Understanding Hydrographs

A hydrograph is a graphical representation that plots the discharge (flow rate) of a river or stream over time. It essentially shows how a river's flow changes in response to various factors, primarily precipitation events within its drainage basin.

Hydrograph Utility in Runoff Estimation

The shape and characteristics of a hydrograph provide vital information about the relationship between rainfall and the resulting streamflow (runoff).

• Runoff Rate: The peak of the hydrograph indicates the maximum runoff rate experienced at the measurement point following a rainfall event. The rising and falling limbs show how the rate changes over time.
• Runoff Volume: The total area beneath the hydrograph curve over a specific period represents the total volume of water that has flowed past that point. This directly corresponds to the total runoff volume generated by the catchment area during that time.

While related to rainfall, the hydrograph specifically measures the output (runoff) rather than the input (rainfall rate, frequency, or intensity) directly. Therefore, it is most useful for estimating the characteristics of the runoff itself.

Based on this, a hydrograph is primarily useful for estimating runoff rate and runoff volume.