UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY MAP SERIES NO. 25, February, 1967


FLORIDA BOARD OF CONSERVATION
published by DIVISION OF GEOLOGY


published by DIVISION OF GEOLOGY


JAN.


FEB.


MAR.


APR.


MAY


JUNE


JULY


SEPT.


FIGURE 1. MAXIMUM, MINIMUM, AND MEDIAN DAILY TEMPERATURE.


PERCENT OF TIME


0 0 0 0 0
rh ( W 0) 0 4N <-


0n N


9O.













7/


65 A










50 --
RECORD USED: 7 YEARS OCT. 1953 TO SEPT. 1960

45 _
0 0 0 0 0 0 0 0 o0 0 0


-DISCHARGE,
DISCHARGE, CFS


0 0 0


82



83








tas













TEP__RAR E LLE_D \\


SF M A M J J A S O N D
TEMPERATURE EQUALLED OR EXCEEDED, F.


NEAR COCOA



LOCATION MAP


FIGURE 2. CUMULATIVE FREQUENCY OF FIGURE 3. CUMULATIVE FREQUENCY
COMBINATIONS OF TEMP. AND DISCHARGE. OF TEMPERATURE BY MONTHS.


FIGURE 4. MAXIMUM, MINIMUM, AND MEDIAN DAILY THERMAL CAPACITY.


Temperature and Chemical Characteristics of the St. Johns River Near Cocoa, Florida

BY
KENNETH A. MacKICHAN
U. S. GEOLOGICAL SURVEY


100



90



U: 80


S70


I0
I-
60



50



40


OCT. is
RECORD USED: 7 YEARS -OCT. 195MAXMUM 84F. TO SEPT. 1960
















RECORD USED: 7 YEARS --OCT. 1953 TO SEPT. 1960


The temperature of the St. Johns River near Cocoa has
been read daily for 7 years, more than 2,500 readings. The
chemical quality of the river has been measured for 9 years,
more than 3,000 readings. The purpose of this report is to
present these data in a compact and readily usable form.
The illustrations have been designed to answer practical
and commonly asked questions about the water temperature
and water quality of the St. Johns River. Figures on page
1 describe the thermal character of the stream and figures
on page 2 describe the chemical constituents and physical
properties of the water.
A water sample was collected and the temperature
of the river was measured once a day at the bridge on State
Highway 520, 8.8 miles west of Cocoa from October 1,
1953, to September 30, 1960. The specific electrical con-
ductance of each sample was measured and a single sample
was composite from groups of approximately 10 daily
samples. The composite samples were analyzed for about
16 chemical and physical properties. A continuous con-
ductivity recorder was operated at the bridge from October
1, 1960, to September 30, 1962. During this time samples
were taken periodically and analyzed for approximately 16
constituents and physical properties. Discharge records
have been collected at this site since October 1953.
Temperature is an important factor of water quality.
This is very evident for a direct use such as a coolant. The
effect of temperatures on aquatic biota is less evident but
nonetheless very important. The tolerance of fish to certain
toxin substances has been shown to vary widely with'
temperature. Oxygen is more soluble in cold water than
in warm water, hence the reduction of oxygen concen-
trations by pollution is especially serious during periods
of high temperatures when oxygen levels are already low.
Increased temperature also accelerates biological activity
including that of the oxygen-utilizing bacteria which de-
compose organic wastes. These pollutional effects may
be especially serious when low flow conditions coincide
with high temperatures.
The maximum, minimum, and median observed


FIGURE 5. MAXIMUM, MINIMUM, AND MEDIAN DAILY THERMAL LOAD.


.5




I 1000
I-
D
z
S 500
5 oo
S400
Li
300
m
m 200
z
0
-i
-j
S 100
5-
H



z 30
0 20
0
-j
< 10

Li
I
H -


PERCENT OF TIME

FIGURE 6. CUMULATIVE
FREQUENCY OF THERMAL
LOAD AND CAPACITY.


100

90 ^V__^ /:/Y_




,o A/ '-/
















J M A M J Jd A S O N D D
(A) THERMAL LOAD, MILLION
BTU PER MINUTE
80 20--- --/ ^ ^ ---











40 -V^- ---- l\





-i F M A M J J A S 0 N D
(A) THERMAL LOAD,' MILLION
BTU PER MINUTE


(B) THERMAL CAPACITY TO 95F.,
MILLION BTU PER MINUTE


FIGURE 7. CUMULATIVE FREQUENCY OF THERMAL LOAD AND CAP


FLiilRID(n GEfJi


LOGIC SUF


x^T '


















j F M A M J J A S 0 N D
(C) THERMAL CAPACITY TO 100.F,
MILLION BTU PER MINUTE


CITY BY MONTHS.


G 3931
.Ci
RVEY MAP SERIES No.S5
_9'


temperatures for each day of the year are shown in figure 1.
For example, 84o F. was the highest temperature observed
on any October 15th. Similarly, 72' F. was the lowest
temperature observed on any October 15th. The median
October 15 reading was 77' F.
The cumulative frequency curve (fig. 2) shows the
percent of time that two requirements were met (1) the
water temperature was equal to or less than a given value
and (2) the discharge was equal to or greater than a given
value. For example, suppose that 600 cubic feet per second
of water of less than 85 F. is peeded. The 85 F. line
and the 600 cubic feet per second line intersect at 61
percent of the time. Therefore, sufficient water (600 cubic
feet per second or more) having a suitable temperature
(85 F. or less) is available 61 percent of the time.
Sometimes water of a certain temperature is needed
for part of a year. Figure 3 shows the percent of time
selected temperatures are equaled or exceeded during each
month. For example, a temperature of 80 F. is exceeded
92 percent of the time in July but only 19 percent of the
time in October.
If water is used for cooling, it is important to know
the capacity of a stream to carry away heat (thermal
capacity) without exceeding a given temperature and to
know the amount of heat the stream is carrying (thermal
load). The thermal capacity and thermal load of the St.
Johns River are expressed herewith in BTU (British
Thermal Units) per minute. A BTU is the quantity of
heat required to raise the temperature of one pound of
water one degree Fahrenheit.
The thermal load of the St. Johns River has been
computed above a base of 400 F. The thermal capacity has
been computed to 95 F. and 1000 F. The thermal capacity
to 95' F. or 1000 F. is the number of, BTU's required to
raise the river's temperature from the measured tempera-
ture to 95 F. or 1000 F. The maximum, minimum, and
median daily thermal capacity of the river is shown in
figure 4. For example, the smallest thermal capacity to
1000 F. observed on any October 15th was 38 million


BTU's per minute. This means that, during the seven years
of record, the St. Johns River could have carried at least
38 million additional BTU's per minute on any October
15th without the river temperature exceeding 1000 F.
after the water was thoroughly mixed. If a 1000 F. temper-
ature is undesirable but a 95 0 F. temperature is permissible,
the minimum thermal capacity on any October 15th would
have been 30 million BTU's per minute. Figure 5 is similar
to figure 4 except it shows the maximum, minimum, and
median daily thermal load.
The cumulative frequency curves of thermal capacity
and thermal load (fig. 6) show that if the maximum per-
missible temperature of the receiving stream is 100' F.,
the thermal capacity equals or exceeds 200 million BTU's
25 percent of the time. Therefore, an input of 200 million
BTU's per minute will overload the stream 75 percent
of the time. If the maximum permissible temperature is
only 950 F., the stream will be overloaded 82 percent of
the time.
Figure 7a shows the percent of time selected thermal
loads are equaled or exceeded during each month. Similar
curves of thermal capacity for 95 F. and 100 F. are
shown in figures 7b and 7c. For example, in June the
thermal capacity to 1000 F. equals or exceeds 20 million
BTU's per minute 72 percent of the time; the addition
of 20 million BTU's per minute would overload the
stream 28 percent of the time.
Electrical conductivity is closely related to total dis-
solved solids and some of the common constituents in
water. To a fair degree dissolved solids in parts per
million in St. Johns River water near Cocoa can be com-
puted by multiplying the specific conductance in micromhos
at 25 C. by 0.54 and substracting 9. Daily dissolved solids
have been computed from the specific conductance readings.
The maximum, minimum, and median dissolved
solids for each day of the year are shown in figure 8.
For example, 1,380 ppm was the greatest concentration of
dissolved solids on any May 15th. Similarly, 144 ppm
was the least concentration of dissolved solids on any May


OCT.


NOV.


a: a 5 o 0


I I


B












180
500


160



140 400



120


300


S ________________________ __MNIMU144PPM
OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT.

FIGURE 8. MAXIMUM, MINIMUM, AND MEDIAN DAILY DISSOLVED SOLIDS AND DISSOLVED SOLIDS EQUALED OR EXCEEDED 5 AND 25 PERCENT OF THE TIME BY MONTHS


50-240-


02
20


1100


1000



900


8001


700


I- I


2000








1500

a.
z

0
-J

O 1000
w
-J
0
o




500


iiIii~ ___ ~ ___ ___ -- ___ ___ __


5 10 20 30 40 1


0 60 70 80 90 95 98 99


200 -

100 -

0
.5


-_oj 0 j


PERCENT OF TIME

FIGURE 9. CUMULATIVE FREQUENCY CURVE OF DISSOLVED SOL IDS.


15th. The median dissolved solids on May 15th was
297 ppm. Dissolved solids exceeded 297 ppm on May 15th
in four years and were less than 297 ppm in four years.
Generally, it is most important to know the frequency
of occurrence of concentrations in the high range. There-
fore, the concentration of dissolved solids equaled or
exceeded 5 and 25 percent of the time during each month
is also shown on figure 8. For example, on 25 percent of
the days in May the dissolved solids are likely to equal
or exceed 400 ppm but on 5 percent of the days in May
the dissolved solids are likely to equal or exceed 1,380 ppm.
The cumulative frequency curve of dissolved solids
(fig. 9) shows the percent of time that the dissolved solids
equal or exceed a given value. For example, the dissolved
solids exceeded 500 parts per million 18 percent of the
time. This means that on the average, dissolved solids
will equal or exceed 500 ppm on or about 66 days per year.
The use of the graphs can be illustrated by solving
the following problem: Assume the St. Johns River near
Cocoa is proposed for a public water supply. According to
the State Board of Health, the water should not contain
more than 500 ppm of dissolved solids. Will the St. Johns
River at Cocoa meet this requirement? Figure 9 shows
the dissolved solids equal or exceed 500 ppm 18 percent
of the time. Figure 8 shows that the median dissolved
solids is consistently less than 500 ppm but that dissolved
solids have exceeded 500 ppm on almost every day of the
year. Furthermore, the dissolved solids have exceeded
500 ppm more than 5 percent of the time in every month
of the year and in June and July the dissolved solids ex-
ceeded 500 ppm more than 25 percent of the time.
Although the concentration of dissolved solids is
quite variable, the composition of the dissolved solids is
quite uniform. That is the percent chloride, sodium,
calcium, and other major constituents is almost constant.
Because the percentage of the major constituents is almost
constant, their concentrations can be computed by multiply-
ing the concentration of dissolved solids by a factor. Using


the factors shown in table 1, auxiliary scales for calcium,
sodium, bicarbonate, sulfate, chloride, and hardness have
been computed and plotted at the right side of figures
8 and 9. The zero of the auxiliary scales do not coincide
with the zero of the dissolved solids scale because of the
B value in the conversion formula.
Figures 8 and 9 become graphs of any of the six
constituents listed. The auxiliary scales give approximate
values. The results for individual days, such as the maxi-
mum and minimum in figure 8, are less accurate than
frequencies such as given in figure 9. The results are least
accurate for constituents having a small A term (table 1).
For example, the auxiliary scales for calcium and bicarbo-
nate are least accurate for this stream.
The use of the auxiliary scales can be illustrated by
determining whether chloride concentrations are satisfactory
for a public water supply. Chloride concentration in public
supplies should not exceed 250 ppm. According to figure 9,
chlorides will equal or exceed 250 ppm 15 percent of the
time. Figure 8 gives additional information about the prob-
able occurrence of chlorides exceeding 250 ppm. The
chloride concentration has never exceeded 250 ppm on a
few days in September and October. It was equal to or
greater than 250 ppm for less than 5 percent of the time
during September and was equal to or greater than 250
ppm less than 25 percent of the time in every month
except June and July.
Some constituents and physical properties are either
not related to conductivity or occur in small concentrations.
The frequency of distribution of these constituents or
properties are shown in figures 10 and 11. For example,
iron concentration in public water supplies should not
exceed .30 ppm. Figure 10B shows that the concentration
of iron in the St. Johns River exceeded 0.30 ppm in about
two percent of the samples which is about equivalent to
two percent of the time. The extremes and'medians of the
8 characteristics determined are given in table 2.
Figure 12 shows the maximum, minimum, and median
flow in cubic feet per second on each day of the year.


TABLE 1.-Conversion factors dissolved solids to major
ionized constituents [constituent concentration =
(A x dissolved solids) B]


Constituent

Calcium (Ca)

Sodium (Na)

Bicarbonate (HCOz)

Sulfate (SO4)

Chloride (Cl)

Hardness as CaCO,


A B


.057 +25

.11 1

.50 -14

.34 +13


0


iL
0 40
I-
z
E
UC


TABLE 2.-Maximum, minimum, and median selected
chemical and physical characteristics of water from St.
Johns River near Cocoa, October 1953 to September
1960.

(Results are from 10-day composites and are expressed in
parts per million except pH and color)

Characteristic Maximum Median Minimum


Silica (SiO )

Iron (Fe)

Magnesium (Mg)

Potassium (K)

Fluoride (F)

Nitrate (NO )

pH

Color


16. 4.2 0.2

.49 .08 .00

28. 4.9 .00

6.0 .5 .0

.3 .1 .0

3.1 .0 .0

7.9 7.1 6.4

280 120 45


80


601 i


252 SAMPLES


40 I |i 40


201 ------


0 N (N t 4 4 4 T
C N 4-


PARTS PER MILLION
(A) SILICA


o 0


r- m a
0 0 6
M Cs 4


PARTS PER MILLION
(B) IRON

FIGURE 10. FREQUENCY GRAPHS OF


6
4 4
Cs) C
o e. <
4


- (N CM Cs
4D 0 4l 4
(N (j < (N


80


PARTS PER MILLION
(C) MAGNESIUM
SILICA, IRON, MAGNESIUM, AND POTASSIUM.


S ea n C 4 0
0 0! 0 0 0

PARTS PER MILLION
(D) POTASSIUM


0 0 0


PARTS PER MILLION
(A) FLUORIDE


60 1


260 SAMPLES


(A SAMPLE CONTAINING
3.1 PPM IS NOT SHOWN)


60--


40 | I-40


.J
-I
a
4
z Z

'- ,n 4n N^ -, Cs 1
o E R4 MI ION

PARTS PER MILLION


4 4D 4 0. ^j 4 0 40
wD wD N0 N" N' N- N


o o


4 N 4 .- Cs 4- N- 4-
S0 0 *
4 4 0 0 0 0 0
o (N 4r D 4 0


FIGURE 12. MAXIMUM, MINIMUM, AND MEDIAN DISCHARGE.


(D) COLOR


1600

1500 -

1400

1300 -

1200

1100

1000

900 --



700

600

500



300


0


200


0


20


I


265 SAMPLES






















w
-J

Si
<
ul
--- I L


257 SAMPLES


20





z
0
Z l I


265 SAMPLES


0-
C


(B) NITRATE (C) PH
FIGURE 11. FREQUENCY GRAPHS OF FLUORIDE, NITRATE, PH, AND COLOR.


I


I


1


Ou