Water quality of Tehri dam reservoir and contributing rivers in the Himalayan region, India

In nature, the main resources for the availability of water are ponds, lakes, tanks, rivers, and shallow water basins. The water quality available in these water bodies is subjected for continuous change which is due to eutrophication of these water bodies. The water quality often becomes a problem to sustain it. The present investigation was undertaken to study water quality parameters of the Tehri dam reservoir and contributing rivers with an objective to indicate changes in the quality of waters in the contributing rivers and in the reservoir after impoundment and to suggest suitable measures to protect reservoir water quality. Temperature of Bhagirathi river water ranged between 16 and 28 °C while Tehri reservoir water showed it in between 29.5 and 32 °C. DO levels in the reservoir varied between 8.4 and 9.6 mg/L which are similar to river water (8.4–9.4 mg/L). Thus, there is no effect of impounding of river water on the DO which is sufficient for sustaining fisheries and other aquatic lives. Tehri dam reservoir water shows lower turbidity as compared to river water. River Bhagirathi had unique features of the presence of certain radioactive elements and specific groups of coliphages that are likely to maintain self-preservation of the water. DO, COD, BOD, heavy metals, radioactive elements, etc., were within permissible limits, as per categories ‘B‘ and ‘C’, specified by CPCB for outdoor bathing and drinking water source with conventional treatment. However, such waters also fulfill categories ‘D’ and ‘E’, designated for propagating wildlife/fish and irrigation/cooling purpose, respectively. Biological parameters of phytoplankton and zooplankton were analyzed to determine the effect of impounding on the flora and fauna of reservoir, wherein plankton diversities in river and reservoir samples were comparable. The Palmer’s Pollution Index ranged between 3 and 5 for phytoplankton while Shannon–Wiener Diversity Index varied from 2 to 2.86 for zooplankton, indicating low to moderate productive waters.