s 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:
,πexp 4
yu x
WCxyCHuxE k
Ex u
 
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-
ble 2).
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 [12]:
Table 1. Computational units in the Xiangyang Reach of the
Han River.
Computational unit Environmental
functional category Length (m)
Shenwan-Xianrendu 38.5
Xianrendu-Baijiawan 47.2
Baijiawan-Zhakou 14
Zhakou-Qianying 12
Qianying-Yujiahu 7.6
Yujiahu-Guo’an 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
and tributary
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
EaHU (4)
UgHI (5)
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.
5. Conclusion
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
6. Acknowledgements
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
for providing necessary data.
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