Riverbank filtration: a case study of four sites in the hilly regions of Uttarakhand, India

Riverbank filtration (RBF) schemes based on the filtration of the river water through adjacent aquifers have been successfully implemented in the plains globally. In the mountainous regions, alluvial aquifers are generally narrow and restricted to the riverbanks. The present study assesses the possibility and potential of RBF in the lower Himalayan region for drinking water supply. Production wells (18–30 m deep) were commissioned on the banks of the rivers (1) Alaknanda in Srinagar (546 m a.m.s.l.) and Kaleshwar (Karnaprayag; 778 m a.m.s.l.); (2) East Nayar in Satpuli (576 m a.m.s.l.) and (3) Mandakini in Agastyamuni (783 m a.m.s.l.) in Uttarakhand, India. Waters from the rivers, production wells, and hand pumps were analyzed for major ions, coliforms and stable isotopes (δ18O and δ2H). The wells delivered coliform- and turbidity-free water even during monsoon. The proportion of the bank filtrate was site specific and also varied from monsoon to non-monsoon periods. The Satpuli scheme draws almost completely bank filtrate round the year. The other three schemes substantially draw groundwater and its proportion increases in monsoon. In Srinagar, the well water was chemically similar to the ground water but isotopically similar to the river water. The region also has a complex hydrology with paths that deliver river water containing coliforms and even suspended silt up to ~ 0.5 km inland. A severe flooding event during the study period affected the RBF sites in Srinagar and Kaleshwar, thereby indicating the need to make RBF wells flood proof. In general, the study shows RBF to be an effective and sustainable option to supply drinking water in a few regions of lower Himalayas.