What is Flood Hydrograph or Storm Hydrograph or Total Runoff Hydrograph?

Flood Hydrograph/Storm Hydrograph/Total Runoff Hydrograph-

It is a continuous plot of instantaneous discharge (runoff) v / s time.  

It results from a combination of physiographic and meteorological conditions in a watershed and represents the integrated effects of climate, hydrologic losses, surface runoff, interflow, and groundwater flow.  

Factors that influence the hydrograph shape and volume 

  • Meteorological factors 
  • Physiographic or watershed factors and 
  • Human factors 

Flood hydrograph has three characteristic regions: 

(i) Rising limb AB: Curve Joining point A, the starting point of the rising curve and point B, the point of inflection.  It is concave in shape and the shape depends both upon the rainfall and the catchment parameters.

(ii) Crest segment BC: with a peak P between two points of inflation B and C.  For large catchments it usually occurs occasionally after the rains are over.  

(iii) Falling limb / recession limb: The curve starts from the second point of CD C and the size depends only on the catchment parameters because by then the rain has stopped.

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