DEPARTMENT OF THE ARMY
CORPS OF ENGINEERS

THE

BULLETIN

OF THE

BEACH EROSION BOARD

OFFICE, CHIEF OF ENGINEERS
WASHINGTON, D.C.

VOL. 3 OCTOBER 1, 1949

Vo!.

Marine Biological Lyte.

LIBRARY

OCT 171949
WOODS HOLE, Ass,

NO.

3 Me.g

DEPARTMENT OF THE ARMY

CORPS OF ENGINEERS

THE BULLETIN

OF THE
BEACH EROSION BOARD

TABLE OF CONTENTS

Page

Recent Contributions of Wave Research to Harbor

ISVALINSEISUNE? oo 000000000000000000000000000 900000000000 1
Combining Leadline and Echo-Sounding Methods in

Surveys of Submarine CanyonsS ......ccccece. D0d000000000 21
Forecasting Breakers and Surf on a Straight Beach

@ye Iabislobhrs lever’ g9000000000000000 99009900000000006 23
Construction of Additional Beach Erosion Board

Rescarnch wha casleishile’Soyocrarciersicvelclolel clove) ole SO OOUOaOD OO OCOOOU 33
Beach Erosion Studies ..... NUOO.O BOs OOD UO OSU oO DOUG oOo. 35
Beach Frosion Literature ..0..c.ccccescc0c00e 90000000000 399

VOL. 3 NO. 4

wmnet UA OA

0301 00448

i)

a

RECENT CONTRIBUTIONS OF WAVE RESEARCH
TO HARBOR ENGINEERING

The following article was first published in limited
issue as Technical Report HE-116-267, Fluid Mechanics
Laboratory, University of California. It is re-
produced here to disseminate valuable wave concept

principles among coastal engineers and other persons
having an interest in the action of waves and surf.
The paper was prepared by Mr. J. W. Johnson, Univer-
sity of California, July 1948.

The planning and execution of the extensive amphibious operations dur-
ing the recent war stimulated extensive research in the problems of waves,
surf, and related phenomena. The results of some of these investigations
have definite peacetime application to harbor engineering, and a review of
these developments to acquaint engineers with the methods appears desirable
at this time. The principal problems that are discussed pertain primarily
to the compilation of basic design data and the use of these data in the
design, construction, and operation of engineering structures exposed to
wave action. This discussion is confined to a consideration of waves
caused by wind. Other waves, such as surging in harbors or seismic sea
waves are relatively less important in most engineering investigations.
Only the broad aspects of the problem of wave action are presented; however,
sufficient references are given to permit the interested reader to study
further into the details of the techniques of application. The principles
apply equally well to wave action either on the ocean or on lakes and pro-
tected bays.

The Characteristics of Waves

The waves under consideration in this paper are those generated by
the action of wind on the water surface. Such waves are characterized
primarily by two factors: the height which is the difference in elevation
between the trough and crest of the wave, and the period which is the
time between the passage of two consecutive crests past a fixed point.
Other characteristics, such as wave length and wave velocity, may be
derived from the wave period. The characteristics of the waves generated
in a particular storm depend on three factors: the fetch which is the
distance the wind blows over the water surface; the average speed of the
wind over the fetch; and the length of time that the wind blows. In
general, the longer, farther, and faster the wind blows, the higher will
be the waves and the greater their period, length and velocity. For a
particular fetch and wind speed there is a maximum wave height regardless
of how long the wind blows; or for a particular wind speed, either fetch
or wind duration might limit the maximum height.

On the Pacific Coast the height of the wave usually is limited by the
wind duration, because in the major genrating areas the fetches are so long

and the wind speed so high that a relatively long duration would be required
for the waves to reach the limiting height. Such durations are rather infre-
quent. In lakes and land-locked bays the fetch is limited by the size of the
body of water, and large waves, therefore, cannot be formed. Within the
generating area, steep, short-crested waves of all possible heights, lengths,
and period are present, and many of them break as whitecaps. The waves
which leave a generating area and move into relatively calm water (commonly
called the decay area) are know as swell. The length, period, and velocity
of the swell gradually increase with distance from the generating area;
whereas, the height gradually decreases. In the Pacific Ocean where the
generating areas may be several thousand miles from the coast, the decay
distances are relatively large. The waves which travel such long distances
become very regular, and when they reach the coast they become a series of
long, low, and fairly regular undulations which usually are called ground
swells. In deep water the presence of this swell may be almost totally ob-
scured by small waves which are newly formed by local winds. It should be
mentioned that in relatively small bodies of waters, as lakes and bays,
which are subjected to wind action the entire water surface usually is a
generating area. There is no decay area in such instances and the waves
lose their energy during the storm by breaking on an adjacent shore.

Waves usually are classed as either deep-water or shallow-water waves.
When waves are moving in water depths less than half the wave length, their
motion is influenced by the bottom. Thus, waves moving in depths greater
than half a wave length are termed deep-water waves, and when moving in
lesser depths they are considered as shallow-water waves. Shallow-water
waves moving into shoaling water undergo important transformations. The
velocity and length of the waves decrease, while the period remains the
same, and the total energy is slightly reduced by bottom friction. Except
for a small initial decrease in height when the wave first "feels the
bottom", and height usually increases up to the point of breaking. If
Waves approach a shore line at an angle, the inshore portion of the wave
travels at a lower velocity than the portion in deeper water. The result
of refraction is a change in the wave heights and the direction of travel,
with the wave fronts becoming oriented nearly parallel to the bottom con-
tours. These factors may vary considerably at closely adjacent points on
a coast, due solely to the underwater topography. For example, refraction
concentrates wave energy over submarine ridges, causing the waves to in-
crease considerably in height. Qver a submarine canyon, on the other hand,
low wave heights occur due to the spreading of wave energy. Methods of
estimating the changes in wave heights and direction of travel are dis-
cussed subsequently.

For waves with a relatively large ratio of height to length in deep
water (usually short—period waves) the breaker height is about the same
as the wave height in deep water, but for waves with a small height-length
ratio in deep water (usually long-period waves) the breakers become much
higher than the deep-water height. A long low swell which hardly may be
observed in deep water can thus cause higher breakers than short period
waves of much greater deep-water height (Figure 1). It is the swell which
usually is responsible for the predominant breakers in the surf zone and
for damaging coastal structures.

Since there is considerable variability in wave height and wave length
in the waves leaving a generating area, it is necessary to define statisti-
cally the significance of the waves. Actually the higher waves are the
most important from an engineering standpoint; hence, in stating the mean
height of the waves that exist over a period of an hour or two it is ad-
visable to consider only the higher of the waves that are present. OQb-
viously, every ripple should not enter into forming an average. As a con-
sequence of these considerations the present practice in stating the
average wave height is to give the average height of the higher one-third
of all observed waves. Where the observation is precise, as in analyzing
the records of wave recorders, the average of the higher one-third of the
major train of waves is used. This average is called the “significant
wave height!

Compilation of Design Data

An engineer engaged in the design of coastal works must have a method
of estimating the highest waves which might be expected due to a given
design wind or, perhaps of more importance, he should have adequate data
on the characteristics of the waves to be expected for the different
seasons at any particular point. For the engineer engaged in construction
work or in handling floating equipment, statistical information alone is
insufficient for his operations. He must have definite information on the
wave conditions that will exist at the time of his operations. Methods
and instruments for providing such information are available and are now
in use. Statistical data on the frequency of occurrence of waves of various
heights at any given lecality can be assembled from direct observation
over a period of time, much as is done in assembling stream flow data for
flood-flow predictions. This procedure, of course, requires the installa-
tion of suitable recorders for measurement of the height and period of the
waves. Several years of record also must be assembled before reliable
average conditions can be determined.

The Department of Pngineering at the University of California, in
cooperation with the U. S. Navy, has had wave recorders in operation for
almost a year at Point Sur, California, and Hecta Head, Oregon. ‘These
recorders will provide sufficient coverage of the Pacific coast to permit
a compilation of statistical data on wave conditions at selected points
along the coast. Wave data for intermediate localities can be estimated
by interpolation. Records from the wave records also provide a means of
checking the method of forecasting waves from weather charts as discussed
later.

A brief discussion of the instruments which have been developed for
recording waves is of interest at this point. For coastal points, the
swell, as previously mentioned, is the predominate factor to consider in
the design of structures; hence, wave recorders such as those installed
on the Pacific coast are designed for obtaining information on only the
larger waves or what is called the "significant" waves. Of the various
recorders which have been developed by the University of California, all

operate on the method of recording pressure fluctuations at the sea bottom
and transposing these values to a surface wave height (Figure 2). The
fundamental principle of the method is that surface waves induce pressure
fluctuations in the entire column of water between the surface and the sea
bottom. For a particular depth of water and wave height, the amplitude of
these fluctuations depends on the wave period. These fluctuations are
filtered out by hydrodynamic action for the very short period waves, and
only the fluctuations for the longer period waves are recorded. The in-
strument consists simply of an underwater unit to pick up and convert
pressure fluctuations into electrical signals which are transmitted through
a cable to a strip chart recorder on shore. Two types of units have been
employed. In one of these instruments the pressure fluctuations at the

sea bottom actuate a small potentiometer through a system of bellows, and
these signals are transmitted to a bridge and recorder unit on shore. A
"slow leak" device in the underwater unit eliminates the effect of tides
and other very long waves. In the second type of instrument the underwater
pressure unit consists of an air-filled rubber bellows which contains a
thermopile. The changes in pressure due to the passage of a wave causes

a change in temperature of the air in the bellows. This change in
temperature is related to the waye period and the height of the wave at the
surface and is recorded on a instrument located on shore. Programming
switches usually are provided so that the recorders will operate at high
speed for 20 minutes in each 6-hour period. This high speed record permits
the determination of both height and period of the waves; whereas, the
low-speed record permits only height determinations. From the high-speed
section of the recorder charts the average height of the highest one-third
of the waves is determined and recorded as the significant waves occurr-—
ing at that time (Figure 3).

For recording wave characteristics on relatively small bodies of
water, such as lakes and bays, the same basic principle of using an
underwater unit to screen out the relatively small waves is employed.
The details of the units differ due to the relatively small~pressure
fluctuations which exist and due to the response characteristics of the
recorders.

In addition to the use of wave recorders, statistical information on
wave conditions at a given locality can be assembled from established
relationships between the characteristics of the waves and the fetch and
generating wind. These relationships were developed by The Scripps
Institution of Oceanography of the University of California and have been
presented in graphical form. These graphs permit the determination of
the height and period of the wave which will result from a wind of given
speed and duration blowing over a given fetch. The wave height given by
these relationships is the significant wave height as previously mentioned;
that is, it is the average height of the highest one-third of all waves
present. These curves originally appeared in the U. S. Navy Hydrographic
Office publication, "Wind Waves and Swell, Principles in Forecasting",
Misc. Report No. 11,275. As additional data on wave conditions were ob-
tained from shore recorders the curves were revised and presented in
Wave Report No. 73 of the Scripps Institution of Oceanography in March
1948. Also see the Bulletin of the Baach Erosion Board, Special Issue No.
ky onlay ik, USyAsio

The character of the significant waves in a generating area c&an be
obtained from the Scripps charts provided the variables of wind velocity,
fetch, and duration are known. In lakes or protected bays, local wind
records are suitable for estimating the wave conditions that can exist at
any particular locality. In fact, all past wind records of velocity,
direction, and duration can be used in conjunction with the charts and a
statistical compilation then made of the anticipated wave conditions at a
selected point. These data on wave heights then can be summarized in the
form of direction roses. Information of this type is of considerable
value to the designing engineer, as it not only gives the wave character-
istics which structures must be designed to withstand, but it also permits
an investigation to be made as to whether structures are economically
justified in view of the frequency of occurrence of waves of a damaging
character.

For a locality on an exposed coast, where critical wave conditions
result from swell which is generated by storms occurring at considerable
distance from the coast, local wind records are of relatively small value
in the compilation of significant wave characteristics. Thus, where large
scale wind patterns are involved, there are seldom sufficient weather
reports to determine these patterns directly from ship or island ob-
servations. However, there is a very close relationship between the speed
and direction of the wind and the atmospheric pressure gradient. This
latter factor can be determined from a weather chart. The pressure field
is not difficult to determine, even from only widely scattered reports.
The winds, therefore, are computed from the pressure gradient scales from
a weather chart and whatever wind osserwations are available are used to
check the computed values. A consideration of the orientation of the
isobars on a weather chart also permits an estimate to be made of the
extent of the generating area and, consequently, the value of the fetch
and the direction of wave propagation. By these methods of forecasting,

a statistical study can be made of the waves reaching a region of the
coast. Such an analysis has been made by the Scripps Institution of
Oceanography in cooperation with the Los Angeles District for Pacific
coast stations. The results of the studies have been compiled into wave
"roses" for five stations located along the Pacific coast at approximately
150 mile intervals from San Diego, California, to Cape Blanco, Oregon.
These statistical summaries, Figure 4, give wave conditions in deep water
and are basic data in the design of all future works on this portion of
the coast.

The use of weather charts in estimating wave conditions at a par-
ticular locality can be used to advantage by engineers involved in con-
structing coastal works or in using floating equipment which is ex-
posed to wave action. Although engineers usually plan their immediate
work on the local weather reports, in many cases it is the swell, coming
from storms occurring several days previously at a distant locality,
which actually affects their operations. A 24-hour forecast of wave con-
ditions that might exist at a particular point for a short time in the
future would be of unquestioned value to the construction engineer.
Usually it is not possible to make a reliahle forecast for more than two
days in advance, The details of utilizing daily weather charts for making

wave forecasts or in using historical weather charts for compiling
statistical data on waves that probably resulted from storms in the past
_is beyond the scope of this paper, For the techniques of the procedure

the reader is referred to Hydrographic Office Publication No. ll, 275
mentioned above. For a complete description of the theory involved re-
ference should be made to U. S. Navy Hydrographic Publication 601, “Wind
Sea and Swell: Theory of Relations for Forecasting", by Sverdrup and

Munk, March 1947. The accuracy of wave predictions which are made from
weather charts is of interest to engineers who rely on such information.

To provide such data foreaasting of sea and swell for comparison with ob-
servations was initiated shortly after the installation of the wave record-
ers at Point Sur and Heceta Head. Several months of wave records have per-
mitted a statistical analysis to be made of the accuracy of the forecast—
ing method. The comparison at Point Sur covered about 270 forecasts from
April to December 1947. At Heceta Head comparisons covered the period May
to December 1947 and involved about 200 forecasts. The actual comparison
of recorded to forecast values was, in general, good. A statistical
analysis shows that 97 per cent of the recorded significant increases in
wave height were forecast. Sixty-nine of the arrival times were pre-
dicted within six hours. The arrival times usually were predicted earlier
than those actually occurring. Fifty-three per cent of the forecast wave
heights were within one foot of the recorded heights, and eighty per cent
were within two feet. Sixty-three per cent of the forecast periods were
within two seconds of the recorded periocs. The forecast periods usually
were lower than the recorded periods. In general, it can be stated that
the forecasting technique results in a high degree of reliability for fore-
casting the arrival of significant increases in wave height, and for pro-
gnosticating the heights of the waves. These two factors are the important
items controlling marine and shore activities. A complete discussion of
the accuracy of forecasting appears in the article "A Comparison Between
Recorded and Forecast Waves on the Pacific Coast" by J. D. Isaacs and
Thorndike Saville, Jr., which was presented before the New York Academy

of Sciences, March 1948.

Refraction of Waves

As mentioned above, when waves move shoreward and approach a shore
line at an angle, refraction occurs and important changes to the height
and direction of travel of the waves results. The magnitude of these
changes is best considered to be a map which shows the wave crests at a
given time, or the successive positions of a particular wave as it moves
shoreward, Figure 5 shows a typical diagram which was prepared for the
area in the vicinity of Moss Landing in Monterey Bay, California. Note
that on this diagram there are a series of lines, orthogonals, drawn
perpendicular to the wave crests. These orthogonal lines are used in
estimating variations in wave height due to refraction. Such estimates
are made by assuming that the wave energy between any two orthogonals
remains constant and, for steady state conditions, the same energy
should flow past all positions between the orthogonals. A consideration
of the fundamental equation for the power of a wave shows that the ratio

6

of wave height between two points is

where bp and bj are the distances between orthogonals at points 2 and 1,
respectively. The right-hand member of this equation is termed a "refrac-
tion coefficient". A convergence of orthogonals indicates a concentration
of wave energy (large wave heights), and a divergence of orthogonals
indicates a spreading out of energy (low wave heights).

A refraction diagram can be prepared for a selected locality by merely
tracing, from a vertical aerial photograph, the wave crests onto a trans-
parent overlays; however, to cover the whole range of wave periods and
directions that a compilation of statistical data on wave characteristics
indicate as being possible, refraction diagrams are constructed graphically
by means of special scales. The details of this graphical method are
described in the publication “Graphical Construction of Wave Refraction
Diagrams", U. S. Navy Hydrographic Publication No. 605.

Once a series of refraction diagrams for various periods and directions
have been prepared for a given locality, orthogonals to the wave crests
can be constructed and refraction coefficients then computed by the above
equation from measurements taken directly from the diagrams. Such coeffic-
ients afford a convenient method of comparing wave heights at various
localities. On Figure 5, for example, refraction coefficients (that is,
ratios of wave height at given points to the deep-water wave height) are
given for various points along the shore for 10-second period waves from
WSW. Examination of this figure indicates that wave heights near Moss
Landing would be approximately half of the deep-water height. That such
a condition exists under actual wave conditions is indicated by Figure 6
which shows an aerial photograph of Moss Landing and vicinity. Note the
"flat! water at the end of the pier where the Monterey Canyon approaches
the shore, Small boat operators have long recognized that the sea is
relatively calm at the head of a submarine canyon.

Wave refraction analyses are rapidly approaching the status of a
standard component of shore line investigations. The primary value of re-
fraction diagrams is in evaluating the relative degrees of exposure of
coastal points to wave action; that is, their application permits the
determination of the critical direction and wave period from which damage
can be expected, When used in connection with wave forecasts from
synoptic weather charts, refraction diagrams permit the forecaster to
predict, for at least a day in advance, the wave conditions that will ex-
ist at a given point. Such forecasts are of great importance to the con-
struction engineer engaged in operations along the coast. The decision as
to the most desirable location for a permenent installation such as a
breakwater or docking facilities must be made by the design engineer using
statistical wave data and refraction diagrams. Usually only a few pericds
and directions need be drawn even for quantitative use, the remaining
conditions being supplied by inspection and interpolation. After some
experience an engineer very often can substitute a mental construction of

a refraction diagram for the graphical development.

In addition to the evaluation of the relative degree of exposure of
coastal points to wave action, refraction diagrams also can be used to
determine prevailing directions of littoral currents and other factors
which are of great importance in the transportation of beach materials.
Thus, from a refraction diagram the angle between the wave front at the
point of breaking and the shore and the breaker height can be determined.
The strength of the littoral current is a function of this breaker angle,
the beach slope, and the breaker height. The interruption of the normal
movement of littoral drift by the installation of coastal structures may
and has had serious effects in the vicinity of the works, For example,
at Santa Monica and Santa Barbara, California, the construction of break-
waters so interferred with the wave action ( and consequently the littoral
drift) that heavy deposits of sand occurred upcoast from the structures
and serious erosion resulted to the beaches on the downcoast side. Both
the Santa Monica breakwater and the original breakwater at Santa Barbara
were constructed approximately parallel to the shore with the expectation
that the sand transported by littoral currents would continue to move un-
interrupted down the coast. Wave refraction around the breakwater, how-
ever, was such that the littoral current carrying the sand was greatly
reduced in strength with the result that serious shoaling occurred to
the lee of the structure. Similar difficulty of upcoast deposits and
downcoast scour has occurred at Oceanside, Alamitos Bay, and Port
Hueneme, California, where jetties more or less perpendicular to the coast—
line has been constructed in an attempt to stabilize the harbor entrances.
Periodic pumping of the sand from the upcoast deposits to the opposite
side of these entrances appears to be the only solution in keeping the
harbors open and in supplying sand to the downcoast beaches.

In addition to the refraction of waves due to bottom effects,
refraction can result in some instances from tidal currents. A current
which opposes waves entering an inlet may have the effect of increasing
the steepness of the waves and cause them to break. Such conditions
very often occur on the ebb tide at many harbor entrances and may prove
extremely hazardous to shipping operations. A consideration of the wave
and current characteristic permits a designer to orient a harbor entrance
so that the undesirable effects of wave refraction by currents can be
greatly minimized,

Wave Diffraction

Wave diffraction is considered to be the phenomenon in which water
waves are propagated into a sheltered region formed by a breakwater or
similar barrier which interrupts a portion of an otherwise regular wave
train. A knowledge of diffraction behavior has important application in
the design and location of breakwaters in connection with harbor develop-
ment. It also appears to have an application to the distribution of wave
energy along beaches located in the lee of headlands and offshore islands.

The sheltering effect of a breakwater of finite length and vertical
impermeable walls depends upon diffraction of the incident waves around
the ends of the breakwater. The phenomenon is analagous to the diffraction
of light, and a theory of breakwater diffraction has been adapted from the
theory of physical optics. To check the applicability of this theory to
problems of breakwater design a series of model studies was made in the
wave tank at University of California, Berkeley, California. The tests
consisted primarily of generating waves which moved toward a model break-
water that could be given various orientations. Heights of the incident
waves as well as wave heights at various points in the lee of the break-
water were measured by recording instruments. The conclusions from these
tests were that the general form of the wave-diffraction theory was
verified. Good agreement was obtained for the region sheltered by the
breakwater for all angles of incidence investigated (that is, from 0° to
135°). Outside of the geometric shadow the experimental wave heights were
considerably less than the theoretical heights. In general the theoretical
solution may be applied to the location and design of breakwaters with
conservative results. In other words, the predicted wave heights in
disturbed regions in the lee of the breakwater will be somewhat larger
than the height of waves that may be expected in nature. No effect on
diffraction resulted from rounding the tip of the breakwater. It should
be noted that the diffraction theory applies only to waves in deep water;
that is, refraction effects are not included in the treatment.

The use of the wave diffraction theory in breakwater design problems
is made convenient when summarized in a diagram which shows curves of
equal values of diffraction coefficients on a coordinate system in which
the origin is at the breakwater tip; the diffraction coefficient in this
instance being defined as the ratio of the diffracted wave height to the
incident wave height. Figure 7 shows such a generalized diagram where
coordinates at a particular point are expressed as a multiple of the
wave length. It is of interest to note on this diagram that along the
geome tric shadow the wave heights are one-half of the height of the in-
cident waves, and that waves slightly greater in height than the incident
waves are possible beyond the breakwater.

The use of a diffraction diagram in arriving at the most desirable
alignment of a breakwater first necessitates the selection of the design
wave from a consideration of the factors discussed above; that is, the
height, period and direction of the incident wave from which protection
is to be provided, A large scale map of the general area at the proposed
breakwater is required and the direction (or directions) of the critical
waves is indicated. For the given wave period the wave length is
computed and a diagram showing curves of equal wave diffraction coeffic- —
jients similar to Figure 7, is plotted on transparent paper with the
same length scale as the map of the general area. This transparent

paper with the same length scale as the map of the general area. This
transparent overlay then may be moved around on the map(keeping the geo-
metric shadow parallel to the direction of wave travel) until the desired
degree of protection for a selected reach of the shore line has been ob-
tained. The location of the breakwater tip is thus determined. For

example, Figure 8 shows such an analysis for the orientation of proposed
breakwaters at Hunters Point in San Francisco Bay, California. From

an analysis of available wind observations it was found that relatively
high waves of 3.6-second period (wave length of 66 feet) could be ex-
pected from the SE and from SSE. For this period a diffraction coeffic-—
ient diagram was computed and plotted on transparent paper. With a
specified clearance of 2.700 feet between the pier and the proposed
breakwater and the specification that the docking facilities would not be
subjected to waves more than one-half the height of the incident waves,
the overlays were shifted over the map until the desired degree of pro-
tection was attained. Examination of this figure shows that waves from
the SE were used at the northerly end of the breakwater and waves from
the SSE were used for the southerly end, as these conditions were con-
sidered to be the most serious. Thus, for waves approaching Hunters Point
from the SE to SSE sector the breakwater orientation shown in Figure 8
assures the designer that wave heights in the docking area will be
sufficiently small so as not to interfere with normal operations. For
this orientation two positions of the southern tip are shown--one for
present development and a second for ultimate development. For the latter
condition, note that by placing a portion of the southern end of the
breakwater at an angle to the main section the same degree of protection
can be achieved at the dock area with a shorter gverall length of break—
water o

The treatment of diffraction problems, as discussed above, is con=
cerned with waves moving past a breakwater tip with an infinite expanse
of water existing off the tip. In many harbors, however, waves may move
through a relatively narrow gap in a breakwater; hence, diffraction takes
place at the tip on the two sides of the gap and changes in wave height
in the lee of breakwater will be different than if a single tip existed.
A theory for this condition also has been developed, and model studies
for verification have been made. As in the case of diffraction at a
Single breakwater tip, the application of the results to the determination
of wave heights within a harbor is made convenient by the use of trans-
parent overlays.

The generalized diagrams for determining sheltering effects due to
the diffraction of waves and the generalized scales for the graphical
construction of refraction diagrams are of considerable value to the design
engineer, These aids permit the analytical solution of many problems con-
nected with harbor design and eliminate the necessity, in many instances,
of relatively expensive model studies.

Wave Action on Structures

Considerable attention has been devoted in the past to the structural
design of installations exposed to wave action. A review of the principles
employed in stress determinations is beyond the scope of this paper, and
the discussion above is confined entirely to the methods of determining
the characteristic of the waves which would impose the most critical
stresses. Thus, the height, period, and direction of the highest waves,
that are possible at a specified offshore point in deep water, can be

10

estimated by an examination of past weather charts (in the case of the sea
coast) or from wind records (for a lake or bay). The principles of re-
fraction and diffraction permit a designer to determine the characteristics
of these same waves at any other point after they have moved shoreward,.
That location where a structure will receive the most favorable protection
from wave action, therefore, can be selected with confidence.

It should be recognized that maximum stresses are developed when
waves break directly on a structure. Even though wave heights ata
structure may be less than the offshore waves, as a result of refraction
or diffraction, the breaking of these waves may induce relatively high
stresses; consequently, the expected point at which waves will break
should be considered in the final analysis of a design. In some cases it
is possible to avoid excessive stresses induced by breaking waves, by
orienting the structure such that much of the wave energy is reflected by
the structure itself, or much of the wave energy may be dissipated by
forcing the wave to break before it reaches the structure.

As previously mentioned, wind generated waves usually are the most
important to consider in harbor design. However, in areas subject to long-
period ground swell, surging often becomes a serious problem because the
period of the ground sweli may be close to the fundamental, or first, or
second harmonic of the natural period of oscillation of the body of water
within the harbor. In many instances the natural period of a basin and,
therefore the possibility of surging, can be determined by simple com-
putation from the dimensions of the body of water. In harbors of re-
latively complicated dimensions, however, a resort to model studies may
be necessary to completely solve the problem of surging.

Acknowledgment

With the exception of the wave forecasting method which was develop-
ed at the Scripps Institution of Oceanography, La Jolla, the various
developments described above resulted from investifations made at the
University of California by the Department of Engineering, Berkeley.
This work was sponsored by the Bureau of Ships and the Office of Naval
Research.

11

Figure l. Aerial photograph showing wave conditions at Morro Bay, California. Small wind waves

and a long low swell are present. Note that the swell is almost invisible in deep water
but peaks up near shore to form the predominant breakers.

*Jeplooel eABM ETOYS qeotdhy @ JO WeIZBTp oTQBUIEYyoS °g emMIdtTy

GV3H 3YNSS3Yd YSLVM-Y30NN

31avo SNINVWENS GBYOWNY wy YU
YOLONGNOD - 3SYHL —.. 3. y 2 Y

SAONe NOILVLO14

WOIMAHdS =

‘4

s aqavo Aone

oe f;
Bina pee “iY 7
Bel é NOLLOV SINVNAGOHGAH AB LNO
ae | VY g3uaL4 S3AVM GOIad LYOHS
,on@ 9V14

=

YSaMOd 8 39dINS

13

CE oes” 4
a
a
a

po BODES RES SR OREREGSEES enon ==— ao coeneas
SEEEEEEE EEE EEE

Gnaneas ae
GES GaeZe0ea See eee an nnn

Pee eee aon If eatataialera sleet
Saba. — ~=5 258: BEE EEE ae ie

MAY 9, 1948

SEE fdas aescaeeetseseee

eae CP HEH HEH

“v8 nN sav Wind "OD one
@eeeeeeoneoewaeenenaeaeseoeeee @ @ @ @

oc Hoo DSS ee es 5— SS °C0 00d PEE SIGOREA F2o08,
= 5 ray Taint 7

Note the typical

14

variation in the height and period of the waves.

Sample chart from a shore wave recorder.

Figure Se

STATISTICAL SUMMARY OF WAVES
FOR STATION AT LAT. 35°N. & LONG. I2i°W
FOR THE YEARS 1936-37-38

SUMMER
JUNE, JULY; AUG, SEPT.

TRANSITION
APRIL, MAY; OCT. NOV.

WINTER
DEC, JAN.; FEB, MAR.

Figure 4, Typical direction roses which show the percentage of total
days when wave heights were less than a given value.

13

Ss ‘Sls

MSM WOUS - 93S O! GOlN3d
VINYOSITV9 “SNIGNV1 SSOW
WVYSVIG NOILOVY43aY SAVM

“M177W M0138 SWOH1V4 NI SH1d30 —- —- —— ——
43343 NI 31v9S

ONIGNYT ssON eA, Hp

eka

<<
os

Figure 6. Aeriais photograph showing typical wave conditions at Moss Landing, California.

1]

= qm] 0} aol No
© oO; Oo} OF o|—| —/—
¥
=
oO
Qa
aq
r
7)
)
x
|
Ww
=
(oe)
Ww
CG)
(0) 10
eee)
\ SCALE OF VALUES
xX N
< OF M AND %
Be y
BREAKWATER MUST \ | _ HEIGHT OF DIFFRACTED WAVE

LIE IN THIS ZONE : K = “HEIGHT OF INCIDENT WAVE

LOCATE TIP OF /7
BREAKWATER HERE,
7

Va

7

Yin

7

DIRECTION OF INCIDENT WAVES

WAVE DIFFRACTION BEHIND A VERTICAL IMPERMEABLE BREAKWATER
FIG. 7

~ POINT AVISADERO

HUNTERS POINT

S
=z
wi
=
a.
fo)
—s
w
>
WwW
a
ry)
Ee
S
[=)
w
=
=

PROPOSED PIERS

ULTIMATE DEVELOPMENT

2S SSS SS SS SSS See =

|

VICINITY MAP

Ss

A OAKLAND

Sy,

4 SAN FRANCISCO
BAY

PACIFIC OCEAN

DEPTHS IN FEET AT MLLW —-——-—— 20
500 [-) 500 1000-1500

FIGURE 8 - ILLUSTRATION OF THE USE OF DIFFRACTION DIAGRAMS IN DETERMINING THE ORIENTATION OF BREAKWATERS WHICH GIVE THE GREATEST
DEGREE OF PROTECTION AGAINST WAVE ACTION

STREAM GAGING UNIT MOUNTED ON STERN OF DUKW
- FIGURE |

WINOING DRUM AND COUNTING DEVICE OF THE
STREAM GAGING UNIT
FIGURE 2

20

COMBINING LEADLINE AND ECHO-SOUNDING
METHODS IN SURVEYS OF SUBMARINE CANYONS

The Field Research Group of the Beach Erosion Poard was required in
connection with littoral drift studies to make an accurate hydrographic
survey of the head of the submarine canyon off Redondo Beach, California.
The walls of the canyon are very steep, often exceeding slopes of 1:1,
and the use of an echo sounder for determining submarine relief in this
case was not considered sufficiently accurate.

The usual survey procedure of the Field Research Group is to take echo
soundings on given ranges, starting from deep water and running shoreward.
The echo-sounding equipment is operated from an amphibious truck (DUKW)
and horizontal control is maintained by two radio-—equipped shore stations.
It was desirable to continue utilizing this method as far as possible,
however the working schedule of the Group did not allow time for detailed
leadline sounding by this process. A more rapid method was devised using
heavy duty stream gaging equipment in conjunction with the echo sounder.

A standard stream gaging unit was borrowed from the Los Angeles Office,
U.S. Geological Survey, consisting of a 100-pound streamlined lead weight
fastened to a stainless steel wire and supported by a collapsible boom,
see Figure 1. The wire winding drum is equipped with a counting device
(Figure 2) that reads to tenths of feet. This equipment is normally used
for stream gaging from bridges with either a 100- or 50-pound lead weight.

Operational tests were conducted with both the 50- and 100- pound
weight, to determine the optimum operating speed of the DUKW, and the
feasibility of running ranges both seaward and landward, It was found that
by reducing the speed of the DUKW from about 450 feet per minute (normal
operating speed) to 180 feet per minute, and using the 100-pound weight
the sounding line would not “bow't or "drag" appreciably in depths as great
as 150 fest. The characteristics of the depth counter are such that_if
the weight was allowed to run nearly free, the instant the lead weight
touched bottom and the line slacked the counter would stop long enough for
a reading to be taken before continuing to indicate. Thus by running the
range seaward, or downslope, the leadline could be dropped and the brake
applied as soon as the indicator showed bottom, the forward speed of the
DUKW then would quickly drag the weight into deep water, the line would
resume vertical, and another sounding could be taken. It was found after
a few hours training that the leadsman could take leadline soundings at
15 to 20 second intervals (45 to 60 feet sounding interval) in depths as
great as 150 feet.

While the echo-sounder recording does not show true vertical depths
it is useful to show the relative detail in the vicinity of the leadline
soundings.

The working procedure of the group was to start from the shore end

of the canyon and travel seaward at a rate of 180 feet per minute, using
both the echo sounder and the leadline. The leadsman would take soundings

21

as rapidly as possible. The operator of the echo sounder would watch the
leadline and as the lead struck bottom, mark a "fix" on the echo-sounder
recording and call "fix" over the radio to signal the shore stations to
cut in the horizontal position of the DUKW. By utilizing this procedure
accurate leadline soundings were plotted every 45 to 60 feet and the echo-
sounder recordings were used to fill in details between successive lead-
line soundings.

The characteristics of submarine canyons make this sounding technique
practical, The relatively steep slopes of the canyon are usually firm sand,
clay or rock thus eliminating the possible objection of sinkage into the
bottom of the 100-pound lead weight.

It is believed that the combination of leadline and echo sounder
methods described provides a satisfactory means of obtaining relatively
accurate depth information on the slopes of submarine canyons or other very
steep submarine slopes.

22

FORECASTING BREAKERS AND SURF ON A STRAIGHT
BEACH OF INFINITE LENGTH

GENERALIZED DIAGRAMS FOR FORECASTING BREAKERS AND SURF
ON_A STRAIGHT BEACH OF INFINITE LENGTH

The following memoranda were first published in limited
issue as Technical Reports HE-116-13 and HE-116-67,
Fluid Mechanics Laboratory, University of California.
They are reproduced here to bring the wave forecasting

methods therein to the attention of research workers and
other persons interested in wave forecasting. The
memoranda were prepared by the staff of the Department
of Engineering, University of California, February 1947.

In forecasting the characteristics of breakers and surf at a particular
beach, the process is simplified with the aid of diagrams. From a deep
water forecast of wave height (H)), period (T), and wave direction, a fore-
cast also may be made of breaker height (H;,), depth at breaker (dp), angle
of breaker with the bottom contours (@pb ), and distance from edge of still
water to breaker (X)). The surf forecasts are made simple with the aid of
diagrams presented in "Breakers and Surf, Principles in Forecasting", H.0.
No. 234, and Supplementary. data; however, the forecast can be simplified
further by means of other diagrams obtained by replotting the curves in
Manual No. 234. Figure 1 shows such a plot in which all forecast computa-
tions are made graphically from diagrams appearing on a single page. This
figure applied only to Las Pulgas Beach near Oceanside, Californias; however,
many of the diagrams are general in character and can be used at any
locality by merely shifting scales. Figure 2 shows the basic diagrams which
can be adapted to any beach. The discussion to follow describes the method
of plotting each of the individual diagrams as well as explaining the steps
necessary in adapting the data to any beach such as Las Pulgas Beach (Fig-
ure 1).

Breaker Height

When waves with a particular steepness in deep water (H, ho) approach
a straight shore line of infinite length with wave crests parallel to the
bottom contours, the height of the waves changes according to the ourve

of YEN as a function of d/Lg shown in Plate I of H.O. Manual No. 234.

The value of d/L, at which the waves break depends on the initial steepness
(H,/Lo)- If, however, the waves in deep water make an angle ct with the
shore, as they move into shallow water, refraction occurs and wave heights
are reduced. The angle with which the waves make with the bottom contours
depends on the value of d/Lo and the deep water angle &, +. This re-
lationship is shown in Plate II (H.O. No. 234). Also shown in this plate
are corresponding values of k, the correction factor to wave height because
of refraction.

By definition, the following relationships may be expressed; k = Be

Oo

23

FEET

I=

STILLWATER DEPTH AT BREAKER d

26

24

20

233

263 273 283 293

WNW.
+

243
WoW,

253
¥

VALUES OF H,/T*

5678910 15 20
PERIOD,T—-SECONDS

28 24 20 16 12 8 4 (0) sw. ssw $ SSE
BREAKER HEIGHT, H,—-FEET 233 223 213 203 193 183 173 163 153 143
DIRECTION OF WAVES—TRUE AZIMUTH
233 243 253 263 273 283 293 303

a

nm
fe}

G

LOS ANGELES
LAS PULGAS BEACH—S™\_
SAN DIEGO

BREAKER ANGLE, ©,—- DEGREES

LOCATION MAP

SW
223

Nn
fo}

+
S)
183

ssw

213 203 193 \73 163

DIRECTION OF WAVES—-TRUE AZIMUTH

o

F

STILLWATER DEPTH AT BREAKER,

oo}

10 12 U
PERIOD, T— SECONDS

4

WAVE CHARACTERISTICS FROM FORECAST:-
Ho#=10 FT.,T=9.5 SEC., AZIMUTH= 202.5 DEG.
DETERMINE SURF CHARACTERISTICS WHEN
THE STAGE OF TIDE !S +3.5 FT.

SURF

200
DISTAN

FROM CHART A: FOR T= 9.5 SEC.,Ho/T® 0.11
FROM CHART B: FROM INTERSECTION
OF THE CURVE H,/T*=©O.I| AND AZI-
MUTH OF 202.5 DEG. DRAW HORIZONTAL
LINE TO CURVE OF H,=10 FT. ON CHART
C; THEREFORE, BREAKER HEIGHT, Hell. FT.

FORECASTING GHA
FOR
LAS PULGAS BEACH

FIGURE |
24

800 1000 1200 1400 1600

400
CE FROM EDGE OF STILLWATER, X,- FEET

600

FROM CHART D: FOR T=9.5 SEC. AND H,
=ILIFT, DEPTH AT BREAKER, d= 139 FT.
FROM CHART E:FOR Ho/T'=0.Il AND
AZIMUTH OF 202.5 DEG.,@,=12.5 DEG.
FROM GHART F:FOR 4,=13.9 FT. AND A
TIDE OF + 3.5 FT.,X,=725 FT.

RT

STILLWATER DEPTH AT BREAKER d, FEET

C

28 24 20 16 12 8 4 fe)
BREAKER HEIGHT, H,—FEET

26

10 20 30 40 50
Q&.— DEGREES

24

20

ine

22 Ae
WA \6 C=] EUREKA

«
;

| al SAN DIEGO

LOCATION MAP

| F Hb
ae)
REE ee etl
JL
2 IL u
0 D
4 6 8 10 12 14 16 18

PERIOD, T- SECONDS

60

a

@ 0

BREAKER ANGLE, ,

- DEGREES
ny N
fo)

>

70

80 90

0.04lA
3 4 5678910 15 20
PERIOD, T- SECONDS

20

SURF FORECASTING CHART

FIGURE 2
2

30 40 50 60 70
& . — DEGREES

or
k= H' 4 /Uo
Eyien

Replacing Ly in the denominator by 5.121

B= (bod) oe 638 (2)
(ip /T*)
By a combination of Plates { and II (H.0. No. 234) and the use of Equation
(2) a curve to show the relationship between H,/H. and @o can be constructed
(Diagram B of Figure 2). Breaker height Hp then can be obtained from another
diagram which shows values of H,/Ho plotted against Hp with curves of con-
stant H, (Diagram C, Figure 2).
The procedure in computing data for plotting Diagram B is as follows:
Assume a value of H,/L, = 0.0780
Then H,/T = 0.078 x 5.12 = 0.40

For various assumed values of dp /Lo computations are made in tabular form,
(Table I).

TABLE I
PLOTTING DATA FOR DIAGRAM B

H,/L, = 0.078 (H)/T* = 0.40)

oc Xp
Assumed HYa. Hb ; k Hy HAs. deg.
Value Ls AT Hi'o = _Ho Ho From Plate II
of From Plate I (H.0. Lo Lo Col. 3 H.Q. No. 234 with
dy /Lo No. 234) times Cols. (1) and (4) as
Col. 4 Arguments

(1) (2) (3) (4) (5) (6) (7)
0.06 0.0445 1.03 0.570 0.59 74 03 340
0.07 0.052 1.02 0.666 0.68 68.5 3407

Computations as shown in Table I are made with other values of H [io
Cross plots then permit a diagram to be constructed with Hp/H plotted
against &g for various constant values OE» Bly lie or H/T (see Diagram
B, Figure 2). In order to eliminate a slide-rule computation of ey, from
the forecast values of Hj and T, Diagram A has been prepared.

26

It is to be noted that for a particular beach the scale showing values
of &, in Diagram B could be replaced by a scale which shows the true
azimuth of the wave direction. For example, in the diagram for Las Pulgas
Beach (Figure 1) the true azimuth of the beach is 233 degrees; hence, this
azimuth is equivalent to an oc, of zero degrees. Points of the compass
also may be indicated on the scale.

Diagram C is plotted alongside Diagram B with a common ordinate
scale, Hp/Ho- Thus, for a particular wave direction &» and value of Ho /T
obtained from Diagram A, Hp/Ho is obtained from “iagram B. For this value
of Hp/Ho, the breaker height Hp is obtained from-Diagram C for the forecast
value of Ho.

Breaker Depth

To obtain the depth of breaking for breakers of a certain height and
period, the data is Plate III of H.Q. No. 234 has been replotted to give
Diagram D. For a particular period the depth of breaking, dp, is obtained
from Plate III for various breaker heights, Hp. These plotting data are
given in Table II.

TABLE II
VALUES AT DEPTH OF BREAKING

(Obtained from Plate III. H.Q. No. 234)

T (sec.)
H

fate (h, 5 6 a] 8 9 1 12 WA 16 18
1 Lok bes} eS) dees. 2 ss, WesOn 2eOl eel ada eee oe seo.
2 205 2.6 2.8 BOO) Bo@® BoB BGA | BOO BGS) Ak AO
3 Boll 3.8 AO Lo® Mok Bo® AS 502 Dom 6.0 6.2
4 508) Boll Sol 508 SoH Syovl) 6.0 6565 PO Woh Vor
5 7.0 6.5 653 855 Oo6G 68 WoS Po Go2 BG GO
6 Siew, 8.0 FoS YoS Vo B60 Boh Goll QoS WO WOoA
Y] 10.9 9.5 Og 845 G43 Gee QoS MOss: Woes -Wiloe Loe
8 Wil - UO.2 Ws Ws Wss} WOsG Whos Woe 12.6 Loo
9 Tle alee Tales) GSS hl 266 NSCS SoS WAG
10 W355 W297 NA.5 IA.6 W246) Wiss W268) W552 18.6
abe WG62 WAo® Wo US57 WAO WSO 6.2 W6.5 Le9)
12 W762 WS WHA Was US Wos2 WHos W/o Woe
13} Wei, UVR WG. WSs2 W383 Woe WGo5 Wo MWos
14 W560) W755 7.5 WSS WS Aol #2056
5 WH Woy? 2065 Alo, Bhai
20.5 Bs a5 x 23\.3}

o/h 3

ze 20.8 2).
17 Pals 23.2 240
18 D205, ASSES) 2502
19 QO 5
20 27.9

The depth of breaker, dp, is determined from Diagram D for the forecast
period, T, and the breaker height, Hp, obtained from Diagram C.

Breaker Angle

The angle with which the breakers make with the bottom contours is
obtained from the same data used in preparing Diagram B. Referring to
Table I, it is noted that breaker angle, Zp , and deep water wave direction
&oq ,» will give a family of curves of constant H,/T. such a plot is
shown in Diagram HE, Figure 2, As in the case of Diagram B, the scale of
&o may be replaced by true azimuth when a particular beach is under con-
sideration. Thus, in Figure 1 for Las Pulgas Beach, the true azimuth and
compass points are shown instead of the deep water angle, X) .

Distance to Breaker from Edge of Still Water

The distance Xp, from the edge of still water to the point of break-
ing is a function of the bottom profile and the stage of the tide. A
simple diagram to give this distance would be merely a bottom profile with
various stages of the tide indicated as shown in the following sketch.

Tide stage

With the stage of tide known and the depth at breaking determined from
Diagram D, the point at breaking can be located. The distance from this
point to the edge of still water is scaled from the sketch. Because such a
diagram requires a sliding scale, a family of profile curves is used to
simplify the procedure. The intersections between the water surface (at
various stages of the tide) and the bottom are determined, and the profiles
below these points then are plotted with the above mentioned intersections
at a common point. Diagram F (Figure 1) shows such a diagram for Las
Pulgas Beach, It is to be noted that Diagrams A-E, inclusive, are general
in character and apply to any straight beach with proper notation as to the
Co scales in Diagrams B and £; however, Diagram F is different for each
locality and therefore is omitted from the general diagrams, Figure 2.

When available it is also planned to include a diagram for forecasting
the strength of the littoral current.

28

MEMORANDUM CONCERNING THE WATER DEPTH AND WAVE
ANGLE AT THE POINT OF BREAKING

Methods in use for determining the water depth and the angle between
the wave crest and the depth contour, at the point at which waves break,
appear to be susceptible to some simplification for straight shore lines.
Only the breaker condition is desired. The quantities given by the fore—

cast are &, , T, and H,. The refraction coefficient, k or Hb /Ho » is a

function of «»g and d/f only. Using these quantities and the experiment-—

ally determined breaking conditions from Plate I of "Breakers and Surf,
Principles in Forecasting", H. 0. No. 234, the curves are as shown in
Figure 1.

; The method of solution is to assume values of (d,/T?) and obtain
H'o from the curve for the pertinent value of &_ . Multiply the true
Ho
value of #o_ by Hlo and compare with the value of ("Q)p. At the

rahe ae [2

breaking condition,

Foy «(Hoy , Ho
Pe) hae

As an example of the method, assume the following conditions:

Xo = 40°

Ho = 5 ft.

tT = 10 see.
Therefore

Ho = 0.05

By trial and error,

———

Assume
Gye GL ke eo a
2 “oe Gas on )
0.10 0.052 0.88 0.044
0.09 0.044 0.88 0.044

The correct value of d,p/T, therefore, is 0.09 and the corresponding
values of other terms are:
ae 0.044

72

and the depth at breaking is,
dp, = 0.09 x 10* =9 ft.

From Figure l,

Hb = 1.47
Ho

and the height of the breaker is,
Hp = 1.47 x 5 = TA ft.

From Plate II of "Breakers and Surf", H. 0. No. 234, (Figure 2) a copy of
which is attached for convenience, the breaker angle is computed as follows:

“a 8 = 0.0176
ig (Gel2y G0)

Then from Plate II, for this value of dp/L, and @_ = 40°, the breaker
angle is,

eae 2°

This method of computation is an alternate method to the generalized
diagrams for forecasting breakers and surf presented above.

It involves a trial and error computation; whereas, the method utiliz—
ing generalized diagrams does not, all computations being made graphically.

30

oe
(mae ie 2RE ie eee
QO:

ee a Ne ee ee en RIC
| ea es ee a eee eee
een area oe iS aS nnmeean

i he Ae eI II
gos [J

po ese
JERE eles ett
Oo re

So

)

H
(AG
°

'
eu)

REFRACTION COEFFICIENT

BREAKER CHARACTERISTICS

DETERMINATION OF WAVE HEIGHT AND DEPTH OF
WATER AT POINT OF BREAKING FOR WAVES ON A
BEACH OF INFINITE LENGTH

FIGURE |

Jl

1.0

Da agwaa

H+
[TN PEE AE
PAT AT

aS =SSsee
==

= Ed

gris
SSSES555

Sesscse

03
d/L,

.02

.005 .007 Ol

U
002 003

49 18126

Fig. 2. Change in Wave Direction and Height Due to Refraction on Beaches with
Straight, Parallel Depth Contours

CONSTRUCTION OF ADDITIONAL BEACH EROSION
BOARD RESEARCH FACILITIES

The Beach Erosion Board research facilities are being expanded by the
construction of a large wave tank and a coast model test basin. Plans and
specifications for the tanks were prepared in conjunction with the District
Engineer, Corps of Engineers, Washington, D. C. and the construction is
being performed under the general supervision of the District Engineer.

The contractor is Blackwell Engineering Company, Warrenton, Virginia. The
work is to be completed in 270 calendar days for a total contract cost of
$354,958. This contract is about 25 per cent complete at the time this
publication goes to press.

Wave Tank

The wave tank will be 635 feet long, 15 feet wide, and 20 feet deep.
Generation of waves is to be accomplished by a pusher-—type wave generator
capable of producing a maximum wave 6 feet in height and 300 feet in
length, in a normal water depth of 15 feet. The tank will be built of
reinforced concrete with the top of the tank 4 feet above the finished
grade, A working platform traveling longitudinally on rails, anchored to
top of the tank wall will provide access and measurement facilities during
the experiments. Three stop-log slots will be built in the walls to
allow partition of the tank into variable lengths and reduce water re-
quirements. The tank will be used for the study of the design of upstream
slope protection for earth dams, s8a walls, breakwaters, other harbor pro-
tective structures, and other structures subject to wave action.

The design of the large wave tank presented numerous problems which
were studied in a 1:12 scale model in the Board's laboratory to assist
in the actual design of the tank.

Coast Model Test Basin

The basin will be 300 feet by 150 feet in plan and 3 feet deep.
Reinforced concrete construction is to be used throughout the basin
structure with the 3 feet perimeter wall extending above finished grade.
A test area of about 200 feet by 100 feet, with a water depth of 2 feet
in the offshore, will be utilized in conducting tests. Wave generators
will produce a maximum wave in the magnitude of 2/3 feet in height in the
2-foot water depth. In order to provide flexibility in the location and
arrangement of the wave generating equipment, the equipment will be con-
structed in several units. The type of wave generator to be utilized in
the coast model basin is being investigated by small scale model studies.
In conjunction with the basin a storage reservoir 40 feet square and 11
feet deep will be constructed to function as a sump, with pump facilities,
for simulating tides. Two pumps, one 4,500 gpm and the other 2,200 gpm,
will provide for water circulation to the basin.

The basin will be used to study methods of controlling inlets to
prevent damage to adjacent shores; means of reducing wave and current

33

action on beaches; the general behavior of barrier beaches; methods of pro-
tecting and building beaches without damaging adjacent beaches; plans to
prevent shoaling of navigation channels; and specific areas of severe
coastal erosion when warranted.

34

BEACH EROSION STUDIES

The principal types of beach erosion reports of studies at specific
localities are the following:

a. Cooperative studies (authorization by the Chief of
Ingineers in accordance with Section 2, River and
Harbor Act approved on 3 July 1930).

b. Preliminary examinations and surveys (Congressional
authorization by reference to locality by name).

c. Reports on shore line changes which may result from
improvements of the entrances at the mouths of rivers
and inlets (Section 5, Public Law No. 409, 74th Con-

gress).

d. Reports on shore protection of Federal property
(authorization by the Chief of Rngineers).

Of these types of studies, cooperative beach erosion studies are
the type most frequently made when a community desires investigation
of its particular problem. As these studies have, consequently
greater general interest, information concerning studies of specific
localities contained in these quarterly bulletins will be confined to
cooperative studies. Information about other types of studies can be
obtained upon inquiry to this office.

Cooperative studies of beach erosion are studies made by the
Corps of Engineers in cooperation with appropriate agencies of the
various States by authority of Section 2, of the River and Harbor Act
approved on 3 July 1930. By executive ruling the cost of these studies
is divided equally between the United States and the cooperative agency.
Information concerning the initiation of a cooperative study may be
obtained from any District Mngineer of the Corps of Engineers. After
a report on a cooperative study has been transmitted to Congress, a
summary thereof is included in the next issue of this bulletin. A list
of cooperative studies now in progress follows:

COOPERATIVE BEACH EROSION STUDIES IN PROGRESS
NEW HAMPSHIRE

HAMPTON BEACH. Cooperative Agency: New Hampshire Shore and Beach
Preservation and Development Commission.

Problem: To determine the best method of preventing further
erosion and of stabilizing and restoring the beaches;
also to determine the extent of silting and erosion
in the harbor.

35

MASSACHUSETTS

METROPOLITAN DISTRICT BEACHES, BOSTON. Cooperating Agency: Metropoli-
tan District Commission (for the Commonwealth of Massachusetts).

Problem: To determine the best methods of preventing further
erosion, of stabilizing and improving the beaches, and
of protecting the sea walls of Lynn Shore Reservation,
Nahant Beach Parkway, Revere Beach, Quincy Shore, Nan-

tasket Beach.

SALISBURY BEACH. Cooperating Agency: Department of Public Works (for
the Commonwealth of Massachusetts).

Problem: To determine the best methods of preventing further
beach erosion. This will be a final report to report

dated 26 August 1941.
CONNECTICUT

STATE OF CONNECTICUT. Cooperating Agency: State of Connecticut
(Acting through the Flood Control and Water Policy Com-

mission).
Problem: To determine the most suitable methods of stabilizing
and improving the shore line. Sections of the coast

will be studied in order of priority as requested by
the cooperating agency until the entire coast is in-

cluded.
NEW JERSEY

OCEAN CITY. Cooperating Agency: City of Ocean City.

To determine the causes of erosion or accretion and
the effect of previously constructed groins and
structures, and to recommend remedial measures to
prevent further erosion and to restore the beaches.

Problem:

VIRGINIA
VIRGINIA BEACH. Cooperating Agency: Town of Virginia Beach.

To determine the methods for the improvement and pro-

Problem:
tection of the beach and existing concrete sea wall.

SOUTH CAROLINA

STATE OF SOUTH CAROLINA. Cooperating Agency: State Highway Depart—

ment.

To determine the best method of preventing erosion,

Pro blem:
stabilizing and improving the beaches.

36

LOUISIANA

LAKE PONTCHARTRAIN. Cooperating Agency: Soard of Levee Commissioners,
Orleans Levee District.

Problem: To determine the best method of effecting necessary
repairs to the existing sea wall and the desirability
of building an artificial beach to provide protection
to the wall and also to provide additional recreational
beach area.

mekas

GALVESTON COUNTY. Cooperating Agency: County Commissioners Court
ef Galveston County.

Problem; To determine the best method of providing a permanent
beach and the necessity for further protection or
extending the sea wall within the area bounded by the
Galveston South Jetty and Eight Mile Road.

‘CALIFORNIA

STATE OF CALIFORNIA. Cooperating Agency: Division of Beaches and
Parks, State of California.

Problem: To conduct a study of the problems of beach erosion and
shore protection along the entire coast of California.
The initial studies are to be made in the Ventura-Port
Hueneme area and the Santa Monica area.

WISCONSIN
RACINE COUNTY. Cooperating Agency: Racine County.

Problem: To prevent erosion by waves and currents, and to deter-
mine the most suitable methods for protection, re-
storation and development of beaches.

ILLINOIS

STATE OF ILLINOIS. Cooperating Agency: Department of Public Works
and Buildings, Division of Waterways, State of Illinois.

Problem: To determine the best method of preventing further
erosion and of protecting the Lake Michigan shore
line within the Illinois boundaries,

OHIO

STATE OF OHIQ. Cooperating Agency: State of Ohio (Acting through
the Superintendent of Public Works).

3?

Problem:

To determine the best method of preventing further
erosion of and stabilizing existing beaches, of
restoring and creating new beaches, and appropriate
locations for the development of recreational
facilities by the State along the Lake Erie shore

line.

TERRITORY OF HAWAITL

WAIKIKI BEACH. Cooperating Agency: Board of Harbor Commissioners,
Territory of Hawaii.

Problem:

To determine the most suitable method of preventing
erosion, and of incréasing the usable recreational
beach area, and to determine the extent of Federal
aid in effecting the desired improvement.

38

BEACH EROSION LITERATURE

There are listed below some recent acquisitions of the Board's lib-
rary which are considered to be of general interest. Copies of these
publications can be obtained on 30-day loan by interested official agen-
cies.

"Sea Waves and Microseisms," J. Darbyshire, Admiralty Research Laboratory,
Teddington, England, A.R.L./R. 1/103.50/W, March 1948.

The paper reports the comparison of wave records at Perranporth with
with simultaneous seismorgraph records at Kew made to detect the
influence of two mid-Atlantic storms on microseismic activity.
Meteorological charts for the storms are shown. Graphs show the
spectra of the waves and mi¢roseisms obtained by submitting the
records to frequency analysis. One of the conclusions states that
the period of the waves is double that of the corresponding micro-
seisms «

"A Theory of Microseism Generation,” M. S. Longnet-Higgins., Admiralty
Research Laboratory, Teddington, England, A.R.L./R.2/103.50/M,
August 1948.

In the report a theoretical justification is given for the theory
that microseisms of period 3 to 10 seconds originate in regions of
wave interference in the sea. It is show that the unattenuated
pressure variations in a standing wave are due to simultaneous
changes in the vertical momentum of the whole wave train. Varia-
tions in the mean pressure occur only when there is interference
between groups of waves of the same frequency travelling in op-
posite directions, they are twice the wave frequency and are propor-
tional to the product of the amplitudes of the two opposing groups.
Simultaneous pressure variations over a wide area will give rise

to compression in the water and sea bed. By considering the effect
of an application of pressure to the surface of the water it is
shown that the displacement of the ground should be of the same
order of magnitude as that observed. The conditions of wave inter-
ference necessary for microseism generation should occur in a moving
cyclonic depression or to a less extent when waves are reflected
from a steep coast. The doubling of the wave frequency implied by
theory is well supported by observation.

"Water Tables in Marine Beaches," K. 0. Emery and J. F. Foster, Journal
of Marine Research, Vol. VIII, No. 3, November 1948.

An attempt to learn the relationships between beach characteristics
and changing water levels within the beach is made in this study.
Measurements of the changing water table profiles in several

beaches throughout a tidal cycle show the presence of an inter-
change of water between the ocean and the sand pores. Water escapes
from the beach during ebb tide with a velocity sufficient to

39

elutriate silt grains. Some water is drawn by capillarity to the
sand surface where it evaporates, cementing the sand into a hard
crust. Water table profiles are shown for the ebbing and flooding
tides.

"Influence of the Water Table on Beach Aggradation and Degradation,"
U. S. Grant, Journal of Marine Research, Yol. VII, No. 3, November 1948.

Large waves provide the dynamic factors in rapid beach erosion, but
the wetness or dryness of the beach contributes in an important
manner to its erosion or aggradation. A high water table accele-
rates beach erosion, and conversely, a low water table may result
in pronounced aggradation of the foreshore. A sensitive water
table on a beach will have an important bearing on the method of
artificial sand replenishment by sluicing.

40