Water quality in the Tapi River

Surat is located along the river Tapi which is west-flowing and drains into the Gulf of Khambat in the Arabian Sea. The Tapi is the main source of water for Surat and the city’s dependence on groundwater for its daily needs is only 10 per cent (Parthasarathy & Raja, 2013). Going by the experience in Ahmedabad, where the Sabarmati receives all the industrial effluents and sewage, it is natural for us to analyse the water quality in the Tapi in Surat. The water quality in the Tapi is analysed at two locations: (1) Kathor, which is upstream of Surat city and (2) ONGC Bridge, which is near Hazira and downstream of the city, before the river meets the Gulf of Khambat. The data analysed is the monthly data for the period of April 2013 to December 2017 and consists of 57 readings. The analysis for the water quality in the Tapi river is summarised in Table 9.1.

We have observed that the average values for all the parameters of river water quality, for the study period, are found to be within the desirable limits, irrespective of their location—upstream or downstream of the city. However, when we analyse the monthly details (Appendix II), it can be seen that there is some deterioration in the quality at the downstream monitoring station.

The pH of the river water quality is always within the permissible range of 6.5—8.5, irrespective of the monitoring location. The average value of the pH for the study period at the upstream end is 8 and at the downstream end is 7.7.

The average value for the DO at the upstream end is 7 mg/1. The monthly monitoring details reveal that during the study period there are no readings at the upstream end when the DO is observed as less than 5 mg/1. However, the average value for the DO reduces to 5 mg/1 at the downstream end, which means that although there is some degradation in the river water quality as it flows through the city, the average value is still within the desired levels. For the DO, at the downstream end, out of 57 monthly readings, there are 24 occasions when it is observed as below the desired value of 5 mg/1.

The average value for the BOD at the upstream end is only 1 mg/1 and at the downstream end, it is 3 mg/1, again within the permissible limits. Out of 57 monthly observations, there are only two occasions when the BOD levels at the upstream end are more than 3 mg/1 (at 4.4 mg/1), which still falls within the last priority for remediation as per the CPCB criteria (Chapter 6, Table 6.1). At the downstream end, there are ten observations where the BOD values are more than 3 mg/1. The maximum observed value is still 16 mg/1, which is much lower than the BOD values observed in the Sabarmati. The levels for the COD display a similar trend, though COD is not a parameter included in the ‘designated best use criteria.’ The lower COD values in the Tapi water indicate that the river is not polluted by industrial effluents.

TABLE 9.1 Tapi River water quality: Upstream and downstream of Surat city

Source: Unpublished data from GPCB.

The average levels of total coliforms in the river, a direct indicator of faecal contamination of the river from sewage, are also within the permissible limit of 500 MPN/100 ml, both at the upstream and at the downstream monitoring points, though on a few occasions the maximum values are more than the permissible levels.

The water quality in the Tapi, unlike the Sabarmati, is observed to be good. These observations are the reason that the Tapi in particular, and Surat in general, has not been included in the list of critically polluted areas in Gujarat. The point to be pondered further is whether the somewhat better water quality in the Tapi, in contrast to the Sabarmati, is an indicator of pollution being under control in Surat or whether there is more to it than meets the eye. It is difficult to accept ‘pollution under check’ if we consider what was learnt from Ahmedabad, especially because Surat is a hub of the textile sector, which is known to be water pollution intensive.

For further analysis, and to have a better spatial understanding of the situation, the industrial areas, the CETPs, the STPs and the monitoring points of the GPCB have been mapped and presented in Figure 9.1. The details when plotted on the map reveal that all the industrial estates, the CETPs as well as the STPs are located near some creek (khadi) or the other. It, therefore, becomes necessary to analyse the water quality of these creeks which actually receive the discharge from the CETPs and the STPs in Surat. All the creeks finally meet the Mindola estuary, which ultimately flows into the gulf of Khambat.