Hydrograph is a graph showing variations of discharge with tome, at a particular point of a stream. It shows the time distribution of total runoff at the point of measurement.

As runoff includes the contributions from surface runoff, sub-surface runoff and ground water runoff, the hydrograph can be regarded as an integral expression of the physiographic and climatic characteristics that govern the relations between rainfall and runoff.

Single peaked hydrograph

Components of a single peaked hydrograph :

The essential components of a single peaked hydrograph resulting from an isolated storm:

• The rising limb (AB)
• The peak or crest element (BPC)
• The recession limb (CD)

Rising Limb : The rising limb is the ascending portion of the hydrograph corresponding the increase of discharge due to gradual formation of storage in the channels existing in the area and also over the watershed surface. It is also known as the concentration curve.

Peak or crest element : The peak or crest segment includes the part of the hydrograph from the inflection point B on the rising limb to an inflection point C on the recession limb. It indicates the peak flow rate.

Recession limb : The recession limb extends from the point of inflection C of the crest segment to the point D, the point of commencement of natural ground water flow. The recession limb indicates the storage contribution from surface storage, interflow and ground water flow.