WATER SUPPLY STUDY
LITTLE MARTEE RIVER
NEAR WIDU'"U FLORIDA
1700 me- PIAkT7
FLORIDA POWER & LIGHT COMPANY
IV. Location and Description
1. Cooling Reservoir
2. Diversion Channel
3. Pumping Station
V. Water Requirements
VI. Hydrological Aspects
LIST OF ITTJUCT.rTIONS
Plate 1 Area Map
Plate 2 Reservoir Layout
Plate 3 Average Minimum Flows
Plate 4 Historic Flows and Net Diversions
Plate 5 Pumping Station Layout
Plate 6 Pumping Station, Plan & Section
Plate 7 Water Quality
Plate 8 Reservoir Area Capacity
n ;~ip~A~F~~l~r~ ~~aar ? ~ e~~~brPL'r~ ss~Er
I. 11T:10DC:)1 CTION
Florida Power and Light Company engaged Brown & Root, Inc. to
perform engineering services required to develop a water supply for a
cooling reservoir for a 1700 M electric power plant in the vicinity of
Port Manatee. Previous power plant site selection studies indicated that
a favorable location for a 1700 MJ4 power plant and reservoir was in the
northern part of Manatee County, Florida, south of and adjacent to the
Little Manatee River and six (6) miles south of Wimauma, Florida. A water
supply from an existing stream can be developed by creating an "impoundment
on the stream and diverting water from the impoundment. Another method of
development would require a large capacity "scalping" pumping station
that would take flows directly from the stream with no impoundment. Both
types of facilities were investigated. An impoundment on a river would
require an embankment across the stream and the inundation of several
hundred acres of land even for a relatively small capacity impoundment
while a "scalping" pumping station would require no impoundment. Therefore,
a "scalping" pumping station, taking water directly from the river has been
adopted as the type of facility to furnish the required quantity of water
since it would have less ecological effect on the stream and adjacent
Conclusions drawn from this study show that a "scalping" type
pump station can be developed on the Little manatee River in Manatee
County capable of delivering the required amount of water. Results of
the study furnish the following pertinent facts:
SA. The Little Manatee River has sufficient flow to provide the water
B. The average diversion rate required may be accomplished with a
scalping type pumping station with a pumping capacity of 135 cfs.
C. The 22 cfs average reduction of flow in the stream represents approxi-
mately 13% of the average long term flow in the river at the point of
diversion and-approximately 8% of the average long term flow in the
S river at its mouth.
The purpose of this study was to investigate the feasibility of
developing a water supply in the Port Manatee Area that would be capable
of furnishing the water required for a cooling reservoir that would
serve a 1700 MWJ power plant. Of primary importance is the fact that the
diversion facility must have the least possible ecological effect on the
stream and the adjacent land area.
(. IV. If< TAT2CI: A:*:D i TSTPTIcn
i The cooling reservoir and diversion facility would be located 6
miles south of Wimauma, Florida, on the south bank of the Little
Manatee River, approximately 19 river miles upstream from the mouth,
1.5 miles downstream from the confluence with the South Fork as
shown on the Area M.ap, Plate 1.
1. Cooling Reservoir. The cooling reservoir would be located
south of the Little-Manatee River as shown on Plate 2. The
reservoir would be formed by an earth embankment constructed of
material at the site. The embankment would have an average
height of approximately 20 feet. The existing soil on which
.the embankment would be constructed will supply an adequate
foundation for the embankment. A preliminary soils exploration
has been made by National Soils Services, Inc.'which is included
herein as Appendix "A". The reservoir would have a surface
area of approximately 2575 acres at minimum operating level
and4000 acres at maximum operating level or the top of the
conservation pool as shown on plate 8. The water level in the
reservoir would fluctuate in proportion to the rate of water
pumped from the river. The rate of pumpage is influenced by
the amount of flow in the river. Therefore, conservation storage
is provided so that the reservoir size is maintained above the
S2. Diversion Channel. In conjunction with the pumping station,
a diversion channel will be required at the river. Construc-
tion at the river would be limited to an open channel connecting
the river to the pumping station through which the water diverted
from the river would be conveyed to the pumping station as shown
on Plate 5. The channel would be approximately 250 feet in length,
trapezoidal in shape.
The depth of the river at the point of the intake channel
connection varies from 1 foot to 2.feet.
3. Pumping Station. Water would be lifted by the pumping station
from the end of the channel as shown on layout on Plate 5.
SThe pumping station shown on Plate 6 would be of concrete
construction, with approximate dimensions shown and sized to
"accommodate various pumps with a total pumping capacity of 135
cfs. As the water enters the sumps, it would pass through a
steel trash rack capable of excluding only large objects such
as tree limbs and objects with a small dimension of- more than 3
inches. After passing through the trash rack, the flow would
proceed to a dual flow traveling screen. The screen would be
of 3/8 inch mesh. As the objects collect on the screen, the
screen would rotate and the collected objects will be removed
I from the screen by water jets and deposited in a trash trough
i for removal to another location. The velocity of flow through
Sthe screens would be limited to .5 ft/sec. or less to avoid
impaling small fish on the screen.
I "y After passing through the traveling screen, the water would
proceed to a pump sump and then be lifted by the pump to the dis-
charge line. The pumps would be vertical turbine or mixed flow
propeller pumps, electric motor driven. The pumps would vary in
capacity from approximately 2,500 gpm to 20,000 gpm. Various
operating combinations would be employed to vary the flow taken
from the river up to 135 cfs.
S------------- -- -* -
V. WAT q I"T-W : "V::
The amount of water required for a cooling reservoir is made up of
seepage from the reservoir, the net natural evaporation that would have
occurred from the water surface if no heat was added by the power plant
and the forced evaporation attributable to the heat induced from the power
plant. The long term average water requirements are as follows:
Forced evaporation 18 cfs
Natural evaporation 1 c'fs
Seepage (assumed) :2 cfs
Total Cooling Reservoir.Losses 21 cfs
The forced evaporation loss attributal to the heat induced from the plant
is based on an average monthly weather and water temperature data and a
plant heat rejection rate of 6.0 x 109 BTU/r (about 80% station capacity).
The natural evaporation loss has been-based on records of the past
thirty (30) years which indicate that the average rainfall is forty-eight
(48) inches per year and the average gross natural- evaporation is about
fifty-one (51) inches per year resulting in a net natural evaporation of
about 1 cfs.
The seepage rate was assumed to be 2 cfs. The seepage rate may be
greater but rates greater than this would most likely return to the
river, Seepage from the reservoir will supply water to the shallow
ground water in the shallow sand deposits in the vicinity of the
facility. Soil borings made to date indicate that the perched water table
is some 3 to 5 feet below the ground surface.
- '..-- -.-... ... .'---. --... ,.__.- ."
I 1 V I. HY.rD1 LCTICAL AcPECTS
i Records of flow in the Little Manatee River have been recorded by
the United States Geological Survey since March, 1939, and are available
through October, 1971. The study and data herein is based on that period
of record. The gage where flows have been measured is located 25 feet
Downstream from the bridge on U.S. Highway 301. The drainage area at
the gage is approximately 145 square miles and the average flow is 182
cfs which indicates a runoff of 1.25 cfs per square mile. The drainage
area at the proposed diversion is approximately 134 square miles and the
average flow is based on the unit runoff. Therefore, the flow at the
point of diversion would be in the range o 168 cfsy The total drainage
area at the mouth of the Little Manatee is approximately 210 square miles.
Water in the Little Manatee River is brackish for varying distances
(depending upon tide and flow in the river) upstream from its confluence
with Tampa Bay. Records of chemical analyses at the gage near the bridge
on U.S. Highway 301 have been published by the U.S. Geological Survey
(see Plate 7). These records indicate that little or no ocean water has
been observed in the Little Manatee River at its observation point. There-
fore, no salt water should ever be present in the river at the point of
*diversion upstream from the gage.
The presence of the reservoir would reduce the drainage area contributing
to the Little Manatee by approximately 2400 acres and to the Manatee River
by approximately 2,700 acres (see Plate 2). Based on the drainage area
contribution to flow into the Little Manatee River of 1.25 cfs per square
"1, -*~ --1-
U ------ ---- ---- --- -
______________ __ _____ ____ ___
mile, (which is probably higher than exists since the area is in the u, i r
reaches of the drainage area) the flow into the Manatee River would
be reduced by approximately 5 cfs due to the presence of the lake. The
flow into the Little Manatee River will likewise be reduced by approxi-
mately 5 cfs. The drainage area contributing directly to the cooling
reservoir (not including the reservoir surface) is approximately 1100
acres all of which would normally contribute flow to the Manatee River.
These 1100 acres will contribute approximately 2 cfs to the cooling
reservoir based on the long term average.
The reservoir will be operated at a level such* that releases will
occur during periods of excessive rainfall. Theoretical operation of the
reservoir over a thirty-three (33) year period indicates that the releases
would average 12 cfs.
Months during which flood releases were made and a tabulation of
these releases in 1,000 acre-feet per month is shown in Table A.
Releases From Reservoir in 1000 Acre-Feet
SYear Jan -Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
"1939_ f J 4.8 1 B .3
19j01 1.3 0.7 ___ 0.2j 1.5 2.8 0.6_
.1941 __ 0.1 1.5 1.7 2.0 2.
1942 1.1 0.7 1.5 1. 3 1.8 1..
1943 2.1 1.7 0.3
194 i l .... 1.3
19 _5 3.1 3 4,1 2.7 1.1_ __
1946 0.2 0.5 _4.6 2.2 2.6 T1.6
19?47 2.3 1.2 2.0 3.7 3.9 43 1.2 0.8o 0
"19486 2.7 0.3 1.1 1.2 2.8 ,28 .1.1 0.3
"1-949 _____. __ __ 0.2 3.5 0.____
S1950 ____ ___ 3.3 0.9 -2.2
S1951 0.2 0.7 1f.3 .. 2.5 3.2 0.1 0.1 .
1952" 0 0. 4 178i 2.5 0 -6 0.2
93 1.3 I 1.2 .1. 3.91. 0.6i 1.6
1 -954 0.31 0.4 1.5 2.2 0.t 2.*1 0.1 178 0.6
_19_55 0s__ 3.2 2.9 __
195...-- --,-! :-- .. -,--, 39--- --- -- -----:-]
1957 3.7 3.5 3.9 2.0 O _
195 I7.8-TT 1- 1.7 1.2 1.0 0.2i 1.6 2.1 o7. 0.3 0.7T, 1
1959 1.2i 0.7 4.2T 7 2.5 3. 0 2.-4 3.5 2.0 2.1 0.7
1960 _1.2 3.7 6.9 2.6 2.7 3.2
1961 1.31 o__
1962 3.4 2.5 04 0.71
*1963 2.6 0.8 2.7 1.84 1.9 0.8
194i 0T0.8 1 1.3 I 1.3 1.3 2.0 __
1965 __ ____ ___ 3.2 1.9 1.0 0.5
S1966 1.4! 1.01 0.2 2.1j 2.5 1.6. 1.4 0.,
S197 _____ .7 o7.8
19687 j I I_ 1 2~, 1.4 1.2 0.9 1.j0
'1969 0.6: 0.7 ]-.8 1.5 0.9 4.0 1. 1.04 1.9 1.7
1970 1.0 1.3 2.0 !0.2j 0.7 I t I i
____________________^^^^ --- -------------
H An accounting of the water as it effects the lont term flows in tih
Little Manatee River is as follows:
Pumped from River 29 cfs
Reduction of flow due to reduction in
drainage area 5 cfs
Releases returned to the river (12)cfs
Total reduction of flow in the Little
Manatee River 22 cfs
It is understood that Florida Statutes stipulate-that diversions
should not occur at such times when the flow in the stream is less than
the "average minimum flow". The "average minimum flow" has been defined
as the average of the five lowest monthly mean discharges for each month,
S occ urri n during the past 20 years of natural flow. The graph for the
"average minimum flow" in the Little Manatee River at the point of diver-
sion upstream from U. S. Highway 301 is shown on plate 3. The values
are based on the 20 years record prior to October, 1971. In the evaluation
of the pumping station sizes required to divert an average of 29 cfs, no
diversions have been made when the flow in. the stream is less than the
"average minimum flow" and no diversion large enough to reduce the flow
below the "average minimum flow" has been included in the analysis.
The pumping station capacity has been made such that it would be
capable of taking from the stream more flow on the long term average
than is required. This safety factor has been provided because; (a) all
the water available to be pumped would be difficult to divert; (b) the
Historical record is only 30 years, therefore, a more severe drought
may occur over a long period of time.
The historical flows in the river at the pumping station and the
net diversions if the diversion had taken place are shown on Plate 4.
The amount of water diverted each month was calculated on a daily basis
using record daily flows. For example, if the flow in the river was
100 cfs on a particular day and the "average minimum flow" was 47 cfs for
that particular day, an amount of water approaching 53 cfs would be
diverted from the river by the pumps if the cooling reservoir level was
below the top of conservation level. If the reservoir had been full,
no diversion would have been made.
The total Little Manatee River drainage area at its confluence with
Tampa Bay is approximately 210 square miles. At the average runoff of
1.25 cfs per square mile, the long term average flow would be approxi-
mately 262 cfs. The drainage area upstream from the point of diversion,
134 square miles represents 64% of the total drainage, area. The average
minimum flows in the river represent approximately 20%o of the river flow.
Therefore, on a drainage area and stream flow ratio basis, no water would.
be diverted from the stream when the flow into the bay was less than 20%o
of the average flow in the river.
The fresh water-salt water interface location in the Little Manatee
River is influenced by several factors including the rate of flow in the
river, the tide level and movement and the cross section of the river.
The flows in the river vary widely from over l4,000 cfs to almost zero.
r-pn The presence of the pumping station and cooling reservoir will not allt,'
the flows in the river when they are below approximately 20% of the avcrV:i
Slows and therefore will have no effect on the location of the fresh water-
salt water interface at times of low flows.
Investigations of water quality in the river indicate that at times
of low flows the water is brackish in the vicinity of its confluence with
Curiosity Creek and that the water quality increases markedly upstream from
this location. It should be noted also that at this location and down-
stream to Tampa Bay, the river cross section is relatively large when
compared to the cross section upstream from this point. The fact that the
river cross section changes significantly in this vicinity undoubtedly has
a great influence on the location of the fresh water-salt water interface.
SDiversion from the stream by the pumping station will occur mostly when
flow in the stream is moderate to high. Therefore, the Lcation of the
fresh water-salt water interface should be influenced only slightly by the
diversion of water from the stream since diversions will take place only
when flows are moderate to high ahd since the interface is also greatly
influenced by the stream cross section.
_~~17.~G;~~~ --. I^/ ^---- .---~--------g~_Trn~t~~clq~, C---rr
The Little Manatee River at the point of diversion south of Wiraurr.a,
Florida, has, from an engineering standpoint sufficient flows to meet the
needs of a cooling reservoir serving a 1700 MW power plant. These diver-
sions could be accomplished without the benefit of an impoundment on the
river. The long term average reduction in flow in the Little Manatee
River would be 22 cfs and in the Manatee River the average reduction in
flow would probably be less than 5 cfs.
i- ---. *
I+. ; .+
NATIONAL SOIL SERVICES, INC. ".'nr' ,
"HOU:; I O Al A. IST ANCH'A AN
r, -' */ 04002 GULf SJ fi LT IOUSTON. I( .:AS 77017 Ml ',lIN ', tl.;,)
PRELIMINARY SITE STUDY
COOLING WATER RESERVOIR
FLORIDA POWER & LIGHT COMPANY
Mid-Valicy, Inc. Report No. 7228
P. O. Box 2634 April 1, 1972
Houston, Texas 77001
Attention: Mr. C. Fick
Submitted here is our interim report on the investigation of site conditions for Cooling
Water Reservoir in the vicinity of Tampa, Floirda. This investigation was made to define
general soils and geologic conditions for a location designated as the Willow Site. This
study was authorized on March 15, 1972.
Stratigraphy in the area was developed by seven borings located as shown on Plate 1 in
the report illustrations. Undisturbed samples of the clays and standard penetration samples of
-the sands were obtained at approximately five foot intervals to depths ranging from 55 to 140
feet. Resistivity logs were also developed for each location to verify field classification and
facilitate correlation between adjacent borings.
The soils encountered are shown on the logs of borings, Plates 2 thru 8, dnd a key to
i the log terms is shown on Plate 9. Resistance to penetration of the sampler indicated in the
-- blows per foot column and cohesive strength measured with a hand penetrometer is tabulated
'v^ at respective sample depth. The estimated surface elevation at each location and observed
4 groundwater levels are also shown.
ANALYSES AND RECOMMENDATIONS
General Soils and Geologic Conditions
The data have been combined to develop the generalized profile shown on Plate 10.
Correlation was developed based on similarity of soil type and geologic origin.
The study shows that soils present at this site consist of interbedded silty sands, clayey
sands, and sandy clays from the surface to depths ranging from 25 to 58 feet or Eley +44 to
Elev -10. These deposits represent Pliocene and Pleistocene terrace sediments, specifically,
J & the Wicomico and Penholloway terraces. The sands are silty and clayey and, based on the
standard penetration data, range from loose to medium dense. The sandy clays which usually
occur at shallow depths are medium to low plasticity strata that will be relatively impervious
although discontinuous throughout the site.
The entire reservoir area is underlain by very stiff to hard greenish gray sandy clay and
clay with limestone lenses. These strata which are typical of the Hawthorne formation of
Miocene age extend to depths in excess of 140 feet, Elev -78. Geologic studies in *
Hillsborough and Manatee Counties indicate this formation extends to depths in excess of
250 feet and is underlain by the Tampa limestone; the Hawthorne formation acts as an aquiclude
or confining layer for the underlying limestone which is the major aquifer in this region.
Elevation of the Hawthorne surface is indicated in parenthesis at each boring location.
S- The relatively low elevation in the area of borings CB-5 and CB-6 may be indicative of stream
erosion and migration in this area that resulted in a deeply incised valley during Miocene
-- II.T ~-":--r~n~)r~-:nr~n-rrlc*~-^rY -- I 1.....................................................lr~n~r- *
time. The former Miocene drainage pattern may presently be reflected by the Manatee River
Topographic maps of this area and site inspection show the presence of numerous surface
depressions ranging in size from 200 to 1000 feet. Depressions of this shape and frequency
are indicative of solution activity in this region. However, preliminary investigations at an
alternate site, west of this study area, and regional geologic data indicate that formation of
these depressions is confined to soils above the Hawthorne formation and is not a reflection
of a deep seated solution activity. Detailed studies will be required to define .the cause of
these depressions and potential effect on foundation requirements for the proposed facilities.
Cooling Water Reservoir
The proposed site will be suitable for development of a cooling water reservoir. Soils
available for embankment construction consist of silty sands, fine sands, and a limited quan-
tity of sandy clay. A homogeneous section.with an upstream slope protection zone of soil
cement is recommended for this relatively long embankment system. A nominal keytrench
approximately five feet below surface grade should be planned for the section. Site prepa-
ration can be .limited to clearing and grubbing; stripping will not be required except for
organic surface soils and muck in the stream valleys. Borrow soils can be obtained immediately
adjacent to the embankment and sandy clays for impervious zone construction will be
available from borrow pits in the uplands extending to depths in the order of 25 feet. The
embankment could be constructed with interior slopes of 1:2.5 and exterior slopes of 1:3.
Seepage losses from the reservoir would develop primarily through the shallow soils
overlying the Hawthorne formation. Based on previous analyses for similar soils, it is
-,m~M -r:' .: -- '-r LI
estimated that seepage losses will be in the order of 0.036 gpm per foot of crmbarimnt.,
Power Plant Foundations
The study and general geology of this region shows that foundation soils in the power
plant area will consist of medium dense to dense sands underlain by strong and incompressible
sandy clays. These deposits are suitable for shallow support of all power plant structures.
Allowable loading for foundations will range from six to 10 kips per square foot depending
on relative foundation dimensions, depths, and permissible settlement. Wellpoint dewatering
will be required for foundation construction below eight to 19 feet and the excavated soils
consisting predominately of sands will be suitable for backfill in structure areas and general
Intake and discharge canals for the power plant will be constructed predominately in
the sands. Permanent slopes in the order of one vertical on 2.5 horizontal can be planned
and erosion protection by means of soil cement will be required for the canal invert and slopes.
Dewatering may be required for installation of the soil cement sections. The excavated soils
will be suitable for embankment construction.
We appreciate the opportunity to perform this study. Please call upon us if we can be
of further assistance.
Very truly yours,
NATIONAL SOIL SERVICES, INC.
Ralph F. Reuss
o RFR:mws : i '
Copies submitted: 7 V
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130 ---- -- -- ---- ---
Prior to October 1,1971.
Little manatee River 3.5 Miles
i 0 JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.
The Average Minimum Flow is the / FLORIDA POWER & LIGHT CO.
Average of the Five Lowest Monthly WATER SUPPLY DEVELOPMENT STUDY
Mean Discharges for Each Month
Occuring During the 20 Years
Prior to October I, 1971. AVERAGE MINIMUM FLOW
SData is for Pumping Station Site on
Little Manatee River 3.5 Miles
Upstreom from U.S G.S. Gaging
S...-...March I972 LAE-
\ \ N
Mean Hy / er
Ln Low ar
E4/ 1 0
BROWN ROOT NC.
I_________ __ ___ ----
CAPACITY IN 1000
65 60 55 50 45 40
7.Top Conservation Sforage- lev 66. _
I \2,575 A7c.
SBolom Conserva lio7n Sorcpe e5ev. 5
%455 ... ..
S50 ---- .
3 5 : -
3 4S - -----------------
30 .I|.... .... -.. ___
0 500 /000 /500 2000 2500
AR EJ IN ,7CRES
.. /ICRE -FEET
30 25 20 /S /1 5
./ \ \ i. ^ z-/6, 3062 ,QcFf.
1 4 4 i ...
S i ; .. i
i i 4
: I I I I
3000 3500 4000 4500
FLORIDA POWER 8 LIGHT CO.
WATER SUPPLY DEVELOPMENT STUDY
BROWN 8 ROOT INC.
APRIL 1972 PLATE-8
***----..-.---. -----.- .1 - -^.I--- ^ ______ I. -- -- --------- --- ---- 11I II ------ -- --------- ---------- i-- --- ---- I------------------------- "
S ......... .... .. ..-; -- .... ... .. .. .. ... .........-- ~--- - -- c --
"" 860 400 450
,JkJ .# "
', FLRD POE LIH O
6 80 -- --- -. ...- ---- -.. .......
> 0 ... FE.. MAR. APR. MAY JUNE JUL AUG. SEPOCT. NOV. DEC.
NOT FLORIDA POWER 0-LIGHT CO.
The Average Minimum Flow is the WAT ER SUPPLY DEVELOPMENT STUDY
Average of the Five Lowest Monthly
Mean Discharges for Each Month
Occurring During the 20 Years
Prior to October I, 1971. AVERAGE MINIMUM FLOW
IaDote is for Pumping Station Site on
Little r4I-anatee River 3.5 Miles
Upstream from US G.S. Gaging
S:tN.:t F'; 2-3005 Aear -':m BROWN Y ROOT SiC. PLATE -3
i IMarch 1972 1