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Water and Carbon Cycles

Excess runoff: natural and human causes

  • 2 things to know
  • Component 2

Overview

Excess runoff, how embankments and levees can make flooding worse and river basin mismanagement.

What you need to know

Answer each one before you reveal it.

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Key term

What is meant by excess runoff?

Key term

Explain how prolonged precipitation generates excess runoff.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by excess runoff?

    Model answer

    Excess runoff is water reaching the channel faster than it can be carried away. Discharge then exceeds bankfull capacity and flooding follows.

  2. 2

    Explain how prolonged precipitation generates excess runoff.

    Model answer

    Weeks of rain fill the soil moisture and groundwater stores until the catchment is saturated. Further rain can only run off the surface, so discharge climbs sharply.

  3. 3

    Give a British example of flooding caused by prolonged precipitation.

    Model answer

    The Somerset Levels flooded for weeks in the winter of 2013 to 2014 after an exceptional run of Atlantic storms. Saturated ground and a high water table left nowhere for the water to go.

  4. 4

    Explain how an intense storm generates excess runoff.

    Model answer

    Rainfall intensity exceeds the soil's infiltration capacity within minutes. Almost the entire rainfall total travels overland, producing a flash flood in small steep catchments.

  5. 5

    Which UK settlement suffered a severe flash flood in August 2004?

    Model answer

    Boscastle in Cornwall was devastated by a flash flood in August 2004. Intense convectional rain over the steep Valency catchment upstream caused the event.

  6. 6

    Explain how monsoon rainfall generates excess runoff.

    Model answer

    The summer monsoon delivers the great majority of the year's rain in three or four months. River channels and soils cannot absorb that concentrated total, so extensive flooding follows.

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