The index was developed to evaluate the water-quality profile of river Ganga in its entire stretch and to identify the reaches where the gap between the desired and the existing water quality is significant enough to warrant urgent pollution control measures. This index was based on the NSF-WQI (Brown et al., 1970), with slight modifications in terms of weightages to confirm to the water-quality criteria for different categories of uses as set by the Central Water Pollution Board, India (Sarkar and Abbasi 2006).
To assign weightages, significance ratings were given to all the selected parameters. A temporary weight of 1 was assigned to the parameter which received highest significance rating. All other temporary weights were obtained by dividing each individual mean rating with the highest. Each temporary weight was then divided by the sum of all weights to arrive at the final weights. These weights were modified to suit the water quality criteria for different categories of uses.
Categorization Table
Table 1. Water class as per Index score.
Standards Required
None water quality standard is required for the calculation of this index method.
Variables Selection
A list of parameters was selected through Delphi.
Calculation of River Ganga Index:
where Wi is weight associated with ith water quality parameter, Ii denotes sub-index for ith water quality parameter. i = 1, 2, . . ., n and p denotes number of considered water quality parameters.
Sub-index values were obtained by using sub-index equations as shown in Table 1.
Table 2. Method of obtaining weights and modified weights
Table 3. Mathematical expression for sub-index values
Case Studies based on River Ganga Index
The River Ganga Index is regarded as one of the most holy and sacred rivers of the world from time immemorial. The evaluation of river water quality is a critical element in the assessment of water resources. The quality/potability of water that is consumed defines the base line of protection against many diseases and infections. The present study aimed to calculate Water Quality Index (WQI) by the analysis of sixteen physico-chemical parameters on the basis of River Ganga index of Ved Prakash, weighted arithmetic index and WQI by National sanitation foundation (NSF) to assess the suitability of water for drinking, irrigation purposes and other human uses. These three water quality indices have been used to assess variation in the quality of the River Ganga at monitored locations over an 11-year period. Application of three different indexes to assess the water quality over a period of 11 years shows minor variations in water quality. Index values as per River Ganga Index by Ved Prakash et al. from 2000 to 2010 ranged between medium to good, Index values as per NSF Index for years 2000–2010 indicate good water quality, while Index values as per the weighted arithmetic index method for the study period indicate poor water quality.
References
Bhutiani, R., Khanna, D. R., Kulkarni, D., & Ruhela, M. (2014). Assessment of Ganga river ecosystem at Haridwar, Uttarakhand, India with reference to water quality indices. Applied Water Science, 1-7, doi:10.1007/s13201-014-0206-6.