Pradip K. Sikdar

Impacts on groundwater recharge areas of megacity pumping: analysis of potential contamination of Kolkata, India, water supply

Abstract Water supply to the world’s megacities is a problem of quantity and quality that will be a priority in the coming decades. Heavy pumping of groundwater beneath these urban centres, particularly in regions with low natural topographic gradients, such as deltas and floodplains, can fundamentally alter the hydrological system. These changes affect recharge area locations, which may shift closer to the city centre than before development, thereby increasing the potential for contamination. Hydrogeological simulation analysis allows evaluation of the impact on past, present and future pumping for the region of Kolkata, India, on recharge area locations in an aquifer that supplies water to over 13 million people. Relocated recharge areas are compared with known surface contamination sources, with a focus on sustainable management of this urban groundwater resource. The study highlights the impacts of pumping on water sources for long-term development of stressed city aquifers and for future water supply in deltaic and floodplain regions of the world. Editor D. Koutsoyiannis Citation Sahu, P., Michael, H.A., Voss, C.I., and Sikdar, P.K., 2013. Impacts on groundwater recharge areas of megacity pumping: analysis of potential contamination of Kolkata, India, water supply. Hydrological Sciences Journal, 58 (6), 1340–1360.

Numerical modelling of groundwater flow to understand the impacts of pumping on arsenic migration in the aquifer of North Bengal Plain

In this paper, numerical simulations of regional-scale groundwater flow of North Bengal Plain have been carried out with special emphasis on the arsenic (As)-rich alluvium filled gap between the Rajmahal hills on the west and the Garo hills on the east. The proposed concern of this modelling arose from development that has led to large water table declines in the urban area of English Bazar block, Malda district, West Bengal and possible transport of As in the near future from the adjacent As-polluted aquifer. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Modelling indicates that current pumping has significantly changed the groundwater flowpaths from pre-development condition. At the present pumping rate, the pumping wells of the urban area may remain uncontaminated till the next 25 yrs, considering only pure advection of water but some water from the As-polluted zone may enter wells by 50 yrs. But geochemical and other processes such as adsorption, precipitation, redox reaction and microbial activity may significantly retard the predicted rate by advective transport. In the rural areas, majority of the water pumped from the aquifer is for irrigation, which is continuously re-applied on the surface. The near-vertical nature of the flowpaths indicates that, where As is present or released at shallow depths, it will continue to occur in pumping wells. Modelling also indicates that placing all the pumping wells at depths below 100 m may not provide As-free water permanently.

Hydrogeological Assessment for Development and Management of Baseflow for Public Water Supply in Semi-arid and Fluoride Affected Hard Rock Areas

Worldwide, water resources in arid and semi-arid regions are finite; water tables are very low and run off is very high. Many of these areas have rapid growth of population resulting in increasing demand for water, deteriorating water quality, increasing environmental degradation and impending climate change. This situation requires more effort to assess water resources for local, regional and national planning and management in order to sustain development. Most of the economically viable development of water resources has already been implemented (Hamdy et al. 1995). The gap between demand and supply of water is increasing steadily in these regions. Therefore, it has now become imperative to develop innovative management options to close the gap between demand and supply of water which should take into consideration environmental concerns (Shadeed et al. 2007). In these areas groundwater is commonly the most important water resource. In many areas the groundwater has been over-exploited leading to the rapid fall in the water table or increase in the cost of exploitation because of the nature and disposition of the aquifer system. Baseflow which is a component of stream flow that is attributed to shallow groundwater discharge has generally been left unutilized. Therefore, development of baseflow for small to medium water supplies can be an important component of water management strategies in semi-arid areas of the world, in general and India, in particular.

Way Forward and Future Strategies

The average rainfall in South Asia is plentiful with respect to global standards. Most of this rain falls in relatively brief period during the monsoon, which also differs from region to region. The vagaries of the climate coupled with man-made climate change have driven the farmers, households and industries to increasingly depend on groundwater rather than surface water. This dependence has led to deterioration in the South Asia’s groundwater (Chap. 1), in general, and India’s groundwater (Chap. 2), in particular, in terms of over-exploitation, water quality deterioration, saline water intrusion and threat of land subsidence.

Problems and Challenges for Groundwater Management in South Asia

South Asia represents the southern region of the Asian continent, which comprises Afghanistan, Bangladesh, Bhutan, Maldives, Nepal, India, Pakistan and Sri Lanka. Topographically, it is dominated by the Indian Plate, which rises above sea level as Nepal and northern parts of India situated south of the Himalayas and the Hindu Kush. South Asia is bounded on the south by the Indian Ocean and on land by West Asia, Central Asia, East Asia, and Southeast Asia. South Asia covers about 5.1 million km2, which is 11.51% of the Asian continent or 3.4% of the world’s land surface area. The region is home to about 39.5% of Asia’s population and over 24% of the world’s population, making it both the most populous and the most densely populated geographical region in the world. The important rivers of South Asia are Ganges, Indus and Brahmaputra. These rivers have contributed to the rise and prosperity of some of the earliest civilizations in history and today are the source of livelihood for millions. The South Asian river basins, most of which have their source in the Himalayas, support rich ecosystems and irrigate millions of hectares of fields, thereby supporting some of the highest population densities in the world.

Pumping Test for Aquifers: Analysis and Evaluation

A pumping test is a field experiment in which a well is pumped at a controlled rate and water-level response (drawdown) is measured in one or more surrounding observation wells and optionally in the pumped well (control well) itself. Response data from pumping tests are used to estimate the hydraulic properties of aquifers, evaluate well performance and identify aquifer boundaries. Aquifer test and aquifer performance test (APT) are alternate designations for a pumping test.

Numerical Groundwater Modelling

A model is a representation of a physical system to predict its behaviour over time. Models may be conceptual, physical or mathematical. A conceptual model is a representation of a system using general rules and concepts. A physical model is a physical copy of the system in a reduced scale. A mathematical model is a representation of a system using mathematical concepts and language. Mathematical models may be analytical or numerical. Numerical models are those that use numerical time-stepping procedure to understand the models behaviour over time, whereas analytical models have a closed form solution which can be expressed as a mathematical analytic function. Analytical models do not require much data, but their application is limited to obtain solutions for simple problems. But numerical models are useful for handling more complicated problems.

Modelling the Potential Impact of Small-Scale Pumping Near Future Water Supply Wells in a Stressed Aquifer in South Western Bengal Basin on Groundwater Flow

This paper highlights the importance and effectiveness of groundwater modelling to water managers to protect stressed aquifer systems and to address conflicting interests and requirements in their decision making process. The study area is located in south western Bengal Basin which is a part of the lower deltaic plain of the River Ganga and lies on the eastern side of the River Hugli, a distributory of River Ganga. The aquifer is sandwiched between two aquitards and is semi-confined in nature. Steady-state model results indicate that groundwater pumping in a proposed housing complex in Kolkata city located just outside the eastern margin of East Kolkata Wetlands (EKW) far outweigh the topographic and geologic controls of the unperturbed groundwater flow system and shifts recharge areas towards the pumping centres. A small part of the groundwater is also recharged from far areas in the south and southwest. Drawdowns due to present and future pumping in the project area extend over a large area which results in interference effect in wells outside the project area. Therefore, part of the city wells will experience an additional fall in the piezometric head. The simulation results indicate that the aquifer is already stressed and therefore it may not be wise to abstract groundwater further. The required water for the housing complex may be obtained from other sources. If other sources of water are not available then as the last resort groundwater may be developed. In such case further groundwater development by wells of high yield around the project area should be avoided. It is also imperative that steps should be taken to artificially recharge the aquifer by roof top rainwater harvesting.

An approach to an integrated micro-watershed management plan of outer Himalayan range of Himachal Pradesh, India

Due to the ever-increasing demand on water resource, the pressure on its judicious utilization is also increasing. Besides being precious, this resource is also complex to manage on account of its dynamic behaviour. In India emphasis is being placed on making the local-level users participate in the management of natural resources at the watershed level. Therefore, it is imperative that local-level organizations be strengthened by providing the integrated watershed management tools which are user-friendly, but still use all the scientific knowledge to arrive at the appropriate decisions. This paper demonstrates the use of GIS-based overlay method for local-level planning, incorporating the sustainability aspects of watershed development. A case study has been taken in the Lower Bhangal Micro-watershed of the outer Himalayan range to demonstrate the approach of matrix/ranking and overlay methods to delineate priority areas for watershed management plan.