Streamflow

Streamflow is the movement of water through a natural or artificial channel. It is commonly quantified as discharge: the volume passing a point per unit time.

Discharge (hydrology): The volume of water flowing past a cross-section per unit time. This is the standard quantitative measure of streamflow.
Open-channel flow: Fluid flow with a free surface exposed to atmospheric pressure. Natural streams are a major setting for this broader type of flow.
Stream gauge: An instrument or station that records water level or discharge in a stream. Gauge records provide the observations used to track streamflow.
Flood: An overflow of water that inundates land not normally covered by it. Floods occur when streamflow exceeds channel or floodplain capacity.
Hydrograph: A graph showing how water level or discharge at a location changes over time. Hydrographs reveal the timing and magnitude of streamflow changes.
Cross section (hydrology): A vertical profile across a river channel used to describe its shape and measure flow. Discharge measurements depend on the area of a channel cross-section.
Streamflow forecasting: The prediction of future river discharge using weather, watershed, and flow data. Forecasts anticipate changing flows for warnings and water operations.
Drought: A prolonged period of unusually low water availability relative to normal conditions. Low streamflow is a key hydrologic expression of drought.
Manning formula: An empirical equation estimating flow velocity in open channels from channel geometry, slope, and roughness. It estimates channel velocity and discharge from physical channel properties.
Stage (hydrology): The height of a water surface above a reference elevation at a specified location. Stage is measured directly and often used to infer streamflow.

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