Glossary
Term |
Definition |
Reference |
|---|---|---|
Climate Year |
A continuous 12-month period selected to present data relative to climatic phenomena during which the annual low-flow period normally occurs. The climate year used by the U.S. Geological Survey runs from April 1 to March 31, and is designated by the year in which it ends. |
|
Cubic feet per second (cfs) |
A rate of the flow, in streams and rivers, for example. It is equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One “cfs” is equal to 7.48 gallons of water flowing each second. |
|
Discharge |
The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second. Typically, synonymous with streamflow or flow. |
|
Drainage Basin |
Land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. Also called a “watershed.” |
|
Exceedance Probability |
The probability a given flow value will be equaled or exceeded during a given time period. |
|
Flow duration curve |
A cumulative frequency curve showing the percent of time specified discharges were equaled or exceeded during a given period of record. |
|
Hydrograph |
A plot of streamflow (discharge) versus time. |
|
Hydrologic Unit |
Hydrologic units and associated n-digit (2-16) hydrologic unit codes (HUC2-16s) belong to a widely used geographic framework for the conterminous United States (CONUS). Each unit defines a geographic area representing part or all of a surface drainage basin or a combination of drainage basins. For example, cataloging units (HUC8s) are each represented with unique eight-digit numeric identifiers, and they subdivide larger six-digit accounting units (HUC6s), four-digit subregions (HUC4s) and two-digit regions (HUC2s) into smaller areas designated by the U.S. Water Resources Council and the USGS’s National Water Data Network. |
|
hyswap |
HYdrologic Surface Water Analysis Package |
|
Metadata |
Data that provides information about other data. |
|
NWIS |
National Water Information System |
|
Percentile |
The value below which a given percentage of observations in a group of observations fall. For example, the 20th percentile is the value below which 20 percent of the observations may be found. |
|
Raster hydrograph |
Pixed-based visualization of, typically, streamflow data with years on the y-axis and days on the x-axis. |
|
Rating Curve |
A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station. |
|
Recurrence Interval |
The average number of years between floods of a certain size is the recurrence interval or return period. The actual number of years between floods of any given size varies a lot because of the naturally changing climate. |
|
Runoff |
(1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it. |
|
Stage |
The water level above some arbitrary point in the river and is commonly measured in feet. |
|
Streamflow |
The water discharge that occurs in a natural channel. Typically, synonymous with discharge or flow. |
|
Water Year |
A continuous 12-month period selected to present data relative to hydrologic or meteorological phenomena during which a complete annual hydrologic cycle normally occurs. The water year used by the U.S. Geological Survey runs from October 1 through September 30, and is designated by the year in which it ends. |