The Flood hydrograph

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The Flood hydrograph

• A brief explanation-
• By Paul P., Dean M., George W., James S., Chris
  O.

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• Shows variation in discharge(m3 per sec) over
  time.
• Storm hydrograph shows effects of rainfall input.
• The average levels represent the base flow of
  water produced from groundwater supply.
• The two limbs are called the rising and recession
  limbs while the time delay between max rainfall
  and max river discharge is called the lag time.

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• The flood hydrograph

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• A-DISCHARGE
• B-LAG TIME (Affected by rock permeability and
  vegetation interception)
• C-PEAK DISCHARGE
• D-ZONE OF FLOOD RISK
• E-NORMAL (BASE) DISCHARGE
• F-RECESSION LIMB
• G-RISING LIMB

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How is it affected?

• Intensity and duration of rainfall
• Seasonal weather conditions
• Residual moisture eg. Saturation increases angle
  of rising limb
• Vegetation cover (affects interception)
• Size and slope angle of drainage basin (lowers
  and increases peak discharge respectively)
• Urbanisation eg. Concreting increases speed of
  water reaching the channel