Full text of DOI:10.1007/BF02909783

Vol. 44 No. 5
SCIENCE IN CHINA (Series D)
May 2001
A prediction of sea level rising amplitude in 2030 and
defensive countermeasures in the Zhujiang delta
HUANG Zhenguo (;ó³)1, ZHANG Weiqiang (Æꢀœ)1,
WU Houshui (Qꢀꢀ)1, CHEN Tegu (G‹ꢀ)2, FAN Jinchun (³&)3,
JIANG Peilin (Þꢀ)3, LI Zihao (3Ý)4 & HUANG Bensheng (;‡›)4
1. Guangzhou Institute of Geography, Guangzhou 510070, China;
2. South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;
3. Zhujiang River Water Resources Commission, Guangzhou 510611, China;
4. Water Conservancy and Hydroelectric Power Resources Institute of Guangdong Province, Guangzhou 510610,
China
Correspondence should be addressed to Huang Zhenguo (email: zwq@gis.sti.gd.cn)
Received July 7, 1999
Abstract By analysing comprehensively the factors such as theoretical sea level, abnormal fluc-
tuation of sea level, rising amplitude of floodtide water level and land deformation, a rising ampli-
tude of 22 33 cm of relative sea level by the year of 2030 is forecasted in the Zhujiang Delta.
From the forecasted amplitude of 30 cm, using hydraulic and hydrometric models the scope influ-
enced by sea level rise is delimited and the reappearing periods of floodtide water level, protecting
ability of embankments, design parameters of water conservancy project, drain waterlogging, sa-
line intrusion, resource of mud beach and comprehensive prevention measures are discussed.
Keywords: sea level, prevention, Zhujiang Delta.
Forecasts about the potential rising amplitude of the relative sea level in the Zhujiang Delta
during the 40-year period (1990 2030) differ greatly, ranging from 9.24 cm to 40 cm[1 5]. The
rising amplitude in the coming several decades will be influenced mainly by four factors. This
paper gives the four factors and the countermeasures.
1
The rising value of theoretical sea level
The tide gauge stations of Hong Kong and Macau have the longest series of tide gauge re-
cords over 70 years since 1925 in South China but there are some shortcomings of records in these
stations. The records during 1930 1949 were absent in Hong Kong. The station of Macau was
moved three times during 1963 1981 and the stage error in tide records can be found. Taking the
year of 1959 as a contact point, the former stage (1925 1958) is a series of monthly sea level of
Macau in which the datum surface is converted to the datum of the sea chart of Hong Kong, and
the later stage (1959 1996) is a series of monthly sea level of Hong Kong, thus a uniform series
of sea level change during the past 72 years of two stations can be made. Moreover using the di-
rect and inverse Fourier transform to filter out the effects of periodic variation, i.e. high frequency

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components (with period less than 4 years), a series of lowpass filter is obtained and then from
single-element linear regression the rising rate of sea level during the past 72 years is calculated to
be (1.8 0.1) mm/a.
The rate of 1.8 mm/a can be regarded as a rising rate of theoretical sea level in the area of
Zhujiang estuary. The rising rate of relative sea level during a united period (1955 1994) in the
five stations along the coast of the Zhujiang Delta was 2.3 mm/a, 1.8 mm/a is less than 2.3 mm/a,
so the rate of 1.8 mm/a is reasonable and comparable to that of global background value such as
1.0 1.5 mm/a[6], 1.8 mm/a[7] and 1.75 mm/a[8]. In Honolulu and San Francisco located at similar
latitude to Hong Kong the rate was 1.5 mm/a (1904 1992) and 2.0 mm/a (1855 1992)[8] re-
spectively. In a short period (1954 1983) the submergence rate resulting in compression of
ground was 5.4 mm/a and the emergence rate of crust was 1 mm/a[9], but the rising rate of relative
sea level was 6 mm/a during the similar period (1961 1984)[10], so that the rising rate of theo-
retical sea level is calculated to be 1.6 mm/a which proved the reasonableness of 1.8 mm/a.
Based on a series of tide gauges over 50 years a nonlinear equation for secular trend of sea
level can be established. To assume the secular trend of sea level is nonlinear an equation can be
obtained as follows:
Z(t) = a0 + a1t + a2t2 + a3t3 + a4t 4 + a5t−1
−t
+ a6t −2 + a7t1/ 2 + a8t−1/ 2 + a9 + a10Int,
(1)
where Z (t) is the rising amplitude of sea level; t, time; a0 a10, coefficients to be determined. Us-
ing suitable transform formula (1) can be changed into a multielement linear equation as follows:
x1 = t, x2 = t 2 , x3 = t3 , x4 = t4 , x5 = t −1, x6 = t−2
x7 = t1/ 2 , x8 = t−1/ 2 , x9 = e−t , x10 = Int
,
and formula (1) can be rewritten as follows:
Z(t) = a0 + a1x1 + a2 x2 + a3 x3 + a4 x4 + a5 x5
+ a6 x6 + a7 x7 + a8 x8 + a9 x9 + a10 x10 .
(2)
A series of tide gauges during the past 72 years in Hong Kong and Macau is substituted into
formula (2). Using progressive regression to choose the terms which are of large contribution to
Z (t) and to determine the coefficients, a nonlinear equation of sea level change in Hong Kong and
Macau can be obtained as follows:
Z(t)H, M = 40.85 + 6.19 ×10−12 t 4 .
(3)
From formula (3), it is obvious that the sea level shows a secular trend of exponential rising.
In other words, the rise of sea level will speed up with time. Based on formula (3) the calculation
for sea level rise can be traced back. For example, the rise amplitude was 18 cm at a rate of 1.8
mm/a during 1890 1990; the rise rate in the early 20th century was 1.7 mm/a and 2.0 mm/a in
the 1990s. Taking the year of 1990 as a starting point, the result of calculation from formula (3)

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shows that the rise amplitude of sea level may be 8 cm at a rate of 2.0 mm/a by the year of 2030. It
is slightly less than that of global background value. From the prediction of IPCC (1995)[8], the
best scheme of global mean temperature rising is 2.0 , the highest, 3.5 and the lowest, 1.0
;
by the year 2010, as for the corresponding rise amplitude of theoretical sea level, the best scheme
is 48 cm, the highest, 95 cm and the lowest, 15 cm. Therefore the best prediction is temperature
increase by 0.6 and sea level rising by 12 cm at a rate of 3.0 mm/a by the year of 2030[11]
.
2
Abnormally high fluctuation value of relative sea level
The disparity in height between sea level calculated from the secular trend equation and the
observed sea level shows an amplitude of fluctuation of sea level. It can be expressed as follows:
′
±
A = Z (t) − Z(t) / n,
(4)
∑
where A is the fluctuation amplitude; Z ( t), the observed value of tide gauges at a certain year;
Z(t), the value calculated from the equation for the corresponding year; and n, the number of years.
The positive fluctuation value of A represents an abnormally high sea level. The calculated re-
sults (1955 1994) for seven stations of the Zhujiang Delta show (table 1 and fig.1) that the larg-
est average fluctuation value is 6.4 cm for the three stations outside the estuary and it is 12.1 cm
for the four stations inside the estuary. It reveals that being affected by runoff and human factors
the fluctuation amplitude increases from outside to inside of the estuary.
Table 1 Abnormally high fluctuation amplitude of rising of relative sea level in the Zhujiang Delta
Situation in the
Tide gauge station
The largest fluctuation amplitude / cm
Average / cm
Zhujiang estuary
Sanshakou
Nansha
10.8
11.9
15.0
10.5
8.4
Inside
12.1
Wanqingsha
Hengmen
Denglongshan
Sanzao
Outside
5.6
6.4
Chiwan
5.1
3
Additional value of rising of relative sea level
Owing to the rising of sea level the hightide water level increases in the estuary area. The in-
crease amplitude may be higher than that of sea level rise but not a superposition of hightide water
level and sea level. The additional value above the rising sea level should be considered to calcu-
late the practical rising amplitude of relative sea level in the future.
Taking the hightide water level of Sanzao station outside the estuary as a representation of
sea level change, a relation between sea level change and hightide water level in various tide
gauge stations of the Zhujiang Delta can be established as follows:

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Fig. 1. The scope influenced by sea level rise in the Zhujiang Delta.
water level; limit of saline intrusion at present; tide gauge station;
Isoline of rising amplitude of floodtide
planning water gate; regulation
and reclamation area in the estuary. A, Slightly influenced area; B, influenced area; C, heavily influenced area.
Z2 = C1Z1 + βQ + αZ1Q + C2 ,
(5)
where Z2 is the hightide water level in various stations; Z1, the hightide water level in Sanzao sta-
tion; Q, the discharge in Makou station located at upper course of the delta; α and β, slope; C1 and
C2, constant. α, β, C1 and C2 can be obtained by interrelative analysis calculation.
According to 190 representative floods during the past 40 years and 7 classes of discharge in
Makou station, the corresponding relation of hightide water level between Sanzao and other sta-
tions is established for 39 stations. The result shows a good interrelation between Sanzao station
(sea level change) and other stations (hightide water level) inside the estuary.

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The amplitude (∆Z2) of increase of hightide water level of the stations inside the estuary in-
fluenced by the amplitude (∆Z1) of sea level rise can be calculated from formula (5) as follows:
∆ Z2 = (αQ + C1 )∆Z1.
(6)
Based on the dry discharge of 2000 m3/s in Makou station the increase amplitude of hightide
water level in 11 stations inside the estuary influenced by sea level rise of 30 cm in Sanzao can be
calculated from formula (6) (table 2). There are two conditions that reflect fully the impacts of sea
level rise, the dry discharge and the storm surge. There was an extremely severe storm surge on
September 17, 1993 and the highest tidal level has been recorded, but the runoff was small (dis-
charge of 11800 m3/s in Makou) at that time. Taking the combination of flood and tide during the
typical year (Sept. 1993), using one-dimensional and two-dimensional hydraulic models for un-
steady flow, the increase amplitude of hightide level for various representative stations under a
condition of sea level rise by 30 cm is calculated (table 2). The underwater stream channel relief
map with a scale of 1/5000 made after the 1980s is used for calculation. 255 reaches and 948 cal-
culating sections are arranged, in which the step lengths of space and time are 1 2 km and 5 s for
one-dimensional, 250 m and 1 s for two-dimensional.
Table 2 Increase amplitude (cm) of hightide level caused by sea level rise in the Zhujiang estuary
Sea level rise by 30 cm
Tide gauge station
Under condition of dry discharge
Under condition of extremely severe
in Makou station
storm surge and small runoff
Huangpu
Sanshakou
Nansha
Wanqingsha
Hengmen
Denglongshan
Huangjin
Hengshan
Sanjiangkou
Huangchong
Xipaotai
32
31
32
32
31
30
31
32
35
35
35
29
31
30
29
31
30
28
28
25
28
30
From table 2, it is obvious that the increase amplitude of hightide level caused by sea level
rise in estuary area will be able to overstep the rising amplitude of sea level in all the stations un-
der the condition of dry discharge based on hydrometric model. Moreover a trend of decrease
along the way from outside to inside can be seen. However the result calculated by hydraulic
model shows that even under the condition of extremely severe storm surge, the overstepping ap-
pears in one or two stations only. This difference might not be caused by different calculation
models but by the condition of discharge. Because the discharge in the typical year (Sept. 1993)
used for hydraulic calculation is quite large, the impacts of sea level rise did not fully represent.
Hydrometric calculation reveals that if sea level rose by 30 cm, the rising amplitude of hightide
level of the tide gauge stations in the estuary may be higher than 30 cm by 2 5 cm and the
overstepping value might be larger for the year with extremely severe storm surge and dry runoff.

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4
The ground submergence value caused by land deformation
There are some branches of leveling extending from the first-class leveling line of Hang-
zhou-Guangzhou-Nanning to the coastal zone in Guangdong area. The length of leveling and the
number of stations totaled 2380 km and 269 in Guangdong, from which the releveled data of 132
stations along the coastal zone are chosen. Analysing the data for each station, rejecting the error
data caused by unstable stations or surveying, deciding the reliability of coincident points, the data
with long time span of repeated leveling are used as fully as possible. The amplitude of land de-
formation which is the result after counteracting positive value with negative value is aggregated
unitedly to the “zero point” of Zhaoan located at the boundary between Guangdong and Fujian
provinces and then the rate (mm/a) of land deformation in each station can be obtained. The result
of repeated leveling by 8 periods along 5 branches of leveling line confirms that the rate of land
deformation is tending to zero (0 +0.1 mm/a) during 1966 1986. An isoline map of deforma-
tion rate based on the “zero point” of Zhaoan
is compiled in the coastal zone of Guangdong,
and the part of Zhujiang estuary is shown in
fig.21).
As shown in fig. 2, according to 24 rep-
resentative stations which are chosen from 71
stations in the Zhujiang Delta area, the data
of leveling by 3 5 periods during 1951
1989 show the rate of submergence of
2.0
mm/a for 10 stations, 1.5 1.7 mm/a for 5
stations, 1.1 1.3 mm/a for 4 stations and
1.0 mm/a for 5 stations. Therefore it is gener-
ally agreed that the rate of ground submer-
gence is 1.5 2.0 mm/a in the plain of Zhu-
jiang Delta and an amplitude of rising of rela- Fig. 2. Isoline map of land deformation rate in the Zhujiang
Delta area. (Unit: mm/a, −: submergence, +: emergence,
:
tive sea level during the 40 years is calculated
to be 6 8 cm.
leveling station)
It is reported that the rate of land deformation in the sea area of Modaomen nearby Mang-
zhou island reaches −7 mm/a during 1953 1987[1 3]. But it seems impossible because of the
submergence like a funnel. Analysing the 71 stations in the Zhujiang Delta area the maximum of
submergence is −2.5 mm/a only. Besides, a submergence rate is −1.7 mm/a in the station on the
east bank of Modaomen from 2 periods of leveling during 1964 1989. Moreover a rising rate of
1) Lu Ruqi et al., An isoline map of land deformation rate along the coastal zone of Guangdong, 1996.

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SCIENCE IN CHINA (Series D)
Vol. 44
2.0 mm/a of relative sea level in Denglongshan station nearby Modaomen during 1959 1994 has
been calculated. The above data are all far different from the rate of –7 mm/a.
5
Countermeasures
As mentioned above, according to 8 cm of rising of theoretical sea level, 6.4 12.1 cm of
abnormally high fluctuation, 2 5 cm of overstepping amplitude of floodtide water level and 6
8
cm of ground submergence, the relative sea level may rise by an amplitude of 22 33 cm during
1990 2030.
The impacts would not be overlooked even the relative sea level rise is 30 cm. From above,
to choose the typical year (Sept. 1993) which fully represented the influence of sea level rise,
based on hydraulic calculation for 24 stations, according to the isolines of 5 cm and 25 cm of in-
crease amplitude of the highest floodtide water level, the influence of sea level rise can be divided
into three areas, the slightly influenced area, the influenced area and the heavily influenced area
(fig. 1A, B, C). The increase amplitude of floodtide water level averages 1.3 cm in area A, 18.2
cm in area B and 29.2 cm in area C respectively. This amplitude can be regarded as a parameter to
raise the design highest tide level of coastal engineering.
If the sea level rises 30 cm represented by Sanzao station, using the different discharge which
is corresponding with the four classes of reappearing period, i.e. once 100 years, 50 years, 20
years and 10 years, the increase amplitude of the highest floodtide water level is calculated by
hydrometric model for 17 stations respectively. Comparing the calculated result with the highest
floodtide water level at present, the change of reappearing period can be forecasted as follows:
reducing by half in the influenced area and by one and a half or two in the heavily influenced area
so that the design standard of embankments should be raised correspondingly.
The embankments protecting cultivated land of above 10000 mu (1.5 × 107 km2) in the Zhu-
jiang Delta totaled 95 sections and 2608.57 km long except the slightly influenced area, of which
the embankments that did not reach the present design standard are 1126.1 km long, accounting
for 43.2% of the total. It is necessary to make all of these embankments (2608.75 km) influenced
by sea level rise to reach the design standard and to raise also their height in the light of the in-
crease amplitude of the highest floodtide water level caused by sea level rising of 30 cm. In this
case the total engineering will be 1752.54 104m3, and the investment, 21.03 108 yuan RMB.
This is not a small number but the direct economic loss was 22.18 108 yuan caused by the severe
flood in June 1994 in the Zhujiang Delta.
The observed highest water level of storm surges in the four stations of Huangpu, Nansha,
Denglongshan and Huangchong inside the heavily influenced area already exceeded the design
tide level by 0.8 1.2 m. The water level of storm surges of once 100 years scale will be reduced
to once 30 40 years in the four stations if the sea level rises by 30 cm. Therefore the design stan-
dard of the highest tide level should be raised in the light of the rising amplitude of sea level.

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Rising of sea level leads to strengthen the wave energy and to heighten the wave. At present
the design wave height is on the low side. For example the airport of Shenzhen has been inundated
twice by seawater overflowing the dyke since 1991. According to the calculation in stations of
Chiwan, Gaolan island and Gao island of Hong Kong the design wave height should be raised by
24 27 cm when the sea level rises 30 cm.
It is necessary to reformulate the design elevation of drainage pipeline in cities because they
are now on the low side in common. For example the drainage elevation in Guangzhou has been
raised from 1.73 m (Zhujiang datum) in the 1950s to 2.75 m at present but the highest water level
reached 2.44 m during recent years so that drainage is still difficult. Besides, the drainage eleva-
tions in Shenzhen and Zhuhai are higher than the mean sea level by 1.20 m and 1.24 m only, so it
is necessary to drain waterlogging by water pumps 12% of a year in Shenzhen and 11% of a year
in Zhuhai respectively.
In the case of the typical year (Sept. 1993), if the sea level rises 30 cm, the increase ampli-
tude of the lowest lowtide level is calculated by hydraulic model for 24 stations. The amplitude on
average is 3 cm, 14.7 cm and 23.9 cm in areas A, B and C respectively, less than that of the high-
est hightide level. However due to the rising of lowtide level the standard of drain waterlogging
must be raised by using more installed capacity of electric drainage. The low land with an eleva-
tion less than 0.5 m which requires electric drainage accounted for 27.1% of the cultivated land
protected by embankments in the Zhujiang Delta. The area ratio of low land will increase to
41.9%, i.e. expanding by 5.4 104 hm2 if sea level rises 30 cm. It is necessary to increase the in-
stalled capacity to 10.51 104 kW and the investment to 14 108 yuan RMB for the fixed electric
drainage stations only.
In the light of the dry discharge in Makou station the mean increase of tidal range is calcu-
lated by hydrometric model for 37 stations if sea level rises 30 cm, which is 11 cm, 14 cm and 17
cm in areas A, B and C respectively. Increase of tidal range will give rise to saline intrusion. The
calculated result shows that if sea level rises 25 cm the increase ratio of monthly mean salinity is
about 20% in the three stations of Denglongshan, Huangjin and Xipaotai under the condition of
similar discharge. However since the 1960s because the runoff of Zhujiang River increased by 51
m3/s per year on average during 1959 1984, moreover the river mouth is extending forwards to
the sea resulting in strengthening of runoff dynamic process, the mean salinity in various stations
reduced by 30% 74%. In that case little impact of sea level rise was given to the increase of sa-
linity. According to the calculation by using the LWS model (Ippen and Harleman model) and
HWS model (Saveniji model) taking the salinity of 2.0 as a mark under the conditions of dry sea-
son, high tide and sea level rising of 30 cm, it is shown that the distance of saline intrusion in the
eight rivermouths is less than 15 km generally (fig.1).
There is an area of 13.78 104 hm2 of mud beach in the Zhujiang estuary which accounts for
31.1% of the total area of mud beach in Guangdong Province, of which the area not yet exploited

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Vol. 44
is 6.76 104 hm2 accounting for 49% of the total. If sea level rises 30 cm, its impact on the in-
crease of mud beach resource might be weak. The rate of sea level rise is counted in millimetres
(7.5 mm/a), but that of accumulation of beach is counted in centimetres such as 2.0 cm/a (1964
1984) in Lingdingyang, 4.2 cm/a (1983 1994) in Modaomen, 3.2 cm/a (1977 1990) in Jitimen
and 2.5 cm/a (1977 1988) in Yamen. The rising of 30 cm of sea level will make the increase
quality of mud beach reduce by 23.4%. In other words the area of mud beach should increase by
10.03 104 hm2 originally until 2030 but it may be reduced by 0.65 104 hm2 in fact.
Sea level will rise 30 cm but the rivermouth is extending towards the sea. In the light of the
typical year (Sept. 1993), the rising amplitude of the highest floodtide water level is calculated by
hydraulic model for 24 stations, the rising amplitude on average is 0.3 cm, 9.3 cm and 18.1 cm in
areas A, B and C respectively, far less than that when the rivermouth does not extend. Therefore it
is important to carry out the programme dredging the estuary. The suitable extending distance of
the rivermouths is designed as follows: 14 km in Modaomen, 15 km in Hengmen, 20 km in
Hongqimen and 24 km in Jiaomen. At the same time the five dominant water conservancy pro-
jects, the water gates of Sixianjiao, Makou, Nanhua, Jitimen and Shilong (fig. 1) should be con-
structed one after another to regulate the runoff from Xijiang River and Beijiang River, and the
flood discharge safety, irrigation in dry season, resisting saline intrusion, condition of shipping and
providing water along the mainstream of Dongjiang River can be all ensured and improved in the
future.
Acknowledgements This work was part of an important project of Guangdong Province (No. 930816): On the impacts
of sea level change and its countermeasures in Guangdong.
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