Groundwater is the backbone of India’s agriculture and drinking water security. The scarcity of water resources and ever increasing demands placed on them makes it vital that groundwater resources are identified, quantified and managed in a way that prevents over-exploitation and consequent economic losses or environmental damage.
Groundwater, owing to its decentralised availability and easy accessibility, forms the largest share of drinking water supply in India. As per the Planning Commission, more than 80 per cent of groundwater is used for agriculture and drinking. Wells including tube wells provide for 61 per cent of water for irrigation followed by the canals which is 24.5 per cent (Planning Commission, 2009).
The unplanned and non-scientific development of water resources leading to over-exploitation is being further accelerated due to changing rainfall patterns, water pollution and saline water ingression. Water is being lifted from increasingly deeper levels resulting in drying up of large number of dug, bore and tube wells and springs and also to an increase in the cost of groundwater extraction.
The assessment made by Central Ground Water Board published as ‘Ground Water Resources Estimation, 1995’, estimated total replenishable ground water in India to be 432 billion cubic meter (BCM) with a net draft of 115 BCM (stage of exploitation as 32 per cent).With increased development of ground water, the net ground water draft increased to 231 BCM (stage of exploitation of 58 per cent) in 2004 and 245 BCM in 2011 (stage of exploitation 62 per cent).The number of over exploited districts increased from 3 per cent in 1995 to 15 per cent in 2011 in the country (Central Ground Water Board, 2013).
The increasing dependence on groundwater without due regard to the recharging capacities of aquifers to conserve the surface runoff or rainwater or snowmelt has resulted in the large-scale and often indiscriminate outcomes. In western alluvial plains of Indo-Gangetic region, groundwater has been exploited even more than 200 per cent while in Peninsular region ground water development has reached critical and over exploited stage (Central Ground Water Board, 2013).
Water scarcity management through ground water recharge
There has been a paradigm shift from general ‘groundwater management’ to specific ‘aquifer management’ over the last decade. The occurrence and movement of ground water in various aquifer systems are highly complex due to the diversified geological formations with considerable lithological and chronological variations, complex tectonic framework, climatic dissimilarities and various hydro-chemical conditions. This necessitates the need to understand each aquifer to assess the potentials of aquifers and their disposition in 3D; hydrological parameters, water quality and their relationship within the surface water systems. Thus, the priority in planning of potential hydro-geological units has become management of aquifer units.
Aquifers are the natural reservoirs available in subsurface and are most viable options for storage of water harvested from available surplus runoff whereas water stored in tanks and ponds is severely affected with evaporation losses. The studies carried out on evaporation rates in various parts of the country show that evaporation losses could be as high as up to 2.5 m per year (Fig 1).
Each aquifer has its own characteristic property to store and yield rain water. In general hard rock aquifers are quite susceptible to recharge, but storage does not sustain for long, resulting flow into discharge areas. However, alluvial aquifers are more sustainable recharge reservoirs and can store large amount of water for longer duration if necessary space is available in aquifer systems. It is recommended that to the extent possible, harvested rain water should be stored in subsurface reservoirs i.e. ‘aquifers’ in order to prevent the losses of evaporation.
Aquifer mapping for groundwater recharge
Aquifer mapping is a process wherein a combination of geologic, geophysical, hydrologic and chemical field and laboratory analyses are applied to characterise the quantity, quality and sustainability of ground water in aquifers. Presently aquifer units have been segregated into 14 principal aquifers and 42 major aquifers (Fig. 2).
Alluvium covers over 31 per cent of the country and includes the major Indo-Gangetic-Brahmaputra alluvial plains, forming a highly potential regional multiple aquifer system to a depth of more than 800 m. Alluvium aquifers also include minor/localised aquifers as valley fills in mountainous and rocky terrains. These aquifers are multi-layered and aerially extensive.
In peninsular region granite, gneisses, quartzite, schist, shale etc. form the main aquifers with poor to moderate yields occupying approximately 35 per cent of the area. Basalts, sandstones, limestone and other sedimentary rocks form multiple aquifers with moderate to high yields and cover 34 per cent of the area. In the Deccan Plateau Region, basalt (16 per cent area) and Basal Granite Complex along with granites, gneisses, shale, schist, etc. form the major shallow unconfined aquifers in weathered and fractured zone, ranging in depth to about 50 m and fractured zones to about 100 m (Table 1).
The alluvial aquifers are being over-exploited in Rajasthan, Haryana, Punjab, Uttar Pradesh, Maharashtra, Tamil Nadu and Gujarat. Basalt and lacerates and multi layered sand stones (sedimentary) in Madhya Pradesh, Maharashtra, Karnataka and in Rajasthan while crystalline rock aquifers in Rajasthan, Andhra Pradesh Karnataka and Tamil Nadu states also fall in the same category (Fig. 2, Table 2 and Table 3).
Table 2: Aquifer wise Area under Over Exploited Blocks (Area in Sq Km)
Table 3: Aquifer wise Area under Critical Blocks (Area in Sq Km)
In the most of states there is no separate organisation dealing with groundwater. Maharashtra, Rajasthan, Karnataka and Tamil Nadu are, however, the exceptions that have GIS enabled groundwater departments. Considering the fact that groundwater will become increasingly pertinent to our existence, it is right time to attend to following points:
- Preparation of a GIS based state/district/basin wise hydro-geological atlas; and,
- Develop the software for community to assess ground water resources, on a GIS Platform.
Groundwater recharge and rejuvenation of aquifers
Artificial recharge is a process by which ground water is augmented through percolation of stored or flowing surface water which otherwise do not reach the aquifers. The imbalance between natural replenishment of groundwater reservoir and continued excessive exploitation of ground water has caused the over-exploitation of ground water. This has resulted in declining groundwater levels and drying up of aquifers particularly in low rainfall regions and drying rivers or reduction in river flows. The important techniques used for recharging are surface spreading and sub-surface techniques, recharge pits and shafts, induced recharge from surface water sources etc. In addition to the above, ground water sealing cementation techniques are also used to arrest subsurface flows. It has been observed that implementation of recharge projects has arrested declining ground water levels to a larger extent (Table 4).
Assessment of recharge potential of aquifers
Despite availability of source water as surplus runoff, one of the most important aspects of groundwater recharge is availability of de-saturated space in respective aquifers for ground water storage. An attempt was made to assess the recharge potentials of the aquifers based on unsaturated thickness of aquifer during pre-monsoon 1989 and 2009 periods. Based on the specific yield and thickness of unsaturated zone, it was approximated that total volume of water required to recharge the aquifer in order to bring the basin wise water level up to 3 m below ground level is 1240 BCM.
Basin/watershed/micro watershed wise water resources planning
Studies related to watershed resource planning identify areas having surplus/deficit water, both in term of surface and ground water. The net result will be how to cater to the deficit areas and how to conserve surplus water, if any. Presently numerous water harvesting structures and tube wells are being constructed/drilled without assessing their impact. It might be possible that due to the construction of new water harvesting systems, the existing structures may not get filled to their capacity. Such situations can be avoided. This will also help in inter-basin links and diversion of water for irrigation or drinking purposes for deficit areas.
Methods of water conservation
Rainwater harvesting of storm water from roads: Huge volume of runoff is generated during the rainy season from national/state highways and urban/rural roads. This water can be harvested and either stored or recharged to ground water after proper filtration and treatment.
Abandoned mine pits for rainwater harvesting: The states which are rich in minerals and mining activity are also having numerous abandoned mine pits in which water impounds and evaporates during summers resulting into water loss to evaporation. These abandoned mine pits can be converted as rainwater harvesting and artificial recharge structures can augment ground water reserves.
Evaporation suppression: Evaporation from the surface water bodies in the arid and semi arid regions like Rajasthan, Haryana, Maharashtra etc. ranges from 1.0 to 2.5 m per annum, out of which about 80 per cent is during summer causing huge loss to available water resources. Ecofriendly techniques are available the application of which can reduce evaporation by 20-60 per cent (Central Water Commission, 2006).
Traditional wisdom and water harvesting: Since ages, people across different regions of India have experienced either excess or scarce water due to varied rainfall and land topography and had adopted to traditional practices to harvest or collect water from rain, streams and rivers. Some of traditional water harvesting structures and systems in use in different parts of India are Johads where monsoon water slowly seeping into recharge groundwater is collected and soil moisture is maintained. Sometimes, Johads are interconnected with a gully or deep channels with a single outlet in a river or stream nearby to prevent structural damage. Bawdi/Jhalara are step wells. Renovation of few of them in Rajasthan has restored their huge water storing capacity. With the use of electric pumps to draw water, they are useful during dry periods. Bamboo drip irrigation technique lets downward flow of water by gravity. The main advantage of the system is that it does not pollute like plastic counterparts and is very economical and simple to construct. Kere are large tanks with boundaries around a stream for a provision for overflow of excess water and outlets for irrigation and feeding channels. Phads refer to earthen embankments built on a river that divert water for agricultural use. Kund is a large saucer-shaped deep pit covered by a dome ranging from a few meters to 100 sq km in diameter. It has a gradual slope which allows water to flow into the deep pit. This pit is lined with limestone and ash which naturally purify the collected water of dust, dirt and silt. Naula is a stone-lined tank which catches dripping water from springs and streams. Zing is a channel built to divert glacial water into a storage tank while surangas are vertical man-made excavations in hill slopes that act as a tunnel network where water from the top to the bottom of the hill is captured in the porous soil. This water is then channelled into large tanks, which can be used for agriculture and livelihood purposes.
Mandatory rain water harvesting
Union Government and State Government are making efforts for popularising concept of rain water harvesting and artificial recharge to ground water in the Country. Central Ground Water Authority (CGWA) has issued advisory to administrative personnel of all states and union territories and the Indian Ministry of Urban Development to take necessary measures for adopting rain water harvesting/artificial recharge in all the government buildings. State governments have made rainwater harvesting mandatory by adopting a model bill or including provisions in the building bylaws or through suitable government orders.
Successful planning and management of rain water harvesting and artificial recharge to ground water often requires consideration of many water management objectives. They are water routing capabilities, economics, offsite effects as well as hydro-geological factors including aquifer characterisation. Artificial recharge projects can be a valuable component of a groundwater management for long-term sustainability of groundwater supply, improvement of basin water quality and providing sustainability to ground water sources. Under all circumstance, peoples participation and awareness for adoption of rain water harvesting is most essential. Unless stakeholders do not adopt rain water harvesting and artificial recharge to ground water religiously, the crisis of ground water availability will continue.
Central Ground Water Board (CGWB). 2012. Aquifer Systems of India.
Central Ground Water Board (CGWB). 2012. Impact Assessment of demonstrative rain water harvesting & artificial recharge projects – unpublished reports of CGWB.
Central Ground Water Board (CGWB). 2013. Dynamic Ground Water Resources of India (as of 2011).
Central Water Commission (CWC). 2006. Evaporation Control in Reservoirs.
Planning Commission. 2009. Report of The Steering Committee on Water Resources and Sanitation for Twelfth Five Year Plan (2012-2017).