WATER QUALITY MODELING OF LAKE BANK FILTRATION AT NAINITAL USING MODFLOW-2005

Abstract

The water-supply system at Nainital, Uttarakhand is quite different in India and quite similar to places in Europe, where the water supply is met with bank filtration mechanisms. At Nainital, the nearby lake area out of total 12 tube wells there are 8 tube wells which are in good operating condition and are located at a distance of less than 100 m from the lake and are being used to extract the lake water as well as subsurface ground water flowing towards the lake. The study carried out is mainly to model the effects on water quality due to lake bank filtration that includes in reduction in bacteriological load and change in concentration of inorganic solids in the tube well water respectively due to filtration and dissolution of minerals from intervening dolomite strata. Ground water and surface water are hydraulically interconnected, but the interactions are difficult to observe and measure. In many situations, surface water bodies gain water and solutes from ground water system and in others the surface-water body is a source of ground-water recharge and causes changes in ground-water quality. As a result, withdrawal of water from streams can deplete ground water or conversely, pumping of ground water can deplete water in streams, lakes, or wetlands. Pollution of surface water can cause degradation of ground-water quality and conversely pollution of ground water can degrade surface water quality. Thus, effective land and water management requires a clear understanding of the linkages between ground water and surface water as it applies to any given hydrologic setting. In this thesis, groundwater model was simulated for a study area located in the Nainital lake, Nainital. A steady state, sub regional ground water flow model was developed for evaluation of water quality of Nainital lake using MODFLOW 2005. The single layer flow model simulated the existing hydrogeological system and the dominant processes involved in Lake Bank filtration processes controlling ground water flow. The flow path lines, draw-downs, hydraulic head contours and flow path lines were also determined. Flow path lines show the actual flow pattern of the Lake water during the pumping. It has been found that while total bacterial population is removed via filtration long before its natural die-off, flow of water through porous media of the intervening dolomite strata dissolves significant amounts of solids in the lake bank filtered water. ix