Titles should never contain abbreviations, e

Time series analysis of shoreline changes in Gonghyunjin and Songjiho Beaches, South Korea
1415
Time series analysis of shoreline changes in Gonghyunjin and
Songjiho Beaches, South Korea using aerial photographs and
remotely sensed imagery
In-Ho Kim†, Hyung-Seok Lee‡, Dong-Seob Song†
†Dept. of Ocean Construction Engineering,
Kangwon National University, Samcheok,
245-711, South Korea
[email protected]
[email protected]
‡ Dept. of Civil and Environmental Engineering,
Hanzhong University, Donghae,
240-713, South Korea
[email protected] (Corresponding author)
www.cerf-jcr.org
ABSTRACT
Kim, I.H., Lee, H.S. and Song, D.S., 2013. Time series analysis of shoreline changes in Gonghyunjin and Songjiho
Beaches, South Korea using aerial photographs and remotely sensed imagery, Proceedings 12th International Coastal
Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1415-1420, ISSN 0749-0208.
www.JCRonline.org
Given the speed and pervasiveness of anthropogenic landcover changes, especially in coastal areas, monitoring
shoreline alterations and their impacts is critical for intelligent coastal development and beach use management. In this
study, we describe a monitoring and analysis framework that uses aerial photography, remotely sensed imagery, and
field surveys to detect changes in beach width and area along Gonghyunjin and Songjiho Beaches in South Korea. We
used IKONOS imagery acquired in 2004; aerial photographs captured in 1991, 2005, 2009 and 2010; and field surveys
conducted in 2010 and 2011. Based on comparisons of these data sources, we detected widespread erosion on both
beaches starting in 2004, resulting in 12% reduction in the plane area of these beaches between 2004 and 2010. Most
dramatically, we noted that beach width eroded by 28.5 m at the point 700 m south of Gonghyunjin Harbor, and similar
declines occurred at several other locations. Erosion occurred at these locations because extended breakwaters in the
Gonghyunjin Harbor either blocked or interrupted drift sand transport processes, causing sand to be carried away from
some locations without accretion to replenish it. In addition, according to field surveys, we determined that erosion and
accretion processes continued to vary seasonally in 2010 and 2011, resulting in smaller overall changes than those in the
study years prior to 2010. However, we suggest that severe erosion may occur in the future at some locations if sand
continues to be transported north onto Songjiho Beach without replenishment. Thus, we demonstrated that the
construction of artificial structures around the harbor caused changes along the shoreline. Our monitoring framework
has important applications for future observation of anthropogenically driven changes to this coastal area and serves as
an applicable tool in other coastal regions worldwide.
ADDITIONAL INDEX WORDS: Aerial photographs, IKONOS image, shoreline change, beach width, plane area.
INTRODUCTION
The eastern coast of South Korea has historically exhibited a
seasonal equilibrium where waves from the northeast erode
beaches during winter months while waves from the southeast
redeposit sand in summer months. Recent anthropogenic
development along this coast, however, has caused substantial
erosion on top of the natural equilibrium patterns. In response, the
South Korean government has established a coastal monitoring
system to detect changes in area along the shoreline and to
establish appropriate usage plans. As part of this system,
photogrammetric and remote sensing approaches have been
proposed as efficient methods for monitoring shoreline changes.
Previous studies have successfully used such approaches in
similar applications. For example, multiple studies have used
series of aerial photographs to monitor erosion conditions and
shoreline changes (e.g., Li et al., 1998; Pornpinatepong et al.,
2005; Sesli et al., 2009; Sesli, 2010). Similarly, Chalabi et al.
(2006) used both IKONOS imagery and aerial photographs to
monitor shoreline alterations in Malaysia. In addition, recent
changes in the Niger Delta coastline were determined through a
time series analysis of satellite imagery (Adegoke et al., 2010).
____________________
DOI: 10.2112/SI65-239.1 received 07 December 2012; accepted 06
March 2013.
© Coastal Education & Research Foundation 2013
In such studies, the shoreline can be delineated according to
multiple techniques, including visual inspection or digital number
(DN) analysis (where the boundary between water and land is
detected according to changes in an image’s digital numbers;
Marfai et al., 2008). In one study (Muhammad, 2009), the
shoreline was delineated through the manual digitization of the
dry to wet sand boundary in aerial photographs. In addition,
topographic maps and other images can be used as supplementary
information for determining shoreline locations (Marfai et al.,
2008). In general, these previous studies establish that aerial
photography and remotely sensed imagery can be effectively used
to distinguish shorelines, beach area, and changes in those
elements.
In this study, we analyzed long-term changes in shoreline
characteristics along Gonghyunjin and Songjiho Beaches in the
eastern coast of Gangwon province, South Korea. We specifically
used aerial photographs and remotely sensed imagery to examine
trends in beach width in response to erosion and accretion that
could be attributable to the construction of artificial structures
along a local harbor.
STUDY AREA
This study focused on approximately 5 km of shoreline that is
part of the Gonghyunjin and Songjiho Beaches in Gangwon
Journal of Coastal Research, Special Issue No. 65, 2013
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Kim, et al.
province, South Korea (Figure 1(a)). In this region, a 140 m
northern breakwater was constructed in Gonghyunjin Harbor in
1967, and a 535 m eastern breakwater was constructed in 2005.
An additional 225 m southern breakwater and a 60 m groin were
constructed in 2007 (Figure 1(b)).
Along this stretch of shoreline, waves move in a northeast to
southeast direction in spring and summer whereas they tend to
move in a northeast to east direction in fall and winter. A strong
current that allows for drift sand transport from south to north is
typically most noticeable when waves flow from the northeast to
the east/southeast.
Recently, the stretch of Gonghyunjin Beach between Gajin and
Gonghyunjin Harbors has exhibited a consistent decrease in beach
area while accretion has been observed only in front of
commercial areas south of Gajin Harbor. In addition, the sandy
stretch of Songjiho Beach between Gonghyunjin and Oho Harbors
displayed a consistent increase in beach area only near the
southern breakwater of Gonghyunjin Harbor (Figure 1(c)). The
southern area in Songjiho Beach (Figure 1(d)), on the other hand,
recently exhibited distinct periods of erosion during spring and
summer and accretion during fall and winter.
MATERIALS AND METHODS
Orthorectification and Delineation of Shoreline
We mapped the study area using aerial photographs taken in
1991, 2005, 2009 and 2010 by the National Geographic
Information Institute (NGII; Table 1). We also used IKONOS
imagery of the area captured in 2004 (Table 1). IKONOS imagery
and photography were geometrically orthorectified using a Digital
Elevation Model (DEM) produced with the national digital map
(scale 1:5,000). We orthorectified both types of imagery in the
software PG-STTEMER v.4.2. We were then able to digitize and
analyze changes in beach area based on this orthorectified imagery.
The change in beach width and plane area was calculated using
AutoCAD 2010.
For the analysis of shoreline change, we estimated the beach
width in sections each year by dividing the shoreline into a total of
40 control sections delineated at 100-m intervals (Figure 3(a)). In
addition, the analysis of shorelines with large tidal differences
typically requires tidal-level adjustments according to the time of
day the image was captured. However, because tidal difference in
our study area were less than 20 cm, which is less than the
difference in height between the tallest waves and a flat sea, a tidal
adjustment was not necessary for shoreline delineation in this
study.
Field Surveys for Analysis of Beach Changes after
2010
We conducted four shoreline and cross-shore profiling surveys
over a span of 15 months (June 2010, November 2010, March
2011, and September 2011) to assess beach characteristics after
2010. We acquired coordinates for shoreline points at 1-s intervals
while traveling along the swash zone using a Differential GPS
(DGPS). We registered these points to the orthorectified 2009
photograph and 2004 image. The edge of onshore was set as the
reference line (Figure 5).
We defined the zone from Gonghyunjin Harbor to Gajin Harbor
on the north as the “KH01 sector” and the zone from Gonghyunjin
Harbor to Oho Harbor on the south as the “KH02 sector”. We
defined 20 control sections in KH01 and 40 control sections in
KH02 at 50 m intervals. To determine the overall variations in
shoreline characteristics after 2010, we estimated beach area for
both sectors (KH01 and KH02) as well as the change in area for 6
sectors.
RESULTS
Changes in the Study Area between 1994 and 2010
According to the 1991 aerial photograph of the study area, a
curved sandy beach existed south and north of Gonghyunjin
Harbor, and Juk Island (Figure 1) functioned as an offshore
breakwater such that the shoreline along the mainland protruded
out into Juk Island. In addition, the 1,405 m northern breakwater
had been constructed in the Gonghyunjin Harbor at this time.
However, this breakwater was too short for the inside of harbor to
be clearly visible in the photograph, and the natural shoreline
appeared intact (Figure 2(a)). In comparison, the IKONOS image
Table 1. Characteristics of aerial photographs and remotely
sensed imagery used in this study.
Acquisition date Type of data
Figure 1. Location of the study area encompassing (a)
Gonghyunjin and Songjiho Beaches in Gangwon province,
South Korea. This study area included (b) the southern beach
below Gonghyunjin Harbor (Sept. 2011), (c) a 60 m groin with
tetrapods (Nov. 2011), and (d) beach view to be eroded (Sept.
2011).
Resolution (meters)
Nov. 1991
Aerial Photographs
Dec. 2004
IKONOS (Multispectral) 1.0m
Nov. 2005
Aerial Photographs
1.0m
Aug. 2009
Sept. 2010.
Aerial Photographs
Aerial Photographs
1.0m
0.5m
Journal of Coastal Research, Special Issue No. 65, 2013
1.0m after scanning
Time series analysis of shoreline changes in Gonghyunjin and Songjiho Beaches, South Korea
from 2004 showed that, 13 years later, the 515 m eastern
breakwater and 140 m northern breakwater had been constructed.
We also observed an increase in area for both Songjiho Beach and
for the southern portion of Gonghyunjin Harbor below the
southern breakwater. We also noted a tombolo linking Juk Island
to the mainland (Figure 2(b)). Furthermore, a comparison of the
2004 IKONOS image to the 2005 aerial photograph illustrated the
completion of the now 535 m eastern breakwater as well as a
substantial corresponding increase in the southern shoreline below
the southern breakwater of Gonghyunjin Harbor. We also
demonstrated that, after the construction of the eastern breakwater
of Gonghyunjin Harbor in 2005, a wave shielding area formed
during winter months as the breakwater separated the longshore
current and drift sands. This initiated erosion processes at the 700
m point (section no. 15 in Figure 3(a)) below the southern
breakwater while also creating sand deposits near the breakwater
and inside Gonghyunjin Harbor (Figure 2(c)).
Examination of the 2009 aerial photograph revealed the current
shape of Gonghyunjin Harbor as it exists today as well as
substantial increases in shoreline due to accretion along the
southern beach below Gonghyunjin Harbor. In addition, we
observed that the beach width for the area around the 700 m point
below the southern breakwater (which was originally formed by
the wave shielding area) was narrower compared to 2005 (Figure
2(d)). Overall beach erosion also occurred over the 3 km zone
along the shoreline to Oho Harbor. Finally, we noted that the
beach width and area in our study region remained became stable
after 2010 (Figure 2(e)).
General trends in changes to beach area from 1991 to 2010 are
shown in Table 2. We observed that beach area consistently
decreased after 2004 due to beach erosion between 2004 and
2010; beach area along the Gonghyunjin and Songjiho Beaches
decreased by approximately 25% and 12%, respectively.
The largest change in beach width was seen near the southern
(a) Nov. 1991
(b) Dec. 2004
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Table 2. Plane area changes in each beach by year.
Year
Area (m2 )
Gonghyunjin Beach Songjiho Beach
Total
Nov. 1991 50,533
269,777
320,310
Dec. 2004 60,092
364,015
424,107
Nov. 2005 51,358
345,706
397,064
Aug. 2009 47,480
320,114
367,594
Sept. 2010 45,227
321,097
366,324
breakwater of Gonghyunjin Harbor (section no. 11 in Figure 3(a))
where beach width increased by 227.1 m from 1991 to 2010. In
addition, the area at section no. 36 (Figure 3(a)) decreased by 84.1
m between 2004 and 2010. The northern (sections 2-10 in Figure
3(a)) and southern (sections 19-39 in Figure 3(a)) shores of
Gonghyunjin Harbor experienced continuous erosion after 2004
whereas accretion occurred along the southern shore below the
southern breakwater of Gonghyunjin Harbor. This was likely
caused by the change in drift sand transport processes following
the formation of the wave shielding area near section no. 16.
Finally, the most severe change occurred in the cross-shore area at
section no. 15, indicating a drift sand transport inside
Gonghyunjin Harbor. However, despite these changes, the beaches
became stable with natural seasonal variation in beach width after
2009 (Figure 3(b)).
Figure 4 shows area changes from the southern breakwater of
Gonghyunjin Harbor to the 700 m below the southern breakwater.
Although the overall shoreline in 2004 was stable (Figure 4(a)),
approximately 30,491 m2 of sand in the south was moved to the
north after the extension of the breakwater (Figure 4(b)).
Ultimately, the northern area increased by 31,221 m2 (Figure 4(c))
(c) Nov. 2005
(d) Aug. 2009
(e) Sept. 2010
Figure 2. Changes in shoreline and beach area from 1991 to 2010. Major events that likely led to changes in shoreline near
Gonghyunjin Harbor include (a) the completion of the 140 m northern breakwater in 1967, (c) the completion of the 535 m eastern
breakwater in 2005, and (d) the completion of the 255 m southern breakwater and the 60 m groin at the end of 2007.
Journal of Coastal Research, Special Issue No. 65, 2013
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Kim, et al.
(a)
0
250
Meters
500
(b)
Figure 3. (a) Control sections at 100 m intervals along Gonghyunjin Beach (1-10) and Songjiho Beach (11-40) used in analysis of (b)
changes in beach width from 1991 to 2010.
Figure 4. Planar change along the southern beach of the southern breakwater in Gonghyunjin Harbor according to (a) IKONOS imagery
captured in Dec. 2004 before the extension of the breakwater, (b) aerial photography taken in Sept. 2010 after the extension of the
breakwater, and (c) shoreline surveys completed in Sept. 2011. Summary changes are shown in panel (d) where Ⓐ corresponds to panel
(a), Ⓑcorresponds to panel (c), Ⓒ shows accretion from 2004 to 2011 (approximately 31,221 m2), and Ⓓ shows erosion from 2004 to
2011 (approximately 3,100 m2).
Journal of Coastal Research, Special Issue No. 65, 2013
Time series analysis of shoreline changes in Gonghyunjin and Songjiho Beaches, South Korea
while the southern area decreased by 3,100 m2 (Figure 4(d)) by
2011.
Beach Changes according to Field Surveys after
2010
Beach width decreased in the KH01 sector and increased
between sections no. 1 and 6 in KH02 (Figure 5). Beach width of
the other sections in KH02 sector decreased compared to previous
data while also fluctuating due to erosion and accretion. After the
completion of the southern breakwater at the end of 2007, the
beach width along Songjiho Beach in KH02 fluctuated and
became generally narrower after 2009 (Figure 5(b)). Thus, we
conclude that this beach appears to exist in an equilibrium
condition.
As illustrated in Figure 6, field survey results showed that the
plane area of Gonghyunjin Beach (KH01 sector) decreased
consistently from 2004 while the plane area in the northern side of
Songjiho Beach (lower zone of Gonghyunjin Harbor; KH02-A)
continued to increase. The southern shore (KH02-B), on the other
hand, experienced overall erosion with seasonal cycles in erosion
and accretion. From 2004 to 2009, the northern area (KH02-A)
approximately 700 m south of Gonghyunjin Harbor increased by
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22,486 m2 while the southern area (KH02-B) decreased by 36,069
m2 (Table 3). In 2009 compared to 2004, Gonghyunjin Beach
showed a rapid decrease in plane area by up to (-) 29%.
CONCLUSION
Analysis of long-term trends in beach width and area, based on
aerial photographs and IKONOS imagery, showed that
Gonghyunjin and Songjiho Beaches decreased by 25% and 12% in
area, respectively, from 2004 to 2010. Owing to erosion at the 600
m section south of the southern breakwater in Gonghyunjin
Harbor, beach width was reduced to approximately 28.5 m at that
location. We concluded that this severe reduction in shoreline was
due to the blockage and separation of natural sand transport
processes caused by the formation of a wave shielding area
following the completion of the eastern breakwaters in
Gonghyunjin Harbor. In addition, the southern shore of the
southern breakwater in Gonghyunjin Harbor exhibited accretion
processes beginning in 2004 while the northern shore (i.e.,
Gonghyunjin Beach) as well as the southern shore (i.e., Songjiho
Beach) below Gonghyunjin Harbor continued to erode. Field
surveys conducted on the study region in 2010 and 2011 showed
that continuous cycles of erosion and accretion have resulted in
(Unit: meters)
(Unit: meters)
Figure 5. Changes in beach width at specific control sections along (a) KH01 (Gonghyunjin Beach) and (b) KH02 (Songjiho Beach) from
2004 to 2011 based on IKONOS imagery, aerial photographs, and field surveys. Control sections shown in photographs correspond to
columns in the tables.
Journal of Coastal Research, Special Issue No. 65, 2013
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Kim, et al.
(a) KH01 sector
(b) KH02 sector
Figure 6. Changes in plane area along sectors of (a) KH01 and (b) KH02 from 2004 to 2011 based on IKONOS imagery, aerial
photographs, and field surveys.
Table 3. Changes of area in KH01 and KH02 sectors.
Changes of area (m2 )
Year
KH01-A
KH01-B
KH01-C
KH02-A
KH02-B
KH02-C
Dec. 2004(image) – Aug.2009(photo)
-4,292
-9,977
-2,895
22,486
-36,069
-31,812
Aug. 2009(photo) – Jun. 2010
-1,033
-527
-13
2,317
-9,295
-771
Jun. 2010 – Nov. 2010
-138
-444
-249
4,095
-1,009
6,637
Nov. 2010 – Mar. 2011
-7
2,308
676
3,355
9,558
8,875
Mar. 2011 – Sept. 2011
38
-3,605
-972
10,530
-24,519
-13,363
only small differences in shoreline structure since 2009. However,
we hypothesize that sand transport to the north in Songjiho Beach
could result in severe erosion on this stretch of shoreline in the
future.
Our results underscore that construction in coastal areas can
lead to widespread changes in the natural coastal structure and
environment. Therefore, quantitative projections of the impacts of
such development projects should be considered before
construction is initiated. The results of this study can be
generalized and applied to other regions to help coastal managers
consider the implications of specific coastline modifications to the
natural environment. We also established a powerful methodology
for conducting long-term coastline monitoring studies in other
areas.
ACKNOWLEDGEMENT
This work was funded by the Korea Meteorological
Administration Research and Development Program under Grant
CATER no.2012-2023.
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