hydrograph

thumb|upright=1.2|A stream hydrograph. Increases in stream flow follow rainfall or [[snowmelt. The gradual decay in flow after the peaks reflects diminishing supply from groundwater.]]

A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in units of cubic meters per second (m³/s) or cubic feet per second (cfs). Hydrographs often relate changes of precipitation to changes in discharge over time. The term can also refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network. Graphs are commonly used in the design of sewerage, more specifically, the design of surface water sewerage systems and combined sewers.