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Revisions to Florida Geological Survey Special Publication 52
[Florida Springs Nomenclature Committee (FSNC); December, 2005]
swallet The opening through which a stream loses all or part of its water to the subsurface; or a
place where a stream may sink into alluvium in a streambed without the presence of a
depression. It is synonymous with swallow hole (Modified from Neuendorf, Mehl, and
swallow hole See swallet.
ponor Hole in the bottom or side of a closed depression through which water passes to or from
an underground channel (Modified from Field, 1999).
spring magnitude A category based on the volume of flow from a spring per unit time.
The classification system (Table 2) used in Florida is based on Meinzer (1927).
Table 2a. Spring Magnitude
Magnitude Metric Units English Units
1 > 2.832 cms > 100 cfs (> 64.6 mgd)
2 > 0.283 to 2.832 cms > 10 tol00 cfs (> 6.46 to 64.6 mgd)
3 > 0.028 to 0.283 cms > 1 to 10 cfs (> 0.646 to 6.46 mgd)
4 > 0.0063 to 0.028 cms > 100 gpm to 1 cfs (> 100 to 448gpm)
5 > 0.631 to 6.308 lps > 10 to 100 gpm
6 > 0.063 to 0.631 lps> 1 to 10 gpm
7 > 0.473 to 3.785 1pm > 1 pint/min to 1 gpm
8 < 0.473 1pm < 1 pint/min
cubic meters per second
cubic feet per second
million gallons per day
gallons per minute
lps = liters per second
pint/min = pints per minute
1pm = liters per minute
Notes regarding magnitude One discharge measurement is enough to place a spring into one
of the eight magnitude categories. However, springs have dynamic flows. A spring
categorized as being a first-magnitude spring at one moment in time may not continue to
remain in the same category. Furthermore, recent interest in spring monitoring has
resulted in large numbers of discharge measurements since 2000. These post-2000
samples bias the long-term flow calculations with regards to determining the magnitude
of the spring, unless corrections are taken. Therefore, the FSNC (2005 ) decided that the
magnitude of a spring is to be based on a weighted median value of all discharge
measurements for the period of record.
The median of a set of scores is the middle value when the scores are arranged in
increasing (or decreasing) order. That is half the data are below the median and half the
data are above the median. The steps in computing the median of a data set (Sullivan,
2004) are as follows:
1. Arrange the data in ascending order.
2. Determine the number of observations, n.
3. Determine the observation in the middle of the data set.
If the number of observations is odd, then the median is exactly in the middle of
the data set. That is, the median is the observation that lies in the (n + 1)/2
If the number of observations is even, then the median is the arithmetic mean of
the two middle observations in the data set. That is, the median is the arithmetic
mean (average) of the data values that lie in the (n/2) and the [(n/2) + 1]
As an example, refer to Table 2b. Note the hypothetical data sets have already been
arranged in ascending order.
Table 2b. Median Examples
Example Data Set 1 Example Data Set 2
n = 7 (odd) n = 8 (even)
Observation Value ith Position Observation Value ith Position
121 1 122 1
136 2 145 2
139 3 165 3
158 4 165 4
164 5 166 5
169 6 187 6
198 7 191 7
(n + 1)/2 position = (7 + 1)/2 = (8/2) =4 (n/2) position = (8/2) = 4
Observation at the 4th position =158 [(n/2) + 1] position = (4 + 1) = 5
Median = 158 Mean ofobs. at 4th and 5th positions =
(165 + 166)/2 = 165.5
Median = 165.5
The revised method for determining the weighted, median flow of a spring is a two step
process. First, the median annual flow for each year of the period of record is
determined. In years where only one discharge measurement was taken, the single
measurement will represent a sample of the flow for that year. If two or more discharge
measurements were taken in a single year, then the median of the flow measurements for
that year will be used. Second, these median or representative flow values are assumed
to represent the years in which measurements were obtained. Thus, the medians or
representative samples of all flow measurements will be used to determine the weighted,
long-term median flow and magnitude of the spring (FSNC, 2005). An example is found
in Table 2c.
Table 2c. Example of Calculation of the Median of Annual Flow Medians
Annual Representative or
Date Discharge (CFS) Median Flow (CFS)
02/01/1947 135 135 (1947)
03/01/1964 127 127(1964)
10/15/1980 146 146(1980)
03/02/2003 84 87 (2003)
06/04/2004 86 91 (2004)
08/04/2005 90 90 (2005)
Note there are six years in which discharge measurements for the spring were obtained.
In ascending order, the median or representative flow values are 87, 90, 91, 127, 135, and
146 CFS. Since there is an even number of years with flow measurements, the median
annual flow for the period of record is the midpoint between the two middle annual flow
medians and representative samples when they are arranged in ascending order. The
median annual flow is the mean (midpoint) of 91 and 127 CFS or 109 CFS. For the long-
term period of record, the spring is considered a first-magnitude spring.
It is recognized that historically, many springs in Florida have kept one magnitude
category, even though the discharge may have changed considerably from when it was
first assigned a magnitude. For this reason, a historical category is acceptable in the
Florida Springs Classification System. For example, the discharge of a spring may have
been taken in 1946. At that time it was classified as a first-magnitude spring. No other
measurement was taken until 2001, when three discharge measurements were taken. The
median value for the two annual medians reveals that the spring should be re-classified to
a second-magnitude spring in 2001. Nevertheless, it can still be considered a historical
first-magnitude spring. The term historical refers to the period of time prior to 2001.
The location of a discharge measurement is critical for defining the magnitude of a
spring. Whenever possible, a discharge measurement should be restricted to a vent or
seep. However, this is often impractical. For example, the only place to take a
measurement may be in a spring run downstream where multiple springs have discharged
into the run. For this reason, whenever a discharge measurement or water sample is
taken, the springs (vents or seeps) included in the measurement need to be reported. The
exact location of the discharge measurement (using a Global Positional System with
approved locational specifications) and a standardized locational reference point for each
measurement is encouraged.
historical spring magnitude A special spring classification category based on the
median volume of flow from a spring per unit time, based on discharge data obtained
prior to the year 2001 (FSNC, 2005). See spring magnitude.
The FSNC believes the meanings of key spring terms and an understanding as to how
they differ are extremely important for the hydrogeology community in its efforts to better
appreciate the dynamics of Florida's springs. These special terms (underlined in the glossary)
are listed below in alphabetical order:
historical spring magnitude,
seep (or spring seep),
springshed (or spring recharge basin), and
vent (or spring vent).
New References Cited
Neuendorf, K.K.E., Mehl, J.P., and Jackson, J.A., (eds.), 2005, Glossary of Geology, fifth ed.:
American Geological Institute, Alexandria, VA, 779 p.)
Sullivan, M., 2004, Statistics, Informed Decisions Using Data, Upper Saddle River, NJ., Prentice
Hall, 823 p.
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