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NUSC Report No. 4005

O 00

Salinity Distribution in the Thames River: New London to Norwich, Connecticut F. SODERBERG ANTHONY B. BRUNO

EMIL

F./M Environment and Optical Systems Division

1 April 1971

NAVAL UNDERWATER SYSTEMS CENTER Newport, Rhode Island 02840

Approved for public release; distribution unlimited. NATIONAI TECHNICAL INFORMATION SERVICE Sp> rmfiold V»

22151

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DOCUMENT CONTROL DATA R&D IIV

1

i lasstln ation at llllv, body ul »h\ira< f «mi mile

.1 /«• entered *»!••« rfi

OS'(,iN»''NO »f tivil» {Corporate author)

UNCLASSIFIED

Naval Underwater Systems Center Newport, Rhode Island 02840 RI.PO«!

'•'" '•»••

:», HI I'UKi « l cciui ' > CL»S5

IlILE

SALINITY DISTRIBUTION IN THE THAMES RIVER: NEW LONDON TO NORWICH, CONNECTICUT 4

OfsCRiP T i VI NOTES (Type ol report and inclusive date*)

Research Report 5

»glHOBiSi (First name, middle initial. Ia»t name)

Emil F. Soderberg Anthony B. Bruno 6

REPORT DATE

7«.

8«.

CONTRACT OR GRANT NO

h. PROJEC T NO

TOTAL NO

Of PACES

lb. NO Of ncrs

97

1 April 1971

18

9(1. ORIGINATOR'S REPORT NuMfrRiSi

A-026-00-00 ZFXX 112 001

NUSC Report No. 4005 6.*>. OTHER REPORT NOiSl (Any other numbers that may be assigned thi* report)

10

DISTRIBUTION «TATEMENT

Approved for public release; distribution unlimited, II

SUPPLEMENTARY NOTES

M

SPONSORING Ml LI ' ARv ACTIVIT-

Department of the Navy 13

ABSTRACT

Observations of temperature, electrical conductivity, and salinity in the Thames River, Connecticut, mode over a 12-month period, are used to provide u preliminary description of the Thames River estuary. Longitudinal profiles of the river are presented to show the effects of upland stream discharge upo.i the fresr/salt structure of the river. The freshwater discharge into the estuary is usually small, and during most of the year the waters of the Thames River are of relatively high salinity throughout its length. During periods of high stream discharge, however, the head of the salt wedge may be pushed several kilometers downiver by the freshwater inflow to the estuary. This report describes the salinity distribution in the river in terms of salinity stratification as a function of distance along the length of the river, with volume of freshwater discharge as the parameter.

STdocument may be better ^.ftudled on microficht

DD,Fre,1473 S N CIO?-Old-6*00

tPAGE

'

UNCLASSIFIED S'MMTIIV CIH>.'ifi'alion

ABSTRACT Observations of temperature, electrical conductivity, and salinity in the Thames River, Connecticut, made ovc a 12-month period, are used to provide a preliminary description of the Thames River estuary. Longitudinal profiles of the river are presented to show the effects of upland stream discharge upon the fresh/salt structure of the river. The freshwater discharge into the estuary is usually small, and during most of the year the waters of the Thames River are of relatively high salinity throughout its length. During periods of high stream discharge, however, the head of the salt wedge may be pushed several kilometers downriver by the freshwater inflow to the estuary. This report describes the salinity distribution in the river in terms of saiinity stratification as a function of distance along the length of the river, with volume of freshwater discharge as the parameter.

ADMINISTRATIVE INFORMATION This work was performed under NUSC Project No. A-026-00-00, Principal Investigator, E. F. Soderberg, Code SA3, (EM Environment and Optical Systems Division), and Navy S.-bpro,ect and Task No. ZF XX 112 001, Program Manager, Dr. J. H. Huth, DLP MAT03L4. The technical reviewer for this report was C. L. Brown, Jr., Code TA131 (Oceanography Branch, of the Ocean Sciences Division). The authors gratefully acknowledge the cooperation of C. E. Thomas, Jr., E. L. Burke, F. Ruggles, and M. A. Cervione, Jr., of the United States Geological Survey, Water Resources Division, Harfford

Connecticut, who have provided both the hydro-

iogical data on the tributaries of the Thames River and some valuable comments on their measurements.

j^REVIEWED AND APPROVED: 1 April 1971

'iA^tJChxi^ Associate Director, Sensors Naval Underwater Systems Centei

A

UNCLASSIFIED Security d"Us»lfic«tion H E V

WO»DS

Thames River, Connecticut Salinity Distribution Electrical Conductivity Measurement Estuaries Flushing Shallow Water Environmental Factors

DD ,'.r..1473 i«*« I NOV «8

(PAGE 2)

UNCLASSIFIED Security Cjassific at inn

TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS

ill

LIST OF TABLES

vii

INTRODUCTION

1

DESCRIPTION OF THE THAMES RIVER ESTUARY

2

METHODS

6

UPLAND FRESHWATER DISCHARGE

9

RESULTS Temperature Electrical Conductivity Salinity

11 i1 li 11

• .

SALINITY PROFILES OF THE THAMES RIVER

14

SALINITY STRATIFICATION

22

FLUSHING TIME




o) y

IV9 9.1 m

2.2 m (DEPTHi

10.4 m

w

_ 685 m

183 m 966 m •8.2 m

786 m 4298 m-

620 ,T> 8130m

11 m 1102 m 8308 m •

Fig. 2. Transverse Depth Profile* at 15 of the 16 Measurement Sites along the Thames River Viewed Upriver with the West Side to the Left ond the East Sid* to the Right. (The vertical exaggeration of depth is approximately 14:1. River width, maximum depth, ond cross-sectiono! am« u—

u. 80

n »— A) z 60

•\

y so

VX

'*s

V ••,,

'•«., \.

10

i.o r 1.1 Mill 100 125

200

400

600

1000

I

I 2000

I

L-l .1 JUL 4000

6000

10000

J

L 20000

R (ft3/stc) - DISCHARGE VOLUME Fig. 4. Exceedance Curve tor the Daily Total Freshwater Discharge Meosured at Gaging Stations Q, S, and Y. (To obtain discharge va;u»s i?i n«3 >ic, multiply volu« in ftVsec by 0.02834. Note that the crithmetic average (224"' ft- sec) tor the period at interest occurs at the 36-percent exceedance level.)

RESULTS Only the general results of the observations of electrical conductivity, temperature, and salinity in the Thames River arediscussed here. The detailed results are presented graphically in Appendix A. One of the authors (ABB) has also computed and plotted the sound-velocity profiles associated with the conductivity, temperature, and salinity conditions for 14of the 26days. These graphs are presented in Appendix D. TEMPERATURE Figure 5A shows the variation through the year of the temperature of two selected portions of the river: the deeper waters of New London Harbor and the near-surface waters of the upper estuary. The temperature of the deeper half of the body of salt water in the harbor varied almost sinusoidally through the year, ranging from a high of 19.5°C during early September to 1.1°C during early March, with an estimated mean for the year of 10.4°C. Crossings of the mean value (extrapolated) occurred in early December and early Jene. The temperature of the fresher water overlying the salt wedge in the upper reaches of the river reflects the influence of seasonal land and air temperatures. The temperature of this surface water was found to be nearly the same as that of the underlying salt water during the winter, being a degree or two colder during Januar, and February and a degree or so warmer than the salt water during March. When the spring rains came, however, the temperature differential between the fresh surface waters and the underlying salt water increased steadily from a difference of o.6°C on 7 April to 7.6°C on 5 May 1969, then dipped to a difference of 5.2°C on 12 May before increasing further to 8. l°Con 9 June 1969. During the preceding July, the freshwater temperature exceeded the salt-water temperature by 7.5 to 10°C. ELECTRICAL CONDUCTIVITY The values of electrical conductivity for the salt water also varied almost sinusoidally, having a maximum in early September of approximately 42 miliimhos per centimeter (mmhos/cm) and a minimum in early March of about 26 mmhos/cm (Fig. 5B). The near-surface waters of the upper reaches ot the river had conductivity values ranging from a maximum of 26 mmhos/cm on 9 October 1968 (Site 13) when there was low freshwater discharge and high water temperature, down to less than 1 mmho/cm during periods of significant amounts of freshwater discharge. SALINITY Figure 5C shows the variation through the year of the sea water salinity in the lower depths of the channel in New London Harbor at Site 2. The salinity cf the deeper half of this body of sea water was found to Me between 31.3 and 31,5r'/oo during period:- of low freshwater discharge, falling to as low as 29.3%0(5 May 1969) during the spring rains.

n

30r

20

ft ^ Ui

10 -

O in -i—J 5 12 19 JU168

I ä AUG

' i T j fff 16 26 9 16 1 SEP OCT NOV Fig. 5A.

914 2227 5 12 20 JAN FEB

M-

it.

6 13 20 27 MAR

1 I I I 2130 5 12 APR MAY

9 JUN69

-L—I L 2! 30512 APR MAY

9 JUN69

Temperature Variation through the Year

40

38 h 36 34 32 u 30 D a 28

z

O 26

I i I 5 12 19

5

JU168

AUG

I I I l I 914 2227 512 20

-]_J l_L 16 26 9 16 1 SEP OCT NOV Fig. 5B.

JAN

FEB

J 6 1320 27 MAR

L 7

Electrical Conductivity Variation through the Year

32r

>-

31 -

•-

Z in

30-

29

1 1-1 5 12 19

5

JUL63

AUG

16 ib SEP

!_L 9 16

9142227 5 12 20

1

OCT NOV Fig. 5C.

JAN

FEB

1 I I I I 613 2027 7 MAR

I .11 I 21 30 5 12 APR MAY

9 JUN69

Salinity Variation through the Year

Fiq. 5. Graphs of Temperoture, Electrical Conductivity, and Salinity for the Deepest Portion of the Salt Wedge in New London Harbor (at Site 2), Plotted as Functions of Date of Measurement. (Figure 5A also shows the temperoture variation of the near-surface waters in the upper reaches of the estuary, indicated by the open circles.)

At some places along the river, near the outfalls of some of the larger industrial power plants, plumes of warmer water have been observed at various subsurface depths. Studies of the shape, extent, and duration of these plumes require measurements of finer spatial and temporal resolution than those reported here. Indications of such plumes ore seen in the temperature curves of the following figures in Appendix A:

12

fr

Figure

Site

A-5

7, 8, 9, 10, and 11

A-8

8 and 9

A-13

9 and 10

A-16

7

A-17

9

A-18

3 and 9

A-19

8 and 9

indication of a subsurface temperature maximum did not necessarily result in the appearance of a subsurface conductivity maximum because the delay between readings of temperature and conductivity (approximately one-half minute) allowed time for the boat to drift away from the plume or for the plume to shift position (a matter of a few meters). The occurrence of a subsurface temperature maximum was also observed in the data obtained in the thermal structure survey mentioned in the Introduction. The following -formation was released through the courtesy of Mr. Daniel T. Hedden, Northeast Utilities Service Company, Hartford, Connecticut3: The portion of the Thames River in the vicinity of the Montville electric power plant was intensively surveyed during the period August 12 to September 24, 1968, to determine the temperature distribution in the river and the relationship of the temperature to the volume of hcured coolant water being discharged from the plant. In therourse of these measurements, which were made for the Northeast Utilities Service Company by the Marine Research Laboratory (Raytheon), indications were found of a sub-surface temperature maximum which extended over a limited region in the vicinity of the coolant discharge point. W. Owen has proposed the following mechanism toexplain this sub-surface temperature maximum. It appears that the cooling water for the power plant is taken from waters below thehalocline, and is heated by passage through the plant, then discharged (at a shallower depth) into the fresher water above the halocline. Even though the heated discharge water is warmer than the surface water, it is more dense and it sinks to its own density level, producing a

13

sub-surface temperature maximum in a stable density profile. The location of thesub-suitace maximum upstream or downstream from the discharge point varied with the tide phase, but maintained its identity for a significant length of time before being dissipated. (Personal communication, Wadsworth Owen, July 19690 SALINITY PROFILES OF THE THAMES RIVER The data on salinity versus depth were used to develop longitudinal profiles of salinity distribution as a function of location along the length of the river. A computer program was used to perform a linear interpolation between depths, and the resulting contours of constant salinity were printed out on a Calcomp plotter. The longitudinal profiles of saiinity distribu'ion along the river are shown in chronological order ir Figs. 6 through 12. The numbers associated with the contours represent values of saiinity in parts per thousand. The ordinate values represent depth in meters below the river surface. Along the right-hand margin are the date of measurement, the time of occurrence of high or low tide at the Connecticut State Pier (near Sile 4), and the combined value of freshwater discharge at gaging stations Q, S, arid Y averaged over the two days preceding the date of measurement. The measurement site numbers are shown along the abscissa, and the time of measurement at each site are shown along the top of each individual profile. (The times shown are local times: Eastern Standard Time for the data taken from 1 November 1968 through 21 Aprii 1969, and Eastern Daylight Time otherwise.) The outline of the river bottom does not represent the channel center depth but rather is the bottom depth at the point of measurement, generally to one side or the other of the center of the channel. (The measured mfdchannel depths are shown in Fig. 2.) At the top of each page, a map of the river reflects the surface salinity distribution for the topmost profile in each figure. To allow visual comparison between profiles, the dividing line between the salt water ana the overlying fresh warer was chosen tobe the salinity contour representing a vaiue of ten pans per rhousana. That this is a reasonable choice may be seen by referring to the salinity versus depth graphs of Appendix "ߣ The 10 parts per thousand value is the point at which the salinity value has decreased to approximately l/e (or about 37 percent) of the maximum salinity value measured at a given site. The large vertical exaggeraticn (250 : 1) gives an imore Monistic view of what happens to *he fresh/salt structure for various values of frei- . •"••-.' discharge. The

14

DISTANCE (kmI FROM NOKWICH BASIN

1339 1320

1902

124*

122«

121« 1200

TIME (h) 1145 IISO 1113

1100

104«

101,1

1019

0*55

0*31

5 JUL 1968 LOW TIDE 1148h •v.. 62.6 m3 /»ec

29

29.9

-«-'

1400(390 1339

ISIS

I2SS

1131 1221

I20S

1143 1114

1103

1031

« • •

1020

4' —*

0»S3

0937

ft

•—

0909 79

12 JUL '968 HIGH TIDE 1154h 30.3m3/»ec

80

1300

1319 I33S

1392 1409 1420

1*47

1310

1920

1949

l«04 • 29.3

1229

1207 1190

IISS

1114

1100

1043

1024

1009

098*

0942

09IC ;2t

Fig. 6.

19 JUL 1968 HIGH TIDE ,8,2K

25.4 m3/»ec

5AUG1968 LOW TIDE 1324h 12.9m3/i«c

Salinity Profiles of the Thames River for 5, 12, and 19 July and 5 August 1968

15

10

12

14

DISTANCE (km! FROM NORWICH BASIN

1331 III« 1303 0 r •—y— |

1248

i**T | Ifl

TIME (r.) itll IIST 1144 1134 III« 1088 1042 1027 1011 ——^*——^fa"i^—*^

0»5* IT

0*33 I

" It mil— i

20.6 mVwc

[tt.4

:

in

16 SEP 1968 LOW T|pE |U2h

^n:ii'i" iiiTiTff-:^BiBMi^i^Miii»iP'iii»5Wi^M^—^^a».a

26 SEP 1968 HIGH TIDE 1248h 6.1 m3/wc

-*——*——*

1324

O o

iiS«

•*-

1307

1244 1231

1218

!t40

1046

1933

ISIS 1482

142* 1412 138«

1330

-*-

*

*-

1024

1012

0883

0034

0917

. 1320 1802

105»

1028

1003

4

9 0CT 1968 ... HIGH TIDE 1148h *'* 11.3 m3/««*

8

12 16

Or— 4i

50

31 31.1

16 OCT 1968 LOW TIDE 1206h 9.7m3/$«c

8 12 16 | I | I | I | 16 18 20 22 24 0 10 20 30 40 0 10 20 30 40

| I | I | I | I | 16 18 20 22 24 0 10 20 30 40 0 10 20 30 40

Conductivity, Temperature, and Salinity Profiles for 5 July 1968

*C m

3-

91300 12~ 0-

-12 -0

3-

-3

6-

-6

®

^ 12 — T 20 30 40 0 10 20 30 40

Fig. A-3. Conductivity, Temperature, and Salinity Profiles for 19 July 1°

36

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