Journal of Water Resource and Protection, 2012, 4, 634-637
http://dx.doi.org/10.4236/jwarp.2012.48073 Published Online August 2012 (http://www.SciRP.org/journal/jwarp)
Estimation of Water Environmental Capacity Considering
Hydraulic Project Operation in the Xiangyan g Reach of
the Han River, Central China
Chen Sun, Hongjuan Wu
School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, China
Email: email@example.com, firstname.lastname@example.org
Received May 28, 2012; revised June 30, 2012; accepted July 8, 2012
Using the Xiangyang Reach of the Han River as an example, this paper evaluates the changes of water environmental
capacity after the implementation of Cuijiaying Hydro-junction project. The allowable pollutant loads entering the
Xiangyang Reach were estimated using two-dimensional steady state water quality model with different data sets. The
water environmental capacity has declined in the reservoir area of the Cuijiaying Hydro-junction project during the
low-flow period; it is appearing to increase slightly in the upper and lower stream of this reservoir. However, the state
of flow may turn into the state of reservoirs flow in the reservoir area, and the changes of hydrological regime may
cause the water flow and the nutrient contents suitable for the occurrence of ecological environment problems.
Keywords: Han River; Water Environmental Capacity; Cascade Development; Pollutant Loading
The Han River is the longest tributary of the Yangtze
River, with a watercourse length of 1577 km and a total
drainage area of 159,000 km2. The Han River Basin is
one of the major agricultural production bases in China,
and plays a significant role in regional economic devel-
opment. Due to its plentiful water resources , the Ba-
sin cascade development is being implemented .
Meanwhile, changes of hydrological regime may inevi-
tably impact the aquatic environment of the Han River,
especially to the water environmental capacity. Moreover,
the rapid urbanization and industrialization are beginning
to affect water quality in this area. From 1992 to 2005,
large-scale algal blooms had taken place five times in the
middle and lower reaches of the Han River because of
the ecological environment degradation .
Total amount control for water pollutants is one of the
main methods to resolve water environmental problems
in China [4,5]. Comprehensively understanding the water
environmental capacity, namely the maximum allowable
pollutant loads discharging into the water body, is a pre-
requisite to effective pollution control. With the aim of
providing a valuable aid to the strategies of water pollu-
tion control, the influence of water conservancy projects
on water environmental capacity is increasingly draw
more attention in China [6-8].
The current study aims to estimate the water environ-
mental capacity through a case study of the Xiangyang
Reach of the Han River in Central China. Using two-
dimensional steady state water quality model, we evalu-
ated the variation of water environmental capacity con-
sidering the dam operation in this area.
2. Study Area
Xiangyang city is located in the middle reach of the Han
River (Figure 1). With a total area of 19,727.68 km2, it
has a population of around 5,888,786 in 2009. The Han
River runs through the city from north to south with a
length of 195,000 m. There are five tributaries in the
Xiangyang Reach: South River, North River, Xiaoqing
River, Tangbai River, and Man River. The Cuijiaying
Hydro-junction project, located in downstream of the
Xiangyang urban area, is the third step of cascade devel-
opment in the middle and lower reaches of the Han River
. Normal storage level of the project is 62.73 m. The
project, which is mainly used for shipping and electricity
generation, has been completed in July, 2010.
According to the actuality of total amount control for
water pollutants in China , chemical oxygen demand
(COD) and ammonia nitrogen (NH3-N) were selected as
the calculation factors in this study. We divided the
Xiangyang Reach of the Hn River into six computa- a
opyright © 2012 SciRes. JWARP
C. SUN, H. J. WU 635
Figure 1. Study area.
tional units based on the water environmental function
zone of Hubei Province , as shown in Table 1. The
point source pollution data in 2007 for this study was
obtained from the Xiangyang Environmental Monitoring
As the river width of the Han River is usually in ex-
cess of 200 meters, it is necessary to consider the varia-
tion of pollutants in longitudinal dispersion and horizon-
tal diffusion . Two-dimensional water quality model,
therefore, is suitable for calculation of water environ-
mental capacity under given the unique hydrological
conditions within the Xiangyang Reach.
Under steady flow conditions, fundamental equation of
two-dimensional water quality model is written as:
where ux is the longitudinal velocity (m/s); uy is the hori-
zontal velocity (m/s); Ex is the longitudinal dispersion
coefficient (m2/s); Ey is the horizontal diffusion coeffi-
cient (m2/s); C is the contaminant concentration (mg/L);
K is the decay coefficient (1/d); x is the longitudinal co-
ordinates (m); y is the horizontal coordinates (m).
Supposing uy and Ex are approximate to zero under
conditions of little changes in water depth, Equation (1)
is converted to the following expression:
where M is the pollutant emission rate (g/s); C0 is the
background pollutant concentration of the river (mg/L);
C is the pollutant concentration (mg/L); K is the decay
coefficient (1/d); x is the longitudinal coordinates (m); y
is the horizontal coordinates (m); h is the average water
depth (m); u is the average longitudinal velocity (m/s).
Assuming the degradation of background pollutant
concentration is negligible, the model which can be ap-
plied to estimate water environmental capacity in the
Xiangyang Reach gives the following formula:
where W is the water environmental capacity (t/a).
30Q10 is selected as the design flow (314 m3/s) in the
light of data from the Xiangyang hydrometric station,
and the designed flow velocity is 0.31 m/s. The river
depth and width are derived from our investigation (Ta-
The horizontal diffusion coefficient (Ey) is usually de-
termined by the empirical correlation or field survey
method. In this study, we adopted the following empiri-
cal correlations :
Table 1. Computational units in the Xiangyang Reach of the
Computational unit Environmental
functional category Length (m)
Shenwan-Xianrendu Ⅱ 38.5
Xianrendu-Baijiawan Ⅱ 47.2
Baijiawan-Zhakou Ⅲ 14
Zhakou-Qianying Ⅲ 12
Qianying-Yujiahu Ⅲ 7.6
Yujiahu-Guo’an Ⅱ 53.2
Copyright © 2012 SciRes. JWARP
C. SUN, H. J. WU
Table 2. Average river width and depth of each com-
putational unit in the Xiangyang Reach.
Computational unit Sewage outlet
Jiangshan 180 2.8
Damingqu 180 2.8
Xianrendu-Baijiawan Jinhuan 235 2.7
Xiaoqing River 323 2.42
Tianjiu 160 3.3
Nanqu 323 4.52
Yuliangzhou 160 3.3
power plant 390 3.35
Yujiahu-Guoan Yakou 390 3.35
where ay is non-dimensional coefficient; H is average
river depth (m); U* is frictional velocity (m/s); g is grav-
ity acceleration (m/s2); I is gradient of the river (‰).
According to the Surface water environmental capac-
ity of Hubei Province Technical Report, decay coeffi-
cient (K) is assigned values as follows: KCOD = 0.18d –
NH-N = 0.08d – 1. The upper limit value of water
quality standard is selected as the background pollutant
concentration of the Xiangyang Reach.
4. Results and Discussion
4.1. Pollution in the Xiangyang Reach of the Han
In 2007, the quantity of waste water entering the Xian-
gyang Reach was 130,414,000 t. The amount of COD
was 38,741 t, and NH3-N was 4418.43 t. Table 3 shows
the amount of pollutants entering the Xiangyang Reach
from various pollution sources. Municipal domestic
sewage was the primary point source pollution, account-
ing for nearly 64% of COD and 62% of NH3-N, respect-
tively. Table 4 shows the quantity of pollutants from
point source pollution in each computational unit. The
pollutant loading mainly originates from Xiangyang ur-
ban area with the highest population densities. The
chemical fiber industry, textile industry, pharmaceutical
industry, and chemical industry are four major industrial
pollution sources, whose COD accounted for nearly 76%
of industrial pollution.
4.2. Changes of the Hydrological Regime
The Cuijiaying Hydro-junction project has mainly exerted
Table 3. The quantity of pollutants from various pollution
sources entering the Xiangyang Reach in 2007.
Pollution source COD (t) NH3-N (t)
Municipal domestic sewage 21905.2 2267.7
Industrial sewage 12388.5 1418.2
Animal breeding 1758.2 353.6
Rural area sewage 1735.2 188.2
Farmland runoff 951.1 190.3
Urban runoff 2.7 0.3
Table 4. The amount of pollutants from point source pol-
lution in each computational uint in 2007.
Computational unit COD (t) NH3-N (t)
Shenwan-Xianrendu 6802.6 553.4
Xianrendu-Baijiawan 11640.6 1256.7
Zhakou-Qianying 10608.1 949
Qianying-Yujiahu 785.4 653.1
Yujiahu-Guo’an 4401 814.4
effects on the hydrological regime of the following two
areas: the reservoir area and downstream of this project.
The flow of reservoir area (backwater area) is mainly in-
fluenced by the upstream flow and runoff, and the de-
signed flow of this area is 554 m3/s. The water level
increased from 2.66 m to 62.73 m, and the designed flow
velocity is 0.138 m/s. The state of flow may turn into the
state of reservoirs flow in the reservoir region, and the
hydrological regime changes cause the water flow and
the nutrient contents suitable for the occurrence of eco-
logical environment problems.
Meanwhile, the minimum discharging downstream
flow (490 m3/s) is used for designed flow of downstream
of the dam. The designed flow velocity is 0.57 m/s, and
the water level has increased by 0.15 m.
4.3. Water Environmental Capacity in the
Xiangyang Reach of the Han River
Based on the specified water quality and hydrological
patterns, the water environmental capacity in the Xiang-
yang Reach of the Han River was estimated. The results
are shown in Table 5, which are the maximum allowable
pollutants loading entering the river (there is no outfall in
the unit of Baijiawan-Zhakou, so this unit does not need
to calculate). The water environmental capacity after the
implementation of the cascade project is shown in Table
6. The water environmental capacity has declined in the
reservoir area (Zhakou-Qianying) during the low-flow
Copyright © 2012 SciRes. JWARP
C. SUN, H. J. WU
Copyright © 2012 SciRes. JWARP
Table 5. Water environmental capacity in the Xiangyang
Reach of the Han River.
Computational unit COD (t/a) NH3-N (t/a)
Shenwan-Xianrendu 3614.1 576.34
Xianrendu-Baijiawan 1904.4 177.11
Zhakou-Qianying 44986.2 2278.76
Qianying-Yujiahu 3570.1 224.13
Yujiahu-Guo’an 9852.23 197.46
Table 6. Water environmental capacity in the Xiangyang
Reach after the implementation of the Cuijiaying project.
Computational unit COD (t/a) NH3-N (t/a)
Shenwan-Xianrendu 3728.3 592.51
Xianrendu-Baijiawan 1905.5 177.6
Zhakou-Qianying 42661.3 2112.2
Qianying-Yujiahu 3612.3 235.1
Yujiahu-Guo’an 10007.6 203.78
period, and it is appearing to increase slightly in the up-
per and lower stream (Shenwan-Baijiawan, Qianying-
Guo’an) of this project.
Applying two-dimensional steady state water quality
model, we estimated the water environmental capacity of
the Xiangyang Reach. Owing to the influence of cascade
development, there is a decline of water environmental
capacity in the reservoir region, also a growth in the up-
per and lower stream of the dam. However, the flow rate
has declined in the reservoir area, and what should be
done is to look for the influence of the cascade develop-
ment on the aquatic eco-environment. The reservoir area
should be a priority region for pollution control. The case
study of the Xiangyang Reach shows that municipal do-
mestic sewage was one of the major point source pollu-
tion, which contributed the most COD load entering the
Han River in 2007. Improvement of sewage treatment
facilities should be considered by policy makers in this
This study was supported by the Environmental Protec-
tion S&T Program of Hubei Province. The authors thank
the Hubei Provincial Environmental Protection Depart-
ment and Xiangyang Environmental Protection Agency
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