eng handbook - ch 87 - coastal engineering

XIII

Coastal and Ocean

Engineering

87 Shallow Water and Deep Water Engineering

John B. Herbich

Wave Phenomena • Sediment Processes • Beach Profile • Longshore Sediment Transport • Coastal Structures • Navigational Channels • Marine Foundations • Oil Spills • Offshore Structures

1586_book.fm Monday, May 10, 2004 12:54 PM

87

Shallow Water and Deep

Water Engineering

87.1 Wave Phenomena

Airy (Low Amplitude) • Cnoidal (Shallow Water, Long Waves) • Stream Function • Stokian (Third Order)

87.2 Sediment Processes

87.3 Beach Profile

87.4 Longshore Sediment Transport

General Energy Flux Equation • Threshold of Sand Movement by Waves

87.5 Coastal Structures

Seawalls • Breakwaters

87.6 Navigational Channels

87.7 Marine Foundations

87.8 Oil Spills

87.9 Offshore Structures

Ocean engineering is a relatively new branch of engineering. The need for this new specialty was recognizedin the 1960s. Several universities, including Texas A&M, MIT, Florida Atlantic, the U.S. Coast GuardAcademy, and the U.S. Naval Academy, have established undergraduate degree programs in ocean engineer-ing. Several universities have also developed programs at the graduate level specializing in ocean engineering.

Ocean and coastal engineering covers many topics, generally divided between shallow water (coastalengineering) and deep water (ocean engineering), shown in Figure 87.1 and Figure 87.2.

87.1 Wave Phenomena

Wave phenomena are of great importance in coastal and ocean engineering. Waves determine thecomposition and geometry of beaches. Since waves interact with human-made shore structures oroffshore structures, safe design of these structures depends to a large extent on the selected wavecharacteristics. The structural stability criteria are often stated in terms of extreme environmentalconditions (wave heights, periods, water levels, astronomical tides, storm surges, tsunamis, and winds).Waves in the ocean constantly change and are irregular in shape, particularly when under the influenceof wind; such waves are called

seas.

When waves are no longer under the influence of wind and are outof the generating area, they are referred to as

swells.

Many wave theories have been developed, includingthe Airy, cnoidal, solitary, stream function, Stokian, and so forth. Figure 87.3 describes the regions ofvalidity for various wave theories. Cnoidal and stream function theories apply principally to shallow

John B. Herbich

Texas A & M University Consulting & Research Services, Inc.

1586_book.fm Page 1 Monday, May 10, 2004 12:54 PM

87

-2

The Engineering Handbook, Second Edition

and transitional water, whereas Airy and Stokian theories apply to transitional and deep water (Airyapplies to low amplitude waves).

Airy (Low Amplitude)

Wavelength is given by the following equations.

Shallow water (87.1)

Transitional water (87.2)

Deep water (87.3)

where

T

=

wave period;

g

=

acceleration due to gravity;

h

=

water depth; and

C

=

wave celerity. Subscript

o

denotes deep water conditions.

Cnoidal (Shallow Water, Long Waves)

The theory originally developed by Boussinesq [1877] has been studied and presented in more usableform by several researchers. Wavelength is given by

FIGURE 87.1

Coastal engineering (shallow water).

FIGURE 87.2

Ocean engineering (deep water).

Wave Phenomena

Characteristics DesignValues

Sediment Processes

Onshore-Offshore

Littoral

Navigation Channels

Design Construction Maintenance ContaminatedSedimentRemoval

Dredging Dredging Dredging Dredging Dredging Dredging

Coastal Structures

Seawalls Groins Breakwater

ShoreConnected

Detached

Marine Foundation

Shallow Deep

Oil Spills

Containment Removal

Ports & Harbors

Design Construction Maintenance ContaminatedSedimentRemoval

Wave Phenomena

Characteristics Design Values

Offshore Pipelines

Stability

Offshore Structures

Floating Fixed Tension

DynamicPositioning

NavalArchitecture

StructuralAnalysis

PileDriving

L T gh CT= =

LgT h

L= Ê

ËÁˆ¯

2

2

2

pp

tanh

LgT

C To o= =2

2p


Shallow Water and Deep Water Engineering

87

-3

(87.4)

and wave period by

(87.5)

FIGURE 87.3

Regions of validity for various wave theories (

Source:

Le Méhauté, B. 1969.

An Introduction to Hydro-dynamics and Water Waves,

Report No. ERL 118-POL3-1&2. U.S. Department of Commerce, Environmental ScienceServices Administration, Washington, DC.)

Shallow water

dL

= 0.040

= 0.00155d

gT2

dgT2

= 0.0792d

gT2

dL

= 0.500

Transitional water Deep water

Stokes’ 3rd order

Linear (Airy) Theory

Str

eam

Fun

ctio

n V

0.0004 0.001 0.002 0.004 0.006 0.01 0.02 0.04 0.06 0.1 0.2 0.3 0.4

StreamFunction

V

Croidal Theory

Stokes’ 2nd order

= 0.14H0

L0

BREAKING

Break

ing lim

it (Soli

tary w

ave t

heor

y

Hd

= 0.

78)

−

NONBREAKING

H = HB

4

Stokes’ 4th order

~~ 26 L2H

d3

Ld

HkK k= 16

3

3

( )

Tg

h

y

H

h

y

kK k

H

y k

E k

K k

t

t

t

=+ -

ÊËÁ

ˆ¯

È

Î

ÍÍÍÍÍ

˘

˚

˙˙˙˙˙

16

31

1

22

( )

( )

( )


87

-4

The Engineering Handbook, Second Edition

where

y

t

=

distance from the bottom to the wave trough;

k

=

modulus of the elliptic integrals;

K

(

k

)

=

complete elliptic integral of the first kind; and

E

(

k

)

=

complete elliptic integral of the second kind.Cnoidal waves are periodic and of permanent form; thus

L

=

CT

.

Stream Function

Stream function was developed by Dean [1977] and is of analytical form with the wavelength

L

, coeffi-cients

X

(

n

), and the value of stream function on the free surface

y

h

determined numerically. Theexpression for the stream function,

y

, for a wave system rendered stationary by a reference frame movingwith the speed of the wave,

C

, is

(87.6)

with the coordinate

z

referenced to the mean water level;

U

is a uniform current.Stream function (Table 87.1) provides values of wavelength

L

¢

=

L

/

L

o

,

h¢

c

=

h

c

/

H

(water surface elevationabove mean water),

h¢

t

=

h

t

/

H

(wave surface elevation below mean water),

u

¢

c

(horizontal dimensionlessvelocity at the crest), (maximum dimensionless vertical velocity), (

F

¢

D

)

m

(maximum dimensionlessdrag force), and (

F

¢

I

)

m

(maximum dimensionless inertia force).

Stokian (Third Order)

Wavelength is given by

(87.7)

87.2 Sediment Processes

Along the coasts the ocean meets land. Waves, currents, tsunamis, and storms have been shaping thebeaches for many thousands of years. Beaches form the first defense against the waves and are constantlymoving on, off, and along the shore (littoral drift). Figure 87.4 provides a definition for terms describinga typical beach profile. The shoreline behavior is very complex and difficult to understand; it cannot beexpressed by equations because many of the processes are site specific. Researchers have, however,developed equations that should be summarized. There are two basic sediment movements:

1. On- and offshore2. Parallel to the shore and at an angle to the shore.

87.3 Beach Profile

Information on beach profiles is essential in designing structural modifications (such as seawalls, revet-ments, and breakwaters, both connected and detached, pipeline crossings, and beach replenishment.Bruun [1954] indicated that many beach profiles (Figure 87.5) can be represented by

h

(

x

)

=

Ax

2/3

where

h

is the water depth at a distance

x

offshore, and

A

is a dimensional scale parameter.Dean [1977] showed that

H

b

/

wT

is an important parameter distinguishing

barred

profiles fromnonbarred profiles (where

H

b

is breaking wave height,

w

is fall velocity of sediment in water, and

T

iswave period). This parameter is consistent with the following beach profiles in nature:

y p p= -ÊËÁ

ˆ¯

+ +ÈÎÍ

˘˚

ÊËÁ

ˆ¯

=ÂL

TU z X n

n

Lh z

nx

Ln

NN

( )sinh ( ) cos2 2

1

¢wm

LgT h

L

H

L

h L h L

d L= Ê

ËÁˆ¯

+ ÊËÁ

ˆ¯

+ +È

ÎÍ

˘

˚˙

ÏÌÔ

ÓÔ

¸˝ÔÔ

2 2 2

42

21

5 2 4 2 4

8 2pp p p p

ptanh

cosh( / ) cosh ( /

sinh ( / )


Shallow Water and Deep Water Engineering

87

-5

TABLE 87.1

Selected Summary of Tabulated Dimensionless Stream Function Quantities

Case

h

/

L

o

H

/

L

0

L

¢

(Bottom)

1-A 0.002 0.00039 0.120 0.910

-

0.090 49.68 13.31 10˚ 2574.0 815.6 10˚ 1.571-B 0.002 0.00078 0.128 0.938

-

0.062 47.32 15.57 10˚ 2774.6 1027.0 10˚ 1.451-C 0.002 0.00117 0.137 0.951

-

0.049 43.64 14.98 10˚ 2861.0 1043.5 10˚ 1.351-D 0.002 0.00156 0.146 0.959

-

0.041 40.02 13.63 10˚ 2985.6 1001.7 10˚ 1.292-A 0.005 0.00097 0.187 0.857

-

0.143 29.82 8.70 20˚ 907.0 327.1 20˚ 1.462-B 0.005 0.00195 0.199 0.904

-

0.096 29.08 9.29 10˚ 1007.9 407.1 10˚ 1.362-C 0.005 0.00293 0.211 0.927

-

0.073 26.71 9.85 10˚ 1060.7 465.7 10˚ 1.232-D 0.005 0.00388 0.223 0.944

-

0.056 23.98 9.47 10˚ 1128.4 465.2 10˚ 1.113-A 0.01 0.00195 0.260 0.799

-

0.201 19.83 6.22 30˚ 390.3 162.1 30˚ 1.343-B 0.01 0.00389 0.276 0.865

-

0.135 19.87 7.34 20˚ 457.3 209.0 20˚ 1.283-C 0.01 0.00582 0.292 0.898

-

0.102 18.47 6.98 20˚ 494.7 225.6 10˚ 1.163-D 0.01 0.00775 0.308 0.922

-

0.078 16.46 6.22 10˚ 535.4 242.4 10˚ 1.044-A 0.02 0.00390 0.359 0.722

-

0.278 12.82 4.50 30˚ 156.3 82.2 30˚ 1.184-B 0.02 0.00777 0.380 0.810

-

0.190 13.35 5.38 30˚ 197.6 103.4 20˚ 1.164-C 0.02 0.01168 0.401 0.858

-

0.142 12.58 5.29 20˚ 222.9 116.1 20˚ 1.064-D 0.02 0.01555 0.422 0.889

-0.111 11.29 4.99 20˚ 242.4 113.5 20˚ 0.975-A 0.05 0.00975 0.541 0.623 -0.377 7.20 3.44 50˚ 44.3 37.6 50˚ 0.935-B 0.05 0.01951 0.566 0.716 -0.284 7.66 3.69 50˚ 59.1 38.5 50˚ 0.945-C 0.05 0.02916 0.597 0.784 -0.216 7.41 3.63 30˚ 72.0 47.1 30˚ 0.885-D 0.05 0.03900 0.627 0.839 -0.161 6.47 3.16 30˚ 85.5 45.1 20˚ 0.766-A 0.10 0.0183 0.718 0.571 -0.429 4.88 3.16 75˚ 17.12 22.62 75˚ 0.736-B 0.10 0.0366 0.744 0.642 -0.358 5.09 3.07 50˚ 22.37 23.67 50˚ 0.736-C 0.10 0.0549 0.783 0.713 -0.287 5.00 2.98 50˚ 28.79 23.64 30˚ 0.706-D 0.10 0.0730 0.824 0.782 -0.218 4.43 2.44 50˚ 36.48 22.43 30˚ 0.627-A 0.20 0.0313 0.899 0.544 -0.456 3.63 3.05 75˚ 6.69 13.86 75˚ 0.467-B 0.20 0.0625 0.931 0.593 -0.407 3.64 2.93 75˚ 8.60 13.61 75˚ 0.477-C 0.20 0.0938 0.981 0.653 -0.347 3.54 2.49 50˚ 11.31 13.31 50˚ 0.477-D 0.20 0.1245 1.035 0.724 -0.276 3.16 2.14 50˚ 15.16 11.68 50˚ 0.448-A 0.50 0.0420 1.013 0.534 -0.466 3.11 2.99 75˚ 2.09 6.20 75˚ 0.0908-B 0.50 0.0840 1.059 0.570 -0.430 3.01 2.85 75˚ 2.71 6.21 75˚ 0.1018-C 0.50 0.1260 1.125 0.611 -0.389 2.86 2.62 75˚ 3.53 5.96 75˚ 0.1168-D 0.50 0.1681 1.194 0.677 -0.323 2.57 1.94 50˚ 4.96 5.36 50˚ 0.1209-A 1.00 0.0427 1.017 0.534 -0.466 3.09 2.99 75˚ 1.025 3.116 75˚ 0.0049-B 1.00 0.0852 1.065 0.569 -0.431 2.98 2.85 75˚ 1.329 3.126 75˚ 0.0059-C 1.00 0.1280 1.133 0.609 -0.391 2.83 2.62 75˚ 1.720 3.011 75˚ 0.0089-D 1.00 0.1697 1.211 0.661 -0.339 2.60 1.99 75˚ 2.303 2.836 50˚ 0.00910-A 2.00 0.0426 1.018 0.533 -0.467 3.09 2.99 75˚ 0.513 1.558 75˚ -0.00110-B 2.00 0.0852 1.065 0.569 -0.431 2.98 2.85 75˚ 0.664 1.563 75˚ 0.00010-C 2.00 0.1275 1.134 0.608 -0.392 2.83 2.63 75˚ 0.860 1.510 75˚ -0.00110-D 2.00 0.1704 1.222 0.657 -0.343 2.62 2.04 75˚ 1.137 1.479 50˚ 0.0000

Notes: (1) Except where obvious or noted otherwise, dimensionless quantities are presented for mean water elevation. (2)The maximum dimensionless drag and inertial forces apply for a piling extending through the entire water column. (3)Subscripts m, c, and t denote “maximum,” “crest,” and “trough,” respectively.

Source: Dean, R. G. 1991. Beach profiles. In Handbook of Coastal and Ocean Engineering, Volume 2, ed. J. B. Herbich. Gulf,Houston. Copyright 1990 by Gulf Publishing Company, Houston. Used with permission. All rights reserved.

¢hc ¢ht ¢uc ¢w m* q( )*¢w m ( )¢FD m ( )*¢FI m q( )*¢FI m

¢pDc


87-6 The Engineering Handbook, Second Edition

When , one can expect bar formation. (87.8a)

When , a monotonic profile can be expected. (87.8b)

Later, on the basis of large laboratory data, Kriebel et al. [1986] found the value of 2.3 rather than 0.85in Equation (87.8a) and Equation (87.8b).

87.4 Longshore Sediment Transport

The longshore transport (Q) is the volumetric rate of sand movement parallel to the shoreline. Muchlongshore transport occurs in the surf zone and is caused by the approach of waves at an angle to theshoreline.

FIGURE 87.4 Visual definition of terms describing a typical beach profile. (Source: Department of the Army. 1987.Shore Protection Manual, vols. I and II. Department of the Army, Corps of Engineers, Coastal Engineering ResearchCenter, Waterways Experiment Station, Vicksburg, MS.)

Milder slope profiles

High waves

Short periods

Small sediment diameter

Ï

ÌÔÔ

ÓÔÔ

Steeper profiles

Low waves

Long periods

Large sediment diameter

Ï

ÌÔÔ

ÓÔÔ

H

wTb > 0 85.

H

wTb < 0 85.

Plunge point

High water level

Surf Zone

Breakers

Offshore

Nearshore zone(defines area of nearshore currents)

Inshore or shoreface(extends through breaker zone)

Beach or shore

Coastal area

Backshore Foreshore

Coast

Beach scarp

Crest of berm

Ordinary low water level

Bottom

Berms

luffor scarpment


Shallow Water and Deep Water Engineering 87-7

Longshore transport rate (Q, given in unit volume per second) is assumed to depend upon thelongshore component of wave energy flux, Pls (Department of the Army, 1984):

(87.9)

where K = dimensionless empirical coefficient (based on field measurements) = 0.39; rs = density ofsand; r = density of water; g = acceleration due to gravity; and a = ratio of the volume of solids to totalvolume, accounting for sand porosity = 0.6.

General Energy Flux Equation

The energy flux per unit length of wave crest or, equivalently, the rate at which wave energy is transmittedacross a plane of unit width perpendicular to the direction of wave advance, is

P = ECg (87.10)

where E is wave energy density and Cg is wave group speed. The wave energy density is calculated by

(87.11)

where r is mass density of water, g is acceleration of gravity, and H is wave height.If the wave crests make an angle a with the shoreline, the energy flux in the direction of wave advance

per unit length of beach is

(87.12)

The longshore component of wave energy flux is

(87.13)

FIGURE 87.5 Beach profile scale factor, A, versus sediment diameter, D, in relationship h = Ax2/3. (Source: Dean, R.G. 1991. Beach profiles. In Handbook of Coastal and Ocean Engineering, Volume 2, ed. J. B. Herbich. Gulf, Houston.Copyright 1990 by Gulf Publishing Company, Houston. Used with permission. All rights reserved.)

Suggested EmpiricalRelationship

From Hughes’Field Results

From Swart’s LaboratoryResults

From Individual Field Profiles Where a Range of Sand Sizes Was Given

0.010.01

0.1 1.0

1.0

0.10

10.0 100.0SEDIMENT SIZE, D (mm)

SE

DIM

EN

T S

CA

LE P

AR

AM

ET

ER

, A(m

1/3 )

QK

gP

sls=

-( )r r a

EgH= r 2

8

PgH

C gcos cosa r a=2

8

P PgH

Cl g= =cos sin cos sina a r a a2

8



or

(87.14)

Threshold of Sand Movement by Waves

The threshold of sand movement by wave action has been investigated by a number of researchers [e.g.,Tsuchiya, 1991]. Figure 87.6 shows the modified Shields diagram, where t*c = 1/eyi(Dv*), and yi(Dv*) isa function of sediment-fluid number only, plotted as a function of Dv*.

The empirical formula shown by dashed lines is as follows:

(87.15)

87.5 Coastal Structures

Wave forces act on coastal and offshore structures; the forces may be classified as due to non-breaking,breaking, and broken waves. Fixed coastal structures include:

1. Wall-type structures such as seawalls, bulkheads, revetments, and certain types of breakwaters2. Pile-supported structures such as piers and offshore platforms3. Rubble structures such as breakwaters, groins, and revetments

Seawalls

Forces due to nonbreaking waves may be calculated using Sainflou or Miche–Rundgren formulas.Employing the Miche–Rundgren formula, the pressure distribution is

FIGURE 87.6 Threshold of sand movement by waves with Shields, Sleath, and Tsuchiya empirical curves, as wellas the theoretical curve. (Source: Tsuchiya, Y. 1991. Threshold of sand movement. In Handbook of Coastal and OceanEngineering, Volume 2, ed. J. B. Herbich. Gulf, Houston. Copyright 1990 by Gulf Publishing Company, Houston.Used with permission. All rights reserved.)

21

2

2

4

4

4

8

8

6

6

10 2 4 86 102

10−1

10−22 4 86 103 2 4 86 104 2 4

Bagnold

Goddet

Manohar

Rance & WarrenTheoretical curves

Theoretical curve

TurbulentLaminar

Shields

Empirical formula

20010050

200

100d 0

/D = 50

Dν∗

τ *c

Pg

H Cl g= r a16

22 sin

t * *

*/

*

*/

*

*

.

.

.

.

c v

v v

v v

v

D

D D

D D

D

= £

= £ £

£ £

£

-

0 20 1

0 20 1 20

0 010 20 125

0 050 125

23

13

for

for

= for

= for



(87.16)

where c = wave reflection coefficient; g = unit weight of water; Hi = incident wave height; h = waterdepth; and L = wavelength.

Figure 87.7 shows the pressure distribution at a vertical wall at the crest and trough of a clapotis.Forces due to breaking waves may be estimated by Minikin and Goda methods. The Minikin method

described by the Department of the Army [1984] estimates the maximum pressure (assumed to act onthe SWL) to be:

(87.17)

where pm is the maximum dynamic pressure, Hb is the breaker height, ds is the depth at the toe of thewall, D is the depth one wavelength in front of the wall, and LD is the wavelength in water depth D. Thedistribution of dynamic pressure is shown in Figure 87.8. The pressure decreases parabolically from pm

at the WL to zero at a distance of Hb/2 above and below the SWL. The force represented by the areaunder the dynamic pressure distribution is

(87.18)

Goda’s method [1985] assumes a trapezoidal pressure distribution (Figure 87.9). The pressure extendsto a point measured from SWL at a distance given by h*:

h* = 0.75(1 + cos b)Hmax (87.19)

in which b denotes the angle between the direction of wave approach and a line normal to the breakwater.The wave pressure at the wall is given by

FIGURE 87.7 Pressure distributions for nonbreaking waves. (Source: Department of the Army. 1987. Shore ProtectionManual, vols. I and II. Department of the Army, Corps of Engineers, Coastal Engineering Research Center, WaterwaysExperiment Station, Vicksburg, MS.)

d

Fc

γh p1

Crest of Clapotis at Wall

h0

Actual PressureDistribution

Hydrostatic PressureDistribution

F1

γhp1

Trough of Clapotis of Wall

Actual PressureDistribution

Hydrostatic PressureDistribution

A A

SWL SWL

pH

h Li

1

1

2 2= +Ê

ËÁˆ¯

c gpcosh( / )

pH

L

d

DD dm

b

D

ss= +101g ( )

Rp H

mm b=3



(87.20)

(87.21)

(87.22)

in which

(87.23)

(87.24)

FIGURE 87.8 Minikin wave pressure diagram. (Source: Department of the Army. 1987. Shore Protection Manual,vols. I and II. Department of the Army, Corps of Engineers, Coastal Engineering Research Center, WaterwaysExperiment Station, Vicksburg, MS.)

FIGURE 87.9 Distribution of wave pressure on an upright section of a vertical breakwater. (Source: Goda, Y. 1990.Random wave interaction with structures. In Handbook of Coastal and Ocean Engineering, Volume 1, ed. J. B. Herbich.Gulf, Houston. Copyright 1990 by Gulf Publishing Company, Houston. Used with permission. All rights reserved.)

SWL

ds

pm

Hb

Dynamic ComponentHydrostatic Component

Combined Total

γ (ds +Hb 2

)

p1

pu

p2

p3

hc

η*

h

d h′Buoyancy

p H1 1 221

21= + +( cos )( cos ) maxb a a b g

pp

h L21

2=

cosh( / )p

p p3 3 1= a

a pp1

2

0 6 0 54

4= +

È

ÎÍ

˘

˚˙. .

/

sinh( / )

h L

h L

a 2

2

3

2=- Ê

ËÁˆ¯

È

ÎÍÍ

˘

˚˙˙

min ,max

max

h d

h

H

d

d

Hb

b



(87.25)

Breakwaters

Rubble-mound breakwaters are the oldest form of breakwaters, dating back to Roman times. The rubblemound is protected by larger rocks or artificial concrete units. This protective layer is usually referred toas armor or cover layer.

(87.26)

where W = weight in newtons or pounds of an individual armor unit in the primary cover layer; gr =unit weight (saturated surface dry) of armor unit in N/m3 or lb/ft3; Sr = specific gravity of armor unit,relative to the water at the structure (Sr = wr/ww); gw = unit weight of water: freshwater = 9800 N/m3 (62.4lb/ft3); seawater = 10,047 N/m3 (64.0 lb/ft3); q = angle of structure slope measured from horizontal indegrees; and KD = stability coefficient that varies primarily with the shape of the armor units, roughnessof the armor unit surface, sharpness of edges, and degree of interlocking obtained in placement.

Figure 87.10 presents the recommended three-layer section of a rubble-mound breakwater. Note thatunderlayer units are given in terms of W, the weight of armor units.

Automated coastal engineering system (ACES) describes the computer programs available for thedesign of breakwaters using Hudson and related equations.

Van der Meer [1987] developed stability formulas for plunging (breaking) waves and for surging(nonbreaking) waves. For plunging waves,

(87.27)

For surging waves,

(87.28)

whereHs = significant wave height at the toe of the structure

FIGURE 87.10 Rubble-mound section for wave exposure on both sides with moderate overtopping conditions.(Source: Department of the Army. 1987. Shore Protection Manual, vols. I and II. Department of the Army, Corps ofEngineers, Coastal Engineering Research Center, Waterways Experiment Station, Vicksburg, MS.)

Crest Width

Breakwater Crest

Max. Design SWL

SWL (Minimum) W

W/10

W/10 W/200 to W/4000 −1.3 H

SWL (Minimum)

3r2r

Recommended Three-layer Section

ap3 1 1

1

2= - ¢ -

È

ÎÍ

˘

˚˙

h

h h Lcosh( / )

WH

K Sr

D r

=-

gq

3

31( ) cot

H D P S Ns n z/ * . ( / ). .D 500 18 0 26 2x =

H D P S Ns n zp/ . ( / ) cot. .D 50

0 13 0 21 0= - a x



xz = surf similarity parameter,

Tz = zero up-crossing wave perioda = slope angleD = relative mass density of the stone, D = ra/(r - 1)

ra = mass density of the stoner = mass density of water

Dn50 = nominal diameter of the stone, Dn50 = (W50/ra)1/3

W50 = 50% value (median) of the mass distribution curveP = permeability coefficient of the structureS = damage level, A = erosion area in a cross-sectionN = number of waves (storm duration)

Influence of breakwater slope angle is depicted in Figure 87.11.

87.6 Navigational Channels

The development of very large commercial craft (VLCC) and ultralarge commercial craft (ULCC) forcedmany government planners and port managers to evaluate existing channels. Navigational channels allowlarge vessels to reach harbors. Of paramount design consideration is the safety of vessels in a channel,particularly when passing [Herbich, 1992].

Vessel behavior in channels is a function of bottom suction, bank suction, interference of passing ships,waves, winds, and currents. Most major maritime countries have criteria regarding the depth and widthof channels. The international commission ICORELS (sponsored by the Permanent International Asso-ciation of Navigation Congresses — PIANC) recommends that general criteria for gross underkeelclearances can be given for drawing up preliminary plans:

FIGURE 87.11 Influence of slope angle. (Source: Van der Meer, J. W. 1990. Rubble mounds — Recent modifications.In Handbook of Coastal and Ocean Engineering, Volume 1, ed. J. B. Herbich. Gulf, Houston, TX. Copyright 1990 byGulf Publishing Company, Houston, TX. Used with permission. All rights reserved.)

0 1 2 3 4 5 6 872

3

4

5

6

7

8

cot α = 6

cot α = 4cot α = 3 cot α = 2

cot α = 1.5

PLUNGING WAVES SURGING WAVES

Wav

e he

ight

Hs

(m)

ξz = cot α/ Hs/Lz

Dn50 = 1 m ∆ = 1.6 S = 5 P = 0.5 N = 3000

x a

pz

s zH gT

tan

/2 2

S A Dn= / 502



• Open sea area. When exposed to strong and long stern or quarter swells where speed may be high,the gross underkeel clearance should be about 20% of the maximum draft of the large ships tobe received.

• Waiting area. When exposed to strong or long swells, the gross underkeel clearance should beabout 15% of the draft.

• Channel. For sections exposed to long swells, the gross underkeel clearance should be about 15%of the draft.

The Engineering Manual [U.S. Army Corps of Engineers, 1983] provides guidance for the layout anddesign of deep-draft navigation channels. Table 87.2 provides the general criteria for channel widths.

87.7 Marine Foundations

Design of marine foundations is an integral part of any design of marine structures. The design criteriarequire a thorough understanding of marine geology; geotechnical properties of sediments at a givenlocation; and wind, wave, currents, tides, and surges during maximum storm conditions. In the arcticareas information on fast ice and pack ice is required for the design of offshore structures (on artificialislands) and offshore pipelines.

A number of soil engineering parameters are required, as shown in Table 87.3. Many of the propertiesmay be obtained employing standard geotechnical methods. Geotechnical surveys and mapping of seabedcharacteristics have reached a high degree of sophistication. High-resolution geophysical surveys deter-mine water depth, seafloor imagery, and vertical profiles. Bottom-mapping systems include multibeambathymetry, sea beam, side-scan sonars, and subbottom profilers (including shallow, medium, and deeppenetration types).

The geotechnical investigation is designed to include sediment stratigraphy; sediment types; andsediment properties, including density, strength, and deformational characteristics. Deployment systemsemployed for sampling in situ include self-contained units, drilling rigs, and submersibles. (Figure 87.12shows the deployment systems.)

There are many in situ testing devices; these include the vane shear test, cone penetrometer test, pressuremeter, shear vane velocity tools, temperature probes, natural gamma logger, and so forth [Young, 1991].

87.8 Oil Spills

The best method of controlling oil pollution is to prevent oil spills in the first place. This may includesuch techniques as rapid removal of oil from stricken tankers, continuous monitoring of oil wells, killingwild wells at sea, and containing oil spills under the water surface. Spilled oil, being lighter than water,floats on the water surface and spreads laterally. As oil is spilled, several regimes are generally assumed:

TABLE 87.2 General Criteria for Channel Widths

Location

Minimum Channel Width in Percent of Beam

Vessel Controllability Channels withYawing ForcesVery Good Good Poor

Maneuvering lane, straight channel 160 180 200 Judgmenta

Bend, 26˚ turn 325 370 415 Judgmenta

Bend, 40˚ turn 385 440 490 Judgmenta

Ship clearance 80 80 80 100 but not lessthan 100 ft

Bank clearance 60 60 plus 60 plus 150

a Judgment will have to be based on local conditions at each project.Source: U.S. Army Corps of Engineers. 1983. Engineering Manual: Hydraulic Design of Deep

Draft Navigation Projects, EM 1110-2-1613. U.S. Army Corps of Engineers, Washington, DC.


87-14T

he E

ngin

eering H

and

book

, Second

Ed

ition

TABLE 87.3 Soil Engineering Parameters Normally Required for Categories of Geotechnical Engineering Applications

ApplicationSoil

ClassificationGrainSize

AtterbergLimits

Strength Properties Common Properties

Subbottom Depthof Survey

Clay Sand Clay Sand

Su, St f¢ f or Su Cv, k Cc Cc

Shallow foundation Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 1.5 to 2 ¥ foundation widthDeadweight anchors Yes No No Yes Yes Yes No No No No 1.5 to 2 ¥ anchor widthDeep pile foundations Yes Yes Yes Yes Yes Yes No Yes Yes No 1 to 1.5 ¥ pile group width, below

individual pile tipsPile anchors Yes Yes Yes Yes Yes Yes No No No No To depth of pile anchorDirect-embedment anchors Yes Yes No Yes Yes Yes Yes Yes No No To expected penetration of anchor,

maximum 33 to 50 ft clay; 13 to 33 ft sandDrag anchors Yes Yes No Yes No No No No No No 33 to 50 ft clay; 10 to ft sand for large

anchorsPenetration Yes Yes No Yes No Yes Yes No No No 33 to 50 ft clay; 13 to 33 ft sandBreakout Yes Yes Yes Yes Yes Yes Yes No No No 1 ¥ object width plus embedment depthScour Yes Yes No Yes No No No No No No 3.3 to ft; related to object size and

water motionSlope stability Yes Yes Yes Yes Yes Yes No No No No 33 to 100 ft; more on rare occasions

Note: Su = udrained shear strength; St = sensitivity; = drained cohesion intercept; f¢ = drained friction angle; f = undrained friction angle for sands rapidly sheared; Cv =coefficient of consolidation; k = permeability; Cc = compression index.

Source: Marine Board, National Research Council. 1989. Our Seabed Frontier — Challenges and Choices, National Academy Press, Washington, DC.

c , ¢f

16 12

16 12

c

1586_book.fm Page 14 M

onday, May 10, 2004 12:54 PM


gravity-inertial, gravity-viscous, and surface tension. In the early stage, generally less than 1 h, the gravity-inertial regime, or inertial spread, dominates and is described by

(87.29)

where R = radius of the oil slick; k4 = nondimensional coefficient experimentally determined to be 1.14;D = the ratio of the absolute difference between the densities of sea water and the oil to that of seawater;g = force of gravity; L = original volume of oil spilled; and t = time.

When the oil film thickness becomes equal to the viscous layer in the water, a transition occurs fromthe gravity-inertial regime to the gravity-viscous regime. This viscous spreading is described by

(87.30)

where k5 is the nondimensional coefficient determined to be about 1.45, v is the kinematic viscosity ofwater, D is the ratio of the difference between density of seawater and oil, L is the original volume ofspilled oil, and t is the time.

FIGURE 87.12 Deployment systems used for sampling, in situ, and experimental testings. (Source: Marine Board,National Research Council. 1989. Our Seabed Frontier — Challenges and Choices, National Academy Press, Washing-ton, DC.)

SUBMERSIBLE

SingleUmbilical

Small Vessel

ThrustingPlatform

In Situ Tool/Sampler

Sensor

Testrod

Fixed CarrierTool

StabilizingMass

Drill String

Umbilical

Drill Ship

DRILLING RIG

SELF-CONTAINED UNIT

In SituTool/Sampler

R k gLt= 42 1 4( ) /D

Radius of oil slock = = 5R kgL t

v

D 2 3 2

1 2

16/

/

/ÊËÁ

ˆ¯



The last phase, the surface tension regime, occurs when the oil film thickness drops below a criticallevel, which is a function of the net surface tension, the mass densities of the oil and the water, and theforce of gravity. The surface tension spread is described by

(87.31)

where k6 = 2.30, experimentally determined; s = surface tension; and r = density of water.For large spills, on the order of 10,000 tons, inertial and viscous spreading will dominate for about

the first week, with the surface tension spread controlling thereafter.Although the exact mechanisms that cause the termination of spreading are unknown, the terminal

areas of several oil slicks have been observed and used to determine an analytical relationship for themaximum area of a given oil spill based on the properties of the oil. This is described by

(87.32)

where Ka = undetermined constant or order unit; V = volume of oil that can be dissolved in this layer;D = diffusivity; and s = solubility of the significant oil fractions in the water.

In addition, the area covered by the oil slick is not allowed to exceed AT ; therefore, spreading isterminated at the time

(87.33)

Oil may be set up by wind and current against a barrier; any containment device must take the setupestimates into account. There are a number of containment devices (barriers) that prevent oil fromspreading. Most mechanical-type oil containment barriers fail in wave heights greater than 2 ft, whenthe wave steepness ratio is greater than 0.08, and in currents normal to the barrier greater than about0.7 knots.

Oil may also be removed from the water surface by skimming devices. Most mechanical skimmingdevices have only been able to work in waves less than 2 to 3 ft in height, in moderate currents.

87.9 Offshore Structures

Many types of offshore structures have been developed since 1947, when the first steel structure wasinstalled in 18 feet of water. Since that time over 4100 template-platforms have been constructed on theU.S. continental shelf in water depths less than 600 feet (Figure 87.13).

Deep-water marine structures include gravity platforms, fixed platforms, guyed tower, tension-legplatform, and a buoyant compliant tower (Figure 87.14).

Wave forces on certain types of offshore platforms are computed by the Morrison equation, which iswritten as the sum of two individual forces, inertia and drag. The equation may be written as

(87.34)

The force, f, as a function of time, t, is written as a function of the horizontal water particle velocity,u(t), and the horizontal water particle acceleration, , at the axis of the cylinder, and is dependent on

R kt

v=

ÊËÁ

ˆ¯6

2 3

2

1 4sr

/

A KV

vD sT a=ÊËÁ

ˆ¯

sr

2 6

2 3 6

18/

tV

s

v

D

K

ka= Ê

ËÁˆ¯

ÊËÁ

ˆ¯

Ê

ËÁˆ

¯r

s p

12 14

62

23/ / /

f t C D u t C D u t u tM D( ) ˙( ) ( ) ( )= +r p r4

1

22

˙( )u t



FIGURE 87.13 Template-type pile foundation structure. (Source: Young, A. G. 1991. Marine foundation studies.In Handbook of Coastal and Ocean Engineering, Volume 2, ed. J. B. Herbich. Gulf, Houston. Copyright 1990 by GulfPublishing Company, Houston. Used with permission. All rights reserved.)

FIGURE 87.14 Range of water depths for various types of deep-water marine structures. (Source: Marine Board,National Research Council. 1989. Our Seabed Frontier — Challenges and Choices, National Academy Press, Washing-ton, DC.)

1:7 Batter

8 Main Piles–1.2 m diameter–Welded at top–91.5 m penet.

4 Skirt Piles–grouted in

sleeves

12–Well Structure

Template Weight 19.5 mn

El. − 85 m

Pile LoadsUlt. Axial Capacity

18 mn

Design Lat. Load1 mn

El. +5 m

00

100

200

300

400

500

6002000

1500

1000

500

FLOATINGPLATFORM

TETHERS

SEABEDANCHORPILES

GUY-LINES

WATERDEPTH

FEET METERS

GRAVITYPLATFORM

0–700 FEET(0–200 METERS)

FIXEDPLATFORM

0–1000 FEET(0–300 METERS)

GUYEDTOWER

700–2000 FEET(200–600 METERS)

TENSION-LEGPLATFORM

1000–3000 FEET(300–900 METERS)

BUOYANTCOMPLIANT TOWER

1000–2500 FEET(300–750 METERS)



the water density, r. The quantities CM and CD are defined as the inertia (or mass) coefficient and thedrag coefficient, respectively.

The design and dynamic analysis of offshore platforms, which include jacket structures, topsidestructures, pile foundations, and dynamic analysis, may be found in Hsu [1991]; discussion of waveforces is given in Chakrabarti [1991].

Defining Terms

Armor unit — A relatively large quarry stone or concrete shape that is selected to fit specified geometriccharacteristics and density. It is usually of nearly uniform size and usually large enough torequire individual placement. In normal cases it is used as primary wave protection and isplaced in thicknesses of at least two units.

Artificial nourishment — The process of replenishing a beach with material (usually sand) obtainedfrom another location.

Attenuation — (1) A lessening of the amplitude of a wave with distance from the origin. (2) The decreaseof water-particle motion with increasing depth. Particle motion resulting from surface oscilla-tory waves attenuates rapidly with depth and practically disappears at a depth equal to a surfacewavelength.

Bar — A submerged or emerged embankment of sand, gravel, or other unconsolidated material built onthe sea floor in shallow water by waves and currents.

Diffraction — The phenomenon by which energy is transmitted laterally along a wave crest. When apart of a train of waves is interrupted by a barrier, such as a breakwater, the effect of diffractionis manifested by propagation of waves into the sheltered region within the barrier’s geometricshadow.

Dunes — (1) Ridges or mounds of loose, wind-blown material, usually sand. (2) Bed forms smaller thanbars but larger than ripples that are out of phase with any water-surface gravity waves associatedwith them.

Ebb current — The tidal current away from shore or down a tidal stream, usually associated with thedecrease in height of the tide.

Fetch — The area in which seas are generated by a wind having a fairly constant direction and speed.Sometimes used synonymously with fetch length or generating area.

Flood current — The tidal current toward shore or up a tidal stream, usually associated with an increasein the height of the tide.

Groin — A shore protection structure built (usually perpendicular to the shoreline) to trap littoral driftor retard erosion of the shore.

Harbor oscillation (harbor surging) — The nontidal vertical water movement in a harbor or bay. Thevertical motions are usually low, but when oscillations are excited by a tsunami or storm surge,they may be quite large. Variable winds, air oscillations, or surf beat also may cause oscillations.See seiche.

Hurricane — An intense tropical cyclone in which winds tend to spiral inward toward a core of lowpressure, with maximum surface wind velocities that equal or exceed 33.5 meters per second(75 mph or 65 knots) for several minutes or longer at some points. Tropical storm is the termapplied if maximum winds are less than 33.5 meters per second.

Mean high water (MHW) — The average height of the high waters over a 19-year period. For shorterperiods of observations, corrections are applied to eliminate known variations and reduce theresults to the equivalent of a mean 19-year value.

Probable maximum water level — A hypothetical water level (exclusive of wave run-up from normalwind-generated waves) that might result from the most severe combination of hydrometeoro-logical, geoseismic, and other geophysical factors and that is considered reasonably possible inthe region involved, with each of these factors considered as affecting the locality in a maximummanner. This level represents the physical response of a body of water to maximum applied



phenomena such as hurricanes, moving squall lines, other cyclonic meteorological events,tsunamis, and astronomical tide, combined with maximum probable ambient hydrologicalconditions such as wave setup, rainfall, runoff, and river flow. It is a water level with virtuallyno risk of being exceeded.

Refraction — (1) The process by which the direction of a wave moving in shallow water at an angle tothe contours is changed. The part of the wave advancing in shallower water moves more slowlythan that part still advancing in deeper water, causing the wave crest to bend toward alignmentwith the underwater contours. (2) The bending of wave crests by currents.

Scour — Removal of underwater material by waves and currents, especially at the base or toe of a shorestructure.

Seawall — A structure separating land and water areas, primarily designed to prevent erosion and otherdamage due to wave action.

Seiche — (1) A standing wave oscillation of an enclosed water body that continues, pendulum fashion,after the cessation of the originating force, which may have been either seismic or atmospheric.(2) An oscillation of a fluid body in response to a disturbing force having the same frequencyas the natural frequency of the fluid system. Tides are now considered to be seiches inducedprimarily by the periodic forces caused by the sun and moon.

Significant wave — A statistical term relating to the one-third highest waves of a given wave group anddefined by the average of their heights and periods. The composition of the higher wavesdepends upon the extent to which the lower wave are considered.

Wave spectrum — In ocean wave studies, a graph, table, or mathematical equation showing the distri-bution of wave energy as a function of wave frequency. The spectrum may be based on obser-vations or theoretical considerations. Several forms of graphical display are widely used.

References

Boussinesq, J. 1877. Essai sur la theorie des eaux courantes, Mem. divers Savants a L’Academie des Science, No. 32:56.

Bruun, P. 1954. Coast Erosion and the Development of Beach Profiles, Tech. Memo. No. 44, 1954. BeachErosion Board, U.S. Army Corps of Engineers.

Chakrabarti, S. K. 1991. Wave forces on offshore structures. In Handbook of Coastal and Ocean Engineer-ing, Volume 2, ed. J. B. Herbich. Gulf Publishing Co., Houston.

Dean, R. G. 1977. Equilibrium Beach Profiles: U.S. Atlantic and Gulf Coasts, Ocean Engineering T.R. No.12. Department of Civil Engineering, University of Delaware, Newark, DE.

Dean, R. G. 1990. Stream function wave theory and applications. In Handbook of Coastal and OceanEngineering, Volume 1, ed. J. B. Herbich. Gulf Publishing Co., Houston.

Dean, R. G. 1991. Beach profiles. In Handbook of Coastal and Ocean Engineering, Volume 2, ed. J. B.Herbich. Gulf Publishing Co., Houston.

Department of the Army. 1987. Shore Protection Manual, vols. I and II. Department of the Army, Corpsof Engineers, Coastal Engineering Research Center, Waterways Experiment Station, Vicksburg, MS.

Department of the Army. 1992. Automated Coastal Engineering System, Department of the Army, Corpsof Engineers, Coastal Engineering Research Center, Waterways Experiment Station, Vicksburg, MS.

Goda, Y. 1985. Random Seas and Design of Maritime Structures, Tokyo University Press, Tokyo,Goda, Y. 1990. Random wave interaction with structures. In Handbook of Coastal and Ocean Engineering,

Volume 1, ed. J. B. Herbich. Gulf Publishing Co., Houston.Herbich, J. B. (Ed.) 1990 (vol. 1), 1991 (vol. 2), 1992 (vol. 3). Handbook of Coastal and Ocean Engineering,

Gulf Publishing Co., Houston.Hsu, T. H. 1991. Design and dynamic analysis of offshore platforms. In Handbook of Coastal and Ocean

Engineering, Volume 2, ed. J. B. Herbich. Gulf Publishing Co., Houston.Kriebel, D. L., Dally, W. R., and Dean, R. G. 1986. Undistorted Froude Number for Surf Zone Sediment

Transport, Proc. 20th Coastal Engineering Conference, ASCE. pp. 1296–1310.



Le Méhauté, B. 1969. An Introduction to Hydrodynamics and Water Waves, Report No. ERL 118-POL3-1&2. U.S. Department of Commerce, Environmental Science Services Administration, Washington,DC.

Tsuchiya, Y. 1991. Threshold of sand movement. In Handbook of Coastal and Ocean Engineering, Volume2, ed. J. B. Herbich. Gulf Publishing Co., Houston.

U.S. Army Corps of Engineers. 1983. Engineering Manual: Hydraulic Design of Deep Draft NavigationProjects, EM 1110-2-1613. U.S. Army Corps of Engineers, Washington, DC.

Van der Meer, J. W. 1987. Stability of breakwater armor layers — Design formula. J. Coastal Engin.11(3):219–239.

Van der Meer, J. W. 1990. Rubble mounds — Recent modifications. In Handbook of Coastal and OceanEngineering, Volume 1, ed. J. B. Herbich. Gulf Publishing Co., Houston.

Young, A. G. 1991. Marine foundation studies. In Handbook of Coastal and Ocean Engineering, Volume2, ed. J. B. Herbich. Gulf Publishing Co., Houston, TX.

Further Information

ASCE Journal of Waterway, Port, Coastal and Ocean Engineering: Published bimonthly by the AmericanSociety of Civil Engineers. Reports advances in coastal and ocean engineering.

ASCE specialty conference proceedings: Published by the American Society of Civil Engineers. Reportadvances in coastal and ocean engineering.

PIANC Bulletin: Published quarterly by the Permanent International Association of Navigation Con-gresses, Brussels, Belgium. Reports case studies.

Coastal Engineering Research Center (Technical reports, contract reports, miscellaneous papers): Pub-lished by the Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS.

Sea Technology: Published monthly by Compass Publications, Inc., Arlington, VA.IEEE proceedings of ocean conferences: Published by the Institute of Electrical and Electronics Engineers.

Report advances in ocean engineering.Offshore Technology Conference Preprints: Published by the Offshore Technology Conference, Dallas,

TX. Report annually on topics in ocean engineering.Marine Board, National Research Council reports: Published by the National Academy Press, Washington,

DC.American Gas Association project reports: Published by the American Gas Association, Arlington, VA.American Petroleum Institute standards: Published by the American Petroleum Institute, Dallas.Marine Technology Society conference proceedings: Published by the Marine Technology Society, Hous-

ton.World Dredging, Mining & Construction: Published monthly by Wodcon Association, Irvine, CA.Terra et Aqua: Published by the International Association of Dredging Companies, The Hague, the

Netherlands.Center for Dredging Studies abstracts: Published by the Center for Dredging Studies, Texas A&M Univer-

sity, College Station, TX.Komar, P. D. 1983. Handbook of Coastal Processes and Erosion, CRC Press, Boca Raton, FL. A series of

papers on coastal processes, beach erosion, and replenishment.Bruun, P. 1989–90. Port Engineering, vols. 1 and 2, 4th ed. Gulf, Houston. A comprehensive treatment

on port and harbor design.International Dredging Review: Bimonthly, Fort Collins, CO.Technical Standards for Port and Harbour Facilities in Japan, 1980: Published by the Overseas Coastal Area

Development Institute of Japan, 3-2-4 Kasumigaseki, Chiyoda-ku, Tokyo, Japan.Herbich, J. B., Schiller, R. E., Jr., Watanabe, R. K., and Dunlap, W. A. 1987. Seafloor Scour. Marcel Dekker,

New York. Design guidelines for ocean-founded structures.Grace, R. A. 1978. Marine Outfalls Systems, Prentice Hall, Englewood Cliffs, NJ. A comprehensive treat-

ment of marine outfalls.



Herbich, J. B. 1981. Offshore Pipelines Design Elements, Marcel Dekker, New York. Information relatingto design of offshore pipelines.

Herbich, J. B. 1992. Handbook of Dredging Engineering, McGraw-Hill, New York. A comprehensive treatiseon the subject of dredging engineering.


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