Water resources management in the Ganges Basin: reducing the seasonality of water availability and identifying potential processes for contamination of arsenic-safe deep groundwater
Date
2016
Authors
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Publisher
University of Delaware
Abstract
This study addresses two major water resources management issues in the Ganges River Basin. First, natural seasonality in river flow together with a lack of management in the upper Ganges Basin causes extensive flooding all over the basin during the monsoon season and little or no flow in the Ganges River in the lower basin area during the dry season. Dry season flow in the Ganges is essential for irrigation and for maintaining the salinity balance in the Ganges estuary, crucial for the survival of the world’s largest mangrove forest, the Sundarbans. Second, dangerous concentration of naturally occurring Arsenic (As) in shallow groundwater, the drinking water source for tens of millions of people, is ubiquitous in the lower Ganges Basin, i.e. the Bengal Delta Plain. Deep (>150 m depth) groundwater in this area is As-safe and the primary As mitigation option. However, vulnerability of this important deep resource to future contamination in this highly heterogeneous Bengal Delta aquifer is not well characterized. ☐ In Chapter 2, this study shows that conjunctive use of groundwater and surface water involving seasonal subsurface storage of a portion of the monsoonal river flow has the potential to reduce flood intensity during the monsoon season and increase water availability during the dry season. In Chapter 3, this study identifies the effects of large-scale aquifer heterogeneity on contaminant transport and determines the vulnerability of As-safe deep groundwater to contamination near Dhaka city, a mega-city with one of the worst groundwater depletion cases in the world. It shows that concentrated pumping in Dhaka city is affecting water resources regionally in two ways, first, by lowering the hydraulic head in the deep aquifer in outlying areas and thereby making it inaccessible by typical hand-pumps and second, by creating fast, unpredictable contamination pathways that can contaminate the deep groundwater within decades. In Chapter 4, this study shows that deep (>150 m) groundwater is already As contaminated in an extensive area in the SW Bengal Basin where there are no clay layers present between the shallow Holocene and the deep Pleistocene aquifers. In these areas, a naturally deep groundwater flow system develops and transports contaminated water to depth. This study has direct implications for managing water resources in the transboundary Ganges River Basin and in similar areas around the world for enhancing dry season water supply and ensuring sustainability of deep groundwater for As mitigation. Additionally, it provides a better understanding of river-aquifer-human interactions over a large scale and determines the role of aquifer heterogeneity and intensive pumping on basin-scale groundwater contamination problems.
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Keywords
Aquifer heterogeneity, Arsenic, Deep groundwater, Ganges Basin, Mega-city pumping, Transboundary basins