Nevada Water Science Center

Nevada Flood Chronology


Definition of Terms

Alluvial Fans
A fan-shaped landform created over time by the deposition of eroded sediment from a river or stream when its flow is suddenly slowed as it reaches flatter land.
Based on or consisting of reports or observations of usually unscientific observers.
Annual Exceedance Probability(AEP)
The probability, or odds, of a flood of a given magnitude being equaled or exceeded in any given year. For example, a 1-percent AEP indicates that a particular flow magnitude has a 0.01 probability, or a 1% chance, of being equaled or exceeded in any given year.
Annual Peak Flow
The maximum discharge/streamflow occurring in a water year, in cubic feet per second (cfs).
Cubic feet per second.
Digital Flood Insurance Rate Map (DFIRM)
A collection of digital data that are used in GIS systems for creating new Flood Insurance Rate Maps (FIRMs) URL:
Discharge Date
Date the peak flow measurement was made.
Both terms are used to describe the actual flow in streams.
Drainage Area
The area upstream from an outlet (often a gaging station site) from which runoff accumulates and drains to the outlet point.
Federal Emergency Management Agency. URL:
Flood Insurance Rate Map (FIRM)
Maps produced by FEMA that show areas subject to flooding. The flood risk information presented on the FIRM is based on historic, meteorological, hydrologic, and hydraulic data, as well as open-space conditions, flood control works, and development. URL:
Flood Frequency
Statistically derived estimate of the annual exceedance probability, expressed as a percent, of a flood of a given magnitude being equaled or exceeded for any given year a particular location.
The source of a stream or river.
Historic Peak
Observed or inferred during years when there was no systematic observation of streamflow. Peak of record is only historic if it occurs outside the systematic period.
Specific events where some information about the range that the peak falls within is known.
Measurement Type
The method used to measure streamflow. Types of measurements listed in this web site include (a) water-stage recorders — electronic devices that continuously measure the river stage at 15-minute intervals, (b) crest-stage recorders — measure only the stage, or height of flow in the channel, and (c) indirect measurements — uses field evidence such as high-water marks and mathematical equations to estimate a peak flow after the peak flow for a flood event has occurred.
The Nevada Division of Emergency Management is one of the divisions of the Department of Public Safety. The mission of NDEM is to cCoordinate efforts to protect lives and property; to prevent, respond to, recover form and mitigate all threats, hazards and emergencies. URL:
The Nevada Division of Water Resources is one of the divisions of the Nevada Department of Conservation and Natural Resources. The mission of NDWR is to conserve, protect, manage and enhance the State's water resources for Nevada's citizens through the appropriation and reallocation of the public waters. URL:
The National Flood Insurance Program is a Federal program enabling property owners in participating communities to purchase insurance protection against losses from flooding. This insurance is designed to provide an insurance alternative to disaster assistance to meet the escalating costs of repairing damage to buildings and their contents caused by floods. URL:
National Oceanic and Atmospheric Administration. URL:
Natural Resources Conservation Service. URL:
U.S. Geological Survey’s Web-based National Water Information System. URL:
National Weather Service. URL:
Peak Flow
The maximum instantaneous discharge for a stream or river at a given location and it usually occurs at or near the time of maximum stage. Peak flows are either directly measured or estimated using stage-discharge or slope-area methods.
Perception Threshold
Years where we know something about the range of peaks that would have been observed.
Period of Record
The time period during which data was collected at a particular site.
Landform lying or formed at the base of mountains gently sloping to a region of flat land.
A watery mixture.
An acronym for SNOwpack TELemetry: a snowpack and related climate data collection system installed, operated, and maintained by the Natural Resources Conservation Service, U.S. Department of Agriculture. For more information, visit the SNOTEL web site at <>.
The height of a water surface above an established point or datum.
Systematic Peak
Recorded during one or more periods of regular data collection; may be from the continuous record or from a crest stage gage. May include the peak of record.
The water's final destination.
U.S Army Corp of Engineers. URL:
Water Year
Water year is the 12-month period beginning October 1 and ending September 30 and is designated by the calendar year in which it ends. For example, the water year from October 1, 2005 to September 30, 2006 is designated as the 2006 water year.

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