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Study Notes

Flood hydrographs explained

Level:
AS, A-Level
Board:
AQA, Edexcel, OCR, IB, Eduqas, WJEC

Last updated 22 Mar 2021

What are flood hydrographs? This study note explains them.

Flood hydrographs are graphs that show how a drainage basin responds to a period of rainfall.

They are used to plan for flood situations and times of drought. They show the river discharge that occurs as a result of precipitation from an earlier storm.

Key terms on the hydrograph, illustrated below, are:

  • Peak rainfall – time of the highest rainfall level.
  • Peak discharge – time of the highest river channel level.
  • Lag time – difference in time between the peak rainfall and peak discharge.
  • Rising limb – the increase in river discharge.
  • Falling limb – the fall in river discharge.
  • Base flow – normal river level.
Flood Hydrograph

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