Flood hydrographs explained

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.