Tạp chí Khoa học và Công nghệ 52 (4B) (2014) 201-209
ZONING THE SURFACE WATER QUALITY ACCORDING TO
WATER QUALITY INDEX (WQI) IN BAC LIEU PROVINCE
Ton Nu Phuong Anh1, Le Trong Dieu Hien2, Pham Van Tat1
1
Department of Environment, University of Hoa Sen, Ho Chi Minh City
2
Department of Environment, University of Thu Dau Mot, Binh Duong province
*
Email: vantat@gmail.com
Received: 11 Aug 2014; Accepted for Publication: 25 Sep 2014
ABSTRACT
GIS is a powerful tool for solutions of many environmental challenges and especially in
water field such as assessing water quality and managing water resources on a local or regional
scale [1,2]. The geo-referenced characteristics and spatial relationships of water system can be
represented by GIS. However, the predictive and related analytical capacities are the most
powerful functions of GIS which are useful and necessary for water resource problems solving.
In this paper we applied the interpolation function in GIS technology and Surfer software to
zone the surface water quality in Bac Lieu province according to indicators: pH, DO, BOD 5,
COD, TSS, NH4+ and coli form. A series of data related to these indicators in five years 20072010 and 2013 was collected to be the input data for the interpolation. Then, the interpolation
maps of indicators through years were built to compare and assess surface water quality in Bac
Lieu province. In addition, the sensible solutions to manage surface water quality are suggested
in this paper.
Keywords: surface water quality, GIS, interpolation, environmental management.
1. INTRODUCTION
The Bac Lieu Province, Vietnam is the part of the Ca Mau Peninsula and Me Kong Delta as
well. It shares the border with Can Tho City and Soc Trang Province in the northern, the East
Sea in the southeast, Ca Mau and Kien Giang provinces in the western (Figure 1).It has a
population of 830,000 with approximately eighty-five per cent of population is engaged in
agriculture and fisheries activities [3,4]. According to provincial Department of Natural
Resources and Environment [5,6], the water surface of Bac Lieu Province including the rivers,
lakes and stream has been significantly polluted by untreated waste water discharged from
agriculture, shrimp hatching activities, hospitals and factories. In 2013, samples of surface water
from 30 different places were collected to test the indicators pH, DO, BOD5, COD, TSS, NH4+
and coli form in water in province. The results of the test revealed that the toxicity levels of
water between 1 and 3.7 times of the legal limit [6]. Two main reasons which cause this situation
are that most aquaculture processing factories and hospitals were not equipped with proper waste
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Ton Nu Phuong Anh, Le Trong Dieu Hien, Pham Van Tat
water treatment systems and the use of chemicals and fertilizers still proliferated among
agricultural and shrimp hatching activities.
The aim of this paper is zoning the surface water quality in Bac Lieu province according to
Water Quality Index (WQI) to support the development of a sustainable water management plan
which will be easily adopted from the local authorities. For this reason, some the available
hydrological data collected have been integrated and analyzed into GIS technology. Then,
through the interpolation function in GIS and Surfer software, several thematic maps have been
created using the collected hydrological data. Via these maps, the managers could recognize the
change in quality of water in each area of province. From that the suitable solutions would be
applied for each case.
The method using interpolation has been applying by many scientists on the world. In his
study, Yammani used IDW method to locate groundwater quality zones suitable for different
usages like irrigation and drinking water [7]. Similarly, Rangzan et al also used IDW to create
the layers of maps to locate promising well sites based on the water quality [8]. Babiker et al
based on IDW to zone the groundwater quality index which is synthesized from different water
quality data (Cl, Na, Ca) [9]. Raikar & Sneha presented their case study on the water quality
analysis which was carried out at the Bhadravathi Taluk, Karnataka, India. The spatial
distribution of twelve physico-chemical parameters and thematic maps were created by using
IDW function in GIS. As the result, most of the sampling locations are under Good category that
present for the suitability of water for human use. The reason was given to explain for this
situation is that the industrialization and agricultural disposal some of the sampling locations
became unfit [10]. Noha Donia identified the areas on Temsah lake is suitable for each use
(swimming, fishing, and other uses) on spatial maps within GIS [11]. Kumar et al attempted to
map the spatial variation of surface water quality parameters namely pH, Electrical Conductivity
(EC), Total Dissolved Solids, Total hardness, Ammonia, Nitrate and BOD for Thamirabarani
River Basin of Tirunelveli District, Tamil Nadu using GIS. The final thematic map shows three
priority classes of water quality including Good, Moderate and Poor zones of the study area and
provides a guideline for the suitability of water for domestic purposes [12].
2. METHODOLOGY
Seven variables describing water
quality: pH, DO, BOD5, COD, TSS,
NH4+ and coli form of surface water
from 30 different places in province
(Figure 3) were provided by Center
for environmental consultancy and
technology, the South branch of
Vietnam environmental administrator.
The monitoring locations were chosen
according to three standards (1) the
sample point provides representative
data at that spot (representative data:
refers to the degree to which the data
represents the actual environmental
conditions at the time of monitoring.
In this case, it should reflect the water
Figure 1. Map of sample location.
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Zoning the surface water quality according to water quality index (WQI) in Bac Lieu province
quality integrated across and through the water column and not isolated element), (2) the reach
approach uses multiple sites to reflect conditions and trends for a segment of stream, and (3) the
basin scale uses multiple reaches to reflect conditions and trends throughout a watershed [13].
In addition to the “scientific” considerations for monitoring sites, the “practical” approach
is also considered, for example, the easy access locations (such as road crossings) or a section of
a stream channel with good water mixing. In these sites, the data would represent the site’s
average water quality condition. The monitored indicators were carried out in five years 2007 to
2010 and 2013 in two seasons: raining and dry.
WQI calculation is applied according to 879 /QĐ-TCMT of Ministry of natural resources
and environmental of Vietnam [1]. The formula 1 is used to calculate the WQI:
WQI pH  1 5
1 2

WQI 
WQI
x
WQI b xWQI c 


a

100  5 a 1
2 b1

1/ 3
(1)
where WQIa values include the corresponding value WQI to three variables DO, BOD5, COD,
and NH4; WQIb values involve the value WQITSS and the value WQIColi with the symbol WQIC.
Once the overall WQI score is known, it can be compared against a scale to determine how
healthy the water is. The Table 1 presents the WQI scale.
Table 1. WQI scales from ministry of natural resources and environmental of Vietnam, 2011 [1].
WQI value
Quality level
Color
91 – 100
Excellent water quality
Blue
76 – 90
Good water quality
Green
51 – 75
Medium or average water quality
Yellow
26 – 50
Fair water quality
Orange
0 – 25
Poor water quality
Red
Then, the WQI data calculated have been integrated and analyzed into GIS technology. In
GIS, the Inverse Distance Weighted (IDW) interpolation was applied. IDW interpolation
explicitly implements the assumption that things that are close to one another are more alike than
those that are farther apart. To predict a value for any unmeasured location, IDW uses the
measured values surrounding the prediction location.
The measured values closest to the prediction location have more influence on the predicted
value than those farther away. IDW assumes that each measured point has a local influence that
diminishes with distance.
It gives greater weights to points closest to the prediction location, and the weights diminish
as a function of distance [2]. The below calculation is interpolation formula according to IDW.
n
Z ( S 0 )   i Z ( S i ) with i 
i 1
Dij p
n
D
i 1
(2)
p
ij
where Dij is the separate distance from point i to j; p is power value. As the distance increases,
the weights decrease rapidly. The rate at which the weights decrease is dependent on the value
of p. If p = 0, there is no decrease with distance, and because each weight λi is the same, the
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Ton Nu Phuong Anh, Le Trong Dieu Hien, Pham Van Tat
prediction will be the mean of all the data values in the search neighborhood. As p increases, the
weights for distant points decrease rapidly. If the p value is very high, only the immediate
surrounding points will influence the prediction [2].
In this paper we use p = 2. As the result, several thematic maps have been created using the
collected hydrological data. The maps would present the WQI of each indictor for whole Bac
Lieu area according to color presented in the Table 1.
3. RESULT AND DISCUSSION
3.1. WQIpH
According to calculated value of WQIpH and interpolated result of WQIpH (all of value of
WQIpH are equal 100) in five years from 2007 to 2010 and 2013, pH indicator in surface water in
Bac Lieu province is still excellent. Therefore, the local management should control closely to
remain this high level.
3.2. WQIDO
There was an upward trend in WQIDO from 2007 to 2009 in surface water in Bac Lieu. It
ranged from 25 to 50 in 2007, this indicator was better in three years 2008, 2009 and in 2013
which fluctuated from 50 to 100. However, this indicator decreased in 2010 because there was a
considerable amount of wastewater with high content of organic substances which discharged
into river system in Bac Lieu [5]. As we can see from the map of 2010, the values of WQIDO in
two districts namely Phuoc Long and Hong Dan ranged from 25 to 50 which were lower the
value in 2008, 2009 and in 2013. Compare to other years, the WQIDO in 2013 improved
significantly, most of the values of WQIDO were over 50. The polluted control and wastewater
treatment activites were performed thoughfully in 2013 [14,15] can explain for why the water
quality in 2013 was better than previous years.
Note
WQIDO
a) Year 2007
b) 2013
QCVN 08/2008 [1]
(91,100)
A1
(76,90)
A2
(50,75)
B1
(25,50)
B2
(1,25)
Figure 2. Tendency of WQIDO.
Because of the charateristic of river system (straight and wide canals, ditchs cross the sea,
then the considerable amount of water flow in the Southern area of 1A highway, the speed of
water flow is very fast, the dissolvable of DO in water is high), the WQIDO in the Southern area
of 1A highway is higher than the North area of 1A highway. Thus, the DO indicator in surface
water in Bac Lieu province is considerated. However, it shoud be continous to suggest the
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Zoning the surface water quality according to water quality index (WQI) in Bac Lieu province
efficient sollutions to ramain and improve the DO content in water in Bac Lieu. Besides, it is
essential to attach special importance to the water zone in Quan Lo – Phung Hiep Canal because
this canal is the core canal which supplies the water for agriculture and industry in the North
area of 1A highway [16,17].
3.3. WQIBOD5
From the calculated WQIBOD5 and interpolated results, there is an upward tendency in
BOD5 pollution in surface water in Bac Lieu province. The map below presents this trend in
period from 2007 to 2010 and 2013 (Figure 3). The WQIBOD5 in 2007 was in a situation at an
alarming rate. Most of WQIBOD5 in this year were under 26 and even some places in province,
WQIBOD5 were at red level. However, there was considerable improvement in WQIBOD5 in 2008.
The WQIBOD5 ranged from 76-90. Yet, this indicator decreased gradually in later years (2009,
2010 and 2013). The reason explains WQIBOD5 in surface water in Bac Lieu province went up
through years is that a large amount of wastewater from agriculture, cattle–breeding, aquaculture
and industry have been discharged directly into river system without any treatment [16,18].
Note
WQIBOD
5
a) 2007
b) 2013
QCVN 08/2008 [1]
(91,100)
A1
(76,90)
A2
(51,75)
B1
(26,50)
B2
(1,25)
Figure 3. Tendency of WQIBOD5.
3.4. WQINH4+
In period from 2007 to 2010 and in 2013, there was a positive tendency in WQINH4+ in
surface water in Bac Lieu province. In 2013, it is easy to see from the figure 4, WQINH4+
increased significantly. WQINH4+ in almost of water sources in province are over 75.
Note
WQINH4+
a) 2007
b) 2013
Figure 4. Tendency of WQINH4+ through years.
5
QCVN 08/2008 [1]
(91,100)
A1
(76,90)
A2
(50,75)
B1
(25,50)
B2
(1,25)
Ton Nu Phuong Anh, Le Trong Dieu Hien, Pham Van Tat
There were some places in two districts namely Dong Hai and Vinh Loi which have
WQINH4+ fewer than 75. Thus, Amoni content in water sources in Bac Lieu met the allowed
standard. It should be remain this situation to avoid Amoni pollution because Amoni would
effect to haman being and animals at a determined concentration [3].
3.5. WQITSS
The interpolated results represent the WQITSS were very low ranging from 1 to 50. Some
reasons could explain for the increase of TSS content in surface water in Bac Lieu province (1)
the water zone in province is salt water, or brackish water which contains a lot of minerals; (2)
water zone has been received the wastewater from aquaculture and enterprises (3) the geological
condition of coastline in the Southern is week, hence it would cause the landslide when it is
affect by the power of wave [5]. Therefore, some solutions should be implemented to overcome
the TSS pollution such as diking and landslide prevention.
Note
QCVN 08/2008 [1]
WQITSS
a) 2007
b) 2013
(91,100)
A1
(76,90)
A2
(51,75)
B1
(26,50)
B2
(1,25)
Figure 5. Tendency of WQITSS.
3.6. WQIColiform
The period from 2007 – 2010 and 2013, there was also an upward tendency of WQIColiform.
From 2007 to 2010, the water zones in Quan Lo – Phung Hiep canal and Bac Lieu – Ca Mau
canal were polluted highly by microorganisms [17]. WQIColiform in many places in province are 1.
WQIColif
a) 2007
b) 2013
Figure 6. Tendency of WQIColiform.
6
Note
QCVN 08/2008 [1]
(91,100)
A1
(76,90)
A2
(51,75)
B1
(26,50)
B2
(1,25)
Zoning the surface water quality according to water quality index (WQI) in Bac Lieu province
In 2013, the WQIColiform increased considerably, many areas in the south province got the
value of 100. In the northern, the WQIColiform improved considerably compared to 2010, but the
values of WQIColiform are still fewer than 50. Therefore, there is a signal to recognize that water
zone on the north area of province is getting polluted by microorganisms.
3.7. WQItotal
Note
WQItotal
QCVN 08/2008 [1]
75-90
51-75
26-50
0-25
a) 2007
b) 2013
Figure 7. Tendency of WQI.
The value of WQI total present the quality of surface water because it is calculated based
on the value of other indicators such as pH, COD, BOD5, TSS, NH4+ and coli form. The partial
values like coli form only present the microbial indictor in surface water, does not manifest the
total quality of surface water. That is the reason why the authors use the indicator of WQI total.
Table 2. The difference between interpolated value and sample value.
No
Geographical coordinate
X (m)
Interpolated value
(WQI total)
Sample value
(WQI total)
Error
Y (m)
1
539287
1060375
59
63
4
2
550197
1021194
61
54
7
3
545572
1000840
16
17
1
The interpolated results presents the quality of surface in Bac Lieu province is getting
polluted at medium level (example: Quan Lo- Phung Hiep canal and Bac Lieu- Ca Mau canal)
and high level (example: Chua Phat canal and Huyen Ke canal) [17]. Therefore, some solutions
should be implemented to deal with this situation such as (1) The wastewater from aquaculture,
from industry, form households, hospitals, commercial centres (especially in Bac Lieu city,
Phuoc Long, Gia Rai, Hoa Binh towns)… should be collected and treated before it runs into
received environment (2) Any violation should be punished strictly (3) Bac Lieu Government
should invest in construct the wastewater treatment systems (4) Last but not least, local
government also focuses on diking and landslide prevention.
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Ton Nu Phuong Anh, Le Trong Dieu Hien, Pham Van Tat
The Table 2 presents the errors between interpolated value and sample value of WQI total.
It is obvious that there are occurrences of errors; this is because in GIS, IDW interpolation was
applied, the predicted value (unmeasured value) would be assigned by the value of measured
value which is closest to the predicted value. Therefore, a number of samples are not great (30
samples) would lead to the errors in interpolation. The interpolated result would be better when
the number of sample is great. On the other hand, this study just considers the IDW method,
does not consider the influence of other conditions such as speed of flow, the rainfall or
discharged output. However, the errors are not consider and accepted because although there are
errors, the quality of water is still in the rank of Table 1. For example, both 59 and 63 lie are in
the rank of Good water quality. The similarly results are considered with other value.
4. CONCLUSION
According to Carbone et al [6] and Shamsi [18], the multiple systems, data sources, and
enormous quantities of time are required in water resource management. GIS is a power tool
which could satisfy these requirements. It could also integrate the metadata into dynamic models
and facilitate increased data sharing among the environmental modeling community [18,19].
Several new local, state and federal on the world have been applied this technology in their
water management activities and Vietnam is no exception. In this work, GIS applications were
combined with hydrologic data of surface water in Bac Lieu to result the interpolated maps of
presenting the quality of surface water according to WQI of indicators pH, BOD 5, COD, NH4+,
TSS and Coli form. Then, authors made a comparison the change of the water quality through
years to find out the tendency of pollution level. This result would contribute to increase both
environmental protection and coverage of human water demands in Bac Lieu province.
However, there are only six indicators which were collected and interpolated in this paper. Some
indicators such as Cl- and Fe should be monitored to discover the pollution level of salty in
surface water in Bac Lieu province. Moreover, there is existence of indicator PO 43- in the
formula calculating the WQI. Therefore, this indicator should be also monitored.
5. REFERENCE
1. Bộ Tài nguyên và Môi trường - Quyết định về việc ban hành sổ tay tính toán chỉ số chất
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Nhà xuất bản ĐH Quốc Gia TP.HCM, 2010, 120-200.
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trạng môi trường tỉnh Bạc Liêu giai đoạn 2006-2010”.
6. Vietnam News - Bac Lieu waters spoiled’, Vietnam News, The national English language
daily, (2014).
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Zoning the surface water quality according to water quality index (WQI) in Bac Lieu province
7. Yammani, S - Groundwater quality suitable zones identification: application of GIS,
Chittoor area, Andhra Pradesh, India,’Environ. Geol. 53 (1) (2007) 201–210.
8. Rangzan K, Charchi A, Abshirini E and Dinger J - Remote sensing and GIS approach for
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& Geoscience (IJRSG) 2 (2011) (3) 24-29.
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tỉnh Bạc Liêu”, (2013), 50.
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17. Hoanh C.T., Tuong T.P., Kam S.P., Phong N.D., Ngoc N.V. & Lehmann E. - Using GISlinkedhydraulic model for managing water quality conflict for shrimp and rice production in
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Proceedings of MODSIM 2001, International Congress on Modelling and Simulation.
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(GIS) in water resources, A review water Resources Management 10 (1996) 251-277.
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Ton Nu Phuong Anh, Le Trong Dieu Hien, Pham Van Tat
PHÂN VÙNG CHẤT LƯỢNG NƯỚC MẶT TỈNH BẠC LIÊU THEO CHỈ SỐ WQI
Tôn Nữ Phương Anh1, Lê Trọng Diệu Hiền2, Phạm Văn Tất1, *
Bộ môn Môi trường, Trường Đại học Hoa Sen, Thành phố Hồ Chí Minh
1
2
Khoa Môi trường, Trường Đại học Thủ Dầu Một, Tỉnh Bình Dương
*
Email: vantat@gmail.com
TÓM TẮT
GIS là một công cụ rất hữu hiệu được sử dụng nhiều trong lĩnh vực quản lý môi trường và
đặc biệt là trong lĩnh vực về quản lý nguồn nước hay đánh giá chất lượng nước. Những tính chất
liên quan về địa chất hay không gian của hệ thống sông ngòi có thể được thể hiện bằng công cụ
GIS. Tuy nhiên khả nằng dự đoán và phân tích tương quan là chức năng mạnh nhất của GIS.
Những chức năng này hữu dụng và cần thiết trong giải quyết những vấn đề về nguồn nước.
Trong nghiên cứu này, chúng tôi ứng dụng công cụ nội suy trong GIS kết hợp với phần mềm
Surfer để phân vùng chất lượng nước mặt ở tỉnh Bạc Liêu theo các thông số pH, DO, BOD 5,
COD, TSS, NH4+ and coli form. Một loạt các dữ liệu liên quan đến các thông số này trong vòng
5 năm từ 2007-2010 và năm 2013 được thu thập để làm dữ liệu đầu vào cho quá trình nội suy.
Sau đó, các bản đồ nội suy của các thông số qua các năm được xây dựng để đánh giá chất lượng
nước mặt tỉnh Bac Liêu. Ngoài ra, những biện pháp quản lý nguồn nước mặt cũng được đề xuất
trong nghiên cứu này.
Từ khóa: chất lượng nước mặt, GIS, nội suy, quản lý môi trường.
10