3.2.3.5 Urban drainage Quiz: AQA Geography, Unit 2

The 20 questions

1. What is the main effect of urban surfaces on the hydrological cycle?

   • No effect because drainage systems remove all water instantly
   • Increased infiltration because urban soils are highly permeable
   • Impermeable surfaces increase surface runoff and reduce infiltration into the ground
   • Reduced surface runoff because cities have more vegetation

2. On a hydrograph, what does a shorter lag time usually indicate in an urbanised catchment?

   • Rainfall has stopped completely before the river responds
   • Water reaches the river more quickly, producing a faster response to rainfall
   • The river has dried up and no runoff is recorded
   • Water takes longer to reach the river because of reduced runoff

3. Which change in an urbanised drainage basin most directly increases peak river discharge?

   • Greater infiltration into deep permeable soils
   • Reduced rainfall intensity across the entire catchment
   • Greater area of impermeable surfaces and drains that speed water to the channel
   • Increased storage in ponds and wetlands across the basin

4. A catchment's urbanisation rises from 10% to 50% impermeable cover. What is the most likely effect on flood risk?

   • Lower flood risk, because impermeable surfaces slow runoff
   • No change, because drains move water at the same speed as before
   • Higher peak discharge and greater flood risk for the same rainfall event
   • Lower peak discharge because more water is stored in urban soils

5. Which sustainable urban drainage system uses a shallow vegetated channel to slow and filter runoff?

   • Soakaway
   • Storm drain
   • Sewage outfall
   • Swale

6. Which SUDS feature is best suited to reducing runoff from a car park?

   • Impermeable tarmac that drains straight to a storm drain
   • Permeable paving that lets water infiltrate through the surface
   • A high kerb that prevents any water from reaching the ground
   • A concrete channel that accelerates flows to the river

7. A river restoration scheme in an urban catchment is best described as aiming to:

   • Straighten the channel to speed water through the city, removing bends and vegetation so flows reach the outfall as quickly as possible
   • Replace the river with a concrete flood channel along its full length, lining the banks and bed so that water moves at a steady speed
   • Reconnect the channel to its floodplain, reduce pollution and improve habitat
   • Culvert the river entirely underground to prevent flooding, sealing the channel from the surface so that no further flooding can occur

8. Which catchment characteristic would most reduce the flashiness of an urban river?

   • Steep channel gradients with no vegetation along the banks, which carry water quickly from the upland catchment to the city outfall
   • Large areas of green space and ponds that store runoff before it reaches the channel
   • Dense networks of storm drains feeding the river quickly, with every street gully connected directly to the channel by a short pipe
   • Extensive paved car parks draining directly to the river, so that runoff from every vehicle bay enters the channel within minutes

9. Which statement about urban water management is most accurate?

   • Sustainable drainage avoids all use of vegetation and soil, relying instead on concrete channels that never hold any water at all
   • Sustainable drainage aims to remove all water from the city as fast as possible, using large pipes to carry every storm away quickly
   • Sustainable drainage increases flood peaks on purpose to protect downstream areas, pushing water into the lower catchment in short bursts
   • Sustainable drainage aims to mimic natural runoff patterns by slowing, storing and infiltrating water

10. A hydrograph for an urban catchment shows a peak discharge of 60 cumecs compared with 25 cumecs before urbanisation, for the same storm. What is the percentage increase in peak discharge?

    • 240%
    • 35%
    • 140%
    • 60%

11. Which argument best evaluates the value of SUDS in a heavily built-up city?

    • They have no effect on flood peaks and only add cost, because their storage capacity is too small to change runoff in any real storm
    • They are only useful in rural catchments with no development, because urban surfaces cannot be fitted with any sustainable features
    • They work in every city without any maintenance or land take, since they need no space and require no upkeep once installed
    • They reduce peak flows and pollution but may need space and maintenance, which can limit use in dense areas

12. Which pair of processes best explains why flooding is often more severe after urban development?

    • Reduced runoff and more natural wetland storage across the catchment, because urban growth tends to restore lost floodplain wetlands
    • More permeable surfaces and greater storage capacity in the basin, so flood peaks fall as urban development spreads across the land
    • Increased runoff from impermeable surfaces and reduced storage in the drainage basin
    • Increased infiltration from paved surfaces and extended lag times, as urban soils absorb more rainfall before it reaches the river

13. A city's storm drains are designed for a 1 in 30-year storm, but a 1 in 100-year storm causes flooding. What does this illustrate?

    • Drainage capacity is exceeded by extreme rainfall, so systems may fail during rare events
    • Drainage is unrelated to rainfall intensity, since the capacity of pipes depends only on their material and the age of the network
    • Flooding is caused only by river channels rather than the drainage system, so the storm drains are never the source of any flooding
    • Drains are working perfectly for all storms, including the rarest, because the design standard already accounts for every possible event

14. Which catchment management approach best addresses water pollution from urban runoff?

    • Source control such as green roofs and rain gardens that treat runoff near where it falls
    • Discharging all runoff untreated straight into the nearest river, which avoids the cost of treatment and sends the water away quickly
    • Increasing the number of road gullies that bypass treatment, so that polluted water reaches the river without any filtering along the way
    • Removing all vegetation to make runoff drain faster, which clears the surface so that water and pollutants move straight into the channel

15. Which statement about urban groundwater is most accurate?

    • Urban groundwater recharge always increases because of paved surfaces, which channel rain into the ground through drains and cracks
    • Urban rivers always have higher baseflow than rural rivers, because sewage discharges keep the channel full through the dry season
    • Reduced infiltration in cities can lower groundwater recharge and affect baseflow to rivers
    • Groundwater has no connection to urban drainage, since the water table is isolated from pipes, sewers and surface channels in cities

16. Which combination best describes the typical effect of urbanisation on the urban water cycle?

    • Unchanged runoff with no pollution impacts on water bodies, because cities drain water so efficiently that streams remain clean
    • Reduced peak flows and increased evapotranspiration from paved areas, since sealed surfaces lose more water to the air each day
    • Higher runoff and peak flows, reduced infiltration and evapotranspiration, and increased pollution load in streams
    • Lower runoff and higher infiltration across the whole city, as paved surfaces let water soak into the ground more readily than before

17. A catchment is 40 km2 and 30% of it is impermeable. Which computed value gives the impermeable area?

    • 12 km2
    • 30 km2
    • 28 km2
    • 4 km2

18. A river channel in a city is culverted underground for a long stretch. Which drainage consequence is most likely?

    • Less surface storage and conveyance capacity that can increase flood risk downstream
    • Greater floodplain storage and reduced peak flows, since the underground channel spreads water over a wider area of the valley
    • Improved habitat for fish along the reach, because the culvert gives fish a stable channel that is protected from storm flows
    • Lower pollutant loads entering the channel from runoff, because the culvert filters water as it passes beneath the surface streets

19. Which hydrological term describes water that soaks into the ground and recharges groundwater?

    • Evaporation
    • Overland flow
    • Interception
    • Infiltration

20. A green roof retains 60% of rainfall during a storm of 20 mm. How much rainfall runs off the roof?

    • 12 mm
    • 4 mm
    • 20 mm
    • 8 mm

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