HYDROLOGICAL PROCESSES
Hydrol. Process. 23, 1565– 1574 (2009)
Published online 30 March 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/hyp.7268
Spatial assessment of hydrologic alteration across the Pearl
River Delta, China, and possible underlying causes
Qiang Zhang*1 Chong-Yu Xu,2 Yongqin David Chen3 and Tao Yang4
1
Institute of Space and Earth Information Science, The Chinese University of Hong Kong, Shatin, Hong Kong, China
2 Department of Geosciences, University of Oslo, Norway
Department of Geography and Resource Management, The Chinese University of Hong Kong, Shatin, Hong Kong, China
State Key Laboratory of Hydrology-Water Resources and Hydraulics Engineering, Hohai University, Nanjing 210098, China
3
4
Abstract:
The alterations of the water level across the Pearl River Delta (PRD) were investigated using a ‘range of variability approach’
(RVA) based on monthly water level datasets extracted from 17 gauging stations. A mapping method was used to illustrate
the spatial patterns in the degrees of alteration of water levels. The results indicated that more stations showing moderate
and high alterations in monthly mean maximum and minimum water levels when compared with monthly maximum and
minimum water levels. River channels characterized by higher alterations of water levels were observed mainly in the regions
north of 22° 300 N. Alterations of water levels across the PRD were a consequence of various influencing factors. However,
changed hypsography due to extensive and intensive human activities, particularly the large-scale dredging and excavation of
the river sand, may be taken as one of the major causes for the substantial hydrologic alteration. This study indicated that the
river channels characterized by altered water levels are mostly those characterized by highly and moderately intensive sand
dredging. The changed ratio of the streamflow between Makou and Sanshui stations, the major upstream flow control stations,
also influenced the water level alterations of the Pearl River delta. The results of this study will be of great significance
in water resources management and better human mitigation of the natural hazards due to the altered water level under the
changing environment. Copyright  2009 John Wiley & Sons, Ltd.
KEY WORDS
hydrologic alteration; water level; range of variability approach; Pearl River Delta
Received 25 July 2008; Accepted 26 October 2007
INTRODUCTION
River deltas are mostly heavily populated and play
a paramount role in regional economic development.
The population of the world is increasingly moving
towards the coast—about 60% (¾3Ð6 billion) of the
world’s population lives within 60 km (37 miles) of the
coast (UNESCO, 1998). Human settlements, large cities
on river deltas and a large proportion of the global
economic productivity derived from river deltas render them exceptionally important in the development of
human society. This may be why the river deltas are
receiving increasing concerns from hydrologists, fluvial
geomorphologists and policymakers (Pont et al., 2002;
Syvitski et al., 2005; Ericson et al., 2006; Yang et al.,
2006). The Pearl River Delta (PRD) has a very dense
agglomeration of over 100 towns and cities and has
been the fastest developing region in the economy of
China since the country adopted the ‘open door and
reform’ policy in the late 1970s. On less than 0Ð5% of
the country’s territory, the PRD produces about 20%
of the national GDP, attracts about 30% of Foreign
Direct Investment, and contributes about 40% of exports
* Correspondence to: Qiang Zhang, Institute of Space and Earth
Information Science, The Chinese University of Hong Kong, Shatin,
Hong Kong, China.
E-mail: zhangqnj@gmail.com
Copyright  2009 John Wiley & Sons, Ltd.
(therefore called the ‘World Factory’). Another important attribute of the PRD is that it has one of the most
complicated deltaic drainage systems in the world with
a drainage density of 0Ð68–1Ð07 km km2 (Chen and
Chen, 2002).
Due to rapid urbanization and industrialization, the
PRD region has witnessed environmental changes within
only one to two decades whereas comparable changes
in developed countries may have occurred over as much
as one century of development. Human activities such
as engineering construction and other modifications of
the Pearl River network in such a changing environment might cause hydrologic alterations in terms of
river flows, stages, and flow partition at river bifurcations, channel cross-sections and hydraulic gradients.
Changes in these hydrologic regimes may have crucial
implications for almost all aspects of water resources
management in the region, including flood protection,
land use, water supply, channel navigation, and water
pollution control. Abnormally high or low water levels have the potential to give rise to salinity intrusion,
flood inundation and waterlogging, negatively influencing the economic development and human activities in
the PRD. Therefore, hydrologic alterations and, presumably, associated causes have already raised considerable
concerns from Chinese researchers (Luo et al., 2000;
Liu et al., 2003; Chen et al., 2004; Yang et al., 2002).
1566
Q. ZHANG ET AL.
Growing requirements for building materials stimulated
extensive and intensive in-channel dredging and sand
mining. During the period 1984–1999, the total amount
of the sand removed from the river channel was about
17Ð6 times more than the annual sediment deposition
and about 120 times more than the total suspended sediment transport of the Pearl River (Luo et al., 2000).
In a recent study, Luo et al. (2007) discussed two side
effects of in-channel sand excavation on the hydrology of the Pearl River Delta: (1) positive effects are
decreased chances of flood damage, improved navigating conditions, and more water inputs to rapid economically growing regions; (2) negative effects include
increased grade slope and instability of the riverbank,
disruption of navigation in upstream dredging pits during
dry seasons, and brackish-water intrusion. Thus, quantitative evaluation of hydrologic alterations across the PRD
will be of scientific and practical importance in regional
water resources management and human mitigation of
hydrologic hazards such as flood, drought, and salinity
intrusion.
Numerous researchers have developed hydrologic
indices with the aim of quantifying the hydrologic alterations which were believed to be sensitive to various
human perturbations. Previous studies usually emphasized individual indices such as the average flow, mean
daily flow, skewness of streamflow, peak discharge,
flood frequency, slope of flood-frequency curves, seasonal distribution of monthly streamflow, flow and flood
frequency duration curves, and annual discharge series
analysis. However, more recent studies have tended to
adopt multivariable approaches to quantify the hydrologic alterations (Hughes and James, 1989; Richter et al.,
1996, 1997, 1998; Extence et al., 1999; Clausen and
Biggs, 2000; Pettit et al., 2001; Shiau and Wu, 2004). To
quantitively evaluate the degree to which human activities impact the hydrologic regimes within an ecosystem, Richter et al. (1996) proposed an approach referred
to as ‘Indicators of Hydrologic Alteration’ (IHA). This
technique is based on either hydrologic data available
within an ecosystem or model-generated data. Numerous
researchers have illustrated that the range of streamflow
regime is one of the major driving forces influencing the
river ecosystem (Stanford and Ward, 1996; Poff et al.,
1997) and is also one of the key factors sustaining aquatic
environments (NRC, 1992). Richter et al. (1997) proposed the Range of Variability Approach (RVA) with
the aim of attaining river management eco-targets. This
approach (IHA, Richter et al., 1995, 1996) involves 33
hydrologic parameters devoted to measuring hydrologic
alterations in terms of streamflow magnitude, timing,
frequency, duration and rate of change. This method
has been applied to evaluate hydrologic alterations in
many river basins of the world. Galat and Lipkin (2000)
studied the hydrologic alterations of the Missouri River
using the Index of Hydrologic Alteration (IHA), indicating that the river flows were heavily influenced by
the reservoirs. Shiau and Wu (2004) applied the RVA
to investigate the hydrologic alterations within two time
Copyright  2009 John Wiley & Sons, Ltd.
intervals separated by the construction of a diversion
weir on Chou-Shui Creek, Taiwan, suggesting that natural flow restoration was expected to promote the natural
stream biota. Yang et al. (2008) studied the spatial variability of hydrologic alterations due to dam construction
along the middle and lower Yellow River, China, over
five decades.
The RVA method was believed to be a practical
and effective approach to river restoration planning.
However, there are still some defects in the previous
literature about hydrologic alteration assessment (Yang
et al., 2008): (1) the validity of the hydrologic alteration
assessment must be carefully considered when flow
records are insufficient for pre- or post-impact periods
or both; (2) since there is usually more than one dam
on a river, it is hard to distinguish which dam plays
the major role in influencing the degree of hydrologic
alteration downstream. Within the PRD, no dams were
constructed, so the change points decided by the Lepage
model and Bayesian model (Chen et al., 2008) were
accepted as the time thresholds to evaluate the degree
of alteration of water levels before and after change
points. Hydrologic alterations before and after the change
points were analysed using the technique of Richter et al.
(1995, 1996). It should be noted here that the data
available in the PRD are monthly data. Therefore, in
this study we will modify the technique proposed by
Richter et al. (1995, 1996) so that the modified approach
can satisfy our requirements in quantitative evaluation
of hydrologic alterations (alterations of water levels in
this study) based on the monthly water level data we
have for the PRD. This study attempts to answer the
questions: (1) to what degree do the water levels alter
across the PRD? and (2) what could be the alteration
behaviour of the water levels on different time scales,
such as monthly and annually? Thus, the objectives
of this study are to qualitatively evaluate the degree
of alteration of water levels and to investigate the
spatial variability of alterations in water levels across
the PRD using the RVA and a mapping technique.
We believe that this study should be scientifically and
practically significant in regional human mitigation of
natural hazards and environmental conservation under the
changing environment in the coastal regions.
DATA PREPARATION
The hydrologic data used in this study are: (1) monthly
maximum and minimum water levels; and (2) monthly
mean high and low water levels. All these data were
collected from 17 gauging stations in the PRD region
(Figure 1). Table I displays detailed information regarding the water level data. The time duration of the dataset
covers 1958–2005. The water level data before 1989
are extracted from the Hydrologic Year Book (published
by the Hydrologic Bureau of the Ministry of Water
Resources of China) and those after 1989 are provided
by the Water Bureau of Guangdong Province. Figure 1
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
1567
HYDROLOGIC ALTERATION ACROSS THE PEARL RIVER DELTA
Figure 1. Location of the Pearl River Delta in China and gauging stations. The river channels denoted with numbers are where the gauging stations
are located. The names of the river channels are as follows: 1: North mainstream East River; 2: Modaomen channel; 3: Hengmen channel; 4: Yamen
channel; 5: Jitimen channel; 6: Qianhangxian channel; 7: Xijiang channel; 8: Xi’nanyong channel; 9: Ronggui channel; 10: Jiaomen channel; 11:
Shunde channel; 12: Shawan channel; 13: Beijiang Channel; 14: Tanjiang channel; 15: South mainstem East River; 16: Hongqili channel; 17: Xiaolan
channel; 18: Hutiaomen channel. The Pearl River Delta is divided into three parts based on its geomorphology: I the upper Pearl River Delta; II the
middle Pearl River Delta; and III the lower Pearl River Delta. Region I, region II and region III divided by dashed lines are the upper, middle and
lower PRD
Table I. Dataset of water levels in the Pearl River Delta and the river channels where the gauging stations are located
Upper PRD
Middle PRD
Lower PRD
Station name
Longitude
Latitude
Series length
Missing data
River channels
Sanshui
Jiangmen
Laoyagang
Nanhua
Rongqi
Sanduo
Shizui
Xiaolan
Dasheng
Denglongshan
Hengmen
Huangjin
Huangpu
Nansha
Sanshakou
Sishengwei
Zhuyin
112° 500
113° 070
113° 120
113° 050
113° 160
112° 590
112° 540
113° 140
113° 320
113° 240
113° 310
113° 170
113° 280
113° 340
113° 300
113° 360
113° 170
23° 100
22° 360
23° 140
22° 480
22° 470
22° 590
22° 280
22° 410
23° 030
22° 140
22° 350
22° 080
23° 060
22° 450
22° 540
22° 550
22° 220
1958–2005
1958–2005
1958–2005
1958–2005
1958–2005
1958–2005
1959–2005
1975–2005
1958–2005
1959–2005
1959–2005
1965–2005
1958–2005
1963–2005
1958–2005
1958–2005
1959–2005
Sep.-Dec. 1959; 1960
2000
Dec. 1959
Beijiang channel
Xijiang channel
Xi’nanyong channel
Ronggui channel
Ronggui c
Shunde channel
Tanjiang channel
Xiaolan channel
North mainstem East River
Modaomen channel
Hengmen channel
Jitimen channel
Qianhangxian channel
Jiaomen channel
Shawan channel
South mainstem East River
Modaomen channel
shows that these 17 gauging stations cover the PRD well
and can reflect the main variation properties of the water
levels. Missing data were inserted based on data at neighbouring stations using a regression method (R2 > 0Ð8 and
R2 > 0Ð95). Single missing data items were replaced by
the average of neighbouring values (Chen et al., 2008).
Copyright  2009 John Wiley & Sons, Ltd.
Nov.-Dec. 1968; 2000
Jun.-Dec. 1963
Jan.-Sep. 1958
1959
1964
METHODOLOGY
The original RVA uses 33 hydrologic parameters to evaluate the hydrologic alterations, which are categorized
into five groups addressing the magnitude, timing, frequency, duration, and rate of change (Richter et al.,
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
1568
Q. ZHANG ET AL.
1997). However the data we have do not allow us to follow exactly the hydrologic parameters defined by Richter
et al. (1997). Therefore, in this study, we followed the
main theme of the RVA technique but modified the hydrologic parameters to achieve our research objectives. The
parameters adopted were: monthly maximum (minimum)
water levels, annual maximum (minimum) water levels,
and monthly mean high (low) water levels, and these
hydrologic parameters are listed in Table II. Generally,
the mean, standard deviation, and range of these parameters were computed with reference to the change point
time intervals. Here we made the time the change point
took place as the reference time with which we divided
the whole time series into two parts. The mean, standard deviation, and range of the parameters defined were
computed in the two time intervals.
There are many statistical techniques available to
detect change point within the time series. The statistical
methods commonly used to detect change points are
the Bayesian model (Chernoff and Zacks, 1963; Berger,
1985; Kotz and Wu, 2000; Xiong and Guo, 2004), the
Lepage test (Lepage, 1971), the moving t-test, and so
forth. We analysed the water level time series for change
point with these statistical methods, and then identified
the change point with >95% confidence level. If there
were more than one change points, we accepted one
change point which was more significant than the others,
if any. If no change point was significant, we took the
change point with higher significance level for the sake
of further analysis. The above change point detecting
methods and the results were reported in an earlier
publication (Chen et al., 2008). For the sake of concise
presentation of this work, we do not list the change points
in this present paper; rather, we just cite the reference
and use the results. There are six time series (monthly
maximum (minimum) water level; monthly mean high
(low) water level; and annual maximum (minimum)
water level) for each station, so there are altogether
850 time series to be analysed. After change points
were determined, we followed the procedure of the RVA
technique to obtain the alterations in water level across
the PRD.
The RVA target range of each hydrologic parameter
was decided by selected percentile thresholds or a simple
multiple of the standard derivations for the natural or
pre-change-point water level series. The management
objectives were not to have the river attain the target
range every year; rather, they were to attain the range
at the same frequency as occurred in the natural or prealteration water level regime. For example, attainment of
Table II. Statistics of 13 indicators of hydrologic alteration of monthly maximum and monthly minimum water levels for 17 gauges
in the Pearl River Delta region. DS: Dasheng station; DLS: Denglongshan station; HM: Hengmen station; HJ: Huangjin station; HP:
Huangpu station; JM: Jiangmen station; LYG: Laoyagang station; NH: Nanhua station; NS: Nansha station; RQ: Rongqi station; SD:
Sanduo station; SSK: Sanshakou station; SS: Sanshui station; SZ: Shizui station; SSW: Sishengwei station; XL: Xiaolan station; ZY:
Zhuyin station
IHA
DS
DLS
HM
HJ
Monthly maximum water level
Jan.
0Ð03 0Ð08 0Ð55 0Ð00
Feb. 0Ð03 0Ð43 0Ð31 0Ð14
Mar. 0Ð12 0Ð08 0Ð43 0Ð00
Apr. 0Ð23 0Ð14 0Ð37 0Ð00
May 0Ð09 0Ð29 0Ð43 0Ð00
Jun.
0Ð03 0Ð04 0Ð49 0Ð07
Jul.
0Ð14 0Ð14 0Ð31 0Ð00
Aug. 0Ð14 0Ð14 0Ð31 0Ð00
Sep. 0Ð09 0Ð14 0Ð31 0Ð07
Oct.
0Ð03 0Ð29 0Ð31 0Ð00
Nov. 0Ð20 0Ð08 0Ð49 0Ð00
Dec. 0Ð03 0Ð21 0Ð55 0Ð08
Ann. 0Ð03 0Ð08 0Ð37 0Ð00
Monthly minimum water level
Jan.
0Ð31 0Ð33 0Ð07 0Ð06
Feb. 0Ð37 0Ð01 0Ð02 0Ð02
Mar. 0Ð31 0Ð06 0Ð10 0Ð06
Apr. 0Ð43 0Ð06 0Ð07 0Ð06
May 0Ð37 0Ð06 0Ð02 0Ð02
Jun.
0Ð01 0Ð11 0Ð10 0Ð02
Jul.
0Ð37 0Ð03 0Ð07 0Ð02
Aug. 0Ð31 0Ð01 0Ð10 0Ð11
Sep. 0Ð37 0Ð11 0Ð07 0Ð05
Oct.
0Ð49 0Ð11 0Ð07 0Ð15
Nov. 0Ð31 0Ð11 0Ð02 0Ð11
Dec. 0Ð31 0Ð11 0Ð07 0Ð23
Ann. 0Ð14 0Ð01 0Ð02 0Ð04
HP
JM
LYG
NH
NS
RQ
SD
SSK
SS
SZ
SSW
XL
ZY
0Ð41
0Ð23
0Ð27
0Ð27
0Ð23
0Ð23
0Ð41
0Ð27
0Ð23
0Ð23
0Ð23
0Ð27
0Ð27
0Ð96
0Ð96
0Ð96
0Ð96
1Ð05
1Ð05
1Ð05
1Ð05
1Ð05
1Ð05
0Ð88
1Ð05
1Ð05
0Ð04
0Ð12
0Ð13
0Ð04
0Ð04
0Ð04
0Ð04
0Ð22
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð14
0Ð14
0Ð36
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð36
0Ð43
0Ð09
0Ð09
0Ð14
0Ð06
0Ð17
0Ð06
0Ð06
0Ð25
0Ð03
0Ð06
0Ð12
0Ð09
0Ð17
0Ð09
0Ð12
0Ð09
0Ð33
0Ð01
0Ð05
0Ð18
0Ð11
0Ð18
0Ð18
0Ð18
0Ð18
0Ð11
0Ð05
0Ð33
0Ð18
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð12
0Ð04
0Ð04
0Ð10
0Ð17
0Ð12
0Ð26
0Ð22
0Ð12
0Ð17
0Ð17
0Ð22
0Ð14
0Ð01
0Ð07
0Ð17
0Ð14
0Ð09
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð04
0Ð14
0Ð14
0Ð03
0Ð33
0Ð20
0Ð52
0Ð08
0Ð40
0Ð14
0Ð14
0Ð20
0Ð40
0Ð14
0Ð20
0Ð20
0Ð14
0Ð19
0Ð10
0Ð31
0Ð27
0Ð10
0Ð31
0Ð19
0Ð27
0Ð14
0Ð10
0Ð19
0Ð19
0Ð02
0Ð14
0Ð02
0Ð02
0Ð02
0Ð02
0Ð02
0Ð02
0Ð02
0Ð22
0Ð13
0Ð02
0Ð02
0Ð33
0Ð06
0Ð11
0Ð33
0Ð11
0Ð11
0Ð11
0Ð01
0Ð06
0Ð39
0Ð27
0Ð11
0Ð11
0Ð20
0Ð00
0Ð06
0Ð17
0Ð06
0Ð06
0Ð00
0Ð06
0Ð01
0Ð00
0Ð11
0Ð17
0Ð07
0Ð14
0Ð23
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð06
0Ð14
0Ð14
0Ð33
0Ð02
0Ð04
0Ð01
0Ð16
0Ð06
0Ð16
0Ð06
0Ð04
0Ð01
0Ð10
0Ð10
0Ð06
0Ð06
0Ð01
0Ð14
0Ð04
0Ð43
0Ð04
0Ð04
0Ð43
0Ð14
0Ð09
0Ð14
0Ð09
0Ð30
0Ð14
0Ð30
0Ð14
0Ð07
0Ð29
0Ð00
0Ð07
0Ð13
0Ð07
0Ð07
0Ð00
0Ð14
0Ð20
0Ð43
0Ð02
0Ð28
0Ð28
0Ð33
0Ð28
0Ð33
0Ð28
1Ð00
0Ð33
0Ð28
0Ð17
0Ð33
0Ð22
0Ð14
0Ð21
0Ð13
0Ð13
0Ð03
0Ð13
0Ð13
0Ð03
0Ð13
0Ð03
0Ð13
0Ð13
0Ð10
0Ð05
0Ð17
0Ð10
0Ð26
0Ð12
0Ð07
0Ð17
0Ð17
0Ð12
0Ð12
0Ð17
0Ð22
0Ð12
0Ð01
0Ð14
0Ð09
0Ð01
0Ð14
0Ð14
0Ð14
0Ð14
0Ð09
0Ð14
0Ð09
0Ð14
0Ð14
0Ð36
0Ð10
0Ð05
0Ð11
0Ð11
0Ð11
0Ð05
0Ð10
0Ð10
0Ð05
0Ð10
0Ð05
0Ð05
0Ð08
0Ð04
0Ð21
0Ð21
0Ð02
0Ð15
0Ð21
0Ð02
0Ð15
0Ð21
0Ð27
0Ð02
0Ð09
0Ð17
0Ð10
0Ð05
0Ð10
0Ð18
0Ð10
0Ð10
0Ð05
0Ð10
0Ð05
0Ð10
0Ð20
0Ð18
0Ð08
0Ð10
0Ð14
0Ð19
0Ð08
0Ð05
0Ð05
0Ð14
0Ð19
0Ð10
0Ð05
0Ð19
0Ð21
0Ð16
Moderate (0Ð34– 0Ð67) and high alterations (0Ð68–1) marked in bold. 0–0Ð33 denotes little or no alteration.
Copyright  2009 John Wiley & Sons, Ltd.
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
HYDROLOGIC ALTERATION ACROSS THE PEARL RIVER DELTA
Figure 2. Spatial distribution of mean degree of alteration in monthly
maximum water levels for the Pearl River Delta area, China: (1) light
grey zones represent little or no alteration 0–33% (L, low); (2) medium
grey zones represent moderate alteration 34–67% (M, medium); (3) dark
grey zones represent high degrees of alteration 68–100% (H, high)
RVA target range defined by the 25th and 75th percentile
values of a particular parameter would be expected in
only 50% of years. The degree to which the RVA target
ranges were not attained was accepted as a measure
of hydrologic alteration. This measure of hydrologic
alteration, expressed as a percentage, can be obtained as:
Observed frequency - Expected frequency
ð 100
Expected frequency
1
Initially, ‘observed’ is the count of years with the
observed values of the hydrologic parameter falling
within the targeted range; ‘expected’ is the count of the
years with the values expected to fall within the targeted
range. Hydrologic alteration will be zero when the
observed frequency of post-change-point annual values
falling within the RVA target range equals the expected
frequency (The Nature Conservancy, 2001).
RESULTS AND DISCUSSION
Alteration degrees for hydrologic items of individual
month
Table II displays the absolute values of hydrologic
alteration indicators in terms of monthly maximum (minimum) water levels and annual maximum (minimum)
water levels for 17 gauging stations in the study region.
It indicates that more stations show higher hydrologic
Copyright  2009 John Wiley & Sons, Ltd.
1569
Figure 3. Spatial distribution of mean degree of alteration in monthly
minimum water levels for the Pearl River Delta area, China: (1) light
grey zones represent little or no alteration 0–33% (L, low); (2) medium
grey zones represent moderate alteration 34–67% (M, medium); (3) dark
grey zones represent a high degree of alteration 68–100% (H, high)
alterations in terms of monthly maximum water level
when compared with monthly minimum water level.
High alteration of monthly maximum water level can be
observed in Jiangmen station, and moderate alteration in
Hengmen station and Dasheng station. As for the specific time the alteration occurred, higher alteration of
monthly maximum water level at more than three stations can be observed in January, March, April, June,
and October (Table II). Table II also indicates that higher
alteration of monthly maximum water level was identified mainly in Modaomen channel, Hengmen channel,
Qianhangxian channel, Ronggui channel, and Tanjiang
channel (Table II, Figure 1). With respect to alterations
of monthly minimum water level, the number of months
showing high alteration was much less than those showing high alteration of monthly maximum water level.
Higher alterations of annual maximum water level can
be observed at two stations, Hengmen and Jiangmen;
only one station showed higher alteration of annual minimum water level, Sanshui. Regarding the alteration of
monthly mean maximum and minimum water level, more
stations demonstrated high alteration of monthly mean
minimum water level (eight stations) when compared
with monthly mean maximum water level (five stations) (Table III). High alteration of monthly mean maximum water level occurred mainly in July, October and
November. Huangpu station and Nansha station had more
months with high degrees of alteration in monthly mean
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
1570
Q. ZHANG ET AL.
Table III. Statistic of 13 indicators of hydrologic alteration of monthly mean maximum and monthly mean minimum water levels for
17 gauges in the Pearl River Delta region. DS: Dasheng station; DLS: Denglongshan station; HM: Hengmen station; HJ: Huangjin
station; HP: Huangpu station; JM: Jiangmen station; LYG: Laoyagang station; NH: Nanhua station; NS: Nansha station; RQ: Rongqi
station; SD: Sanduo station; SSK: Sanshakou station; SS: Sanshui station; SZ: Shizui station; SSW: Sishengwei station; XL: Xiaolan
station; ZY: Zhuyin station
IHA
DS
Monthly mean
Jan.
0Ð03
Feb. 0Ð05
Mar. 0Ð02
Apr. 0Ð12
May 0Ð05
Jun.
0Ð05
Jul.
0Ð12
Aug. 0Ð05
Sep. 0Ð03
Oct.
0Ð12
Nov. 0Ð19
Dec. 0Ð19
Monthly mean
Jan.
0Ð04
Feb. 0Ð13
Mar. 0Ð04
Apr. 0Ð04
May 0Ð04
Jun.
0Ð03
Jul.
0Ð04
Aug. 0Ð11
Sep. 0Ð13
Oct.
0Ð22
Nov. 0Ð20
Dec. 0Ð12
DLS
HM
HJ
HP
maximum water level
0Ð01 0Ð13 0Ð10 0Ð30
0Ð09 0Ð13 0Ð10 0Ð19
0Ð08 0Ð02 0Ð10 0Ð09
0Ð06 0Ð01 0Ð07 0Ð24
0Ð15 0Ð13 0Ð05 0Ð37
0Ð01 0Ð17 0Ð03 0Ð71
0Ð01 0Ð08 0Ð03 0Ð37
0Ð08 0Ð03 0Ð05 0Ð24
0Ð08 0Ð08 0Ð10 0Ð30
0Ð01 0Ð03 0Ð03 0Ð37
0Ð03 0Ð03 0Ð10 0Ð37
0Ð01 0Ð07 0Ð20 0Ð55
minimum water level
0Ð06 0Ð12 0Ð17 0Ð12
0Ð30 0Ð03 0Ð01 0Ð18
0Ð25 0Ð30 0Ð17 0Ð19
0Ð15 0Ð12 0Ð04 0Ð30
0Ð30 0Ð05 0Ð04 0Ð24
0Ð30 0Ð12 0Ð17 0Ð12
0Ð25 0Ð12 0Ð10 0Ð03
0Ð30 0Ð05 0Ð10 0Ð12
0Ð30 0Ð12 0Ð13 0Ð18
0Ð25 0Ð05 0Ð13 0Ð12
0Ð25 0Ð18 0Ð01 0Ð12
0Ð87 0Ð08 0Ð04 0Ð12
JM
LYG
NH
NS
RQ
SD
SSK
SS
SZ
SSW
XL
ZY
0Ð28
0Ð22
0Ð28
0Ð22
0Ð33
0Ð33
0Ð33
0Ð33
0Ð33
0Ð91
0Ð33
0Ð28
0Ð23
0Ð03
0Ð05
0Ð05
0Ð05
0Ð14
0Ð33
0Ð14
0Ð14
0Ð14
0Ð14
0Ð05
0Ð30
0Ð04
0Ð14
0Ð09
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð56
0Ð43
0Ð01
0Ð45
0Ð38
0Ð43
0Ð45
0Ð45
0Ð48
0Ð38
0Ð48
0Ð38
0Ð43
0Ð43
0Ð43
0Ð22
0Ð33
0Ð33
0Ð22
0Ð28
0Ð33
0Ð33
0Ð33
0Ð33
0Ð28
0Ð33
0Ð17
0Ð17
0Ð22
0Ð13
0Ð13
0Ð13
0Ð13
0Ð22
0Ð17
0Ð13
0Ð02
0Ð17
0Ð04
0Ð07
0Ð03
0Ð03
0Ð03
0Ð03
0Ð07
0Ð19
0Ð09
0Ð03
0Ð03
0Ð03
0Ð23
0Ð02
0Ð02
0Ð10
0Ð02
0Ð07
0Ð07
0Ð40
0Ð02
0Ð02
0Ð07
0Ð07
0Ð02
0Ð05
0Ð05
0Ð03
0Ð32
0Ð02
0Ð05
0Ð05
0Ð05
0Ð04
0Ð25
0Ð11
0Ð14
0Ð05
0Ð19
0Ð17
0Ð11
0Ð06
0Ð04
0Ð00
0Ð05
0Ð05
0Ð05
0Ð16
0Ð17
0Ð14
0Ð04
0Ð06
0Ð04
0Ð04
0Ð04
0Ð14
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð21
0Ð21
0Ð11
0Ð06
0Ð06
0Ð06
0Ð06
0Ð11
0Ð11
0Ð06
0Ð11
0Ð11
0Ð33
0Ð33
0Ð17
0Ð28
0Ð33
0Ð33
0Ð33
0Ð33
1Ð00
0Ð28
0Ð33
0Ð17
0Ð14
0Ð02
0Ð14
0Ð33
0Ð23
0Ð23
0Ð23
0Ð23
0Ð06
0Ð31
0Ð22
0Ð14
0Ð01
0Ð09
0Ð36
0Ð09
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð14
0Ð09
0Ð36
0Ð29
0Ð20
0Ð07
0Ð00
0Ð06
0Ð14
0Ð07
0Ð43
0Ð20
0Ð07
0Ð25
0Ð20
0Ð13
0Ð28
0Ð33
0Ð22
0Ð33
0Ð33
0Ð33
0Ð28
0Ð33
0Ð33
0Ð22
0Ð22
0Ð18
0Ð04
0Ð12
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð04
0Ð28
0Ð21
0Ð20
0Ð40
0Ð21
0Ð47
0Ð15
0Ð15
0Ð34
0Ð09
0Ð27
0Ð21
0Ð19
0Ð18
0Ð24
0Ð01
0Ð18
0Ð05
0Ð18
0Ð11
0Ð11
0Ð18
0Ð11
0Ð47
0Ð18
0Ð09
0Ð05
0Ð20
0Ð06
0Ð06
0Ð05
0Ð43
0Ð13
0Ð00
0Ð09
0Ð13
0Ð11
0Ð12
0Ð12
0Ð05
0Ð05
0Ð03
0Ð05
0Ð02
0Ð12
0Ð03
0Ð12
0Ð05
0Ð19
0Ð20
0Ð29
0Ð29
0Ð29
0Ð29
0Ð20
0Ð29
0Ð29
0Ð93
0Ð29
0Ð29
0Ð29
0Ð01
0Ð06
0Ð11
0Ð11
0Ð06
0Ð11
0Ð39
0Ð06
0Ð01
0Ð07
0Ð01
0Ð27
Moderate (0Ð34– 0Ð67) and high alterations (0Ð68–1) marked in bold. 0–0Ð33 denotes little or no alteration.
maximum water level when compared with the other stations, and these two stations are located in Qianhuangxian
channel and Jiaomen channel, respectively (Figure 1).
In terms of specific stations, only one or two months
were characterized by high alterations of monthly mean
minimum water levels, and these stations are located
in Modaomen channel, Xijiang channel, Ronggui channel, Jiaomen channel, Shawan channel, Tanjiang channel,
Xiaolan channel (Figure 1).
Spatial distribution of alteration degrees for monthly
and annual maximum (minimum) water levels
Using the mapping method of Richter et al. (1998),
we determined the average hydrologic degrees of alteration for individual hydrologic items in the PRD
(Figures 2–5), i.e. monthly maximum (minimum) water
levels and annual maximum (minimum) water levels.
Figure 2 illustrates the spatial distribution of mean degree
of alteration in monthly maximum water levels for the
PRD. It can be observed on Figure 2 that a majority
of the river channels were characterized by low alteration of monthly maximum water levels. Moderate alterations were detected in the Hengmen channel, Xiaolan
channel and river channels near the Xiaolan station and
Rongqi station. The river channel between Tianhe station
and Jiaomen station was characterized by high degrees
of alteration in monthly maximum water level. With
Copyright  2009 John Wiley & Sons, Ltd.
respect to monthly minimum water level (Figure 3), only
the north mainstream East River and Ronggui channel
were characterized by moderate degrees of alteration in
monthly minimum water level; low degrees of alteration
were identified in the remaining channels of the PRD.
The spatial distribution of the degree of alteration in
annual maximum water level is illustrated in Figure 4.
Almost all the river channels within the PRD except the
river channel between Tianhe and Jiangmen stations were
characterized by low degrees of alteration in annual maximum water level. A similar situation occurs found for the
annual minimum water level (Figure 5); however the difference is that a moderate degree of alteration of annual
minimum water level was observed in the river channel
upstream to Sanshui station (Figure 5).
Spatial distribution of alteration degrees for monthly
mean maximum (minimum) water level
Figures 6 and 7 illustrate the spatial patterns of the
degrees of alteration in monthly mean maximum (minimum) water levels. Considerably different spatial patterns
in the degrees of alteration in monthly mean maximum
water level (Figure 6) and in monthly mean minimum
water level (Figure 7) can be observed when compared
with the patterns for monthly (annual) maximum (minimum) water levels in the PRD. It can be seen from
Figure 6 that moderate degrees of alteration in monthly
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
HYDROLOGIC ALTERATION ACROSS THE PEARL RIVER DELTA
1571
Figure 4. Spatial distribution of mean degree of alteration in annual
maximum water levels for the Pearl River Delta area, China: (1) light
grey zones represent little or no alteration 0–33% (L, low); (2) medium
grey zones represent moderate alteration 34–67% (M, medium); (3) dark
grey zone represents a high degree of alteration 68–100% (H, high)
Figure 5. Spatial distribution of mean degree of alteration in annual
minimum water levels for the Pearl River Delta area, China. (1) light
grey zones represent little or no alteration 0–33% (L, low); (2) medium
grey zones represent moderate alteration 34–67% (M, medium); (3) dark
grey zones represent a high degree of alteration 68–100% (H, high)
mean maximum water level were observed in numerous
river channels within the PRD. In particular, moderate
degrees of alteration in monthly mean maximum water
level were identified in the Shunde channel, Qianhangxian channel, Shawan channel, Hengmen channel, Xiaolan
channel, Xijiang channel, Hongqili channel and channel
between Tianhe station and Jiangmen station (Figures 1
and 6). Therefore, a majority of river channels in the
hinterland of the PRD were characterized by moderate
degrees of alteration. The remaining river channels were
dominated mainly by low degrees of alteration in monthly
mean maximum water level. Most river channels had low
degrees of alteration in monthly mean minimum water
level. Moderate degrees of alteration can be identified
only in Hengmen channel, Xiaolan channel, channels near
the Rongqi station and the channel between Tianhe and
Jiangmen stations. Other channels within the PRD were
dominated by low degrees of alteration in monthly mean
minimum water levels.
that changed hypsography due to extensive and intensive
human activities, particularly the large-scale dredging and
excavation of river sand, could be one of the major causes
of the substantial hydrologic alteration (Luo et al., 2002;
2007). Figure 8 illustrates different degrees of intensity of
in-channel sand dredging (Chen and Chen, 2002). Visual
comparison of Figure 8 and Figures 2–7 shows the correlation between sand dredging and degree of alteration
in water levels in the PRD. Generally, river channels
characterized by moderate and high degrees of alteration
were those subject to moderately and highly intensive
dredging. River networks of the PRD north of 22° 300 N
were mostly dominated by moderate degrees of monthly
mean maximum water level. Figure 8 indicates that these
river channels were also characterized by moderately and
highly intensive levels of dredging. Degrees of alteration
in other water level components, e.g. monthly maximum
(minimum) water level and monthly mean minimum
water level, also exhibited a close relation with intensity
of sand dredging. River channels upstream of the river
channels characterized by moderate degrees of alteration
were generally subject to highly intensive dredging.
Changes in the divided flow ratio within various
water courses also drove the alterations in water level.
Luo et al. (2007) indicated that the divided flow ratio
increased by 8Ð8% at the Sanshui Station on the upper part
of the North River network from the early 1980s to 1999.
The large-scale hydrologic alteration of monthly mean
maximum water levels in most river channels north of
Possible causes
The alterations in water levels within the PRD region
were not driven by one individual factor. All the influencing factors impacting on the changes in water levels
interact with each other. Therefore, the effects of the
influencing factors on water levels are dynamic and their
relative importance changes. Furthermore, for specific
river channels, the major factors influencing water level
variations may be different. Earlier research indicated
Copyright  2009 John Wiley & Sons, Ltd.
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
1572
Q. ZHANG ET AL.
Figure 6. Spatial distribution of mean degree of alteration in monthly
mean maximum water levels for the Pearl River Delta area, China:
(1) light grey zones represent little or no alteration 0–33% (L, low);
(2) medium grey zones represent moderate alteration 34–67% (M,
medium); (3) dark grey zones represent a high degree of alteration
68– 100% (H, high)
22° 300 N of the PRD region can be partly attributed to this
changed divided flow ratio at the Sanshui station. Furthermore, sand dredging or excavation in one river channel
affected the scouring and deposition process of its downstream river channels, which absolutely led to associated
alterations in water level of its downstream river channels. Since the water levels of the PRD region were also
influenced by tidal processes (Huang et al., 1999), it is
particularly true for the water level changes in river channels closer to coastal regions. Stations with months characterized by higher water level alterations were observed
largely along the Xijiang Channel, Modaomen channel,
river channels in the hinterland of the PRD and also river
channels near to the coastal regions. These observations
support the point that altered hydrologic processes of the
rivers upstream of the PRD and tidal variations were
also partly responsible for water level alterations in the
PRD. Therefore, water level alterations in the PRD were
the consequence of natural processes such as hydrologic
processes in the rivers upstream of the PRD and tidal variations along the coastal regions, and also human activities
such as in-channel sand dredging. These factors played
different roles in terms of specific river channels.
CONCLUSIONS
We quantitively analysed alterations in water levels
within the PRD region using a modified RVA approach.
Some interesting conclusions can be drawn as follows:
Copyright  2009 John Wiley & Sons, Ltd.
Figure 7. Spatial distribution of mean alteration degree of monthly mean
minimum water levels for the Pearl River Delta area, China: (1) light
grey zones represent little or no alteration 0–33% (L, low); (2) medium
grey zones represent moderate alteration 34–67% (M, medium); (3) dark
grey zones represent a high degree of alteration 68–100% (H, high)
1) Regarding water level alterations in specific months,
higher degrees of alteration in water level were
detected in the monthly maximum water level. More
stations showed high alterations in monthly mean minimum water level when compared with results for
monthly mean maximum water level. In terms of mean
degree of alteration in water levels, more river channels were characterized by high alterations in monthly
mean maximum water levels. Therefore, it seems that
the changes in high water levels may be more sensitive to external influences than changes in low water
levels. Chen et al. (2008) found altered water levels
across the Pearl River basin. In this study, we found
that higher water level alterations can be observed in
specific months in specific river channels, while low
average degrees of alteration in water levels occur in
most river channels within the Pearl River delta.
2) Greater alterations in water levels were observed in
river channels within the PRD north of 22° 300 N, the
Xijiang channel and also in the river channels near to
coastal regions. With respect to mean degree of alteration, only sporadic river channels are characterized
by high degrees of alteration in monthly maximum
(minimum) water level, monthly mean minimum water
level, and annual maximum (minimum) water level.
However, a majority of river channels distributed in
the regions of the PRD north of 22° 300 N were predominantly characterized by moderate degrees of alteration
in monthly mean maximum water level. Therefore,
Hydrol. Process. 23, 1565– 1574 (2009)
DOI: 10.1002/hyp
HYDROLOGIC ALTERATION ACROSS THE PEARL RIVER DELTA
1573
ACKNOWLEDGEMENTS
The work described in this paper was fully supported by
a grant from the Research Grants Council of the Hong
Kong Special Administrative Region, China (Project No.
CUHK4627/05H), National Natural Science Foundation
of China (Grant No.: 40701015) and Program of Introducing Talents of Discipline to Universities—the 111
Project of Hohai University. Cordial thanks should be
extended to three anonymous reviewers and the editor-inchief, Professor Malcolm G Anderson for their invaluable
comments which greatly improved the quality of this
paper.
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Figure 8. River channels featured by different intensities of the in-channel
sand dredging (after Chen and Chen, 2002). The solid lines marked with
I and II show the demarcation of flood and flood– tidal areas (line A)
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et al., 1999)
the alteration of monthly mean maximum water level
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PRD. Study by Luo et al. (2007) indicated that from
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