Introduction

The karst (krs or kras, a Slavic term meaning ‘stony ground’) is a near-surface landscape developed mostly in carbonate lithology due to the dissolution processes associated with groundwater flow. The term was coined by the father of karst geomorphology, Jovan Cvijic, in 1893 in the publication Das Karstphanomen (Ford 2006). The landscape with exo- and endo-karst features (karren and karrenfield, sinkholes, swallow holes, dry valleys, poljes, ouvalas, blind valleys, dolines, underground drainage system, caves, springs and a number of beautiful depositional speleothems) is called a karst landscape (Ford and Williams 2007; Andreo et al. 2010). Dissolution of carbonate rocks (i.e., limestones and dolomites), gypsum and halite leads to the formation of true karst (Bakalowicz 2005). Sometimes sandstones/quartzites are also prone to karstification (pseudo-karst) under favorable hydrogeochemical conditions (Wray 2003; Ford and Williams 2007).

Carbonate rocks cover 20 % of the world’s continents and are home for nearly 17 % of the world’s population. Karst is developed in these rocks globally (Fig. 1) and presents unique characteristics which have specific consequences for land and water-resources management (e.g. White et al. 1997; Ford and Williams 2007). Karst areas have also been known for their valuable water resources for millennia, as nearly 25 % of the human population utilizes groundwater derived from karst aquifer systems, either directly or indirectly (Ford and Williams 2007).

Fig. 1
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Major carbonate rock outcrops (red areas), which provide a close global-scale estimate of karst regions (Ford and Williams 2007). Map downloaded from Circle of Blue (2010)

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Specific characteristics in terms of karst morphology and hydraulic/hydrodynamic processes, developed by dissolution, make karst aquifers different and more complex than other aquifers (Bakalowicz 2005). These aquifers are characterized by dual recharge (focused recharge through swallow-holes and diffuse recharge), dual flow properties (high in conduits and low in the rock matrix), and dual storage properties (high in the rock matrix and low in the conduits; Hobbs and Smart 1986). They are characterised by a triple porosity system consisting of dissolution-enlarged conduits, fractures and primary pores (White 2002; Ford and Williams 2007). The nature of flow is laminar (i.e., Darcian) in fractures and pores and usually turbulent in conduits. Readers are encouraged to refer to Legrand and Stringfield (1973); Ford and Williams (2007); Andreo et al. (2010); Ghasemizadeh et al. (2012) for further information about these aquifers. The objective of this paper is to review the work carried out on carbonate formations and aquifer systems in India and highlight their importance in terms of groundwater and other resources (construction material, cement production, touristic potential). The scope of this paper outlines the management of groundwater in limestone terrains using karst-specific studies (e.g., Goldscheider and Drew 2007). The paper also addresses the assessment of suitable methods for exploitation and management of groundwater in karst aquifers.

Karst hydrogeology: practical issues

Typical karst areas are represented by a general lack of soil cover, absent or a low density of surface streams, presence of disappearing (sinking) streams and highly variable groundwater flow velocities (high in channels and low in matrix), groundwater flow through solution channels, presence of large caves and springs as major outlet of groundwater flow with a highly variable discharge, and water chemistry. However karst can also exist with its specificities under non-karstic rock cover and, therefore, without presence of typical karst features at the surface; this context is described as mantled karst or covered karst. Given such highly complex nature of karst aquifer systems, their hydraulic characterization and modeling can be extremely challenging. Watershed delineation in karst may be challenging: the total watershed may be comprised of the karst outcrops where diffuse recharge occurs and surface watershed of streams that infiltrates in the karst by swallow-holes; also, the presence of inter-basin groundwater flow through solution channels is common, meaning that two aquifer systems may share partly common watersheds. Interpolation and extrapolation methods give unsatisfactory results due to the presence of usually irregular and discontinuous groundwater levels. The rate and direction of groundwater flow is usually undetermined which may cause poor predictability of their water resources. The estimation of representative hydraulic conductivity is difficult because it is highly scale-dependent with a strong increase from local-scale measurements (e.g., on limestone core) to basin-scale estimates (e.g., modeling; Kiraly 1975).

In general, karst areas are not suitable for waste disposal sites due to thin soils and the possibility of rapid groundwater infiltration through high permeability zones. Thus, karst aquifers are highly prone to contamination and pollution. Progressive dissolution weakens the overlying rock mass above the caves causing subsidence and engineering-related problems (e.g., collapse sinkholes, suffosion sinkholes, subsidence sinkholes). Construction of dams and reservoirs is challenging in karst because of likely water leakage through high permeability zones. The degree of karstification varies depending on the geo-climatic context and the nature of the carbonate rocks (degree of primary fissuration, bedding planes frequency, primary porosity, etc.).

Indian scenario

Carbonate rocks are widely present in India, either directly exposed at the surface or as buried geologic layers. The Indian stratigraphic record reveals the presence of carbonate rocks from Precambrian to Tertiary periods mostly consisting of limestones and dolomites (Fig. 2). Highly karstified carbonate rocks are well developed in certain areas of the country in different geomorphological and climatic zones particularly within different sedimentary basins (e.g., Cuddapah, Vindhyan and Chattisgarh) and Himalayan regions. A detailed map of carbonate and karstified rocks of India was prepared using a wide range of information (Fig. 3) which will help to update the world karst data base (Fig. 1) and the International Association of Hydrogeologists (IAH) World Karst Aquifer Mapping Project (IAH 2013).

Fig. 2
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Stratigraphic record of geology showing the major carbonate units in India (compiled from Wadia 1939; Adyalkar 1977; Murty 1988; GSI 1997; Kumar 1985a, b). Abbreviations: SG super group; Gr group; Fm formation; Ls limestone; Do dolomite

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Fig. 3
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Map of India showing karstified and potential karst (carbonate) aquifers of India. The maap is compiled from different sources which are referenced in the paper. Thin lines in the map represent state boundaries. Boundaries of the map are marked as per UNO Map No. 3953 and 4140, Rev. 4, 2011. C Cuddapah basin; K Kaladgi basin; B Bhima basin; PG Pranhita-Godavari basin; I Indravati basin; Ch Chattisgarh basin; MP Madhya Pradesh; G Gujarat; R Rajasthan; H Himalayan region

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As seen in Fig. 3, carbonate rocks include rocks that are clearly karstified and rocks for which the degree of karstification is poorly known. Non-karstified rocks have not been subjected to geological processes such as dissolution and have remained as homogenous formations. The karstified rocks are strongly subjected to dissolution processes and were karstified during the past humid conditions, with some of them showing relict karst features which are sometimes hidden (paleo-karst). Many karstified massifs possess spectacular surface and sub-surface features including the longest and deepest caves (Fig. 4) of India.

Fig. 4
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A window to the underground. a Munagamanu cave in the Cuddapah basin (Andhra Pradesh); b Belum cave, Cuddapah basin; c Amarnath Cave, Kashmir; d Borra Cave, Vishakhapatnam (Andhra Pradesh)

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From the available data, it is estimated that karst and carbonate rocks, which have potential for karstification, cover about 3 % of the country’s total area. The karstified rocks are also concealed beneath the soils or buried deep under the surface geology in many areas of India; for example karst in the Borunda area of Rajasthan is covered under a thick blanket of sand (Meijerink 2007). These deep karstified rocks may also serve as good aquifers in areas where groundwater overexploitation or contamination problems occur in other aquifers.

Literature survey

The first study of karst formations of India was concerned with the geological aspects and was carried out by William King (King 1872, 1882) of the Geological Survey of India. Although the geology of various carbonate rocks, limestone, dolomites, etc. of this region were discussed by later researchers, the studies about karstification, aquifer systems and hydrogeological characteristics are very limited, which is evident from the very few scientific publications related to karst hydrology and karstification in India. A significant study on the karstic nature of limestone formations of India was first reported by Adyalkar (1977) but no further work on the characterization and nature of karst aquifers is recorded. Murty (1988) outlined the major carbonate formations and karstic horizons in the Indian stratigraphy. The occurrence of karst aquifers in India and the groundwater potential has also been assessed by a few individuals and organizations. Using similar methodology applied in other porous groundwater media, the Groundwater Estimation Committee (GEC 2009) has estimated the specific yield of carbonate aquifers of India at 0.03 and of karstified rocks at 0.08. Although in 2011 the Central Groundwater Board (CGWB) brought out a detailed report on the groundwater scenario of major cities of India and highlighted the general groundwater conditions in the country, there was no emphasis (in the report) on the study of karst aquifers. Details furnished about the karst-related keywords in the GEC and CGWB groundwater reports (Table 1) throw light on this shortcoming. The following sections provide an overview of the literature available about the carbonate aquifers of India.

Table 1 Representation of karst-specific terminology in four selected reports on groundwater (i.e. the number of times that keywords were mentioned in the text) published by the Groundwater Estimation Committee (GEC) and Central Groundwater Board (CGWB)
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Carbonate rock hydrogeological properties

Proterozoic sedimentary basins in mainland India

Singh (1985a, b) discussed the nature of karstified formations of the Proterozoic Period in the Vindhyan System, particularly extending in the Rewa region of Madhya Pradesh, Central India. The paper defined surface karst features, such as karren, sinkholes, fluvio-karst, sinking streams, springs, etc. He also highlighted the nature of karst formations and porosity and groundwater flow properties in karst aquifers. It was calculated that the primary porosity of such karst formations is only 7 %, but no quantitative information about the conduit porosity was provided. CGWB (2009) published an overview of groundwater resources in Chhatarpur district (Madhya Pradesh), but no information was provided on the karst aquifers of this area. Saifuddin (2000) suggested that more humid conditions existed in the past and this culminated in the karstification of marbles in the Vindhyan basin which is demonstrated by the presence of paleo-karst features, which can be used as indicators to locate aquifer zones. Using geological and hydrogeological information, Venkatanarayana et al. (1999), who observed that the flow in the aquifer is mostly of conduit type, gave a conceptual model of the Kuteshwar limestone aquifer of Madhya Pradesh, which is highly karstified. Earlier, Singh (1985a, b) also developed a hydrogeological model of the karstified Kuteshwar aquifer. The study reveals the presence of three porosities (matrix, fracture and conduit) and the abundance of sub-surface karst features (i.e., fractures, crevices and solution voids). He further inferred from the packer test data that the hydraulic conductivity of limestone aquifer decreased from ~1.03 m/day near the Chhoti Mahanadi River to ~3 × 10–4 m/day away from the river and the conduit porosity varies from 12.5 to 43 %.

Singh (1985a, b) also discussed the protection of the Kuteshwar limestone aquifer from the possible effects of dam and reservoir construction. According to him, the construction of a dam on the limestone will not have any major consequences on the hydrogeological regime of the area. Although the rocks are karstic in nature, Singh (1985a, b) did not mention the possible activation of the dissolution processes by the enhanced infiltration of surface water, which is more aggressive than the stored groundwater. In the future, this may enlarge the already present cavities and could lead to many engineering problems, like subsidence, failure of dam, reservoir water loss, etc.

Evaluating the pollution susceptibility of karst aquifers through a DRASTIC approach, Dubey et al. (2006) suggested that the shallower parts of the Bhander limestone aquifer (Madhya Pradesh, India) are more prone to pollution than the deeper parts. Without taking the heterogeneity of the aquifer characteristics into account, the authors recommended some measures for evaluating the future pollution of the groundwater.

Karst aquifers constitute a large source of groundwater in Chattisgarh (CGWB 2012), which is also indicated by a large number of wells used for groundwater withdrawal. The CGWB study reveals that more than 50 % of all the wells existing in the area are located in limestone aquifers. The aquifers in this area have a specific yield of 1–2 % and transmissivity values ranging between 4 and 140 m2/day. From the water-table fluctuation method, annual recharge of 60–220 mm/year was estimated. Using stable oxygen and hydrogen isotopes and water chemistry, Sinha et al. (2002) assessed the contamination problems in the Chandi limestone formation of Raipur city of Chattisgarh. According to them, the aquifer is prone to contamination and pollution from landfills, waste disposal sites and other anthropogenic sources; however, their work fails to consider the aquifer as karstified.

The paper by Ruggieri and Biswas (2011) is about the geometric setup of the karst system of the Python Cave area of Chattisgarh. They surveyed and mapped the subsurface karst conduits and concluded that the cave system is controlled by the tectonic structural pattern of the area. The area is also an example of well-developed karst terrains located in a complex geological system of Precambrian age.

Shibasaki et al. (1985) investigated the karst formations of the Cuddapah basin of southern India. The study was based on the geological field information collected from many karstified areas. The results provided an encouraging preliminary picture about the regional karstification in the Cuddapah basin, while a broader speleological view of the caves of different parts of India was given in other studies (Gebauer and Abele 1983; Gebauer 1985, 1997; H. D. Gebauer, Mandhip-Khol., “Resources on the speleology of Chhattisgarh State, India”, unpublished report, 2007). These surveys have led to the discovery of many significant caves which currently constitute the backbone of a growing tourist activity.

Dar et al. (2010, 2011a, b and 2012) highlighted the significance of karst aquifers of India and focused on the need to include karst-specific methodologies for their characterizing and management. Detailed karst hydrogeological studies were carried out in the Cuddapah sedimentary basin (Dar et al. 2011a, b). The three karstified geological units (Vempalle dolomite, Narji and Koilkuntla limestones) possess prominent surface and sub-surface karst features in this semi-arid region. The paper discussed the groundwater occurrence, flow and transport and the role of karst geomorphology on different groundwater processes in these highly karstified rocks. A model of karstification was proposed by Dar et al. (2011a, b; Fig. 5) to provide information related to the past climatic changes as well as other changes responsible for the karstification in southern India. These aquifers are highly exploited for water and other resources (building stones, lime for cement factories), which have large impacts on the environment and ecology of the area. Dar (2013) carried this work forward by incorporating results from multiple approaches (geology, geomorphology, hydrology, hydrochemistry, isotopes, tracers, speleology) in the semi-arid Cuddapah basin where karst groundwater is the sole perennial water source. The results were discussed in terms of the hydrogeological characterization of the karstified rocks and recharge mechanisms, using the hydrogeochemistry of groundwater taken from springs, bore-wells, cave streams, etc. (F. A. Dar, CSIR-NGRI, unpublished paper, 2014) discussed the possible geochemical processes that lead to the evolution of karst water chemistry in the Narji limestone of the Cuddapah basin.

Fig. 5
figure 5

A conceptual model of karstification in the Cuddapah basin, India. Three stages of karst development are explained (Dar et al. 2011a, b). Initial phase: Development of maze cave systems in a confined setting during more humid conditions prior to the onset of monsoonal conditions and Western Ghats uplifting at ~8 Ma when sea level was ~100 m higher than present level. Middle phase: Following tectonic uplift, a positive relief favoured surface runoff and progressive erosion of overlying layers exposed Narji limestone, and anastomosic phreatic cave systems develop. Western Ghats uplift lead to semi-arid conditions. Current phase: Water table progressively deepens, maze cave systems became inactive (relict caves) and the aquifer became unconfined, inducing a deeper level of karstification (present state) forming phreatic caves. Fast infiltration favours more dissolution through sinkholes, etc.

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Himalaya range and foothills

From the available hydrogeological data, it is evident that the Kashmir Valley of the Himalayan region has significant karst aquifers. The stratigraphic record reveals that the carbonate rocks exposed in the Himalayan region are mostly Palaeozoic to Cenozoic in age. Some of these carbonate rocks are a source of many permanent springs (Fig. 6), the water of which is used for drinking, irrigation and other purposes. Verinag spring in the Anantnag district serves as an originating source for the River Jhelum, a major river flowing through the Kashmir Valley. During an expedition, British karst researchers explored many Himalayan areas, particularly the Valley of Kashmir, and provided an overview of the karst features found in the carbonate rocks of this area (Waltham 1972). Chadha (1975) discussed the nature of karst features along with the occurrence and mode of formation of phytokarst in the Great Limestone formations of Udhampur district of Jammu and Kashmir, India. According to them, these carbonate rocks were subjected to the action of blue green algae which enhanced the mode of normal karstification and formed phytokarst features. Earlier, few authors provided a detailed study of the dolostones of this area without discussing the phytokarst features (Chadha 1975). From the field and tracer test data, Coward et al. (1972) gave an explanation about the hydrogeological configuration of the major karst areas of Kashmir. Based on tracing test results, they concluded that some springs flow with large discharge and are recharged both by diffuse infiltration and point infiltration in upgradient streams. The spring water is utilized for many uses and this exploitation of spring water is increasing day by day. Jeelani (2005, 2010) measured the water quality of some karst springs of the Kashmir Valley and discussed various related health and environmental issues resulting from the polluted waters. Based on the hydrochemistry of the springs of the valley, a conceptual model was also proposed by Jeelani (2004), while in another publication, Jeelani (2008) discussed the impacts of climate change on the karst springs of Kashmir and concluded that these springs are highly vulnerable to climate changes. The study by Jeelani et al. (2010) analyzed the nature of recharge in karst springs of the Lidder Valley of the Kashmir Himalayas using isotopic data of water from springs, streams and precipitation. According to them, the altitudinal effect on groundwater recharge is observed from the isotopic signature of the waters; additionally, they also concluded that the recharge to the karst aquifers is dominated by snowmelt in the area. In a similar study (Bhat and Jeelani 2012), water chemistry and isotope data were used to delineate the recharge zones in these karst springs. These karst springs are also under threat from human activities and their water resources must be conserved for sustainable use (e.g., Jeelani et al. 2012).

Fig. 6
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Some of the karst springs in India: a Verinag Spring, Kashmir b Yaganti Spring, Kurnool (Andhra Pradesh)

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It is also observed from the literature that north eastern India is famous for karst landscapes. Karst is well developed in the Kopili River Basin of Assam with well-developed karst landforms (Kumar 1985a, b). Brooks (1995) carried out speleological studies in the caves of Meghalaya and explored largest cave systems, while in the same area, Arbenz and Weidmann (2003) described several large cave systems with active underground rivers including Krem Liat Prah with over 30 km of explored conduits, which is likely the longest cave system of India. Many karst springs drain out in the form of conduits from these karst aquifers at many locations but no accessible documentation is yet available.

Limestone mining activities

Limestone areas of India are extensively exploited for use in cement factories, which are operated at large scale, serving as the economic backbone in many areas. Groundwater around cement factories also causes serious environmental problems. The mining activity has large and negative impacts on the sustainability of water resources (Limaye 2003), which are also due to elevated concentration of major ions (Ca2+, Mg2+, etc.) that may easily get released from the mining waste. A study by Soni (2007) has argued that the operation of limestone mines will not adversely affect the karst aquifers of the Chandrapur area of Madhya Pradesh. Without taking advantage of any proper scientific methodology, the author recommended that the diversion of surface drainage will be feasible to carry out the mining operation without having any impact on the local hydrological or environmental setup of the area. This contradicts the position, when considering the impacts of mining on karst aquifers, as discussed by many authors all over the world (LaMoreaux et al. 1997; Milanovic 2002; Coxon 2011; Urich 2002; Bonacci and Rubinic 2009). Limestone mining can have local environmental as well as social impacts in many areas of Western India (Ranade 2007). The remotely sensed data used by Rande (2007) to detect the land-use changes on the surface gave no mention of how this will affect the groundwater and surface-water regime of the area. Water-balance studies were undertaken for a limestone mining area of Tamil Nadu (Chaulya 2009) without considering limestone as a specific media where conventional groundwater estimation methodology is not valid due to the karstic nature of these rocks.

Saline intrusion in coastal carbonate aquifers

In the case of coastal carbonate aquifers, saline intrusion may reach a given aquifer very easily through solution channels, which has not been discussed in detail so far with respect to India, except in limited studies (Limaye 1988 and 2003; Pujari and Soni 2009). Small-scale karst features are present in the 50-m thick coastal Milionitic limestone of Gujarat (Limaye 1988); the aquifer is under threat due to saline intrusion. Using geophysical methods, potential groundwater bearing zones were located in Gujarat, but no detailed studies were undertaken. Seawater intrusion is the main problem for groundwater resources in many coastal areas of Gujarat and the situation can worsen with more pumping and mismanaged limestone mining activities (Pujari and Soni 2009). According to Pujari and Soni (2009), electrical resistivity tomography studies have shown that mining pits are particularly prone to seawater intrusion; although the limestone is also karstified to some extent, karstic properties of the aquifer were not considered in their results. Seawater intrusion problems in karstified carbonate aquifers of western Rajasthan have been discussed by Rushton and Raghava Rao (1988); seawater intrusion has contaminated the aquifer to a large extent due to irrigation causing drawdown in certain areas. The aquifer recharge was estimated by utilizing the daily soil-moisture-balance technique. The specific yield varies from 0.12 for the karstified limestone to 0.04 for the less permeable limestone of Rajasthan.

Geophysical approaches in karst regions

Geophysics is an important tool in detecting underground solution channels in limestone aquifers (Dutta et al. 1970; Limaye 1988; Singh and Chauhan 2002; Pujari and Soni 2009). The results help to determine the depth to fractures and solution channels along with quantification of the water resources. Singh and Chauhan (2002) also highlighted the importance of ground penetrating radar (GPR) in assessing the impact of limestone mining on groundwater exploration and management in India; based on the geophysical results, they suggested that limestone mining should be limited to a certain depth so that solution channels and enlarged fractures may not become exposed. Geophysical methods were also used in the Kurnool area of southern India to test the reliability of these methods in delineating karst related features (Chandra et al. 1987); their results showed that different electrical geophysical methods can help to delineate the lateral extent and orientation of the solution cavities in karst aquifers in the Kurnool district. These methods have not been extended to other karst areas. Using geological and geophysical investigations as a tool, Venkatanarayana and Rao (1989) delineated the karst structures in some areas of the Cuddapah basin.

Other scientific studies regarding karst

Karst areas of India have been studied for the nature of diversity of living organisms dwelling inside many caves of the Himalayan region, in terms of their physiological, metabolic and behavioral characteristics in space and time, a concept called biospeleology (Biswas and Biswas 2014; Rajput and Biswas 2012a, b; Ruedi et al. 2012; Biswas and Shrotriya 2011). Biswas and Shrotriya (2011) discussed the factors (darkness, high humidity and constant geophysical factors) responsible for making harsh sub-surface cave ecosystems unique, where life is possible. Cave environments were certainly utilized by pre-historic people for their habitation. Such environments are deteriorating constantly due to a number of factors which degrade these pre-historic dwellings (Biswas 2009; Biswas et al. 2013; Rajput and Biswas 2012a, b).

Speleothems deposited in the caves are a reliable source of record for paleo-climatic reconstruction. Many researchers used data from caves as proxies for paleo-climate reconstruction in India (Kotlia et al. 2012; Sanwal et al. 2013; Laskar et al. 2011, 2013; Yadava and Ramesh 2001, 2005, 2006; Yadava et al. 2004; Lone et al. 2014; Sinha et al. 2005, 2007). δ18O data generated from stalagmites of Valmiki cave of Cuddapah Basin suggested an increase in moisture content in Indian Summer Monsoon during the last deglaciation at ~14,800 years BP in southern India, which lead to the deposition of speleothems in these caves (Lone et al. 2014). They concluded that aragonite is the major component of stalagmites because of the dolomitic nature of the host rock favored by degassing of CO2. These studies focused on the climatic variability but lack in correlating this moisture variability with karstification processes.

Caves were used as favorable locations by Paleolithic and Neolithic people in southern India for their habitation, where they developed industries in the caves and valley floors of the carbonate rocks some 74,000 years ago (Petraglia et al. 2009); however, these types of studies have not extended further to the other karst areas of India.

Significance of carbonate terrains in India

Carbonate rocks and their intrinsic resources, particularly water, are becoming economically more and more important due to the relatively good quality and quantity of these waters. In certain parts of the Indian sub-continent, karst aquifer systems are of vital importance as they serve as the primary sources for drinking-water supply and are extensively exploited for irrigation purposes, particularly in semi-arid and arid regions. For example, in southern India, karstified rocks yield a large quantity of water and supply many drought prone areas of the Cuddapah basin (Dar et al. 2011a, b). Karst springs also supply the large population of the Kashmir Valley and are a source of large rivers such as the River Jhelum (Fig. 6a). A number of karst springs and caves of India also have religious importance as well (Fig. 6b), and many caves additionally possess various beautiful architectural secondary calcite depositional features which may serve as proxies for paleo-climatic reconstruction studies.

Carbonate-rock areas are exploited at a rising rate for their mineral resources (limestone, Fig. 7) in India, and a wide variety of natural and cultural habitats, like soils, forests, caves, etc. are highly vulnerable to impacts from such human activities (Fig. 7). A general limestone-mining map of India is given in the website of Maps of India (2007). The limestone is used for a number of societal applications (detailed uses of limestone can be found in the website of Longclifee Quarries Limited (2014).

Fig. 7
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A view of limestone exploitation in India: a limestone quarrying in Kolimigundla mandal of Kurnool district, Andhra Pradesh; b Birmitrapur mine, Jharkhand; c largest limestone mine Dhaneshwar, Rajasthan; d limestone mining, Satna MP

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Future perspectives on karst hydrogeology in India

Karst aquifers have received much attention from the worldwide scientific community over the past two decades due to increasing importance of their resources (e.g., Andreo et al. 2010). However, karst aquifers and the discussion related to the karstification processes have been somewhat neglected by the hydrogeological community in India. The literature review suggests that the very limited studies about groundwater characteristics in karst terrains of India have not taken the specificities of karst into consideration (Dar et al. 2011a, b). This is also evident from Table 1, which shows that the reports and publications from major groundwater research organizations lack proper definition, explanation and treatment of karst aquifers.

Since carbonate areas are also widely used for their resources (e.g., limestone mining) in India, the need arises to fully characterize them in order to understand their system behaviour, geometry, fluxes, etc. The karstic or dissolved nature of these rocks must be considered for careful planning and future research and development programmes in karst areas of the country. Adequate management programs will help to prevent future depletion of karst resource quantity and quality. The future studies should focus on understanding the aquifers’ hydrodynamic behavior, their hydraulic heterogeneity, adequate groundwater modeling flow and transport, speleogenesis and its relation to tectonics, etc.

Further, accessibility to safe drinking water is threatened by rapid contamination, overexploitation, saltwater intrusion and inappropriate irrigation practices (Fig. 8a) in such areas. Water-quality assessment in karstified aquifers is important as the recharging water carries contaminants and a large amount of eroded material (sediments/soil) concentrates into fractures and dissolution channels very rapidly, making the aquifers highly vulnerable to contamination. The sediments can clog pores, fractures and even underground channels, thereby reducing the pore space and limiting the quantity of stored water; thus, it is important to understand the contamination and pollution problems and to study the interactions between water and rock material in detail. Studying artificial recharge (managed aquifer recharge) is needed because groundwater is being exploited at a rising rate. The potential to store recharging water in limestone aquifers in order to replenish the exploitation loses and for reclamation and reuse is of growing interest to meet the increasing demands for water.

Fig. 8
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Carbonate areas used for other purposes which can have land- and water-management-related problems. a Extensive paddy agriculture in Kurnool; b Owk reservoir on Narji limestone, Kurnool (Andhra Pradesh); c development of sinkholes in agricultural lands due to extensive exploitation of groundwater in the Nossam area of the Kurnool district

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Exploitation of carbonate areas, whether for groundwater exploitation or quarrying, has created a number of irreversible environmental problems. Water-table depletion may lead to the sudden appearance of sinkhole collapses as observed in the Nossam area (Fig. 8c) of the Kurnool district (Dar et al. 2011a, b). Possible potential impacts resulting from climate change could add further problems (LaMoreaux et al. 1997; Milanovic 2002; Ford and Williams 2007). In the Kolimigundla mandal of the Kurnool district, an existing limestone quarry area is increasing in areal extent at a rate of 0.6 km2/year (Dar et al. 2011a, b). More elaborate research on the impact of limestone mining on groundwater is necessary. A few carbonate terrains of the country are sites of dams and reservoirs developed to store surface water for future uses (Fig. 8b). Unexpected collapses, reservoir leaks and inaccurate groundwater budgeting, etc. may occur in such areas. It is therefore, necessary for the public and for planners to avoid any possible catastrophic events that are likely to occur due to karstic nature of the rocks.

The proper study of karst resources will strengthen further research and will improve techniques of groundwater monitoring, assessment methods and management practices in these highly complex geological systems. It will help in protecting important karst eco-systems from possible anthropogenic impacts. A broader communication between scientists from multi-disciplinary research fields (geology, geochemistry, biology, ecology and geography, etc.) can fertilize new scientific findings and will encourage new students to carry out their research in this challenging field. Paleo-karst study using cave sediments, speleothems, etc. is a developing concept which helps to reconstruct the past historical records of changing climate. Geophysical applications in karst areas provide new opportunities for hydro-geophysical investigations. Carbonate dissolution is also a contributor of the global carbon cycle (Liu et al. 2010); hence, the studies focusing on present dissolutional processes will add to further knowledge for environmental and climatic studies.

Conclusion

Scientific studies devoted to carbonate aquifers are much needed in India, as these aquifers are highly heterogeneous and anisotropic and groundwater management is not easy. Preliminary estimates have shown that ~3 % of the India’s total area is occupied by carbonate rocks in various geo-climatic settings. These rocks form potential groundwater resources for a significant portion of the country’s population. It is estimated that ~35 million people in India are utilizing groundwater of karst aquifers for human consumption, livestock, irrigation practices and industrial uses. These aquifers are still treated with indifference in India where karst-specific methodology has not been utilized to characterize them. The existing scientific literature has shown that karst-related information is lacking in most of the publications. There is a lot of scope to test and develop karst-related methodologies in India, especially when considering that karst groundwater resources may be threatened by large-scale mining (quarries), industrial contamination, urban spreading, irrigation practices and climate change effects. Therefore, these aquifers need adequate characterization involving state-of-the-art methodologies and by taking the specific heterogeneity of the aquifer into account.