In hydrology

Hydrology

Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...

, stage refers to the water level in a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 or stream

Stream

A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...

 with respect to a chosen reference height. Stage is important because direct measurements of river discharge

Discharge (hydrology)

In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...

 are very difficult while water surface elevation measurements are comparatively easy. In order to convert stage into dicharge, scientists can use a combination of tracer studies, observations of high water mark

High water mark

High water mark may refer to:*Ordinary high water mark, a landscape marking such as floodwater staining left by the highest level of water...

s, numerical modeling]], and/or satellite or aerial photography

Aerial photography

Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure. Cameras may be hand held or mounted, and photographs may be taken by a photographer, triggered remotely or...

. The relationship between stage and discharge is called a rating curve

Rating curve

In hydrology, a Rating curve is a graph of discharge versus stage for a given point on a stream, usually at gauging stations, where the stream discharge is measured across the stream channel with a flow meter . Numerous measurements of stream discharge are made over a range of stream stages...

.