(1,443 sites)
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Real-time data are time-series (recorded at fixed intervals) data from automated equipment and represent
the most current hydrologic conditions. Measurements are commonly recorded
at 5-60 minute intervals and transmitted to the NWIS database every 1-4 hours.
Real-time data are available online for 31 days.
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(6,434 sites)
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Daily values are summarized from time-series
data for each day for the period of record and may represent the daily
mean, median, maximum, minimum, and/or other derived value. Daily values include
approved, quality-assured data that may be published, and more recent
provisional data, whose accuracy has not been verified.
Example.
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(2,530 sites)
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Statistics are computed from approved daily mean time-series data at each site.
These links provide summaries of approved historical daily values for daily,
monthly, and annual (water year or calendar year) time periods.
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(371,441 sites)
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Data from field and/or laboratory analyses of water samples,
biological tissue, stream sediments, or other environmental samples.
Data include approved, quality-assured data that may be published,
and more recent provisional data, whose accuracy has not been verified.
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Introduction
The U.S. Geological Survey's (USGS) National Water Information
System (NWIS) is a comprehensive and distributed application that
supports the acquisition, processing, and long-term storage of water
data. NWISWeb serves as the publicly available portal to a
geographically seamless set of much of the water data maintained
within NWIS
(additional background).
The USGS collects and analyzes chemical, physical, and biological
properties of water, sediment and tissue samples from across the
Nation. The NWISWeb discrete sample data
base is a compilation of over 4.4 million historical water quality
analyses in the USGS district data bases through September 2005. The
discrete sample data is a large and complex set of data that has
been collected by a variety of projects ranging from national
programs to studies in small watersheds. Users should review the help notes and particularly the data
retrieval precautions before beginning any retrieval or analysis
of data from this data set. Additions of more current data,
modifications to ancillary information, and enhanced retrieval
options to help users find and appropriately use the data they need
are planned for a future release of NWISWeb.
At selected surface-water and ground-water sites, the USGS maintains
instruments that continuously record physical and chemical
characteristics of the water including pH, specific conductance,
temperature, dissolved oxygen, and percent dissolved-oxygen
saturation. Supporting data such as air temperature and barometric
pressure are also available at some sites. At sites where this
information is transmitted automatically, data are available from
the real-time data system. Once
a complete day of readings are received from a site, daily summary data are generated and made
available online. Annually, the USGS finalizes and publishes the
daily data in a series of water-data reports.
You may find additional water-quality data of interest in
EPA STORET.
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Tutorial explaining how to perform water quality retrievals and understand the results of real-time data and discrete water-quality measurements.
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