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Intervention of Human Activities on Geomorphological Evolution of Coastal Areas: Cases from Turkey

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Intervention of Human Activities on Geomorphological Evolution of Coastal Areas: Cases from Turkey

5
Intervention of Human Activities on
Geomorphological Evolution of Coastal Areas:
Cases from Turkey
Cüneyt Baykal1, Ayşen Ergin1 and Işıkhan Güler2
1Middle East Technical University, Department of Civil Engineering,
Ocean Engineering Research Center,
2Yüksel Proje International Co. Inc.,
Turkey
1. Introduction
Coastal engineers, geomorphologists and scientists have been trying to understand and find
the answer to one simple and a major question among a wide variety of challenging coastal
problems for decades. Where will the shoreline be tomorrow? Or after a severe storm? Or
next year? Or in a decade? In other words, how will the coasts of our earth evolve in time?
And where do we stand as human being in this highly complex, yet fragile evolution of
coasts?
Coastal areas are often highly scenic and offer plenty of natural resources. Over 50 percent
of the world’s population lives within 200 kilometers of coastline (Hinrichsen, 1994;
Deichmann, 1996). According to the projections of future population, 75 percent of the
world’s population, or 6.3 billion people, could reside in coastal areas by 2025 (Hinrichsen,
1996). Increasing population and urbanization at coastal areas, unconscious exploitation of
natural resources, incompetent management and education strategies and lack of control
mechanisms increase the complexity of problems and severity of measures at coastal areas.
One major coastal problem that almost every country with some kilometers of coastline
faces and spends millions of dollars to solve the imbalance in coastal sediment budget at
coastlines, resulting in severe erosion or accretion problems and loss of income from tourism
and other coastal opportunities. Miami Beach, in Florida is a typical example for the above
given problem. In the early 1970s, there was severe erosion at Miami Beach, where it was
lined with seawalls, and compartmented by long steel groins. The numbers of visitors to
Miami Beach and hotel occupancy rates were in decline. As a remedial measure, from 1976
to 1981, the Miami Beach Nourishment Project was undertaken, widening the beach by 100
m over a length of 16 km at a cost of $64 million USD. The project required in excess of 10
million cubic meters of sand obtained from offshore borrow areas by large hydraulic
dredges. (Dean & Dalrymple, 2002). As a result, number of visitors at the beach increased
from 8 million in 1978 to 21 million in 1983 (Houston, 1995a).
To control sediment budget at coastal areas, several types of measures are applied. These
measures are categorized in two groups as hard measures (jetties, groins, detached
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breakwaters, seawalls, dykes etc.) and soft measures (beach nourishments, sediment traps,
etc.). The hard measures involve the construction of solid structures within the intertidal
zone to reduce wave energy and stop the sea from interacting with the hinterland. In
contrast, soft measures generally avoid the solid structure approach, but use natural
environments and sediments to reduce wave action (French, 2001; Dean, 2002). However,
application of these measures usually fails or does not work as planned if applied without a
clear understanding of the picture in the problematic coastal area and a well-designed and
strictly implemented integrated coastal zone and river basin management structure.
This chapter gives brief information on the theoretical background of sources of sediment
transport mechanisms and physical and numerical modeling attempts to understand these
mechanisms. The governing parameters of these mechanisms and their temporal and spatial
effects on the geomorphology of coastal areas are briefly discussed. Special emphasis is
given to the numerical modeling of shoreline changes due to longshore sediment transport
which becomes one of the governing mechanisms in the long term at coastlines where
human induced activities put a pressure on the sediment supply resources e.g. dunes, cliffs
and rivers. Two case studies of coastal erosion problems from Turkey are covered in this
chapter, focusing on the numerical modeling of shoreline changes around coastal defense
structures. The first case study is from northern coasts of Turkey, Bafra alluvial plain where
the Kızılırmak River discharges into the Black Sea. It is one of the RAMSAR protection sites
in Turkey. It has a rich biodiversity and is an important habitat for globally endangered bird
species. The amount of sediment carried by the river has reduced drastically after the
construction of flow regulation structures on the river, which led to serious coastal land
erosion at the river mouth. The second case study, as another example to human induced
type of coastal erosion problems, is from one of the touristic areas of Turkey, Side beaches in
Antalya at southern coasts of Turkey. Alteration of the characteristics of the sea bottom
topography due to touristic considerations led a serious erosion problem in front of the
Perissia Hotel, in Side. For these two cases, the implemented remedial coastal defense
measures, the shoreline changes after the implementation of these measures and
applications of numerical modeling to predict these shoreline changes are covered within
the case studies.
2. Sediment transport at coastal areas
Coastal areas are the environments with a very sensitive and dynamic balance governed by
various complex physical processes. The shape of coastal landforms is a response of the
materials that are available to these processes acting on them (Woodroffe, 2003). Among
these processes, sediment transport plays an important role in continuous geomorphological
evolution of coastal areas. This evolution mainly depends on the sources and sinks (losses)
of the sediment budget of the coastal area. Major sources of sediment in coastal areas are
weathering of cliffs by marine action (waves, tides and currents), wind and rain, freeze-thaw
process and groundwater flow, sediment carried by rivers, dunes, wind-blown inland
material, biogenic materials such as shells and coral fragments especially in some tropical
areas and human induced sources like artificial beach nourishment, nearshore disposal of
dredged soil and industrial waste tipping. The losses in the sediment budget can be listed as
erosion by waves, tides and currents, submarine canyons, human extraction along rivers
(sand mining) and at nearshore for commercial purposes or improve navigation, damming
Intervention of Human Activities on
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of rivers and streams, fishing by the use of explosives and trapping of sand on the upstream
side of the coastal structures (CIRIA, 1996).
Sediment in coastal areas are transported in longshore and cross-shore directions by waves,
by tidal and other steady or quasi steady currents like wind induced circulation, by winds
from land (cliffs, dunes and inland), by rivers, small streams and gullies and also by human
agencies. In temporal scale, effects of longshore sediment transport become more distinct in
long term (years or decades) like recession of shoreline or accretion of sediments. As for the
short term event like seasonal changes or significant storm events, cross-shore movement of
sediments becomes the main actor in geomorphological changes in coastal areas such as bar
formations in the surf zone (Kamphuis, 2000; Masselink & Hughes, 2003).
2.1 Numerical modeling of sediment transport
Prediction of morphological changes in coastal areas mostly depends on determination of
long and short term effects of these transport mechanisms and changes in source-sink
parameters of sediment budgets of coastal areas. Depending on the effective coastal
processes, sediment budget knowledge and scope of the study, coastal sediment transport
problems can be solved using physical modeling techniques (Hamilton & Ebersole, 2001;
Wang et al., 2002; Gravens & Wang, 2007; Kökpınar et al., 2007), or with numerical
morphological models expanding from one-dimensional (Hanson, 1987; Dabees &
Kamphuis, 1998) to sophisticated 2D or 3D models (Roelvink et al., 2009), or with analytical
and empirical approaches. Both empirical and analytical solutions give quick results to the
scientists and engineers and are quite practical in early stages of understanding the coastal
problems, computation of beach evolution and preliminary design studies, yet, for a
detailed investigation of natural processes in coastal areas, physical or numerical models are
commonly implemented. Compared to physical modeling, numerical models possess certain
advantages in allowing the investigation of a wide range of parameters, adaptability to a
variety of sites, economical operation, and the absence of scale effects (Hanson, 1987). These
advantages sometimes may lead misuse of these models or misinterpretation of the results
of these models due to lack of knowledge related to the actual site conditions. The uses of
numerical models change for different spatial and temporal scales. For example, one-
dimensional numerical shoreline change models are preferable for most of the cases due to
their applicability in wide ranged temporal (from 1 year up to 20 years) and spatial scales
(from 0.5 kilometer up to 10 kilometers), whereas more sophisticated 2D and 3D models are
generally utilized for medium-term (up to 10 years) and short (a single storm up to 1 year)
shoreline changes, respectively, due to their complexity and intensive computations
(Hanson et al., 2003).
2.1.1 One-line theory
The fundamentals of shoreline change models were first established by Pelnard-Considere
(1956), who set down the basic assumptions of the “one-line” theory, derived a
mathematical model, and compared the solution of shoreline change at a groin with
laboratory experiments. The basic assumption of “one-line” theory is the concept of
“equilibrium beach profile”, that cross-shore transport effects such as storm-induced erosion
and cyclical movement of shoreline position associated with seasonal changes in wave
climate are assumed to cancel over a long simulation period. In this concept, the change of
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122
shoreline position (in cross-shore direction) in time is due to longshore sediment transport
and local sources or sinks along the coast (such as river discharges, beach nourishment or
net cross-shore sand loss). The boundaries of “equilibrium beach profile” are the berm
height (B) on land, maximum elevation of sediment transport during the uprush (Masselink
& Hughes, 2003), and closure depth (DC) at sea, which is limiting depth beyond which no
significant longshore and cross-shore transports take place due to littoral transport
processes (Mangor, 2004), (Fig. 1).
Fig. 1. Definition sketch for conservation of mass for a sandy beach system (Baykal, 2006)
Based on the above given assumption, “one-line” theory is expressed with the following
differential equation which is also called as sand continuity equation,
t,lst
C
Q
y1q
t(DB) x

=− ⋅ +

∂+

(1)
where y is the shoreline position, x is the longshore coordinate, t is the time, Qt,lst is the total
longshore sand transport rate, q represents local sand sources or sinks. Hallermeier (1978)
relates the closure depth to Hs,12 and Ts which are the significant wave height exceeded 12
hours per year and corresponding significant period respectively (Eq.2).
2
s,12
Cs,12 2
s
H
D 2.28 H 68.5 ( )
gT
=⋅ −⋅ (2)
For the cases where the governing transport mechanism is assumed to be longshore
sediment transport only, Hanson (1987) suggests to use the limiting depth of longshore
sediment transport computed with the same equation (Eq.2) using significant breaking
wave height (Hs,b) instead of Hs,12.
For the total longshore sediment transport rates including both bed and suspended
sediment loads, the most widely used equations are Coastal Engineering Research Center of
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Geomorphological Evolution of Coastal Areas: Cases from Turkey
123
The United States Army Corps of Engineers [thereafter CERC or USACE] (1984) and
Kamphuis (1991) formulas. These formulas consider only wave generated currents and
disregard other mechanisms like tidal or wind-induced currents. In CERC formula (Eq.3),
the total volume of sand transported alongshore is related to the longshore component of
wave power per unit length of beach,
5/2
t,lst b
s,b
sb
g
K
QHsin(2α)
16 (ρ/ρ1) (1 p) γ
=⋅
⋅− (3)
where Qt,lst is the total volume of sediment moving alongshore per unit time (m3/sec), K is
the dimensionless empirical proportionality coefficient given by Komar & Inman (1970) as
KSPM sig = 0.39 based on field studies utilizing the significant wave height, ρs is sediment
density taken as 2,650 kg/m3 for quartz-density sand, ρ is the water density (1,025 kg/m3
for 33 parts per thousand (ppt) salt water and 1,000 kg/m3 for fresh water), g is the
gravitational acceleration (9.81 m/sec2) and p is the in-place sediment porosity that may be
taken as 0.4. The breaker index (γb: ratio of breaking wave height to breaking depth) is taken
as 0.78 for flat beaches (Weggel, 1972). Hs,b and αb are the significant breaking wave height
and breaking wave angle respectively.
In the Kamphuis’s (1991) formula (Eq.4), the effect of significant wave period (Ts), median
particle size in surf zone (D50) and the beach slope (mb) at the depth of breaking, the slope
over one or two wavelengths seaward of the breaker line are taken into consideration in
addition to the significant breaking wave height and breaking wave angle.
2 3/2 3/4 1/4 3/5
t,lst s,b s 50 b
b
Q2.27HTmDsin(2α)
=⋅⋅⋅ ⋅ (4)
Both CERC (1984) and Kamphuis (1991) formulas are utilized in shoreline evolution models
extensively. Although these expressions have been verified in several researches for years,
their predictive capabilities are limited mostly by site specific conditions (i.e. bathymetrical
conditions, wave climate characteristics, sediment size and grading). Wang et al. (2002) state
that Kamphuis (1991) formula produces more consistent predictions than the CERC formula
for both spilling and plunging breaking wave conditions due to inclusion of wave period in
the expression, which has significant influence on the breaker type. However, it seems most
appropriate to use the CERC formula for high energy wave events and the Kamphuis (1991)
formula for low-energy events (less than 1 m in wave height).
2.1.2 An example to one-line numerical modeling
For the purpose of understanding and predicting long term shoreline changes under the
actions of wind waves, a numerical shoreline change model, CSIM (acronym for Numerical
Model for Coastline-Structure Interaction), based on “one-line” theory is written in Ocean
Engineering Research Center of Civil Engineering Department in Middle East Technical
University (Şafak, 2006; Artagan, 2006; Baykal, 2006 and Esen 2007).
The numerical model is based on “one-line” theory with a built-in wave transformation
module capable of simulating combined wave refraction and diffraction mechanisms in the
vicinity of coastal structures such as groins and offshore breakwaters. It solves the sand
continuity equation with both explicit and implicit finite difference schemes. The model can
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124
also simulate shoreline changes for some other coastal defense measure applications such as
seawalls and artificial beach nourishment. The significant breaking wave heights in the surf
zone are computed with formula given in CEM (2003);
1/5
22
4/5 2/5 b0
s,b s,0 g0 0 22
bb0
gHgsin(α)
H(H)[Ccos(α)] γγC

⋅⋅
=⋅⋅ ⋅



(5)
where Hs,b is the significant breaking wave height, Hs,0 is the deep water significant wave
height, α0 is the deep water wave angle between wave crests and bottom contours, C0 and
Cg0 are the deep water wave celerity and group celerity, respectively.
For combined effects of wave diffraction and refraction in the shadow zone of the coastal
defense structures, Kamphuis’s methodology (2000), which is based on Goda’s diffraction
diagrams (Goda et al., 1978), and refraction of regular waves are utilized. Combined effects
of wave diffraction from multiple sources like consecutive offshore breakwaters are
considered based on Vafaei’s (1992) approach which is basically vectorial summation of
wave rays coming from different sources of diffraction in proportion to the square of
diffracted wave heights of these rays. More details and applications of the numerical model
are given in Ergin et al. (2006) and Güler et al. (2008).
3. Case study-1: Coastal erosion problem at the Kızılırmak River mouth
In most of the developing countries, denser the population in coastal areas, the more
vulnerable they become to severe environmental problems such as coastal erosion,
exploitation and depletion of natural resources and extinction of endangered species.
Wetlands at coastal areas are one of the most adversely affected areas due to their diverse
floras and faunas. In Turkey, there are 13 sites designated as “Wetlands of International
Importance” with a total surface area of 179,898 ha and 5 of these sites are located at coastal
areas. One of these sites is Bafra alluvial plain (Kızılırmak Delta) where the Kızılırmak River
discharges into the Black Sea. The site was designated as RAMSAR Area in 15.04.1998. It has
a surface area of 21,700 ha including dunes, beaches, shallow lakes, seasonal marshes and
wooded areas (URL-1). Numerous species of water birds, several of which are globally
threatened, breed at this site. Over 92,000 water birds of various species winter at the site. In
recent years, eutrophication, deforestation, illegal constructions and coastal erosion have
become increasingly problematic in Kızılırmak coastal wetland (Kuleli et al., 2011). The
location of Bafra alluvial plain is shown in Fig.2 and Fig.3.
The Kızılırmak River, which rises in the Eastern Anatolian Mountains, flows in a
northwestern direction and discharges into the Black Sea by forming a conic alluvial delta
(Fig. 2). It is the longest river in Turkey, with a length of 1,355 km, draining a basin of 74,515
km2 (Kökpınar et al., 2007). The amount of sediment carried by the Kızılırmak River was
23.1 million tons/year till 1960’s prior to any flow regulatory structures and decreased to 18
million tons/year following the construction of Hirfanlı Dam in 1960, and almost came to a
cease with the total amount of 0.46 million tons/year after the constructions of Altınkaya
Dam in 1988 and Derbent Dam in 1991 (Hay, 1994). This drastic decrease in the amount of
sediment carried by the Kızılırmak River resulted in severe erosion with a maximum 1 km
wide band of shoreline since 1988 according to the Regional Directorate of State Hydraulic
Works and from local residents (Kökpınar et al., 2007).
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Fig. 2. Location of Bafra alluvial plain
Regarding the coastal erosion problem at Bafra alluvial plain, Kuleli et al. (2011) focused on
the shoreline change rate analysis by automatic image analysis techniques using multi-
temporal Landsat images and Digital Shoreline Analysis System (DSAS) along five Ramsar
wetlands of Turkey. For Kızılırmak Delta, they have used three satellite images for the years
1989, 1999 and 2009 and found 16.1 m/year erosion rate for the Kızılırmak Delta.
Fig. 3. Bafra alluvial plain and plan view of the existing shore protection system at the
Kızılırmak River mouth (Google Earth, 2011)
TURKEY
Mediterranean Sea
Black Sea
Black Sea
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The first remedial measure against this severe coastal erosion problem at the river mouth
was held in 2000 by State Hydraulic Works (DSİ) based on the findings of the physical and
mathematical model studies conducted at the Hydraulic Model Laboratory of DSİ in
Ankara, Turkey (Kökpınar et al., 2007). It was composed of two Y-type and one I-type groins
constructed at the eastern shoreline of the river mouth (Fig. 3). Ergin et al. (2006) studied the
shoreline changes around these structures with the numerical shoreline change model,
CSIM, using the shoreline measurements taken in 1999 (April) and 2003 (January) by DSİ.
Despite utilizing T-groins instead of Y-groins and the numerical model’s lack of capability of
modeling tombolo formation, the model results was in good agreement quantitatively with
the field measurements, especially at western sides (updrift) of second and third groins.
After the construction of first remedial system (two Y-type and one I-type groins), the
shoreline retreat slowed down between the groins and trapping of sediment initiated.
However, recession at the shoreline due to wave action continued to the east from the third
groin (I-groin) as almost no sediment is carried by the Kızılırmak River. Later, two jetties
were constructed at the west and east sides of river mouth between the years 2001-2004 to
prevent seasonal closure of the river mouth. Between the years 2004-2005, the coastal
defense system was extended with the construction five more I-type groins to prevent the
collapse of drainage channel. Although, the drainage channel has been saved against wave
action constructing the new series of five I-type groins, shoreline retreat at the east side of
the defense system could not been prevented and continued to further east.
In this study, the performance of the second series of groins (5 I-type groins) and the
shoreline changes around these groins between the years 2003-2007 are studied using the
one-dimensional numerical shoreline change model, CSIM. The corresponding shoreline
GPS measurements were provided by Regional Directorate of DSİ (Fig. 4).
Fig. 4. Kızılırmak River mouth shore protection system plan view
3.1 Wave climate study: Kızılırmak River mouth
Long term geomorphological evolution of coastal areas under wave action results from
series of short-term wave events occurring randomly. When there exist no time histories of
these wave events or no continuous wave measurements, yet, wind measurements exist for
such coastal areas, wave hindcasting studies are performed. For each wave direction, the
wind velocities and effective fetch distances are used to hindcast the wave climate history of
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the site and a long-term wave statistics study is carried out to determine yearly or seasonal
deep water wave characteristics.
There exist no continuous wave measurements for the shores close to Bafra alluvial plain.
Therefore, a wave hindcasting study has been performed using hourly average wind data
measured at 10 m above ground level by Sinop Meteorological Station between the years
2000-2009, obtained from General Directorate of Meteorological Affairs (DMİGM). The
location of the river mouth is open to waves approaching from a wide directional sector
from West to East-South-East. The effective fetch distances for the directions in this
directional sector are determined from the navigation maps of Navigation, Hydrography
and Oceanography Department of Turkish Naval Forces (SHODB). In the computation of
effective fetch distances, for each direction, the effective generation area is considered as a
sector from -22.5 to +22.5 totally covering an area of 45 with 7.5 intervals (USACE, 1984).
The effective fetch directions and distances are shown in Fig. 5.
Fig. 5. Wave directions for Bafra region (Google Earth, 2011)
Using the effective fetch distances and the wind data obtained from Sinop Coastal
Meteorological Station, deep water wave parameters (Hs0 : deep water significant wave
height, Ts : significant wave period) are obtained for the storms occurred during 10 years
(2000-2009) by using the numerical model, W61, developed at Middle East Technical
University, Department of Civil Engineering, Ocean Engineering Research Center (Ergin &
Özhan, 1986; Ergin et al., 2008; Ergin et al., 2009).
The characteristic deep water wave steepness value (Hs0/L0), the ratio of deep water
significant wave height (Hs0) to the corresponding deep water wave length (L0), for the
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project area is obtained as 0.040 from deep water significant wave heights and deep water
wave lengths computed from corresponding significant wave periods (Ts) of each individual
storm (L0 = gTs2/2π where g is gravitational acceleration in m/s2).
To represent the actual wave conditions better and minimize the effect of wave data
sequence in one-line numerical shoreline change modeling as discussed in Şafak (2006), a
seasonal based wave data input is prepared. For this purpose, long term wave statistics is
carried out for seasonal wave data. The hindcasted wave data is classified in 0.4m ranges for
each season (winter season is assumed to include January, February and March, the other
seasons followed accordingly) and the cumulative number of occurrences of each wave
height class is plotted on to a semi-log graphical paper. The cumulative exceedance
probability of deep water significant wave height, Hs0, is given as;
[
]
s0 s0
Q( H ) exp (H B)/A>= (6)
where Q(>Hs0) is the cumulative exceedance probability of a deep water significant wave
height (Hs0). This equation indicates that if data points corresponding to Hs0 and Q(>Hs0) are
plotted on a semi-log graphical paper (Hs0 on normal, and Q(>Hs0) on logarithmic scales),
they should lie on a straight line with a slope of A and intercept of B when Q(>Hs0) is the
horizontal axis.
Another major assumption in the preparation of wave data input is such that the effects of
smaller but more frequent waves are considered to be more appropriate for a better
representation of long term wave climate rather than higher waves with less frequency. By
using the long-term statistics in seasonal time scale, the representative deep water significant
heights (Hrs,0) of waves coming from every direction, their periods and seasonal frequencies in
hours for each season are calculated using (Güler, 1997; Güler et al., 1998 and Şafak, 2006);
ii
rs,0
i
(P H )
HP
=
(7)
where Hi is the wave height and Pi is the occurrence probability of wave height Hi.
Occurrence probability (Pi) of wave height (Hi) is computed by using the corresponding
occurrence durations within the given range as follows;
ii i
PQ(Hk)Q(Hk)=−−+ (8)
where Q is the exceedance probability and k is an assigned range to compute occurrence
probability. In Table 1, the seasonal wave data input for the model consisting of
representative wave heights (Hrs,0), corresponding periods (Ts) and seasonal occurrence
durations (Δt in hours) from all directions is presented.
As seen from Table 1, for all seasons the highest occurrences of waves within the range of 1
meter are from West-North-West and North-West.
3.2 Numerical modeling study: Kızılırmak River mouth
The shoreline changes between the second series of groins (5 I-type groins) constructed in
addition to the first part (between years 2004-2005) starting from Groin-3 to Groin-8 with
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200 meter spacing between adjacent groins (Fig. 4) are studied using the one-dimensional
numerical shoreline change model, CSIM. The shoreline measurements for the years 2003
and 2007 are discretized at 10 m intervals. Starting from Groin-3, the apparent lengths of the
groins are given as 175, 195, 200, 200, 180 and 175 meters respectively. From the sieve
analyses of the sediment samples taken from the site, the median grain size diameter (D50) is
determined as 0.23 millimeters (Kökpınar et al., 2007). The berm height (B), the landward
end of the active profile, is assumed as 2 meters. In the application of numerical modeling
for the case in the Kızılırmak River mouth, it is assumed that no source or sink exists. The
sequence of wave data input (Table 1) in the simulation starts with spring waves from W to
ESE directions and continues with summer, autumn and winter waves.
Directions
WINTER SPRING SUMMER AUTUMN
Hrs,0 Ts Δt Hrs,0 Ts Δt Hrs,0 Ts Δt Hrs,0 Ts Δt
(m) (sec) (hrs) (m) (sec) (hrs) (m) (sec) (hrs) (m) (sec) (hrs)
W 1.59 5.07 5.3 0.94 3.90 0.5 0.76 3.50 1.3 1.63 5.13 6.4
WNW 1.05 4.12 462.5 0.94 3.89 544.0 1.07 4.16 323.5 1.08 4.17 368.5
NW 1.08 4.17 391.4 0.86 3.72 149.2 1.18 4.36 119.9 1.05 4.11 221.2
NNW 1.03 4.09 100.1 0.72 3.41 113.1 0.81 3.62 172.3 1.19 4.39 124.0
N 0.91 3.83 66.7 0.58 3.06 16.3 0.70 3.36 41.4 1.13 4.27 13.5
NNE 0.83 3.66 14.4 0.70 3.35 17.0 0.63 3.20 22.4 0.84 3.67 28.6
NE 0.80 3.58 3.8 0.64 3.20 2.4 1.82 5.42 1.9 1.10 4.21 6.7
ENE 1.18 4.37 14.4 0.74 3.47 7.3 0.86 3.73 11.3 1.07 4.15 10.9
E 0.89 3.79 3.5 0.58 3.05 0.9 1.17 4.35 3.5 1.08 4.18 3.5
ESE 0.79 3.56 32.6 0.65 3.25 56.0 0.73 3.42 31.8 0.77 3.53 33.0
Table 1. Representative wave heights, corresponding periods and seasonal occurrence
durations from all directions for each season
The sediment transport formulas are mostly based on various laboratory and field
measurements. As the accuracy of these formulas may change from one site to another
depending on the wave characteristics, grading of sediment, existing currents (tidal or wind
induced) and sea bottom topography, direct use of these formulas may not reflect the actual
sediment transport rates for the site studied. Therefore, calibration of these kinds of
numerical models needs to be performed beforehand. For this study, the shoreline retreat at
the downdrift of Groin-8 from 2003 till 2007 is used to calibrate the model.
The sea level variations of the Black Sea, where semidiurnal tides are dominant with a
spring tidal range of 8-12 cm, has been largely controlled by a seasonal variation (inter-
annual change) of 20–40 cm maximum in June (Alpar, 2009; Vigo et al., 2005; Bondar, 2007).
The inter-decadal sea level variations have a period of 30 years and are in the order of 16 cm
(Trifonova & Grudeva, 2002). The sea level variations produced by the atmospheric pressure
changes or by sudden changes of wind direction could reach 10-20 cm with periods of 1-5
hours (Bondar, 2007). In the computations, the effects of these sea level variations are
disregarded. The results of the simulations are given in Fig. 6.
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-100
0
100
200
300
400
500
600
800 1200 1600 2000 2400 2800 3200 3600 4000 4400
Cross-shore Distance, y (m)
Alongshore Distance, x (m)
Measured 18.04.2003
Measured 08.02.2007
Computed 2007, CSIM
N
Groin-8
Groin-7
Groin-6
Groin-5
Groin-4
Groin-3
Fig. 6. Comparison of the site measurements with the numerical simulation (Groin series
and downdrift of Groin-8)
3.3 Results and discussion: Kızılırmak River mouth
In the design of coastal defense structures such as shore perpendicular groins as in the case
of the Kızılırmak River mouth, adverse effects of the defense structures at the adjacent
shores have to be studied before the implementation of the project. In this case study, as an
application of the numerical model, the shoreline changes both between coastal defense
structures and adjacent shore are studied together.
Fig.6 shows that the shoreline changes between groins could only be simulated
qualitatively; yet, the shoreline retreat after Groin-8 is in good agreement with the
measurement quantitatively. For the groin system, the numerical model results reflect the
shoreline changes qualitatively but not quantitatively. A reason for the inconsistency
between the measured and computed shoreline positions for the year 2007 at the groin series
might be due to the actual bypassing amount of sediment from the first 2 Y-type and 1 I-
type groin system is not well defined. Also the small amount of the sediment carried by the
river is neglected in the computations as no reliable knowledge or measurements regarding
the amount of sediment carried by the river exist. As for the downstream shore adjacent to
Groin-8, the agreement between the numerical model results and measurements are in good
agreement both qualitatively and quantitatively.
4. Case study-2: Coastal erosion problem in Side, Perissia Hotel Beach
The second example for the adverse effects of anthropogenic activities on geomorphological
evolution of coastal areas is from one of the touristic areas of Turkey; Perissia Hotel Beach,
located in Side in Antalya at southern coasts of Turkey (Fig. 7). Side is one of the resort
towns in Antalya, heavily utilized by touristic activities with numerous hotels. The closest
rivers to Side are the Manavgat River (at 93 km in length, app. 12.5 km to Perissia Hotel
Beach) and Köprü Çay stream, one of the finest rafting sites in Mediterranean region (at 14
km in length, app. 19 km to Perissia Hotel Beach). There are two dams on the Manavgat
River; Oymapınar (1984) and Manavgat (1987) dams. The Manavgat River drains a
Intervention of Human Activities on
Geomorphological Evolution of Coastal Areas: Cases from Turkey
131
topographic basin of 928 km2 extending to the northern Taurus mountain range and with
the addition of several closed basins (Mesozoic limestone aquifers), it has a total drainage
area of 9,100 km2, one of the major catchment basins in the Mediterranean coastal area
(Yurtsever & Payne, 1986). The direction of the net longshore drift is from East to West.
Fig. 7. Location of Side, Perissia Hotel beach and effective fetch distances for all directions
(Google Earth, 2011)
The beach in front of Perissia Hotel is approximately 300 meters long and the width of the
beach was approximately 50 meters before 1999. It is protected by naturally existing rocky
formations at the east and west boundaries of the beach which extend 25 meters into the sea
and a 120 meter long pier at the center of the beach, rocky formations lay underneath. The
major protection for the beach against erosion due to wave attack was the rocky formations
which were located at approximately 1-1.5 meter water depths and 60-100 meters offshore
acting as submerged breakwaters and dissipating the energies of the approaching waves.
However, the rocky formations in the western part of the beach were removed from the sea
bottom in respond to customer needs in 1999. Altering the characteristics of the sea bottom
topography, a serious erosion problem (retreating approximately 30 meters) was initiated at
the beach mostly due to offshore movement of sands under wave action especially in winter
season (Fig. 8). Remedial attempts utilizing artificial nourishment and construction of a
groin of 25 meter long and 2 meter wide behind the pier could provide some amount of
accretion at eastern part of the beach but did not work properly for the rest of the beach.
For the purpose of finding a consistent and effective remedial measure for the coastal
erosion problem at Perissia Beach, site investigations and bathymetrical surveys were
performed, wave climate of the region was determined and numerical modeling studies
Studies on Environmental and Applied Geomorphology
132
were carried out for alternative solutions by Güler et al. (2008). The wave climate of the
region was determined carrying out a wave hindcasting study using the hourly average
wind data measured by the nearest coastal meteorological station (Alanya Meteorological
Station) for the years 1993-2004 which is obtained from DMİGM. The dominant wave
directions were found to be South-South-East, South and South-South-West directions.
Alternative solutions for the coastal erosion problem including hard and soft measures were
discussed in detail in view of effectiveness.
Fig. 8. Perissia Hotel Beach at Side; shoreline retreat due to erosion over the years, red line
shows the shoreline position approximately in August, 2006 (a: view of the western part of
the beach from sea, b: view of the eastern part of the beach from sea; pictures from 1999;
Güler et al., 2008)
The coastal protection system proposed was composed of several measures including both
hard and soft measures, considering geomorphological features of the beach, sediment
trapping capacity, possible harm to neighboring beaches and also scenic beauty. It was
planned to be applied in three stages. The first stage is the construction of a 40 meters groin,
15 meters of which is at the land part, at the western border of the beach in addition to the
existing groin at the mid-beach. This groin was planned to be a low crested structure, which
will be at mean sea level at high tides and during storm events. It was actually planned to
use the existing rocky formation at the western edge of the beach and strengthen it up to 25
meters seaward from the beach. The second stage includes the construction of a 40 meters
submerged breakwater which is 30 meters away from pier and 60 meters offshore at the
western part of the pier with a crest height 1 meter below still water level. The final stage
was the nourishment of the western part of the beach between to groins (one existing and
one constructed) at least 30 meters from the shoreline having a median grain size of around
1 mm (approximately 7000 m3 of sand). It was left optional to utilize gabion structures in
front of the nourished area against wave action in cross-shore direction. The median grain
size diameter (D50) was found as 0.15 millimeters from the sieve analyses of the sediment
samples taken from the site (Ergin et al., 2006). The summary of the proposed solution is
shown in Fig. 9.
A recent site investigation was performed in January, 2010. Applied measures are
investigated and the current shoreline position was measured. During the site investigation,
it is found that the implemented remedial measures differ than the proposed coastal defense
system presented above slightly in dimension and construction sequence:
N
(a) (b)
N
Intervention of Human Activities on
Geomorphological Evolution of Coastal Areas: Cases from Turkey
133
Western groin is extended to 15 meters towards the sea.
Existing 25 meters long groin underneath the pier was removed for aesthetic reasons.
Approximately 6000 m3 sand artificially added to the beach.
The construction of the submerged offshore breakwater is delayed. The existing 25
meters long groin underneath the pier was removed.
Fig. 9. Proposed remedial measures for the shoreline erosion at Perissia Hotel Beach at Side
and nearshore bathymetry (18.11.2006)
Fig. 10. Condition of Perissia Hotel Beach at Side at 09.01.2010, applied coastal defense
structures and nearshore bathymetry (18.11.2006)
Studies on Environmental and Applied Geomorphology
134
The implemented remedial structures and condition of the beach during the site
investigation are shown in Fig. 10. In this study, the implemented measures are discussed
and shoreline changes between the years 2006-2010 are studied with one-dimensional
numerical shoreline change model, CSIM.
4.1 Wave climate study: Side, Perissia Hotel Beach
To obtain the wave climate in the last ten years at Side, a wave hindcasting study is
performed using the using hourly average wind data measured at 10 m above ground level
by Alanya Meteorological Station between the years 1993-2004, obtained from DMİGM. For
each direction, the effective fetch distances are determined for each direction with an
effective generation area as a sector from -22.5° to +22.5° totally covering an area of 45° with
7.5° intervals, from South-East to West using the navigation maps of SHODB. The effective
fetch directions and the effective fetch distances are shown in Fig. 7.
Using the effective fetch distances and the wind data obtained from Alanya Coastal
Meteorological Station, deep water wave parameters (Hs0 : deep water significant wave
height, Ts : significant wave period) are obtained for the storms occurred during 12 years
(1993-2004) by using the numerical model, W61, developed at Middle East Technical
University, Department of Civil Engineering, Ocean Engineering Research Center. The
characteristic deep water wave steepness value (Hs0/L0) for the project area is obtained as
0.042 from deep water significant wave heights and deep water wave lengths computed
from corresponding significant wave periods of each individual storm.
The wave conditions in Mediterranean Sea are moderate compared to the Black Sea. There is
not a very significant difference between the wave characteristics and their occurrences
between the seasons. Therefore, for Side, an annual based wave data input sequence is
prepared for the numerical model to carry out long term wave statistics and determination
of representative deep water significant wave characteristics for each direction. The wave
data input for the model consisting of representative wave heights, corresponding periods
and annual frequencies for all directions are presented in Table 2.
Directions Hrs,0
(m)
Ts
(sec)
Δt
(hrs)
W 0.77 3.42 11
WSW 0.84 3.59 119
SW 0.88 3.67 53
SSW 1.01 3.93 137
S 0.97 3.84 229
SSE 1.04 3.99 26
SE 0.88 3.67 4
Table 2. Representative wave conditions and annual occurrence durations for all directions
(Güler et al., 2008)
Intervention of Human Activities on
Geomorphological Evolution of Coastal Areas: Cases from Turkey
135
4.2 Numerical modeling study: Side, Perissia Hotel Beach
For the numerical modeling of the applied coastal defense measure system, the shoreline at
western part of the beach is assumed to be nourished till the end of the newly constructed
groin at land side which makes approximately 5600 m2 of nourishment area. It is assumed
that the shoreline remained same till the construction of the western groin. The length of the
western groin is 52 meters from the nourished shoreline of 2008. The rocky formations
shown in Fig. 9 and 10 are modeled as submerged offshore breakwaters at various crest
heights, widths and distances from shoreline. Submerged breakwaters or such rocky
formations close to still water level force the waves to break and dissipate their energies and
create sheltered wave fields behind the formations. The wave heights behind such structures
are computed using diffraction terms and transmission coefficients (Ct=Ht/Hi, ratio of
transmitted wave height to incoming wave height) in CSIM. Depending on geometrical
properties of the rocky formations given in the bathymetry measured in 18.11.2006, the
transmission coefficients are roughly computed using below given equation (CIRIA, CUR,
CETMEF, 2007) where Rc is the crest height from still water level and Hs is the significant
wave height in at the toe of the structure.
tcs
C0.460.3R/H=− for -1.13 < Rc/Hs < 1.2 (9)
The berm height (B), the landward end of the active profile, is assumed as 1.5 meters according
to the site investigations. The sequence of wave data input (Table 2) in the simulation starts
from W to SE directions for each year. For the calibration of the numerical model, the shoreline
retreat after the construction of the groin till January, 2010 has been used.
Alpar et al. (1995) gives a 0.21 meters spring range of semi-diurnal tidal variations together
with a seasonal variation of 0.18 meters sea level variations for Antalya based on sea level
measurements of Antalya station for the years 1935-1976. The effects of sea level variations
are disregarded in the computations.
The computed position of shoreline using CSIM and measured shoreline positions for the
dates 18.11.2006 and 09.01.2010 are given in Fig. 11.
4.3 Results and discussion: Side, Perissia Hotel Beach
As seen from Fig. 11, the shoreline change computed by the numerical model in the eastern
part of the beach is in agreement with the measured shoreline both qualitatively and
quantitatively. The erosion at the eastern part of the beach is due to the removal of the 25
meters long groin underneath the pier.
For the western part of the beach, the shoreline changes are in agreement qualitatively but not
quantitatively. The accretion and erosion at the toe of the groin both on the eastern and
western sides are in very good agreement with the measured shoreline in 2010 both
qualitatively and quantitatively. The main reason for the quantitative disagreement between
measured and computed results for the western part of the beach is due to disregarding the
cross-shore sediment transport in the computations. In this area, which is bounded with the
pier and the groin, the cross-shore sediment transport appears to be more effective and has to
be included in the computations at the further stages of investigations. The excessive erosion
in the western part of the beach could be reduced with the construction of the proposed
submerged offshore breakwater (Fig. 9) which will reduce the cross-shore sediment transport.
Studies on Environmental and Applied Geomorphology
136
50
70
90
110
130
150
170
190
210
230
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440
Cross-shore Distance, y (m)
Alongshore Distance, x (m)
Nourished Shoreline, 2008
Measured 18.11.2006
Measured 09.01.2010
Computed 2010, CSIM
N
Fig. 11. Perissia Hotel Beach at Side; shoreline retreat due to erosion over the years, red line
shows
Fig. 12. Two panoramic views of the Perissia Hotel Beach at 26.07.2006 and 09.01.2010
showing the before and after remedial measures
The coastal erosion problem faced with in Perissia Hotel Beach is a very important example
of the erosion caused by alteration and harming of the natural balance in a coastal area,
which results from damaging and removing the rocky formations, naturally acting as
submerged breakwaters or reefs and thus, protecting the beach against wave action. Such an
application has initiated and accelerated the erosion at Perissia Hotel Beach. In Fig. 12, the
Intervention of Human Activities on
Geomorphological Evolution of Coastal Areas: Cases from Turkey
137
panoramic views of the beach at two different dates are given. The restoration of the
western part of the shoreline is clearly seen in these pictures. However, the shoreline in
eastern part started to retreat in return due to the removal of the groin underneath the pier.
This retreat may be controlled by the implementation of the proposed remedial structures
such as submerged offshore breakwater.
5. Conclusion
In this chapter, governing parameters of the geomorphological evolution of the coastal areas
are briefly discussed in the view of sediment budget concept. Numerical modeling of the
sediment transport mechanisms in coastal areas is discussed putting emphasis on one-
dimensional numerical modeling which has been used as an effective tool by scientists and
engineers for years to understand and predict shoreline changes in long term due to coastal
erosion problems. In the case studies given above, the general approach for predicting
shoreline changes at coastal areas, where human induced coastal erosion has become a
chronic problem, is discussed. The Kızılırmak River mouth is a typical example of the effects
of flow regulation structures on rivers and wetlands of alluvial plains fed by these rivers
and resulting in severe coastal erosion problems in return. While silting of the reservoirs
decreases the economic life of them, the coastal areas at downstream of these reservoirs
hunger the silted material and degrades day by day. Perissia beach case is again another
typical example of direct human intervention on the geomorphological and coastal-
hydrodynamic processes at the beaches and resulting in erosion problems. These two cases
stress the importance of the sustainable use of the resources in the long term for the benefit
of mankind and of developing more sophisticated tools and methodologies to provide a
better understanding and prediction capabilities of the adverse effects of anthropogenic
activities at coastal areas.
6. Acknowledgements
The authors are thankful to General Directorate of State Hydraulic Works (DSİGM) and
Bafra Plain Irrigation Project Directorate of DSİ for providing shoreline measurements of the
Kızılırmak River mouth, to General Directorate of Meteorological Affairs (DMİGM) for
providing wind data of Sinop and Alanya Meteorological Stations, to Navigation,
Hydrography and Oceanography Department of Turkish Naval Forces (SHODB) for
providing navigational maps used in computations. The authors also would like to thank to
Prof.Dr. Ahmet Cevdet Yalçıner, Dr. Ilgar Şafak, Salih Serkan Artagan and Mustafa Esen for
their efforts and supports in various stages of the above given studies.
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