hydraulics and stability of tidal inletstidal tidal tidal inlets 20. abstract (continue on reverse...

75
i ' , 1 Hydraulics and Stability of Tidal Inlets by Fro ncis F. Esco ffier GITI REPORT 13 August 1977 Prepared for U.S. Army Coastal Engineering Research Center under Contract DACW72-74-C-0005 GENERAL INVESTIGATION OF TIDAL INLETS A Program of Research Conducted Jointly by U.S. Army Coastal Engineering Research Center, Fort Belvoir, Virginia U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi Department of the Army Corps of Engineers APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

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Page 1: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

i ' ,

1 • •

Hydraulics and Stability of Tidal Inlets

by

Fro ncis F. Esco ffier

GITI REPORT 13

R_~_D ~

August 1977

Prepared for

U.S. Army Coastal Engineering Research Center

under

Contract DACW72-74-C-0005

GENERAL INVESTIGATION OF TIDAL INLETS

A Program of Research Conducted Jointly by

U.S. Army Coastal Engineering Research Center, Fort Belvoir, Virginia U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi

Department of the Army Corps of Engineers

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

Page 2: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

or republieation of any eredit to U.S.

this publieation available

distribution

National ATTN:

authorized

Drum

United

are not to

the lJ .S.

single Additional

Service

Page 3: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

CATALOG NUM8ER

4. TITLE (limd Subtitle) 5. TYPE OF REPORT II PERIOD COVERED

llYDR}\ULICS AND STABT LITY OF TIDAL INLETS inal

6. PERFORMING ORG. REPORT NUMBER

7. AU THOR(o) S. CONTRACT OR GRANT NUM8ER(8)

Franc F. Escoffier DACW72-74-C-0005

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. TASK

11.

earch Center Belvoir, Vi

F 31019

12. REPORT DATE

2 14. MONITORING AGENCY NAME Ii ADORESS(if different from Controlling Office) 15. SECURITY CLASS. (0/ this report)

UNCLASSIFIED

IS,.. DOWNGRADING

16. DISTRIBUTION STATEMENT (of this Report)

for lie release, distribution unlimited.

17, DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report)

18, SUPPLEMENTARY NOTES

19. KEY WORDS (Continue on reverse side if necessary and identIfy by block number)

Functional des Inlet

Tidal Tidal Tidal inlets

20. ABSTRACT (Continue on reverse side if neC'$994it'y and

This report presents a summary 0 basic develop-ments to is of the and related stability of tidal inlets. ar, it covers the work Brown ( and Keulegan un inlet ic calculat • and O'Brien (1931, 1966), Jarrett (19 Bruun ( , Johnson (1973), O'Brien and Dean (19 ,and Es coffier ( on the of inlet channel stabU The original inlet tabi concept Escoffier is extended in Ii of recent

DD EotTlON OF I NOV 65 IS OBSOLETE UNCLASSIFIED

Page 4: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

UNCLASS TF TEO

work. The report also contains brief discussions on tidal inlet characteristics and functional design requirements as well as case studies of selected inlets on the U.S. coasts.

2 UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS

Page 5: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

FOREWORD

This results from work done under Contract No. DACW72-74-C-0005 between the author and the Coastal Research Center (CERC). It is one of a series of from the of General Invest ion of elidal Inlets (GITI) > which is under the tech-nical surveillance of CERC and is conducted CERC, the U.S.

Station ) other Government

The retired, coastal

Escoffier ic as a consultant in

firms and the of

Dr. R.r1. Sorensen, Chief, Coastal Structures Branch, was the con-tract monitor for the , under the s ion of R.P.

, Chief, Research Division.

Technical Directors of CERC and WES were T. Saville, Jr. and F.R. Brown, lye

Comments on this publication are invited.

lication in accordance with Public Law 166th, 79th 31 1945, as supplemented Public Law 172,

7 November 1963.

Colonel, of Commander and Director Commander and Director Waterways Station Coastal Research Center

:3

Page 6: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

PREFACE

1. The of its Ci vii Works program sponsored, over the pas years, researcn into the behavior ar-acteristics of tidal inlets. The ' interest in ti let research stems its responsib es for navi on, beach erosion and control, and d Tasked wi the creation and of Ie U. S. w mil ions of

of material each year from tidal inlets that conne the ocean with bays, estuaries, and lagoons. Design and construction

exis tidal inlets are an ffices. In some red. Devel

c ris cs of inlets is tion and inlet stabili

s of storm surges role in the of

but 0 because and egress of flood bays and lagoons.

2. A research (GITl) was deve

the General Inves of Tidal Inlets tative data for ~se in design

of inlets and inlet i ectives:

It is des to meet the fol

the effects of wave action tidal inlet s tabili and

characteristics necessary to design e

new inlets, and and inlets; to evaluate il of tidal inlets; and

inlet tabili

The GITl is divided classification, ) inl

fication s ics

exist among c

s inlet

mental factors that control these characteristics. keeps the related

an in in characteristics of inlets.

b. The object are to define tide- flow

tions in the vicinity of coastal inlets and to cleve these TIle inlet ics s is

( let

three areas: (1) idealized inlet model s evaluation of state-of-the-art physical and numerical models. and ( inlet hydrauli cs.

4

Page 7: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

"

The Idealized Inlet Mode 1 the effect

tructures on discharge, head loss and ve b of realistic inlet tide

ests zoidal inlet was conducted order that subs inlet models

number of

on on

( Eval The ectives f this mine the usefulness and model in

ay sys ems, determine whether economical are us in the

Inlet would be used along

exi techniques.

to deter-

and b c data was co at Masonboro Inlet f ical mode w initiated in 1969

have been sin then. In additi three exis numerical models were applied to ct the inlet I cs • Extensive field data were collected Inlet in 74 for e evaluat-

the c cal numerical models.

of relationsh

on thes

c. In s s to invest

wave action tion, channe into four bed mode and

and ne spe

The basic the interactions

at tidal lets as

( studies o

materials is of

tides, draul mor-

( Model Materials Evaluation. This evaluation was initi-ated in 1969 to de data on the response of movable-bed mode mate-rials to waves and flow to allow se on of the b materials for inlet models.

Movab le- Bed study is to evaluate the state-of-the-art of , in this case movable-bed inlet model Since, in many cases movable-bed mode is the on tool available for the response of an inlet to , the i li ties and limi tations of these mode Is must be established.

5

Page 8: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

( a report entitled, of an Uncontrol Inlet Beach Erosion Board b to aid

Pro of inlets are and a al on

are studies to define the the respons f inlet navi

Field and office studies 0

the e

of natural sand channels to

ance at inlets. natural , and the effects of inlets on acent beaches.

is

4 is published in the GITI report series becaus it presents summary plus additional insi on some of the more tant works on tidal inlet and tabili It utes to the inlet parts (3b. of the GITL

6

Page 9: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

CONTENTS

CONVERSION FACTORS. U.S. CUSTOMARY TO METRIC

SYMBOLS AND DEFINITIONS

I INTRODUCTION. .

II CHARACTERISTICS OF NATURAL INLETS

III INLET HYDRAULICS.

IV INLET STABILITY • •

V FUNCTIONAL DESIGN REQUIREMENTS.

VI CASE STUDIES ......... . 1. Masonboro Inlet, North Carolina 2. Rollover Fish Pass, Texas .. 3. Mission Inlet, California

LITERATURE CITED. . .

APPENDIX SUGGESTIONS FOR INLET DESIGN.

TABLES

) 9

10

15

15

19

41

53

S5 57 S9 63

66

71

1 Values of ~ and ........... 20

2 Resistance coefficient as on bed form for flume • .• 23

3 Coefficient C in tidal prism formula and ratio bay to ocean tidal range. · . . 31

4 Value of band N for the O'Brien 31, 1966) equilibrium formula t, 1976) .... · .. 42

S Tidal amp1i phase lags. and maximum head di at Gal ves ton Bay, Texas . . . . . . . . . . . . . . . 62

FIGURES 1 barrier beach tidal inlet. 17

2 Offset classification of an inlet. 18

3 of quadratic and linear formulas. 26

4 Surface level fluctuations of sea and basin. 30

7

Page 10: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

FI -Continued

5 Sin T C versus the coeffi of etion ....

6 from Brown (192 and Keu1egan ( versus the coefficient of repletion .

7 \! from Brown 6 versus the coe

8 Ph as from Brown coefficient of

9 Schematic inlet and narrow uniform

10 Tidal m-inlet area

and (196 versus the

b wi th

11 des of inte limi ts and and

1

13

and \! versus

and various values of \!

coeffic ent K"

coefficien , K

versus repletion

14 Definition for the stability number, A.

15 Nons channels, southern California

16 Masonboro Inlet, North Carolina ...

17 Area map show location of Rollover Fish Pass, Texas.

18 Rollover Fish Pass, Texas, 1970.

19 Mission Inlet, Cali fornia

8

36

43

46

48

48

o

56

8

o

61

64

Page 11: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

cubic

acres

ounces

ton,

! To obtain Celsius

To obtain Kelvin

U. S. CUSTOMARY METRIC

measurement m

0.0283

1 x

0.1

from Fahrenheit

usc formula: K

9

meters

meters

cubic meters

meters

meters

meters

newton meters

metric tons

metric tons

+ 5.

Page 12: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

a'

SYMBOLS AND DEFINITIONS

area of bay

initial value of in an inlet

amplitude tide in bay

cross-sectional area in gorge of inlet low mean sea level)

a cross-sectional area in sub reach of inlet

ao amplitude of tide at sea

, aE

B I, B"

b

C

C1

D

f

g

j

K

K'

limits of

coefficients in

in 47

8

coefficient in the O'Brien librium formula

coefficient in the Keulegan method

coefficient in the 0' en stabi formula

water in bay

wave energy in

ach friction

per foot of beach per second

cient

acceleration of

head due to acceleration in hypothetical ar bay

head due to bottom friction in cal ar bay

elevation of water surface in bay

elevation of water surface in sea

subsc identi a sub reach in an inlet

in ion 61

, s 1etion coefficient

tial value 0 K in an inlet change

lunisolar diurnal of the tide

10

Page 13: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

L

M

m

N

n

p

Q

R

r

s

T

t

u

v

SYMBOLS AND DEFINITIONS--

effective of an inlet

len of a ical rec

len of subreach in an inlet

gross annual littoral drift

cipal lunar semidiurnal component of the tide

coefficient for combined entrance and exit losses

in on 44

lunar ell c semidi urnal component of the tide

Manning's ss coefficient

1 unar di urnal o the tide

wetted in an inlet cross section

discharge of water an in 1 e tor b ay c ros sse c t ion

maximum dis or discharge at st of tide

c radius in an inlet gorge

ic radius in subreach of an inlet

ratio used in the classification of tides

solar semidiurnal of the tide

exponent on 60

component of the water-surface s due to acceleration

component of the water-surface slope due to bottom friction

od of a tidal cycle

time

dimensionless measure of the veloci equation 33

Vm, defined

mean veloci of water in a eros section

I I

Page 14: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

w

w

x

a

B

n

SYMBOLS AND DEFINITIONS--Continued

maximum value of V the s

for sand t threshold ve

width of cal

annual wave power

width of inlet entrance

of the tide

distance in bay, measured landward from inlet

dimensionless measure of the cross-sectional area in an inlet

measure of stabili defined

dimens onless number defined

unit wei of water; also

dimensionless nwnber defined by

total loss of head in an inlet

on 47

ion 57

e angle defined

on 53

combined entrance and exit losses of head in an inlet

loss of head due to bottom friction in an inlet

70

nm maximum value of n

ns

8

s

IT

a

value of n for which the and linear formulas agree

measure of time in a tidal cycle

dimensionless measure 0 stahil

dimensionless number defined

librium value of I;,

value of in an inlet

301416

ionless number defined

12

defined on 59

ion

eh

Page 15: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

v

1.0

1.0'

1.0"

AND DEFINITIONS-

ar measure of the 1 of time from slack ti inlet to midtide in the sea

dimensionless measure of the veIoei , defined

librium value of v

tidal hi

e

i.e., the amount of water stored in and low water

ial tidal sm; i.e., the value of the tida the full tidal range of the sea is admitted

of a of tide

in an

bay between

sm if

radian for the diurnal the tide

radian for the semidiurnal of the tide

13

54

Page 16: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to
Page 17: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

HYDRAULICS AND STABILITY OF TIDAL INLETS

by F.

I . INTRODUCTI ON

An inlet is a short, narrow waterway that connects a »a lagoon, or an es to a body of water, general a sea. This ort discusses those inlets where the body of water is tidal and where the inlets are effected by sedimentary processes. Many inlets are pas-sages through barrier islands ly along shorelines of coastal plains.

In lets ly are entrances to harbors and are important igation. Inlets also contribute to the ecology of associated caus an exchange of water with the sea. At times, this water p a si ficant in the control of the salini ty of the water, in the dilution of industrial and muni wastes, and in the mi of fish.

to nav­by of

Inlets sometimes pose certain problems; e.g., the depth of water in the channel may be navi on or the channel may shift too much. The of water between the sea and the may also be more or less than desired or the inlet may cause acent

to erode.

II. CHARACTERISTICS OF NATURAL INLETS

Some inlets are features of the coast whose exist-ence may antedate historical records; other inlets are formed possib storms or floods, and ect to closure by natural forces. An in let may also be cial; i. e. , a land

by man. Inlets are often found on coasts formed by the sition of sediments past geo c ages have inner which are likely to be river val that have been submerged by the rise in sea level that occurred the recent geo c epoch.

The actual effect of a hurricane or even of an windstorm on inlet formation or modification cannot be cted with accuracy. The storm may cause the of a new inlet or the en of an exis inlet by barrier beach. Also, the accu-mulated water in the bay caused by the wind tide or by the from tributaries may breach the barrier beach and create or enlarge an inlet. However. littoral drift by the storm may block an inlet to an extent of closure either at that time or later. This subject is discussed by Johnson (1919). Brown (1928), and Pierce (19

The rise and fall of the tide in the sea causes a flow of water into and out of the inlet which in turn causes the water level in the to

15

Page 18: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

rise and fall. The runoff which enters the from its tributaries also contributes to the flow through the inlet, but usual this is minor. The Ii ttora 1 dri ft whi ch arrives at an in let is carried in to the inlet the flood current, and ted the inner end of the

1 to form a shoal. TIle ebb current then carries of the sand back to the sea where some is ited as an outer bar at the sea-ward end (Fig. 1). The sand which is on the shoal or the outer bar is sand that is sediment

TIlis loss is like drift beaches.

At most inlets a of the littoral drift passes the inlet and continues a course on the downdrift beach; this s called

sing occurs as a continuous or intermittent process. Tidal currents carry a large of sand back and forth the inlet where more sand is constant added the littoral On the down-drift side of the outer bar there is often an extensive shoal, and at each ebbtide the outgoing current its some sand on the shoal. The

waves drive the sand shoreward to the beach where it resumes a course as of the I transport.

Bruun and Gerri tsen ( dis and "tidal-flow s stated combinations of these two forms and that seems to on the ratio between the flow.

between "bar that most as the form which littoral drift and the tidal

The rate at which es an inlet is not ordinari to the rate at which the drift arrives at the inlet. The differ-ence may be ited on shoal, on the outer bar, or However, the excess of sand causes the inlet to mi Part of the sand is ited on the ft side of the inlet while the downdrift side erodes> and as a result the inlet is di$placed do~~dri Some inlets mi ft, such as Redfish Pass on the west coast of Florida, ly, in such cases, the rate at which sand is. assed exceeds the longshore sediment

The confi in ft and classification of inlets. Galvin (1971) (Fig,

of inlets varies, and these variations shore confi a bas s for the

The following four groups were re zed

The ft shore extends seaward the entrance.

Si the downdri

ficant on ft side, The offset is on side and exceeds the minimum width of the inlet.

Si ficant on the downdrift side and inlet.

on downdrift side, The et is the minimum width of the

16

Page 19: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

---- --------

Figure 1.

I !

.---- Boy S

---------

G

----------

cal b beach tidal inlet.

17

Page 20: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

I. lopping

20. U rift Of

Oowndrift Offset

N ligible Offset

::;.

F 2. classification of an inlet > 19

18

Page 21: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

(3) Ie The > if any, s minimum width of the inlet.

Galvin concluded that group 1 inlets deve where and most the direction, and to maintain the inlet. 2a and 2b inlets occur

tions similar to group 1 that an able littoral exists in a direction opposite to that 0 littoral

In group 2b inlets, the littoral than in group 2a inlets. 3 inlets occur on

trans­less

lit-toral rates in the two directions are

The size of inlets varies The entrance to Delaware is an ionally large inlet with an about 12 miles wide. Phil

Inlet, a small intermittent inlet 15 miles west of Panama Ci ,Flori is an e e of an inlet at the opposite extreme. The size of the

varies from about 100 feet to a closed inlet. A number of selected inlets in the order of throat area, are in Table I (O'Brien, 1966).

III INLET HYDRAULICS

The flow of water th inlets is caused the tides; the flow from the tributaries to the bay is a minor factor. As the sea level rises and falls with the tide, the flow of water th an inlet causes the level of water in the bay to also rise and fall. At any instant the flow the inlet on the difference

the sea and bay formula is used in this because to be-

cause information about values for 's coefficient, n, is available. However, the foIl limitations should be considered:

The available values for 's n are based on observations made in uniform (prismati channels and their reliabil in nonuniform channels such as those usual found in inlets is uncertain.

(b) resistance varies due to the presence or absence es and other bed forms which are sect to variation during the tidal e.

(c) Little is known about the loss of head that takes place due to the contraction and expansion of the current pass through the inlet.

Cd) The formula is for temporal accelerations.

flow and thus

Manning I s formula for the loss of head due to ic friction is:

(1)

19

Page 22: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

Inlet

Golden Gate Willapa North Edisto River Tomales Fire Is land Jones Inlet Punta Banda

Ro Ii llamook East

Charleston Humbo Idt San Diego Coos Umpqua Absecon Morichee

Nahalem Siuslaw Mission Bay

lIe Beach

Pendleton Boat Basin

Table 1. Values of

Location on diurnal tide. st

3)

5.1 Pacific 2.50 x

Atlantic 4.58 x

Pacific 1. 58 x

Atlantic 2.18 x

Atlantic 1.5 x

Pacific 2.99 x

One j

Atlantic 3.7 Pacific 2.11 x

Atlantic 7.6 x

Two jetties

3. Pacific 2.43 x 10 10

Gulf of 1.59 x 10 10

Mexico Atlantic 5.75 x 109

Pacific 4.38 x Pacific 3.38 x

Pacific 2.84 x

Pad fic 2.20 x

Atlantic 1. 48 x

Atlantic 1.57 x 10 9 Pacific 7.73 x 10 8

Pacific 6.0 x 108

Paci fie 4.64 x 10 8

Pacific 4.2 x 1 Padfi 3.89 x 10 8

Paci fic 1. 98 x 108

Pacific 1. 14 x 10 7

20

Minimum flow area at entrance channel

below MSL ac

2)

9. 3.94 x

9.95 3.6 3.56

.89 5.46 x 10 3

8.6 3.69 x

1. 15 x

5.08 x 1 2.85 x 105 2. x 1

1.44 x 105

7.55 x 1 6.17 x

6.11 x

4.62 x

3.13 x

2.04 x

1.98 x

1.12 x

1.10 x

1.04 x 104

10 10 1

1966)

Page 23: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

where i the loss in head due to i friction, L is the

the channel n is the Mann V is the mean velocity of the water, and s This formula assumes that the unit of is the foot; if the meter is used, the factor 1.486 should be deleted. In a uniform smati channel, s s the len of the channe ; in a nonuniform chan-nel it is convenient to divide of the channe into a number of subreaches denoted the subs The friction-loss term becomes the sum of the losses in the subreaches or

where it is assumed that the same value of n holds in all of the sub­reaches, This an be rewritten as

where Q is the di > and is the cross -sectional area in the subreach. It s now assumed that the L is an effective that, when used in unction with the area, and the radius, R. of the gorge, will Id the same value of the following holds:

When this is solved for the result obtained is'

L (2)

The entrance and exit losses should be added to the losses due to friction. two losses are combined into s Ie

m

where eration of often

is the combined entrance and exit losses, g is the accel-, and m is an coefficient value which is

the value one.

ions (1) and ( can be combined to Id:

+ g

Page 24: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

the coefficient,

so that

v for 1l o ,

and

for 1l < 0 »

where the sign of 1l must be changed when the direction of the flow is reversed. Because of the difficulties in nand m, there is some in combining the effects into the one coefficient which can, in some cases, be evaluated direct from observed data.

and for sible the value

values for the Darcy-Weisbach friction coefficient, f, 's n, and shows the wide range of values that are pos­

these coefficients. For this reason it is preferable to base of n on actual measurements in the inlet channel. However, if

ible, the value of n = 0.025 is suggested as a reason-on. Simi , for the m the value one

is suggested.

Al tides in the sea are composed of many components, only a few are enough to p a significant the tidal currents in inlets. These are the prin

and 01 , 1940). The astronomical explanation 0 the in Pillsbury (1940) and Dronkers (1964). Periods

components in hours are:

In classi tides Oceanic and Atmosphe

12.42

12.00

12.66

23.

25.82

the National Ocean of the National c stration (NOAA) uses the formula:

K r :::::

22

(7)

Page 25: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to
Page 26: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

where,

r 0.5 semidiurnal

o. r 2.0 mixed

2.0 r diurnal

calculations for diurnal component a semidiurnal

represented 24.84 hours or ad of 12.

Where the as diurnal, single is used; where the ide is are combined. A suitable formula is:

B' sin w' t B" sin 't + ¢)

where an ion to the tide in the ea, il' are coefficients and w' and wI!

¢ e difference between components, t time are the radian cies for the diurnal and semi-

diurnal of the ti ive In any case the coefficients, B' and BI!, and e angle ¢ cted to

the icted tide onal Oceanic and c Admin-1 76).

A number of methods have been devel for lcu a tidal inlet when that inlet is the on one conne

otherwise closed to the sea. The more accurate methods of a di tal Masch, Brandes, and 1977; See ig, Barris der in methods which are to hand calculation are in this s Brown I s (1928) linear method and KeulegaJ1 s nonlinear method. The fol assumptions are made in both methods:

surface in the bay remains horizontal the tidal cycle.

111e wall of the are vertical so that the water-area remains constant.

The and surface runoff inflow to b is zero.

No densi currents are

) The tide in curve.

sea is a s Ie sinusoidal

( The cycle is small

variation in the inlet durin the so that the cross e onal

ic radius can be assumed to remain const

24

1

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leration the many U ..

two bas ons

Q :::

and

(l

where Q s the disch the inlet, reckoned posltlve on the floodtide and on the ebbtide; the water-surface area in the bay; t is time; are the water-surface elevations in the and in the respecti ve continui which states that the inflow to the at which water i stored in the ence in water level between the sea and the inlet channe .

In the linear method the rl p aced with

and that on becomes:

-hand side of

,ill on of is equal to the rate

the differ-the head loss in

on (10) is re-

( 11)

where ns s the value of n for which the c and the linear formulas eld the same dis (Fi!!. The assumption is made that the tide is either diurnal or semidiurnal, not mixed. The tides in the

and in the sea are represented

cos 8 (

and

ao sin (e - T) (l

where,

8 wt (

25

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1010

Figure 3. son ic and linear formulas.

26

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ao and ab are the amplitudes 0 the tide respective withe radian value 8 at midtide on a tuted into the

Q

is obtained. (l ion (11) to obtain:

sin (8 - T)

i'ihen identi

+

in

1 and

cos 8

sin (8 T) sin 8 cos

is introduced and the terms are

8

(

in the sea and in of the tide' and

When on ( s

substi-

C 5)

are now substituted

-""--~~- sin 8 .

- cos 8 sin

this becomes:

COS T - sin e - (ao sin T - ab) cos e o .

As in

and

must be must be s

ao cos

sin

These are then solved to eld:

tan T :::

and

sin T =

of 8> the two sions zero; this Ids:

(1

(18)

Brown (1928) assumed ns to be equal to the i.e .• the value when the veloci of the water in

maximum value of the inlet reaches a

on (1 the result maximum. I f on ( i subtracted from is:

sin (8 - + cos 8 (

27

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which on ate substitution from ( and (1 becomes:

cos sin 8

the maximum value of th express on to

cos T

when this is substituted into (1

tan T

which can be rewritten

K > (2

where

K

s known as the repletion coefficient. Eliminat g ons (and Ids the ion'

+

whi ch can be 0 1 ved for ab with the res~lt:

The following expres ion for the dis the s of the tide, is obtained

similar for the value of the mean veloci in gorge at the time of of the tide is

Vm

A sample lem illus the use of the method scuss below.

The non inear method deve Keulegan (1967) than the Brown method. The sea level in this method

28

is more accurate the Brown

)

..

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tabular ficient, K, is

follow

tics of an inlet can be sian for K s:

A of tidal curves obtained 4. Detai Is on how such

196

Ie sinusoidal curve; however methods are used to the

the the in both

sed in terms of that number. The expres-

K

Keulegan's method is sho~~ in Figure can be ca culated are Keulegan

The two dimensionless numbers, sin and ,are as functions f K Table 3 and cal in Figure 5. These numbers are used

to obtain other ties needed in inle tudies means the following ons:

sin (

:;t =:: sin (2

1T:;tC ::: (2

In these ons:;t in the bay between hi

od.

s the tidal sm and low water in the

the amount of water stored ,and T is the tidal

The relati between w T is the

2" (30) w

The elimination :;t between ons ( and 9) elds the on:

C sin T •

which in view of ion (30), can be rewritten as:

C sin (3

The c expression for the maximum velocity, s:

C sin (32)

29

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4. Surface level fluctuations of sea and basin.

30

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Table 3. Coefficient C in tidal SID formula and ratio of bay to ocean tidal

K sin C

0.1 0.1158 0.8106 0,2 0.2293 0.8116 0, 0.3387 0.8128 0.4 0.4414 0.8153 0.5 0.5359 0.8184

0.6 0.6209 0.8225 0.7 0.6955 0.8288 0.8 0.7592 0.8344 0.9 0.8165 0.8427 1.0 0.8555 0.8522

1.2 0.9168 0.8751 1.4 0.9536 0.9016 1. 0.9745 0.9267 1.8 0.9861 0.9484 2.0 0.9926 0.9650

3.0 0.9996 0.9950

31

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s n c

K

Figure s. Sin and C versus the coefficient 0 repletion.

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To facilitate the use of the Brown and methods and to per-mi t camp arison of the two methods> it is convenient to represent the results in the form of curves of dimensionless numbers plotted as func­tions of the repletion coefficient, K. This h as been done for the ratio in Values for the Brown method were calculated with ) and those for the method were taken from Table in mind that

ab sin T ::::

An examination of the two curves shows that the Keulegan method tidal amplitudes in the than the Brown method. To

the maximum ve the dimensionless number,

u '"

s introduced. From the Brown method shows

u

and from (32) the method shows

U ::: C sin T

ng these hlO values of u in Figure show that the elds velocities than the Keulegan method. To

arrive at curves representing the of the tide behind the sea tide, the fol relati was used:

1T + 4> ;:;: -

2

where q, is the lag under consideration. Substituting this into on (l Ids

cos 4>

which s the used to arrive at the lues of lotted in

(

(

(

(

(3

Figure 8. In the Keulegan method the and there can be no question about

tide is not sinusoidal for the curve as a whole. The

curve in the figure shows the for the of maximum di

The fol calculation illustrates the use of the Brown and methods. An inlet is assumed to be described by the values:

33

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7 ( coeffi rep

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00°

90°

80°

70°

60°

cp 50°

OJ 40° (j)

3 0

3 4

K

8. 96 ent 0 repletion.

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::::: 3 x 10 8 square feet

1.5 x square feet

p 10 feet

R ::: .5 10 3 :::: IS feet

L 4 x 10 3 feet

ao ::: feet

n ::: 0.025

m '" 1

g ::: 32.14 feet per second

T .42 x 600 44 712 seconds (semidiurnal tide)

w ::: 6.2 44, = 1.405 10- 4 second -1

From these values are obtained:

+ + 0.58

K 1.17

5. feet per second.

Values for ab ao> u, and $ are taken from Figures 6 7, and 8; values for and are calculated with the formulas:

x 2 x

5. u

3 x

1.5

37

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The

An motions narrow

where IV the ered from

arrive at second bottom res and the di

W Clt

+

dth

o >

Q W (

t

remains constant motion obtained in thi

which due elevation of the the ion

a constant· the e on 0

consid­tance on

. Q, the

function th

on »·the

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b

I x

1:1~'-'---------------------------~

Figure 9. ic in and rectan wi

39

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where s the of the It is then assumed that the follows the s Ie sinusoida ction,

and

where D due to

Q (

WD D ( v

the of water in leration is:

wt .

wt

cos wt

The water-surface

sin wt

At hi water this slope reaches the maximum absolute value

I max (

(

(41)

the difference in level between the at that time is

extremi of the

dx ( )

0

The water­ s to bottom fri on expressed in terms IS s cient is

nv ) in view of ion 1) becomes:

\

) (

At midtide this s reaches the maximum lute value of

(

40

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the difference that time is:

The

level between the two

( 2 dx =:

that an assumed

of at

(

the as

son with

A number of studies have cons aspects draulics that go those considered in the Brown and grul methods. Baines accounted for the effect of acce on in the inlet and out that some inlets this results in bay range

than that in the sea; Kreeke (196 accounted for freshwater inflow to the The calculations of Shemdin and in-cluded the ffect of acceleration in the inlet some of the harmonics of the tide. Oliveira (19 devel a method which allowed both the inlet cross section and the water-surface area f the with the progress of the tidal eye A bib1i of ics and other

of tidal inlets is

INLET STABI LITI

Some and with little ; others are 1, or a matter of considerable the c characteristics which govern the

to natural forces. It s to be able to determine tabili of inlets. Some

of the current theories that re to stabi i in this ction; however, these theories are on inlet which is stable weather a severe storm. Furthermore, these theories are ct to revi addi tional in is

A re that defines the stability inlets was 0' Brien (1931, sectional area in

the formula:

He found a close relati between the cross-the gorge an inlet and the tidal sm in ts

(

where is the cross- ectional area in the gorge measured below mean sea level» and is the tidal or volume of water tored in the

between the hi and the low waters to the diurnal or the range tide. The values of O'Brien are:

Inlets with two etties

Inlets without jetties

41

N

4.69 x 10 4 0.85

.00 x 10- 5 1.00

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the The in

(19 many inlets were ana zed.

the 4 and,6, are shown

in which data de;termine i

to

ences existed between the dal inlets on Atlantic, ,

onal area relationsh ts 0 the Uni

States. Jarrett's conclusions were:

Un ettied and s -jettied inlets on the Atlantic, and Pacific coasts exhibited different ~ versus ac

as a result of differences in the tidal and wave characteristics between these coasts.

The available data did not appear to warrant any modification in the ~ versus ac relati for jettied inlets ori 1 O'Brien (1931

The values of band N obtained Jarrett are in 4.

Tabl 4, the O'Brien (19 1. 1966) ),

librium

Atlantic, All One j Two jetties

Atlantic coast All One or no je Two jetties

Gulf coast All No j Two

Pacifi coas All

1

Inlets

Pacific coasts

42

b

5.74 x 10 .04 x 10-

3.76 x 10-4

x 10-4

10

N

0.95 1.0 0.86

1. 05 1.07 0.95

0.84 0.86

1

0.91 .10

0.85

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10'

107~~~~~~~~~~ __ ~~ __ ~~~~~~~~~~~ I

A-Mi Flow Area

Figure 10. Tidal sm inlet relat onship.

43

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Various theories re to the proposed. Bruun and Gerritsen ( the ratio as a measure of tabi li

li of inlets and Bruun (1966»

where M is the that:

have been proposed

annual gross littoral drift. Bruun (19 observed

200 gave stabili ty

200 100 gave fair stabili

100 > gave poor stabil

Bruun and Gerritsen (1 that for a diurnal tide the ratio should be replaced with the ratio 2M.

Bruun (1966, 19 do not refer to ratio that it should be used in all cases.

Carothers and Innis ( discussed the stabili of inlets and offered an exp lanation of how the processes of accretion and erosion on the outer bar fl ••• the automatic mechanism to maintain c balance between the various rates of sediment and littoral

to the authors this means that when the littoral an excess of sediment into an inlet, the sediment is

ited on the outer bar the floodtide and is removed the ebbtide, and returned to the li ttoral dri ft. However, Carothers and Innis do not propose a la to determine whether a inlet is stable or unstable.

coasts of on, Johnson (19 and California and

studied inlets on the concluded that, "Wave power appears to be the most

factor o I Brien (1931, 1 ratio of the wave

the stabili of tidal inlets." He for closure criterion, dal energy per tidal cycle or

the

(

If in which wave energy in foot per foot of beach per second; T duration of tidal cycle, in seconds; w width of entrance.

tide ampl tude, in feet· and y unit wei t of water, in per cubic foot." O'Brien reasoned that there a critical

of this ratio and that j f C1 exceeds the cri ti 1 value, the inlet remains open but if is less than the critical value. the inlet closes f the sto:rm duration exceeds a ce:rtain time. However, Johnson found that insufficient data this cri teri on and used the s lified

the

form sm

Johnson ( plott the

drawing

44

is the 1 range of the ocean

the results of his t the

that

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have closed from those that have remained open. That line can be the formula:

7.32 x 1011 o. 0 ( 46)

where is the annual wave power of sea and swel near inlet in foot per foot per year and tial tidal sm.

O'Brien and Dean ( have proposed a stabil index, S, defined as:

(47)

where is the maximum veloc of the inlet. is the ld veloci for sand is the cross-sectional area in the gorge, is the value of ac at the of the curve, and aE is the value of ac at the intersection of that curve with the O'Brien librium veloci curve (Fig. I as discussed below. The stability index, the of an inlet to resist closure under conditions of

A method for inves g the stabili of inlets was suggested Escoffier (1 He a diagram in ,vhich the veloci > ,is plotted the cross-sectional area, ac, as the latter is assumed to vary Over a wide range of values. It was assumed that librium

a cular value for and , that value was plotted as a line leI to the axis. However, the use of

's and O'Brien's formulas ts construction of a better , and the librium value for is not a constant but varies

with the repletion coefficient, K.

It is to express K as:

8)

where

(

a == (50)

and

( . 45

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Maximum ity Curve 0' s(l iii um

Figure 11. c des tion of inte on limits and aE.

46

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ons ) (32), and are used to at the fol ex-ion for

C sin 1)

and ( and 0) are then used to obtain

where

C sin T (5

Convenient this introduces the dimensionless veloci

v (5

on

where

is used to eliminate Q from

and obtain

;:;: be ) are then used to e

K in )-N

(

on (44) to eld:

from on

N-l

E has been added to indicate the librium value for E,. , the librium value for the dimensionl s veloci \) becomes:

Figure 12 shows v and plotted as functions of K. The intersections A and B in the figure are of librium wi th A an unstable point and B a stable one; this can be seen that a small deviation from the conditions represented

5)

6)

7)

8)

into on forces that tend to increase or reinforce the deviation, whereas a similar deviation at B sets into forces that tend to restore the inlet to librium If the iation at pOint A is an increase in the of the inlet the ve loci of the water will increase and the cons erosion wi I cause the in et to increase further in size. A imilar deviation at B will cause

47

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v

Fi gure 12. and v versus repletion coefficient, K.

v

Figure 13. and various values of v versus repletion coefficient, K.

48

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..

the velocity to diminish and the accretion will cause the inlet to diminish in si and therefore to move back toward the A decrease in the inlet area at A will diminish the flow ve to cause a further area decrease, etc" until closure. A decrease in area at B increases the flow ve scour and a return to B. Figure 13 shows three possible relative positions between the two curves. The v curve plots to intersect the

curve in two • one unstable and the other stable, The second \i curve on of wi th the curve which must be classed as an unstable The third Is to touch the curve and cons is not

All of the stabili formulas that have been mentioned are empirical and ect to revision with the progress of research, The O'Brien formula and the stabili diagrams gs, 12 and 1 which are based on it do not explicit contain the littoral drift or the wave power as a variable, However, it can be assumed that either or both of these

ties p the Hon of the curve and in this way and the stabl of an inlet; e,g. the as ition f the first v curve in I is 1 littoral drift or smal wave power. The lower positions of the other two curves mi then be re-flections of littoral drifts or wave powers, The est curve thus be as the most stable which suggests that the the curve mi ,in some \vay, be trans lated into a measure of stabi . An examination of and Fi 11 indi that to some extent the stabi li de ).

s such limits of with the Thi Ie

the a cation of how the size of the

enter into the determination of of

index,

an wave power may

The idea of trans the hei of the v curve a measure of stabi li can also be carried out as follows, 14 shows an v and an vE curve. The ratio of v to for the value of K, which makes v a maximum, elds the dimensionless number,

The condition A :> 1 indicates stab:Ui ,but the value of II can be

)

taken as a measure of the of stabi However, to convert this con into a usable form it wi 11 be necessary to an expression for \! as a of the repletion coeffi here assumed that as erosion or accretion causes the dimensions of an inlet to , the ities, and~. will vary according to the formulas ~

ac a'

49

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..

( ) mox. 1/

1/ max

Figure 14. Definition diagram for the stabili number '\.

50

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I

)

and

K K' )

v

For the e the are chosen. The first on> 1966) ch expresses

that the is general than in smal ones, The second value i derived from it is assumed that the influence of the coefficient. The in and becomes> to of accuracy, 0, l' then becomes:

as the method in which v

From ion

v '" K' -0,

between and K t s possible At that point

K '" 0,64

sin T 0.651

0,840

• 21 0.765

is obtained

1

is known stabl determine the

it that value

1 -N '" B* K (sin T)

1 -N x 0.64 x 0.651

B*

and

0.765 VE 0.840 x 0.64 x

1111 1.423 x 0,65 ! K!-0.21

:;;: 0,988 , K' -0.21 for N 0,85

0.926 , K! -0. 1 for N 1. 00

channels

)

Keulegan' of K for

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or to a sufficient of accuracy,

When this formula is used it must be understood, that the favorable condition. A > 1. does not that the at K = K' is a stable

but a stable solution exists; i.e,. the one the in Figure 14. If a of stable librium exists it wi 11 to a value of K than the one for which v is a maximum. i, e. • than about K :::; 0.64,

Problems arise when a communicates with the sea two or more inlets. If the water surface in the remains horizontal

the tidal cycle, the foIl conclusions can be drawn from the theories of stabili

The repletion coefficient, K, for the as a whole is the sum of the values of that coefficient

for the inlets.

A value of which on the holds for all of the inlets and librium for the

that the value of ~ value.

for each inlet shall be

( The unstable. If the value of for any inlet is inlets, inlet others and will en

than the values for the other a velocl than the

it the entire tidal

K,

However, observation indicates that some which communicate with the two or more inlets are stable. For example, the formed

lla Sound, Charlotte Harbor, and Pine Island Sound on the west coast of Florida has six inlets and the system appears to be stable. !lO\vever, since the has a expanse and is most shallOW, it can be assumed that there are ficant variations the in the the amplitude and in the of the tide. lag may occur at a small inlet and cause larger velocities in that inlet than at the other inlets. The resul erosion would cause the small inlet to enlarge until the increase in flow the inlet causes

of reduction in the to establish a condition of librium.

To determine the s tabi li calculate the amplitudes and

of one of several inlets lags of the tide in the

finite-difference method such as This is done twice for two assumed

the one devel Dronkers ( sizes of the inlet. the initial si

and a larger or smaller assumed erosion or accretion.

1 size that the result of After the ampl tudes and the lags

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for the two assumed sizes the inlet have been mum veloci for each case is calculated. decrease when the si of the inlet increases or to increase size of the inlet decreases the inlet is j to be stable. wise, it i unstable.

V. FUNCTIONAL DESIGN REMENTS

the maxi­to

when the Other-

In p the of an inlet. ectives which may be involved are:

of the inlet. ebbtide to carry out

the floodtide.

the inlet. An inlet may not be in a con-dition because the channel bas too small a cross-sectional area or too a Section Then

ate to en the cross section or to shorten the channe should be taken. Also, the inlet may be mi too or the of the channel over the outer bar may be shifting excessive to arrest these processes may then desirable.

a channe of dimensions for

Before discussing means for the of an inlet. some of the natural factors that enter into the determination of that should be mentioned. These include:

( that enters the causes the ebb flow

from its trib-the inlet to

exceed thus favors the outward of sand,

At many inlets the tidal flow has i.e .• hi water is followed lower low the outward flow of the tidal takes place in

of time than the inward flow. of the ebb current tends to be

the flood current. At a few inlets. the

trans­than

quence is reversed. a run-in exists, and the rent tends to have the

The ebbtide than on loci ties and a

of water channel is less the to hi ve-

on the ebbtide.

( water-surface of a is than at low tide \vhich the velocities and

to be greater on the ebbtide than on the floodtide.

53

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acceleration or deceleration in that current. i of an lerat current ater than current, I the banks of an in current, that current wi 1 have a

current,

The in channel resi t.ance sometimes the alinement of

The

The etties and bank g for the ebb current,

to remove the sand current, Bank a inement of the inlet

bank erosion,

revetments or to reduce shoal

Genera etties are necessary to stab lize outer bar and to the mi on of the inlet.

noz Ie to direct the ebb current acros where channel is des red and as

harbor, exclude, to some extent wave-driven the jetties and the inlet banks an linement that converges

toward the sea the gorge i made to a posi the outer the jetties. The veloci will that

scouring action of the ebb current on outer be

Ordinari • the outer ends of the jetties are extended to the where the natural is to the ct of the on channeL To determine the between the outer the jetties two considerations are the needs of and the desirabili of

a gorge area that atisfies. at leas the 0 Brien librium formula. However some variation in the value of the area

is possible when to the 0' formula, 1:];, ,e. shorten the channe the ti the

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the

nons TIle determinat of the

the cope of this (197 ~ and

Most natural inlets thdraw sand from the the sand on the outer bars on the

that these losses it bene

acent beaches and shoals. To the extent

the beaches. How-ever, equal

in one direction is

cause accretion on one Since the amount of

direction the j the inlet and

will ordinari the other currents and is usual de-waves s

sirable equal to de for artificial s of

> Coastal Research Center

scussion assumed that the inlet to be is natura gorge area wi 11 remain the same and that arti s will on be necessary to supple-ment the natural s of the inlet. However, in some cases a navi Ie sage may be desired into a harbor or a that too smaIl to de either s tab Ie channe I or tha t meets the needs of navi ion, is po ible to obtain a channel of the desi dimensions a nons inlet. The etties extended water to complete exclude

the littoral drift. is then to the desired dimen to pre lude the movement of the

channel di

either the tidal currents or the waves. Under Ie to obtain gorge area

the O'Brien formula. and will occur, the entire net littoral

must be p cial The combination of uch an oversized inlet with a small inner to the admission of excessive wave action into the ; cons > consideration should be to the possible need for wave absorbers or beaches in the basin. Four nons inlets on the P fic coast in outhern Cali a are Marina de ami tos Beach, and Mission Mission Inlet cus ed in Section VI; a of several nons inlets plotted on an O'Brien shown in Figure 15.

VI. CASE STUDIES

th s that can

on were selected because e in the of

Page 58: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

(I

omitos 9

11 mum Inlet (f

gure Nons channe s, southern Cali

56

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lina.

\'lith the I at Hi Isboro Inlet. Flori

of the artificial \'leir at Masonboro

rock reef the de-

1965. • and Watts. Vallianos and Jachowski ( » and Dean and Wa ton ( plan of the inlet is shown in Figure 16.

The ect 1 at mean 400 feet wide across the outer • and thence wide to the Atlantic Intracoastal Water-way. TIle mean tidal range in the feet and the range is 4.5 feet. The range the .5 foot less than that in the ocean. The rate estimated to be 120.000 cubic per year northward and 220,000 cubi per year southward. The net rate is the difference between these two or about 100,000 per year southward.

One

southwest of 16 at MLW. About ,300 cubic and placed on Wri

north side of the inlet 3 600 feet weir 1,000 feet and has been in

The elevation the crest of the is 2 feet above MLW. A

weir is about 1,300 feet 400 is a minimum distance of 200 feet

of was from the north of the inlet.

tion basin feet wide> from the weir.

tion basin

Since completion of the north j the j and has encroached on the

• the channel has moved toward Therefore» it

has been necessary to place the j to bank of the

ction the lee side of Accretion has also caused the south

have p a in caus Three factors are believed to

the channel to move northward:

The momentum of the ebb current carries it the j which then acts a wal to deflect the current toward the southeast.

The j shelters the south outer shoal from that would natural to drive the sand southward but leaves the shoal exposed to waves that tend to drive it northward.

57

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Figure 16, onboro Inlet

58

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than the

Ro llover Fi Pass the channe the channe

Ii based

sin wt - in

can be considered as a

(Fig. was the

to stable.

sUIDed hori f the

ffect of the amplitude water level he

de assumed

- ¢) (6

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..

Houston ~

TEXAS

Tr

Gulf

s

1. Area map location of Rollover Fish Pas , Texas.

60

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18. Rollover Fish Pass Texas, November 197U.

61

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¢ i on

angle be rewritten

r in

and

tan y

The maximum dal difference on the inlet is nm on ang be used to show the influence the ampli

on that difference.

The

Prather and

Table 5. Ti at

Location

Galveston Inlet Rollover Fish Pass Rollover Fish Pass

The amplitude of the that at Galveston Inlet

f, This value the shorelines in Eas

on the di ial nm amp tude at Rollover Fish Galveston Inlet. The

Ro lover sh Pas Inle and that thi

Fish Pas

Values of mated to be 0.4 over Fish pI A

0,9

derive representative

and maximum head differential

at Rol over Fish Pas is 1

TIm

eft)

o. 0,75 0.70

as arge as the amplitude in be caused the convergence

However, 0 show the effect of the e cond calcu on was made in whi the

Pass was sumed to be I that that value nm

Galveston at Roll-

es Roll

in if the

Page 65: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

water Rollover

This tendency is ass.

t does not that the sma

inlet on of stable

tted The

ion have

reached.

fore librium and stabili based on I water surface a with more than one inlet

approximations. more re able evaluation f of the inlets, the I lculation

3.

jetties. pas age harbor entrance' the channe the load to the

72) .

discussed in Section IV are neces in thi way to be stable the des

of tabili the possible lIs bottom si lIs, and wei

unusual

, it is the north and the middle j

between the middle and the

sumed

111e has a surface 0 acres. Ori , the

i

Diego River dis inlet between the b

ited oad of sediments.

cantrall sian Beach is confined between the

Loma, The Ri ver. The 1 in the winter. the two movements be

a small shiftin channel mean lower

two headlands of La Jol and and for the beach is San Diego

in the summer and outhward in balance.

111e mean ocean tide the inlet i 3.8 de is 5.4 feet. Mean sea leve I .8 feet above 111e tides have a

with a long runout which, under natural conditions, causes the ebb current to have a sediment than the fl ood curren t .

In the sectional

inlets, an inlet is a cross-S ficant movement 0 sand

to prevent the break of waves, In

63

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..

..

Figure 19. Mission Inlet Cali

64

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a limiting ve of 2 feet per second was as a nons velocity and a of 20 feet was adopted as one whiGh would allow the 16-foot design wave to enter without breaking. The cross-sectional area is more than twice that required by the O'Brien equilibrium formula. The north and the middle jetties were extended to the 2S-foot depth contour to any movement of sand around the ends of the jetties from the adjacent beaches. The jetties were about 9,000 feet apart and the channel in between was to a depth of 20 feet below MLLW to provide the desired cross-sectional area of 19,800 feet below mean tide level. A number of nons inlets, inc p have been plotted on an O'Brien chart in Figure 15.

However, even with a depth of 20 feet be low MLLW the waves in the entrance were so s as to constitute a serious hazard to small boats. Accordingly. the outer 1,000 feet of. the channe 1 were dredged to a 25-foot depth which greatly the navi lity of the outer part.

The unusually entrances at Mission Bay, Alamitos , Newport Harbor, and t>1arina de 1 admi t much wave energy whi ch mus t be di ed of in some way. At Mission Bay, problems were experienced in the two deepwater anchorages, Quivera Basin and Mariners Basin, because of waves that were as high as 2.5 feet. A model study made at WES concluded that excessive wave energy was reaching the inshore end of the entrance chan­nel where that channel makes a 90° left turn into the main channel. The shore at this point is cted by a semicircular rock-revetted slope which reflects too much energy and tends to focus it on the entrance to Mariners Basin. Of the corrective measures tested, the most promising was to convert the semicircular revetment to a series of s -revet-ted sections in echelon that would tend to reflect this energy back out the entrance channe 1 to the ocean.

The of a nonscouring inlet is that it provides a safer and a more reliable entrance channel. The channel allows deeper-draft vessels to use the harbor. The greater width of channel, the lower water velocities, and the absence of breaking waves facilitate the maneuvering of s, cuI sai Iboats. The disadvan are the excessive wave energy that may be admi tted into the harbor and the possible need for artificial bypassing a larger amount of littoral drift than would otherwise be necessary.

65

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LITERATURE CITED

BAINES. W.D., "Tidal Currents in Constricted Inlets," the on Coas 1957, pp. 545-561.

BARWIS, J.H., "Annotated Bibliography on the Geo c, Hydraulic, and Aspects of Tidal Inlets," GITI Report 4, U.S. Army, Corps

of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., and U.S. Army Waterways Experiment Station, Vicksburg, Miss., Jan. 1976.

BROWN, E.L, "Inlets on Sandy Coasts," the l Vol. LIV, 1928, pp. 505-5530

BRUUN, Po, "Tidal Inlets and Li ttaral Drift," Univers Norway, 1966.

BRUUN, p., "Means of Controll Littoral Drift to Protect Beaches, Dunes, Estuaries, and Harbour Entrances ," XXIII International Navigation Congress, Ottawa, 1973 0

BRUUN, P., and GERRITSEN, F., Holland, Amsterdam, 1960 0

Coastal Inle , North

CAROTHERS, H.P •• and INNIS, Fisheries," JoUX'nal

Coastal Vol. 86,

No. WW3, Sept. 1960, pp. 103-128.

COMMITTEE ON TIDAL HYDRAULICS, of Present State of Knowl-edge of Factors Affe Tidal Hydraulics and Related Phenomena, If Report No.3, U.S. Army Engineer Waterways Station, Vicksburg, Miss., May 1965.

R.G .. and WALTON, T .L .• Jro, "Sediment Processes in the of Inlets with Special Reference ." Estu-

Vol. II, c Press, New York, 1975, pp. 129-149.

DRONKERS, J. J. , New York, 1964.

Coos Waters" Wiley,

DUNHAM, J.W., and FINN, A.Aq "Small-Craft Harbors: Design, Construction and Operation," SR-2. Stock No. 0822-00091, U.S. Government o Washington, D.C., Dec. 1974.

ESCOFFIER, F.F., "The Stability of Tidal Inlets," Shore No.4, 1940, pp. 114-115.

Vol. 8,

GALVIN, C.J., Jr., "Inlets and Wave Direction, Wave Climate and Coastal Processes," on Hwncm Massa-chusetts Institute of Techno • Octo 1971, pp. 44-78.

66

Page 69: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

HAY, D., "Harbour Entrances, Channels and Turning Basins, II The and Harbou.r Vol. 4, No. 567, 1968, pp. 269-.276.

HENDERSON, F.M., Open Channel Flow~ Macmillian, New York, 1966.

HERRON, W.J., Jr., "Case History of Mission Bay Inlet, San Diego, California, t! 13th 1972, pp. 801-822.

JARRETT, J.T., "Tidal Prism - Inlet Area Relationships," GITI Report 3, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., and U.S, Army Engineer Waterways Experiment Station, Vicksburg, Miss., Feb. 1976.

JOHNSOH, D. W • , Processes and Shore Development .. Wiley, New York. 1919.

JOHNSON, J.W., "Characteristics and Behavior of Pacific Coast Tidal Inlets. II Jou.rnal Waterways.. Coastal

Vol o 99, No. WW3, Aug 0 1973, pp. 325-339.

KEULEGAN, G.H., "Tidal Flow in Entrances Water-Level Fluctuations of Basins in Communication with Seas," Technical Bulletin No. 14. Committee on Tidal Hydraulics, U.S. Army Waterways Experiment Station, Vicksburg, Miss .• July 1967.

KING, D. B., liThe Dynamics of Inlets and Bays, tf Technical Report 22, Coastal and Oce c Engineering ,Univers of Florida, Gainesville, Fla., 1974.

KRAY, C.J., llDesign of Sh Waterways .. Harbors and Feb o 1973, pp. 89-110.

Maneuvering Areas, If Division .. Vol. 99, No, WWl,

KREEKE J., "Water-Level Fluctuations and Flow in Tidal Inlets," Jou.rnal of Waterways Harbors Division .. Vol. 93, No. WW4, Nov. 1967, pp. 97-106.

MAGNUSON, N. C., "Planning and Design of a Masonboro Inlet, North Carolina," Coas

Santa Barbara, f., 1965, ppo 807-820.

}.1AGNUSON, N.C., "Planning and Design of a Low-Weir Section Jetty," and Harbors Vo 1. 93, No. WW2,

May 1967.

MASCH, F. D" BRANDES, R. J., and Hydrodynamics (WRE)," App. 2,

l

REAGAN, J.D., "Numerical Simulation of GITI Report 6, l Inlet .. lvorth Caro U. S. Army, Corps

, Coastal Engineering Research Center, Fort Belvoir, Va., and U.S. (in

Army Engineer Waterways Experiment Station, Vi > r-Uss., on, 1977).

67

Page 70: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, "Tide Tables, East Coast of North and South America Including Greenland," National Ocean Survey, Rockvi lIe, Md., 1976.

O'BRIEN, M.P., "Estuary Ti Prism Re to Entrance Areas," Z Vol. I, No.8, 1931, pp. 738-739.

"Equilibrium Flow Areas of Tidal Inlets on of Co as

Coasts. " VoL I •

• pp. 676-686.

o I BRIEN, M. P q and DEAN» R. G., "Hydrauli cs Coastal Inlets, l! 1 Co as

1972, pp. 761-7800

OFFICE OF THE CHIEF OF ENGINEERS, "Tidal cs, EM 1110-2-1067," • D.C., Aug. 1965.

OLIVEIRA, I .B., "Natural 1

Tidal Inlets," Vol. III,

pp. 1827-1845.

PIERCE, J. W., "Tidal Inlets and Washover Fans ,If Vol. 78, No.2, Mar. 1970, ppo 230-234 0

PILLSBURY. B •• U.S, Government Print , DoC., 19400

Office,

PRATHER, S.R •• and SORENSEN, RoM., "A Field Investi on of Rollover Fish Pass, Bolivar Peninsula, Texas," Coastal and Ocean Division, Texas A&M Universi • College Station, Texo, 1972.

RAYNER, A.C., and MAGNUSON, N.C •• "Stabilization of Masonboro Inlet

of

North Carolina and acent Shores," Shore Vol. 34, No.2, OcL 19660

SEELIG, W., HARRIS, D.L., and Numerical Model of Inlet of and (in

SHEMDIN, O.H., and FORNEY, R.M., "Tidal Motion ~asfu ~.

25-2242.

SIMONS, D.B., and RICHARDSON, Professional

D.C., 1966

.V., "Res tan 442J, .S

68

Fort Belvoir, Va. Miss.,

Page 71: Hydraulics and Stability of Tidal InletsTidal Tidal Tidal inlets 20. ABSTRACT (Continue on reverse side if neC'$994it'y and This report presents a summary 0 basic develop-ments to

TASK FORCE ON FRICTION FACTORS IN OPEN CHANNELS, "Friction Factors in Channels," Journa"l Vol. 89, No. HY2,

Mar. 1963, pp. 97-143.

U,S. A~fi, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH Manua 2d edo, Vols. I, II. and III, Stock

No. 008-022-00077-1~ U.S, Government ce, o Co, 1975, 1,160 pp.

WATTS, G .M .. VALLIANOS, and JACHOWSKI, R.A., "The ance of Controll Littoral International Navi ion

WAUGH, R.G.,

WICKER, C.F., "Design of Navi U,S, Army, Corps of

, D. C., Feb Q 1967.

for Sec. 11, Subject 2, XXIII s, Ottawa, Canada, 1973, pp. 254-257.

Channels ," unpub Coastal

69

Vol. 97,

memorandum, Research Center,

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APPENDIX

SUGGESTIONS FOR INLET DESIGN

Information should be obtained concern the needs of the people for whose benefits the inlet is to be developed. If navi on is in-volved, the size of the t vessel that is to use the channel should be determined. The needs that may exist for the control of temperature, salinity. and pollution in the bay should be ascertained.

Available information concerning winds, waves, tides, tidal currents, and littoral drift should be collected. To the extent necessary this information will have to be supplemented by field observations.

Available maps and other forms of both and recent surveys should be collected. It is ly by comparing successive surveys that the past performance of an inlet and the extent of past erosion or ac-cretion of acent shores are determined.

The size of the sediments in the inlet and on the adjacent beaches should be ascertained. It should be determined whether there is any rock exposed or likely to be exposed in the inlet or on the acent shores.

People familiar with the inlet, the bay, and the adjacent shores should be questioned on past ty. A search should be made available written accounts, such as newspaper articles,

, etc.

Inlet design procedure. Define the desired objectives of the de­sign study. If the purpose of the improvement is to serve the dimensions of the channel and its alinement should be determined. If the purpose is to provide for the control of , salini pollution, or other cal factors, the inlet flows most advanta-geous should be termined.

Determine the equilibrium size of the inlet under consideration and evaluate its stabi Past performance of the inlet is However, the conclusions drawn from past ce can be supplemented

consideration of the various measures of librium and stabili descrihed in Section IV.

Determine whether the desired can be achieved alone. If this been tried, the results should he care-

ful evaluated. In general, an inlet can be maintained g alone on if its librium size s and it is stable.

Determine whether etties the inlet indicates it mi closure, or shoals excessive the inlet with jetties.

71

If the past is ect desirable to

of

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Determine whether a nons inlet is needed. In general. the librium size of an inlet with jetties is about the same as that of

the same inlet without jetties. The jetties serve to stabilize the channel but not to en inlet cross-sectional area. If a cross-sectional area is desired, then a non-scouring inlet is the

Determine whether artificial bypass is needed. If there exists an balance between the littoral drift in one direction and that in the opposite direction so that the resultant or net drift is

small, it may be that the natural s by the waves and cur-rents wi 11 be However, such a condition is onal and

is usually necessary.

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.--_____________ . __ . ____ . ___ ---.------------------1

F.

by Francis F. coffier. Center, 1977.

- U.S. Coastal Engineer-

to

in

74-C-0005.

C1l4S4 .U581r no. 13 551.4

ing Bibliography: p. 66.

71,-C-0005.

CB4S4 .lJSill 13 551. 4

Escoffier, Francis F.

Hydraulics and stability - Fort Belvoir, Va. : U.S. Coastal

72 p. : ill. (CITI report 13) Also nesearch Center; DACH72-74-C-0005)

Bibliography: p. 66.

Francis F. Escoffier. Research Center, 1977. - U.S. Coastal Engineer-

Report summarizes several important basic developments pertaining to analysis of the hydraulics and related stability of tidal inlets. The original inlet stability concept proposed by Escoffier is extended in

of recent worle. Tidal inlet characteristics and functional design requirements as well as case studies selected inlets the

coasts are discus8ed~

• Tidal inlets. 2. Tidal hydraulics. 3. Stability. I. Title. III. Series: • Coastal Engineering Research Center. Contract DACW72-74-c-OOOS.

GB454 .15 • US81r no. 13 551.4

Escoffier, Francis F.

and tidal inlets I by Francis F. Escoffier. - Fort Belvoir, Va. Coastal Research Center, 977.

72 p. : ill. (GITI report 1 Also - U.S. Coastal Engineer-ing Research Center; DACW72-74-C-0005)

Bibliography: p. 66. neport summarizes several basic developments pertaining to

analysis of the hydraulics related stability of tidal inlets. inlet concept proposed by Escoffier

light of recent Tidal inlet characteristics and design requirements as well as case studies of selected the

coasts are discussed~

1. inlets. 2. Tidal hydraulics. 3. Stability. 1. Title. III. Series: U.S. Coastal Research Center. Contract DACW72-74-C-OOOS.

GB454 .IS • US81r no. 3 55 .4