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 occurring each year; a "2 Year Flood" has a % chance of occurring 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 along a river, stream, or channel for which measurements of a river gage are representative.
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"). The stage is not a measurement of the actual water depth.
WATER YEAR: Hydrologists dealing with surface-water supply use the 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the year ending September 30, 2005, is called the "2005 water year." (There are a number of reasons for dividing the months in this fashion. The primary one is that it allows all of the seasonal snowfall to be included into the same group).