2.3. Water quality index (WQI)
Water quality index (WQI) was developed on the basis ofAlberta
River Water Quality Index (Alberta WQI 2007) and Guideline Compliance
Index (GCI) (Kotze, 2008) using following equations.
WQI = 100 −
F2
1 + F2
2 + F2
3
1.732
(1)
where
F1 =
Number of water variables that do not meet objective
Total number of water varibles
× 100 (2)
F2 =
Number of test that do not meet objective
Total number of tests
× 100 (3)
F3 =
nse
0.01 nse + 0.01
(4)
where
nse (normalized sum of excursions) =
n
i=1departure
number of tests (5)
Here, departure is the number of times by which an individual
concentration is greater than or less than the objective (reference
value).
If the test value does not exceed objective then departure will
be calculated as:
departurei =
Failed testi
Objectivej
− 1 (6)
Ifthe test value does notfall below objective then departure will
be calculated as:
departurei =
Objectivej
Failed testi
− 1 (7)
WQI score was scaled from 0 to 100 whereas, each site was
classified into one of five quality classes, e.g. excellent (>80), good
(60–80), fair (40–60) and poor (