Introduction to Hydrograph

Fig: Single Peaked Hydrograph

   Hydrograph or Flood hydrograph is the graphical representation of the instantaneous rate of discharge of a stream plotted with respect to time at particular point. In simple words, hydrograph are the graphical drawing used to show how the water flows in a drainage basin respond to a period of rain.

The hydrograph may have a single peak or multiple peaks, depending upon the nature of the storm . If the subsequent storm does not occur before the direct runoff of the first storm ceases, such storm is called isolated storm and it results single peak hydrograph. And if next storm(rainfall) occur before the direct runoff of the first storm ceases then such storm is called complex storm and it results multi-peaked hydrograph.

The beginning of Hydrograph starts when storm starts. As the storm(rain) is commenced, water starts flowing toward the natural stream (river) from the catchment. Slowly the discharge of the river increases (shown as rising limb in the hydrograph) as water is added to the stream from the catchment. Time come when the water from farthest point of the catchment reach the river. In this period river reaches its maximum discharge (shown as peak flow in the hydrograph). Now as the storm ceases and addition of water to the river through storm stops, the remaining water from the catchment still flows to the stream, adding less discharge to the stream than before. Hence discharge of the river slowly decreases, as only the remaining flow from the catchment of previous storm enters the river (shown as falling limb or recession limb in the hydrograph). And slowly base flow is attained and the river carries same discharge as before the storm had arrived.

*Note: The detailed parts and points of single peaked hydrograph are explained in the next post. Please keep following.