Ground-water conditions in southern Florida
Data presented: Water levels at selected site, reported in feet above the National Geodetic Vertical Datum of 1929.
Timeframe of the graph: The current calendar year. One of the consequences of the selected timeframe is that during early January the daily water level line for the current year will appear as a point at the left side of the graph.
Data time lag:
Narrative text: Daily maximum water levels for the current calendar year are compared to the water levels from last year, and to the minimum and maximum daily levels for the corresponding weeks of the year for the site period of record prior to the current water year.
Barring computational errors, the following information is expected to be conveyed in the figure:
"Daily maximum water-level elevation, current year" - The daily maximum water levels (maximum water level recorded in the 24-hour period from midnight to midnight, local time) are retrieved for the the period of time from the beginning of the current calendar year to the time graphed for continuous water elevation.
"Daily maximum water-level elevation, last year" - The daily maximum
water levels (maximum water level recorded in the 24-hour period from
midnight to midnight, local time) are retrieved for the the period of
time 365 prior to the time graphed for continuous water elevation.
For example, if the time period of January 25, 2000 through February 24,
2000 is shown for current continuous water levels, the daily maximum values
for the corresponding dates 365 days previous are retrieved: January 25,
1999 through February 24, 1999. The dates in the data file are modified
accordingly so that they plot with the current data.
"Maximum elevation (by week)" - For the post-1974 period of record for
the well, daily maximum values are grouped by the week of the year they
were recorded for, and certain statistical operations performed. For this
purpose, the first 7 days of the year constitute the first week, the
second 7 days the second week, and so forth. This differs in part from
the Gregorian calendar in that weeks are not measured from Sunday to
Saturday, but from the (7*n) day of the year to the (7n + 6) day of the
year (to define the nth week).
The data shown is the maximum daily maximum for all data for the
appropriate week. Therefore, it is the maximum elevation for that "week".
For plotting purposes, the data point is expressed as being "for" the
4th day of its respective week, not necessarily Wednesday.
"Minimum daily maximum elevation (by week)" - This value is derived
in the same manned as the "Maximum elevation (by week)". However, as it
is the daily maximum values that are compared, this cannot be considered
the true minimum record value for the respective week.
This highlights one of the problems with historical and archival
natural sciences data: eventually the data set becomes too large to
store and retrieve. Because the older, pre-computer storage, data is
largely recorded and archived as daily maximum values, it makes sense
to use daily maximum values for inter-year comparisons so that the
most data can be used. A consequence of this is that for wells with
large daily variations in water level the "minimum" presented is actually
biased "high". When considering the relationship among the data sets
presented in the graph, the daily variation shown by the continuous
data may give a rough indication of the dimension this positive bias.
"Water levels collected during site visits, last year" - Water level data collected during a visit to the site by a field technician. Because the daily value is the maximum water level for the day, this value is often a bit below the daily value of record.
Missing data in a plot (a blank part of a graph, or gaps in a plotted line) can be caused by any of the following:
The station may not have been on the USGS cooperative data collection program for that period of record.
The recorder at the site may have been malfunctioning and the data either lost or not collected.
The data may have failed quality assurance standards and been either deleted or set for non-release.
For these reasons, all data presented on these pages must be considered provisional, even if released for official use elsewhere.
Funding for the USGS to design and maintain this site has been provided through a cooperative agreement with the South Florida Water Management District (SFWMD). Water-level conditions are monitored by the USGS with support from Federal, State, and local cooperators.
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://www.sflorida.er.usgs.gov/edl_data/text/template_43.html
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