Navigating these web pages...

The USGS Groundwater Watch pages present groundwater level data from wells and discharge data from springs currently in a regular measurement program.

Individual wells can be present in multiple networks. For instance, a well with real time instrumentation that is designed to monitor climate effects will be present in at least 3 networks: Real Time, Climate Response, and Active Water Levels. Springs are presented in their own network and incorporated into the Active Water Level network.  Springs are not included in any other networks at this time.

Because most USGS wells and springs are supported through State and local agencies, these web pages generally are designed using political boundaries: by State. If the network contains a large number of sites, there also is a county “layer” of pages. Networks organized by U.S. Principal Aquifers are organized by state and county within the individual Principal Aquifer.

A user has several options for viewing the color-coded maps of water level "conditions", which are the tool for navigating to individual wells and springs.

(1) Static maps created by the MapPoint® software (References to non-Department of the Interior (DOI) products do not constitute an endorsement by the DOI): These image files are relatively small, providing fast navigation even with slow internet connections.

(2) Interactive maps created using Google Maps: These maps provide the user with more flexibility such as the ability to zoom and pan, and to view different backgrounds, such as roads, satellite photography, or USGS topographic maps. One limitation to this approach is the speed at which the pages are “rendered”, or drawn by the browser. The rendering speed is affected by the number of sites in the map. Thus the maps from states or counties with many sites can take a long time to render. We have compromised some flexibility for rendering speed by limiting the number of sites we present in individual maps. County maps contain all of the wells and springs in the county, and additional sites (depicted with low color intensity) in a small buffer around the county boundary. State maps contain all the sites in the State, and additional sites (depicted with low color intensity) in a small buffer around the State boundary.

(3) Interactive maps using Google Earth: Google Earth .kmz files are created daily for each network, and available from a link on the National Map (containing all sites in the network), or on the State map (containing only wells in that State). Use of .kmz files requires the user to install Google Earth software on their local computer. Google Earth software is available at no cost at http://earth.google.com/ . Users are reminded that the color-coded networks map .kmz files must be downloaded each day for an up-to-date view of the network. Individual wells or springs within a Google Earth view should always be up-to-date regardless of when the .kmz files were obtained.

Explanation for Types of Data

There are three types of data available from wells and spings measured by the USGS:

(1) Periodic data from wells are groundwater levels that are incrementally measured, by hand at selected intervals, usually with a steel or electric tape. These measurements typically are made monthly to quarterly. Thus, periodic water level data displayed on these web pages may be the most recent measurement from the well, but still several months old. A triangle is used to symbolize a well with periodic data in Groundwater Watch, Periodic data from springs are instantaneous discharge (flow) measurements made at the site.  Springs with periodic data are depicted by a square with shading in the upper left corner. Periodic data are considered to be "approved data" once they are presented on the internet.

(2) Continuous data are measurements made by an automatic sensing device, recorded by a data logger, and periodically retrieved from the well or spring. The availability of continuous data may lag current conditions by one to several months because they must be retrieved from the field, processed, and loaded into the USGS database. Some continuous data are provisional and subject to revision. A square is used to symbolize a well with continuous data in Groundwater Watch; springs are depicted by a square with shading in the lower right corner.

(3) Real-time data are continuous data that are transmitted from the site to the USGS, usually by satellite or telephone at least once per day. Real-time data reflect current groundwater conditions in the well or at the spring. The real-time data presented on these web pages are one day behind because of the statistical calculations used in the data presentation. All real-time data are provisional and subject to revision. A circle is used to symbolize a well with real-time data in Groundwater Watch; springs are depicted by a partially-shaded square.

Data Updates

Each weekend, all Groundwater Watch networks are refreshed and old contents are completely replaced with new. Therefore, new sites  added to NWISWeb by a local Water Science Center during the week will not show up on Groundwater Watch until the following Monday morning. Currently, due to the volume of data and processing time required, non-real-time daily values are updated weekly.

Each weekday, real-time and periodic data are updated incrementally for sites already in Groundwater Watch, beginning at 4:30 am, starting with states on the east coast and progressing to the west by time zone. Therefore, maps and data for the nation are not completely up-to-date until mid-afternoon, eastern time, Monday through Friday. A time tag at the bottom of the map image indicates the date/time the map was created.

Provisional Data Disclaimer

Some data from real-time sites , and sites  with continuous instrumentation that are not transmitted in real time are considered to be Provisional Data because they have not yet been reviewed and finalized, or approved, by the USGS. These data may be subject to significant revision and should not be cited until reviewed and approved by the U.S. Geological Survey. Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Provisional data are incrementally approved over the course of a year. On these web pages, the approval status of an individual measurement can be determined by (a) the color of the measurement as presented in a hydrograph (red=provisional; blue=approved), and/or the “status code” that is attached to each measurement in the “download data in text format” option.

Explanation of a Percentile

Data are presented within a statistical framework. The percentile provides this statistical framework. A percentile is a value on a scale of one hundred that indicates the percent of a distribution that is equal to or below it. For example, on the map of groundwater levels, the water-level at the 90th percentile is equal to or greater than 90 percent of the monthly median groundwater levels in a given month over the period of record at the well. In general,

  • a percentile greater than 90 is considered much above normal

  • a percentile greater than 75 and less than 90 is considered above normal

  • a percentile between 25 and 75 is considered normal

  • a percentile between 10 and 25 is considered below normal

  • a percentile less than 10 is considered much below normal

    The data category “Low” indicates that the most recent  measurement is lower than the lowest monthly median  in the month of measurement over the period of time that the well or spring has been measured. Similarly, the water-level category “High” indicates that the most recent measurement is higher than the highest monthly median in the month of measurement over the period of time that the well or spring has been measured.

    The data category “Not Ranked” indicates that a data category has not been computed. This is most often due to the fact that there have not been at least 10 years of measurements in the month of the most recent measurement. In the Climate Response Network, a measurement also will be categorized as “Not Ranked” if the measurement is more than 45 days old.

    Groundwater Watch percentile statistics are calculated according to the National Institute of Standards and Technology's (NIST) handbook definition of percentile computations.

    See: http://www.itl.nist.gov/div898/handbook/prc/section2/prc252.htm

    Percentiles are estimated from N measurements as follows:

    For the pth percentile:
    set p(N+1) equal to k + d for k an integer, and d, a fraction greater than or equal to 0 and less than 1.
    For 0 < k < N, Y(p) = Y[k] + d(Y[k+1] - Y[k])
    For k = 0, Y(p) = Y[1]
    For k = N, Y(p) = Y[N]

    Explanation for Statistics on these pages

    The frequency of groundwater measurements is determined by technical and economic factors. Technically, the frequency of measurement is based on the expected variability of the water-level fluctuations and the objectives of the measurements. A shallow well used to monitor drought conditions may be measured hourly and have real-time instrumentation. A deep well in a confined aquifer with a stable water level, or stable water-level trend may be measured once per year. For economic reasons, the measurement frequency at a well may change over time from continuous to periodic due to fluctuations in available funds. In most instances, springs are measured with continuous monitoring equipment at 15-minute intervals as is common for surface-water gaging stations.

    The statistical approach presented in these web pages reflects the diversity of the data sets available for individual wells or springs across the United States. Ideally and for statistical simplicity, hourly or daily values would be available for 30 or more years from every well in every network. However, that is not the case, nor is it even appropriate in some cases to adequately characterize the water level in an aquifer.

    In these pages, water-level or spring discharge measurements are evaluated within a monthly statistical framework. This process permits a uniform approach for sites with frequent data collection and sites with infrequent data collection. Some special circumstances should be explained. In some cases, usually with very old measurements, a measurement may have a partial date--a year with no month/day, or a month with no day. When only a measurement year is available, monthly statistics are calculated using January as the default month. When only a measurement year/month is available, the measurement day is assumed to be the first. This approach is consistent with other components of NWISWeb. Measurements in Groundwater Watch may have a variety of "status codes", meaning the water level may reflect steady-state conditions, or it may be influenced by pumping or by surface water, for instance. All measurements with a numeric value are included in the statistics calculation regardless of status code.

    Four different statistical summaries may be available for a given well. An explanation for these for summaries is included below.


    All available data (periodic and continuous) from an individual well or spring are grouped by month in a given year, ranked, and a median for each Month/Year combination is selected. Individual month/year medians are grouped by month over the period of record (multiple years). These monthly medians are then ranked, and the appropriate statistics are presented based on the following criteria:

    If there are 4 or less years of data for any given month, no statistics are computed for that month. If there are more than 4 years and less than 10 years of data in a given month, the minimum, median, and maximum water levels are displayed in the table, and plotted in the adjacent hydrograph using a vertical line. If there are 10 or more years of data in a given month, water-level or discharge percentiles are computed and displayed in a table and in the adjacent hydrograph using colored monthly bars. When only partial water-level dates are available, hydrographs are generated using the first month (January) and first day of the month for missing month and/or day to be consistent with other components of NWISWeb. Provisional data that have not received final USGS approval are not included in these statistical calculations.


    This section of the web page presents descriptive statistics using only the approved continuous record available from a site. The entire population of approved  daily values  is ranked (regardless of day or month). Percentiles then are computed based on the entire population of daily values. The daily value used in this calculation is determined by the individual USGS office responsible for the data collection, and may be the daily minimum, daily mean, daily maximum, or noon measurement for the day. When multiple types of daily values are available (min, mean, max), the daily value with the longest period of record is used. Provisional data that have not received final USGS approval are not included in these statistical calculations.

    Two year hydrographs are generated when recent daily values data are available.  For spring sites with at least one year of approved daily values, Groundwater Watch produces a flow-duration curve, as described by Searcy in USGS Water Supply Paper 1542a, "Manual of Hydrology: Part 2. Low Flow Techniques". The diagram indicates what percent of time that springflow is equal or exceeded during a given period.  To produce this cumulative frequency curve, the daily flow during the period of approved daily values are ranked by magnitude, and the percent of time during which the flow equaled or exceeded the specified values is computed. 


    This section of the web page presents a summary of groundwater levels and spring discharge measurements using only the periodic record available from a site. The entire population of periodic measurements from a site is evaluated, and the highest and lowest periodic measurements are presented. Periodic measurements available on the web are approved data, and all data are used in statistical calculations.


    This section of the web page presents a summary of all measurement data available from a site, and is not restricted to approved data. The periodic measurements and daily values described above are combined with provisional continuous and real time data. The entire population is evaluated, and the highest and lowest values are presented in the associated table. The plotting priority for the combined data hydrograph is as follows: daily value, real-time value, periodic value.

    Summary of Networks available on Groundwater Watch

    National Networks

    Active Groundwater Network

    The Active Groundwater Level Network contains water levels and site information from more than 20,000 wells and more than 100 springs that have been measured by the USGS or USGS cooperators at least once within the past 407   days. This network includes all of these sites, regardless of measurement frequency, aquifer monitored, or the monitoring objective.

    Climate Response Network

    The USGS maintains a network of wells to monitor the effects of droughts and other climate variability on groundwater levels. The network consists of a national network of about 140 wells monitored as part of the Groundwater Resources Program, supplemented by more than 450 wells across the nation that are monitored as part of the Cooperative Water Program.

    Real-Time Network

    Real-time data typically are recorded at 15-60 minute intervals, stored onsite, and then transmitted to USGS offices every 1 to 4 hours, depending on the data relay technique used. Recording and transmission times may be more frequent during critical events. Data from real-time sites are relayed to USGS offices via satellite, telephone, and/or radio and are available for viewing within minutes of arrival.

    Active Springs Monitoring Sites

    The Active Springs Monitoring Sites network contains springs with current discharge data. This network includes all of the sites in NWISWeb designated as type “Spring”, regardless of measurement frequency or the monitoring objective.

    Long-Term Groundwater Data Network

    The Long-Term Groundwater Data Network is comprised of active wells measured on a periodic, monthly or yearly basis for periods of 20, 30 or 50 years, whose records are at least 80% complete.

    The following measurement frequencies are selectable in these pages

  •   Annual Data:
    		•   at least 1 measurement per year (includes monthly and daily wells)
  •   Monthly Data:
    		•   at least 1 measurement per month (includes daily wells)
  •   Daily Data:
    		•   at least 1 measurement per day.

    The user can select from the following lengths of record:

  •   20 years: 20 or more years of record (includes data in 30 and 50 year data set)

  •   30 years: 30 or more years of record (includes data in 50 year data set)

  •   50 years: 50 or more years of record.

    To be included in the data set, the well record must be 80% complete over the period of interest. For example, selecting wells with 30 years of monthly data means that all wells in the data set will have at least 288 months of measurements (30 yrs x 12 months x 80%).

    By selecting among the various frequency and length of record radio buttons, a user can select the datasets of interest, organized by state.

    • Regional Networks

    High Plains Aquifer Monitoring Network

    The High Plains Aquifer Monitoring Network contains water levels and well information from selected wells measured annually by the USGS and numerous Federal, State, and local water-resources agencies. A network of about 9,000 wells was used to monitor water levels in the High Plains aquifer in 2007. This network consists of many smaller networks of wells measured by numerous agencies. State and local agencies are responsible for the majority of the water-level measurements. The water-level measurements were collected in winter or early spring when irrigation wells typically were not pumping and water levels generally had recovered from the stress of pumping during the previous irrigation season.

    Piedmont and Blue Ridge Aquifer Groundwater Network

    The Piedmont and Blue Ridge Aquifer Groundwater Network is populated by wells completed in the Piedmont and Blue Ridge crystalline-rock aquifers, as defined in the U.S. Geological Survey (http://water.usgs.gov/ogw/aquiferbasics/pbr-crystal.html). Network wells have been measured by the USGS or USGS cooperators at least once within the past 13 months, regardless of measurement frequency or the monitoring objective.

    State and Local Networks

    State and local “networks” are defined by Water Science Centers as a way to group specific collections of wells. These “networks” have a variety of criteria including political divisions, principle aquifers, cooperators, and water management districts, for example. Areally, the networks range from multi-state areas (such as New England) to municipalities (such as Philadelphia).  The list of wells comprising the network is maintained by the Water Science Center. Any USGS Center interested in establishing a local network should contact the Office of Groundwater for further information.

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