The evolvement of a beach depends on many conditions. Erosion and deposition are the most common phenomena during beach evolvement proceeding, whicn can always be found in the same beach. Sediment transport drived by waves or currents changes with season or tide period time. The coastal infrastructures have great influences on sediment transport by changing the nature conditions, so it is the most common approach adopted to deal with beach problems. In China, sand beach getting muddy by depositing silt is another beach problem in addition to erosion. With the population of coastal city growing, it is attracting more attention from researchers . This paper demonstrates an approach of coastal shallows and development in a semi-closed bay. The waves, tidal currents and floods are discussed and the sediment conditions are analyzed. After that, a mud digging and sand beach rebuilding plan is recommended. In the adduced bay, waves are small and varying with wind forces and directions, tidal currents are weak in the most part of the coastal shallows, floods generally happen during July to September accompanying with sediment input the bay every year. The analyzing method and simulation technology can be used in the similar semi-closed bay and be referenced by other coastal areas

Guo-Yaqiong, B.

Ma-Jinrong, A.

Tan-Lixiong, C.

Hasanuddin University Repository

 
 
130 
 
 
Proceedings of the 7th International Conference on Asian and Pacific Coasts  
(APAC 2013) Bali, Indonesia, September 24-26, 2013 
 
 
 
 AN APPROACH OF COASTAL PROTECTION AND DEVELOPMENT  
IN SEMI-CLOSED BAY 
 
A. Ma-Jinrong 
1
, B. Guo-Yaqiong 
2
 and C. Tan-Lixiong 
3
 
 
 
ABSTRACT: The evolvement of a beach depends on many conditions. Erosion and deposition are the most common 
phenomena during beach evolvement proceeding, whicn can always be found in the same beach. Sediment transport 
drived by waves or currents changes with season or tide preod time. The coastal infrastructures have great influences on 
sediment transport by changing the nature conditions, so it is the most common approch adopted to deal with beach 
problems. In China, sand beach getting muddy by depositing silt  is another beach problem in addition to erosion. With 
the population of coastal city growing, it is attracting more attention from researchers . This paper demonstrates an 
approach of coastal shallows and development in a semi-closed bay. The waves, tidal currents and floods are dicussed 
and the sediment conditions are analyzed. After that, a mud digging and sand beach rebuilding plan is recommanded. In 
the adduced bay, waves are small and varying with wind forces and directions, tidal currents are weak in the most part 
of the coastal shallows, floods generally happen during July to Septermber accompanying with sediment input the bay 
every year. The analyzing method and simulation technology can be used in the similar semi-closed bay and be 
referenced by other coastal areas. 
 
Keywords: Sand beach, semi-closed bay, approach, plan. 
 
 
                                                 
1 Nanjing Hydraulic Research Institute, State Key Laboratory of Hydrology-Water Resources, Key Sediment Research Lab of 
Harbors and Waterways of the Ministry of Communications, 223 Guangzhou Road, Nanjing,210029, CHINA 
2 Nanjing Hydraulic Research Institute, 223 Guangzhou Road, Nanjing, 210029, CHINA 
3 The  Bureau of  Land and Resources of Fangchenggang, 30 Yunnan Road, Fangchenggang, 538001, CHINA 
INTRODUCTION 
In terms of regional economic development, 
originally the coastal areas contributed most to economic 
growth. Ports, electric power plants, near shore 
industries, etc. are jammed along the shore lines. Coastal 
beaches are disturbed violently by human activities. 
Natural beautiful beaches are declining while the 
population near the shore land is growing. Chinese 
government has invested a lot to protect some coastal 
areas. An example plan is introduced here about a semi-
closed bay of protection and development. 
This bay is named Fangchenggang west bay with 
open mouth in the south facing the Beibu gulf, located in 
the southwest of China coastal line, covering 
approximately 28 square kilometers. Its east coast has 
been developed into ports area while the north and west 
one will be developed into habitation areas. The 
Fangcheng River is the only rive that runs into the west 
bay at the north-west corner. There are 5 islands, 
ignoring the tine ones, located in the bay area. There is 
no people living in these islands, and about 110,000 
people live around the bay. There are many kinds of 
coastal shores around the bay including artificial, sand, 
mud and some mangrove forest shore. The mud beaches 
are increasing in the past decade for deposition problems 
in the bay. A lot is needed to improve the living 
conditions, among which planning may be the most 
important at the beginning. The following will detail the 
plan for the west bay protection and development. 
 
GENERAL INFORMATION 
 
Shore Line History 
The Fangchenggang west bay is part of the 
Fangchenggang bay which is divided by a south-north 
direction narrow island (Yuman island) into east and 
west parts (Fig.1).  The west bay is a ribbon-shaped 
inland sea with several islands. The largest two islands 
both locate in the north part, which guide the flood of the 
Fangcheng River to pull into three passages from north 
to south. In the middle of the bay, the three passages join 
together to extend to the mouth. 
Fig.1 The location of the Fangchenggang west bay 
N
0 1km 2km
West Yuman The
East
Bay
Island
The
Bay
A.Ma-Jinrong, et al. 
131 
 
Before 1960, most of the bay kept natural except 
some small reclamation works of salt field, agricultures, 
sea cultures, etc.  The islands and troughs have kept 
steady. 
From 1960 to 1980, the shore line has been changed 
by some unplanned dikes that connected the west shore 
to the island in the north-west of the bay and narrowed 
the middle passage of the bay. 
After 1980, the shore lines have been changed with 
the port building, land using, and other human activities. 
The south-west shore lines of the Yuman island have 
been built into ports line and some sea areas have been 
reclaimed into dock dumps. Yuman island became 
longer and wider during 1991-2008 and the entrance of 
the bay has been narrowed to 426m by 1996. A big 
mount of fish farm facilities have been built in the bay 
especially in the north parts. Accompanied with the 
shore line changing and developing, the hydrodynamic 
of the bay has been getting weak and deposition become 
accumulated. 
 
Submarine Geomorphology 
 The study bay is a shallow water area with depth 
usually less than 15m. The water depths decline from the 
north to south. There are three trough-shaped valleys 
derived from the estuary of the Fangcheng River. The 
west trough was blocked apart from the estuary by a 
bank during the 1970s while the middle one half was 
blocked. The east trough is the only main passage of the 
flood discharge after 1980. So the depth of the east 
trough is getting deeper while the other two are getting 
shallower.  The three troughs pass by the two islands and 
joint each other at the middle part of the bay where 
several smaller islands located.  One deeper trough is 
formed at the south part of the bay and lead to the outlet. 
Indicated by submarine topography data of 1980, 
2004, 2007 and 2009, the depths under datum for 
sounding reduction (this is the common water level used 
in the paper) are usually above 0 m in the north part, 
even the deepest trough seldom keeps under 0 m to 
connect the estuary of the Fangcheng River until 2009. 
The deposition occurred mostly at the tidal interval areas 
while scour took place in the down part of the troughs.  
Both the tide and flood currents are not very strong, so 
scour is relatively slow. Deposition is more clearly than 
scour although there is no much sediment inputting 
every year.  The deposition layer accumulated nearly to 
2 meters at some places during the past 30 years. Usually, 
the thickness of deposits in the west part is greater than 
that in the east.  The submarine topography in the south 
part keeps more stable than that in the north.  Some sand 
beaches along the north-west part of the bay have 
changed into muddy shore because of the deposits. 
Climate and Oceanography 
The land areas adjacent to the bay lie in a south 
subtropical oceanic climate. There is rain without snow 
with the mean monthly temperature varied from 14.2 ℃ 
to 28.4 ℃. North monsoon prevails in the winter while 
south monsoon prevails in the summer.  From June to 
September is the rainy season while from November to 
next March is the dry season. The mean annual 
precipitation is 2362.6 mm, 71% of which falls in the 
rainy season and only 6.4% falls in the dry season.  
The tidal system in the bay obeys the one in the 
Beibu gulf which belongs to lunar appulse diurnal tide.  
It means that only one tidal rise and fall happens in the 
common day (diurnal tide), except about 6~8 days out of 
a month two tidal rises and falls occur (semidiurnal tide).  
The tidal difference may be greater than 4.5 m in the 
diurnal tide days while that may be less than 1 m in the 
semidiurnal tide days. The durations of tidal rise and fall 
are different between diurnal tide and semidiurnal tide 
period. The duration of fall is longer in the former and 
may be approximately same in the later. The tide shape 
will change from the mouth to the estuary for both 
marine topography and river discharge reasons.  The tide 
level processes indicate that the duration of fall 
increasing after the nearing to estuary.  The 
characteristic tidal values are shown in the table 1 
according to the records of Fangchenggang tidal station 
from year 1976~1990. 
 
Table 1  Characteristic tidal values of local station 
Items Values(m) 
Highest high water level 5.54 
Lowest low water level -0.29 
Mean sea level 2.27 
Mean high water level 3.67 
Mean low water level 1.12 
Maximum tidal range 5.32 
Mean tidal range 2.39 
 
The tidal current in the bay is limited by the shore 
shape and islands.  The direction of the tidal current is 
approximately parallel to the coastal line in the 
reciprocating flow movement.  The velocities of both 
flood current and ebb current are less than 0.8m/s in the 
most of the area. Usually, the flood current is weaker 
than ebb one, current in the troughs is stronger than in 
the shallows. The velocities in the three north troughs are 
under 0.30m/s mostly except the estuary and some 
narrow marine valleys.  
The mean annual wind speed is 3.8m/s according to 
the local station. The maximum wind speed is 26 m/s  
 An Approach of Coastal Protection and Development in Semi-Closed Bay 
 
 
132 
 
happened in typhoon season. Most wind direction varies 
in N~NNE as shown in Fig.2. 
Fig. 2  The frequency of wind at each direction 
 
The waves in the bay are driven by wind especially 
in the north part water areas for the narrow mouth 
limited the out sea waves insulating. The wave rose map 
is shown in Fig.3. 
Fig. 3  The wave rose map 
 
SEDIMENT PROBLEMS IN THE BAY 
Great changes have taken place in the bay during the 
past three decades. The west passage was shut at the top 
of upstream.  Depositing along the coast beach has 
happened for years, which changed some of the sand 
beach into muddy. 
Sea farming developed fast in the past years, 
especially in the past decade. The piles built in shallows 
and other sea farming facilities have changed the 
dynamics of the tidal currents and increased the deposit.  
The depths of shallows are getting shallower because of 
the continuous depositing problem. 
Reclamation for land or shrimp pool has not been 
stopped yet. Reclamation reduces the water capacity of 
the bay which means the current dynamic will getting 
weak. It will be helpful for sediment depositing, then the 
capacity of the bay will decline more. So, reclamation 
forms a bad cycle to the marine environment of the bay. 
Another problem coming with the decline of water 
capacity of the bay is the channel maintaining. The cost 
has doubled in the past decade for the sediment siltation 
in the port and channel increasing much more though no 
new docks built in the bay.  
Accompanying the sediment deposit, the resources of 
tourism, fishery, mangrove forests, marine ecosystem etc. 
have been affected. 
 
COAST BEACH REBUILT PLAN 
 
The Shore Line Regulation 
The government has signed a project to study, design 
and manage the bay. Shore line regulation is one of 
important work to do, which focuses on two jobs, one is 
to recover some of the uncontrolled reclamations and the 
other is to limit reclamation in the future. The plan of 
shore line regulation is shown in fig.4.  The north island 
will be shaped slide by getting rid of some shrimp pools 
and the west tidal passage will be open to the estuary.  
Two small artificial islands will be built near the west 
passage along the coast. These islands will be developed 
into real estate. Some of the fund of the bay protection 
project will come from the company to build these 
islands. 
All the muddy beach shore will be built into artificial 
shore while nature sand shore, rock shore, mangrove 
forest shore will be kept natural and be protected well. 
 
The Water Area Dredging 
The most north parts of the bay area are shoals, 
which are above low tidal level. There is yellow mud 
scene without blue sea water. A dredged plan is made to 
change it. As shown in fig.4, most of the north part area 
will be dredged to keep water area all the tidal cycle 
except the islands. There are two depths controlled for 
dredging, the west passage area is -0.4m under MSL 
while other places is -0.8 m.  The low water level in the 
dredged area is 0.25 m higher than the Fangcheng station 
given earlier. So, it means the depth will be deeper than 
1.5 m in most days. 
 
A.Ma-Jinrong, et al. 
133 
 
The sand and mud dredged out will be used to fill the 
islands in this bay and the remainder will be transported 
to the out sea for reclamation.  
Fig. 4  Coast beach rebuilt plan 
 
Channel of Yacht Dredging 
The bay area is beautiful because of the mangrove 
forest, islands, blue water, green trees along the shore, 
rich marine species and etc. The yacht channel will be 
developed later for the scene. The bottom of it will be 
dredged to -2.1 m as shown in fig.4.  
The channels are set around the two big islands, 
extending south direction to the middle of the bay, east 
direction to another bay.  
The yacht system will improve the tourism resources 
and conditions of the inhabitants. 
 
Sand Beach Rebuilt 
Decades ago, there were beautiful sand beach 
distributed along the coast of both sides. Especially the 
west coast had white sand beach where is covered by 
dark muddy now. 
To improve tourism resources and inhabitant 
conditions, two artificial sand beaches are planned to 
rebuild along the west and east coast as shown in fig.4.  
 
RESEARCH RESULT 
A series of studies have been made to support the bay 
plan about developing and protecting introduced as 
follows. 
 
Tidal Currents Simulation 
The submarine topograph in the north part of the bay 
is changed by the plan.  A mathematical model is 
established to simulate the tidal currents movements in 
the bay.  
The Water Level Processes 
Tidal processes at the north part will change 
accordingly.  Several sample points shown in fig.6 are 
set to analyze the water level processes before and after 
the project. The tidal levels are shown in fig.5. It is clear 
that low levels drop down while the high levels keep 
same approximately. The duration of ebb tide is 
shortened after the project.  
Fig. 5 Water level processed before and after the project 
 
The Tide Capacity Analyzing 
Characteristic sections shown in fig.4 are set to 
analyze the discharge volume changing which is 
displaced in table 2. Both of the flood and ebb tide 
capacity are increased.  
 
Table 2  tidal influx and its changing(unite: ×108m3) 
Section Section1 Section2 Section3 
Before the construction 1.0783  0.9121  0.6673  
After the 
construction 
Variation 0.1732  0.1763  0.1433  
Rate of 
change 
16.1% 19.3% 21.5% 
 
The Tide Velocity Analyzing 
Several sample points shown in fig.6 are set to 
analyze the velocities of flood and ebb tide. According to 
table 3, both artificial sand beaches encounter no strong 
currents. The sand beaches will keep stable for the 
velocities being seldom greater than sediment incipient 
velocity. Silting problem will not be violent for there 
being little sediment coming with flood from river.  
 
 
 
 
 
bridge
Island
Artificial
N
0 1km
Sand Beach
SandBeach
-0.8m
-0.4m
changlan
island
Island
zhoudun
Island
Island
Ya
ch
t
Ch
an
ne
l 
of
1#
2#
3# 4#
Section1
Yuman
Island
Section2
Section3
1
2
3
4
5
1#
0
1
2
3
4
5
6
0 10 20 30
time(h)
t
i
d
e
 
l
e
v
e
l
 
(
m
)
before after
2#
0
1
2
3
4
5
6
0 5 10 15 20 25 30
time(h)
t
i
d
e
 
l
e
v
e
l
 
(
m
)
before after
3#
0
1
2
3
4
5
6
0 5 10 15 20 25 30
time(h)
t
i
d
e
 
l
e
v
e
l
 
(
m
)
before after
4#
0
1
2
3
4
5
6
0 5 10 15 20 25 30
time(h)
t
i
d
e
 
l
e
v
e
l
 
(
m
)
before after
 An Approach of Coastal Protection and Development in Semi-Closed Bay 
 
 
134 
 
Table 3 the analysis of character velocity (unite:m/s) 
condition 
point 
location 
flood 
strength 
ebb 
strength 
flow velocity 
average 
annual 
discharge 
1 0.09 0.09 
2 0.06 0.08 
3 0.05 0.04 
4 0.03 0.04 
5 0.03 0.04 
the flow of 
average 
flood 
period 
1 0.09 0.10 
2 0.05 0.10 
3 0.03 0.02 
4 0.03 0.05 
5 0.02 0.03 
the flow of 
20 years 
flood 
1 0.10 0.11 
2 0.06 0.14 
3 0.01 0.01 
4 0.02 0.02 
5 0.02 0.01 
 
Wave and Sediment Estimate 
The out sea waves seldom enter the north part of the 
bay. The effective waves are usually driven by the local 
winds. The wave heights related to each direction of 
wind and water depth are calculated by formula based on 
water depth, wind velocity, and wind distance.  The 
capacity of sediment transportation is estimated 
respectively to different beach sites. The results are 
displayed in table 4.  
 
Table 4 incipient velocity of grades sediment and depth 
depth of 
water 
(m) 
sediment grain size(mm) 
0.075 0.25 0.5 0.8 1 2 
0.5 0.309 0.286 0.333 0.384 0.413 0.525 
1 0.346 0.317 0.368 0.424 0.456 0.578 
2 0.394 0.354 0.407 0.468 0.503 0.637 
3 0.430 0.379 0.433 0.496 0.533 0.675 
4 0.461 0.399 0.453 0.518 0.556 0.703 
5 0.489 0.416 0.469 0.535 0.574 0.726 
6 0.514 0.432 0.483 0.550 0.590 0.745 
 
DISCUSSION 
The study bay is a semi-closed bay with weak tidal 
currents, little waves, small sediment input capacity 
which mean the sediment on the bed is less moveable. 
Although the nature conditions are suitable for coast 
infrastructures building, a wrong dike may change a 
beautiful white sand beach into a dark bad small muddy 
place in three decades.  Coast area is rich of natural 
sources. Each infrastructures plan should be carefully 
studied before building.  
Hydraulic dynamics and sediment transportation 
have been studied for this plan to develop and protect the 
bay. The human activities may increase, because the 
tourism resources and inhabitant conditions will be 
improved by this plan. So, the protection plan of the 
environment and ecosystem of the bay should be 
carefully arranged during the later stage.  
 
ACKNOWLEDGEMENTS 
 This study involved cooperation between the 
Guangxi Communications Planning Surveying and 
Designing Institute and the Bureau of Land and 
Resources of Fangchenggang, whom we thank for the 
use of their facilities, field data, and etc. 
 
REFERENCES 
Ma Jinrong(2010). The Report of Reseach on 
Mathematical Model Analyzing the Cause of 
Sedimentation and Treatment Measure in 
Fangchenggang West Bay. Nanjing Hydraulic 
Research Institute. 
Ma Jinrong(2013). The report of Reseach on 
Mathematical Model of Wave and Tide and Sediment 
about the Man-made Beach of Fangchenggang West 
Bay. Nanjing Hydraulic Research Institute.  
Smagorinsky, J.(1963), General Circulation Experiments 
with the Primitive Equations,I. The Basic Experiment, 
Mon. Weather Rev., 91, 99-164. 
LUO Zhao-sen(2004),Sediment transport under the 
coexisting of waves and currents and the prediction 
of sudden sedimentation in navigation channel. 
Journal of sediment reseatch:1-9 
Ma Jinrong, Luo Zhao-sen(2006). The Report of 
Reseach on Mathematical Model of Tide and  
Analysis on the Sediment Accumulation in the 
Whole Programming of Fangchenggang. Nanjing 
Hydraulic Reach Institute. 
Xu Xiao, She Xiaojian, Mao Ning, Zhang Lei, Cun 
Zheng(2012).The research of man-made beach[M]. 
Beijing, the Ocean Press.
 


An approach of coastal protection and development in semi-closed bay

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An approach of coastal protection and development in semi-closed bay

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