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PROTECTION OF NARRAGANSETT
BAY FROM HURRICANE TIDES

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DOCUMENT

COLLECTION /

INTERIM REPORT
February 1957

U. S. Army Engineer Waterways Experiment Station
CORPS OF ENGINEERS
Vicksburg, Mississippi

PROTECTION OF NARRAGANSETT
BAY FROM HURRICANE TIDES

Hydraulic Model Investigation

INTERIM REPORT
February 1957

000

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rmy Engineer Waterways Experiment Station
CORPS OF ENGINEERS
Vicksburg, Mississippi

ARMY-MRC VICKSBURG, MISS.

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PREFACE

The model investigation reported herein was initiated by the Water-
ways Experiment Station in November 1955 at the request of the U. 5S. Army
Engineer Division, New England, CE. Design and construction of the model
were accomplished during the period December 1955-January 1956, hydraulic
adjustment of the model was carried out during February-March 1956, and
the testing of the principal proposed improvement plans, which are dis-
cussed in this report, was accomplished during the period April-September
1956. Supplementary tests currently in progress will be reported in the
comprehensive report to be issued on completion of the entire testing
program.

The Division Engineer of the New England Division during the course
of the investigation was Brig. Gen. Robert J. Fleming, Jr. Personnel of
the New England Division who participated in planning the course of the
model testing program were Messrs. H. J. Kropper, John B. McAleer, and
Lincoln Reid. The model investigation was carried out under the super-
vision of the following engineers of the Waterways Experiment Station:
Vide mee nOcLSON dia. Calc hiOmsbhe hydraulics Davasgwon, Mig. Gieyeb.
Fenwick, Chief of the Rivers and Harbors Branch, and Mr. H. B. Simmons,
Chief of the Estuaries Section, by Messrs. W. H. Bobb and E. B. Jenkins.

This report was prepared by Mr. Simmons.

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PINGING 6 6 6 6 0 6 0 6 0 0 «
PART Gs) INTRODUCTION... .

CONTENTS

Purposes of Investigation .

SCOIS Ost AWobls INSOIS
Was IIONONAOS 6 6 0 0 oO

PAIRME ICIbS WUeI) WOME 6 o 6 6 6

Design Considerations .
Scale Relationships . .
Description of Model

Model Appurtenances . .

PART IT~: VERIFICATION OF MODEL REPRODUCTION

PHENOMENA ....

Astronomical Tides .
Current Velocities .
HumreLrecane Vides! fs. «

PART IV: TESTS AND RESULTS .

Bese HAS “6°08 so

Technique for Testing Improvement

MELCWCDS Istehiy Isteherealeres)) 5 5
Mower Bay, Barriers 7.
Upper Bay Barriers ..

Combination Barrier Plans .

PART V: CONCLUSIONS .

Effects of Barriers on Tides :
Effects of Barrier Locations on Buildup

Effects of Barriers on Tidal Currents .

TABLES 1-6

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PROTECTION OF NARRAGANSETT BAY FROM HURRICANE TIDES

Hydraulic Model Investigation
(Interim Report)

PART I: INTRODUCTION

Purposes of Investigation

1. The principal purposes of the model investiga on of plans for
protection of Narragansett Bay from hurricane tides were to determine:
(a) the effects of barriers installed at various locations in the bay on
both hurricane and astronomical tide heights throughout the bay system,
both landward and seaward from the various structures; (b) the magnitude
of the tidal current velocities that would obtain in the navigation open-
ings of certain of the barriers during both hurricane and astronomical
tides; and (c) the effects of the barriers on tidal current velocities
throughout the bay system for conditions of normal tides. Secondary
purposes of the model investigation included determination of the effects
of the barriers on salinities, temperatures, sedimentation, and flushing

throughout the bay system.
Scope of This Report

2. A total of 36 proposed improvement plans were tested in

the model during the course of the investigation; however, the more
complete testing was limited to those plans found to be most practical
as a result of partial model tests in combination with New England
Division design and economic studies. Plans subjected to more or less
complete testing include plans 27 through 36, and all pertinent data
obtained during model tests of these plans are presented in this re-
port. In addition, the results of several of the partial tests are
reported herein, since these results have a direct bearing on con-

clusions or subsequent test procedures. It is planned to publish a

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© FRESH WATER INFLOW SCALES

0,000 FT
PROTOTYPE 2209 ° 10,000__2
1o 20 FT

Fig. 1. Vicinity map showing location of tide gages

comprehensive report that will include the detailed results of all plans
tested, regardless of whether complete or partial tests were made, since
the test data obtained may be of value in planning and conducting future
investigations of this type. Also, the results of the tests to deter-

mine the effects of the barriers on salinities, temperatures, sedimenta-

tion, and flushing will be included in the final comprehensive report.

The Prototype

3. Narragansett Bay is located on the coast of Rhode Island about
50 miles south of Boston (see location map, fig. 1). The bay system is
about 30 miles long in a north-south direction and 15 miles wide in an
east-west direction, the total area being about 450 square miles. The
inner bay system is connected with the ocean by two major straits, East
Passage and West Passage, and one minor strait formed by the Sakonnet
River. The East Passage is about one mile wide at the mouth and has a
controlling depth of about 70 ft; the West Passage is about two miles
wide at the mouth and has a controlling depth of about 30 ft. The
Sakonnet River is fairly wide and deep in its lower reaches; however,
the control for flow into and out of the inner bay system is a bridge
near Tiverton (see fig. 1) which has a navigation opening only about 100
ft wide and about 30 ft deep.

4, The terrain adjacent to the inner bay system ranges from high
cliffs to low marsh areas which are partially inundated by normal spring
tides. The principal cities and towns located on the bays include
Jamestown and Newport, R. I., near the mouth of the bay system, and
Providence and Bristol, R. I., and Fall River, Mass., near the head of
the bay. The principal defense installations are the Newport Naval Base
and Quonset Point Naval Air Station. There are numerous highly developed
summer recreational facilities throughout the area, and a large number of
the harbors are utilized by commercial fishing and pleasure craft.

5. The mean range of astronomical tides throughout the bay varies
from about 3.6 ft at Newport to about 4.5 ft at Providence. Astronomical

tides in the bay are principally of the stationary wave type, i.e., there

is no appreciable lag between the time of high tide at the entrance and
at the head of the bay, the average time of high tide at Providence being
only about 10 to 20 minutes later than at the entrance some 25 miles away.
Tidal current velocities throughout the bay system produced by astronom-
ical tides are quite moderate, ranging from maximums of about 2.5 ft per
sec in the East and West Passages to less than 1.0 ft per sec in the wide
sections. Only in a few restricted sections, such as that under the
bridge near Tiverton, do current velocities of astronomical tides exceed
about 2.5 £t per sec.

6. The tides generated by tropical hurricanes moving north along
the Atlantic Coast are sometimes much greater in magnitude in the
Narragansett Bay area than the largest astronomical tides, especially
when the hurricane center moves inland to the west of Narragansett Bay,
thus placing the bay in the path of the right front quadrant of the
storm. When the time phasing of the hurricane-generated tide is such
that its peak coincides with high water of the astronomical tide, as was
the case in September 1938 and August 1954, the flooding of low-lying
areas is especially severe and loss of life and damage to property may
be extensive.

(7. The tides generated by hurricanes moving inland on a coast
such as that at the entrance to Narragansett Bay are made up of two major
components: (a) the general rise in sea level produced by the low-pressure
area associated with the hurricane center; and (b) the wind setup, or the
additional rise in sea level produced by the mass transport of water
shoreward by the onshore winds of the right front quadrant of the storm
blowing over the fetch between the Continental Shelf and the shore. The
height of the surge component generated by the wind is dependent on the
wind velocity, fetch, the direction of the storm path with respect to
the alignment of the shore, the bottom slope of the offshore region, and
many other factors.

8. After a hurricane-generated tide enters a bay or estuary such
as Narragansett Bay, the resultant heights attained at various locations
are dependent on two major factors: (a) the gravitational component of

the ocean tide which moves through the entrance and thence through the

bay system essentially as do the normal astronomical tides; and (b) the
local setup caused by hurricane winds blowing over the bay proper. The
first of these factors is usually the more significant, since few if any
interior bay systems provide a sufficient fetch to permit generation of

a large wind setup within the bay. Hurricane winds blowing along the
axis of the bay depress the water-surface elevation near the bay entrance
below that which would have been produced by the gravitational component
alone, and raise the water-surface elevation at the head of the bay above
that which would have been produced by the gravitational component alone.
It may be stated, therefore, that local wind setup over the Narragansett
Bay system could not increase flooding at localities near the bay en-
trance but could appreciably increase flooding at Providence and other

localities near the head of the bay system.

PART II: THE MODEL

Design Considerations

9. Since the most important information desired from the model
with respect to the feasibility of construction of barriers in Narragan-
sett Bay concerned the effects of barriers at various locations on normal
astronomical and hurricane tide heights and current velocities through-
out the bay system (see paragraph a) the principal consideration in
design of the model was that it be capable of providing quantitative
answers to these questions, or that the model test data be susceptible
of adjustment by reliable analytical methods so that the final answers
desired could be obtained.

10. Since the prototype forces involved in the generation of as-
tronomical tides are gravitational forces, a model for study of such
tides and the resulting tidal currents must be designed and operated in
accordance with Froude's law of similitude. Since the major component
of hurricane tides in an inner bay system is the gravitational component,
the propagation of which is likewise governed to a major degree by grav-
itational forces, the Froude law is equally applicable to a model study
of this component.

ll. Model reproduction of the local wind-setup component of a
hurricane tide is a different matter, and this difference was discussed
in detail by all concerned during the planning and design phases of the
model study. Since simulation of wind setup in a large model such as
that of Narragansett Bay would be extremely difficult, time consuming,
and expensive, and since local wind setup can be computed with acceptable
accuracy by known analytical methods, the decision was reached that the
model study would be confined to investigation of gravitational phenomena,
and the wind-setup components would be computed by the New England Divi-
sion. The model was therefore designed and operated in accordance with

Froude's law of similitude.

Scale Relationships

12. The linear scales (model to prototype) selected for the model

were 1:1000 horizontally and 1:100 vertically. These scales were se-
lected on the dual basis of providing the largest model that could be
justified from a cost viewpoint, as well as the smallest model that could
be tolerated from the standpoint of accurate reproduction and measure-
ment of significant phenomena. Use of the above linear scales fixed the
following significant scale relationships (model to prototype): velocity,
1:10; time, 1:100; plan area, 1:1,000,000; cross-sectional area, 1:100,000;
discharge, 1:1,000,000; and volume, 1:100,000,000.

Description of Model

13. The prototype area reproduced in the Narragansett Bay model
is shown on fig. 1. The ocean area reproduced outside the bay entrances
extended from Point Judith on the west to Sakonnet Point on the east,
and included most of Rhode Island Sound. Offshore hydrography in the
ocean was reproduced in detail to the 100-ft contour of depth, and the
Ocean area beyond this contour was utilized for the astronomical tide
and hurricane tide generators which are described subsequently. All of
the inner bay system was included in the model, as well as the tidal
portions of all streams tributary to the bays as far upstream as signif-
icant flooding by hurricane tides of record had occurred.

14. The model was of fixed-bed construction throughout, the bed
and banks being molded of concrete. The hydrography of the bays and
tributary streams was molded carefully in accordance with information
shown on the latest hydrographic surveys made by the Coast and Geodetic
Survey and the Corps of Engineers. The topography of the banks adjacent
to the bays and tributary streams was molded in detail to el 132 ft mlw
at Newport, R. I., in accordance with topographic surveys prepared by
the Geological Survey, so that the extent of flooding by hurricane tides,
as well as the storage effect of such flooding on water-surface eleva-
tions at upstream localities, could be reproduced with maximum accuracy.
Fig. 2 is a general view of the model; a close-up of the Providence

Harbor area is shown on fig. 3.

F CONANICUT

DE ISLAND SOU:
(ATLANTIC OCEAN)

Fig. 2. The model

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=CONSTANT HEAD TANKS AND See i
— UPLAND DISCHARGE WEIRS= =

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WOONASQUATUCKET —p- o. PROVIDENCE 4
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Fig. 3. Providence harbor and vicinity

Model Appurtenances

15. The major appurtenances utilized in operation of the model,
and for measurement of the required phenomena therein, included astronom-
ical and hurricane tide generators, recording tide gages, manually oper-
ated point gages, current velocity meters, and upland discharge weirs.
These appurtenances and their uses are described briefly in the subse-
quent paragraphs.

16. The astronomical tide generator was of a conventional type
used by the Waterways Experiment Station in connection with many estuary
models. Its major components consisted of an underground water-supply
sump located near the model, a large header connecting the sump and the
ocean portion of the model, a mechanized valve installed in the header,
a pumped-discharge line which entered the header on the model side of
the mechanized valve, and an electromechanical control system which
dictated the opening and closing of the mechanized valve. In operation,
the control unit was adjusted to automatically cause precise opening and
closing cycles of movement of the valve, which in turn maintained the
necessary balance between a pumped flow of water to or a gravity flow of
water from the model as required to duplicate the exact rate of rise or
fall of the tide being reproduced. This apparatus consistently maintained
correct water-surface elevations of the model ocean within an accuracy of
about 0.001 ft (0.1 ft prototype). The mechanized valve and the valve-
control unit are shown on figs. 4 and 5, respectively.

17. Hurricane tides could have been reproduced in the model with
the same system used for generation of astronomical tides, or by an in-
dependent system of the same type, except that the large amplitude of
the hurricane tides would have required the use of very large pumps,
valves, and pipes. A study of possible methods of reproducing hurricane
tides indicated that the most practical and economical solution would
be to construct a reservoir (or basin) adjacent to and integral with the
model ocean containing a volume of water somewhat greater than that re-
quired to reproduce the largest hurricane tide to be studied, and to

reproduce the tide by means of a motorized bulkhead in the basin. This

VALVE MOTOR

Fig. 4. Mechanized inflow-outflow valve

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bulkhead was operated in such manner that its forward motion displaced
water from the basin into the model, thus reproducing the rising phase

of the hurricane tide, while its backward motion permitted water to flow
from the model into the basin, thus producing the falling phase of the
tide. The drive motor was of the three-phase type to permit the neces-
sary reversal in direction of movement of the bulkhead, and a PIV (posi-
tive, infinitely variable) speed control unit was installed in the drive
mechanism to permit a highly accurate control over the speed of the bulk-
head. This system was found very satisfactory for generation of hurri-
cane tides, in that the apparatus could be quickly adjusted to reproduce
any desired ocean tide with a minimum of effort, and that tide could then
be duplicated accurately as many times as necessary. The hurricane tide
generator system is shown on fig. 6.

18. Because of the very rapid rate of rise and fall of hurricane
tides, recording tide gages were utilized to measure and record these
tides at various locations throughout the model. The gages consisted of
a roll of recording paper moving on a drum which was revolved at a known
and constant speed by a small synchronuous motor, and a float-supported

pen which inked a continuous record of water-surface elevation on the

“VARIABLE SPEED
REVERSIBLE DRIVE UNIT

Fig. 6. Hurricane tide generator

recording paper. Pin points were projected through small holes in the
recording drum so as to perforate the recording paper at time intervals
equivalent to one hour (prototype),
to maintain a permanent time check
on each record. The recording

gages were mounted on flat base

plates, which in turn were mounted
he on tripods permanently located at
all points in the model at which
hurricane tide data were desired.
The tripod mounts were all adjusted
to a common reference plane, so
that any recording gage could be
moved from one location to any
other location without loss of
time for adjusting its reference
plane. One of these recording
gages is illustrated on fig. 7.
19. Manually operated point
gages, permanently mounted at the

locations of ail prototype tide

gages and at a number of additional
BS Op Tig Rl eN 5 Sine eet SeiSlel e132 locations, were used for measure-
ment of astronomical tide elevations during most of the model tests;
however, the recording gages described above were used for this purpose
during a few tests in which time did not permit use of the point gages.
More precise measurements were possible with the point gages than with
the recording gages, since the measurement was a direct one and did not
involve interpretation of a record. One of the permanent point gages
USEC tite lol) SSSI, Chal. ser, 3hq

20. Most of the measurements of current velocities in the model
were made with miniature Price-type current meters illustrated on fig. 8.
The horizontal dimension of the cup wheel was about 0.083 ft and the

vertical dimension about 0.03 ft. The meters were capable of accurate

measurement of velocities down to a min-
imum of 0.05 ft per sec (0.5 ft per sec
prototype), and they were calibrated
frequently to insure accuracy of
operation.

2l. The upland discharges of the
major tributaries to the bays were meas-
ured by means of Van Leer (California
Pipe) weirs, each weir being supplied
from a separate constant-head tank.

One of the model weirs and its constant-

Fig. 8. Model current meter

head tank may be seen in the background of fig. 3. The upland discharges

introduced in the major tributaries during all tests reported herein,

unless stated differently in the description of a particular test, were

as follows: Pawtuxet River, OO cfs; Woonasquatucket and Moshasuck

Rivers, 400 cfs; Seekonk River, 1500 cfs; and Taunton River, 1400 cfs.

PART Iti: VERIFICATION OF MODEL REPRODUCTION
OF PROTOTYPE PHENOMENA

Astronomical Tides

22. The first step in preparing the model for testing consisted
of verifying the accuracy with which it would reproduce observed normal
astronomical tides. This was accomplished by adjusting the astronomical
tide generator to reproduce a tide of mean range in the model ocean, then
verifying the accuracy with which resulting mean tides were reproduced
throughout the inner bay system. Prototype mean-tide data were avail-
able for a number of gages throughout the bay system, and data for Castle
Hill, Newport, Narragansett Marine Laboratory, Quonset Point, Warwick
Point, Weyerhaeuser Timber Company, and Edgewood Yacht Basin gages (see
fig. 1) were selected for the initial comparison with model data.

23. An ocean tide of mean range was interpolated from observed
records at Block Island (about 22 miles seaward from the bay entrance)
and Newport, since no prototype tidal gaging station was in existence at
a point approximating the location of the inflow-outflow system of the
model astronomical tide generator (designated as ocean head bay, fig. yi
The tide generator was adjusted to reproduce the interpolated tide curve
in the model ocean, and resulting tides at the seven locations listed in
paragraph 22 were measured for comparison with observed prototype mean
tide ranges and elevations. As shown on fig. 9, the high-water and low-
water profiles at all corresponding model and prototype gaging stations
were in close agreement, thus indicating that reproduction of an astro-
nomical tide of mean range in the model ocean would result in accurate
reproduction of the ranges and elevations of this tide throughout the
bay system. This same procedure was repeated, using a spring tide having
a range equal to that observed on 28 December 1955, and the agreement
between model and prototype tidal ranges and elevations at Castle Hill,
Narragansett Marine Laboratory, Weyerhaeuser Timber Company, and Edgewood
Yacht Basin for this condition is also shown on fig. 9. These compar-

isons indicate satisfactory agreement between model and prototype with

LOW WATER PROFILE

ELEVATION IN FEET » MLW NEWPORT

LOW WATER PROFILE

MEAN TIDE

LEGEND

PROTOTYPE
——— Mea

Fig. 9. Verification of astronomical tide heights

respect to ranges and elevations of both mean and spring astronomical

tides throughout the area reproduced in the model.

Current Velocities

24, No attempt was made to obtain a detailed verification of

current velocities throughout the bay system for the tests reported
herein; however, it was considered desirable to check the model reproduc-
tion of prototype current velocities in the principal channels of the bay
system to insure that the distribution of flow among the several channels
was approximately correct. Observed prototype current velocities for
stations 1-6 shown on fig. 10, adjusted to conditions of mean astronom-
ical tide, were obtained from Coast and Geodetic Survey Special Publica-
tion No. 208, entitled, Currents in Narragansett Bay, Buzzards Bay, and
Nantucket and Vineyard Sounds, 1936. Observations were made at similar
locations in the model for conditions of the mean astronomical tide de-
scribed in the preceding paragraph. Comparisons between prototype and
model current velocities for the six velocity stations are shown on figs.
ll and 12, and indicate satisfactory agreement between prototype and

model current velocities at all stations.

Hurricane Tides

Hurricane tides of record

25. Gage records at Newport, Providence, and in some cases at
Somerset, were available for the tides generated in Narragansett Bay by
the hurricanes of September 1938, September 1944, and August 1954. Each
of these hurricane tides was reproduced in the model to determine how
closely the resulting model tides agreed with those of the prototype at
the locations for which prototype gage records were available. However,
the September 1938 hurricane tide was the only one used for model test
purposes; therefore, the comparisons of model and prototype hurricane
tides for conditions of the September 1944 and August 1954 hurricanes
are not included in this report.

26. In the verification tests, the model astronomical tide gen-
erator was first adjusted to reproduce the astronomical tide predicted
for 21 September 1938 (the date of the hurricane), which had a range of
slightly more than 4.0 ft and a high-water elevation of +4.1 ft mlw at

Newport.* The hurricane tide generator was then adjusted by a cut-and-try

* All elevations in this report are referred to mlw at Newport, R. I.,
which is 1.6 ft below msl.

TAUNTON RIVER ABOVE
THIS POINT REALIGNED
TO FALL WITHIN
SHELTER LIMITS

JAMESTOWN |
BRIDGE

\ OCEAN HEADBAY
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LEGEND

| AUIS TIDE

@ VELOCITY STATIONS

| GENERATING BAY
© FRESH WATER INFLOW SCALES

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PROTOTYPE 10,000 Oo 10,000 20,000 FT

| | 10 20 FT

Fig. 10. Location of velocity stations

3dALOLOYWd - GNOD3S Y3d 1334 NI ALIDO713A

AdALOLOYd - GNODSS Y3d 1334 NI ALIDO13A

5 6 u 8

TIME IN HOURS AFTER MOON'S TRANSIT OVER 71°20!

STATION

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3dALOLOYd - GNOD3S Y3d 1333 NI ALIDON3A

4
TIME IN HOURS AFTER MOON'S TRANSIT OVER 71° 20'

STATION 2

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3dALOLOYd - GNOODAS Y3d 1334 NI ALIDO13A

6 7 8 9 10
TIME IN HOURS AFTER MOON'S TRANSIT OVER 71°20!

LEGEND

STATION 3

PROTOTYPE
—--—-—— MODEL

Verification of velocities at stations 1-3

iraljer5 JL,

VELOCITY IN FEET PER SECOND - PROTOTYPE

2.0 2.0
a a
° °
g g
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= =
S
° — °
—
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m LO LO
oO + a
Ww t wW
2.0 t E : 2.0
° 1 2 3 4 5 6 7 8 9 10 Wl 12,0
TIME IN HOURS AFTER MOON'S TRANSIT OVER 71°20!
STATION 4
2.0 + 2.0
—
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a
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= 23 =
=
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= =
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TIME IN HOURS AFTER MOON'S TRANSIT OVER 7I° 20'
STATION 5

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re io = aN LO me

1
A= —t - =
== t
+
° — 0
i.
FA
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=
2.0 : 2.0
° | 2 3 4 5 6 7 6 9 10 WT 12.0

¢
TIME IN HOURS AFTER MOON'S TRANSIT OVER 7I°20'

LEGEND

Fig.

PROTOTYPE STATION 6

MODEL

12. Verification of velocities at stations }-6

VELOCITY IN FEET PER SECOND - PROTOTYPE VELOCITY IN FEET PER SECOND - PROTOTYPE

VELOCITY IN FEET PER SECOND - PROTOTYPE

procedure until the resultant tide at Newport (astronomical tide plus
hurricane tide component) was in agreement with the actual tide recorded
for 21 September 1938. As soon as a successful reproduction of the
Newport tide curve was attained, measurements of the resultant tides at
Providence and Somerset were made for comparison with prototype records.

27. Maximum elevations reached by the September 1938 hurricane
tide at Newport, Providence, and Somerset were 11.7 ft, 17.8 ft, and 14.8
ft, respectively, above mlw at Newport. The elevations reached at Prov-
idence and Somerset were therefore 6.1 ft and 3.1 ft, respectively,
higher than at Newport, including both gravitational buildup and wind
setup. Early computations of wind setup for the 1938 hurricane tide in-
dicated this factor to be about 2.0 ft at Providence and less than 1.0
ft at Somerset, thus indicating the gravitational buildup to have been
of the order of 4.0 ft at Providence and between 2.0 ft and 3.0 ft at
Somerset. The initial test of the 1938 hurricane tide in the model,
during which an elevation of +11. ft mlw was reproduced at Newport, re-
sulted in maximum elevations of +15.5 ft at Providence and +14.8 ft at
Somerset, or gravitational buildups of 3.8 ft and 3.1 ft at Providence
and Somerset, respectively.

28. Since the results of the initial test were in close agreement
with the results of initial computations of wind setup for conditions of
the 1938 hurricane tide, a number of preliminary hurricane tide tests of
proposed barrier plans (through plan 26 of the model study) were made
for these conditions. However, the results of later and more refined
computations of the wind-setup component of the 1938 hurricane tide in-
dicated that the setup at Providence was of the order of 2.8 ft to 3.0
ft, instead of about 2.0 ft as indicated by the early computations. Use
of the refined wind-setup computation indicated that the gravitational
buildup of the 1938 hurricane tide between Newport and Providence was
about 3.1 ft) to 3/3 ft, instead of the 4.0 £t shown by the early computa-
tions and checked by the model during initial tests.

29. The excessive gravitational buildup of the 1938 hurricane
tide in the model indicated a deficiency in model roughness, which con-

sisted only of a rough brushed finish of the concrete bed at the time of

the initial tests. It was suspected from the beginning that the model
roughness was deficient, but the very low current velocities throughout
the model for astronomical tide conditions, plus the close reproduction
of the gravitational buildup of the 1938 hurricane tide, had made addi-
tional roughness seem unnecessary. After the deficiency in roughness
became apparent the Manning "n" of the prototype channels was estimated
to be of the order of 0.026, and roughness elements were added to the
model as required to effect a scale reproduction of this estimated pro-
totype roughness. The model roughness elements consisted of three-
fourth-inch-wide metal strips set vertically into the concrete bed of
the model and extending to the water surface. An average of about one
strip per two square feet of model area was required to duplicate the
estimated prototype roughness.

30. Use of the refined wind-setup computations for the 1938 hur-
ricane tide indicated that the gravitational buildup of this tide over
maximum elevation at Newport was slightly more than 2.0 ft at Somerset
and, as previously stated, was 3.1 to 3.3 ft at Providence. The 1938
hurricane tide was repeated in the model after completion of the rough-
ness adjustment described above and with the hurricane tide generator
adjusted to produce a maximum elevation of +11.9* ft mlw at Newport. It
was found that maximum elevations at Providence and Somerset were 15.2
and 14.2 ft, respectively, above mlw, or a gravitational buildup of 3.3
ft at Providence and 2.3 ft at Somerset. Comparisons of prototype and
model gage records at Newport, Providence, and Somerset for conditions
of the 1938 hurricane tide are shown on fig. 13. Astronomical tide
elevations and ranges shown on fig. 9, and current velocities at several
of the stations for which data are presented on figs. 11 and 12 were re-
checked to determine whether the change in model roughness had effected
changes in astronomical tides and tidal currents. It was found that no

measurable changes had occurred in astronomical tides and tidal currents

* Model high tide was increased 0.2 ft over that recorded in the proto-
type to compensate for the effects of local wind setup which depress
water-surface elevations near the bay entrance.

LEGEND

———— MODEL HURRICANE TIDE
PROTOTYPE HURRICANE TIDE

ELEVATION IN FEET , MLW NEWPORT
a

4 5 6 8 9 to 1202 Sera! 5 6 7 8 9 © tT 20 1 2
TIME It! HOURS AFTER MOON'S TRANSIT OVER 71°20!

NEWPORT PROVIDENCE SOMERSET

Fig. 13. Verification of 1938 hurricane tide heights

from the data shown on figs. 9, 11, and 12.

31. Prototype and model plots of the 1938 hurricane tide curves
at Newport, Providence, and Somerset, shown on fig. 13, indicate that
the time phasing of the peak of the hurricane tide was the same in the
model as in the prototype. Some differences may be noted between proto-
type and model with respect to the slopes of the tide curves, especially
at Somerset, but these differences are thought to be due to wind effects
in the prototype. In addition to the comparisons between prototype and
model tide curves shown on fig. 13, the maximum elevations reached by
the 1938 hurricane tide at numerous locations throughout the bay system
were checked against elevations at corresponding points in the model.
High-water elevations at all points in the wodel were found to be lower
than those at corresponding points in the prototype by amounts approx-
imately equal to the computed wind setup for such locations. It was
therefore concluded that the model would reproduce accurately through-
Out the entire bay system the gravitational component of any hurricane

tide generated in the model ocean.

Design hurricane tides

32. The model hurricane tide generator was designed to reproduce
hurricane tides of greater amplitude than that of September 1938, which
was the greatest hurricane tide of record in the Narragansett Bay area,
to take care of the possibility that later computations might indicate
that tides of greater amplitude are likely to occur in that area. The
hurricane of September 1944 was selected for design purposes, and the
tides that would have been generated at Newport by this hurricane if it
had reached Narragansett Bay at the peak of its intensity were computed
for three assumed speeds of movement of the hurricane center, 20 knots,
30 knots, and 40 knots. These tides, referred to hereinafter as design
tides, were computed by the New England Division and furnished to the
Waterways Experiment Station for use in the model tests.

33. The model reproductions of the 40-knot and 20-knot design
hurricane tides at Newport are shown on fig. 14. The computed tides do
not contain an astronomical tide component as does the 1938 hurricane
tide discussed previously, so adjustment of the model hurricane tide

generator to reproduce the design tides at Newport was accomplished with

1 TF | Phone eae
7 = | |
16 | |
15 |
14
LEGEND |
li | ———— MODEL HURRICANE TIDE |
DESIGN HURRICANE TIDE
12 | 4 [
i Wt
2
FA 10 \
59
= } \
a) +
Ww 1] \
[4 \
: 7 IL |
Zz \ |
E 6 ic
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us r
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—
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-2k 2 —
2 3 4 5 6 7 8 3 10 it} 20 ! 3 4 5 6 2 3 4 5 yf 8 9 10 W 20 i 2 3 4 Ss 6
TIME IN HOURS AFTER MOON'S TRANSIT OVER 71° 20/
DESIGN HURRICANE ADVANCING AT 20 KNOT SPEED DESIGN HURRICANE ADVANCING AT 40 KNOT SPEED

Fig. 14. Verification of design hurricane tides at Newport

the model water surface pooled at mean astronomical tide level (about
41.8 ft mlw). In later model tests involving use of the design hurricane
tides, these tides were reproduced in combination with the astronomical
spring tide range of 4.1 ft at Newport. The 40-knot design tide was used
only briefly during the testing program since this tide was almost iden-
tical at the mouth of the bay with the 1938 hurricane tide used in all
preliminary tests, and no test data for conditions of this design tide
are included in this report. The 30-knot design tide was not used at

all for model test purposes. All hurricane tide test data presented in
subsequent parts of this report were obtained for conditions of the 1938

hurricane tide or the 20-knot design hurricane tide.

PART IV: ‘TESTS AND RESULTS

Base Tests

34. Base tests, or tests of existing prototype conditions, are
made in connection with hydraulic model studies to provide a direct basis
for evaluating the results of subsequent tests incorporating proposed
improvement plans. A measurement of some phenomenon during a plan test,
when compared to a similar measurement made during the base test, will
provide a direct measure of the effects of the plan on the phenomenon
in question. Since it is usually desirable that improvement plans be
tested for more than one basic condition, base tests are made for all of
the conditions for which improvement plans will subsequently be tested.
During the course of the Narragansett Bay model study, several astronom-
ical tide and several hurricane tide base tests were made. The condi-
tions established for these various base tests are described in the sub-
sequent paragraphs.

Astronomical tide base tests

35. Two astronomical tide base tests were used for evaluation of
the model test data. The first involved reproduction of a normal spring
tide, which had a range of 4.1 ft at Newport, a high-water elevation of
+h.1 ft mlw, and a low-water elevation of 0.0 ft mlw. All hurricane
tide tests reported herein were made in conjunction with this astronom-
ical tide, and supplemental current velocity data and astronomical tide
data for all plans reported were obtained for conditions of this tide.
In addition, certain current velocity data and astronomical tide data
for plans 35 and 36 were obtained for conditions of a mean tide having
a range of 3.6 ft at Newport, a high-water elevation of +3.7 ft mlw, and
a low-water elevation of +0.1 ft mlw. Test data presented in subsequent
parts of this report for plans 35 and 36 show which of the above-described
astronomical tides was being used during the test in question.

36. Base test data for astronomical tides and tidal currents are
not shown independently in the remainder of this report; instead, these

data are included in data tabulations for direct comparison with similar

measurements made with the various plans installed in the model. The
tables show whether the base test data presented were obtained for mean
or spring astronomical tides. In all cases comparative plan data were
obtained for the same tide range as were the base test data.
Hurricane tide base tests

37. Hurricane tide base test data presented in this report to
assist in evaluation of plan test data were obtained for one or the other
of the following conditions: (a) the astronomical spring tide range of
4,1 ft at Newport combined with the September 1938 hurricane tide; or
(b) the astronomical spring tide range of 4.1 ft at Newport combined with
the 20-knot design hurricane tide. As described above in connection with
the astronomical base tests, each table presenting base test or plan test
data shows whether the data presented were obtained for the condition
described in (a) or (b) above, or both. Hurricane tide base test data
were obtained at the 29 automatic gage locations shown on fig. 1 for

each of the conditions described above.
Technique for Testing Improvement Plans

38. The testing of proposed barrier plans in the model involved
some precautionary steps to insure that scale effects resulting from
the distorted scales of this model did not adversely affect the accuracy
of model test data, and to obtain all data required for evaluation of
the plan in question. The detailed procedure followed in testing a
proposed barrier plan is described below:

a. If one or more ungated navigation openings were incorporated
"in the design of the plan, each opening was modeled to the
distorted model scales and also to an undistorted scale

of 1:100. The openings and adjacent sections of the
structures were then installed in two flumes in which
depths were molded to conform with the depth at the loca-
tion of the navigation opening in the prototype. The dis-
torted and undistorted openings were next subjected to
tests covering the full range of head differentials to be
expected in the model, the discharge coefficients of the
undistorted openings were determined for each increment of
head differential, and the distorted openings were modi-
fied as required to adjust their discharge coefficients

to those of the undistorted openings. In all cases, the
adjustments required consisted only of rounding the corners
of the sills and abutment walls of the distorted openings
to reduce contraction effects.

The proposed barriers were then installed in the model,
and navigation openings (if any) were adjusted as found
necessary during the flume tests so that their discharge
coefficients were correct throughout the full range of
head differentials.

Both the astronomical tide and hurricane tide generators
were then readjusted to reproduce the same tides in the
ocean portion of the model as occurred during the base
test condition to be used for evaluating the effects of
the plan in question. The readjustment procedure was
necessary because installation of different plans in the
model caused various changes in the tidal prism of the bay
system, both for conditions of astronomical tides and hur-
ricane tides, which in turn would have affected the range
of the ocean tides in the model had not the generators
been readjusted for each barrier plan.

The plan in question was then subjected to all astronom-
ical tide and hurricane tide tests for which information
was desired, and all necessary measurements of resulting
tidal and current phenomena throughout the bay system
were obtained. In the case of a few plans, it was de-
sired to determine in detail the distribution of current
velocities in one or more of the navigation openings for
conditions of maximum hurricane tide head differential and
maximum astronomical tide head differential across the
structures. Because of the small size of the navigation
openings in the distorted model, these data were obtained
by observing the maximum head differentials in the model,
establishing these head differentials in the flume con-
taining the undistorted model of the opening in question,
and obtaining the necessary measurements of velocity dis-
tribution therein.

By following this sequence of steps, all errors in model results that
would have been caused by the distorted model scales were eliminated, and
the test results presented herein may be considered quantitative with

respect to the effects of the various structures in the prototype.

Middle Bay Barriers

The elements of the Middle Bay barrier plan are shown on fig. 15.

FOX POINT BARRIER
| PROVIDENC

FIELD POINT BARRIER TAUNTON RIVER ABOVE

THIS POINT REALIGNED
TO FALL WITHIN
SHELTER LIMITS

ge) PRUDENCE
WEST MIDDLE BAY BARRIER 3 ~ /S. BARRIER

ay l SAKONNET RIVER GATED BARRIER

l EAST MIDDLE BAY BARRIER

ry)

JAMESTOWN
BRIDGE

WEST LOWER BAY BARRIER
CONANICUT /SLAND BARRIER.

41°30°

EAST LOWER BAY BARRIER
RELOCATED WEST LOWER BAY BARRIER

PT JUDITH

—

/
+/

as,

\ | OCEAN HEADBAY

| HURRICANE: TIDE

ikea J.

| cenerarine BAY
| SCALES

PROTOTYPE 10,000 ie} 10,000 20,000 FT

| | MODEL 9

i) 10 20 FT

Fig. 15. Location of barriers

2s)

This plan involved a structure across the West Passage between Pojac
Point and Patience Island (designated West Middle Bay barrier), a struc-
ture closing the gap between Patience and Prudence Islands, a dike
across the Prudence Island marshes, and a structure across the Fast Pas-
sage between Prudence and Aquidneck Islands (designated East Middle Bay
barrier). The model structure in the West Passage was equipped with 33
sluice gates, each 100 ft wide, and that in the East Passage with 34
Similar gates (see fig. 16), in addition to navigation openings in each
passage. A number of preliminary hydraulic tests were made to determine
the maximum current velocity that would obtain in both navigation open-
ings with various numbers of sluice gates open in each barrier. The data
from these tests were to be used to determine the total area of openings
(both sluice gates and navigation openings) required to hold current
velocities in the navigation openings to a maximum of about 4.25 ft per
sec for conditions of an extreme astronomical spring tide range of 5.4
ft at Newport. It was found that a total opening area of about 114,000
sq ft would be required to meet this criterion. No structure was in-
stalled in the Sakonnet River during these tests.

4O. Two degrees of closure of the Middle Bay barrier were tested
tO determine the effects of the structures on hurricane tides. The first
of these, designated plan 22 of the model study, involved complete closure
of the West Passage, complete closure of the Sakonnet River at Old Stone
Bridge, closure of the channel between Patience and Prudence Islands,
and a navigation opening in the East Passage barrier having a sill eleva-
tion of -4O ft mlw, a sill width of 600 ft, abutment side slope of 1 on
1.5, and a crest elevation of +24 ft mlw. Details of this navigation
opening are shown on fig. 16. The hurricane tide test of plan 22 was
made for conditions of the 1948 hurricane tide superimposed on the
astronomical spring tide having a range of 4.1 ft at Newport.

hl. The effects of plan 22 on maximum elevations of hurricane
tides throughout the bay system are shown in table 1, together with the
effects of the plan on the times of hurricane high tides. Only a few
reliable measurements of astronomical tide ranges and elevations were

made during the test of plan 22; these measurements indicate that tidal

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ranges and elevations at gages located downstream from the barriers were
relatively unchanged, while tidal ranges at stations upstream from the
structure were reduced by about 45 to 50 per cent (the elevations of
high water being lowered and those of low water being raised). The maxi-
mum elevations of hurricane tides upstream from the structure were low-
ered by amounts ranging from about 9.0 ft at Warwick to about 11.1 ft
at Providence. Downstream from the structures, however, the elevations
of hurricane tides were increased by amounts ranging up to about 1.4 ft.
The results of this test indicate that barriers located in this region
of the bay would reduce hurricane tide elevations at all locations up-
stream from the barriers but would cause an appreciable buildup downstream
from the structures over elevations without barriers.

h2, Tests of the Middle Bay barriers were also made with the East
Passage navigation opening closed, thus completely closing off the upper
part of the bay. This condition was designated plan 23 of the model
study, and the same conditions of astronomical and hurricane tides were
WSOC TCH Wd WES ES seid wesios Cs jolleha 2c

43. The effects of plan 23 on hurricane tide heights at gages
located downstream from the structures are also shown in table 1, to-
gether with the effects on times of high tide. No tidal data are pre-
sented for gages located upstream from the structures, since that portion
of the bay system was not subject to tidal influence for conditions of
complete closure of the structures. As in the case of plan 22, reliable
measurements of astronomical tide ranges and elevations were made at
only a few locations; these measurements indicate that tide ranges and
elevations at gages located downstream from the barriers for plan 23
were essentially the same as for the base test. The maximum elevations
reached by hurricane tides were increased over those of the base test
at gages located downstream from the barriers, the maximum increases be-
ing just downstream from the West Passage and Hast Passage structures
and in the Sakonnet River. These measurements show that the buildup
downstream from the barriers would be slightly more severe for plan 23
than for plan 22 (maximum of about 2.0 ft for plan 23, compared to about
o/h ate Wore jolla 22).

4h, Prior to the above-described model tests, the Middle Bay
barrier site had been semewedl ly considered to be the optimum location
for barriers in Narragansett Bay for the following reasons: (a) the
Middle Bay site would afford protection to those portions of the bay
system which had experienced the greatest loss of life and property dur-
ing hurricane tides of record; and (b) provisions for navigation through
the structures by large naval vessels would not be involved, since the
major naval bases in the bay are located downstream from the Middle Bay
barriers. Because of the buildup downstream from the structures in-
dicated by the model tests, which amounted to as much as 2.0 ft for tests
involving the 1938 hurricane tide, the Middle Bay barriers were excluded
from further consideration and were not subjected to as detailed testing
as were some of the barrier plans tested subsequently. For example, the
Middle Bay barrier tests reported herein were made prior to and were not
tested with the refined model roughness adjustment described in para-
graph 29 of this report, nor were these barrier plans subjected to hur-
ricane tide tests for conditions of any of the design hurricane tides.
The deficiency in model roughness existing at the time of the Middle Bay
barrier tests probably resulted in slightly higher hurricane tides through-
out the bay system than would have occurred had the roughness been correct
(the addition of roughness lowered the 1938 hurricane tide peak at
Providence by about 0.5 ft). However, since the roughness deficiency
would have affected hurricane tide elevations in the same degree for both
base test and plan test conditions, it was concluded that the buildup
downstream from the model structures indicated by the model tests was of
the proper order of magnitude, and the Middle Bay barrier tests were not

repeated.
Lower Bay Barriers

45. The locations of the various elements of the Lower Bay barrier
plan are shown on fig. 15. The general features of the plan included
closure of the West Passage just downstream from the Jamestown Bridge

(West Lower Bay barrier), closure of East Passage at Bull Point (East

Lower Bay barrier), either complete or partial closure of the Sakonnet
River at Old Stone Bridge, and the diking of low marsh areas on Conanicut
Island. Navigation openings of various depths and widths were considered
for the East Passage, West Passage, and Sakonnet River structures, and
each combination of openings was assigned a test number for identifica-
tion purposes.

46. As in the case of the Middle Bay barriers, initial tests of
the Lower Bay barriers were made for conditions of the extreme astro-
nomical spring tide range of 5.4 ft at Newport to determine an approx-
imate arrangement of navigation openings to satisfy the conflicting re-
quirements of (1) reduction in hurricane tide elevations at Providence,
(2) minimum width of opening specified by the Navy, and (3) reduction
of maximum current velocities to those that can be tolerated by naviga-
tion. Inasmuch as all these criteria were varied over a wide range dur-
ing the course of the model study, this report makes no reference to
the widths and/or velocities that would be acceptable but only presents
data for the various conditions tested in the model. On the basis of
the preliminary tests, a Lower Bay barrier plan (designated plan 29 of
the model study) was devised and subjected to complete testing. It is
pointed out that the refined model roughness adjustment was accomplished
prior to the testing of plan 29 as well as all subsequent plans reported
herein.

47. The locations of the various components of plan 29 were as
described in paragraph 45, and openings for navigation were provided in
the West Passage and East Passage structures as shown on fig. 1/7. The
Sakonnet River closure at Old Stone Bridge also had a navigation opening.
The West Passage opening had a sill elevation of -40 ft mlw and a sill
width of 600 ft; the East Passage opening had a sill elevation of -50 ft
mlw and a sill width of 1000 ft; and the Sakonnet River opening had a
sill elevation of -30 ft mlw and a sill width of 100 ft. The abutment
slopes of the East and West Passage openings were 1.0 vertical on 1.5
horizontal, the slope of the ocean side of the structures was 1.0 vertical
on 2.0 horizontal, and the slope of the bay side was 1.0 vertical on 1.5

horizontal. The Sakonnet River opening had vertical sides and was equipped

| 207 EL4+240

APPROXIMATE BED OF BAY

SECTION A-A

EAST LOWER BAY BARRIER NO SCALE
fa
ri NOTE: ELEVATIONS ARE IN PROTOTYPE FEET.

ELEVATION 0.0 IS MLW NEWPORT WHICH
4 IS 16 FT BELOW MSL 20°
So EL +240

WEST LOWER BAY BARRIER
SCALES IN FEET

SECTION B-B

NO SCALE
HORIZONTAL. '°Q2 ° 1000 2000

VERTICAL 100 io} 100 200

Fig. 17. Details of lower East and West Barriers
for plans 29 and 30
with a gate for complete closure or complete opening. All of the struc-
tures had a crest elevation of +24 ft mlw. The Sakonnet River opening
was closed completely for all astronomical and hurricane tide tests of
plan 29.

48. The astronomical tide test of plan 29 was made for conditions
of the normal spring tide range of 4.1 ft at Newport, and hurricane tide
tests were made for conditions of this astronomical tide in combination
with the 1938 hurricane tide and the 20-knot design hurricane tide.

49. The effects of plan 29 on astronomical tide ranges and eleva-

tions throughout the bay system are shown in table 2, together with the

effects of the plan on maximum elevations of the 1938 hurricane tide and
the 20-knot design hurricane tide. The effect of the plan on times of
high tide are shown in table 3. Astronomical tide ranges were reduced
at all gages upstream from the barriers, the average reduction being of
the order of 25 to 30 per cent, while the times of high water at upstream
gages were delayed by as much as 1.8 hours. The peak of the hurricane
tide at Providence was lowered from +15.1 ft to +7.8 ft mlw for condi-
tions of the 1938 hurricane tide and from +17.2 ft to +9.1 ft for condi-
tions of the 20-knot design hurricane tide. The maximum elevations of
hurricane tides at all other gages upstream from the barriers were ap-
preciably reduced, while the times of high water at these gages were de-
layed by as much as 2.0 hours. No measurements of current velocities
were made in the navigation openings of the East and West Passage struc-
tures during model tests of plan 29.

50. It is emphasized that data contained in this report showing
the effects of barriers on hurricane tide elevations throughout the bay
system apply only to the gravitational component of the hurricane-
generated ocean tide; the effects of local wind setup must be added to
elevations presented herein to arrive at maximum elevations that would
obtain during a hurricane. The reductions in hurricane tide elevations
effected by plan 29 at Providence and other points throughout the upper
bay appear quite large, but it must be remembered that some damage by
hurricane tides begins when the water-surface elevation at Providence
exceeds about +6.6 mlw, and this elevation would be exceeded appreci-
ably by adding the wind component to the model test data presented
nereesitiars

51. The width of the Hast Passage navigation opening for plan 29
was considered at that time to be about the minimum that could be toler-
ated by the Navy. A further reduction in widths or depths of the naviga-
tion openings of the plan, which obviously would have been required to
reduce the absolute elevation of hurricane tides at Providence below that
at which damage begins, was considered untenable at the time. It was
therefore concluded that a Lower Bay barrier plan alone, having ungated

openings for navigation, could not simultaneously meet the requirements

for complete hurricane tide protection at Providence and at the same

time provide a minimum width of ungated opening for navigation that would
meet the requirements of the Navy. It was tentatively concluded, there-
fore, that one of the proposed Upper Bay barrier plans (discussed below)
for the complete protection of Providence, in combination with a Lower
Bay plan for partial or complete protection of the remainder of the bay
system, might provide the most feasible and economical solution of the
over-all problem. Testing of Lower Bay barriers was therefore suspended,
and testing of the Upper Bay barriers was undertaken to determine which
of those proposed would be best for consideration in combination with

a Lower Bay barrier plan.
Upper Bay Barriers

5e. The two Upper Bay barrier sites investigated in the model
were at Field Point and Fox Point (see fig. 15). Provisions for naviga-
tion past the Field Point site would be required, since the Providence
River navigation project extends upstream beyond Field Point, but no pro-
visions for navigation would be required at the Fox Point site. For the
purpose of model tests, it was assumed that proposed barriers at both Field
Point and Fox Point would represent complete closures, since the naviga-
tion passage through the Field Point structure would be designed for com-
plete closure in event of a hurricane. Provisions would also be made at
both barrier sites for pumping upland drainage over the structures, al-
though this feature of the plans was not considered during model tests.
The crest elevation of both structures was +24 ft mlw.

53. The Field Point and Fox Point barriers were designated plans
28 and 27, respectively, of the model study. Tests of plans 28 and 27
were made for the same conditions of astronomical and hurricane tides
as used for plan 29. The effects of these plans on astronomical tide
ranges and elevations, and the effects on hurricane tide heights for
conditions of the 1938 hurricane tide and the 20-knot design hurricane
tide, are shown in table 2. Their effects on times of astronomical and

hurricane high tides throughout the bay system are shown in table 3.

54. The results of the model tests indicated that both the Field
Point and Fox Point barriers would provide complete protection to areas
upstream from the barrier sites, since no overtopping of the structures
by hurricane tides occurred. The effects of these barriers on astronom-
ical and hurricane tide elevations throughout the bay system were
negligible. No significant buildup of hurricane tides downstream from
the barrier sites occurred for conditions of either of the hurricane
tides tested. Elevations observed downstream from the Field Point bar-
TOILSIO (plan 28) were slightly lower for the plan tests than for the base
tests; however, this small reduction in elevation was caused by the
absence of the discharge of the Seekonk River during the tests of this
structure (the discharge was introduced during the base tests, but pro-
visions for pumping the discharge over the structure were not provided
in the plan tests, so the inflow weir on the Seekonk River was cut off
for the plan tests). The Fox Point barrier tests were not affected by
river discharge since this barrier was located upstream from the mouth
of the Seekonk River.

“55. Evaluation of the two upper Bay barriers showed that the Fox
Point barrier would not only afford protection to the critical portions
of Providence in which maximum damage has been caused by hurricane tides
of record but would also be much less costly than the Field Point bar-
rier because of the much greater width of channel and the need for naviga-
tion facilities at this latter site. The Fox Point barrier was therefore

selected for testing in combination with Lower Bay barrier plans.
Combination Barrier Plans
Preliminary combination barrier plans

56. A total of five preliminary combination barrier plans (plans

30 through 34) were proposed for testing in the model to determine the

effects of size of navigation openings in the East and West Passages
On astronomical and hurricane tide elevations throughout the bay system.
All of these plans incorporated the Fox Point barrier in addition to

Lower Bay structures at the locations of those of plan 29, described in

paragraph 45. The locations of the structures of these plans are shown
on fig. 15; the details of the West Passage and East Passage navigation
openings of plan 30 are shown on fig. 17 and those of the other plans
are shown on fig. 18. The navigation opening in the Sakonnet River bar-
rier was similar to that of plan 29 (opening 100 ft wide by 30 ft deep);
however, this opening was completely closed for all tests of plans 30
through 34.

57. In plan 30, the first plan including the Fox Point and Lower
Bay barriers, the Lower Bay barriers and navigation openings were iden-
tical with those of plan 29. The astronomical tide test of plan 30 was
made for conditions of the normal spring tide range of 4.1 ft at Newport,
and hurricane tide tests were made for this tide in combination with the
1938 hurricane tide and the 20-knot design hurricane tide. The effects
of plan 30 on astronomical tide ranges and elevations and on hurricane
tide elevations, and its effects on times of high water for both astro-
nomical and hurricane tides are shown in tables 4 and 3, respectively.
The effects of this plan on both astronomical and hurricane tides
throughout the bay system were almost identical with those of plan 29
described previously. Astronomical tide ranges at gages located up-
stream from the Lower Bay barriers were reduced by an average of about
23 per cent, and hurricane tide elevations at Providence were lowered
from +15.1 ft to +7.9 ft mlw for conditions of the 1938 hurricane tide
and from +17.2 ft to +9.1 ft for conditions of the 20-knot design hur-
ricane tide. No current velocity measurements were made in the naviga-
tion openings of plan 30.

58. The locations of the barriers in the other plans of this series
(31 through 34) were identical with those of plan 30, the only difference
between plans in this series being the arrangement and size of navigation
openings in the East and West Passages (see fig. 18). The combined areas
of the Hast and West Passage navigation openings for this series of plans,
measured at approximately mean-tide level at Newport (+2.0 ft mlw), were
as follows: 104,700 sq ft for plan 33; 94,300 sq ft for plan 32; 73,500
sq ft for plan 31; and 71,060 sq ft for plan 34. The comparable area for
plan 30 was 83,900 sq ft. The model test conditions (astronomical and

WEST LOWER BAY BARRIER EAST LOWER BAY BARRIER
1022/
8/6" ;
EL +240 | aa

|
¢

MLW.

SILL EL-400 SILL EL -50.0

PLAN 31

{~ £
il EL+24.0

S/LL EL-50.0

PLAN 32

MLW.

8/67 (ve | a EL +240
| EL+24.0 i
|

SILL EL -40.0

“e /400° |

PLAN 33

696"

| EL +240
¢

MLW _

SILL EL -400

PLAN 34

496’

| EL+240
¢

S/LL EL -40.0 SILL EL -50.0

PLANS 35 AND 36

NOTE: ELEVATIONS ARE IN PROTYPE FEET. ELEVATION 00 IS
MLW NEWPORT WHICH IS 1.6FT BELOW MSL.

S/LL EL -50.0

Fig. 18. Details of navigation openings, Lower East and West barriers,

plans 31-36

hurricane tides) for these plans were identical with those of plan 30.
The results of tests of these plans are presented in numerical order

in tables 3 and 4; however, in the interest of clarity, the test results
are presented in the following discussion in the order of descending
total area of the navigation openings (plan 335 S25 Bly eiacl 34, in that
order). Plan 32 was not subjected to tests in the model; instead, the
effects of this plan on tidal ranges and elevations were interpolated
from the results of tests of other plans in this series.

59. The effects of the plans on astronomical tide ranges and eleva-
tions, and on hurricane tide elevations, are shown in table 4, and their
effects on times of high tide for both astronomical and hurricane tides
are shown in table 3. All of the plans reduced astronomical tide ranges
at gages located upstream from the Lower Bay barrier, the average re-
duction being of the order of 16 per cent for plan 335) 52 per (centeror
plan 31, and 3/7 per cent for plan 34; the average reduction in range in-
dicated by plan 30 was about 23 per cent. Based on equivalent areas of
navigation opening, it was interpolated that plan 32 would have reduced
astronomical tide ranges upstream from the structure by an average of
about 19 or 20 per cent.

60. Maximum hurricane tide elevations at Providence for conditions
of the 1938 hurricane tide were +8.7 ft mlw for plan 33, +7.2 ft for
plan 31, and +7.1 ft for plan 34. The maximum elevation for plan 30 was
+7.9 ft, and the interpolated elevation for plan 32 at Providence was
about +8.3 ft. For conditions of the 20-knot design hurricane tide, the
maximum elevations at Providence were +10.4 ft mlw for plan 33 and +8.6
ft for plan 31; a test of plan 34 for this condition was not included in
the testing program. The maximum elevation at Providence for plan 30 for
conditions of the 20-knot design hurricane tide was +9.1 ft mlw, and that
interpolated for plan 32 was about +9.7 to +9.8 ft. No current velocity
measurements were made in the navigation openings of the barriers during
tests of this series of plans.

Final combination barrier plans
61. The results of tests of plans 30 through 34 indicated that the

minimum size of navigation openings considered (71,060 sq ft for plan 34)

would not provide the desired reduction in hurricane tide elevations
throughout the upper bay for conditions of the model tests. Two final
combination barrier plans (plans 35 and 36) were proposed for testing
in the model, both of which involved a total area of navigation opening
somewhat less than that of plan 34 (total area of 62,660 sq ft at mean-
tide level for plans 35 and 36 compared to a total area of 71,060 sq ft
for plan 34). The barrier locations for plan 35 were identical with
those of plans 30 through 34, while those for plan 36 were the same ex-
cept that the West Passage barrier was moved about 3.0 miles downstream
from the Jamestown Bridge. The barrier locations for these plans are
shown on fig. 15, and the details of the Hast Passage and West Passage
navigation openings are shown on fig. 18. The Sakonnet River navigation
opening was completely open for all astronomical tide tests of plans 35
and 36 and completely closed for all hurricane tide tests of these plans.
62. Plan 35 was subjected to much more detailed testing in the
model than were any of the previous barrier plans reported herein. As-
tronomical tide tests of this plan were made for conditions of the normal
spring tide used for previous plan tests, and also for conditions of a
mean astronomical tide having a range of 3.6 ft at Newport. Current
velocities were measured at a total of 13 stations through the bay for
conditions of the normal spring tide, and at surface, one-quarter depth,
and one-half depth at three verticals in the East Passage navigation
Opening and at the same depths on the center line of the West Passage
navigation opening for conditions of both spring and mean astronomical
tides. In addition, the maximum head differentials across the Hast Pas-
sage navigation opening were observed in the model during astronomical
tide tests; these maximum head differentials for both spring and mean
tides were then established in the flume containing the undistorted scale
models of the navigation openings, and detailed measurements of current
velocity distribution in the openings were made. Hurricane tide tests of
plan 35 were made for conditions of the normal spring tide combined with
the 1938 hurricane tide and the 20-knot design hurricane tide. The maxi-
mum head differentials across the East and West Passage navigation open-

ings during the hurricane tide tests were also observed in the model, and

were then established in the flume containing the undistorted scale
models of the openings for detailed measurements of current velocity
distribution in the openings for these conditions.

63. The effects of plan 35 on astronomical tide ranges and eleva-
tions for the two conditions tested are shown separately in table 4.

The effects of this plan on hurricane tide elevations are shown in that
part of table 4 which presents astronomical spring tide data, since the
hurricane tide tests were run in combination with that tide. The effects
of the plan on times of high tide for conditions of both astronomical and
hurricane tides are shown in table 3. Spring astronomical tide ranges

at gages located upstream from the Lower Bay barriers were reduced by

an average of about 40 per cent, while mean-tide ranges were reduced by
an average of about 3/ per cent. The maximum elevations of hurricane
tides at Providence were reduced from +15.1 ft mlw to +6.7 ft for condi-
tions of the 1938 hurricane tide and from +17.2 ft to +8.0 ft for condi-
tions of the 20-knot design hurricane tide.

64. The effects of plan 35 on tidal current velocities throughout
the bay are shown in table 5. Base test current velocities in this
table were obtained for conditions of the normal spring tide and no
barriers, while plan test data were obtained for conditions of the same
tide with plan 35 installed in the mode]. The velocity measurements
presented in table 5 indicate that both flood and ebb current velocities
at stations located upstream from the Lower Bay barriers were reduced,
the maximum velocities being reduced by amounts ranging from about 20
per cent to about 60 per cent.

65. Current velocities were measured in the East and West Passage
navigation openings of plan 35 for conditions of both spring and mean
astronomical tides. Measurements were made at the surface, one-quarter
depth, and one-half depth on the center lines of the openings and the
centers of the sills. Two additional verticals, located halfway be-
tween the center lines and the abutments and also on the centers of the
sills were used in the Hast Passage opening. Velocities observed at the
three depths on the center lines of the openings for each hour of a com-

plete tidal cycle are presented in table 6. The additional velocities

observed at verticals on each side of the center line in the East Pas-
sage were essentially equal to those on the center lines and are not
included in this report. Table 6 includes velocity data for the East
and West Passage navigation openings for conditions of both the astro-
nomical tides described above. Maximum flood velocities in the East
Passage opening for spring tide conditions ranged from 8.3 ft per sec

at middepth to 7.4 ft per sec at the surface, while maximum ebb veloc-
ities ranged from 7.6 ft per sec at middepth to 7.3 ft per see at the
surface. For mean-tide conditions, maximum flood velocities ranged from
7.2+ ft per sec at middepth to 6.5 ft per sec at the surface, while maxi-
mum ebb velocities ranged from 7.8 ft per sec at middepth to 7.0 ft per
sec at the surface. In the West Passage for spring tide conditions,
maximum flood velocities ranged from 8.5 ft per sec at middepth to 7.8
ft per sec at the surface, while ebb velocities ranged from 8.3 ft

per sec at middepth to 7.0 ft per sec at the surface; for mean-tide con-
ditions, maximum flood velocities ranged from 8.0 ft per sec at middepth
HO oll WB Gere XO Eke was surface, while ebb velocities ranged from 9.0 ft
per sec at middepth to 7.5 ft per sec at the surface. An attempt was
made to determine the maximum velocity in the Sakonnet River navigation
openings for conditions of mean astronomical tide. Accurate velocity
measurements in that opening were very difficult to obtain because of
the small width of the opening in the model, but the results of measure-
ments made therein indicated the maximum velocity to be of the order of
QO £t per sec.

66. Maximum head differentials observed across the East Passage
structure for tests with astronomical tides were 1.8 ft for spring tide
and 1.3 ft for mean tide. These head differentials were established in
the flume containing the undistorted-scale models of the navigation
openings, and detailed measurements of velocity distributions for both
conditions were made. The lower portion of fig. 19 shows the results of
velocity observations made on the center line of the navigation opening,
from the upstream edge of the sill to the downstream edge and just above
the sill, for conditions of the maximum spring tide head differential

of 1.8 ft. These observations indicate that the point of maximum velocity

+24.0FT

11.8 18

6 Wd 12.3
/ Wd M8
(7)

11.8 Wg
/08 10.7 10.7 10.2 10.8 10,4 10.2 10.7 4h. i

425 FT- = 4925 FT- a
SECTION A-A

VELOCITY OBSERVATIONS AT
1IO-FT INTERVALS, SURFACE TO BOTTOM

424.0 FT ®

TEST CONDITIONS

UPPER POOL EL +18 FT AGTH EB FL GLE
: q UPPER POOL ELEVATION 18 FT

LOWER POOL ELEVATION 0.0 FT

NOTE: VELOCTIES ARE EXPRESSED IN PROTOTYPE
FT PER SEC. ELEVATIONS ARE IN PROTOTYPE
FEET, ELEVATION 0.0 1S MLW NEWPORT WHICH
IS 1.6 FT BELOW MSL.

‘

APPROXIMATE BOTTOM OF BAY EL —/65 FT SCALES

ib Pa f-

BOTTOM VELOCITIES, CENTER LINE pga A Or en eer a

Fig. 19. Velocities in East Passage navigation opening
of plan 35 for maximum head differential, astronomical
spring tide with 4.1-ft range at Newport

just above the sill (10: £6 per sec) was about 60 ft downstream from
the center of the sill; therefore, detailed measurements were made to
determine the distribution of velocities over this entire cross section.
The results of these latter measurements are presented in the upper por-
tion of fig. 19. Velocities were measured at 10-ft increments of depth
from the surface to the sill at 100-ft increments of width across the
navigation opening. These measurements indicate that velocities in the
cross section ranged from a minimum of about 2.6 ft per sec to a maximum
of about 12.9 ft per sec, the point of maximum velocity being at a depth
of about 20 ft below the surface. Similar data for conditions of the
maximum mean-tide head differential of 1.3 ft are presented on fig. 20.
These data show that velocities in the opening ranged from a minimum of
about 2.3 ft per sec to a maximum of about 11.0 ft per sec, the point of

maximum velocity being also at a depth of about 20 ft below the surface.

+24.0FT

8.7 /SILL EL -50.0FT
|

—

SECTION A-A
VELOCITY OBSERVATIONS AT
1O-FT INTERVALS, SURFACE TO BOTTOM

424.0 FT @ 3

UPPER POOL EL #/.3 FT

TEST CONDITIONS

UPPER POOL ELEVATION a(S} Lea
LOWER POOL ELEVATION 0.0 FT

Te 175, ap

75 83|88
2 \72\74 | 60 | 80 | 63 | 90 \S/ILL EL -50.0FT

NOTE; VELOCTIES ARE EXPRESSED IN PROTOTYPE
FT PER SEC. ELEVATIONS ARE IN PROTOTYPE
FEET. ELEVATION 0.0 IS MLW NEWPORT WHICH
{S 1.6 FT BELOW MSL.

SCALES

"\ APPROXIMATE BOTTOM OF BAY EL ~/65 FT
So 100 150 200 250 FT

4h- Le = f- 50 )
HORIZONTAL =e SS ————s

BOTTOM VELOCITIES, CENTER LINE SONI GRIN Ir a0 MINeo MNT eo RENNoor

VERTICAL = a a

Fig. 20. Velocities in Hast Passage navigation opening of plan 35
for maximum head differential, astronomical mean tide with 3.6 ft
range at Newport

67. Maximum hurricane tide head differentials across the Lower
Bay structures of plan 35 occurred for conditions of the 20-knot design
hurricane tide and amounted to 9.6 ft in the Fast Passage and 10.2 ft
in the West Passage. These head differentials were established in the
flume containing the undistorted scale models of both navigation open-
ings, and detailed velocity measurements were made as,described previ-
ously for maximum astronomical tide head differentials. Velocity data
for the East Passage navigation opening are presented on fig. 21, and
those for the West Passage opening are presented on fig. 22. Veloc-
ities in the East Passage opening ranged from a minimum of about O.O ft
per sec near the abutments to a maximum of about 30.9 ft per sec, while
those in the West Passage opening ranged from a minimum of about 24.0 ft
per sec to a maximum of about 26.5 ft per sec. It was not possible to ob-

tain accurate velocity measurements near the abutments of the openings

+24.0FT

238 245 266 272 278 315 325 24.5 /SILL EL -S0.O0FT

a 425 FT- (=
SECTION A-A
VELOCITY OBSERVATIONS AT
IO-FT INTERVALS, SURFACE TO BOTTOM

TEST CONDITIONS

UPPER POOL ELEVATION 9.6 FT
LOWER POOL ELEVATION 0.0 FT

NOTE: VELOCTIES ARE EXPRESSED IN PROTOTYPE
FT PER SEC. ELEVATIONS ARE IN PROTOTYPE
FEET. ELEVATION 00 IS MLW NEWPORT WHICH
1S 16 FT BELOW MSL.

APPROXIMATE BOTTOM OF BAY EL —/65 FT

f- 4o~ SCALES
‘i HORIZONTAL “teams —— "Sr $ "Sig 25 FT
BOTTOM ee CENTER EINE VERTICAL 2 20 40 60 BO 1OORG

Fig. 21. Velocities in Hast Passage navigation opening of
plan 35 for maximum hurricane tide head differential, 20-
knot design hurricane

424.0 FT| 424.0 FT
€
UPPER POOL EL 410.2 FT | |
a €
j LOWER POOL EL OOFT Shey PEO ap _/_ MLW.
| 5 25.5 260 255
1 |
| 26.0 25.5 255
|
52 173 (2! 25 238 25.5, ND acted aX
a 14.2\ /52\| /82\| 200 | 222| 245|255 SILL EL -400 245_255 265 255 25.5 240 245 245 255 SILL EL ~400
- oS aie (229.9 265 239 299 240 265 265 239 vie cone
= fs 1/40 FT- +} +140 FT-
2

v z
(q_ APPROX BOTTOM OF BAY -70 FT, oO SECTION A-A
we rf

‘ms VELOCITY OBSERVATIONS AT
IO-FT INTERVALS. SURFACE TO BOTTOM

BOTTOM VELOCITIES, CENTER LINE

TEST CONDITIONS

UPPER POOL ELEVATION 10.2 FT NOTE: VELOCITIES ARE EXPRESSED IN SCALES
PROTOTYPE FT PER SEC. ELEVATIONS 50 ° 50 100 1so 200 250FT
LOWER POOL ELEVATION 00 FT BEN CAC SIE SC EEUNATIGN HORIZONTAL “jammer is
0.0 IS MLW NEWPORT WHICH IS VERTICAL “im : = = = ——

1.6 FT BELOW MSL

Fig. 22. Velocities in West Passage navigation opening of
plan 35 for maximum hurricane tide head differential, 20-
knot design hurricane

because of extreme turbulence in those areas.

68. Plan 36 was identical with plan 35 except that the West Passage
- barrier was moved downstream about 3.0 miles from the Jamestown Bridge
(see fe I5))3 WAS SELES Cre navigation openings for plan 36 were identical
with those of plan 35 (see fig. 18). Astronomical tide tests were made of
plan 36 for conditions of both spring- and mean-tide ranges, and hurricane
tide tests were made for conditions of the astronomical spring tide in
combination with the 1938 hurricane tide and the 20-knot design hurricane
tide. Current velocities were measured in the East and West Passage navi-
gation openings in the model for conditions of both spring tide and mean
tide; however, velocities were not measured at stations throughout the bay
for this plan, nor were supplementary velocity measurements made in the
flume. Inasmuch as plan 36 was so similar to plan 35, it was considered
that the detailed velocity measurements made for the latter plan would
be adequate to show the effects of plan 36.

69. The effects of plan 36 on astronomical tide ranges and eleva-
tions for conditions of both spring and mean tides are shown separately
in table 4; the effects on elevations of hurricane tides are shown in
that portion of table 4 presenting astronomical spring tide data, since
the hurricane tide tests were made in combination with that tide. The
effects of plan 36 on the times of both astronomical and hurricane high
tides are shown in table 3. Astronomical tide ranges at gages upstream
from the Lower Bay barriers were reduced by an average of about 42 per
cent for conditions of spring tide and by an average of about 0 per cent
for conditions of mean tide. These average reductions in astronomical
tide ranges upstream from the Lower Bay barriers are slightly greater
than occurred for plan 35 and are believed attributable to the slight
increase in surface area upstream from the barrier resulting from reloca-
tion of the West Passage barrier. |

7O. Plan 36 reduced hurricane tide elevations at Providence from
+15.1 ft mlw Newport to +6.0 ft for conditions of the 1938 hurricane tide
and from +17.2 ft to +7.1 ft for conditions of the 2O-knot design hurricane
tide. Hurricane tide elevations at Providence were slightly lower for

plan 36 than for plan 35, and this effect is also believed attributable

to the increase in surface area upstream from the Lower Bay barriers.
71. Current velocities in the East and West Passage navigation
openings of plan 36 for conditions of spring and mean tides were equal
to or slightly greater than those of plan 35. Maximum flood and ebb
currents on all verticals and at all depths were generally 0.1 to 0.3
ft per sec greater than for plan 35 because of the increase in tidal
prism upstream from the barriers. The slightly greater reduction in as-
tronomical tide ranges for plan 36 caused a minor increase in maximum as-
tronomical tide head differentials across the East and West Passage bar-
riers, which resulted in the minor increases in current velocities in
the navigation openings for this plan over those of plan 35. Detailed
current velocity data for plan 36 are not presented herein because of

their similarity to plan 35 data.

ae)
PART V: CONCLUSIONS
Effects of Barriers on Tides

(2. Model test data presented herein are considered to be quan-
titative with respect to the effects of barriers on astronomical tide
ranges, elevations, and times, and also with respect to the effects of
barriers on the gravitational component of hurricane tides. To obtain
information on the absolute elevations that would be attained by hurri-
cane tides at various locations throughout the bay for conditions of the
barrier plans tested in the model, the effects of the local winds of the
hurricane in question must be applied to the model test data. As pointed
out above, all local wind-setup effects have been excluded from the model
tests on the basis of computations of this phenomenon by the New England
Division. Therefore, conclusions as to the absolute extent of the pro-
tection afforded by the barrier arrangements investigated will require
consideration of local wind-setup effects which are beyond the scope of

this report.
Effects of Barrier Locations on Buildup

73. The model tests indicated that barriers located in the central
region of the bay (Middle Bay barrier plans) would cause an appreciable
buildup in hurricane tide elevations downstream from the barriers. The
tests showed that no appreciable buildup would occur downstream from
barriers located near the upper extremity of the bay (Fields Point and
Fox Point barriers) nor downstream from those located near the bay en-
trances (Lower Bay barrier plans). The effects of barrier location on
buildup are illustrated on fig. 23, which shows the buildup in feet over
maximum base test elevations that occurred immediately downstream from
each of the proposed barriers for conditions of the 1938 hurricane tide
(the negative buildup shown at the Field Point barriers was caused by
cutting off the upland discharge, as explained in paragraph 5/1).

74. The degree of gravitational buildup or attenuation of an

NOTE: BUILD-UP IS THE INCREASE IN WATER-SURFACE ELEVATION IN FEET
IMMEDIATELY DOWNSTREAM FROM THE BARRIER RESULTING FROM
INSTALLATION OF THE BARRIER.

BUILD-UP IN FEET

EDGEWOOD
WARWICK POINT,
WEYERHAEUSER
JAMESTOWN
CASTLE HILL

Fig. 23. Effect of barrier location on buildup for conditions
of 1938 hurricane tide

astronomical or hurricane-generated tidal wave as it passes through a
bay or estuary is affected by the depths, widths, shapes, and other
physical characteristics of the system of channels involved. The extent
of buildup of hurricane tides in Narragansett Bay for existing condi-
tions may be illustrated by the fact that the gravitational component
of the 1938 hurricane tide reached a maximum elevation at Providence
(head of the bay) some 3.1 to 3.3 ft higher than at Newport which is
near the bay entrance. This same phenomenon occurs for conditions of
astronomical tides, since the mean elevation of high tide at Providence
is about 0.5 ft higher than at Newport.

(5. ‘Construction of a barrier in the bay results an) the Vossvor
all or part of the storage (tidal prism) upstream from the barrier site,
and the effects of this reduction in storage are reflected by increased
elevations downstream from the barrier over those that would obtain with-
out the structure. The reduction in storage effected by the Upper Bay
barriers was so small in relation to the total volumes of hurricane tides

in the entire bay that no measurable buildup occurred downstream from

pull

these structures. In the case of the Middle Bay barriers, however, the
reduction in storage upstream from the structures represented a large
percentage of the total bay tidal prism occupied by the hurricane tides
tested, and elimination of this storage area resulted in an appreciable
buildup downstream from the structures. In the case of Lower Bay bar-
riers, elimination of the entire storage area of Narragansett Bay would
have only an infinitesimal effect on tides generated by hurricanes in
the open ocean; therefore, no significant buildup occurred on the seaward
side of the Lower Bay structures. Such minor buildup as was indicated
by model tests seaward of the Lower Bay barriers is thought to be at-
tributable to elimination of local drawdown effects caused by high

velocities into the mouth of the bay under existing conditions.

Effects of Barriers on Tidal Currents

76. The effects of the barriers on tidal currents throughout that
portion of the bay system upstream from the barrier site would be in al-
most direct proportion to the effects of the barrier on astronomical
tide ranges; a reduction in tidal range of 30 to 40 per cent would be
accompanied by similar reductions in tidal current velocities. In areas
downstream from the barrier site, the mean velocities of tidal currents
would be reduced by a factor representing the total reduction in tidal
prism upstream from the area in question. The directions of tidal cur-
Kents would be altered appreciabily in the vicinity of barriers, sance
restriction of an existing wide channel to a single ungated navigation
opening would result in funneling the entire flow through the ungated
opening. The use of auxiliary sluice gates, similar to those considered
in connection with the Middle Bay barrier plans, would probably prevent
undesirable changes in current patterns. Current velocities in the um-
gated navigation openings of the plans investigated are affected by the
design of the opening and the head differential across the structure.
Reductions in total area of navigation openings to effect greater pro-
tection to upstream areas from hurricane tides increased head differ-

entials across the structures and therefore increased current velocities

in the navigation openings. Undesirable current velocities in ungated
navigation openings might also be prevented by use of auxiliary sluice
gates as mentioned above.

77. It will be noted that current velocities measured in the navi-
gation openings in the model are appreciably less than those measured in
the flume containing the undistorted models of the navigation openings
for comparable conditions of head differential. The major difference be-
tween velocities for the two conditions is attributable to location of
the points of measurement; the verticals observed in the model were
located on the center of the sills, while the cross sections observed in
the flume were located in the most contracted portion of the jet. Meas-
urements made at identical points in the model and flume for comparable
head differentials indicate that use of steady state flows in the flume
resulted in velocities about five per cent higher than occurred in the
model under tidal flow conditions, for the reason that velocities ap-
parently do not quite attain steady state values under tidal conditions.
Velocity data presented on figs. 19 through 22 are therefore considered
to be of the order of five per cent higher than can be expected in nature

under tidal conditions.

Table 1

Effects of Middle Bay Barriers on Maximum 1938

Hurricane-tide Heights and Times

Base Test

Location Elevation

Plan 22
Narragansett Pier M2} odl
Marine Laboratory W253}
Portsmouth 14.9
Newport W2 oak
Quonset Point M3352
Warwick Point N30 7
Bristol Ferry 13. oh
Somerset 14.6
Edgewood 15) ol
Providence 1553
Nyatt Point 14.2
Sakonnet Point 1262
South Middle West Barrier 14.0
South Middle East Barrier 365

Plan 23
Narragansett Pier NW2o ib
Marine Laboratory Io 3}
Jamestown 12.1
Portsmouth 14.9
Quonset Point 302
Davisville Depot Iso %/
Newport 2d
Sakonnet Point 2 52
South Middle West Barrier 14.0
South Middle Hast Barrier 305
Prudence L307

Note: Elevations are in prototype feet.
which is 1.6 ft below msl. Times of high tide are expressed in terms
of prototype hours after the moon's transit of meridian 71°20'.

Time

733
745

Plan
Hlevation

12.5
12.6
16.3
1353
14.6
Ibe 7
4.6
523
Soll
552
5.0
127
AGS aL
14.3

12H
13.2
Meal
15.9
5c
15.4
13.6
1255
I5)h
1s oth
15353)

Time

fo3}
(oS
eo
7.45
745
8.9
So
Q.1
9.05
Opal
9.0
7-3
15
ae)

ios)
(23D
Wolk
ae
7.45
fod
745
7-3
7+)
oS
Fok

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20-knot
Design

Hurricane

Plan
193
Hurricane
Tide

Normal

20-knot
Design

Hurricane

Table 3
Effect of Lower Bay Barriers on Times of High Water

193
Hurricane
Tide

Base Tests

Normal

Location

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Plan 29

South Middle West Barrier

South Middle East Barrier
Nyatt Point

Bullock Point

Rocky Point
Edgewood

MOAN+ NI CALLS AON Era EC NORE

ft OV OV ON OFV OVNE-O & ANALA

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Plan 30

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(Continued)

Table 3 (Continued)

Base Tests Plan

1938 20-knot 1938 20-knot
Hurricane Design Hurricane Design
Location Normal Tide Hurricane Normal Tide Hurricane
Plan 33
Jamestown 77 75 74 73 7-3 73
Quonset Point Tall 7.6 oS 8.8 8.3 8.6
Providence Ticks) ToS) 7.8 9.4 8.8 9.1
Fort Wetherill 7.6 Tot 7.2 7.8 Was} eS
Newport att Toll oss 8.7 8.2 8.5
South Middle East Barrier Toll Tot Hot 8.9 8.5 8.8
Somerset 7.8 8.2 8.0 94 8.9 9.2
Plan 34
Jamestown ont Tod --- 9.2 73 el
Quonset Point atl Tad i 94 9.0 ---
Providence fol) 39) --- 9.9 9.5 ---
Fort Wetherill 76 7.4 --- iailt 703) ---
Newport Tot 74 --- 9.1 8.8 ---
South Middle East Barrier {orl Tot --- 9.5 9.1 ---
Somerset 7.8 8.2 ==- 9.9 9.6 ---
Plan 35

Narragansett Pier
Marine Laboratory
Jamestown

Quonset Point
Davisville Depot
Cedar Tree Point
Warwick Point
Rocky Point
Edgewood
Providence

Fort Wetherill
Newport

M-15

South Middle East Barrier
Prudence

South Middle West Barrier
Bristol Harbor
Nyatt Point
Bullock Point
Sakonnet Point
Portsmouth
Bristol Ferry
Kickamuit River
North Tiverton
Brayton Point

°
.
.
e

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ies
os
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MW ONADAGHDFUGVUWE FDNY OWN DEW FY HWWP

Somerset . . 10. 10.
Ocean Control . . . °
Plan 36

Marine Laboratory Tiel Hoult Ties 9.5 9.0 9.3
Jamestown Ute Tod T4 9.6 91 94
Warwick Point Tess Ton od 9.7 9.3 9.6
Providence Tas 7-9 Te IO eal: 9.7 10.0
Fort Wetherill 7.6 Toll! (2 7.8 Tos ToS
South Middle East Barrier ar ieeulh Hol 9.7 9.4 9.6
Somerset 7.8 8.2 8.0 aO)SaL 9.8 10.0

Note: Times of high tide are expressed in terms of prototype hours after the moon's
transit of meridian 71921'. A spring astronomical tide having a 4.1-ft range at
Newport was used for all tests.

High

Water

lan

(Hurricane Tide ) (Hurricane Tide)
Base Test (Normal Tide) Plan (Normal Tide ) 193) 20-knot 193 20-knot

High

Water

High

Water

Base Test

High

Water

Tidal

Range

Low

Water

High

Water

Table 4
Plan 3C

Tidal

Range

Low

Water

Effects of Lower Bay-Fox Point Barriers on Tidal Heights

High

Water

Location

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Plan 33
Plan 35

South Middle East Barrier

South Middle East Barrier
Somerset

Fort Wetherill
Somerset

Newport
Fort Wetherill

Newport

Fort Wetherill

Quonset Point
Newport

Providence
Quonset Point

Jamestown
Jamestown
Providence
Jamestown
Quonset Point
Providence

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South Middle West Barrier

South Middle East Barrier
Bristol Harbor

Warren River

Nyatt Point

Marine Laboratory*
Prudence

Jamestown
Cedar Tree Point

Narragansett Pier
Davisville Depot
Warwick Point*
Rocky Point

Fort Wetherill*

Newport*

M-15
Ocean Control*

Quonset Point*
Edgewood*
Providence
Bullock Point
Sakonnet Point
Portsmouth
Bristol Ferry
Kickamuit River
North Tiverton
Brayton Point
Somerset
Weyerhaeuser*
Fall River*

(Continued)

Table 4 (Continued)

Base Test Plan
Hurricane Tide (Hurricane Tide)
Base Test (Normal Tide) Plan (Normal Tide) 1938 20-knot 193 20-knot
High Low Tidal High Low Tidal High High High High
Location Water Water Range Water Water Range Water Water Water Water
Plan 36
Marine Laboratory* 3.9 -0.3 4.2 3.2 0.8 2.4 12.1 14.0 5.3 6.6
Jamestown 3.9 -0.2 AL 3.2 0.8 2.4 11.9 14.3 5.5 6.8
Warwick Point* a) -0.5 4.7 3.2 0.6 2.6 13.5 15.3 5.8 6.6
Providence yk -0.7 5.1 3.2 o.4 2.8 15.1 17.2 6.0 Wels
Fort Wetherill* 4.0 -0.1 41 3.8 -0.2 4.0 ines 13.7 12.2 13.5
South Middle East Barrier 4.3 -0.3 4.6 3.3 0.7 2.6 13.0 15.3 6.0 Tloik
Somerset 4.7 -0.4 5.1 3.5 0.7 2.8 14.2 16.2 6.2 es
Plan 35 (Mean Astronomical Tide, 3.6-ft Range at Newport
Marine Laboratory* Sil 0.1 3.6 3.5 0.1 3.4 ---- ---- ---- ====
Jamestown* 3-7 0.1 3.6 3.5 0.0 3.5 =o=> sd
Quonset Point* 3.6 -0.2 3.8 2.8 0.4 2.4 <<-= ===
Warwick Point* 3.8 -0.3 aa 3.0 o.4 2.6 ---- ----
Edgewood* 3.8 -0.5 4.3 3.0 0.2 2.8 ---- ----
Fort Wetherill* 3.6 0.1 5165 Ben -0.1 3.6 ---- ----
Newport* 3-7 0.1 3.6 2.9 0.6 2.3 ---- ----
North Lower West Barrier* 3.8 0.1 Siarlh 2.9 0.6 2.3 ---- ----
North Lower East Barrier* 3.6 0.0 3.6 2.8 0.6 2.2 ---- ----
Weyerhaeuser* 3.9 -0.2 a 3.0 0.5 2.5 ---- ----
Fall River* 3.9 -0.5 Ky 3.2 0.3 2.9 ---- ----
Ocean Control 3.6 0.1 3.5 3.6 0.1 305) ---- ---- ---- ----
Plan 36 (Mean Astronomical Tide, 3.6-ft Range at Newport
South Lower West Barrier* Bail o.1 3.6 3.2 -0.2 3-4 ---- ----
North Lower West Barrier* 3.8 0.1 Bail 2.8 0.6 2.2 ---- ----
Marine Laboratory* 3-7 0.1 3.6 2.9 0.7 2.2 ---- ----
Quonset Point* 3.6 -0.2 3.8 2.9 0.6 2.3 ---- ----
Warwick Point* 3.8 -0.3 41 3.0 0.6 2.4 ---- ----
Edgewood* 3.8 -0.5 4.3 Beal 0.5 2.6 ---- ----
Fort Wetherill* 3.6 0.1 3.5 3.3 -0.1 3.4 ---- ----
North Lower East Barrier* 3.6 0.0 3.6 2.8 0.7 2.1 ---- ----
Newport* Sill 0.1 3.6 2.9 0.8 2.1 ---- ----
Weyerhaeuser* 3.9 -0.2 4d 3.0 0.5 25 ---- ----
Fall River* 3.9 -0.5 hy 3.2 0.6 2.6 ---- ----
Ocean Control* 3.6 0.1 Sia5) 3-6 0.1 365 ---- ---- ---- -<--

Note: A spring astronomical tide having a 4.1-ft range at Newport was used for all tests. Additional tests of plans 35 and
36 were made using a mean tide having a 3.6-ft range at Newport. Elevations are in prototype feet. Elevation 0.0 is
mlw Newport which is 1.6 ft below msl. ,
* Base test and plan astronomical tide heights for plans 35 and 36 at locations indicated were observed on permanent-
type point gages and are accurate to less than 0.1 ft prototype. All other tide heights were obtained from recording-
type tide gages and are subject to errors of +0.2 ft prototype.

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Table 6

Plan 35

Prototype )

Current Velocities on Center Line of Navigation Openings

of West Barrier

Navigation Opening

Spring Tide

of East Barrier

Navigation Opening

of West Barrier
Navigation Opening

Mean Tide

of East Barrier
Navigation Opening

Depth Middepth

Depth Middepth Surface

Hour Surface

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Times are expressed in terms of prototype hours after the

Minus signs indicate ebbing velocities.
moon's transit of meridian 71°21'.

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