Formation of Stable Sandy Beaches and Beach Erosion Control : A Methodology for Beach Erosion Control Using Headlands and Its Applications
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Formation of Stable Sandy Beaches and Beach Erosion Control
: A Methodology for Beach Erosion Control Using Headlands
and Its Applications
Bulletin of the Disaster Prevention Research Institute (1994),
TypeDepartmental Bulletin Paper
KURENAI : Kyoto University Research Information Repository
Bull. Disas. Prey. Res. Inst. , Kyoto Univ. , Vol. 44, Part 3, No. 383, October, 1994
of Stable Sandy Beaches
for Beach Erosion
and Its Applications
and Beach Erosion Control :
Control Using Headlands
By Yoshito TSUCHIYA
(Manuscript received on January 6, 1994 ; revised on October 14, 1994)
Many attempts have been made to control beach erosion throughout the world, but in the long term none have suc-
ceeded in stabilizing sandy beaches that are being eroded. Almost all the common countermeasures are of little use for
stabilization as they cause beach profiles gradually to become steep. Some beautiful natural sandy beaches exist that are
stable and in equilibrium for longshore sediment transport. The equation for a stable sandy beach is derived from the set
of equations of continuity for beach change and longshore sediment transport under unsteady and nonuniform conditions,
so that theoretical shoreline configurations can be obtained for both static and dynamic stable sandy beaches. The
theoretical shoreline configurations of dynamic stable sandy beaches compare satisfactorily with those of actual sandy
beaches and provide a theoretical background for the formation and existence of natural stable sandy beaches. A meth-
odology for beach erosion control is proposed that is based on this theoretical background by which a series of stable
beaches are formed from eroding sandy beaches. This method also is applied in relation to the large scale coastal be-
havior of sandy beaches. Its application under actual erosion situations has resulted in stabilization based on the esta-
blishment of well-formed stable sandy beaches. A brief description for further improvement of this methodology is also
Acceleration of beach erosion throughout the world is now recognized as being due to the
way humans have developed and utilized coastal zones and river basins. In some areas, beach
erosion has also been accelerated because of a rise in sea level. Because of recent global warm-
ing and the resulting further rise in sea level, beach erosion will become an even more serious
in the next century
must be done
land mass conservation.
as well as our concep-
tion of coastlines of the 21st century. Having been asked') by the Ministry of Construction of
Japan to address these issues, I would like to begin with a short note on future coastlines.
It has been said that in the next century due to recent global warming both the scale of
typhoons and their occurrences may increase and that a rise in sea level of more than about 50
cm may take place. Many years ago, Dr. Torahiko Terada, one of Japan's foremost scientists
said, "Nature is faithful to her custom and experiences" and "Natural disasters are progressive
in relation to civilization, they reoccur only once they have been forgotten." Repetition of ab-
140 Y TSUCHIYA
normal natural forces may result in major catastrophes. The social environment produced in
relation to human activities generally is irreversible, resulting in a linear increase in total en-
tropy such that imbalances between nature and human activities are apt to be accelerated.
Such imbalances may combine with abnormal natural forces that previously have been respon-
sible for major disasters, and sometimes result in types of catastrophes that have never been
experienced. Predictably, this tendency will become more marked in the years to come. His-
torical data on storm surges in Japan indicate that major storm surges will be more frequent
within the first a few decades of the next century, which also may prove true for other natural
phenomena that cause disasters. On the long—term time scale, such variations in the state of
the weather and oceans are typical of ordinary variations in nature ; however, I think that if a
disastrous event impinges on the results of recent human activities, it may well become an ab-
normal event such as has never been experienced before. The relation of the coastline dividing
the land and the sea, therefore, must be discussed in relation to both its preservation and de-
technologies over the millennia as well as have created spiritual cultures and higher civiliza-
tions. Oriental and western civilizations differ essentially in their basic understanding of
nature). Both natural sandy beaches and steep rocky shores show the beauty that waves have
created over long periods of time. In the metaphorical sense, it can be said that there is "civ-
ilization" of waves that creates part of the majestic beauty of nature. The existence of human
beings is of great significance to the harmony that nature and waves have created, as their own
civilizations. In other words, a coexistent civilization must be created between human beings
and nature by we, human beings who have great capability to change nature.
Nature and civilization We human beings have developed sophisticated sciences and
chipelago, is located in one of the most geoscientifically active areas of the earth, and this is
the primary reason for the very beautiful coastlines found here. Imbalances between the long
term creation process of nature and nature as reconstructed by humans exist, such as those re-
sulting in beach collapse and erosion. In Japan, a coastal law has been enacted under which
preservation of coastlines has been started, but difficult problems remain to be solved in the
control of coastlines'). For example, it is clear that longshore sediment transport occurs
within an area called a sedimentation cell and that this can not be controlled by the passage of
laws. It must be kept in mind that nature maintains the continuity of sediment transport.
When reformation of natural features by human beings takes place on a different time scale
than that of nature, there is an inevitable reaction which may result in a major catastrophe.
In terms of coast preservation, the potential of this reaction has to be reduced as much as
Coastline preservation for the long term Our country, which comprises the Japanese ar-
possible by ensuring that there is long—term preservation of coastlines against abnormal natural
forces. It follows that a long—term methodology for the preservation of coasts must be esta-
zoning of coastal areas has to be done for both the utilization and prevervation of coastlines.
Coastlines in greater harmony with nature In various nations, and particularly in Japan,
Formation of Stable Sandy Beaches and Beach Erosion Control :
A Methodology for Beach Erosion Control Using Headlands and Its Applications
So–called bay areas, in which natural features have been reconstructed
well as sandy beaches that are in harmony
areas on the basis of the actual natural circumstances,
than for political reasons. It is necessary that the reconstruction
beings should also be in harmony
level and increases in the scale and frequency of typhoons that are caused by the global warm-
ing, a suitable long–term methodology for coast preservation
Many attempts have been made to control
world 4), but in the long term none have succeeded in stabilizing sandy beaches that are being
eroded. Almost all the common countermeasures
mild–slope revetments and man–made reefs—are
beaches as they cause beach profiles gradually to become steep.
of sandy beaches so that they will be less affected hydraulically
better for the preservation of coastlines than would be the construction
whose strength is dependent on the frontal depth of the water as well as the direct rise in sea
level. Beach erosion in Japan has been increasing annually, and the tendency for erosion will
become even more marked in the future. In many coastal areas, a great number of structures
have been erected and, in general, they have protected the coastlines from severe beach erosion
for more than thirty years. In certain coastal locations some have promoted
cause of the direct influence of the structures
complex problems related to coastal environments.
beaches must be based on new methodologies of long–term beach stabilization
formation gained from the effects of such previous countermeasures
and detached breakwaters, and so on.
Beach erosion in Japan, especially that seen in the reduction
lack of or decrease in sediment source carried by rivers, must be considered
taking into account large scale coastal behavior along the coast of a river delta as a creative
effectively, may exist as
with nature. However, it is better to zone coastal
such as longshore sediment transport,
of natural features by human
process. To counter rises in sea with the natural creation
has to established in this case too.
throughout beach erosion in countries the
; —sea dikes, groins, offshore breakwaters,
of little use for the stabilization
by a rise in sea level would be
of sea dikes and walls
beach collapse be-
and others have produced
of other natural sandy
that reflect in-
such as sea dikes, walls,
of river deltas because of a
over the long term
process of nature.
rivers thereby retaining
which makes coastal stabilization
harmony with nature, coastlines must be stabilized
visioning Japanese coastlines
think we need to determine
to a new "civilization" in which there is beneficial
beings. I believe that coastal beauty that is based on the oriental concept of the inter–related-
ness of humans and nature can be created.
In 1960, Silvester 5) proposed a methodology
control", in which a series of static stable sandy beaches are formed.
odology for beach erosion control ; however, for practical
nature, the theoretical or dynamic background
must be known in order to determine the conditions necessary to their formation.
learned of cshaped bays from Silvester, I have conducted
background of the formation of natural stable sandy beaches.
There are two possible methodologies : One is to recover the sediment from
the coastal river delta and the other is to establish a methodology
possible for a coast that lacks a sediment supply.
and made more natural.
of the next century as being in greater harmony
what will bring coastlines into this greater harmony
with nature, I
that will lead
nature and human between
for beach erosion control called "headland
This is an essential meth-
of the formation of static stable sandy beaches
of our knowledge of
Since I first
research to establish the theoretical
A stable sandy beach is formed
142 Y. TSUCHIYA
under certain boundary
istence of such stable sandy beaches is verified it can be used to derive a methodology
beach erosion control by headlands by which a series of stable sandy beaches can be formed to
stabilize an eroding sandy beach.
From this point of view, I wish to propose a methodology
astal stabilization. First, two types of stable sandy beaches that are formed naturally and their
for beach change.
When this theoretical
The sandy beach is in either a static or
background of the formation or ex-
of beach erosion control for co-
geometry are briefly explained.
port and the equation
is derived. As the fundamental
boundary conditions at the upstream and downstream
required to solve it, reflecting
shoreline change are required
stable sandy beaches, static and dynamic
compared with the configurations
of the theoretical background
Then, from the set of equations for longshore
for continuity of shoreline change, an equation
equation is a second-order
for stable sandy beaches
ends of longshore sediment transport
only two boundary
of a sandy beach.
equilibrium beaches, are derived theoretically
of actual sandy beaches. From the results of the application
of the formation of stable sandy beaches, a methodology
the fact that theoretically
for the stabilization
posed for sandy beach stabilization,
effective as boundary conditions.
establishing a series of stable sandy beaches is discussed in relation to the large scale behavior
of sandy beaches. Three practical applications
rently underway are described to show the applicability of the proposed methodology.
as well as for beach erosion control by headlands that are
Application to the stabilization of eroding sandy beaches by
that have already been made and that is cur-
2. Formation of the Stable Sandy Beach : Theory of Its Existence and Geometry
2. 1 Definition of natural stable sandy beaches and their configurations
There are many kinds of natural sandy beaches.
sandy beach of a C-shaped bay bounded by two headlands.
shaped bay is formed where there is no longshore transport
sandy beach is formed where there is a constant rate of longshore sediment transport
beach. As shown schematically in Fig. 1, Tsuchiya,
Tsuchiya and Shibano 8) defined two types of natural
Silvester ") was the first to focus on the
This type of sandy beach in a C-
of sediment while another type of
Silvester and Shibano 7) and Silvester,
sandy beaches that are in equilibrium
predominant wave predominant wave
AL'92: A Ox
- • • .
(a) Static stable sandy beach. (b) Dynamic stable sandy beach.
Fig. 1. Definition of stable sandy beaches and the notations used.