OOOR64102
BEFORE ON
EXISTING & POTENTIAL CONDITIONS OF THE INTERSTATE WATERS
OF THE ST. CROIX RIVER
FROM PRESCOTT, WISCONSIN TO STILLWATER, MINNESOTA
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
PUBLIC HEALTH SERVICE
REGION V
TWIN CITIES UPPER MISSISSIPPI RIVER PROJECT
MINNEAPOLIS, MINNESOTA
SEPTEMBER,
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TABLE OF CONTENTS
Summary and Conclusions
Background 1
The Area 1
Water Uses 2
Present Water Quality 6
Chemical and Bacteriological 6
Temperature 7
Biological 8
Stream Flow J.O
Proposed Steam-Electric Generating Plant ll
Effects of Proposed Thermal Discharges 11
Stream Temperature 13
Dissolved Oxygen 15
Aquatic Environment l6
Bibliography
Appendix
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SUMMARY AND CONCLUSIONS
1. The lower St, Croix River is used primarily and heavily for
recreation,
2, The waters of the St. Croix River are indicative of a relatively
unpolluted stream suitable for many uses. This is borne out by physical,
chemical, bacteriological and biological indices of quality.
3. The St. Croix River at Stillwater, Minnesota and below is a part
of the pool above Mississippi River Lock and Dam No. 3. The pool elevation
is maintained by controlled discharge through the lock and dam. For this
reason it is more characteristic of a reservoir than a flowing stream.
h. Cooling water, which has received a temperature increase of 17°F,
will experience a drop of 3 - 5° P during its passage through Andersen Bay.
5. The temperature gradient that will occur in the St. Croix River ,
contiguous to the Bay will depend on dispersion patterns in this vicinity.
These patterns can be determined only by a hydraulic model study. The
heated effluent, however, would be expected to stratify at the surface and
remain near the Minnesota shore for some distance downstream.
6. Considering the large volume of water always maintained in Pool
No. 3, it is doubtful that any water in the river one-quarter mile or more
below the Bay would ever exceed 90°F.
7. The stream temperature would be expected to return to normal with-
in a downstream distance of five or six miles.
8. An increase of lk°F or more at the outlet of Andersen Bay, result-
ing from the discharge of cooling water, will raise the temperature at the
City of Bayport's bathing beach to levels unsuitable for swimming.
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9. Increased river temperatures resulting from the discharge of
cooling water will have an insignificant effect on dissolved oxygen con-
centrations at the existing pollutional load.
10. With the increased water temperatures in Andersen Bay, the Bay
will be a source of algal "blooms which will seriously impair the use of
the bathing beach and the marina in the immediate vicinity. The algal
blooms will be carried downstream with a potential for creating further
nuisance conditions.
11, Fish will be attracted to the warmer waters during the winter.
Reentry to colder water may produce occasional fish kills.
12. Thermal discharge to Andersen Bay during the summer will prevent
the growth and production of macro-invertebrates within the Bay and along
the Minnesota shore to a point where the temperature falls to approximately
90°F. The lack of the macro-invertebrates serving as a link in the food
chain will suppress the fish population in the locale.
13. It is beyond the scope of this report to determine if an adequate
zone for fish migration will be retained 'either along the Wisconsin shore
or within lower depths of the river subsequent to thermal discharge. This
is best determined by means of a hydraulic model.
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BACKGROIMD
The Twin Cities Upper Mississippi River Project being conducted as a
special project of the Enforcement Branch of the Division of Water Supply
and Pollution Control, Public Health Service, has within its study area
the St. Croix River from its confluence with the Mississippi River through
the communities of St. Croix Falls and Taylors Falls, a distance of approxi-
mately 53 miles. This report is the result of the first routine intensive
survey of a portion of this river as well as the routine sampling program.
The intensive portion of the study was conducted from the 24th through the
26th of August, 196^. The possible effects of a proposed thermal discharge
into the waters of the area studied are discussed. The area studied extends
from the mouth of the river to approximately mile point 23, opposite the
City of Stillwater, Minnesota. An intensive study on the remainder of the
river within the study area is scheduled for a later date.
THE AREA
The St. Croix River flows from its source in northwestern Wisconsin
in a generally southwesterly to southerly direction to its confluence with
the Mississippi River about forty miles below Minneapolis, Minnesota, The
segment river within the Project's study area, forms a boundary between the
States of Minnesota and Wisconsin. The two principal tributaries to the
segment of river under consideration shown in Figure 1, are the Kinnickinnic
and Willow, both located in Wisconsin. Smaller minor tributaries enter
from the Minnesota side of the river.
The drainage area of this reach of river is sparsely populated with the
largest communities and their 1960 populations being Stillwater, Minnesota,
8100; Hudson, Wisconsin, 298?; Bayport, Minnesota, 3205; and Prescott,
-1-
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Upper limit of Pool No. 3
MINNESOT A
WASHINGTON
COUNTY
W S C 0 N S I N
ft/VER
HASTINGS
indicate* the limit* of Pool No, 3
Bridge
5 River Mile
MINNESOTA
U.S. LOCK « 0AM NO. 9
DEPT OF HEALTH, EDUCATION, S WELFARE
PUBLIC HEALTH SERVICE
LOCATION MAP
LOWER ST CROiX RIVER
TWIN CITIES UPPER MISSISSIPPI
RIVER PROJECT
FIGURE
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Wisconsin, 1536. Other communities along this reach are St. Mary's Point,
Lake St. Croix Beach, Lakeland Shores, Lakeland, Oak Park Heights, and
North Hudson.
WATER USES
MUNICIPAL
At the present time, no communities obtain their water supplies from
the river. The river, however, has been discussed as a possible supple-
mental source of supply for the City of St. Paul.
On the Minnesota side of the river, only the Cities of Stillwater and
Bayport have public sanitary sewer systems. The waste treatment plant at
Stillwater was constructed in I960 and provides primary treatment with
chlorination during critical periods. The Bayport waste treatment plant
is of the activated sludge type designed to treat the wastes from the State
Prison as well as the municipalities own wastes.
On the Wisconsin side, the City of Hudson provides treatment for its
own wastes and those from the community of North Hudson. This plant is of
the trickling filter type, placed in operation during 1960. Chlorination
of the effluent is practiced from May 1 to November 1. The City of Prescott,
borders the St. Croix, but discharges its municipal wastes to the
Mississippi River.
INDUSTRIAL
On the basis of information available, there is only one industry
having a waste water discharge direct to the St. Croix River within the
area under study. This company, which is located in Bayport, discharges
its waste into what is known locally as Andersen Bay. The discharge
appears to have no significant affect on the St. Croix water quality.
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FLOOD CONTROL & COMMERCIAL SHIPPING
There are no existing Federal Projects for flood control in the St.
Croix River Basin. Since 1878, however, there has been a navigation
project on the river from the mouth to river mile 51.8 near Taylors Falls,
Minnesota. This project provides for a 9-foot channel from the mouth to
Stillwater and a 3-foot channel on to Taylors Falls. The project also
provides for harbor and water front facilities at Stillwater. The naviga-
tion Lock and Dam No. 3, located on the Mississippi River 1*1.3 miles be-
low the mouth of the St. Croix, impounds a reach of the river which is
also known as Lake St. Croix. This provides the 9-foot channel within the
lower reaches of the St. Croix River. This lake has an estimated surface
area of 9,336 acres.^'
Commercial navigation on the St. Croix has varied in amounts during
the past ten years with a peak of ^3>1^5 tons transported in 1960. The
commodities shipped were coal and superphosphate.^ '
Commercial shipping information for the past ten years appears in the
Appendix in Table 1.
RECREATION
The waters of the St. Croix River are a focal point for park and
recreational facilities. Although few statistics are available on the
recreational usage of the stream within the area under study, some indica-
tion of this is gained by the following information. In 1962 the bordering
counties of St. Croix and Pierce in Wisconsin and Washington in Minnesota
had a combined population of a little over lOij-,000 of which approximately
kk% were licensed to fish. Also in 1962, Lock and Dam No. 2 separating
the St. Croix River from the Twin Cities area recorded the lockage of
some 2,184 pleasure craft. Undoubtedly a high percentage of those craft
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were in transit between the Twin Cities and the St. Croix River, a river
known for its weekend boating populace. This populace, which is also de-
rived in part from the communities south of Lock and Dam No. 3> engages
in all forms of water oriented sports. These include: swimming, skiing,
fishing, canoeing and sunbathing. Within the reach of river between the
mouth and Stillwater, there are approximately 15 marinas and boat ramps and
at least six designated swimming areas. Swimming is also practiced from
boats throughout the area. Water oriented parks are to be found at the
cities of Stillwater, Bayport and Hudson.
As reported by the State of Wisconsin in 1961, there were ^,235
potential cottage sites on undeveloped lands bordering the Wisconsin por-
tion of Lake St. Croix. When consideration is given to the fact that
frontage uses other than cottage sites and frontage too precipitous to
permit development were not considered, some idea may be gained of the
sparsity with which this area has been populated.
ELECTRICAL GENERATING PLANTS
At the present time there are no electrical power generating plants
located on the St. Croix River within the area under study. There are,
however, six existing hydroelectric power generating plants within the St.
(?\
Croix River Basin.v ' Four of these are located on the Willow River and
two on the Kinnickinnic River.
A hydroelectric installation has been proposed for the St. Croix River
in the vicinity of Stillwater. This potential run-of-river installation
would provide a gross head of 20 feet and have an average annual energy
of 25,200 mwh.(2)
A site in Oak Park Heights, Minnesota has been proposed for a steam-
electric generating plant by the Northern States Power Company. The plant
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would use river water for cooling purposes with discharge being returned
to what is known locally as Andersen Bay. .Additional information on this
proposal can be found on page 11.
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PRESENT WATER QUALITY
CHEMICAL AND BACTERIOLOGICAL
The St. Croix River is a relatively clean stream. Man made wastes
received by it are largely domestic and have undergone some treatment prior
to discharge.
Collectively communities along the 30-mile stretch from Taylors Falls
to Stillwater discharge approximately 200 pounds of BOD per day based on
Federal and State Agency inventories. Stillwater discharges about 1000
pounds of BOD per day. Communities below Stillwater contribute a total of
about 600 pounds of BOD per day. Presenting an extreme case for purposes
of illustration, if all these sources discharged their wastes into the
stream at a common point, the resulting 5-day BOD concentration at a 1000
cfs (minimum average one day flow occurring once in ten years) stream flow
rate would be only 0.3 mg/1. The average 5-day BOD concentration of 5-3
mg/1 found during the summer of 196U at river mile 23-3 opposite Stillwater
suggests that well over 95 percent of the BOD results from agricultural and
natural pollution. The BOD which ranged between 3-5 and 7.6 mg/1 during
this period, was slightly higher than what would be expected for clean
streams.
At this same location, the dissolved oxygen concentration ranged be-
tween 5.7 and 9.2 mg/1 averaging 7.8 mg/1. Percent saturation ranged between
63 and 105, averaging 91• These concentrations are indicative of a rela-
tively clean stream.
The coliform Most Probable Number (MPN) ranged from 300 to 600 indica-
ting very good quality. Waters having an MPN of less than 1000 are con-
sidered safe for bathing by the State of Minnesota.
-6-
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Table 1 summarizes the data obtained during the summer of 1964 and
illustrates that a relatively high stream quality exists over the entire
stretch between Stillwater and the mouth.
Additional data, not shown in Table 1 above, were obtained during a
three day intensive survey conducted August 2U-26, 196U at a stream flow
of approximately 2000 cfs. The temperature and dissolved oxygen concentra-
tion were measured in the morning and afternoon at several locations and
depths at each of 11 stations set up between river miles 1.0 and 23-3.
Results indicated that water quality was uniform over the entire stream
cross section at each station during the sampling period. A summary of
these results is given in Table 2. Although there was no evidence of
stratification during this three day period, it is by no means an indica-
tion that none exists during periods of higher water temperatures and
lower flows.
TEMPERATURE
The only water temperature data on the lower St. Croix River known to
exist is that which has been collected over the years by the Minneapolis-
St. Paul Sanitary District. During routine sampling, the Sanitary District
has taken temperatures of the St. Croix River at Prescott (river mile O.l)
approximately once each week between 10 and 11 AM for more than 15 years.
All temperature data collected in the five-year period between 1959 and 1963>
inclusive, are shown in Figure 2. The maximum temperatures recorded and
month of occurrence for the years between 19^3 and 1963 are given in Table 3.
Stream temperatures were measured between Stillwater (river mile 23.3)
and Prescott (river mile O.l) in the morning on eight occasions this summer.
In each instance, the stream temperature at Stillwater was within 2°C (either
above or below) of the temperature at Prescott. These data, summarized in
-7-
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TABLE 2
SUMMARY OF DO AND TEMPERATURE VALUES AND THEIR VARIATION AT
GIVEN CROSS SECTIONS IN THE ST. CROIX RIVER (August 2^-26, 1.96k)
Station
(River Mile)
23.3
21.3
Upper end of
Andersen Bay
Lower end of
Andersen Bay
19.5
18.0
16.5
1U.O
11.3
5.0
1.0
No. of
Points
Sampled
9
9
3
3
9
9
3
12
3
6
9
Average DO &
Variation ag/1
A.M.
8.^-0.3
6.U-0.8
9.3^0.4
6.8^0.3
6.2^0.5
7.0^0.6
7.2^0.2
6.3^0.8
5.8±O.H
7.3-0.7
5.9*1.0
P.M.
8.9 to .U
6.^1.6
8.3^0.3
7.6-O.U
6.^-0.6
7.1-1.^
7.5^0.3
6.5-0.6
5.0-1.0
7.9-0.6
6.olo.9
Average Temperature
Variation °C
A.M. P.M.
19.0^1.0 Same as A.M.
20.0 to 1.0
19. oti. o "
20. 0^1. 0
20.0-1.0
20.0-1.0
20. oti. o "
20.0-1.0
20.3-1.0
20.8-1.0
20.7-1.0 M
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'0. '
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TABLE 3
HAXH3JM
Year
19U8
19^9
1950
1951
1952
1953
195^
1955
1956
1957
1958
1959
1960
1961
1962
1963
!-!ATER .a»IEERA.rUEES RECORDED
RIVER EETTCEE1T 10:00 and
Month of
Occurrence
August
July
July
July
July
July
July
July
August
-
August
August
August
July
July
July
AT MOUTH OF ST. CROE
11:00 AM*
Maximum Temp.
Recorded °C.
25
27
25
26
25
26
27
27
26
-
26
26
28
26
25
27
* Temperature measurements were made approximately once
each week. Data was collected by the Minneapolis-
St. Paul Sanitary District.
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Table k, indicate that temperature data collected at Frescott is applicable
to the entire reach of the stream between Prescott and Stillwater,
The data collected by the Sanitary District indicates that maximum
stream temperatures occur in July and August of each year. The maximum
temperature recorded by them since 19^8 was 28°C (82.^°F). The average
maximum temperature for the data presented is 26°C (78.8°F).
BIOLOGICAL
A bottom organism study was performed during the month of August, 196^4
to obtain information relating to present water quality. Because of their
habitat preference and poorly developed method of locomotion, these organisms
are subjected to all adverse factors entering their habitat. The majority
of bottom organisms have a life span which equals or exceeds one year; there-
fore, a study of the bottom organism population will reflect river condi-
tions at a given point for a considerable period of time prior to the actual
collection of the samples.
Results of the study indicate that the stream water quality is essen-
tially good and is capable of supporting a wide variety of bottom organisms.
This fact is substantiated by the general diversity of bottom organisms and
the specific presence of the pollution intolerant forms such as Mayflies,
Caddis Flies and Scuds. These data are shown in Figures 3, ^ and 5 and
Appendix Tables 2 and 3«
Silt and natural organics and/or detritus such as decaying leaves,
twigs, bark, etc, were found on the bottom in the river. In Andersen
Bay, there was a considerable amount of organic material that appeared to
be sludge. It was in these areas of silt and natural organic deposition
that most of the sludge worms, blood worms, and phantom midges were found.
These organisms are a typical association found in lakes or reservoirs.
-8-
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TABLE 4
ST. CROIX RIVER WATER TEMPERATURES
BETWEEN MOUTH AND STLLLWATER, MINNESOTA
Date
7-23 -6k
7-28-64
8-10-64
8-19-64
8-24-64
8-25-64
8-26-64
9-9-64
Stillwater
23.3
29°C
28
22
21
19
19
19
21
LOCATION, RIVER MILE
Hudson
18.0 16.5
28°C 28°C
28
23
22
20 20
20 20
20 20
21
Prescott
0.1
28°C
28
23
22
21
21
21
21
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KINNICKINNIC
RIVER
PHANTOM MIOOE3-CHW80RUS
DEPT. OF HEALTH, EDUCATION, S WELARE
PUBLIC HEALTH SERVICE
BOTTOM ORGANISMS
ST. CROIX RIVER
MILE 0.0 to 7.0
TWIN CITIES-UPPER MISSISSIPPI
RIVER PROJECT
FIGURE 3
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SLUDGE WORMS
BLOOD WORMS
MAYFLIES- HEXAaENI*
PHANTOM MIDQE5-CHAOSORU3
0.5
SCALE
o
I MILE
DEPT. OF HEALTH, EDUCATION, a WELWRE
PUBLIC HEALTH SERVICE
BOTTOM ORGANISMS
ST. CROIX RIVER
MILE 8.0 fo 16.0
TWIN CITIES-UPPER MISSISSIPPI
RIVER PROJECT
FIGURE 4
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MAYFLIES-HEXAGESIA
PHANTOM MIDGES-CHAOBORUS
OF HEALTH EDUCATION & WELFARE
PUBLIC HEALTH SERVICE
BOTTOM ORGANISMS
ST. CROiX RIVER
MILE 15.0 to 25
TWIN CITIES-UPPER MISSISSIPPI
RIVER PROJECT
FIGURE 5
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having silt and natural organic as substrate materials. The number of
these organisms does not appear to be particularly high. Information
characterizing the bottom materials can be found in Appendix Table k»
To further substantiate that the river water quality is good, a list
of known fish species, including numerous game species, is found in
Appendix Table 5.
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STREAM FLOW
Stream flow of the St. Groix River at Stillwater is obtainable only
through addition of the flow of the St. Croix River at St. Croix Falls,
Wisconsin and the flow of the Apple River near Somerset, Wisconsin. Al-
though daily gage height readings are taken at Stillwater, no discharge
record for any period is available.
The St. Croix River "below Stillwater is a portion of the pool above
Lock and Dam Wo. 3 on the Mississippi River. However, it is not a station-
ary pool. Flow is maintained past Stillwater at approximately the same
rate as that added by the St. Croix River and all its tributaries above
Stillwater. This is accomplished by regulating the volume of water pass-
ing Lock and Dam No. 3 according to the total volume of water entering
the pool from the Mississippi River, the St. Croix River and their measured
tributaries.
Flows have been computed at Stillwater to provide four graphs defin-
ing expected flow conditions at Stillwater. Mean monthly discharges and
minimum daily discharges based on the ten calendar years of record from
1953 to 1962 inclusive are presented in Figures 6 and 7. Frequency of
minimum flows are presented in Figures 8 and 9« "The recurrence of one
day average low flows is shown for the most recent 10, 20 and 30 years
of published record. The recurrence of seven day average low flows is
shovn for only the ten years of record.
Although flow is maintained on the St. Croix River, velocities are
Very low near Stillwater and Bayport because of the large cross-sectional
area in this vicinity. At a flow of 1000 cfs velocities are of the
magnitude of 0.2 miles per day. Time of travel from river mile 20.5 to
18.5 on the St. Croix River has been computed as approximately nine days
-10-
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MEAN MONTHLY DISCHARGES
FOR THE
SAINT CROiX RIVER at STILLWATER
18,000
17,000
16,000-
15,000-
14,000-
13,000-
12,000-
11,000-
tft
u.
o 10,000-
z
^ 9,000
g
^ 8,000-
7,000-
6,OOO-
5,000-
4,000-
3,000-
2,000- •
1,000 *•
•— . t
| \ FIGURE 6
1 \
1 \ LEGEND
1 » THE MAXIMUM OF THE MEAN MONTHLY
| \ DISCHARGES FOR A TEN YEAR PERIOD OF
/ \ RECORD FROM 1*93 TO 1982 INCLUSIVE.
1 V ""'"" THE AVERASE OF THE MEAN MONTHLY
, \ DISCHARGES FOR A TEN YEAR PERIOD OF
1 \
' . RECORD FROM 1983 TO 1962 INCLUSIVE.
» ' « -*— — — — THE MINIMUM OF THE MEAN MONTHLY
/ \ DISCHARiES FOR A TEN YEAR PERIOD OF
j \ RECORD FROM I9S3 TO 1962 INCLUSIVE.
1
1 \
1 \
1 \
i \
/ \
/ 's.
?y ^^
\ \.
\ \
\ \
\ \
\ \
\ \
\ \
\ \
\ \
\ ^ "\
\ \
\ \
"^^* X\
' / N ^X^ \
/ s — N\ ^\
— '" / e/' \ N^
_ / f* *y **~~~*"***~
,*'''' "^"^ .--""""""* XXNS>»
— ••---.' "».»»•*
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
MONTH
-------
MINIMUM DAILY DISCHARGES
FOR THE
SAINT CROIX RIVER at STILLWATER
FIGURE 7
LEGEND
' THE HISHEST or THE MONTHLY MINIMUM DAILY
DISCHARGES FOR A TEN YEAR PERIOD OP
RECORD PROM 1953 TO 1962 INCLUSIVE.
> THE AVERA8E OP THE MONTHLY MINIMUM DAILY
OI3CHAR0E3 POR A TEN YEAR PERIOD OP
RECORD FROM 1953 TO I8BZ INCLUSIVE.
THE LOWEST OP THE MONTHLY MINIMUM DAILY
DISCHARGES POR A TEN YEAR PERIOD OP
RECORD PROM 1953 TO l»«2 INCLUSIVE.
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
MONTH
-------
V)
u.
o
O
_J
U.
4,6 OO
4,400
4,200
4,OOO
3,800
3,600
3,400
3,200
3,000
2,800-
2,600-
2,40O-
2,200-
2,OOO-
1,800-
1,600-
1,400-
FREQUENCY Of MINIMUM FLOW
FOR AUGUST FOR THE
SAINT CROIX RIVER at STILLWATER
FIGURE 8
O 7 DAY AVERA0E MINIMUM FLOW
X I DAY AVCRA6E MINIMUM FLOW
* BASED ON TEN YEARS OF RECORD
FROM 1*93 TO 1*62 INCLUSIVE.
I DAY
I I 1 1
23456 789
RECURRENCE INTERVAL IN YEARS
10
-------
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41 MOId
-------
for a flow of 1000 cfs and two days for a flow of 3930 cfs.
River mile 20 is slightly upstream from the mouth of Andersen
Bay at Bayport. The volume of water estimated in the St. Croix River from
river mile 20.5 to 18.5 is ?60 million cubic feet. The volume of water
in Andersen Bay is approximately 23 million cubic feet. The stage is
relatively constant between elevations 675.0 and 675-5 feet.
Since the Corps of Engineers maintains Pool No. 3 at elevation 675.0
(1912 datum) at Prescott and since only low flows are under consideration,
a constant stage has been assumed for time of travel and volume determina-
tions.
Additional information and methodology concerning the preparation of
Figures 6, J, 8 and 9 is presented in the Appendix.
PROPOSED STEAM ELECTRIC GENERATING FIAMT
A power company has proposed to locate a steam-electric generating
plant on the St. Croix River at river mile 20.7 on the Minnesota shore in
the community of Oak Park Heights. Cooling water would be withdrawn from
the main stream and discharged into Andersen Bay located behind the pro-
posed site.
The power company's application to the Minnesota Water Pollution
Control Commission indicates that the maximum cooling water discharge rate
will be 660 cfs. The maximum heat rejection will be 2.52 billion BTU/hour,
with the average heat rejection at 2.32 billion BTU/hour. At the 660 cfs
discharge rate then, the maximum temperature increase of the cooling water
will be 17°F. The average temperature increase will be 15.7°F.
EFFECTS OF PROPOSED THERMAL DISCHARGES
AMDERSEN BAY TEMPERATURES
-11-
-------
The volume of water in Andersen Bay is approximately 23 million cubic
feet. At a 660 cfs discharge rate, the average retention time of the cool-
ing water in the Bay would be approximately 10 hours, provided that thorough
mixing occurred.
If the cooling water discharged occupied the entire volume of the Bay,
the average velocity of the cooling water through the Bay would be in the
order of 0.1 ft/sec. This low velocity would not be expected to produce
thorough mixing. It is evident that stratification would be most likely
to occur, with the cooling water, that is, the warmer water, occupying
only the upper layer. Since the entire volume of the Bay probably would
not be utilized, the retention time in the Bay would be less than 10 hours.
During August, the maximum average 5-day air temperature recorded in
Minneapolis is 77.^°F. Minneapolis records were used in the absence of
long term records for Stillwater. The maximum water temperature is
approximately 82.i|-0F (28°C). An increase of 17°F would raise the cooling
water temperature to 99.^°F. Calculations show that this 22°F temperature
; difference of water over air would produce a heat loss from the Bay
to the atmosphere resulting in a temperature drop in the cooling water
of approximately 3°F from one end of the Bay to the other. ^/ The tempera-
ture of the water entering the main stream from the Bay, then, would be a
maximum of li|-0F higher than the main stream during August. Based on the
average heat rejection it would be an average of 13°F higher than the main
stream.
Heat loss from the Bay would be greatest during January when the
average temperature difference between the air and cooling water would be
nearly 37°F. The temperature drop during passage through the Bay at this
time would be approximately 5°F.
-12-
-------
Figure 10 shows the average and maximum temperatures over the year
that would be expected in the upper layer of the Bay, "both before and
alter installation of the power plant.
An increase of li|-0F or more at the outlet of Andersen Bay, resulting
from the discharge of cooling water, will raise the temperature at the City
of Bayport's bathing beach to levels unsuitable for swimming.
STREAM TEMPERATURE
The effect that a given heat output by the power plant will have on
the temperature of the St. Croix River in the vicinity of Bayport is
dependent to some extent on the flow in the river itself. It is not
dependent entirely on the flow, as would first be expected, since the pool
stage from the mouth to Stillwater remains almost constant, within a wide
range of flow.
The portion of the river from mile 23 to the mouth resembles a
reservoir more than it does a flowing stream. This can best be illustrated
by considering the mean velocity of flow past the Bay over a range of flows.
At a 1000 cfs flow (minimum daily flow expected once every 10 years), the
velocity would be about 0.2 mile/day. At 10,000 cfs flow (more than
twice the yearly average) the velocity would be only 2 miles/day. The
area of the stream cross section increases over the next six miles down-
stream thus producing successively lower velocities in this reach.
A close approximation of actual mixing patterns and temperature
gradients resulting from a thermal discharge into this body of vrater
can be reliably determined only by a hydraulic model study. Nevertheless,
some rough approximations can be made of the resulting temperatures in
the absence of such a model. To gain a perspective of probable thermal
-13-
-------
i 8
o
-------
additions to'the river, temperature increases in the immediate vicinity
of the discharge point are first considered. Figure 11 presents this
temperature increase which would result from the uniform addition of heat
to the stream, as related to the stream flow. This would closely approxi-
mate conditions if the water level was not regulated by Lock and Dam No.
3. Stream temperatures that would be expected in August immediately
below the Bay at pertinent stream flows have been calculated and are given
in Table 5.
However, since the water surface is maintained at a relatively con-
stant level, there would always be a considerable volume of water in
addition to the incoming flow that would be available for further dilution.
The amount of water that would be utilized can only be reliably estimated
from a hydraulic model study.
To illustrate the significance of this volume of water in the vicinity
of the Bay, let it be assumed that no flow enters or leaves the two-mile
reach between river miles 18.5 and 20.5 and that the volume of water in
•-j
this segment (approximately 7^0 million Ft.J) is continually recirculated
through the power plant. Pumping at the maximum rate (660 cfs), the
water would be recirculated an average of only once every 13 days. Even
if no heat loss occurred from this reach, the average temperature increase
would, theoretically, be only l°F/day at the maximum heat rejection rate.
For any assumed temperature immediately below Andersen Bay, the re-
sulting temperature occurring at any distance downstream can be calculated
using an equation developed by Velz and Gannon for determining heat losses
in ponds and streams.^-5'
Taking one of the most critical situations ever likely to occur,
assume that the 660 cfs of cooling water leaving the Bay mixed with only
-111-
-------
do'3SV3bONI
-------
TABLE 5
EXPECTED STREAM TEMPERATURES IN AUGUST 3MMEDIATELY BELOW
BAY OUTLET. (ASSUMING AN UPSTREAM TEMPERATURE OF 8
COMPLETE MEC3UG AND UNREGULATED PLOW)
Minimum Daily Consecutive 7-Day
Avg. Flow Drought Flow
(30 Yr. Record) (10 Yr7 Record)
Return Frequency
Once each year
Once in 5 years
Once in 10 years
Once in 20 years
Once in 30 years
Flow
GFS
3930
lltOO
1000
700
550
Maximum
Temperature
op
84.8
89.0
91.6
95.6
99.2
Flow
CFS
1^90
1700
1580
Maximum
Temperature
OF
84.5
87,8
88.2
-------
cfs of water in the main stream. (This would occur at a stream flow
of 1000 cf s with complete mixing). The temperature of the mixture would
be 9.2°F warmer than the upstream temperature. Assuming the upstream
temperature to be at a maximum (Q2.k°j), the temperature of the mixture
would be 91.6 F. The appearance of the temperature profile that would re-
sult downstream is shown in Figure 12. The stream temperature would re-
turn to normal within a distance of five or six miles.
Lower initial temperature increases, resulting from greater mixing
at the Bay confluence than estimated above, would shorten the length of
stream afl'ected as well as lessen the effect itself.
The extremely low velocities present in the nain stream as well as
the Bay would be conducive to stratification of the thermal discharge in
the upper layers unless it were released in a manner that would promote
greater mixing.
The above calculations indicate that with the large volume of water
always on hand for dilation, regardless of the stream flow rate, it is
doubtful that any water in the mainstream one-quarter mile or more below
the Bay would ever exceed 90°F.
DISSOLVED OXYGEN
Higher temperatures affect dissolved oxygen in the stream in two
direct ways. First, it increases the rate of natural self-purification
of organic matter resulting in a greater rate of oxygen depletion. Second,
higher temperatures reduce the solubility of oxygen in water. The
greater the organic pollution, the greater is the effect of higher
temperatures on dissolved oxygen concentrations.
Indirectly, higher temperatures can affect oxygen concentrations in
a third way by promoting increased growth of algae. Algal photosynthesis
-15-
-------
IU
oc
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I
u
ce
ffi
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u.
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CC UJ
-------
produces a net increase in dissolved oxygen during daylight. Algal
respiration, which occurs during the 2k hours, contributes to a net decrease
in dissolved oxygen at night. Upon death, the algae would decompose and
exert an oxygen demand.
The increased temperature resulting from the thermal discharge is
not expected to reduce dissolved oxygen concentrations to a dangerously
low level since the St. Croix River presently contains relatively little
pollution and the stream deoxygenation rate is quite low (approximately
.00^/day at 23°C). If the temperature of a given quantity of river
water were increased from 82°F to 91°F for a period of 20 days (approxi-
mate travel time in the affected reach) with no reaeration, the dissolved
oxygen concentration would be less than 1 mg/1 lower than it would have
been had the temperature not been increased.
The oxygen demand of the river will not be significantly increased
because of the stability and small amount of organic matter present.
In the Bay, the additional organic load produced by the decomposition
of the expected algae blooms, could result in a significant oxygen deple-
tion.
AQUATIC ENVIRONMENT
Water temperature is a factor which determines the distribution and
activity rate of the aquatic environment. The temperature range in which
life activities generally occur is from 32 to 104°F, although severe
changes in aquatic biota will result from prolonged exposure to tempera-
tures of 93°F. Even though waters at higher temperatures sometime con-
tain sufficient dissolved oxygen to support fish life, die off will
sometimes occur since the higher temperatures reduce the resistance to
disease, parasites, competitors and toxic materials. Synergistic
-16-
-------
relationships between temperature and toxic materials are common since,
fl.1_L too often, heated wastes are discharged within the vicinity of domestic
or industrial waste discharges.
With our present knowledge, it is impossible to make precise state-
ments concerning the effects of varying temperature levels on the over-
all "biota of a stream. In general, it appears that in low gradient
streams of the temperate zone, the temperature should not exceed 86 F
(M
for extended periods.
In the Ohio Valley area, studies have indicated that peak summer
vater temperatures should not exceed 93°F at any time or place.^' It
has been found that the upper temperature limits for warm fresh water fish
varied from 8k. 6 to 107.6 F. For fish found in the Lake Erie-Ohio River
Canal area median tolerance limits of 97.5°F, 96.3°F, 95.2°F, 95.0°F, 92.8°F
and 92.3°F, were found for large mouth bass, carp, brown bullheads, black
bullheads, bluegills, and channel catfish respectively. ' ' However,
these median tolerance limits should not be interpreted as the lethal level
because they actually represent a 50 per cent mortality rate and are no
indication of the temperature required for necessary activities and the
survival of the species. Understandably the Ohio River Valley and the
St. Croix River are not directly comparable. An upper limit of 93°F or less
would be expected to prevail in this area.
Based on the above information, the proposed thermal discharge will
have a significant impact on the aquatic environment, in and immediately
below Andersen Bay. Of principal concern is the possible development of
blooms of green and blue-green algae at the elevated temperatures. It is
reasonable to assume that a sufficient concentration of nutrients coming
from farm land drainage, the Stillwater municipal treatment plant and
-17-
-------
miscellaneous tile drains in the Bay area will be present for algal blooms
in the spring. The elevated temperatures of the Bay will provide the
impetus for the blue-green algal blooms to occur during the summer and the
gradual increase in water temperature as the summer progresses, will
probably stimulate additional algal growth.
The effects of algal blooms are well documented. In general, the
recreational use and value of the waters containing such blooms become
negligible. The unsightly green color plus the vile odors produced upon
decomposition of the algae virtually prohibit boating and swimming.
Damage has also been known to occur in the form of discoloration to
paint on boats, piers and in some severe cases on shore side residences.
Recurring algal blooms may reduce the real estate value of shorefront
property.
Aside from stimulation of algal blooms, the thermal discharge to the
Bay in the summer will bring about the demise of the macro-invertebrates
within the Bay and along the Minnesota shore to points where the temperature
decreases to 90°F. The lack of the macro-invertebrates serving as a link
in the food chain will suppress the fish population in the locale.
Pish kills in localized areas occur during the summer in many lakes
throughout the country. Some of these can be related to the large
accumulation of large masses of decomposing algae. Oxygen is consumed
during decomposition and can be reduced below the levels required to
support fish and most aquatic animals.
There is evidence indicating that fish have been killed by toxins
fg\
produced by blue-green algae in Iowa Lakes. yf Mackenthun et al impli-
cates algal decomposition as being partially responsible for a fish kill
in the Yahara River in Wisconsin.'10) In addition there is inferential
-18-
-------
evidence that epidemics of human intestinal disturbances may be caused
by algal toxins. ' ' Algal poisoning is considered to have been respon-
sible for sickness of dogs, cats, cattle, and horses in Saskatchewan.^2'
Warm bay water during winter conditions will undoubtedly attract fish
to the Bay area. The ability of fish to adapt to higher temperatures at
a faster rate than to lower temperatures has resulted in fish kills when
fish have entered warm waters and attempted to return to colder water.
Agersborg reported finding fish dying when attempting to return from 79 F
water to 32° F water with death occurring when the fish moved into areas
(-,0}
10°F cooler. ^ JJ
Additional fish life problems may result at the time of spawning and
hatching unless temperatures are on the average, 26°F below the median
tolerance limit value of a particular fish. This criterion is necessary
to enable many to complete their life cycle.
It appears as though an adequate zone for fish migration will be
retained within the St. Croix Eiver downstream from the proposed thermal
discharge. This should be verified by means of a hydraulic model. This
facet of further study would become more significant should the discharge
].o cat ion of the hoa+.^d wat«r T->A shifhed dnrcctly to the St. Croix River.
-19-
-------
BIBLIOGRAPHY
1, Wisconsin, Department of Conservation, Surface Water Resources of
St. Croix County, by LaVerne M. Sather and C. W. Threinan (Madison, 196l)p.7.
2. Federal Power Commission, Bureau of Power, Planning Status Report,
St. Croix River Basin, Wisconsin - Minnesota, 196^, pp. 5-10.
3. Velz, C. J. and J. J. Gannon (1960). Forecasting Heat Losses in Ponds
and Streams. Journal Water Pollution Control Federation 3_2_ k, p.392.
4. Cairnes, S. Jr. (1956). Effects of Heat on Fish, Industrial Wastes
1 5 pp. 180-183.
5. Tarzwell, C. M. (1957). Water Quality Criteria for Aquatic Life.
Transactions Seminar on Bio Problems in Water Pollution. R. A. Taft
Sanitary Engineering Center, pp. 2^6-272.
6. Brett, J. R. (19^4). Some Lethal Temperature Relations of Algonquin
Park Fishes. Univ. Toronto Stud. Biol. Ser, 52, Publ. Ont. Fish Res. Lab.
No. 63 pp 1-49.
7. Hart, J. S. (19^7). Lethal Temperature Relations of Certain Fish in
the Toronto Region. Trans. Royal Society Canada Vol. kl Wo. 3 pp 57-71.
8. Hart, J. S. (1952). Geographic Variations of Some Physiological and
Morphological Characters in Certain Fresh Water Fish. Univ. Toronto Stud.
Biol. Ser. Wo. 60, 79 pp.
9. Prescott, G. W. (1960). Biological Disturbances Resulting from Algal
Populations in Standing Waters. The Ecology of Algae, Special Publ. No. 2,
Pymatuning Laboratory of Field Biology, University of Pittsburgh, pp 22-37.
10. Mackenthun, K. M., E. F. Herman, and A. F. Bartsch (19^8). A Heavy
Mortality of Fishes Resulting from Decomposition of Algae in the Yahara
River, Wisconsin. Transactions American Fisheries Society 75_ pp 175-180.
-------
11. Tisdale, E, S. (1931). Epidemic of Intestinal Disorders in Charles-
ton, W. Va. Occurring Simultaneously with Unprecedented Water Supply Con-
ditions. American Journal Public Health. 21 pp 198-201,
12. Senior, V. S. (1960). Algal Poisoning in Saskatchewan. Canadian
Journal of Comparative Medicine XXIV 1, p. 26,
13. Agersborg, H. F. K. (1930). The Influence of Temperature on Fish.
Ecology. 11 1, pp. 136-1^4,
-------
APPEHDIX
-------
APPEKDIX IABLE 1
COMMERCIAL SHIPPING ON ST. CROIX RIVER
YEAR
1955
1956
1957
1958
1959
I960
1961
1962
1963
TOTAL
5, SOU
11,259
16,566
16,873
26,891
3U,306
U3,lU5
36,752
33,357
30,567
TONNAGE
COAL PHOSPHATES
llt,<&9 l8,Uo8
17,939 12,628
Ho figures are available at this time for the 196^ navigation
season.
-------
APPENDIX TABLE 2
QUANTITATIVE BOTTOM ORGANISM DATA
ST. CROIX RIVER
August
Mean Wo. of Organisms per Square Foot
Station
(Mileage)
23-5
21.0
20.0
Andersen
Bay
17.7
15.5
Ih.0
12.0
7.0
3.8
0.3
Samples
Taken
6
5
5
I*
6
6
6
6
6
6
k
Sludge
Worms
10
29
65
33
35
16
19
12
U5
122
3
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Worms
7
18
3
U
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1
2
7
8
8
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Hexagenia Midges
sp. Chaoborus
3 1
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83
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15
36
23
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-------
APPENDIX TABLE 5
FISHES OF THE ST. CROIX RIVER
ROUGH FISH
GAME FISH
Lake Sturgeon
Rock Sturgeon
Northern Pike
Walleye
Sanger
Smallmouth Bass
White Bass
Rock Bass
Black Crappie
Bluegill
Pumpkin Seed
Perch
Channel Catfish
Flathead Catfish
Brown Bullhead
Brown Trout
Composit list from:
1. Minnesota Department of Conservation, Division of Game & Fish.
2. Wisconsin Department of Conservation, Surface Water Resources
of St. Croix County by L. M. Sather and C. W. Threinen (Madison,
1961) 51 pp.
Gar (short nose & long nose)
Gizzard Shad
Quillback
Carp
White Sucker
Blue Sucker
Burbot
Sheepshead
Mooneye
Bigmouth Buffalo
Northern Red Horse
-------
STREAM FLOW METHODOLOGY
Stream flow of the St, Croix River at Stillwater is obtainable only
through addition of the flow of the St. Croix River at St. Croix Falls,
Wisconsin and the flow of the Apple River near Somerset Wisconsin. Al-
though daily gage height readings are taken at Stillwater, no discharge
record for any period is available.
The St. Croix River below Stillwater is a portion of the pool above
Lock and Dam No. 3 on the Mississippi River. However, it is not a
stationary pool. Flow is maintained past Stillwater at approximately
the same rate as that added by the St. Croix River and all its tributaries
above Stillwater. This is accomplished by regulating the volume of water
passing Lock and Dam No. 3 according to the total volume of water entering
the pool from the Mississippi River, the St. Croix River and their
measured tributaries.
During periods of extremely high flow the pool stage will increase,
and a balance between inflow at Stillwater and discharge at Lock and Dam
No. 3 may not be maintained. The inflow of the Mississippi River and its
stage are determinate factors. However, in a report of this nature, high
flows are of less concern than low flows, and no consideration will be
given to the effect of large stage variations on the flow at Stillwater.
Adding the recorded flows of the St. Croix River at St. Croix Falls
and of the Apple River near Somerset, results in a close approximation of
the St. Croix River flow at Stillwater. Before addition, the following
must be considered: (l) The flow of the Apple River near Somerset for any
day may be considered to be added to the St. Croix River and then to travel
to Stillwater in the same day; (2) The flow of the St. Croix River at
St, Croix Falls for any day may be considered to pass Stillwater the
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following day. Therefore to obtain the Stillwater flow for any day it
is necessary to add the Apple River flow for that day plus the St. Croix
flow at St. Croix Falls for the previous day.
Daily discharge measurements were begun at St. Croix Falls in
January, 1902, and the records are published by the U, S. Geological Survey
through water year 1962. A water stage recorder is located on the east
bank, 1800 feet downstream from the power plant in St, Croix Falls. The
records are rated as good. For the period of record the maximum discharge
is 5^,900 cfs on May §, 1950, the minimum daily discharge is 75 cfs on
July 17, 1910; and the mean annual discharge is ^,0^3 cfs. The drainage
area above the gage is 5>930 square miles.
Daily discharge measurements were begun on the Apple River near
Somerset at the hydroelectric power plant in October, 191^> and the records
are published by the U.S.G.S. through water year 1962. Headwater and
tailwater gages are read hourly at the power plant 3.5 miles downstream
from Somerset. The records are rated as good except those below 100 cfs,
which are fair. For the period of record the maximum daily discharge is
2,k60 cfs on January 17, 19^-3 > the minimum daily discharge is 7 cfs on
August 21, 1927, September 30, 1929, July 19, 1932 and August 2 and 3,
1933; and the mean annual discharge is 304 cfs. The drainage area above
the dam is 555 square miles.
Summing the mean annual flows of the St. Croix River at St. Croix
Falls and the Apple River near Somerset, the mean annual discharge at
Stillwater is ^,3^7 cfs. The drainage area above Stillwater is approxi-
mately 6,900 square miles.
Flows have been computed at Stillwater to provide four graphs defining
expected flow conditions at Stillwater. Mean monthly discharges and
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minimum daily discharges based on the ten calendar years of record from
1953 to 1962 inclusive are presented in Figures 6 and 7. Frequency of
minimum flows are presented in Figures 8 and 9» The recurrence of one
day average low flows is shown for the most recent 10, 20 and 30 years
of published record. The recurrence of seven day average low flows is
shown for only the ten years of record.
Figure 6 presents mean monthly discharges for the St. Croix River
at Stillwater. The mean monthly discharge for each month for the ten
years of record from 1953 to 1962 was computed by adding the mean monthly
discharges of the St. Croix River at St. Croix Falls and the Apple River
near Somerset. These additions provided ten mean monthly discharges for
each of the twelve months. Selecting the highest of these ten mean
monthly discharges for each month, the maximum of the mean monthly dis-
charges was plotted. Selecting the lowest of these ten mean monthly
discharges for each month, the minimum of the mean monthly discharges
was plotted. Averaging each month's ten mean monthly discharges provided
a plot of the average of the mean monthly discharges.
Figure 7 presents minimum daily discharges. This Figure is identical
to Figure 6 except that instead of using the mean monthly discharge, the
minimum daily discharge for the month is used. Since ten years of record
are considered, there are ten minimum daily discharges for each of the
twelve months. The highest, lowest and average of each of the ten dis-
charges provided a separate plot as above.
The minimum flow at Stillwater is a composite of minimum flows on
the St. Croix and Apple Rivers. Addition of all daily flows for the
ten year period was not undertaken to establish the precise minimum.
However, based on the average flows of the two streams for their periods
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of record, the Apple River flow is 7.5$ of the St. Croix River flow,
Since the contribution of the Apple River is relatively small, the
assumption has been made that a minimum flow recorded at St. Croix Falls
will in most instances, if not always, result in a minimum flow at
Stillwater the second day. By this method the Apple River flow for the
second day has been added to the St. Croix flow, regardless of whether
or not it is a minimum.
Plots of the minimum low flows for each month indicate two periods
of low flow that may be expected during the year. The lowest flows
usually occur during the month of January. The second month of low flow
is August. This being the month of greatest concern when considering
thermal pollution, the frequency of minimum flows was determined for
August only.
The St. Croix River flow at Stillwater was determined for each day
in August for the ten year period of record from 1953 through 1962.
From this tabulation the one day minimum for August was selected for
each of the years and their recurrence intervals determined. By successive
additions the minimum seven day average flow for August was also selected
for each of the years and their recurrence intervals determined. Figure
8 shows the one and seven day minimum flow versus recurrence interval.
Exact minimums were computed to define these curves.
Figure 9 provides a comparison of one day minimum flow frequencies
for August based on 10, 20 and 30 years of record. These minmum flows
for August were again determined by applying the previously defined
method (re: Figure 2).
The expected minimum flows for a given recurrence interval based
on ten and twenty years of record are very nearly the same. The greatest
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variation is 100 cfs at a recurrence interval of eleven years. However.,
the curve "based on thirty years of record varies considerably from the
other two. Because of this variation, the points defining the thirty
year curve are shown in Figure 9« ^e minimum daily flow of August
for 1933, 193^, 1936, 1937 and 1938 define the lower end of the thirty
year curve. All other flows compare closely with the ten and twenty year
flows. The 1930's are recognized as low flow years, but it must "be
realized that flows are regulated at St. Croix Falls. These five minimum
daily flows may reflect an unnatural flow condition where storage is
"being increased above St. Croix Falls during a period of natural low
flow. Therefore, when determining the frequency of low flows based on
the thirty years of record as shown in Figure 9? "the minimum flows pre-
dicted for a recurrence interval from six to thirty-one years are flows
whose natural occurrence is questionable. Although not necessarily
natural, all flow data must be considered. A particular minimum may
result from fluctuations in dam regulation at St. Croix Falls, but such
a minimum must be considered just as possible as minimums resulting from
natural causes.
The following table presents minimum average one day flows for various
recurrence intervals taken from the frequency of minimum flow curve for
the thirty year period of record, Figure 9»
Recurrence Interval Minimum Average One
In Years Day Flow in CFS
1 3930
5 ikOO
10 1000
20 700
30 550
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The following table presents minimum average seven day flows for
various recurrence intervals taken from the frequency of minimum flow
curve for the ten year period of record, Figure 8.
Recurrence Interval Minimum Average Seven
In Years _ Day Flow in CFS _
1
5 1700
10 1580
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