River Speak

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COMMON HYDROLOGIC TERMS AND DEFINITIONS

BANKFULL: An established river stage/elevation at a given location along a river which is intended to represent the maximum safe water level that will not overflow the river banks or cause any significant damage within the river reach.

BASIN: Whole geographic area having a common outlet (such as a river, stream, or lake) for its surface runoff. Also known as drainage area or watershed.

CREST: The highest stage or level of water at a specific point before the water begins to recede.

FLOOD FREQUENCY: The chances that a particular flood event will occur during any given year. The greater the flood, the higher the "Year Flood" Value, but the less chance of occurrence. (i.e. a "100 Year Flood" has a 1% chance of occuring each year).

FLOOD STAGE: The elevation at which overflow of the natural banks of a waterway begins to cause damage or presents a flood-damage hazard near the gage where the elevation is measured (can also be expressed in terms of flood flow).

FLOW: The volume of water that passes through a point of a river during a given time. Usually expressed in cubic feet per second (cfs).

HYDROGRAPH: A graph showing stage, discharge, or other property of a river with respect to time.

REACH: The length of area between two specific points (usually between 2 gages) along a river, stream, or channel.

RUNOFF: The part of precipitation that flows toward a river or stream on the surface of the ground, or through the soil before returning to the surface.

STAGE: The level of the surface of a river or lake above a predetermined base elevation (or "datum").

WATER YEAR: October 1 through September 30.