A graph showing the variation of discharge or water level at a point in a stream over time. It is the fundamental tool for analyzing streamflow response to precipitation.
A hydrograph is a graphical representation of the flow rate (discharge) or water level (stage) at a specific point in a river or stream as a function of time. It is the primary tool used by hydrologists to understand how a watershed responds to precipitation events, snowmelt, or other inputs. A typical storm hydrograph shows several distinct components: the rising limb representing increasing flow as runoff reaches the channel, the peak or crest where maximum discharge occurs, and the recession limb as flow gradually decreases. The shape of a hydrograph is influenced by catchment characteristics such as area, slope, land use, and soil type, as well as storm properties including rainfall intensity, duration, and spatial distribution. Base flow separation techniques are applied to hydrographs to distinguish between direct runoff and groundwater contributions. Hydrograph analysis is essential for flood forecasting, reservoir operations, water supply management, and design of hydraulic structures. Long-term hydrograph records also reveal trends related to climate change and land use modification.