4. Site Suitability Analysis for Identification of Riverbank Filtration (RBF) Sites: Case Study of the Alaknanda River Basin

Demographic and geographic locations of various towns in the study area having proximity to the river like Alaknanda along with its tributaries Mandakini and Pindar make them suitable target locations to get the complications of water shortages. The rivers are malevolent when it comes to supply of water in balance in the times of crucial need as these rivers are basically glacier-fed rivers and their discharge varies with seasonal changes. Due to seasonal variation, only limited direct water abstraction is possible and it results into shortage of water for supply. The potential locations of alluvial deposits were identified by generating thematic GIS maps of land use, terrain, and geology, using a weightage factor. The sites thus identified were characterized using groundwater flow modeling for their optimal abstraction rate, travel time, and flow field of the induced bank filtrate. The purification capacity of the aquifer was estimated for the removal of organic micro-pollutants (OMP) using the SOMA tool and was correlated with the river meandering sinuosity (S). Along the 100 km river stretch, 8–9 locations were found suitable for indirect surface water abstraction. An S-value of around 1.4 resulted in the highest purification capacity and a bank filtrate portion of 44–100% in the abstracted water from 14 wells located 75 m from the riverbank under the defined conditions. The calculated removal of different OMP was 26–91%. Based on this study, potential riverbank filtration (RBF) sites were identified in seven large towns and cities Rishikesh, Ramnager, Haridwar, Dehradun, Roorkee, Kotdwar, and Haldwani having a total population of 1.23 million situated in the flood plains in the Himalayan area.