TA 7 o. 1 Vol. H95 .W34 1945 ox TD O HRO DESIGN HARBOR OF STUDY U. S. WATERWAYS EXPERIM ENT STATION STATION ENT EXPERIM WATERWAYS S. U. HO W, H TENG-KAO CHU HWA, CHAO IKBR, ISSISSIPPI M VICKSBURG, S ZAN-ZIANG HSU ERDCD BY REPRODUCED s c ^ / p / l * a f OPLD BY COMPILED UME I E M LU O V 1945 Y L U J / f o AND WHS TR m d# $ # id ü CTT o * □ B R A C T

MAY 22 1968

Bureau of Reclamation Denver, Colorado BUREAU OF RECLAMATION DENVER LIBRARY ^ A 92098412 ^ ^ .X WAR DEPARTMENT CORPS OF ENGINEERS MISSISSIPPI RIVER COMMISSION U. S. WATERWAYS EXPERIMENT STATION VICKSBURG, MISSISSIPPI

FOREWORD

The principles of harbor design are an important, yet often not clearly understood part of the present accumulation of engineering knowledge. This general lack of under­ standing is due in part to the extreme complexity of the natural phenomena involved in the design of harbors and harbor protective works, and in part to inadequate dissemination of technical literature pertaining to the effects of various harbor designs on wave and surge action. This report was prepared with the hope that it might assist in alleviating to some extent the latter deficiency. Contained herein is a digest of the material compiled over a period of years for use as reference by engineers of the U. S. Waterways Experiment Station working on designs for harbor improvement structures. The report was prepared by Messrs. Chao Hwa, Chu Teng-Kao, and Hsu Zan Ziang, three Chinese harbor engineers, while on a visit to the Lower Mississippi Valley Division office of the U. S. Engineer Department. Mr. Robert Y. Hudson, Engineer in charge of the Wave Action Section of the U. S. Water­ ways Experiment Station, supervised the compilation and furnished the list of references used. The Office, Chief of Engineers, authorized reproduction of the report in its exact form as a publication of general interest and value to the Department-at-Large. Per­ mission to reproduce the report was granted by the International Training Administra­ tion, Washington, D. C., and the Chinese Supply Commission. Data and opinions set forth, and methods described in the report do not necessarily carry the official sanction of the War Department. STUDY OF HARBOR DESIGN

Compiled By Messrs. Chao Hwa, Chu Teng-Kao and Hsu Zan-Ziang

From Reference Material

in the

Engineer Department Research Center Library

U. S. Waterways Experiment Station

Vicksburg, Mississippi

United States of America

Volume I

July 1945 STUDY OF HARBOUR DESIGN

CONTENTS

Foreward i 2£2. Preface ^ Chapter I General Harbour Design 1 . Introduction i 2 • Definition and Types...... ••••••••••••••••• 2 3 * General P rinciples of Harbour D e s i g n ...... • • • • • • • . .. . 3 4 * Harbour Capacity## # # 0 # # # 5 * Site Selection...... ^ 6. General Remarks on Harbour Design D a t a 10 Wind - Waves - Littoral Currents and Drifts - Tides - Seiches - River Flow 7 . Arrangement of Harbour W o r k s . . 21 8. Breakwater A l i g n m e n t #0### 25 9 # General Features of Breakwater with Respect to Their Positions...... 29 10. Harbours at Lagoons • • • • • • • • • ...... 32 11 . Harbour Exposure ...... 33 12 . General Remarks on Entrance ...... 3*7 13 . Entrance Width and Channel Depth Ifi H4.. General Harbour Layout and Other F a c i lit ie s ...... 50 15. Conclusion ...... 53

Bibliography ...... 55

Chapter II Study on Wave Action 1. Introduction ...... ••••♦ ...... 1 2 . History of Wave Study 2 3 . Wave Formation and its Relation with Fetch and Wind Velocity...... ••••••••••• 4 > Theoretical Considerations of Wave M otion...... j 5 . Relationship between Wave Characteristics at Various ...... 6. Wave Action in Relation to Harbour Protection Works . . . . . 19 7 . Calculation of Wave Pressure Against Maritime Structures 30 8. Measurement of Wave C h a ra c te ris tic s ...... 36 Nomenclature ...... ¡g

Bibliography ...... ^5 Chapter III Breakwaters* Design and Construction !• General Description,...... 1 2, Vertical-Wall Breakwater ...... ,,••»,,»•• 3 Construction - Design - Example 3* Underwater F o u n d a tio n s ...... 16 Wave Pressure on a Vertical-Wall Breakwater,,••••*,,•»• 18 5. Rubble-Mound Breakwater,...... 21 Core of Nucleus - Principle Covering - Secondary Covering - Ridge or Parapet - Example 6. Experience in Breakwater Construction (with Experimental Study) 36 Chapter IV Design* Construction and Operation of Harbour Mbdels 1, General Design.• 1 2, Similitude of Harbour Models,• I4. 3* Construction of Harbour Mode Is ...... 11 Ij., Model Appurtenances, llj. 3» Operation of M o d e l s , • 18 6» Solution of Hiavw lotion Problems,23 PREFACE

It is needless to say th^t this special branch of knowledge^

harbour engineering, is still in its cradle stage. Due to the most

complexity of the natural phenomena, no one at present can design a

harbour in such a manner -wholly based on theoretical way.

i«e 'write this report 'with the only purpose to try through this

branch of knowledge to make a reference for our own. We, of course, are

far from a position to present any new ideas, either practical or theo­

retical, on this particular subject.

The report consists of four parts. The first part gives a general

idea about harbour design, such as selection of harbour site and arrange­ ment of harbour works. Many existed harbours of various types are discussed

here for illustration. The second part deals with the theoretical considera­

tions of wave action; recognized theories and formulas are introduced.

The third part gives the methods of design and construction of breakwaters which play a very important part in the whole construction works of a harbour. The fourth part gives a brief discussion of harbour model studies.

The sourcesfrom which the subject matter has been collected dre listed in the bibliography.

Here we wish to express our hearty thanks to Brig. General M. C.

Tyler, President of the Mississippi River Commission, and Mr. G. H.

Matthes, Director of. the U. S, Yfeterways Experiment Station, for their kind arrangement for us to keep study in the Experiment Station on this subject, m especially thank Mr. B. Y. Hudson, Chief of Wave Section, for his kind instruction during the period when we studied in his section.

i His valuable suggestions and directions make possible for us to write this report. Also, we appreciate the kindness of M s s R. F. Heisey, Miss S. E.

Biggers, librarians, and Miss. J. 0. Cook, typist, for their help extended to us.

Chao, Hwa

Chu, Teng-Kao

Hsu, Zan-Ziang

Vicksburg, Mississippi, U.S.A.

July I9J4.5

ii STUDY OP HARBOUR DESIGN

CHAPTER I

GENERAL HARBOUR DESIGN

Introduction

1, As vessels gradually increased in number, size, and importance,

so the need for more spacious accommodation became the more pressing and

the demand for larger and better harbours the more imperative. So the

primitive landing spots for canoes gradually changed into modern, well-

equipped ports. This is just natural response to the growth of our

human economic life, the progress of which indicates the evidence of our

struggling for a better world*

2# Dating back between two and three thousand years prior to the

commencement of the Christian era, an artificial harbour was built up at Tyre by Phoenicians under the stimulation of business. Once Europeans diverted their interest to overseas for colonies after the Dark Ages, the shipping rapidly expanded with a boom of seaports. The governments of nations, or cities, or even private concerns had to invest in the facilitie of a harbour in order to expedite the dispatch of the vessels for their competitive profits# At. the same time, the keen competition in trades between nations and safe-guarding against piracy naturally brought up the naval forces which in turn increased the burden upon the harbours#

In other respects, the small fishery harbours manifested their importance by numbers so that we can not neglect them at all.

3# The Great World Wars caused the extravagant demand upon harbours#

The harbour authorities faced new problems that they never had experienced before, as camouflage against air raids, accommodations for big convoy

fleets, immense space for the anchorage of vessels loaded -with explo­

sives, and of the seaplanes. Bottleneck has become the headache of

our ports, -which still requires to be solved today.

1±. However important the harbours may be, and however long they

may have been developed since thousands of years ago, the science of

harbour engineering still is at its young age. Although we expect so

much of them, yet the factor involved due to natural forces to our

economic demands is so intricate that exact analyses and methods of

control sometimes become impossible. What this treatise tries to explain

is just the first step in the harbour study.

Definition and Types

5* A harbour is a tract of water within which vessels have their

shelter from onset of heavy seas, operate cargo or passenger transfer,

and receive supplies or undergo repairs. Harbours are different from ports, which latter include land facilities and all installations in addition to the harbour.

6. The classification of harbours varies according to what point is emphasized. In fact, many designations are just arbitrary and incom­ plete. For instance, a harbour named a naval harbour does not mean it will deny entry to commercial or fishery vessels. Likewise, a mod e m harbour is never completely natural or artificial as its designation implies, but is just a combination of a certain extent of nature’s works and human efforts.

J. If we have to classify harbours, probably the local site condition is the best standard. By this we have three types, namely,

2 lagoon, jetty, and breakwater harbours.

8. A lagoon harbour looks like a large shallow lake separated

from the sea by a narrow belt of coast. The tides and the fluvial

discharge of any river »flowing into the lagoon would maintain one or

more fairly deep navigable outlets through the coastal fringe. Never­

theless, the lagoons are liable to be gradually silted up if rivers

flowing into them have high quantities of alluvium and heaping action of

the wave is predominant (fig. 1).

9* The jetty harbours are those sites where flat marshy ground,

lying below the level of high water on the sea coast and shut off from

the sandy beach by dikes or sand dimes, are connected with the sea by a

small creek or river, like Calais and Dunkirk along the English Channel.

Jetties are constructed to concentrate the scouring effect of current in

provision for a deep channel (fig. 2).

10. The third class called breakwater harbours is one provided

with expensive marine works which exclude the onset of rolling seas.

Most modern harbours fall into this class and are found at open sea coasts natural bays, gulfs, or estuaries. Because of their grand scale in nature

against natural inimical forces, this type of harbours is the most diffi­

cult in design and construction and accordingly calls for much more

attention than the other two types (fig. 3)*

General Principles of Harbour Design

11. The principal purpose of a harbour is to furnish a necessary shelter for the refuge of the vessels driven by storm and for the transfer of freight and passengers between water carriers and the hinterland of the port. Therefore, an ideal harbour should fulfill the following four requirements: 3 3-A

Provide$ a tract of tranquil water*

b# Grive^ quick dispatch of vessels in all conditions#

_c# Handle^ cargoes at minimum cost with expedient methods# &e d_. Xe- adaptable to the development of the port utilities

and demands#

12* A successful harbour design will attract the greatest patronage

and make one port gain advantage over the other -which may have a better natural harbour without any modern installations#

13# However ideal conditions in a harbour^we »an tfnrdly expeet- at any given location,foeeaw e every place has its peculiar problems#— -'-'' which are complicated and require solution. This is why the design of harbours becomes one of the most difficult branches of civil engineering#

The engineer may avail himself of the past experience of other harbours, but perfect similarity in the physical peculiarities of different locali­ ties seldom, if ever, exists. More, particularly the difference in the force of the sea to be reckoned with in different places and depths is probably far greater than is generally imagined* .■

Harbour Capacity

U*. The harbour capacity is fixed by the hinterland of the port, which means the area of the back country of the port from and to which the commerce of a port moves. Of course, it is more or less elastic and abstract, but the designing engineer can visualize it by an analysis of the amount of exports and imports of that port or in turn by an investi­ gation of vessels that frequent the port. The investigation of the vessels has one more advantage, since the study of hinterland only concerns commerce while the latter also indicates the capacity required by the Navy or fisheries# 1+ 15* The study of the visiting vessels is not so simple as it

looks. Such a study at least includes the following items:

Jju The maximum number of vessels visiting simultaneously in

a day.

b. The fluctuation of that number during a round year which

may be important to decide whether the harbour should be

built for the absolute maximum or rather for the smaller

number of vessels during the larger part of the year.

£• The length of stay of each vessel in the harbour.

<1. The character and amount of each kind of vessel, including

their draft, tonnage, length, width, and special features.

e. The future tendency of marine architecture and demand of

the port either fo r commerce or m ilitary emergency. The

harbour once constructed would stimulate the development

of the port and enlarge the field of transhipment. The

rapidity in the progress of the shipbuilding enterprise

has immensely affected the harbours of the world. Inade­

quate capacity of the harbour to the deep draft of large

ships tends to choke the prosperity of the port to death.

16. Mr. Thomas Stevenson remarked on the capacity of the harbours in his book, 11 Construction of Harbours,” which says that:

Table 1

Kind of Harbour Capacity Required

Refuge 0.5 - 0.33 vessels/acre

Commercial 6 - 111 vessels/acre

Fishing J4Û - 115 vessels/acre

5 "What is listed above is merely the averaged capacities of some harbours

in his time (1886) • Much change has occurred since then. Nevertheless, we may draw some conclusions from his and others1 remarks, as the following!

The principle in determining the capacity of a harbour is

that the accommodation of a harbour varies with the swing

area of each vessel.

b. The swing of a vessel results from:

(1) Wind blow.

(2) Waves, swells, or seiches.

(3) Making berth o^ maneuvering for something else.

(lj.) Adjusting the compass if no Gyro compass is used.

c. The swing area can be roughly calculated by the area

swept by a certain amount of radius. Usually, the radius

equals the length of the vessel plus length of cable paid

out.

jd. The length of vessel varies with the character of the ship.

The usual commercial lines have about 550 ft in their length

on average, while the fishery crafts ordinarily have only

50 to 60 ft. The "Normandie" has a length of 981 ft and

b in. and probably is the longest ship in the world today.

je. The cable varies with the method of mooring and the depth

of water. As a rule, for single mooring the length of cable

equals three times the depth of water, and assumes that

the vessel swings around the anchor. The object in having

6 a long.lead is to render the pull on the anchor as nearly

horizontal as possible, in order that the maximum re sis-*

tance may be opposed to dragging and the most e ffic ie n t

hold of the ground obtained# I f the ve ssel is moored by

two anchors, one ahead of the bow and the other back of

the stem, the swing is but little more than that due to

length of the vessel with necessary amount of clearance#

There is no d e fin ite p ractice fo r the calcu latio n of swing

area for double mooring# Just usually assume 10 ft at each

end of the vessel for clearance and one-third of the swing

circle for the area required# In other words, the vessel

is assumed to sweep about 120 degrees. For example,

Given: Vessel length * 500 f t

Depth of water where anchored « 100 f t

For sin gle mooring, o swing area = (500 + 3 x 100) # /I+8Í4D x 9

■ I46 acres, or say 50 acres

For double mooring,

swing area = 1/3 (500 + 2 x 10)2/: /LMiO x 9

=» 6 ,5 acres, or say 7 acres

1(3¿|0 x 9 sq f t = 1 acre.

Therefore the swing area is much smaller in the second case than in the first. This is a very useful reference for the design of a harbour ■ where the dense traffic has to be accommodated in a lim ited space.

7 f# The capacity of a harbour equals the summation of swing

areas of the vessels that are taking into the harbour

at the same time plus necessary allowance.

The necessary allowance is given for:

(1) The swing of one vessel without fouling the other#

(2) The outgoing and incoming of other vessels between

beWoeai moored#

(3) The anchorage of the vessels which wait for quaran­

tine or custom, or military inspection#

(I4.) The berths of vessels which are loaded with explo­

sives or something else «flammable#

(5) The relief for the sudden congestion of vessels in

the harbour, especially during the storm#

(6) The spaces for loading and unloading contents of

vessels along wharves, piers, or jetties,

(7) A greater margin for the vessels of heavy build and

that are more difficult to handle, like battleships#

A distance apart of two cables (1200 ft) may be quite

adequate for this purpose, and in most cases a cable

and a h a lf would stiff ice#

(8) The great exposure to the weather because the radius

of swing would in crease by wind blow or the anchor

would be broken by heavy gales# h# The capacity of the harbour should not be so great that the

harbour itself becomes the wave generating area#

8 Sit© Selection

17* There are many opinions regarding this subject. Taking the

harbour site freely at our disposal, it should fulfill the following

items as far as possible*

^a. At conveniently accessible stations upon coasts which

are inhospitable and dangerous,

bo On the route of trade.

On the mouth of river, if any, which would be favorable*

do At the place where maximum natural protection from storms

and waves and largest deep water area can be obtained.

Usually bays, gulfs landlocked by headlands, promonotories,

islands, or outlying reefs are the best choice.

At the place where the least natural adverse effects exist,

as fog, ice, littoral drift, heavy storms, big gales, high

tidal range, tidal bore, alluvial river flow, or marine

insects; especially for the fishery harbours, as a shoal

of fish may be missed as easily from sheer inability to

proceed to sea as from the deterrent effect of impending

foul weather.

f. At the locality which has large hinterland and efficient

inland communications*

However, never before was there a harbour site perfectly ideal and subject to our free choice. The -locality at any rate will already have been determined and the preliminary dispositions established before engineers1 services are requisitioned. Many harbours of present days have resulted from needs due to the growth of population or some geological advantages

9 nearby, even though there may be better natural facilities not far away.

It falls the engineers1 lot to utilize existing conditions and prepos­

sesions, and to devise a modus vivendi out of circumstances beyond his

control.

General Remarks on Harbour Design Data

18. It is very important to have necessary and reliable data of

the place where the harbour will be built. By natural order of procedure,

the first point would be to make a survey of the neighborhood, and to

prepare a chart indicating the depths of water in the vicinity. Not only

should a complete set of soundings be taken, but borings should also be

made to ascertain the nature of the ground, its fitness for anchorage,

and the extent to which it lends itself to an economical increase of

depth should this be or become necessary. The depths obviously must be

sufficient to meet the requirements of the deepest draughted vessels which

are likely to frequent the place, and it should not be overlooked that

some allowance is necessary for the pitch or surge, or "send11, of a vessel

in rough weather, whereby its keel descends below the normal level. The depth chart helps in sketching out the limit of breakwater so as, without disregarding other conditions, to keep the works as much as possible an the shoal ground, while at the same time they inclose the greatest possible area of deep water#

19* After the preparation of the s urvey and the plotting of the contour lines, the engineer will search local records for data, and also make observations himself for confirmation, in reference to various natural and meteorological phenomena, and the following will specially claim his attentioni

10 a.* The direction and intensity of the winds and the frequency

of stoms«

b> The height and force of the waves«

£• The range of the tides*

&. The direction and velocity of the currents*

e. Evidence of silting, littoral drift, or coast erosion*

f* The extent of exposure and the maximum "fetch"•

20* It is quite as bad engineering to adopt the unjustifiable

policy of erecting, in sheltered seas, works that are heavy enough for

the open ocean; as, through an underestimated notion of the exposure,

to fall into the opposite error of designing structures that are deficient

in strength and efficiency* For example, the signs of crumbling cliffs

which may lead us to overestimate exposure in some cases are destroyed

much more by gradual attrition of land springs than by effects of heavy

waves# On the other hand, we may underestimate the limit of high surfs

by the existence of vegetation which sometimes may be on a level much

below the high surfs#

21# We shall not dwell in detail on every item listed above, but

just mention some important points that are worth noting#

Winds

22. Wind at high velocity, so called gales, stoms, or hurricanes, may cause more havoc and destruction than a whole 12-months of the prevailing wind* However, the importance of the latter lies in the effect it has upon the coastal contour in its relationship to tides, waves, and currents, the effects of which, though momentarily insignificant, are continuous and cumulative. It is a matter of judgement as to whether the structure should be designed for storms which are exceptional, though

11 on© may have occurred recently. To some extent a design can not take

care of very rare cases at the expense of unnecessary funds.

23# Winds not only d ir e c tly put pressure on the stru c tu re s, but

also generate the waves, increase the tidal range, propogate currents,

or accentuate the littoral drifts. Those agencies are so closely

related that an exact analysis can hardly be achieved#

2 l|* Three examples and a Beaufort Scale are shown below to illustrate

some common methods of recording wind frequency and intensity (fig# Ip-6 ) •

Table 2

Beaufort Scale for Wind

0 denotes Calm Velocity in miles per hour » 0

1 denotes Light Air Velocity in miles per hour » 7

2 denotes Light Breeze Velocity in miles per hour » II4.

3 denotes Gentle Breeze Velocity in miles per hour = 21

4 denotes Moderate Breeze Velocity in miles per hour « 28

5 denotes Fresh Breeze Velocity in miles per hour « 35

6 denotes Strong Breeze Velocity in miles per hour « 1|2

7 denotes Moderate Gale Velocity in miles per hour = 49

8 denotes Fresh Gale Velocity in miles per hour = 56

9 denotes Strong Gale Velocity in miles per horn* * 63

10 denotes Tftiole Gale Velocity in miles per hour = 70

11 denotes Storm Velocity in miles per hour « 77

12 denotes Hurricane Velocity in miles per hour = 84

Wave s

25* The m ysterious product of wind and water with tremendous disruptive power is the sea wave. It is the mightiest of the forces

12 WIND DIAGRAM

N

S S frequencj/ set of' f frequency set o ff from c en te r. from center intensity from intensity from frequency curve, radial lines.

FIG. 4 FIG. 5

N

frequency set o f f from cen ter. Maximum Intensity from circumstance,

FIG. 6

12-A arrayed against the harbour works, upon which it acts with all the magnipotent impulse of a huge battering ram, while at the same time it is equipped with the point of a pick and the edge of a wedge. Because it is of the most complex, the most volatile, the most perti- n'acious and the most incomprehensible, but the most important natural forces in our harbour design, a whole chapter will be devoted to it later. So far as harbour 7/orks are concerned, there are two kinds of waves to deal with of such different, if not opposite* natures that what is beneficial in one case is useless in the other. They are the waves of oscillation and the waves of translation; the latter of which has more effect on the stability of marine works. The wave action is most severe between 15 ft below lw, and ms.l; above this the action is somewhat diminished as the forward translating effect of waves counter­ balance the recoil or baclcward drag of the undertow» Littoral currents and drifts 26. The effects of littoral currents which are prominent in some locations on harbours are twofold. First, it confuses the local regular flow. A reiver which empties into the sea may be checked by the littoral current on the way and caused to discharge its sediments and deviate its natural course. At -the same time the deposits result in bars, deltas^ or shoals, which seriously impede the navigation to and out the harbour. The second influence of the littoral currents is that they, driven by the wind, carry sand and gravel along the shore, which may silt up the whole harbour area. This is called littoral drift.

27. However, the littoral current is only one of the causes that produce littoral drift. The other is the action of waves which attack

15 the shore and stir up the sand and shingles on the beach. The line of

crest of wave is generally perpendicular to the direction of wind, but

on approaching coast the tendency is to wheel and to become more or

less parallel to shore line, owing to the drag or friction of bottom at

one extremity. The lighter materials are carried by both the wave force

along the shore and littoral currents, while the heavier particles are

rolled along the bottom and partake of a zig-zag movement which varies

with the directions of wind and shore (fig. 7 ). Accretion will take

place -where the water is rather stagnant or the flow is obstructed by

natural or artificial structures. The relocation of entrance at Madras

Harbour, the construction of open viaduct at Ziebrugge and island harbours

at Denmark are very instructive examples in this connection.

28. The Madras Harbour breakwaters extend outward about 3,000 ft

from the original lowr -water line, as it was at the conunencement of the

work of construction in I876. Up to the year 1913 a large triangular

area of sand, about 260 acres in extent, had accumulated on the southern

side of the projection, with a base of 9,000 ft along the coast line and

a side of 2 , 0 0 0 ft along the breakwater. Moreover, as shown in fig. 8,

this was not the whole of the accretion, for a narrow strip parallel

the shore had also been formed, extending from the end of the triangle for a distance of nearly I4. miles to the mouth of the River Adyar, and

inclosing an area of 111), acres. On the other hand, northward of the harbour there had been a corresponding erosion for a length of 3 miles along the shore, and it had been found necessary to check this by means of stone revetments. The old entrance to the harbour was centrally situated between the breakwaters, facing east and the sand drifting -re northward found slack water between the pier heads wherein to settle,

with t; result that before it was closed the entrance was shallowing

up at the rate of just one ft per annum over a period of 12 years.

i/Yith the closing of the old entrance and the extension of the eastern

arm, the deposit continued along the whole eastern face until it has been

more or less checked by the extension of the south arm of the breakwater«,

29« Apparently the practical means of remedying the evil due to

solid structures is that of substituting open work for the portion of the

jetty which immediately joins the land. As exemplified at Zubrugge,

columnar structures were constructed as a viaduct to link the solid break«

water to the shore (fig. 9)* Based on the same idea in Denmark island

harbours were built across the littoral drift area at Amager, Snojebuck,

and Hindested (fig. 10-12).

Tides

30. It is quite essential to understand the nature of tides in all

harbour work. A large range of tide causing bad currents and the elevation

or lowering of the vessel at a berth are not only inconvenient but

dangerous, and may require expensive harbour construction to accommodate

vessels safely.

31* A tide is the daily rising and falling of the waters of the

sea, produced by the attraction of the sun and moon. (A rise and fall

of the sea produced by the alternation of day and night breezes, by ( regular rainfall and evaporation, or by any influence which the moon may have on the weather cannot strictly be called a tide.) There are marked diurnal and semi-diurnal inequalities of the barometer, due to

15 x / _ .y N V ('

AMAGER ISLAND HARBOUR

F IG .10

15-A 5NOGEBOEK ISLAND HARBOUR

FIG. II

HUNDESTED ISLAND HARBOUR

FIG. 12

15-B the sun’s heat they may be described as atmospheric-meteorological tides

These are not astronomical tides.

32« The average or usual intervals between diurnal tides are

12 hours and 25 minutes from high water to high water, a retardation

from day to day of 50 minutes. The tide is 50 minutes later each day.

There are daily, semi-daily, and mixed tides in different localities.

33* Spring tide is when the range of tide is at its maximum on

the days after the new and full moon. It is often nearly three times

the range of neap tides. Neap tide is the minimum range of tide on the

day after the first and third quarters.

3h* The needs of the engineer have resulted in studies that

covered the following fieIds:

a. Prediction of tides and the preparation of annual tidal

tables in advance.

b. Determination of datum planes.

£• A study of mean sea level and its relation to crustal

movements.

jd. Development of instruments for observing and predicting

tides, and the study of tidal phenomena in general.

A knowledge of the tide is of great direct importance whenever the depth at low water is approximate to, or less than, the draft of the vessel and whenever docks are constructed to be entered and left at high water.

35« There are two other points in connection with tides that influence the tidal harbour design. One is .tidal prism and the other the tidal bore. The former is the total amount of water that flows into the harbour and out again with the movement of the tide. The Corps of

16 Engineers of the U. S. A. requires certain types of construction at certain ports with regard to the effect on the tidal prism. For i instance, at river ports and confined channels, such as Hew York (Hudson and Hast Fivers) solid pier structures are not permitted be­ cause they would undoubtedly increase the height of the water and the speed of the current when the tide is running. For this reason open- pile piers are required. It would seem from these requirements there has been an undue stress laid upon the difference in the effect upon the tidal prism as between solid piers and open- pile piers, and that the difference in the effect on the tidal flow is not sufficient unduly to influence a choice of structure. Moreover, the tidal prism has a direct effect upon the channel depth and the direction due to changes in the quantity and velocity of the. water of the ebb and flood tide by reason of the resulting tid&lrscour. This is a field for hydrographic observation that has not been given a great deal of study to date and is worthy of more attention. 36. A tidal bore is the beginning of a flood tide marked with suddeness and distinction. It is usually caused by the impact.of a river flowing to the sea encountering an incoming tide. One of the best examples of tidal bores is that of the Estuary of Hangchow, Checkiang, China, where a difference of water level between high and low tide reaches as much as I40 ft, the water rushing into the estuary v/ith great force. However, in most ports they are a negligible factor in harbour design; the subject being introduced here for the sake of completeness and* an item not to be overlooked. 37« Before we leave this part of the topic attention must again be paid to the fact that the tides brought about by the forces of the 17 sun and moon not only change in rising and falling but also involve a

horizontal movement •whi.ch is called tidal currents and is more notice­

able in constricted waters than in open seas. Really the tide is

nothing but the mighty and slow waves which stir the sea to its very

depth. These waves, just as mentioned before, are of two kinds,

progressive and stationary, vihen tide enters into the bay or rivers

from open sea, at some places it sustains the progressive while at the

other places it sustains the stationary, according to the length and

* depth of the body of water. The methods of dealing with these two kinds'

of waves are quite different in nature.

38. Moreover, the tidal current in some cases acts as a breakwater

to the shore. >.nen the rapid—tideway, called ^race** or ^roosts", runs

in such a direction as to be entirely outside of the harbour and at some

distance off, it will, vixile it lasts, have a decided tendency to shelter

the works. But no sooner does the roost disappear towards high water

than a heavy sea assumes its original mighty force against the coast.

If a harbour work is constructed in a race, the masonry would sometimes

be exposed to the action of a very trying and dangerous high-cresting sea.

From careful inquiries, it appears that the true cause of these dangerous breaking water is the encountering of the swell of the ocean and an

I ‘ ' opposing tidal current. Two rapid tides may meet each other without any dangerous effect if there be no ground swell, yet, if they join together in a rough sea during ground swells, the effect of their union is to increase the current, highly dangerous waves being produced. The meeting of the currents, therefore, though not the cause of the waves, is never­ theless sure to increase their height and to make them break. The races

18 T»hich occur in open seas— as, for instance, off headlands and turning

points of the coast— are certain portions of those seas in -which with j

a ground swells the waves break to a greater or less extent, although

the water may be very deep and there may be no wind at the time. At

all such places it will be found that there are rapid tides, and that

the breaking waves are produced when the tide runs against a ground

swell. Therefore, the location of breakwaters relative to the position

of rapid-tideway is a very interesting problem in design. The roosts

might be utilized to check some action of non-tidal waves but it may

also increase the current that -the amount of breakwater.

irrci cauea #oo.

Seiches

39» Ihis is a wave of very great length, an apparent lateral

movement of water in the inclosed harbour areas which causes vessels to

develop a backward and forward motion. This movement is more noticeable upon lakes as the Great Lakes of North America, Lake of Geneva, etc.

Wien the wind blows with considerable velocity in a direction parallel to the longer axis of the lake, or of the water partially constricted, its effect is to lower the level at one end of the confined water and to raise it at the opposite end, thus disturbing the normal condition of hydrost&tis equilibrium. l/®ien the velocity of the wind begins to decrease the water tends to regain a condition of stable equilibrium by a series of oscillations about a line at right angles to the longer axis of the water body and about midway between the extreme ends, the oscillations sometimes continuing for three or four days. The greatest simultaneous difference of level between the two ends of the .water body reaches as

19 high as 13 ft and the period of the oscillation varies from L\D seconds to. 8 minutes./*» ^ •

ijDr Though this kind of evil does harm to certain harbours,

especially those on lakes, the investigation of this subject still as

yet has not been satisfactory* So far as is known the cause of seiches

is the sudden local changes in atmospheric pressure and they would be

more serious by the reflection of wave energy from beaches toward

artificial harbour works. In many naval bases the collision of ships

against piers or some damages to wharves by pulling out the ballards

are due to this cause.

River flow

i+l. Land water entering the sea at any point is deflected by tidal

currents, where they exist, to each side alternatively, with the result

that with the coastal sediment there is a tendency to shoal at some short

distance outwards, forming a bar of various contours. With a strong wind

and littoral current in one predominant direction, there will most likely

be produced, in addition to a bar, a spit or horn (fig. 13) through which

the river may break in times of flood, but which generally reforms. In

any case the shoaling is detrimental and various means have been tried to

remove it.. The most generally accepted methods are by means of project­

ing jetties, or training walls, and dredging.

ij2. The difference in densities of river and sea also gives rise

to another trouble. In some cases the salinity of sea wrater stimulates

the coagulation of matters loaded in the fluvial flow and speeds up the

accretion along the channel as well as at the mouth of the river. While in the other case the salt water encroaches into the upper reaches of

20 20-A the river and becomes a menace to the local water supply system*

i+3# Although the river flow may prosper the growth of fish, an

advantage to the fishery harbour, and decrease the probability of

marine borers1 existence, a rescue to the timber works, «the* early freeze

of ^fehe £*'esli WKTui* at its mouth seriously curtails the usefulness of the

harbour and certainly deprives the port of a part of business received

by the other non-frozen harbours during the same season# This is why

some engineers try to deviate the river flow outside the harbour at a

distance# As to the planning of Great Northern Harbour in China, it

appears that redirecting of the Ching River outside the s ite will be the

first necessity in the construction in order that it be an ice-free harbour

competitive against Tien-Tsien.

i^# The influence of salt water upon the river harbours^by its

importance to both engineering works and sanitary problems.calls much

more attention of harbour engineers at present than before. -Many model

tests have been conducted ;o be very

suggestive and expedient in solving problems of such complexity.

Arrangement of Harbour Works

h 5 * Local conditions principally affect the general arrangement within the harbour area, and each type of harbour has its particular requirement to be furnished.

i|6# Let us first deal with jetty harbours. These harbours generally are located at the mouth of rivers and are of small capacity. The construc­ tion of jetties provides the channel available to ships entering into the port. These jetties usually have been built with solid substructures up to a little above low water level of neap tides and open timber work as a

21 guide for the vessels in high water stage.

14-7• The low solid structure, however, checks the current and

causes the undesirable accretion which will result in the continuing

advance^of low water line and necessitate the extension of jetties, as

the case in Dunkirk Harbour, or other remedies as sluicing basin at

Ostend (fig.2) and dredging at Calais*

IjB. The number, position and height of jetties in connection

with channels are major factors to engineers. These problems should be

traced back to the original local conditions* There is no rule ,of thumb

to decide their general features.

il-9. For one single channel the jetties are either single or double.

Single jetties are necessary only when the nature of flow is such that

erosion is confined to one side of a river, as is the case at bends. In

intermediate positions and straight reaches, and also in places where it

is desirable to direct a stream across from one bank to that opposite, two / parallel walls are requisite; otherwise, the stream will exhibit a tendency

to spread and the channel to shoal.

50. At the mouth of rivers double retaining jetties may be either

parallel or splayed, and the splay may be inwards or outwards, so that the

jetties either converge or diverge as the*/approach the sea. Parallel

retaining jetties serve to maintain the downstream current unimpaired in

strength and velocity; but if they are carried up to any height in tidal

estuaries, they lead to' an accretion which obstructs the flood stream and excludes a considerable portion of the water which would otherwise enter the estuary. Another danger attaching to such jetties is the likelihood of shoaling in the neighborhood of the entrance due to the arrest of

22 littoral drift by the jetties. This drawback has manifested itself in

a numoer of cases, and at Dunkirk, as was cited before, the jetties have

been extended outwards from time to time in order to reach deep water and

to scour away the intermediate deposit which threatened to destroy the

accessibility of the port. Moreover, parallel jetties do little or

nothing towards the dissipation of storm waves passing in from the sea.

It is from this point of view that converging jetties have been designed,

the inclosed area being of the nature of a basin containing a relatively

larger mass of water, upon which external agitation has less effect.

These jetties, in fact, are sometimes adopted so as to form compartments

called wave traps (fig. 10— 15) • The drawback of the system is the same

as that mentioned in connection with parallel jetties, viz, the reduction

in volume and consequently in scouring efficacy of the influent waters.

This objection, of course, only applies to tidal seas.

51* From this last standpoint divergent jetties are preferable, for with their splayed arms they admit the flood tide freely and the outward flow of the ebb maintains the channel in the gradually widening form which is the ideal regime of an estuary. The construction of the sides must not be too rapid or there will be a tendency to throttle the inward flow and pile up the tidal wave until it forms something of the nature of a nboretf* This is dangerous both to navigation and to the stability of the banks. It must be admitted that no great uniformity is exhibited in the expansive ratios of natural estuaries. They fluctuate exceedingly and range in parts from seomthing like 2,550 ft to the mile in the Humber, British, to little more than 100 ft to the mile in the

Severn, British* On the whole, however, it may be said that a ratio of

23 WHITBY HARBOUR, FRONT VIEW OF WAVE TRAP

FIG. 15

PETERHEAD HARBOUR OF REFUGE

FIG. 16

23-A 2,000 ft to the mile constitutes a suitable standard for adoption*

5 2 . The height to which training walls should be raised is also

a question* If nothing more than the mere rectification of a channel

is in view, the jetties will only be of the nature of a low revetment,

confirming and protecting the edge of a newly-formed bank and need not

be raised above low-water level. It has been urged against this, that in

a sandy estuary a channel so formed would soon be silted up with sediment

washed in from adjacent banks over the top of the jetties* There is,

however, no more reason why silting should take place under the new conditions

than there is under the old, and it may be safely assumed that the stream

is powerful enough t o maintain its own bed.

53* .If it be desired to form an entirely fresh channel or to divert

radically an existing one, something more definite than a mere revetment becomes necessary; scarcely anything less than a half-tide wall will suffice

to confine a stream within arbitrary limits and guide it through a novel

environment* The tendency to resume a long—established course must always remain a powerful influence if ever the compelling forces be modified or removed.

Wien land reclamation is definitely aimed at,jetties will be first built up to mean tide levels and then gradually raised until the level of highest and high water is reached. It should be noticed that the deposit will chase away water from parts of the estuary where silting takes place; and unless some other receptacle is provided, the water which has been so displaced will cease altogether from coming into the river from the sea. Then the low-water sectional area at the mouth of the river will &lso be reduced« If* the amount of* water displaced is sufficiently great,

the channel will shut up altogether and the navigation ¡¡Ruined*

55» Therefore, on one hand the action of jetties tends to exclude

water from the sea by causing accretion behind them and causes, on the

other hand, precisely the opposite effect by enlarging and deepening the

main channel of the river between the jetties# The ultimate result of

their employment must be determined in each case by comparing the relative

amount of those two plus (+) and (-) minus quantities#

56# In view of the fact that jetties are essentially of permanent

character as opposed to the general merely transitory results obtained

from dredging and sluicing operations, it is Important to gather the most

complete and trustworthy forecasts available as to the liklihood of their

success, since a mistaken program may entail unfortunate and even disastrous

results, which may be irremediable# This is one more reason why the small

model tests of essential works win the favor of hydraulic engineers# (Jetties

discussed above are sometimes called training walls. A jetty that is pro­

vided only for ships berthing alongside is the same as a wharf, which, of

course, does not deserve very much emphasis in this treatise#)

Breakwater* Alignment

57* As the name implies, the function of breakwater is to break A up and disperse heavy seas, preventing them from exerting their destructive

influence upon the area inclosed for the reception of shipping# Therefore breakwaters are the recourse to complete the natural shelter that may not

serve our purpose and the bold-type of marine works that could completely create our required harbours against the heavy sea#

25 58# The discussion on the design and construction of the break­ water shall be treated in the third chapter* TOiat we are interested in now is their alignment*

59» Again there is no general standard for this subject* The success or failure in the alignment decides the fate of the structure and, in turn, the availability of the harbour* The following are seven typical examples regarding the outstanding features of the breakwater, and though particular to the locality they probably might represent the general practice adopted in many breakwater harbours today*

a* Single breakwater extended out from one shore— Peterhead

Harbour* (fig. 16). The harbour has a breakwater of 3^50 ft

across the outlet of the bay, leaving a single entrance

between its extremity and the opposite shore and inclosing

an area of about 250 acres at low tide, half of which has a

depth of over five fathoms. This type may he adopted at

places other than the bays where some degree of shelter can

be obtained or the exposure comes from one direction only*

The breakwater may be straight as the case cited, or curved

and it extends out from shore perpendicularly or obliquely,

according to the local conditions*

Tu Single breakwater attached to the shore by open viaduct—

Zeebrugge Harbour (fig. 9). It was carried out with the

purpose of affording berths for vessels beyond the influence

of accretion due to littoral drift. The breakwater, provided

with a wide quay with sidings and sheds, and curving round

so as to overlap thoroughly the entrance to the canal and

26 shelter a certain water area, is approached by an open metal viaduct extending out 100 ft from the low water into a depth of 20 ft. The littoral drift is“coming mainly from the west. By this measure the accumulation of silt to the west of the harbour and also in the harbour itself would be prevented. Twin breakwaters—Sunderland Harbour (fig. 17) • "Where no natural shelter exists, or where there is on open sandy shore with considerable littoral, drift, or where the jetty construction is not enough to provide the accommodation for congested traffic, double breakwaters extend out from shore respectively at a distance apart and converge to a central entrance of suitable width. Inclosing harbour by more than two breakw aters—Co.lumbo Harbour (fig. 3)* Some partial embayment or abrupt projection from the coast is utilized in providing shelter from one quarter while breakwaters are built to complete the inclcsure of the site. Note the features of detached breakwater. Single isolated breakwater—Sandy Bay, Massachusetts, U.S.A. (fig. 18). A single isolated breakwater is built in such a position that will make it most effective against the exposure to the waves. This type is adaptable to the place that is in possession of some natural indentation on the coast o A exposure is not so great and changing in direc* tions as undesirable for the shelter required.

27 N

SUNDERLAND HARBOUR GENOA HARBOUR FIG. 17 FIG. 19

SANDY BAY HARBOUR, MASS.

F IG .18

27-A f . Overlapping breakw aters—Columbo and Genoa Harbours

(fig 3 and 19)# To some extent the breakwalrers extended

from the shore overlap each other with respect to the

entrance so as to get more protection from waves inside

the harbour. The outer breakwater of Genoa Harbour i s

made much longer and curved somewhat fu rth er out overlapping

the inner. At Columbo the southwestern breakwater splits

into two at end, of which the longer branch just shelters

the sh orter from the southwest monsoon blowing into the

entrance.

. £ • Island breakwater—Danish fishery harbours (fig. 10-12).

The solid breakwaters are located beyond the zone of littoral

drift at some distance outward from the shore. The basins

cover areas of 0.27, 0.20, 1.62 acres respectively. From the

breakwater open viaducts, wooden or composite, from 330 f t to

660 ft long, lead to the shore and are divided into 13 to

20 bays having spam openings from 20 ft to 30 f t .

60. On the coast of Denmark tides are insignificant, are hardly

perceptible in the Baltic, and do not exceed Ij. ft 6 in. in the North Sea.

Hence, the movement of material which takes place cannot be due to tidal action, v but to the action of the waves, combined with that of load currents, and

are therefore attributable to the effect of wind. The object aimed at by

these three fishing harbours seems to have been accomplished fairly well.

61. As mentioned more than once, the harbour design is nothing

a blind copy. The particular locality has its peculiar features which determine the best alignment of breakwaters. In general, the items that

28 should be investigated for the positions of breakwaters are:

ja.. Configuration of the adjacent coast line,

b/ Extent and d ire ctio n of the exposure.

Amount of sheltered area required and the depth obtainable.

d. Prospect of the accumulation of drift.

e. Occurrence of scour from the proposed works.

.f. The best position for an entrance in respect of shelter

and depth of approach.

General Features of Breakwaters with Respect to their Positions

62. Breakwaters have two general classes. The vertical wall type

is one designed to reflect the waves without breaking, while the mound breakwaters are designed to dissipate the destructive forces of waves by attrition. Therefore, there is an important rule on position which is closely related to the types of breakwaters. The general axis of the break­ water of the first type must be kept at an .angle larger than k5° in the direction from which the storm may be expected. Otherwise the wave would be broken and the mound type would become much more fav o rab le*

6 3 * It is clear that the amount of protection which is produced by a breakwater must be measured by the length of the portion of the wave which i s eith e r destroyed or re fle c te d by i t . The amount of work done by it decreases from the maximum which is at normal incidence to the minimum when the waves come upon it end on, in which last case no work is done, and it ceases to act as a breakwater for waves coming in that direction, excepting to the small extent due to lateral erosion.

614.. The curvature of the breakwater varies with the condition of wind, current, coastal configuration, sea bottom, etc. Usually preference

29 is given to them of horizontal convex outline, or of a poljjnal form,

rather than to one long straight breakwater running at right angles

to ihe worst waves# The principal objection to a straight breakwater ]

does not, however, extend to cases where the heaviest waves strike upon

it obliquely and roll landwards along the seawall.

65* MoreQver, the curved part is the vulnerable point to the

erosion by current and the result will be the collapse of the whole

structure* Mien a breakwater presents to the sea a concave outline or

cants inclined at an angle to each other the waves will act with an almost

explosive violence. This concentration in the scouring action may be very

satisfactorily seen at low water, where an isolated rock or a boulder of

pyramidal form projects above the surface of a sandy sea beach. Pools of

greater or less depth w ill always be found at the angles of the boulder,

while at intermediate parts the level of the sand is much higher. In such

cases the foundations at the convex parts and at the salient angles must

be carried lower than other places; and i f i t is possible concave or abrupt

re-entrant angles should be avoided.

66. With regard to the length of breakwaters, i t ,o f course depends

upon the outline of the site where it is to be located and the extent to

which the breakwater intends to protect. However, it must be noticed that

if a breakwater be so placed in relation to the coast line that waves can

strike upon its inner or landward side, an extension of its length in the

same direction will increase the amount of sea intercepted by it. In this

case the extension must be made in an altered direction or a separate breakwater must be built so as to shelter the inner side, or else an

additional sheltered space of -water or of the shore must be provided in

30 I 2 0 0 0 FT. ______10QO 10QO IG. IG. 20 F 1------J O O ------; OVER HARBOUR ----- D t— !000

3 0 -A which the waves can spread or be expended. 67» The case of Dover Harbour illustrates a good example (fig. 20 ) of a long breakwater obstructing the free flow of the tidal wave and Keeping pend it up so as to increase the velocity of the current round the head to a considerable extent. At Dover the normal speed of the current along the coast was two knots prior to the construction of the breakwater, but as the latter was nearing completion, it was found that the speed of the current was increased at the head to 3*9 knots at flood spring tides. Apart from navigational disadvantages this increase of current speed is not favorable to the structure and tends to wash out the foundations of the head, which is the part of the structure most vulnerable and most subject to buffeting. Another undesirable effect is that the scour caused round the head may be deposited in the harbour on the lee side of the break­ water. There are instances of breakwaters interfering so much with t he‘ normal flow that silting of the harbours result, the consequence being that new breakwaters located and proportioned to meet the conditions have to be constructed and the originals demolished. During construction it is im­ perative to take careful observations of any changes in the set of currents, etc., caused, by the new structure and of the effects of storm waves. Such observations serve to guide the experienced engineer regarding the advisa­ bility or otherwise of modifying the cross s e c tio n sitting the length of wall, the disposition of heads, or the width of entrame© and the amount of foundation protection. Attached hereto are 12 figures (fig. 21-32) that indicate the tidal currents in and out of Dover Harbour prior and subsequent to the completion of the island breakwater. Beforetime, the set of the tide was almost parallel to the shore line, running from Northeast to

31 31-A Notes on fig 21-26

1. H.W.F. & € XI*1 12m j Springtides rise 18’9" Neap rise 15 feet*

2* At about 2i| hrs. before H.W. the water comes in with a rush, changing from slack water to a 2^ kn stream in less than 10 minutes, and eddying and whirling as it enters* The time of insets appears to vary between 2 3/4 hrs and 2 hrs before H.W. but is never later than 2 hrs before nor earlier than 3 hrs,

3. The first of the Eastern going stream set sharply into the

Tiestern Entrance and close along the Breakwater slowly setting more off from the Breakwater until an hr after H.W. when there is an eddy stretching outside and running to the W.S.W. about 2 kn an hr.

4. At the East side of Eastern Arm and Eastern Entrance the stream sets to the N.E. from 2 hrs before to about 1 hr before H.W.

A t all other times it apparently sets to the S.TS. being the true

Western Stream and the eddy from the Eastern Stream.

31-B FIG. 27

2 Hours ArterH.W.

FIG. 30

■5 Hours A f te r H. IV.

FIG. 31

TIDAL CURRENTS IN AND OUT OF DOVER HARBOUR SUBSEQUENT TO THE COMPLETION OF THE ISLAND BREAKWATER

31-C Southwest from Í+-1/2 hours after 1-3/1+ hours before high water, and

from Southwest to Northeast from 2 hours before to I*, hours after high

water* At high water of spring tides the rate of the east-going

stream was about I4. knots, and at low water the west-going stream had

a velocity of 2-1 /2 knots. Both direction and rate of flow were com­

pletely altered after the work was finished. These indicate the

d iffic u lty of forecasting with any degree of accuracy the e ffe ct of

structural works on coastal and tidal currents.

Harbours at Lagoons (fig , l)

68. Harbours at lagoons u tiliz e the b e lt of reefs flanking the

coast with a little additional work to make the shelter complete. There­

fore, the design of lagoon harbours is restricted much to the natural

configuration. The requisition on the engineers1 geniuses is to take the maximum advantage of the natural features so as to save both the construc­

tion and maintenance work*

69* The liability to silting is the greatest disadvantage of this type. Moreover, the approach from the sea to these channels through the fringe of coast is generally impeded by a bar, owing to the scour of the issuing current through those outlet channels becoming gradually too enfeebled, on entering the open sea, to overcome the heaping-up action of the waves to form a continuous beach across these openings. 1 Accordingly, rivers are very valuable in maintaining a lagoon i f they are free from sediment; i f they bring down large amounts of s i l t they must, i f possible, be diverted from the lagoon, while the narrow b elt of land in front of the lagoon must be protected from erosion by the waves on its sea face by

groins or revetments. The depth over the bar in front of an outlet can be improved by concentrating the current through the outlet by je ttie s on

32 each side and dredging, if necessary, 70, In designing a breakwater for protecting a lagoon harbour it may be found better to carry the bulwark straight across ledges of reefs or rock, as a lagoon often possesses such features, than to follow the natural current conditions. However, the bulwark may be severely scoured by the confined waves, since the breaking of a free wave is a very different thing from the breaking of a wave confined by a barrier of masonry, Yifoile the first may be compared to the harmless ignition of a loose heap of gunpowder, the other resembles the dangerous explosion produced by the discharge of a cannon. The design engineer must not take any chance for economy or convenience at expense of safety, t Harbour Exposure 71• The required accommodation, the adaptability of natural features and the dictates of convenience to navigation, in fact, have foremost place in the determination of harbour areas. Tie have dealt with the first two points in connection with the harbour capacity and the selection of site, now we will discuss the third, although these three mutually affect each other with respect to the harbour area. 72. Exposure is certainly the primary consideration for the con­ venience of navigation. Study of subject with respect to wind and wave still is at its budding stage and has not yet achieved any satisfaction. Fortunately, by years of experience and research by harbour authorities we nevertheless have something for our guidance in estimation. -Among these Mr. Thomas Stevenson fs empirical formulas are the most fundamental we have. 73* The first of his formulas is for the determination of wave 33 height by r’fetchn, and the second is applied for the study of reductive

power in terms of wave height within the shelter. Because no matter

which harbour it is the tranquility is the primary requisite and the A/ height of wave naturally is the convenient measure of the extent of

exposure.

7U* The first formula is written as follows:

H - 1.5 / F when F > 30 miles

H -1.5 JT + (2.5 -kfF) when F 30 miles

1*5 is the coefficient for heavy gales.

Different spots of a place have different values of fetch. By this

formula we can get a set of data for comparison so as to decide to what

extent the designed harbour runs with minimum exposure and construction

work at reasonable cost.

75* The measurement of effective fetch is not an easy job which

is quite intricated with the direction and strength of wind, the inter­

vening depth of water, configuration of coast and effects of artificial

structures. The theoretical side of this point we had better drop

to the next chapter. %atave*r we should notice now are:

ja. The maximum limit of fetch is about 500 to 600 miles. In

other words the wave height will not be proportional in every case to.

the line of maximum exposure or fetch. There seems to be no exact limit

to the minimum value of fetch. In short fetches in narrow locks or arms

of the sea, waves are raised higher during every violent gale than the first expression of the formula indicates* though such waves do not go on progressing in height in the same high ratio for any considerable distance. This is why the formula has a second expression with a

(2.5 - h ) correction. J*« The maximum fetch at the site is by no means an in fa llib le

criterion of wave height because t

(1) The several gales do not always blow in the direction

of greatest fetch.

(2) Waves or heavy rollers are sometimes deflected so as

to reach a point on the shore which does not lie upon

th eir path»

(3) The convergency of inlets accentuate the eccentricities

of wave development.

76. To t e s t ify the reductive power of a harbour the second formula will be useful. The reductive power of the harbour is expressed in a ratio - internal area over the width of entrance, while Stevenson’s second formula indicates the relationship between the width of entrance and the exposures

b a ' - 2h [/! . i (1 ♦ /| ) '»/ij ^(1750 feet)

By this formula we can compare the wave height inside and outside the harbour and determine if the width within with respect to that of entrance is suitable. The method of applying this formula is to describe a circle on the ground plan of the harbour from the point of union of the lines of the breakwaters produced seawards, or (what is su fficie n tly near) from the middle point of the entrance. The radius adopted must be equal to the distance (D) between the center of divergence and the place on the break­ water where the reductive power is wanted. The arc of a circle thus described must extend so far as to intersect the two side walls of the harbour, or in cases where one of the breakwaters meets the shore at a shorter distance the arc must be extended to the line of direction of the

35 shorter breakwater produced landward of the highwater line. It is

necessary to observe, however, that in such cases as the last mentioned,

where the shore intervenes, the formula is not applicable unless the

beach slopes sufficiently to allow the waves to spend themselves freely.

The distance B is then measured as a chord between the two points of

intersection; or where the versed sine is large, B should be taken

equal to the length of the arc. It is believed that this formula will

be found to be of general application in all close harbours where the

entrance is of direct and simple nature and in *vfoich there is no recoil

action produced by walls or obstructions to the shoreward motion of the

waves. This is why, in some particulars, the difficulties of design are

inversely proportional to the extent of the works* Questions regarding

reductive power, want of spend and recoil of waves are so troublesome in

small basins that much attention should be given to them.

77* Mr* Stevenson found another expression for -the reduced wave

height by lateral deflection. He said the amount of reduction in the ^

height of a broken wave which passes onwards through the opening and

spreads laterally under lee of the barrier was found to increase directly

as the distance traversed, and as the square root of the number of degrees

in the angle of deflection. The formula given below he said is unconfirmed and simply as a possible approximation for our reference.

x - 1 - K [ i ° Where x represents the ratio of the reduced to the unreduced wave and fit the angle of deflection, K the coefficient variable with the kind of wave. For certain cases K equals 0.06. Care should be taken,again this formula only applies to the waves in uninclosed areas,as roadsteads; . for the waves in close harbours the Stevenson’s second formula must be used. 36 78« la connection with this subject it is worth while to mention one thing more in judging of the exposure of a coast* By many observa­ tions in exposed situations mud cannot repose near the surface# No one would expect to find a muddy shore confronting an open sea where the deep water approaches closely to the shore, though he would not express surprise at finding such a beach on the borders of a land-locked bay or of a sheltered estuary# Although the absence of mud in any locality proves nothing, because the tide currents may sweep it away, or the geological formation may not produce it, its presence seems both a delicate and certain test of the lowest limit to which the disturbance originating at the surface has reached# In short, except for some unique instances, the level below the Surface of low water at which mud reposes on the bottom of the sea is valuable indication of the extent to which the exposure covers* General Remarks on Entrance

79* First of all the position of the entrance deems our careful consideration# It is the opening of a harbour which must be convenient to the ingress and egress of vessels and at the same time not expose the interior to the effects of rolling seas* These two objects, in fact, more or less conflict with each other* 80# A general practice adopted today that the entrance be fixed seaward of every other part of the works on the direction of heaviest waves so that they may run along with and guide vessels into the harbour. This is taking the point of navigation in view* The vessels severely driven by the storm then will not miss the entrance or collide with piers# However, on the other hand, the onset of rolling sea will march on into 37 the interior and give serious agitation because of the wide opening to the sea without any. impedence. 81* The old harbour of Fultency town furnishes a notable example with & view on the other end* It placed the entrance at right angles to the line of movement of the swell so that it seemed to be a very simple and efficacious mode of increasing the reductive power of a harbour. On the contrary, it was later proved a disadvantageous arrangement since a number of vessels were struck by waves on their broadside or quarter at the moment of turning in port (fig* . 82* Therefore some degree of compromise should be made to fit both purposes* The case like the one above cited was to extend the outer pier sufficiently far seaward of the end of the other pier head so as to allow a ship plenty of sea room to shape an easy course* Even if the ship, while rounding in, should be struck by a wave in making a leeway, there is still sufficient time for it to recover itself under shelter of the outer breakwater before reaching the narrow entrance between the piers* In many other harbours the outer breakwater overlapping the inner severs the similar purpose* 83* In a very exposed positions, making entrance deflected to afford some cover to the interior of the harbour is also commonly adopted* The following table on the directions of the entrances of some notable harbours illustrates this idea of giving safe shelter from gales in the prdominant quarter*

38 38-A Table 3

Harbours Gal© From Entrance 0p<

Dunkirk NW HE

Dover SW E

Folkestone SW E

Tyne HE SE

Wear HE SE

B lyth HE SE

81+, We now have another notable departure from the usual practice

that was recommended by Professor V. E. Liakhnitsky. A breakwater

( f ig . 3k) is constructed before the entranoe into the harbour. It pro­

vides a way to conciliate the two contradictory principles of which one

requires the axis of the harbour entrance nearly to coincide with the

sector of the prevailing and strongest winds and to lie at a considerable

distance from the shore, while the other demands that the water area

within the harbour should be sheltered from the action of the vraves.

The time-honoured rule to so design the entrance into a harbour that it

lie between two projecting outer protective works, and to avoid in their

layout any reentrant angles, seems to be disregarded by this innovation.

Similar corrections and improvements w ill no doubt continue to be intro­ duced in accordance with the experience accumulated and the progress of the

theoretical thought in this branch of engineering.

85. There is one more point to be observed with regard to the direction of entrance. If the harbours on a river have a continuous tendency to silt up, are subject to the adverse influences of strong currents, freshets, and floods; and even invaded at times by floating

39 39-A masses of weeds and mud, the entrance should point downstream making

an angle from I4.5 to 60 degrees with the bank and should not open wid^r

than necessary for the admission of the vessels,

86. Some harbours have more than one entrance. The advantage of

this provision is to enable vessels to select their entrance according

to the state of the wind and weather. In addition, it may reduce the

current through entrances where there is a large tidal rise and it may,

under favorable conditions, create a circulation of the water in the

harbour, tending to check the deposit of silt. However, the advantage

is not certain for every case. Somewhere the second opening causes

eddy currents which make the condition much more worse than when only

single entrance is provided, like scouring at reentrant angles, speeding

deposition and m dangerous to the vessels.

87* Therefore the problem of entrance is by no means so simple

as we first imagined, but a function of exposure, local configuration,

currents, and vessels that frequent the port.

Entrance Width, and Channel Depth

88. As regards entrance width the engineer faces again the same dilemna mentioned several times in the preceding paragraphs. On one hand the narrower the entrance the more effectually is the interior secured from -frie ingress of disturbing elements. On the other hand, an entrance must have adequate room for vessels entering not singly and in calm water but also when driven in groups under the stress of heavy sea.

89* Under the heading Harbour Exposure we have discussed the relation between the entrance width and the wave height. With respect to the accommodation^the entrance width varies with the maximum width of each vessel and the possible maximum number of vessels entering the harbour at the same time. Usually the minimum width of practical

entrance for ships of modern dimensions is from 230 ft to 1+90 f t , but

for large commercial ports it should be preferably from 650 ft to

1000 ft wide, while for fishery harbours it is enough from 100 ft to

300 ft wide. Sometimes the entrance channels constitute the anchorage

space tributary to the ships and docks* In such case the width accordingly

should be increased.

90. There are also many other considerations to which the entrance

width is subject. In tidal harbours there is the outrun of the ebb tide

with the cumulative effect of the discharge of any upland waters, all

tending to produce a rapid current in a narrow waterway. And while the

scour induced by this means is beneficial within certain limits in maintain­

ing a deep channel, yet, carried to excess it is likely to prove prejudicial

to the stability of walls and piers by undermining their foundations, and moreover, the rate of flow may be such as to interfere with and probably prevent safe navigation. A velocity of from 3- 1/2 to I4. knots should be

looked upon as the maximum current permissible.

9 1 . A question of channel depth, or in general of harbour depth,

is one for serious consideration. A shallow channel can suffocate the prosperity of the port enough to divert the shipping to other neighboring p o rts.

9 2. From an examination of the proportions of a considerable number of vessels, it turns out that there appears on the average to be a tolerable amount of uniformity among ordinary vessels constructed of timber. Mr.

Stevenson deduced a simple formula.which gives a fairly general approxima­ tion to the tonnage. Yftiere d represents the draught in feet t represents the burden in tons, and a constant depending on build,

t = - and d = 0 / a t ■ a r The ratio of draughts to tonnage has been gradually decreasing/ Por-

i!br timber vessels at present it may be'taken about 7- 1/ 2 . Anyway

the formula tells us the fact that the value of harbours in terms of

tonnage inc-rsass as the cube of depth of water increases.

93* Even though no uniformity has been found between the tonnage

and draught among stream vessels which are most predominating in present

harbours, the value of harbours, whether commercial or naval, surely

increases more than the depth increases. The fact could be explained by

the development of prominent harbours themselves and this is why all modem harbours have invested a large sum yearly to deepen their channels

9U* Generally speaking, an available depth of a harbour should

equal to the maximum draught of the vessels that frequently visit the harbour plus 3 ft for easy navigation, with an additional allowance for the vertical movement (or send) of the ships. The scend is generally

taken at 2/3 of the greatest lift of the wave for ordinary colliers and

1/2 of the lift of the wave for large screw steamers — taking in both cases the lift or height of the wave to be from the lowest fall to the crest. Again we should observe that ships underway draw more water than when at rest, especially in fairly shoal waters.

95* The rising of tides at some places can be utilized to enable ships entering the harbour entrance that has not sufficient depth for vessels of deep draught at low water. Of course accompanying this advantage there is a risk in grounding vessels at ebbs and a necessity of waiting outside the harbour for flood tides. 96. A large port or one of complex topography, such as New York,

may have many channels, some of them adopted only to light-draught

vessels. The depth of the main project channel is, however, the govern­

ing factor. The following are characteristic channel depths, and the

corresponding types of traffic -which they serve.

Channels in Excess of 30 Feet

97* These are provided for deep draft lines of the North Atlantic

and Transatlantic and for few freight vessels. There were in 1920 only

I4.8 ports of importance in the world which could be entered by ships draw­

ing 1(0 ft and over; of these there were only 23 which had depths alongside

their wharves sufficient to accommodate such large vessels, and of these

five could be entered only at high water (Table k - 5 ) •

98. The number in addition, usable for vessels drawing 35 ft, was

59 of these 59 eighteen were harbours which could be entered only at

high tide, and only 214. of the 59 had wharf accommodations, of which 11

were tidal.

Channel Depth of 2 l± to 26 Feet

99» Such channels are characteristic of ports having little foreign

trade, or foreign trade of a class using only medium draft ships, such

as the lumber trade of central and South. America, but having a large

coastwise or intracoastal business. They may be called the major coast­ wise channels.

Channel Depth of 18 to 20 Feet

100. These may be called minor coastwise channels, and are particular ly adapted to the moderate sized steamers and other vessels■which pay an important part in the coastwise movement of lumber. Lesser Depths

101. These are usually found in fishery harbours or in ports

like the small ones on Chesapeake Bay, America, the commerce of -which

is handled by ships traversing comparatively sheltered waters.

102. The following are tables of the depths at some important

ports in the worlds

Table Authorized Depths of Main Channels at United States Ports, 1920

Port Channel Depth, IMean Low lfifeter,Ft.

Portland, Maine Entrance and lower harbour 35 Anchorage and inner harbour 30 Boston, Mass. Puter entrance bo Sea to Navy Yard 135 New York, N. Y. Entrance bo Inner channels 30 and Lfi Philadelphia, Pa. Delaware River to the sea 35 Baltimore, Md. Baltimore to sea 35 Norfold, Va. Entrance and southern branch bP Other channels 2 2 and 25 C harleston, S. C. Sea to Navy Yard (Authorized I|0 ft) 31 Savannah, Ga. Sea to quarantine 25 Harbour 21 and 26 Jacksonvilie, Fla. To ocean 28 Key West, F la . Main channe1 30 Opposite wharves 26 Tampa, F la . Gulf of Mexico to Tampa 27 Mobile, Ala. Entrance channel 30 In harbour 27 New Orleans, La. Southwest Pass 35 South Pass 30 Galveston, Texas Entrance channel 35 Galveston channel 30 Houston, Texas Galveston Bay to Houston 30 Texas City, Texas Galveston Harbour to Texas City 30 Sabin© Pass, Texas Over bar 28 Inside 2 6 Beaumont, Texas Port Arthur to Beaumont 25 San Diego, Calif. Entrance 35 Channel to Municipal pier 32 Los Angelse, Calif. Entrance 35 Inner harbour 30 P ortland, Oregon Mouth to Portland 30 Table 5» Depths of Principal British und Other Countries * Ports

Port uepth at High Water Ft Depth at Low Water Ft

British Ports: Aberdeen basins 25 18 to 22 ChanneIs 27 15 Belfast, channel 31 23 Dock ------15 to 25 Bristol, city docks -- 22 Cardiff, entrance MW 2Ì+ (in docks) Cork 22 Falmouth — 23 Glasgow ~ 23 Hartlepool 33 17 Leith 26 1 1 Liverpool 55 30 London li; to 30 Manchester, canal — 28 Plymouth — 30 Southampton — 35 Chinese Ports: Shanghai 28 20 Hong Kong — 35 to I4O Other Ports: Aden, Arabia -- 30 Alexandria, Egypt — 35 Amsterdam, Holland 33 (canal) Antwerp, Belgium 30 Archangel, Russia — 23 Auckland, N. Z# mmtm 31 Bangkok, Siam — 1 4

Barcelona, Spain — 2 k to 32

a 22 at berths Bordeaux, France M« 20 to 25 Breman, Germany, entrance 22 18 Bremerhaven, Germany 30 22 Brest, France 36 23 Bruges, Belgium — 26 ft 3 in* Buenos Aires, Argentina,

entrance 2 k to 30 Cadiz, Spain 35 or more Calais,! France IÌ4 ft 1 1 in. ‘

— Calcutta, India 2 k to 30 Cherbourg, France 17 Callos, Peru, entrance 25 21 Constantinople, Turkey 22.3 at •wharves Copenhagen, Denmark mmrnrn 2 9 .8 (in free p Danzig 23 Dunkirk, France 29 23 Table $ (Contd)

Port Depth at High Water Ft Depth at Low Water Ft

Etaden 32 23 Fiume, entrance 100 to 120 Quays — 2l+ to 26 Genoa, Italy, entrance 52 to 69 Hamburg, Germany -- 1+0 at new basins Hamburg-Ame r ic an Havana, Cuba, entrance ... 35 Havre, France iii; 15 to 23-1/2 Leghorn, Italy (one of the chief Mediterranean ports) — 35 to l+o Kiel 23 22 to 28 Liban, Russia — 2]+ (in conanercial -harbour) Me lb ou m e , Australia — ■ 2i+ to 28 Montevideo, Uruguay, in outer roads, — 30 in inner harbour —- 21+ Odessa, Russia m m mm 30 (max.) Oporto, Portugal 18 Ostend, Belgium 32 to 35 17 Pernambuco, Brasil 21+ 21 Rio de Janeiro, Brazil 33 (neap tides) Riga 22 __ » Petrograd, Russia — 21 (basin) Rouen 18 10 Singapore, S. S. — Up to 1+5 Stettin 25 21 Stockholm, Sweden 23 Venice — 2?

103* The question of appropriate depth is a very interesting but

complex one, turning as it does on the drafts of vessels in various

forms of trade and on the trend of these drafts in future construction*

Since the introduction of steam, vessels have in general tended to become

of still deeper draft and this tendency continues. The increase is,

however, more noticeable and more regular in the case of the average

vessel than in the case of the largest vessels. (rTgY"~gT).

1 0 l u In the case of very deep draft vessels, with the exception

of oil tankers, there is apparently no decided tendency to go beyond the maximum adopted in the past decade# Vessels like Leviatham, Majestic, etc., were constructed largely on account of commercial rivalry between

different big steamship lines, or national rivalry. It is generally

understood that they were not paying investment^ Careful cost statis­

tics indicate that for the highest grade passenger service on the North

Atlantic the typically most economic vessel has a draft of about JO ft.

The tendency in the postwar construction program of the important Atlantic

lines was toward v esse ls of such d ra fts as these and around 20,000 gross

tons, instead of toward the mammoth types built just before the World War^

105* The following table shows the maximum drafts, loaded and light,

of -the standard vessels constructed by the American Shipping Board, the figures being derived from actual measurements of vessels constructed at different points under the same plans. It may be a very useful reference to the design of channel depths.

Table b Maximum Drafts of the Standard Vessels

t ; U râ F î------3 a t * De ad-Weight a : Light 8 t Type í : Tonnage Loaded t Kean « Forward : o f f . 3 t * ' * a : Ft., In.j Ft. In. t F t .,I n . : F t .,I n . 3 S teel Cargo 12,000 30 6 9 3 - 3 A Troop Cargo 11,800 28 7 - 1 /2 9 2-1/1+ Tanker 10,500 25 7-3/1+ 18 3 17 19 6 Cargo 9 ,6 0 0 27 7 10-1/2 1+ 6 11 3 Cargo 8,800 2l+ 2 11 1+-1/2 8 8 A 1 Cargo 7 ,5 0 0 21+ 5 - 1 /4 9 5 6 6 12 1+ Tanker 7 ,5 0 0 26 0 12 1 12 l 12 1 Cargo 5 ,0 7 5 22 11-3/1+ 8 9 - 1 /2 5 6 11 9 Cargo passenger U,300 21+ 1+-3/1+ 16 7 11 5 - 1 /2 21 8-1/2 Cargo (Lake) l+,000 /21+ 2 9 11 6 6 13 1+ Cargo (Lake) 3,500 21 1 7 6-3/1+ 5 9 - 1 /2 9 1+

hi i

106. The table shows that ocean-going cargo vessels as large

as the standard 8,800-ton vessel would be able to load to maximum draft

on a waterway 25 f t deep at low water, and that such a waterway would

more than meet the requirements for getting out to the ocean newly con­

structed vessels of all the standard classes, Nevertheless, a port with

le ss than 30 ft of water at low tide will be placed in a very unfavorable

position in competition for modem liner traffic, freight or passenger#

There are ju st enough v essels of 27 to 29 f t d raft to make a port second

rate that cannot accommodate them,

107* The usual methods of deepening a channel are (l) converging

the current by training walls or jetties; (2 ) narrowing the channel by

groin s; (3) scouring by ebb tides or sluicing basin, or wave traps,

and (I4.) dredging work. However, a good harbour maintains it s depth by

natural forces and the channel should be located in such a way as not

to be a trap for the passing sands and shingles. As a matter of fact,

the preservation of the depth of harbours at a level lower than that of

the original bottom involves both uncertainty and expense. Where the

deposit is confined to the space between high and low water marks, the

scouring by means of salt or fresh water is comparatively easy; but where

it forms a bar outside of the entrance the possibility of maintaining

permanently a greater depth becomes very doubtful. The efficacy of the

scour, so long as it is not impeded by enlargements of the channel, may be kept up for great distance, but it soon comea to an end after it meets

the sea. 1®ieh the volume of water liberated is great compared with the

a»Wons or channel through which it has to pass, the stagnant water which

originally occupied the channel does not, to the same extent, destroy

UB the momentum as -where the scouring has to be produced by a sudden finite

impulse* In the one case the scouring power depends simply on the re­

lation subsisting between the quantity liberated in a given space of

time and the sectional area of the channel through which it has to pass;

while in the other it depends on the propelling head, and the direction

in which the water leaves the sluice*

108* Dredging either by buckets or suction pipe lines is now

universally the most common method adopted for maintaining the harbour

depth* However, annual expense on its operation and maintenance is rather

prohibitive, and the time has come when port authorities and municipal

exchequers must take a stand against being required to spend millions

to deepen a channel a foot or more in order to accommodate some private

steamship line which wishes to own "the biggest ship in the world," for advertising purposes.

109» Attention also should be paid to the small harbours where deepening the entrances may cause a greater disturbance within. This is due to the negligence of making a proportionate enlargement of the internal area or providing other works at the same time for counteracting the effect.

As the depth of the water is increased waves of greater height reach the entrance and thus gain admission to the interior. The truth of the principle that the run in a harbour increases with the depth of the entrance may be verified every tide at any exposed harbour, -where it will be found that just as the tide rises the difficulty of keeping vessels at their moorings increases. At the port of Sunderland the frequent dredging and widening of the channel at and landwards of the entrance rendered the

b 9 necessity of removing nearly the whole of the inner stone pier and of substituting works of open framework in order to tranquilize the interior. Similar results have been experienced at other harbours. General Harbour Layout and Other Facilities 110. The efficiency of a harbour is to be measured not simply by size or the fundamental works like breakwaters, though very important, but also by performance of the other facilities provided and the design of general layout. 111. Breakwaters or jetties provide the vessels a sheltered area for refuge or convenience for conducting the transhipment of cargoes and passengers, while the other installations and equipment render the quickest dispatch of vessels possible at economic cost. Since ships are useful only in transporting the freight and passengers between ports, the stay of the ship within the harbour curtails her useful functions. 112. T/hat kinds of facilities should be provided for a port largely varies with the purpose that a port or a harbour is designed to serve. A naval harbour may have different requirement from a fishery harbour and the same fishery harbours may have some special installations for different localities. Therefore, we have no panacea for port facilities at any port but try to numerate here the important installa­ tions that to a part may be indispensible. a,. Signals (1) Buoys, with or without lights. (2) Beacons, with or without lights. (3) Channel lights. (UX Sound signals

50 (5) Lightship

(6) Lighthouse

Y/ater front structures

(1) Landing piers

(2) Jetties or wharves

(3) Quays

(J4) Bank revetments

c. Cargo storage

(1) Transit sheds

(2) Warehouses and godowns

(3) Silos

(I4.) Coal bins

(5) Petroleum reservoirs

(6) Timber pond

(7) Refrigerating houses

(8) Ore plants

d* Wet docks (or harbour docks) with or without locks for tiie

loading and unloading at practically constant level*

ÜL* Repair docks

(1) Floating docks

(2) Dry docks or graving docks f* Cargo handling equipments

(1 ) Different kinds of cranes with different capacities (2) Derricks, booms and telfers

(3) Elevators

(to Conveyors

(5) Trailers, trucks and cars

51 £ • Perries

(1) Ferry racks

(2) Transfer bridges

(3) Ferry houses

(l|.) Railroad car and motor car transfers

h. Transportation services

(1) Railroad belt line

(2) Short distance car service

(3) Lighterage and barge transfer

i* Other reducing wave structures

(1) Stilling basins

(2) Cellular structures along the lee side of breakwaters

(3) Small harbour booms

(i4 ) Spending beaches

Defense works

(1) Marine railways

(2) Lift docks

113# In a harbour there are two lines to which all installations are required to observe. The bulkhead line is the line beyond which solid- filled structures may not be built. The pier head line is the line beyond which open-pile structures may not be built. Yihere the local conditions are favorable the distance between the bulkhead and pier head lines is generally made so that steamers of the length using the waterways may be alongside the piers at right angles to the channel* Inhere the narrowness of the waterway makes it impossible to allow this, a combined bulkhead and pier head line is sometimes adopted,in which case the vessels using the

52 f

waterway have to lie parallel to the channel. There may be all kinds

and varieties of conditions between these two. If the distance between

the bulkhead and pier head lines is not sufficient to allow a vessel to

lie at right angles with the channel, the piers may be built at an angle

such that the vessel can lie between the two lines. Also the slip may

be excavated into the shore land inside the established bulkhead line»

111*.. Among all the world ports we cannot find a universally

adopted system of layout. Different local conditions from the varieties

of vessels to geological or meteorlogical differences necessitate special

design for each layout. Generally speaking, the following systems are

usually suitable for certain places and can be adopted singly or in

combination with others.

ja. Pier and slip system

b^. Double pier system

c* Quay and basin system

d. Square basin system

^e. Herringbone system

f. Fork system

Conclusion

115* A harbour is a composite performance of all branches of

engineering. Civil engineering, of course, is the most fundamental

but an engineer of harbours eaaa'tknow nothing abeut mechanical, electri­

cal, chemical, and marine engineering, meterology and hydrology.

Even within the field of civil engineering a harbour design/ifcquires all CUA-J} Aspects of -the* knowledge from -¡fee city planning^ water supply to the materials of construction. EevMeo ~jbhe innumerable variations in

55 titen ihe Manne. different localities make the problem more intricate* The-general W 0y/(s Qre- less thtin General lajoui • 4èh n r layout io not as simple as the iaarine worka, -*»dr the engineer must-have M{

patience in the planning* Waves, winds, currents, drifts, -and those

inimical natural phenomena, are bound together as if they were an

offensive alliance to urge incessant and unrelenting war upon man*s handiwork — sapping, wearing, battering, making subtle inroads and

open breaches, working now by patient effort, long sustained, and now by sudden, prodigious feats, month after month, year in and year out, knowing neither truce nor armistice.

116. Therefore, we cannot hope to deal exhaustively with such

problems as this. It has only to be through experience gained from the

initial results and through the modifications introduced in consequence

that the solution of this difficult problem can be achieved. In fact, harbour engineering is still far from perfection or satisfaction, and further research and developments are soon expected by engineers.

5k List of References

1* Thomas Stevenson: ^Design and Construction of Harbours.w

2# The Encyclopedia Britannica //

3« H. A* Manner: wThe Tide.11

'4* A.S.C.E. Transactions I9 0 I4. Congress Papers No. 6 - Nq . 11.

5« George Stewart: "Range-Action in Harbour,” (Dock and Harbour

Authority, April 19l|3).

6. R. R # Minikin: "Breakwaters” (Dock and Harbour Authority,

April 1914-3)

7* XVIth International Congress of Navigation Reports No. 63-811

8* Captain D # D. Gaillard: "Wave Action in Relation to Engineering

Structures."

9» Brysson Cunningham: Harbour Engineering

10# Roy S. MacElevee: Port Development

55