Urban drainage

What is interception

The temporary storage of water on the leaves of trees and plants

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What is through flow

The lateral (sideways) movement of water downslope through the soil towards the river channel

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What is groundwater flow

The deep circulation of water within the saturated zone of the bedrock which eventually reaches the river

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what is Overland flow

The movement of water over the ground surface due to either the ground being totally saturated or the precipitation rate being higher than the infiltration rate

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What is a hydrograph?

A representation of the response of a river to a storm event

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Explain urban hydrology

- Water is normally transported to the river channel but this is interrupted by urban drainage systems
- Urbanisation removes vegetation so there is less interception and water reaches the surface faster and river faster (shorter lag time)

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.......

- lag time short/ impermeable surfaces and drainage systems in urban areas, so overland flow speed is increased and there is a quick rate to the river
- peak discharge is increased, as evaporation and transpiration are reduced

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What are the changes in natural water flows in an urban area

natural water flows are interrupted in urban areas and some natural processes are reduced but some are increased
There are different inputs and outputs , the addition of 'imported water' and the additional 'wastewater discharge' output

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Soft engineering to prevent flooding:
Afforestation

This is planing trees in the upper part of the drainage basin
interception is increased and slows down flow

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Riverbank conservation?

This is planting bushes and trees to reduce river bank erosion and bank collapse

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Floodplain zoning?

This is restricting different land uses in locations to allow flooding to occur

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River restoration?

This returns the river channel to it's natural course

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Case study:
Channelisation of the LA river
Why was the river channelised?

After devastating floods in the 1930s city authorities decided to channelise the LA river from a natural/ meandering system to cement and controlled

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CS:
What does the river look like

- Not a lot of water
- Unattractive
- No wildlife/ plants
- Large/ lots of space

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CS:
Advantages of the channelisation

- Prevents floods
- Can increase tourism/ publicity as they are shown in movies

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CS:
Disadvantages of the channelisation

Lots of space is taken up which could be used for other things
It is expensive

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What are SuDS- sustainable drainage systems

They are a hybrid of hard/ soft engineering as they involve man made structures , but aim to work with nature// This is an approch to manage rainfall in UA by replicating natural processes in the U landscape to reduce & control flooding

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What are the 4 main characteristics of SuDS

Easy to manage
Resilient to use
Environmentally active
Require little or no energy

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What is stem flow?

The flow of water down the trunks of trees and stems of plants towards the ground

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What is throughfall?

this is when water drips off the leaves of trees and falls directly to the ground surface

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What is evaporation?

This is a physical process by which moisture is lost directly to the atmosphere from water surfaces and the soil due to the effect of air movement and heat

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What is percolation?

this is the vertical movement downwards of water from the soil into the underlying bedrock

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What is infiltration?

this is the movement of water from the ground surface into the soil

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What is transpiration?

This is a biological process by which water is lost from a plant through the stomata in its leaves

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Get Revising

Urban drainage

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Other cards in this set

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