ORIGINAL ARTICLE
Water quality assessment in terms of water quality index (WQI):
case study of the Kolong River, Assam, India
Minakshi Bora
1
•
Dulal C. Goswami
1
Received: 29 February 2016 / Accepted: 18 July 2016 / Published online: 27 July 2016
Ó The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract The Kolong River of Nagaon district, Assam has
been facing serious degradation leading to its current
moribund condition due to a drastic human intervention in
the form of an embankment put across it near its take-off
point from the Brahmaputra River in the year 1964. The
blockage of the river flow was adopted as a flood control
measure to protect its riparian areas, especially the Nagaon
town, from flood hazard. The river, once a blooming dis-
tributary of the mighty Brahmaputra, had high navigability
and rich riparian biodiversity with a well established
agriculturally productive watershed. However, the present
status of Kolong River is highly wretched as a consequence
of the post-dam eff ects thus leaving it as stagnant pools of
polluted water with negligible socio-economic and eco-
logical value. The Central Pollution Control Boa rd, in one
of its report has placed the Kolong River among 275 most
polluted rivers of India. Thus, this study is conducted to
analyze the seasonal water quality status of the Kolong
River in terms of water quality index (WQI). The WQI
scores shows very poor to unsuitable quality of water
samples in almost all the seven sampling sites along the
Kolong River. The water quality is found to be most
deteriorated during monsoon season with an average WQI
value of 122.47 as compared to pre-monsoon and post-
monsoon season having average WQI value of 85.73 and
80.75, respectively. Out of the seven sampling sites,
Hatimura site (S1) and Nagaon Town site (S4) are
observed to be the most polluted sites.
Keywords Kolong River Embankment Post-dam
effects Pollution Water quality index (WQI)
Introduction
Freshwater sources in the form of rivers are very much
essential for the sustenance and well being of a hale and
hearty society. Unfortunately, during the last few decades
these natural resources are continuously being tainted all
around the world for the sake of development and flood
hazard mitigation. However, north-east India is blessed
enough to have bounty of accessible freshwater sources in
the form of various rivers, streams, lakes, swamps, mar-
shes, etc., with the mighty Brahmaputra river along with its
numerous tributaries bifurcating the whole area. These
rivers are the lifelines of these regions acting like arteries
in our body and are supporting the social, ecological, cul-
tural and overall environmental setup. Additionally, these
rivers along with their numerous wetlands formed and feed
by them also serve as the refuge to diverse organisms and
sub-ecosystems.
Natural flow patterns are the heartbeat of a river. Each
component of a flow regime—r anging from low flow to
seasonal floods play a vital role in shaping a river
ecosystem and livelihoods of river-dependent communi-
ties. Until recently, rivers of north-eastern region of India
were in pristine free-flowing and unpolluted condition.
However, during the last few decades in the pursuit to cope
up with rest of the world in terms of development, our
freshwater resources are continuously being tainted and
deteriorated to an inconceivable stage. Out of various
negative anthropogenic acts being perpetuated over our
rivers those requiring special mention are water pollution
from various point and non-point sources, damming (both
& Minakshi Bora
bora1989@rediffmail.com
1
Department of Environmental Science, Gauhati University,
Guwahati, Assam, India
123
Appl Water Sci (2017) 7:3125–3135
DOI 10.1007/s13201-016-0451-y
for hydroelectricity generation as well as flood control),
over abstraction and human encroachment. Ecosystems and
communities dependent on natural flow regime have
already experienced the adverse impacts of altered flow
regimes due to engineering interventions. In nutshell,
dams/embankments have regulated and fragmented the
flows of our rivers—often irreplaceably and as a result, our
rivers are inching towards their ecological and hydrological
death.
Kolong River of Nagaon district in Assam is an
appropriate example of such human intervention which is
facing the gripe for the past fifty years. The Kolong River
which once used to be a prize possession for the people of
the state in general and for the people of Nagaon in
particular, is presently gasping on its death-bed because
of the ruthless and untenable act perpetrated on it in the
name of engineering solution to the increasing flood
hazard attributed to it in the aftermath of the great Assam
earthquake of 1950.
During the years preceding 1964, primarily as a conse-
quence of the great Assam earthquake of 1950 (measuring
8.7 on Richter scale), this region experienced repetition of
large floods due mainly to raised bed level of the
Brahmaputra through massive aggradation vis-a
`
-vis the bed
level of Kolong, leading thereby to its higher flood levels
inundating adjoining low-lying areas like Nagaon. Mainly
as a response to the increasing food hazard faced by the
district administrative headquarter, i.e., the Nagaon town,
an ad hoc flood cont rol measure was undertaken by con-
structing an earthen embankment, known as Hatimura
dyke, across the river’s take-off point near Hatimur a in the
year 1964. This drastic human intervention has end up in
converting the once free flowing river into a string of
alternating dry stretches and stagnant pools during the
decades that fol lowed (Bora and Goswami 2014). The river
in the present scenario with negligible self-purification
capacity is facing severe anthropogenic pressure and acts
as the receiver of huge amount of point and non-po int
pollutants. Consequently, the Kolong River is listed among
the 275 most polluted rivers of India by the Central Pol-
lution Control Board (CPCB 2015). Furthermore, drastic
changes in landuse/landcover (LULC) pattern of the
Kolong River basin have been reported by Bora and Gos-
wami (2016). To restore the health of the Kolong River, a
sustainable river-restoration plan seeks its exigency. Thus,
the overall aim of the present investigation is to finalize the
prevailing water quality inventory of the Kolong River
based on WQI and then to propose effect ive measures to
revitalize the Kolong River withi n the milieu of the con-
tinued urbanization by restoring it to its natural state, while
allowing the river syst em to continue to support flood
management, landscape development and recreational
activities.
A water quality index (WQI) helps in understanding the
general water quality status of a water source and hence it
has been applied for both surface and ground water quality
assessment all around the world since the last few decades
(Samantray et al. 2009; Sharma and Kansal 2011;Alam
and Pathak 2010; Sebastian and Yamakanamardi 2013;
Seth et al. 2014; Tyagi et al. 2013; Bhutiani et al. 2014;
VishnuRadhan et al. 2015; Yadav et al. 2015; Dash et al.
2015; Krishnan et al. 2016; Kaviarasan et al. 2016). The
main purpose of developing a WQI is to transform a
complex set of water quality data into lucid and
exploitable information by which a layman can know the
status of the water source (Akoteyon et al. 2011; Balan
et al. 2012). WQI aims at giving a single value to the water
quality of a source by translating the list of parameters and
their concentrations p resent in a sample into a single value,
which in turn provides an extensive interpretation of the
quality of water and its suitability for various purposes like
drinking, irrigation, fishing etc. (Abbasi 2002).
Although, water pollution is a chief matter of appre-
hension in regard to Kol ong River, the water quality issue
of the river has not yet got its due importance. However,
few scientific investigations on water quality assessment of
Kolong River (Saikia and Sarma 2011; Barbaruah et al.
2012; Khan and Hazarika
2012; Bora and Goswami
2014, 2015) have been reported. Fluoride geochemistry of
Kolong River was discussed elaborately by Saikia and
Sarma (2011). They found that the fluoride concentration
of groundwater samples collected from Kolong River basin
ranged between 0.03 and 5.68 mg/l. Khan and Hazarika
(2012) reported that the increased pollution level of Kolong
River water is mainly attributed by the discharge of various
types of domestic and commercial waste water, sewage and
effluent. Moreover, the truncated river flow accompanied
with diminished flow velocity has reduced the self-assim-
ilation and self-purification capacity of the Kolong River
(Bora and Goswami 2015). Ironically, literature survey
revealed the fact that so far no detailed work on WQI has
been carried out for Kolong River. Hence, in continuation
of our previous work (Bora and Goswami 2014, 2015), the
present investigation is carried out to establish the general
pollution trend of the river and to determine the aptness of
the water for various pu rposes based on a set of observed
water quality parameters. In this context, an attempt has
been made to determine the fitness of various water sam-
ples collected along Kolong River for different uses, using
the ‘weighted arithmetic index method’ given by Brown
et al. (1970).
Study area
This study is conducted in the Kolong River which is an
important river of middle Assam. The Kolong River with a
3126 Appl Water Sci (2017) 7:3125–3135
123
total length of about 212 km is a distributary (Suti in local
language) of the Brahmaputra which branches out from the
near Jakha labandha, about 77 km upstream of Nagaon, and
meets it again at Kajalimukh near Guwahati in a joint
channel with the Kopili River—a major south bank tribu-
tary of Brahmaputra that flows into Kolong near Jagib-
hakatgaon of Morigaon district (Fig. 1). The river during
its course traverses through the plains of Nagaon, Mori-
gaon and Kamrup districts of Assam. During the course
from source to mouth the Kolong River is joined by three
main tributaries namely Misa, Dizu and Haria.
Materials and methods
Water samples were collected from seven sampling sites
viz. Hatimura (S1), Missamukh (S2), Dizumukh (S3),
Nagaon town (S4), Hariamukh (S5), Jagibhakatgaon (S6)
and Kajalimukh (S7) during pre-monsoon (PRM), mon-
soon (MON) and post-monsoon (POM) seas on over a
period of three years, i.e., from January 2012 to November
2015. The details of sam pling sites are shown in Fig. 2.
Various physico-chemical parameters of the water sam-
ples were analyzed by following the standard methods of
APHA (2005) and Trivedy and Goel (1986). A set of ten most
commonly used water quality parameters namely pH, elec-
trical conductivity (EC), total dissolved solid (TDS), total
suspended solid (TSS), chloride, total alkalinity (TA), total
hardness (TH), dissolved oxygen (DO), biochemical oxygen
demand (BOD) and sulphate which, together, reflect the
overall water quality of the Kolong River were selected for
generating the water quality index (WQI). Calculation of
WQI was carried out by following the ‘weighted arithmetic
index method’ (Brown et al. 1970), using the equation:
WQI ¼
X
Q
n
W
n
.
X
W
n
where Q
n
is the quality rating of nth water quality parameter,
W
n
is the unit weight of nth water quality parameter.
The quality rating Q
n
is calculated using the equation
Q
n
¼ 100 ½ðV
n
V
i
Þ=ðV
s
V
i
Þ
where V
n
is the actual amount of nth parameter present, V
i
is
the ideal value of the parameter [V
i
= 0, except for pH
(V
i
= 7) and DO (V
i
= 14.6 mg/l)], V
s
is the standard
permissible value for the nth water quality parameter.
Unit weight (W
n
) is calculated using the formula
W
n
¼ k=V
s
where k is the constant of proportionality and it is
calculated using the equation
k ¼ 1
.
X
1=V
s
¼ 1; 2; ...; n
hi
:
The water quality status (WQS) according to WQI is
shown in Table 1.
Results and discussions
For calculating WQI, the prime pre-requisite is the results
of various water quality analyses. The statistical summary
of the selected water quality parameters at various
Fig. 1 Map showing the study
area
Appl Water Sci (2017) 7:3125–3135 3127
123
sampling sites of the Kolong River during PRM, MON and
POM season is presented in Table 2.
pH generally signifies the degree of acidity or alkalinity
of a water sample. The average pH values for PRM, MON
and POM season were 7.11 ± 0.52, 6.65 ± 0.06 and
6.57 ± 0.34, respectively. Although the average pH values
were within the BIS prescribed limits, however, the mini-
mum pH values during PRM and POM were below the
prescribed limit, i.e., 6.5–8.5. Electrical conductivity
measures the electric current carrying capacity of a water
sample and is directly related to the dissolved ions present
in the water. EC was measured using a digital conductivity
meter and the results were expressed in microsiemen/cen-
timeter. Observed EC values for the water samples of the
Kolong River ranged between 1017–1900 lS/cm (±340),
60–410 lS/cm (±122) and 90–199 lS/cm (±50) during
PRM, MON and POM season, respectively, with the values
exceeding the ICMR standard of 300 lS/cm at some of the
sampling sites during PRM and MON seasons.
TSS and TDS are, respectively, the direct measurement
of total suspended and dissolved particles present in a
water sample and BIS desirable limit for both the
parameters are 500 mg/l. Suspended and dissolved solids
are both organic as well as inorganic in nature. The con-
centration of TSS for the water samples ranged from 65 to
107 mg/l (±13.7) during PRM, from 97.88 to 178.21 mg/l
during MON and from 48 to 78 mg/l during POM season,
which were well within the BIS desirable limit of 500 mg/l.
Similarly, TDS values were also within the desirable limit
with mean values of 313.55 mg/l (± 44.97), 257.69 mg/l
(±32.9) and 153.28 mg/l (±18.66) during PPM, MON and
POM season, respectively.
Hardness implies the lather forming capacity of a water
sample and the two cations mainly responsible for hardness
of water are calcium and magnesium. The observed values
of total hardness for the water samples of the Kolong River
during PRM, MON and POM season ranged from 52 to
164 mg/l (±41.03), 88 to 288 mg/l ( ±70.05) and 72 to
296 mg/l (±87.62), respectively, and the values were
within the desirable limit of 300 mg/l. Based on the
hardness values, Kolong River water generally falls under
moderately hard to hard water category.
Chloride is one of the important WQ parameter and is
widely distributed in nature in the form of salts of sodium
Fig. 2 Map showing sampling
sites
Table 1 WQI range, status and possible usage of the water sample (Brown et al. 1972)
WQI Water quality status (WQS) Possible usage
0–25 Excellent Drinking, irrigation and industrial
26–50 Good Drinking, irrigation and industrial
51–75 Poor Irrigation and industrial
76–100 Very poor Irrigation
Above 100 Unsuitable for drinking and fish culture Proper treatment required before use
3128 Appl Water Sci (2017) 7:3125–3135
123
(NaCl), potassium (KCl) and calcium (CaCl
2
). Various
sources contributing chloride in water are leaching from
various rocks by the process of weathering, surface run-off
from inorganic fertilizers dependent agricultural fields,
irrigation discharge, animal feeds, etc. The average chlo-
ride concentration for the studied water samples during
PRM, MON and POM season were 45.44 to 94.56 mg/l
(±15.6), 45.44 to 71 mg/l (±8.6) and 19.88 to 34.08 mg/l
(±5.2), respectively. The observed chloride concentrations
were well within the desirable limit cited by BIS, i.e.,
250 mg/l.
Amount of total oxygen dissolved in a water body is
termed as dissolved oxygen (DO) and its concentration
depend on physical, chemical and biological activities of
the water body. Estimation of DO is very much essential in
water pollution control. A DO level of 4–6 mg/l is opti-
mum range for a good water quality sustaining aquatic life.
Water sample with DO concentration below this optimum
range is expected to be pollut ed. The mean DO values
ranged from a minimum of 2.96 mg/l (±1.07) during MON
season to a maximum of 9.22 mg/l (±4.9) during PRM
season. DO is nil (0 mg/l) at site S1 during PRM, attributed
chiefly by the high stagnancy of the water source due to
lack of sufficient flow.
The total amount of oxygen required by aerobic micro-
organisms for complete degradation of organic was tes
present in a water body is termed as biochemical oxygen
demand (BOD). Thu s, BOD is an indicator of organic
pollution with higher values indicating higher levels of
organic pollution (Patel et al. 1983). BOD values above
5 mg/l are undesirable and the present analysis revealed the
mean BOD values as 8.19 mg/l (±3.6), 10.98 mg/l (±3.9)
and 7.96 mg/l (±3.8) during PRM, MON and POM season,
respectively, with values exceeding the desirable limit. The
higher values of BOD emphasized the presence of promi-
nent organic pollution source near the sampling sites.
Occurrence of sulphate in river water is mainly natural
in nature contributed chiefly by mineral sources like gyp-
sum, etc. Although in small concentration sulphate is
harmless, however, high concentration of sulphate in
drinking water may cause various intestinal diseases. Mean
sulphate concentration of the water samples under inves-
tigation varied from 12.6 mg/l (±5.4) during PRM season
to 15.45 mg/l (±4.9) during MON season and the values
were within the standard limit of 150 mg/l as per BIS.
Total alkalinity is the capability of an aqueous solution
to neutralize an acid. Alkalinity is due to the various car-
bonate, bicarbonate and hydroxide ions present in water.
The mean concentration of alkalinity in water samples was
observed to be 210.7 mg/l (±70.5), 231.43 mg/l (±96.5)
and 154.14 mg/l (±58.1) during PRM, MON and POM
season, respectively. The mean alkalinity values exceeded
the BIS prescribed limit of 120 mg/l during all the seasons.
WQI analysis
The first step in calculation of WQI following ‘weighted
arithmetic index’ method involves the estimation of ‘unit
weight’ assigned to each physico-chemical parameter
considered for the calculation. By assigning unit-weights,
all the concerned parameters of different units and
dimensions are transformed to a common scale. Table 3
shows the drinking water quality standards and the unit-
weights assigned to each parameter used for calculating the
WQI. Maximum weight, i.e., 0.366 is assigned to both DO
and BOD, thus suggesting the key significa nce of these two
parameters in water quality assessment and their consid-
erable impact on the index.
Table 2 Descriptive statistics for the water quality parameters of the Kolong River
Parameter Pre-monsoon Monsoon Post-monsoon
pH 7.11 ± 0.52 (6.31–7.59) 6.65 ± 0.06 (6.59–6.75) 6.57 ± 0.34 (6.23–7.12)
EC (lS/cm) 1302.3 ± 340 (1017–1900) 170 ± 122 (60–410) 140 ± 50 (90–199)
TDS (mg/l) 313.55 ± 44.97 (250–370) 257.69 ± 32.9 (210.75–299) 153.28 ± 18.66 (122–175)
TSS (mg/l) 81.14 ± 13.7 (65–105) 144.05 ± 27.37 (97.88–178.21) 65.68 ± 16.04 (48–78)
TH (mg/l) 90.86 ± 41.03 (52–164) 140.71 ± 70.5 (88–288) 183.43 ± 87.62 (72–296)
Cl
-
(mg/l) 69.12 ± 15.6 (45.44–94.56) 55.6 ± 8.6 (45.44–71) 25.52 ± 5.2 (19.88–34.08)
DO (mg l
-1
) 9.22 ± 4.9 (0–13.77) 2.96 ± 1.07 (0.81–4.05) 7.8 ± 3 (3.4–12.83)
BOD (mg/l) 8.19 ± 3.6 (4.2–13.3) 10.98 ± 3.9 (7.06–17.8) 7.96 ± 3.8 (4.3–15.01)
SO
4
2
(mg/l)
12.6 ± 5.4 (6.64–21.64) 15.45 ± 4.9 (9.82–21.9) 13.27 ± 4.35 (7.07–20.74)
TA (mg/l) 210.7 ± 70.5 (125–300) 231.43 ± 96.5 (100–360) 154.14 ± 58.1 (100–255)
Values are expressed in mean ± SD (the values in parentheses denotes the range of each parameter)
Appl Water Sci (2017) 7:3125–3135 3129
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