Data and methodology
Unless otherwise stated, the data analysed in this chapter has been acquired from the Gujarat Pollution Control Board (GPCB) and is unpublished. The GPCB is the nodal agency for environment protection at the state level. To assess the river water quality, monthly data has been analysed for the period from April 2011 to March 2017. The agency regularly monitors all major rivers and other water bodies in the state of Gujarat. All the infrastructure in the city to treat sewage and industrial effluents was installed prior to 2011. Even most of the storm water drains which used to discharge into the Sabarmati were intercepted and diverted to STPs as the Sabarmati river front was being developed. The analysis period therefore takes into account the impact of all the environmental infrastructure measures taken to treat pollution and improve the river water quality.
The river water quality has been studied at Hansol Bridge, upstream of Ahmedabad where the river enters Ahmedabad city, and at Miroli, downstream of Ahmedabad after the discharge of treated sewage and industrial effluents. The selection of the sampling locations is aimed to reflect the effects of the city on the health of the river. The upstream sampling location at Hansol Bridge denotes the water quality when the river enters the city and, therefore, the effects of the developments in the city on the river water quality are not reflected at this location. The Miroli monitoring point is the location after the treated sewage and the industrial effluents from the city have been discharged into the river and, thus, represents the effects of the city on the river water quality.
The river water quality has been studied with respect to ‘designated best use’ criteria set by the Central Pollution Control Board (CPCB) for water bodies. According to this concept, out of the several uses a water body is put to, the use that demands the highest quality of water is termed as the ‘designated best use.’ It is an accepted norm and reinforced by the National Green Tribunal (NGT) that all rivers must at least meet the ‘bathing water quality standards’ which means that the water quality should meet the norms which are: pH2 between 6.5 and 8.5; Dissolved Oxygen (DO3) > 5 mg/1; Bio-chemical Oxygen Demand (BOD4) < 3 mg/1; Total Coliforms (TCOL5) measured as MPN'VIOO ml < 500 or less. The river water quality has been studied with respect to these parameters. The analysis has been extended to include Chemical Oxygen Demand (COD) and heavy metals, because the river receives the treated industrial effluents from the city and these parameters directly reflect the pollution from industrial sources.
Many researchers (Lewczuk et al., 2016; Shah & Joshi, 2017) use Water Quality Index (WQI) as a tool to assess the quality of water. WQI represents a number of parameters in the shape of a single value, enabling easy interpretation of monitored data. There are many indices in use, and the most prominent among these is the WQI developed by the National Sanitation Foundation (NSF) of the United States. In India, the NSF WQI is used by the CPCB, with a slight modification in weights. A major limitation of the WQI is that the variations in a particular parameter gets camouflaged in the aggregated value and many a times, an important piece of information with respect to a particular parameter/s is not captured. We have, therefore, analysed the river water quality with respect to ‘bathing water quality standards.’
