A hydrograph is a graph of the flow in a stream over a period of time. Below is a picture of a hydrograph, with stream flow (discharge) in cubic feet per second on the y-axis and time in months on the x-axis. Peaks in the hydrograph are usually a result of precipitation events, while troughs represent drier times.

To read a hydrograph, pick an approximate date and trace a vertical line up to where it intersects the graph. Reading horizontally to the left, you can determine the discharge of the stream for that date.


Text courtesy of Marc Antiniro.