Question

Development of integrated marine water quality index â a gis approach

Answer 1

Development of Integrated Marine Water Quality Index – A GIS
Approach
RM NARAYANAN1
, K J SHARMILA1
, AND M RAMALINGAM2
1Dr. M.G.R Educational and Research Institute, University, Chennai 600 095, India
2
Institute of Remote sensing, Anna University, Chennai
Email: [email protected], [email protected]
1. Introduction:
In the present century the concerns of water resources
engineers are in line with available water quantity.
However, with the rise of pollution in water bodies the
attention has been shifted to the quality of water
resources. Water quality has attained as much
importance as water quantity (Sarkar and Abbasi 2006).
Water quality can be studied scientifically if an accurate
estimate of water quality is available in the form of an
index (Swamee and Tyagi 2000). Water quality
modeling is an ideal approach to simulate physical,
chemical, and biological changes in water bodies. Water
quality characteristics may be classified under three
broad categories: physical, chemical, and biological.
Within each category, a number of quality variables
may be employed. The suitability of a given water
source for an intended use depends on the magnitude of
these quality variables. The quality of water may be
good enough for drinking but not suitable for use as a
coolant in an industry. It may be good for irrigating
some crops but not suitable for irrigating some other
crops. It may be suitable for livestock but not for fish
culture. The quality is a function of anything and
everything the water might have picked up during its
journey from the clouds to the earth to the water body:
in dissolved, colloidal, or suspended form.
Different indices for assessing fresh and coastal water
quality were described with different steps and theories
for constructing a water quality index as discussed by
several authors (Smith 1990, National Research Council
(NRC), 2000). Results and interpretations of water
quality studies are variable (Moore et al 1997), however
there is an agreement in evaluating the tropic status of
coastal waters through phosphorus and nitrogen
concentrations (Jones and Lee 1982, Tomasky et al
1999; National Research Council (NRC) 2000). In this
study an attempt is made to derive the integrated water
quality index incorporating nine major physicochemical
and biological parameters PO4-P (µmol/l), NO3-N
(µmol/l), NO2-N (µmol/l), NH4-N (µmol/l) , DO (ml/l),
pH, Chl a (mg/m³), Sea Surface Temperature (˚C), Total
Suspended Matter (mg/l) for the Cuddalore and
Pondicherry coastal and offshore waters.
2. Water Quality Indices (WQI) - A Review
Horton’s (1965) water quality index which can be
considered as the forerunner of modern WQIs. Ten most
commonly measured water quality parameters were
used in Horton’s index are listed as Dissolved oxygen
(DO), pH, coliforms, specific conductance, alkalinity,
and chloride. Specific conductance was intended to
serve as an approximate measure of total dissolved
solids (TDS), and carbon chloroform extract (CCE) was
included to reflect the influence of organic matter. One
of the variables, sewage treatment (percentage of
population served), was designed to reflect the
effectiveness of abatement activities on the premise that
chemical and biological measures of quality are of little
significance until substantial progress has been made in
eliminating discharges of raw sewage. The index score
is attained with a sum of linear aggregation function.
The function comprises the ratio of weighted sum of
sub-indices and the sum of the weights which is
multiplied by two coefficients M1 and M2, which reflect
temperature and obvious pollution, respectively
1 2
i
n
i 1
i i
n
i 1 M M
w
w I
QI



 
Horton's index is easy to compute, even though the
coefficients M1 and M2 require some tailoring to fit
individual situations. The index structure, its weights
and rating scale are highly subjective as they are based
on the judgment of the author and a few of his
associates.
In the year 1970 Brown et al. has developed a water
quality index analogous in structure to Horton's index.
Greater care in selecting parameters towards developing
a common scale and assigning weights for which
elaborate Delphic exercises were performed. Browns
effort was supported by the National Sanitation
Foundation (NSF) and also referred as NSFWQI with a