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Contemporary Urban Environments

Urban Hydrographs

  • 3 things to know
  • Component 2

Overview

Recall questions on shorter lag times, higher peak discharge, steeper rising limbs and the flashy response of an urban catchment.

What you need to know

Answer each one before you reveal it.

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Key term

Why do urban hydrographs typically show shorter lag times than rural catchments?

Key term

What causes urban hydrographs to show flashier responses with quicker return to base flow?

Key term

What is combined sewer overflow pollution?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why do urban hydrographs typically show shorter lag times than rural catchments?

    Model answer

    Water is transferred rapidly across impermeable surfaces to efficient drainage systems, reducing the time between peak rainfall and peak discharge.

  2. 2

    Explain why urban hydrographs display higher peak discharge than rural equivalents.

    Model answer

    Reduced infiltration and storage means a greater proportion of rainfall becomes surface runoff, and this water reaches channels quickly, concentrating flow into a higher peak.

  3. 3

    Why do urban hydrographs have steeper rising limbs?

    Model answer

    Efficient artificial drainage networks channel runoff rapidly to rivers, causing discharge to increase quickly after rainfall begins.

  4. 4

    What causes urban hydrographs to show flashier responses with quicker return to base flow?

    Model answer

    Limited groundwater recharge means there is less sustained throughflow contribution to maintain river levels, so discharge falls rapidly after the storm peak.

  5. 5

    How does urbanisation increase flood risk?

    Model answer

    Rapid runoff from impermeable surfaces, reduced storage and efficient drainage concentrate water quickly, increasing peak flows that can exceed channel capacity.

  6. 6

    What is combined sewer overflow pollution?

    Model answer

    During heavy rainfall, combined sewers carrying both stormwater and sewage can overflow, discharging untreated sewage and pollutants directly into rivers.

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