Content uploaded by Y. Lacroix
Author content
All content in this area was uploaded by Y. Lacroix on Aug 27, 2018
Content may be subject to copyright.
Application of geospatial technics for prediction of shoreline
changes in Almanarre beach, France
Minh Tuan Vu1,2, Yves Lacroix1,3,*, Van Van Than4, Viet Thanh Nguyen2
1 SEATECH, University of Toulon, La Valette du Var, 83162, France
2 University of Transport and Communications, Hanoi, 100000, Vietnam
3 MEMOCS, Università Degli Studi dell’Aquila, Italy
4 Water Resources University, Hanoi, 100000, Vietnam
*[Email: yves.lacroix@ univ-tlf.fr]
The present study aims to utilize the combination of remote sensing and geographic information system (GIS)
techniques to investigate the historical shoreline changes as well as to predict the position of future shoreline in
Almanarre beach which is being threatened by erosion. The results indicate that the average annual change rate along
Almanarre beach was about -0.24 m/year over the period of 1973-2015, showing an erosive trend. Moreover, the
maximum erosion rate of -0.86 m/year was observed near Landmark B17. The predicted shoreline change in 2020 is
approximately -0.05 m/year, whereas in 2050 it is estimated about -0.22 m/year. The highest erosive areas in future are
estimated around Landmarks B06-08 and Landmarks B16-18 with the maximum recession rates of -0.89 m/year and -
0.94 m/year, respectively. This research should be useful for predicting the shoreline change trend as well as planning for
coastal protection and management.
[Keywords: Almanarre beach, shoreline change, DSAS, erosion and accretion, GIS, remote sensing]
Introduction
The shoreline change is mostly controlled by
natural processes or human activities, or both of them.
The primary natural factors include waves, tides,
winds, currents, storms, sea-level change, and
geomorphological changes resulting from
anthropogenic intervention through construction of
artificial structures, mining of beach sand, offshore
dredging or building of dams on rivers. The shoreline
change results from coastal erosion or accretion,
depending on the dominant processes acting on the
shoreline. The erosion and accretion processes,
especially erosion, greatly affect human life,
cultivation and aquaculture, natural resources, and
waterway transport activities along the coastal zone.
Correspondingly, shoreline mapping and change
detection are essential tasks in safe navigation, coastal
and marine resource management, environmental
protection, and sustainable coastal development and
planning [1].
The shoreline of Almanarre beach has suffered
both accretion and erosion processes due to natural
causes such as waves, winds and storms, or due to
human interference. From the visual comparison of
aerial photographs between 1955 and 1972, Grissac [2]
highlighted the significant decline of the western
branch (down from 50 to 80 m in the center and 75-90
m in the south part) associated mainly with the
degradation of Posidonia seagrass. Several authors [3-5]
have studied the shoreline evolution of Giens tombolo
with the aid of aerial photographs and some field
surveys, using imagery digital processing techniques.
However, this method still suffers some shortcomings
such as low frequency of data acquisition, limited
temporal coverage depending on the flight path of the
airplane; the photogrammetric procedure is costly and
time consuming. Additionally, the spectral range of
these sources is minimal and may introduce errors in
shoreline interpretation [6]. During the recent decades,
remote sensing techniques have developed and are
widely used, being more attractive as they are less
time consuming, inexpensive to implement, have
large ground coverage, and a satisfactory acquisition
repetition. As a result, this technology becomes an
effective solution for monitoring shorelines [7].
a. Location and annual swell rose
b. The studied zones
Fig. 1. The study area.
In this research, a new methodology of remote
sensing and GIS technology along with DSAS was
hired to attain some main objectives: (1) quantify
shoreline changes as well as accretion and erosion in
Almanarre beach over the period from 1973 to 2015;
(2) determine the main factor influencing the
shoreline evolution of this area; and (3) predict the
movement trends of shoreline in the future.
Materials and Methods
Study Area
Almanarre beach is located in the western branch
of Giens double tombolo, South East of France (Fig. 1
(a)). It lies between 6o07’18’’ and 6o08’09’’E of the
eastern longitudes and 43o02’26’’ and 43o04’47’’N of
the northern latitudes. The shoreline of the beach runs
through the study area with an overall direction of
north-south and extends approximately 4.5 km along
the Salt Road. Unlike a normal straight coast, the
bathymetry in this area is highly complex due to the
presence of submerged shoals and cross-shore deep
troughs [3]. An average slope is estimated from 1% to
1.5 % over the entire beach.
The recorded wind data of Hyères station reveals
that the west and southwest winds have strong
influence on the wave agitation and the coastal
morphology in Giens gulf. These winds maintain the
frequency of 25.66% of total observed time. They
also have the high speed with the maximum value of
21.47 m/s in the west direction. The southwest has the
higher frequency of 13.56 %, but the lower average
speed of 5.48 m/s than those in the west speed. On the
other side, the study area is exposed to dominant
waves coming from the west and southwest sectors
with respective frequencies of 36.92% and 28.84%.
The west waves have medium energy with heights of
0.5 to 2.5 m occupying up to 75% of cases, while the
southwest waves generally have low energy with
heights from 0.5 to 1.25 m and periods of less than 6
seconds in 77% of cases. Waves are the main
hydrodynamic process along the coast of Giens
tombolo, as the maximum tidal variation is less than
0.3 m [8].
The sediment is redistributed by the longshore
current drift induced by the oblique wave at the coast.
At 4 m isobaths in northern part of Almanarre beach,
the average longshore current speed is measured
between 3 and 7 cm/s in calm conditions and
increasing 15 to 25 cm/s in storm conditions. The
dominant directions on average are West to South and
South to East, then they meet and mix together to
create cross-shore flow seaward at Central part of
Giens tombolo [9]. There are some small streams
flowing the Gulf of Giens, between the points of
Carqueiranne and Almanarre, but sediment transport
volume is not significant.
For analysis purposes, the study area is divided
into three zones, namely, North zone, Central zone,
and South zone (Fig. 1(b)). The first zone of 1.5 km
length is located between Landmark B01 and
Landmark B14. The Central Zone, 1.35 km long,
starts from Landmark B15 up to Landmark B28
whereas the South Zone with the length of 1.525 km
spreads from Landmark B29 to Landmark B42.
Data Source
A series of satellite images such as Landsat
Multispectral Scanner (MSS), Landsat Thematic
Mapper (TM), Landsat Enhanced Thematic Mapper
(ETM+), and Landsat OLI (Operational Land Imager)
were acquired at non-equidistant intervals between
1973 and 2015. All the images have been collected
almost at the same time in summer season in good
quality to eliminate the effect of sea level rise due to
storms and waves. The details with respect to satellite
images are listed in Table 1. However, the raw
satellite images usually contain many defects, like
radiometric distortion, wedge-shaped gaps, geometric
distortion, presence of noise, etc., due to variations in
the altitude, attitude, and velocity of the sensor
platform [10]. Therefore, they need to be preprocessed
by image enhancement (radiometric calibration,
atmospheric correction, gap filling, pan-sharpening)
and geometric rectification steps before being used as
map base.
Table 1. List of satellite imagery used for the study
SI
no.
Satellite and
sensor
Acquisition
date
(dd/mm/yyyy)
Local
time
Spatial
Resolution
(m)
1
Landsat 1 MSS
01/03/1973
09:51
79
2
Landsat 4 TM
27/08/1988
09:47
30
3
Landsat 7 ETM
28/08/2000
10:08
15/30
4
Landsat 7 ETM
18/08/2008
10:06
15/30
5
Landsat 8 OLI
30/08/2015
10:17
15/30
Analysis Methods
Firstly, the exact shoreline was obtained by using
Matlab code and a nonlinear edge-enhancement
technique with the Canny edge detector. This
technique gives an outstanding delimitation of the
land-water boundary, and is time saving. A colour
composite can be used for extracting the shorelines.
The best colour composites for this technique are
RGB (Red Green Blue) 567 (for Landsat MSS
images), 543 (for Landsat TM and ETM+ images),
and 652 (for Landsat OLI images). These colour
composites nicely enhance the objects and distinguish
clearly between soil, vegetated land, and water, and
are easily digitized. The extracted shorelines were
imported in DSAS module running in ArcGIS
environment.
Secondly, although many methods were available
in the DSAS, the most commonly used, which are
End Point Rate (EPR) calculations and Linear
Regression Rate-of-change (LRR) statistic, were hired
to quantify the shoreline changes in Almanarre beach.
Specifically, EPR was utilized for short term change
analyses (1973-1988; 1988-2000; 2000-2008; 2008-
2015), whereas LRR was applied for long term
change analysis (1973-2015). Based on these settings,
a total of 176 transects along the western tombolo
were generated each of 200 meters perpendicular to
the baseline, at every 25 meters alongshore.
Furthermore, intersection point coordinates between
transect lines and shorelines as well as other statistical
results were also computed by DSAS.
Fig. 2.Actual shoreline position (2015) and predicted shoreline
position (2015) along Almanarre beach with 5 m linear space
transect.
Finally, the distances between multiple historic
shorelines and the baseline at each transect computed
by DSAS was input into the code which the authors
created to predict the positions of shorelines in 2020
and 2050. This code uses linear regression equation
and runs in Matlab. The accuracy and model quality
were defined by using cross-validation of the
estimated past shoreline positions. Particularly, the
positional shift in the estimated shoreline of western
Giens tombolo of 2015 was validated with respect to
actual image (extracted shoreline of 2015). The results
of validation are shown in Fig. 2. It is easily seen that
the predicted shoreline is asymptotically close to the
actual one. The overall error (RMSE) for the entire
Almanarre shoreline was found about 3.32 m. The
value of this error is acceptable and reasonable; hence
this method can be applied for predicting the position
of future shorelines.
Results and Discussion
Historical Shoreline Changes over Period of 1973-
2015
Based on the short-term analysis for North Zone,
the rate of change was measured along 1.5 km, from
Transect 01 to Transect 61 corresponding to
Landmark B01-B14, and both erosion and accretion
were observed, but erosion is dominant (Fig. 3 (a)). In
the period of 1973-1988, most of transects was
deposited with the maximum accretion rate of about
1.51 m/year observed near Landmark B06. However,
from 1988 to 2000, all transects in this zone suffered a
severe retreat with the maximum erosion rate of -2.13
m/year. The main reason of this phenomenon came
from the high frequency of storms. There were 79
heavy seas and storms observed from 1992 to 1999 [3].
This comment is valid for the other zones. The retreat
trend was maintained in the periods of 2000-2008 and
2008-2015 with the highest erosion rates of -1.77 and
-2.89 /year, respectively (Table 2). On the other side,
the long-term analysis of 1973-2015 demonstrates
that 90.16% of transects were subject to erosion,
whereas only 9.84% of those were prograded (Fig. 4).
The high accretion rates are concentrated around
Landmark B01 and B03 due to the blockage of the
main longshore sediment transport oriented West-East
by cross-shore submerged ridge. Inversely, the high
erosion rates are recorded near Landmark B06 and
B08 because this area is directly exposed to the
second prevailing waves from the southwest, which
has frequency of 28.84%.
Central Zone is composed of 54 transects over a
total distance of 1.35 km, from Transect 62-115 in
proportion to Landmark B15-B28. The short-term
analysis indicates that this zone has been undergoing
both accretion and erosion, as shown in Fig. 3 (b). In
the 1973-1988 period, only area from Landmark B16
to 18 was eroded with the maximum rate of -0.7
m/year. The remainders were prograded with the
maximum accretion rate of 1.75 m/year. As the first
zone from 1988 to 2000, most of transects in Central
Zone was retreated at the mean rate of -1.27 m/year.
Nevertheless, during the 2000-2008 period, 100% of
transects advanced seaward with the maximum
accretion rate of 1.7 m/year (Table 2). The sudden
positive trend in the shoreline change rate came from
the annual beach nourishment in this period. The
negative trend reappeared in the period 2008-2015
with the mean rate of -0.76 m/year. With regard to the
overall shoreline changes, 61% of transects record
erosion and 39% of transects record accretion.
Erosion frequently occurred from Landmark B16 to
B18 where deep trough nearly reaches the beach and
the slope of the nearshore zone is steeper. As a result,
the waves approach the shoreline with high energy
and take away sand from the beach. Moreover, this
area is immediately influenced by the combination of
wave action coming from the southwest and west
sectors with total frequency of 65.76%. Otherwise,
the area from Landmark B19 to B29 is advancing at
the maximum accretion rate of 0.46 m/year induced
by the cross-shore sediment transport channel [2].
The South Zone stretches over 61 transects (No.
116-176), corresponding to Landmark B29 to B42.
Fig. 3 (c) represents the shoreline change of South
Zone between 1973 and 2015. Generally, the erosion
and accretion phenomenon happen alternatively, but
erosion predominantly dominates in most of transects.
During the period of 1973-1988, the maximum
erosion and accretion rates are -1 and 2.14 m/year,
respectively. The 72% of transects in this period were
deposited at the mean rate of 0.51 m/year.
Nonetheless, the longshore pattern was completely
changed to erosion with mean rate of -0.74 m/year
between 1988 and 2000. The negative trend was kept
over the periods of 2000-2008 and 2008-2015 with
the average erosion rates of -0.61 and -0.06 m/year,
respectively (Table 2). Additionally, the long-term
analysis reveals a slight accretion with the maximum
rate of 0.46 m/year from Landmark B30 to B36 and
erosion at the maximum rate of -0.71 m/year from
Landmark B36 to B42 over the period of 1973-2015
(Fig. 4). According to Grissac [2], the Giens channel of
cross-shore sediment transport results in deposition in
the area from Landmark B30 to B36. The eroded area
may be provoked by the direct effect of northwest
waves accompanied with the strongest winds of
Mistral from the Rhone Valley.
a. North Zone from Landmark B01-B14 (Transects 1-61)
b. Central Zone from Landmark B15-B28 (Transects 62-115)
c. South Zone from Landmark B29-B42 (Transects 116-176)
Fig. 3. Positions of shorelines and transect lines as well as shoreline
change rates using EPR method along Almanarre beach over a
period of 1973-2015.
Fig. 4. The variation of shoreline change rates using LRR and EPR
methods along Almanarre beach over a period of 1973-2015.
Table 2. The statistical summary of shoreline change rate for Almanarre beach over a period of 1973-2015
Zone
Period
Total no.
of
transects
Coast
length
(m)
Min
rate
(m/yr)
Max
rate
(m/yr)
Mean
rate
(m/yr)
No. of
eroded
transects
No. of
accreted
transects
% of
eroded
transects
% of
accreted
transects
North
1973-1988
61
1500
-0.79
1.51
0.53
19
42
30.65
69.35
1988-2000
-2.13
-0.03
-1.27
61
0
100
0
2000-2008
-1.77
2.55
-0.19
36
25
59
41
2008-2015
-2.89
2.36
-0.1
42
19
68.85
31.15
1973-2015
-0.83
0.38
-0.22
55
6
90.16
9.84
Central
1973-1988
54
1350
-0.7
1.75
0.66
6
48
11.11
88.89
1988-2000
-2.36
0.03
-1.27
52
2
96.3
3.7
2000-2008
0.02
1.7
0.74
0
54
0
100
2008-2015
-1.61
-0.06
-0.76
54
0
100
0
1973-2015
-0.86
0.46
-0.11
33
21
61.11
38.89
South
1973-1988
61
1525
-1
2.14
0.51
17
44
27.87
72.13
1988-2000
-1.93
0.71
-0.74
52
9
85.25
14.75
2000-2008
-2.41
1.1
-0.61
44
17
72.13
27.87
2008-2015
-2.62
1.68
-0.06
31
30
50.82
49.18
1973-2015
-0.71
0.46
-0.15
45
16
73.77
26.23
Future Shoreline Changes over Period of 2015-2050
The shoreline of Almanarre beach has been
predicted for short term (2020) and long term (2050)
by using linear regression analysis. In this prediction,
the shoreline change rate has been estimated from
chronological observations, but the extreme events,
viz. storm and sea level rise due to global warming,
have not been taken into account. Fig. 5 represents the
positions of future shorelines and the shoreline change
rates, whereas Table 3 summarizes statistical results
of shoreline change assessment in Almanarre beach;
they concretize the maximum, minimum and mean
shoreline changes as well as % of accreted and eroded
transects for periods: 2015-2020, 2020-2050, and
2015-2050.
In the first region, North Zone, the shoreline
recession is observed in all periods of 2015-2020,
2020-2050 and 2015-2050 (Fig. 5(a)) with the
average erosion rate of -0.36 m/year, -0.32 m/year,
and -0.33 m/year respectively. All transects, except
transect no 1-5 that are subjected to accretion, exhibit
erosion in the period of 2015-2020 with the maximum
retreat rate of -1.77 m/year around Landmarks B13
and B14. However, in the next periods of 2020-2050
and 2015-2050, the maximum recession rates are seen
in the vicinity around Landmark B07-08 with the
values of -0.84 m/year and -0.89 m/year (Table 3).
This is the most vulnerable area to erosion in North
Zone. Moreover, the % of eroded transects drastically
increased over time, from 67.21% in the period of
2015-2020 to 90.16% in the period of 2020-2050.
In the next region, Central Zone, the results of
statistical analysis obtained for 54 transects illustrate
alternating areas of erosion and accretion, but
majority of transects show erosion (Fig. 5(b)). During
all the periods, the maximum erosion rates are mainly
concentrated in the area between Landmarks B16 and
B17, while the maximum progradation rates are
observed between Landmarks B20 and B22 that
coincide with the position of the cross-shore sediment
transport channel. In the period of 2015-2020, 62% of
transects were subject to deposition with the
maximum accretion rate of 2.32 m/year at Landmark
B20 (Table 3). Nonetheless, the positive trend will be
suddenly changed to the negative trend in the next
periods. Particularly, 61.11% of eroded transects are
recorded with the maximum recession rate of -0.87
m/year during the period 2020-2050, whereas the
eroded transects are predicted at about 57.4% with the
maximum erosion rate of -0.94 m/year between 2015
and 2050 (Table 3). Additionally, the prediction of
future shoreline positions also reveals that the
shoreline between Landmark B16 and B18 will be the
most seriously eroded area.
Table 3. Statistical summary of shoreline change rate for Almanarre beach over a period of 2015-2050
Zone
Period
Total
no. of
transects
Coast
length
(m)
Min rate
(m/yr)
Max
rate
(m/yr)
Mean rate
(m/yr)
No. of
eroded
transects
No. of
accreted
transects
% of
eroded
transects
% of
accreted
transects
North
2015-2020
-1.77
2.59
-0.36
41
20
67.21
32.79
-1.77
2.59
2020-2050
-0.84
0.39
-0.32
55
6
90.16
9.84
-0.84
0.39
2015-2050
-0.89
0.66
-0.33
58
3
95.1
4.9
-0.89
0.66
Central
2015-2020
-1.8
2.32
0.26
20
34
37
63
-1.8
2.32
2020-2050
-0.87
0.46
-0.16
33
21
61.11
38.89
-0.87
0.46
2015-2050
-0.94
0.67
-0.11
31
23
57.4
42.6
-0.94
0.67
South
2015-2020
-2.5
2.62
0
29
32
47.54
52.46
-2.5
2.62
2020-2050
-0.72
0.47
-0.23
45
16
73.77
26.23
-0.72
0.47
2015-2050
-0.91
0.54
-0.2
42
19
68.85
31.15
-0.91
0.54
For the last zone of Almanarre beach, a complex
pattern of shoreline evolution is predicted with areas
in erosion alternating with areas in accretion (Fig.
5(c)). In the period of 2015-2020, the eroded and
accreted transects are almost the same with 48% and
52%, respectively. The maximum recession and
accumulation rates are predicted about -2.5 m/year
and 2.62 m/year (Table 3). The accretion areas are
also forecasted in the vicinity of Landmarks B31-33
and B35-37. In the next periods of 2020-2050 and
2015-2050, recession is dominant towards accretion
with the average erosion rates of -0.23 m/year and -
0.2 m/year, respectively. The maximum accretion
rates are predicted to take place around Landmark
B38-39, while the maximum erosion rates can be
observed near Landmark B35-36. Finally, Fig. 5 (c)
also shows that the area between Landmark B37 and
B42 could be subject to severe erosion in future.
a. North Zone from Landmark B01-B14 (Transects 1-61)
b. Central Zone from Landmark B15-B28 (Transects 62-115)
c. South Zone from Landmark B29-B42 (Transects 116-176)
Fig. 5. Positions of shorelines and transect lines as well as
shoreline change rates using EPR method along Almanarre beach
over a period of 2015-2050.
Conclusion
The study on the shoreline changes in Giens
tombolo from 1973 to 2015 reveals that the shoreline
of Almanarre beach has experienced both erosion and
accretion, but erosion is dominant. Especially, most of
transects along this zone were subject to erosion
recently, from 2008 up to now. The main causes of
this recession are due to the action of waves
accompanied with the near-shore bathymetry.
Additionally, there is no sediment supply feeding the
beach frequently, viz. no river mouths flow in Giens
gulf. Furthermore, the prediction of shoreline
positions in 2020 and 2050 reveals that the erosive
tendency will settle, particularly and severely in the
areas of Landmarks B07-08 and Landmarks B16-18.
Finally, this study also demonstrates that the beach
nourishment method only saves the coastal area for
summer activities in the short term.
The results of this study strongly confirms that the
combination of remote sensing, geospatial techniques
coupled with DSAS along with linear regression
method is very helpful for investigating the shoreline
movement over time (both short term and long term)
as well as predicting the position of future shoreline
with reasonable accuracy. Moreover, this method also
provides a comprehensive view of erosion and
accretion patterns of the coastal realms. The shoreline
changes obtained from this study can be useful for the
decision makers and coastal managers to sustainably
manage the coast of Hyères, and scientists to propose
adaptive protection measures.
Acknowledgment
This work was financially supported by the 911
Project of Vietnam International Education
Development, Ministry of Education and Training,
Vietnam (Grant No. 911). The authors are grateful to
EOL, CETMEF, CEREMA, SHOM, and REFMAR
for providing the in situ measurement data. The
authors also sincerely thank the USGS for sharing the
free Landsat series images as well as for the making
the DSAS available on their website.
References
1. Cassé, C., et al., Remote sensing application for coastline
detection in Ca Mau, Mekong delta, in International
Symposium on Geoinformatics for Spatial Infrastructure
Development in Earth and Allied Sciences. 2012: Ho
Chi Minh City, Vietnam.
2. Jeudy De Grissac, A., Sédimentologie dynamique des rades
d'Hyères et de Giens (Var). Problèmes
d'Aménagements. 1975, Université d'Aix-Marseille II:
Marseille. p. 86 + annexes.
3. Courtaud, J., Dynamiques geomorphologiques et risques
littoraux cas du tombolo de giens (Var, France
méridionale). 2000, Université Aix-Marseille I. p. 263.
4. Capanni, R., Étude et gestion intégrée des transferts
sédimentaires dans le système Gapeau/rade d'Hyères.
2011, Aix Marseille 1.
5. Than, V.V., Modélisation d'érosion côtière : application à la
partie Ouest du tombolo de Giens, in LATP. 2015, Aix
Marseille Université: Marseille. p. 400.
6. Alesheikh, A.A., A. Ghorbanali, and N. Nouri, Coastline
change detection using remote sensing. International
Journal of Environmental Science & Technology, 2007.
4(1): p. 61-66.
7. Winarso, G., J. janto, and S. Budhiman, The potential
application of remote sensing data for coastal study, in
22nd Asian Conference on Remote Sensing. 2001:
Singapore.
8. SOGREAH, Etudes sédimentologiques de la rade d Hyères.
Littoral de port Pothuau à la Badine. 1988. p. 68 +
annexes et cartes.
9. Lacroix, Y., et al., Analysis of a Coupled Hydro-
Sedimentological Numerical Model for the Tombolo of
GIENS. International Journal of Environmental,
Ecological, Geological and Geophysical Engineering,
2015. 9(3): p. 117 - 124.
10. Lillesand, T.M., R.W. Kiefer, and J.W. Chipman, Remote
sensing and image interpretation. 2008: John Wiley &
Sons.