Water Quality Indices (WQI) - Water Quality Management: Assessment and Interpretation - page 21

and subjective engineering assessments of water quality. Schaefer and Janardan
( 1979 ) also described another three indices using raw material and Chi-square
distribution. Two of these three mentioned indices, B1 and B2, do not exhibit
suf

cient bias to serve as a general measure of water quality, although they may
prove very useful in some speci c situations. The third index, index C, can be

applied quantitatively on monitoring stations. Steinhart et al. ( 1982 ) presented an
index to help summarize technical information on the status of, and trends in lake
water quality. Although the index was developed for the near-shore water of the
Great Lakes of North America, they claimed that the index concept was practicable
to other temperate lakes of generally high water quality. They attempted to mini-
mize the vulnerability of the index by employing the following strategies:

Selecting variables relevant to the uses of the lake under study

￿

Constructing rating curves based on established criteria

￿

Focusing on variables for which data are available and reliable

￿

Providing a reporting format that supplements the overall index number

￿

￿ Creating an index that can be revised easily to re ect new knowledge or

changing priorities

￿ Noting possible pitfall in suitable places, and

Providing an optional user guide on request to further safeguard against possible
nuisances.
House ( 1990 ) compared the results of the WQI applied to data collected by the
Severn Trent Water Authority for

￿

fiscal years 1978/1979 and 1979/1980, and the
value of the information derived using this index to that produced by the application
of the National Water Council classi cation employed by the United Kingdom

water industry. The study highlighted a number of advantages of using an index
over NWC classi

cation. Smith ( 1990 ) studied the WQI in New Zealand. The index
development in the country was linked to the legislation of recommended Water
Quality Standards. The indices were intended to assist in the dissemination of water
quality information, particularly to lay-people.
Barbiroli et al. ( 1992 ) proposed a new three structured method to obtain syn-
thetic quality indices for air and water. The index is unique in the sense that besides
the final indices, several intermediate indices are also computed, allowing the

environmental managers to have indices at different degrees of aggregate. This
particular methodology is permitted for:

Selection of physical, chemical, and biological parameters for air and water,
de

￿

nition of the variability of the selected parameters, the transformation of the
value assumed by the various parameters in sub indices characterizes by a variable
interval from 0, which represents minimum quality to 10, the maximum quality;

￿ Eventual weighting of parameters; and

￿ Construction of intermediate indices and the final synthetic index through the

use of a suitable aggregate function. The method was designed to be as general
and objective as possible, while still having the luxury of being adaptable to

t

particular situations.