to rural areas?
- warmer air in cities can hold more moisture
- dust and pollution make more condensation nuclei
How much precipitation is surface run of is in rural, suburban and central urban in percentages?
rural- 10%
Suburban- 30%
Central urban- 55%
Why are drains needed in urban areas?
Impermeable surfaces like concrete stops water infiltrating into the ground causing surface runoff so drains are needed to remove water quickly to reduce flooding
Name 4 hard engineering strategies to reduce flooding in urban areas.
river straightneing
natural levees
diversion spillways
river channelisation
What is river straightening and how does it prevent flooding?
straightening the channel to allow water to flow rapidly to prevent it from flooding
What is natural levees and how do they prevent flooding?
banks either side of the river which can be made higher to create embankments which can hold back flood water in the river to reduce flooding
Whats diversion spillways and how do they prevent flooding?
They are flood relief channels which bypass the main channel which are only used for emergencies and are controlled by gates in order to move water quickly if the channel gets full and creates a flood risk
What is river channelisation and how does it prevent flooding?
like river straightening but uses concrete which reduces friction so it increase the rate of flow
What are the 2 disadvantage of river straightening?
- may increase flood risk downstream
- may cause more erosion and will destroy natural habitats
What is a disadvantage of river channelisation?
it damages the local ecosystems and looks unsightly
What are the 4 soft engineering strategies to reduce flooding in urban areas?
afforestation
riverbank conservation
floodplain zoning
river restoration
What is afforestation and how does it prevent flooding?
planting trees which interrupts the flow of water and helps soak up the water and through evapotranspiration get rid of it into the atmosphere
What is riverbank conservation and how does it prevent flooding?
planting bushes and trees to reduce lateral erosion, this is because their roots stablise the banks to reduce flooding
What is floodplain zoning and how does it prevent flooding?
It restricts different land uses to different parts of the floodplain to stop urban areas from being flooded as floodplains are there to store flood water and not to be built on
What is river restoration and how does it prevent flooding?
it involves returning a river to its natural cause
What does SuDS stand for?
sustainable drainage system
What are SuDS?
realistic yet environmentally friendly replication of natural drainage systems in any built environment as they hold back and slow surface run off from developments and allow natural processes to break down pollutants
What are swales?
wide, shallow drainage channels that are normally dry
What are permeable road and pavement surfaces?
the use of porous block paving and concrete to allow the infiltration of water into the ground
What are infiltration trenches?
gravel filled drains and filter strips
What are bioretention basins?
gravel and/or sand filtration layers beneath reed beds and other wetland area to collect, store and filter dirty water
What are detention basins?
excavated basins to act as holding ponds for water storage during flood events
What are rain gardens?
shallow landscape depressions planted with flowers and shrubs
What are green roofs?
super-insulating wildflower habitats with minimal runoff to gutters
What are the benefits of SuDS?
- slow down surface run off and reduce the risk of flooding
- prevent water pollution
- provide valuable habitats for wildlife in urban areas
- create green spaces for people in urban areas
What SuDS did Lamb Drove, Cambourne use?
green roof
permeable paving
swale
retention pond
filter strip
detention basin
water butt
Why did Lamb Drove, Cambourne build SuDS?
It had a development of 35 ‘affordable’ homes on the floodplain where flooding was a major concern- the SuDS have added social value to both residents and community while improving the biodiveristy and ecology of the area.
