Definition of Hydrograph:
A hydrograph of a stream as defined by Wisler and Brater is a graphical representation of its fluctuations in flow arranged in chronological order. A complete hydrograph shows every minor variation in flow and can therefore be obtained only from an instrument that continuously records these changes, for no stream is constant in flow even for short periods of time.
Uses of Unit Hydrograph:
The Unit Hydrographss establish a relationship between the effective rainfall hyetograph (ERH) and direct runoff hydrograph (DRH) for a catchment
They are of great use in:
i. The development of flood hydrographs for extreme rainfall magnitudes (for use in the design of hydraulic structures)
ii. Extension of flood flow records based on rainfall records
iii. Development of flood forecasting and warning systems based on rainfall