Case studies on water quality - A presentation by ACWADAM

This presentation by ACWADAM deals with monitoring of water quality in a watershed. It describes the process of going about conducting a hydrogeological study of the watershed, right from the study of the basic geology to the importance of the quality of groundwater in the watershed. The main hydrogeological provinces of India are described - (a) Hard rock regimes: Crystalline rocks, Volcanic (Deccan basalt), (b) Alluvial regimes, and (c) Consolidated sedimentary regimes: Soft sedimentary, Hard sedimentary.

The case study of Karnataka helps understand the hydrogeology of peninsular metamorphics. It explains how porosity and permeability can be attributed to fracturing and weathering. The major fracturing is generally localized occurring in linear zones. Weathered zones account for majority of the storage whereas fractures allow relatively faster movement of water. Hard rock aquifers are limited in their extent and thickness and thus have relatively limited storage. The case study also explains the drainage overlay on geology, the geological cross-section, the history of groundwater development and based on these presents a treatment map.

The case study from North Bihar deals with the hydrogeology of alluvial areas. Thick, unconsolidated alluvium layers can store very large volumes of groundwater in extensive layers of sands or silt. Groundwater movement can be quite slow in alluvial deposits, but storage volumes are large. 

The plain region over which the Himalayan rivers flow are marked by heavy sediment load and high vulnerability to floods. Major rivers like Ganga, Gandak, Kosi that originate in the Himalayan region are perennial. The area is marked by quaternary alluvium which is primarily very loose unconsolidated sand, silt and clay with a high primary porosity. For ages dugwells that yielded sufficient quantity of water have been the main source of water for drinking and domestic purposes in the region. Increased dependence on hand pumps or ‘chapakals’ which are used for abstracting groundwater have taken people away from their traditional source i.e., dugwells.

This presentation is part of the training modules on planning, development and management of groundwater with special reference to watershed management programmes by ACWADAM. Please write to ACWADAM at acwadam@vsnl.net for sourcing these presentations.