HYDROGRAPH AND ITS COMPONENTS
A hydrograph of a catchment produced by a storm is a graphical representation of discharge rate of a stream with respect to the time from the commencement of storm. It is an inverted U shaped diagram.
Hydrograph generally contains the following three parts.
1. Rising Limb
2. Peak (or Crest) Segment
3. Falling (or Recession) Limb
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| Fig : Element of flood hydrograph |
1. Rising Limb : It is the ascending curved portion of the hydrograph. The rising limb rises slowly in the early stage of the flood but more rapidly toward the end portion. The shape of rising limb depends on duration and intensity distribution of rainfall. This is because in early stages the losses is more and water reaches to the stream faster.
2. Peak Segment (or Crest Segment) : Peak segment is shown by inverted U in the hydrograph. This is the part which is taken as matter of interest by hydrologists. Peak of hydrograph occurs when all parts of basins contribute at the outlet simultaneously at the maximum rate. Depending upon the rainfall-basin characterstics, the peak may be sharp, flat or may have several well defined peaks.
3. Falling Limb (or Recession Limb) : Recession Limb represents the withdrawal of water from the storage built up during the early phase of hydrograph. It extends from the point of inflection at the end of the crest to the beginning of the natural groundwater flow. The shape of recession limb depends upon basin characteristics only and independent of the storm.
