Urban Drainage Flashcards
What is a drainage basin
The area of a land drained by a river and its tributaries
What is a watershed
The boundary dividing the drainage basin from another
What is precipitation
Rain snow
What is interception
Things stopping precipitation from reaching the ground
What is transpiration
Evaporation from leaves
What is evaporation
Water turning to gas
What is surface storage
Eg puddles
What is infiltration
Water being absorbed into the soil
What is surface run off and overland flow
Water running on surface of ground- to river or drains
Happens in impermeable areas
Happens at slope
What is soil moisture
Water in soil
What is percolation
Water being absorbed into rocks
What is groundwater
Water in the ground
What is ground water flow
Water flowing through the ground
What is throughflow
Water flowing through soil
Eg of input
Precipitation
Eg of storage
Interception
Surface storage
Soil moisture
Groundwater
What are flows
Ground water flow
Through flow
Percolation
Infiltration
Surface run off and overland flow
Eg of output
Evaporation
Transpiration
River channel
Hydrological cycle in urban environment
Evaporation
to precipitation
to surface storage (back to evaporation or)
run off
Hydrological cycle in rural environments
Evapotranspiration to precipitation
to interception by vegetation (can be evaporated)
to surface storage (can be evaporated)
to surface run off AND soil water storage
to ground water storage
Storm hydrograph
Basin lag time
Time between the highest rainfall and highest discharge in hours —
Happens as only 9% of water lands in the river and the other % has to make its way through flows etc
What is the line with the rising and recession limb
Storm hydrograph
Line shows discharge in metres squared per second
What is base flow
Storm hydrograph
The usual flow of the river
What is recovery rate
Storm hydrograph
Where through flow an the main line meet
What are sustainable drainage systems
Hold back and slow surface run off in urban areas and allow natural processes to break down pollutants
Name the 7 sustainable urban drainage systems
Swales
Permeable roads
Bio retention basins
Detention basins
Rain gardens
Green roofs
Water butts
How do Swales work
Wide shallow channels which store excess water
How do permeable roads and pavements work
Absorb rain water
How do bio retention basins work
Contain gravel or sand layers beneath reed beds
The basins collect and filter water as well as providing habitats
How do detention basins work
Like bio retention basins but are designed only to store water and prevent flooding
They are usually dry
How do green roofs work
Planted with wild flowers and absorb rainwater to reduce run off
How do water butts work
Connected to down pipes and collects rain water from house roofs
What are some of the benefits of suds
Slows down surface run off allowing infiltration- reducing risk of flood and sewer and drain overflow
Polluted water an be filtered as infiltrated in ground
More infiltration means more groundwater and potentially less drought
Wildlife habitats are improved
Green space improve the physical feel and emphasise the aesthetic appeal of new developments
6 urban flood management strategies
Land use zoning
Dredging
Flood walls
Flood warning
Straightening the channel and channelisation
River restoration
Explain land use zoning
Restrict the construction of buildings and other impermeable surfaces on the flood plain
Can provide sport and recreational opportunities but restricts short term economic potential
Can’t undo what’s done
Explain dredging
Deepen the river channel and increase its capacity
Material removed from river bed can be used to build up river banks
But ugly and will need to be repeated
Explain flood walls
Construct hugger river banks and increase the channels capacity
Higher river banks walls will allow greater discharge
Reduced flood risk but ugly and expensive to do and maintain
Explain flood warnings
Prepare people so lives can be saved
Doesn’t always work
Property destroyed
Explain Chanel straightening and channelisation
Remove meanders and increase the velocity of river flow
The Increased velocity means that the river will travel at a faster rate but floods made be displaced downstream to the point where the river slows/meanders
Explain river restoration
Returning the river to a more natural state by restoring habitats, recreating meanders and removing obstructions to create a more natural system
Wildlife habitat is restored but local residents may oppose to the plan as they don’t understand how it can reduce flooding- BUT EDUCATE THEM?
