DSpace at VNU: An analysis of coastal erosion in the tropical rapid accretion delta of the Red River, Vietnam

Journal of Asian Earth Sciences 43 (2012) 98–109

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Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes

An analysis of coastal erosion in the tropical rapid accretion delta of the Red
River, Vietnam
Do Minh Duc a,⇑, Mai Trong Nhuan b, Chu Van Ngoi a
a
b

Faculty of Geology, College of Science, Vietnam National University, Hanoi, 334 Nguyen Trai, Thanh Xuan, Hanoi, Viet Nam
Vietnam National University, Hanoi, 144 Xuan Thuy, Cau Giay, Hanoi, Viet Nam

a r t i c l e

i n f o

Article history:
Received 9 November 2010
Received in revised form 8 August 2011
Accepted 10 August 2011
Available online 13 September 2011
Keywords:
Red River delta
Shoreline
Accretion
Erosion
Sediment transport

a b s t r a c t
The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system.
Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the
evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps
(1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths
(Ba Lat, Lach, and Day), leading to rapid accretion (up to 100 m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either
between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The
evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars
can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level
rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach
profiles, sea level rise, typhoon, and storm surge.
Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction
The Red River begins from the mountains of Yunnan province
(China). The Red River delta in Vietnam territory is formed by
the Red and Thai Binh river systems, which is commonly called
the Red River system (Fig. 1). The delta is about 15,000 km2. It is
a rich agricultural area and densely populated. Along the coastline,
the interaction between the sea and big rivers has created a typical
tropical natural condition which is suitable for tourism, agricultural and aquaculture development.
The Red River delta develops in a very dynamic fluvial and marine environment. The river basin is characterized by an alternation
of wet and dry seasons producing a huge total annual suspended
sediment load (Hoekstra and Van Weering, 2007). The delta is river
dominated (Fig. 2). The annual amount of sediment transported by
the Red River system into the East Vietnam Sea is about
82 Â 106 m3. In the wet season (from April to September), about
90% of the annual sediment supply is transported through the various distributaries (Nhuan et al., 1996). Of the total amount of sediment supplied, 11.7% passes through the Van Uc and Thai Binh
river mouths, 11.8% through the Tra Ly river mouth, 37.8% through

the Red River (Ba Lat) mouth and 23.7% through the Day river
mouth (Duc et al., 2007).
⇑ Corresponding author. Tel.: +84 4912042804; fax: +84 4 38583061.
E-mail address: (D.M. Duc).
1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jseaes.2011.08.014

The northern part of the coast (from Ba Lat to Hai Phong) has a
diurnal tidal regime with average amplitude of 2.5–3.5 m. In the
southern part, from Ba Lat to Day mouth, the tide is mixed with
a diurnal dominance. The average tidal amplitude is 2–3 m (Nhuan
et al., 1996). Waves usually have a dominant direction from the
east, northeast during the dry season (October–March) and from
east, southeast during the wet season (April–September). The average and maximum wave heights are 0.7–1.3 m. Wave heights in severe typhoons can reach over 5 m (Nhuan et al., 1996).
The large amount of sediments has made the delta a rapid continuous advancing to the sea. Old shorelines of the delta are recognized through series of old sand bars, historical and anthropogenic
proofs (Hoan and Phai, 1995). The delta was enlarged 20–30 km
from the 10th to 15th century and 10 km from 15th to 19th century (Fig. 1). Sediments supplied by the big mouths (Tra Ly, Ba
Lat, Lach, and Day) are mainly deposited at shallow sea and form
sand bars in front of the mouths. They protect shorelines behind
against wave and current attacks making a suitable condition for
rapid accretion.
Most of sediments discharged from rivers deposit in front of the
river mouths and causes rapid accretion. As a consequence, severe
shoreline retreat occurs at some other places due to sediment deficit. Erosion coast in the Red River delta has length and area much
less than those of accretion coast. However, it has seriously
damaged the coastal villages and made an obstacle for economic
development in the region. The distribution of erosion shoreline


D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

99

Fig. 1. Red River system and locations of old shorelines.

can be a typical characteristic of the Red River delta. They are
either in the middle of the big river mouths (Hai Hau) or very close
to them (Giao Long, Giao Phong, and Nghia Phuc).
The paper has objective to outline shoreline change in the recent time and find out the physical mechanism of erosion in the
tropical rapid accretion delta of the Red River. Recent evolvement
of shoreline and the reasons are elucidated by the analysis of
topographical maps and nearshore sediment transport. Factors
affecting shoreline retreat such as typhoon, sea level rise, and upstream dams are studied to assess potential acceleration of erosion
and its impacts to coastal structures.

2. Materials and methods
2.1. Topographical maps
A series of topographical maps are used to investigate recent
changes of shoreline (Table 1). The maps were established using
different co-ordinate systems and scales. WGS-84 stands for World
Geodetic System which is currently the reference system being
used by the Global positioning system. WGS-60 is one of the

Fig. 2. The Red River in the chart of delta classification of Coleman and Wright
(1975).


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D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

Table 1
List of recent topographical maps.
Year

1930
1965
1985
1995
2001

Co-ordinate
Datum

Ellipsoid

–
WGS-60
HN-72
VN-2000
VN-2000

–
WGS-60
Krasovski
WGS-84
WGS-84

former systems of WGS-84. HN-72 or Hanoi-72 is the system of
Vietnam which was used before 2000. It used Krasovski ellipsoid
and the datum (origin co-ordination) was transferred from Moscow to Hanoi. It is not a spatial unified system and requires different formulas to convert to other systems. VN-2000 is the current

national geodetic system in Vietnam. The origin co-ordination
was installed in Hanoi. VN-2000 is a unified system for the whole
country.
Maps are scanned and then the shoreline in each map is digitized in MapInfo software. The vector maps are then transformed
to the same scale and datum which is used here as WGS-84. The
converting procedures follow the instruction of the circular on
‘‘Guidelines for the Application of VN-2000 System’’, established on
20 June 2001 by the General Department for Land Survey (Ministry
of Natural Resources and Environment). The 1930 map is separately analyzed. Some national roads are assumed not to be changed and can be reference to overlay this map with 1965 map.
Because of uncertainty for 1930 map the change of shoreline from
1930 to 1965 has not high reality.
Shoreline in topographical maps is considered as the line between seawater and land when water level is at longterm mean
tide. The tide range at Hondau station (Quang Ninh province) is
used for the North Vietnam where the longterm spring tide is
4.0 m. Obviously the longterm neap tide is 0 m. Therefore shoreline

Scale

Note

1:250,000
1:50,000
1:50,000
1:50,000
1:50,000

Published
Published
Published
Published

1978
1991
2001
2005 (Ba Lat mouth only)

of the Red River delta in topographical maps is defined at the mean
sea level of 2.0 m above the neap tide.
2.2. Sediment sampling and testing
A rectangle net of survey along the coast of Hai Hau at the
depths of 0–30 m was set up. The distances between investigation
points are 2.5 km and 5 km in the depths of shallower and deeper
than 10 m water deep, respectively (Fig. 3). During the fieldwork
small ships were used. The position of sampling stations was determined using a GPS with an accuracy of 5–100 m. A total of 52 sediment samples were taken by grab sampler. This is a part of
investigation in the Red River coast in 1996 and 2000 (referred
to Duc et al. (2007)).
Grain size distributions of sediment samples were analyzed by
means of sieve for the sandy fractions (sieve sizes: 2, 1, 0.5, 0.25,
0.125 and 0.063 mm), and by means of pipette analysis for samples
containing particles smaller than 63 lm.
A thin-walled tube (ASTM, 2001) was manually inserted to surface sediment in tidal flat to take undisturbed geotechnical samples. Six samples were retrieved along the coast in 2008 (Fig. 3).
Water content (W), bulk density (c), and grain density (D) of sediments are defined in the laboratory. Porosity (n) of sediment is
then defined as:

Fig. 3. Sediment sampling locations.


D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

n¼1À

c
qs ð1 þ 0:01WÞ

ð1Þ

McLaren and Bowles (1985) proposed a hypothesis that relates
two cases of grain-size trends to net transport paths. According to
this model, along the direction of net transport sediments can be
either better sorted, finer and more negative skewed (measured
in / units) or better sorted, coarser and more positively skewed.
The model has been re-examined by Gao and Collins, 1990 and
1992. They proposed a procedure to define two dimensional net
sediment transport pathways, including some steps as follows:
(1) comparisons of grain size parameters at a station with the ones
at adjoining stations (the distance between them is not longer than
a characteristic distance. It represents the space-scale of sampling)
to define unit vectors, i.e. if there is one or not a net sediment
transport from the station to another; trend vector at a station is
defined by sum of unit vectors; (2) averaging trend vector at the
station and other ones of adjoining stations to remove noise and
define transport vectors and (3) significance test on the transport
vectors. The parameters of sorting, mean diameter of grain sizes,
and skewness are considered to be equal importance in defining
net sediment transport pathways.
The grab sampler takes sediment samples from the bottom surface to the depth of 10–15 cm. It may represent different time periods (e.g., a longer or shorter periods are taken into accounts at sites
of higher and lower sedimentation rates, respectively). The characteristic distance in this area is assumed to be 5 km, which is the
longest distance between two adjacent sample stations. The differences of sedimentation rates between stations of shorter than 5 km
apart are supposed to be small. At about assumed characteristic
distance, the difference in recent sedimentation rates achieved

by 210Pb analysis in 2 gravity cores (i.e. cores 6 and 7 off the southwest coast of Hai Hau) is only 0.5 cm/y (van den Bergh et al., 2007).
Therefore the assumption is acceptable.
2.4. Longshore sediment transport
Waves change the propagating direction when they reach to the
shallow water it due to bottom fiction. To a certain depth waves
break and induce currents. The currents then cause longshore sediment transport which is the main reason of coastal erosion. Volume of sediment transport is estimated by CERC formula (US
Army Corps of Engineers, 2002: Manual of Coastal Engineering).
The potential longshore sediment transport rate, dependent on
an available quantity of littoral material, is most commonly correlated with the so-called longshore component of wave energy flux
or power:

Pl ¼ ðEcg Þb sin ab cos ab ðN=sÞ
Eb ¼

cgb

qgH2b
8

ðN=sÞ

!
c
2khb
ðm=sÞ
1þ
¼
2
2
sinh khb

k ¼ 2p=Ls

The amount of longshore sediment transport is expressed as the
volume transport rate (Ql) which is estimated by the formula:

Ql ¼

2.3. Net sediment transport

ð2Þ
ð3Þ

ð4Þ
ð5Þ

where Eb is the wave energy evaluated at the breaker line, ab the
wave angle relative to the shoreline (°), Hb the wave height at breaking (m), cgb the wave group speed at the breaker line, Ls the wave
length (m), c the wave velocity (m/s), q the density of water (kg/
m3), g the gravitational acceleration (g = 9.82 m/s2), and hb is the
depth of wave break (m).

101

K
Pl ðm3 =sÞ
ðqs À qÞgð1 À nÞ

ð6Þ

where K is the experimental coefficient, equal to 0.39, qs the
density of sediment grains (kg/m3), and n is the porosity of
sediments.
3. Results
3.1. Shoreline change
The overlaying of maps shows quantitative figures of shoreline
change at the coast (Fig. 4 and Table 2). The Red River delta is
intensively moved seaward at the big river mouths such as Ba
Lat, Day, and Lach. The distribution of erosion comes between
accretion segments.
The average velocity of accretion is 65 m/y (1930–1965), 84 m/y
(1965–1985), and 60 m/y (1985–1995) at the Ba Lat mouth (Table
2). The propagation of shoreline has close relation to the formation
and enlargement of sand bars (Fig. 5). A small bar (Vanh sand bar)
was formed during the period from 1930 to 1965. The main direction of development is to the NE (left bank of the river). The mouth
was then rapidly moved toward the sea (1965–1985). The Vanh
bar was intensively extended, and two other bars (Ngan and Lu)
were formed. The accretion at the right bank was dominant. The
seaside of Lu bar in 1985 was 7.1 km away from 1965 shoreline,
i.e. an advancing rate of 350 m/y on average. This period is considered as the strongest development of the Ba Lat mouth. Following
that mechanism a new series of sand bars was formed during the
period 1985–1995, which was then enlarging and connected to
each other in 2001. The mouth developed symmetrically.
The Lach and Day river mouths have not typical mechanism of
propagation as the Ba Lat mouth. Beside the sediment budget
transported from the Ninh Co and Day rivers, longshore sediments
from erosion at Hai Hau is intercepted by river currents and deposited in between the mouths and sand bars. However there are still
some small creeks between bars. Their channels change frequently
and are easy to be filled up. Therefore a large continuous area of tidal flat is formed at the Day and Lach mouths. The average accretion rates were 95–110 m/y and 27–35 m/y, respectively.
Sediment is mainly deposited at the big river mouths, causing

erosion in other places. The erosion occurs either near the big river
mouths or in the middle of them. It has caused land loss of several
villages (Fig. 6). Nearby the Ba Lat mouth, the shoreline of 22 km
in Giao Long and Giao Phong was eroded during the period 1930–
1965. The maximum retreat rate at Giao Phong was 24 m/y. The erosion was even more severe in the period 1965–1985 with the average velocity of 1.5 times larger than it was in 1930–1965. However
the erosion was interrupted in 1985–1995 along with the southward enlargement of the Lu bar. A short segment of 2.5 km was recorded as weak erosion in 1995. The remaining 18 km of shoreline
turned to be very strong accretion. The shoreline moved seaward
100–430 m during the period 1985–1995. Another eroding coast
is Nghia Phuc which situates nearby the Lach mouth. Erosion has taken place since 1965 in the length of about 0.5 km. The retreat rate
was 8–10 m/y. The shoreline is now at the trough of sea dikes.
The most severe erosion is the coast of six coastal communes
(Hai Dong, Hai Ly, Hai Chinh, Hai Trieu, Hai Hoa, and Hai Thinh)
in Hai Hau district. The erosion is considered to start from the
beginning of the 20th century (1905) (Pruszak et al., 2002). It has
a close relation to the degradation of the Ha Lan river mouth (the
former main river mouth of the Red River system at that time).
The clear evidence of Ha Lan mouth degradation can be found at
Giao Long and Giao Phong shorelines where were continuously


102

D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

Fig. 4. Shoreline change in Hai Hau coast and adjacent areas.

Table 2
Accretion and erosion at the Red River delta coast.
Segment

Accretion
Length (km)

a

Erosion
Average rate (m/y)

Area (ha/y)

Length (km)

Average rate (m/y)

Area (ha/y)

1930–1965
Ba Lat mouth
Ha Lan – Lach mouth
South Lach mouth
Day moutha

19.5
4.5
4.5
10.0

65
5
27

95

126.8
2.3
12.2
95

22
17.5
–
–

12
15
–
–

26.4
74.3
–
–

1965–1985
Ba Lat mouth
Ha Lan – Lach mouth
South Lach mouth
Day moutha

21
1.7

4.0
12.3

84
6
35
110

176.4
1.0
14
135.3

20
20.3
0.5
0.8

18
10
10
3

36
20.3
0.5
0.2

1985–1995
Ba Lat mouth

Ha Lan – Lach mouth
South Lach mouth
Day moutha

21
0.5
4.0
12.5

60
4
28
100

126
0.2
11.2
125

2.5
21.5
0.5
1.5

2.5
11
8
4

0.6

23.7
0.4
0.6

The shoreline of the Day mouth in Ninh Binh province was not taken into account.

accreted with rapid rates (reaching to 100 m/year in some segments during the period of 1905–1930) (Fig. 4). However the main
river mouth was then shifted to the Ba Lat mouth and shorelines
changed to erosion. During the period 1930–1965 the maximum
retreat rate was 22 m/y in Hai Ly and Hai Chinh communes. The
Hai Ly coast was then significantly eroded in 1965–1985. The average rate was 21 m/y. At the same period the rates were 5 m/y at
Hai Dong coast and 11 m/y at Hai Chinh–Hai Thinh coast. The
south part of Hai Thinh commune was accreted. Upto 1995, major
parts of shoreline reached to the trough of sea dikes, i.e. the water
level at the mean tide touched the dikes. Lateral movement is
stopped. Shoreline retreat is only realized at some segments in
Hai Ly and Hai Chinh where the former dikes were broken and
the locations of new dikes shifted landward. Shoreline change at
other parts of the Hai Hau coast cannot be estimated by topographical maps. The evolvement of erosion is then recognized by the

change of bottom topography and landscapes on the beach during
low tide (see Section 3.2).
Nowadays, the shoreline in Hai Dong has been changed to
accretion (by eye-seeing and personal conversation with local
authority for some recent years). However the erosion continues
to increase in other segments. The most severe erosion segment
is now shifting to Hai Thinh commune. It is very significant by a
series of three photos taken at the same place at the coast of Hai
Thinh commune from 2003 to 2005. Figs. 7 and 8 show that a small
tent for mineral exploitation was almost disappeared during

10 months (from 02 September 2003 to 25 July 2004). The shoreline retreated about 30 m. Nine months later all the pine trees were
destroyed. The shoreline reached to the sea dike with a lateral
movement of about 40–50 m (Fig. 9). The result proves an actual
situation of increasing erosion that is opposite to a remark of recent decrease of erosion (Pruszak et al., 2002).


D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

103

Fig. 6. Land loss due to erosion in Hai Ly commune.

Fig. 7. Hai Thinh, 02 September 2003.

Fig. 8. Hai Thinh, 25 July 2004.
Fig. 5. Recent progress of the Ba Lat mouth.

3.2. Nearshore topography change
The erosion has caused a remarkable change of bottom topography along the coast. The depth contour of 3 m in 1985 is approximately matched with the one of 5 m in 1965 (Fig. 10). The 2 m

contour (if is considered as the middle between 1 and 3 m contours) was moved landward 1–2 km from 1965 to 1985. The contour then continued moving 1.5–3 km from 1985 to 1995. The
maximum movement occurred at the south of Giao Phong commune. An opposite sign of erosion is also recognized at the north
part of Giao Phong commune where the 2 m contour of 1995 intercepts the one of 1985.


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D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109
Table 4
Wave parameters at the Hai Hau station (01 January 1976–31 December 1994)

(Pruszak et al., 2002).

Fig. 9. Hai Thinh, 17 April 2005.

Fig. 10. Nearshore topography change.

3.3. Sediment properties and net transport
Laboratory testing of undisturbed soil samples (Table 3) shows
that nearshore sand is medium sand with the porosity of 0.42–
0.49. Grain size parameters of surface sediments are shown in
Table 8. Based on grain sizes, two main types of sediments are defined such as sand and silt. Sand is distributed along the shoreline
in water depths of 3–5 m, except to the southeast of the Red River
mouth, where sand extends down to the water depth of 15 m
(Fig. 11). The recent sand is very well sorted and consists on
average for 98.5% of sandy and 1.5% of silt particles. Silt is widely

No.

Hs (m)

Tp (s)

h (°)

ab (°)

Duration (days)

1
2

3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

0.57
1.22

1.67
2.04
0.51
1.13
1.79
1.99
2.48
3.20
0.80
1.16
1.91
2.50
4.25
0.59
1.32
1.60
2.03
2.52
3.25
0.50
1.19
1.74
0.54
0.47
1.28
1.76
0.39

2.93
5.14

6.49
7.00
3.00
5.13
5.94
6.82
7.18
8.20
2.65
5.00
6.00
7.00
8.25
3.27
5.12
6.00
7.47
7.79
9.05
3.11
5.44
6.79
3.20
5.80
9.36
11.00
5.00

87.5
81.7

81.6
77.0
65.0
63.6
73.2
68.8
67.6
63.5
43.0
43.0
43.0
43.0
40.0
20.0
18.4
26.0
16.7
18.4
24.0
À3.2
1.2
11.8
À22.6
À47.0
À63.4
À47.0
À70.0

44.5
50.3

50.4
55.0
67.0
68.4
58.8
63.2
64.4
68.5
89.0
89.0
89.0
89.0
92.0
112.0
113.6
106.0
115.3
113.6
108.0
À3.2
130.8
120.2
154.6
179.0
195.4
179.0
202.0

36.5
35.1

1.4
0.2
10.9
2.2
9.9
4.6
4.2
0.7
19.1
3.8
0.3
0.1
0.1
3.4
1.8
0.2
0.7
0.2
0.1
11.0
7.0
0.4
7.4
33.1
0.1
0.1
3.2

distributed along the coast stretching from northeast to southwest.
Most of the silt is poorly sorted. The composition is dominated on

average by 70% silt, 22% clay and 8% sand. Besides, sandy silt distributes at the eastern and southeastern margin of the study area
at the depth is over 25–30 m. It is the old sediment units (Duc
et al., 2007).
A set of 52 sediment is used to define the net transport according to the method of Gao and Collins, 1992. The results in Fig. 11
shows that the sediment from the Ba Lat mouth is not deposited
nearshore, but moves seaward up to the water depth of 25 m. It
is very significant along the Giao Long – Ha Lan coast at the depth
of 5–25 m. In Hai Thinh shoreline, the sediment is transported
along the coast southwestward. In Giao Long–Giao Phong shoreline, the sediment is transported along coast northeastward. The
reason may be the northeast waves do not have strong effect on
the coast because of the sand bars in front of the Red River mouth.
3.4. Longshore sediment transport
The volume of longshore sediment transport is calculated by the
formula (6), with the wave monitoring data at Hai Ly from 1976 to
1994 (Table 4). The result shows that the sediment is dominantly
transported southwestward by the northeast and east waves. The

Table 3
Physical properties of nearshore sand.
No.

1
2
3
4
5
6

Sample

H2
H4
H5
H6
H8
H11

Percentage of grain sizes (mm)
1.00.50

0.500.25

0.250.125

0.1250.063

>
0.063

0.2
0.0
0.9
6.1
0.1
0.8

2.7
2.8
92.8
3.7

97.9
1.6

92.0
94.1
0.4
94.3
0.1
93.4

3.0
1.0
1.0
1.2
0.5
1.9

2.2
2.1
4.9
0.6
1.5
2.3

Water content
(%)

Bulk density
(g/cm3)

Grain density
(g/cm3)

Porosity

26.8
29.5
35.0
34.5
34.7
29.5

1.96
1.92
1.87
1.86
1.85
1.94

2.66
2.67
2.68
2.68
2.69
2.67

0.42
0.44
0.48
0.48

0.49
0.44


D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

105

Fig. 11. Net sediment transport pathways at the Hai Hau coast (1985 topography, map of surface sediment is extracted from Duc et al. (2007)).

volume is 654,078–801,078 m3/year in Hai Dong and Hai Ly section (Table 5). The figure of Nghia Phuc section is 440,979 m3/y.
Volume of southwestward transport at Giao Long section (1965)
was 741,335. It gives an evidence of strong erosion in this area during the period 1965–1985. Sediment transport changed to northeastward at this section in the context of 1995 topography. The
volume is 80,798 m3/y.

4. Discussion
4.1. Impacts of sea level rise
IPCC (2007) indicated a clear trend of sea level rise (SLR) worldwide with the average rate of 1.8 mm/y over 1961–2003. A comparative study on impacts of SLR has confirmed that Vietnam is the
most vulnerable country to sea level rise in Southeast Asia and
one of top five most vulnerable countries in the world (Susmita
et al., 2007). Relative SLR in Vietnam is mainly calculated from
tide-gauge data collected at the four chief stations: Hon Dau (Quang
Ninh province – North Vietnam), Da Nang, Qui Nhon (Center Part)
and Vung Tau (South Vietnam). The longest tide data is achieved
at Hon Dau station from 1960 to 2000. The SLR of 1.9 mm a year
has been observed in this period (Hanh and Furukawa, 2007). Thuy
(1995) analyzed two tidal gauges in the North coast, one is at Hon
Dau and another is at Hai Hau. The result shows that from 1950s
to 1990s the average rate of SLR is 2.24 mm/y. The recorded data
of four chief stations shows that the increments in sea level varying

from 1.75 to 2.56 mm/y along the coast of Vietnam in 50 recent
years. It is 3 mm/y over 1993–2008 (MONRE, 2009).
To estimate the increase of shoreline erosion the formula of the
so-called Brunn’s rule (1962) is used. The formula shows the relation between SLR and the increase of shoreline erosion as
following:

R1 ¼ 0:001S

LÃ
ðmÞ
h þB
Ã

ð7Þ

where S is the SLR (mm/y); R1 the exceeding rate of erosion due to
SLR (m/y); L⁄ and (h⁄ + B) are the width and vertical extent of the
active beach profile.
The results (Table 6) show that the increase of erosion rate can
reach to 0.14–0.31 m/y along the coast of the Red River delta. However the erosion rate depends on many factors such as human
activity, change of direction of sediment flow, waves, and currents
(Duc et al., 2007). It is hard to define the accurate contribution of
SLR on the increase of erosion rate. To have a raw estimation of
SLR effect, the erosion rate at the south Hai Thinh commune is taken into account. The rates were approximately 0 and 11 m/y during the period 1965–1985 and 1985–1995, respectively. It is about
40 m/y in 2005. Therefore SLR contributes 34% to the increase of
erosion rate during the period 1965–1995 and 12% from 1995 to
2005.
4.2. Impacts of tropical cyclones
Tropical cyclone is a typical climatic event in the North Vietnam. The so-called storm season often starts in June and ends in
October. About 13% of the total tropical cyclones attacked the

country landed on the North coast. Tropical cyclones, especially typhoons have caused many severe lost of properties and lives. For
instant, the typhoon PAT (23 October 1998) made 500,000 homeless and 90 death in the North coast. The imprints of typhoons
are recognized at the 22 m water deep by laminated sand layers
between silty clay layers in a gravity core (van den Bergh et al.,
2007). Storm surge due strong winds and heavy rainfall in a typhoon can reach to a height of 2.6 m (Table 7). This phenomenon
always leads to serious losses. The most recent Damrey typhoon
landed in the high spring tide caused very disastrous damages on


106

D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

Table 5
Volumes of longshore sediment transport.

a

Location

Beach slope

Shoreline orientation (°)

SW

NE

Total (m3/y)a

Giao Long (1965)
Giao Long (1995)
Hai Dong
Hai Ly
Nghia Phuc

0.00800
0.00400
0.01500
0.01000
0.00455

44
76
42
42
42

1,000,002
275,402
878,094
716,962
483,375

À258,667
À356,200
À77,016
À62,884
À42,396

741,335
À80,798
801,078
654,078
440,979

‘‘Plus’’ and ‘‘minus’’ are sediment transport to the SW and NE, respectively.

Table 6
Increase of erosion rate due to SLR.
Section

SLR (mm/y)

h⁄ (m)

B (m)

L⁄ (m)

Increase of erosion rate (m/y)

Giao Phong
Hai Dong
Hai Hoa-Hai Thinh
Nghia Phuc

2.24
2.24
2.24

2.24

5.4
7.0
10.4
5.3

2.0
2.0
2.0
2.0

556.7
821.6
1377.6
473.8

0.17
0.20
0.25
0.15

Table 7
Heights of storm surge in severe typhoons.
No.

Typhoon

Date of formation

Landing place

Storm surge height (m)

1
2
3
4
5
6
7
8

PHILLIS
ROSE
RUTH
JOE
WARREN
PAT
DOT
DAMREY

02
08
10
18
16
18
16
19

Nam Dinh, Ninh Binh
Nam Dinh
Thanh Hoa
Hai Phong
Thai Binh, Nam Dinh
Hai Phong
Hai Phong
Nam Dinh, Hai Phong

1.10
2.56
2.50
1.94
1.15
0.78
1.92
2.50

July 1966
September 1968
December 1973
July 1980
August 1981
October 1988
May 1989
September 2005

sea dikes, mangrove, shrimp ponds, and infrastructure. Hundreds
thousand people had to emigrate.

According to the formula of Kriebel and Dean (1993) the retreat
distance caused by extreme wave heights can be estimated as
following:

RðtÞ ¼ R1 ð1 À eÀt=T s Þ ðmÞ
R1 ¼

Hs ðW b À hb =mo Þ
ðmÞ
B þ hb À Hs =2

Wb ¼

 3=2
hb
ðmÞ
A

T s ¼ 320


À1
hb mo W b
1þ þ
ðsÞ
B
hb
g 1=2 A
Hb3=2

3

ð8Þ
ð9Þ

ð10Þ

ð11Þ

where Hs is the significant wave height (m), Hb the wave height at
breaking (m), hb the depth of wave break (m), Wb the width of
breaking wave zone (m), B the height of berm (m), mo the beach
slope, t the duration of extreme wave heights (h), A the sediment
scale or equilibrium profile parameter (m1/3), R(t) is the retreat
distance caused by extreme wave heights (m).
The recorded wave heights during typhoons at Hai Hau tide station (1976–1994) were 3.2–4.25 m (Table 4). Table 8 indicates that
the erosion rate can reach to 7.1 m when the wave height is 4.25 m
and the duration is 2.4 h.
The research of NCDC (1996) emphasized the increase in the
number of tropical cyclones attacked Vietnamese coast during
the period 1920–1994. The most recent statistical data of the
annual number of tropical cyclones shows that the number of cyclones does not have any clear trend during the period 1960–
1990s. It had a significant reduction in number from 2000 to

2004 and then has been increasing very rapidly from 2005 up to
present (Duc et al., 2009). This matter cannot all be claimed on climate change. However it is evidence showing that the variability of
extreme events at the coast occurring more complicated. Kleinen
(2007) suggested an increase in occurrence and intensity of typhoons in the Western part of the Pacific, especially the ones that
hit Vietnam. The threat of typhoons on coastal zone in general and
on sea dike stability in particularly is expected to be more serious

in the near future.
The analysis of statistical data on typhoons of the National
Centre for Meteorology and Hydrology () shows that there were 86 typhoons directly hit the coast
of the Red River delta over 1962–2010, i.e. an average of two typhoons annually. The return periods of typhoons with the intensity
of equal or greater than 10, 11, 12, and 13 (Beaufort scale) are
about 3, 5, 10, and 21.5 years, respectively (Fig. 12). As recognized
from the Damrey typhoon (September 2005), storm surge and
wave-run up were the main reasons for sea dike destruction and
coastal flooding. The correlation between typhoon intensity and

Fig. 12. Return periods of typhoons.


107

D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

Fig. 13. Correlation between storm surge height and intensity of typhoon.

Fig. 15. Current concrete seadike system.

Fig. 14. Estimated storm surge height and the return period (storm surge height is
estimated by the regression equation in Fig. 13).

storm surge (Fig. 13) indicates a unit increase of typhoon intensity
causes an increase of about 30 cm of storm surge height.
To assess combined impacts of typhoon and SLR on storm surge
height, medium emission scenario (B2) is taken into account. The
B2 scenario expects that sea level in Vietnam will rise 30 and
75 cm in 2050 and 2100, respectively (MONRE, 2009). As shown

in Fig. 14, the return period of a 2.6 m storm surge height reduces
from 20 years at the present to 9 years in 2050 and only 4.5 years
in 2100.
4.3. Upstream dams
The Hoa Binh dam (fully operated in 1989) does not change the
amount of water but reduced 56% of suspended sediment budget
in the downstream flow as recorded at Son Tay and Hanoi hydrological monitoring stations (Table 9). Sediment transported to the coast
can also derive from lateral and bottom erosion along the channels,
but no monitoring data about suspended matters in river flows near
the coast is recorded. Meanwhile the accretion rate decreased from
84 m/year (1965–1985) to 60 m/year (1985–1995) at the Ba Lat

mouth. It shows a tendency of reduction in coastal accretion due
to dam construction. In the near future, as Tuyen Quang, Son La
and other hydropower plants will be operating the sediment supply
for the coast is going to decrease significantly. The reduction of
accretion at the river mouths and more severe erosion in the Hai
Hau coast are irreversible.
4.4. Suggestion of coastal protection
The protection of the costal zone in the Red River delta is very
important because of high population density and economic benefits. Sea dike is the most important measure to protect the coast.
Simple dikes of compacted soils were common in the 1980s. The
dikes are easy to be eroded and severely damaged in a typhoon.
Such type of dikes is still at some parts of the coast in the Hai Chinh
and Hai Dong communes. To reinforce the dikes groynes were
used. They were constructed by a chain of concrete tubes with
diameter of 1 m, thickness of 10 cm, and height of 1.5 m. The tubes
were filled up with sand bags and placed continuously at the depth
of 0.5 m under beach surface. The distance between groynes is
80 m. Mangrove forest is another measure against coastal erosion.

A hundred meters of mature mangrove can reduce 0.1 m of wave
height (Mazda et al., 1997; Quartel et al., 2007). However it cannot
be used in areas of severe erosion. The sea dikes at erosion coasts,
i.e. Hai Hau and Nghia Phuc have been intensively reinforced since
1998, especially after the Damrey typhoon in September 2005.
Dikes have mild slope of 1:2.2-3 with the height extended to
+4.5 to 5.5 m and. The dike footing was placed at the depth of

Table 8
Erosion rate caused by an extreme wave height.
Section

S (m)

hb (m)

Hb (m)

B (m)

mo

D50 (mm)

A (m1/3)

T (h)

R(t) (m)

Giao Phong
Hai Dong
Hai Hoa-Hai Thinh
Nghia Phuc

4.25
4.25
4.25
4.25

6.96
9.23
8.18
8.83

3.15
4.10
3.78
3.23

2.00
2.00
2.00
2.00

0.0040
0.0150
0.0100
0.0045

0.143
0.143
0.147
0.157

0.0798
0.0798
0.0840
0.0872

2.4
2.4
2.4
2.4

6.6
7.1
3.1
3.6

Table 9
Average water, sediment discharge before and after Hoa Binh dam.
Parameter

Station
Son Tay

Average water discharge (bill. m3/year)
Average sediment budget (106 T/year)

Ha Noi

1956–1988

1989–1994

1995–1998

1956–1988

1989–1994

1995–1998

112
117

106
65

120
51.5

85
71

76
45

89

–


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D.M. Duc et al. / Journal of Asian Earth Sciences 43 (2012) 98–109

Table 10
Rates of beach lowering at Hai Hau coast.
Location

Beach slope

Height of berm (m)

Width of beach (m)

Erosion rate (m/y)

Rate of beach lowering (cm/y)

Hai
Hai
Hai
Hai
Hai
Hai

0.0150
0.0150

0.0150
0.0150
0.0100
0.0100

2.5
2.5
2.5
2.5
2.5
2.5

200
180
250
225
210
260

5.0
12.0
15.0
20.0
21.0
7.0

6.3
16.7
15.0
22.2

25.0
6.7

Dong
Ly
Chinh
Trieu
Hoa
Thinh

Table 11
Suggested preventive measures against coastal erosion.
Driving
factors

Consequences

Required measures

Typhoon

Increase
erosion rate
Instability of
seadikes

Raise height of dikes Concrete
revetment Land-use planning

Sea level

rise
Sediment
deficit

Supporting measures regarding the erosion rate
<2 m/y

2–5 m/y

5–10 m/y

>10 m/y

Mangrove

Groynes
Mangrove

Groynes Seadike
toe protection

Groynes Seadike toe protection Breakwater
Internal standby dike Evacuation

1.5 m. Revetment of polygonal pre-cast concrete with the mass of
100–200 kg and chains of tripods were also used to reinforce dikes
(Fig. 15).
Shoreline cannot keep lateral movement in front of the sea
dikes. A large amount of sediments on the beach is washed away
that causes lowering of beach profile and scour at the toe of sea

dikes. The rate of beach lowering is approximately estimated by
the physical model of Barnett and Wang (1988). Assuming the volume of sediment transported is similar to the value before the construction of the dike then the relation between erosion rate and
rate of beach lowering can be referred as follows:

Dh ¼ 100DY Â b=l

ð12Þ

where Dh is the rate of beach lowering (cm/y), DY the erosion rate
(m/y), l the width of beach from shoreline to the depth of mean sea
level (m), and b is the height of berm (m).
The calculation shows that rates of beach lowering are high at
Hai Ly, Hai Chinh, Hai Trieu, and Hai Hoa (Table 10) with the values
of 15–25 cm/y. The current concrete sea dikes have foots placed at
the depth of 1.5 m. Therefore the dike’s foot can be destroyed in 6–
10 years. Lowering of beach profile is the most serious threat to
long-term stability of sea dikes.
The current sea dike system is expected to suffer typhoons up to
the intensity of 10, landing during mean tide. Worse situations
such as stronger typhoon with surge storms can destroy sea dikes
and force local people to move to safe places. To adapt to coastal
disaster in such case the counter measures have to focus on all aspects of protection, accommodation, and evacuation (Klein et al.,
1999). However permanent immigration is impossible. Because it
requires the land capacity and jobs for almost people who have
only known aquaculture, fishing, and salty production. Reinforcement to ensure the long-term stability of sea dikes is an essential
requirement for socio-economic development. Depending on erosion rates the preventive measures are suggested in Table 11.

unequally. It is intensively deposited at the big river mouths (Ba
Lat, Lach, and Day) and leads to the formation of sand bars in front
of the mouths. The rapid enlargement of sand bars reduces wave

attacks and makes suitable environment for sediment deposition
in channels between shoreline and bars. Shoreline is therefore
advancing at both land and sea sides of the bars. When channels
are mostly filled up, river flows will bring sediments further off
the coast and form a new series of sand bars. This mechanism is
periodical with the return period of about 20 years.
Unequal distribution of sediments causes local erosion at the
coast of the Red River delta. Severe erosion is occurred either between the river mouths or nearby them. The erosion is due to
the wave-induced longshore sediment transport and the deficit
of sediment supply from river mouths. Shoreline erosion nearby
the river mouths (Giao Long, Giao Phong, and Nghia Phuc) depends
closely on the evolvement of sand bars. It is strongly eroded when
a new series of sand bars has just formed and then turns to be rapid
accretion when crest of the bars above the mean sea level. Erosion
between big river mouths, i.e. Hai Hau coast, keeps being severe.
The recent advancement of shoreline at the Ba Lat and Day mouths
cannot help to reduce erosion in Hai Hau.
SLR and reduction of sediment supply due to upstream hydropower plants are expected to reduce accretion and accelerate erosion along the coast of the Red River delta. Erosion lowers beach
profiles and threats seriously the stability of sea dikes. Moreover
tropical typhoon and storm surge seem to be increasing in intensity. As the projected SLR of the medium emission scenario (B2)
in Vietnam, the return period of the highest recorded storm surge
is 2 and 4 times shorter in 2050 and 2100, respectively.
Acknowledgements
The paper is funded by the National Foundation for Science and
Technology Development (NAFOSTED). The authors also would like
to thank the Asia Pacific Network for Global Change Research
(APN) for the support through the Project coded CIA2009-06-Duc.

5. Conclusions
Tropical condition has brought the Red River a large amount of

sediments. Accretion is dominant and coastline of the delta is
advancing rapidly. However sediment supply is distributed

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