Opportunities for energy-free groundwater extraction through artificial autoflow well: a conceptual feasibility in Indian context

doi:10.21203/rs.3.rs-4282288/v1

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Opportunities for energy-free groundwater extraction through artificial autoflow well: a conceptual feasibility in Indian context

https://doi.org/10.21203/rs.3.rs-4282288/v1

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Prospects for converting a water well tapping confined aquifer into an artificial autoflow well exists in several areas. However, the energy advantage offered by a confined aquifer is generally ignored and even in areas where the piezometric head in the well rests at very shallow depth from the ground surface, pumps are lowered for extracting groundwater. In this paper, we present a conceptual feasibility of converting wells constructed in confined aquifers into an artificial autoflow well. There exists a promising prospect of creating an artificial autoflow condition which can lower the dependence on energy for groundwater extraction. Such wells are feasible in areas with multi-aquifer set-up where a thick layer of surficial clay overlies the main aquifers making the area unsuitable for dugwells; areas where the water level in the top unconfined aquifer (phreatic aquifer) has declined below 20 m from ground level resulting in drying up of dugwells and shallow handpumps and; areas where the shallow aquifer is contaminated and not suitable for drinking and domestic uses and the deeper confined aquifers are contamination free. A suitable design for an artificial autoflow well is proposed in the paper which can provide an energy free alternative for groundwater extraction for meeting the requirement of small and marginal farmers as well as for meeting the drinking and domestic requirements of rural households in areas where the shallow aquifer system is either contaminated or desaturated.

Autoflow wells

confined aquifers

groundwater extraction

piezometric head

marginal farmers

Groundwater is an energy-intensive resource as the development of groundwater is inextricably linked to the consumption of energy resources. Sources of energy i.e electricity, solar or fossil fuels are necessary for pumping out groundwater from the aquifers. This aspect of groundwater development makes it a non-neutral resource from the consumers' point of view as people having access to energy sources enjoy the advantage of harnessing the resource. The only exception to the development of groundwater without the expense of energy is encountered in areas that have autoflow wells also known as flowing artesian wells. In Washington State, USA, autoflow wells are regarded as uncontaminated groundwater resources in the event of a power failure [1]. Autoflow wells have been utilized as a water source for irrigation in the United States since the 18th century. Autoflow wells have been reported in various African countries, such as Chad, Kenya, Libya, Madagascar, Sudan, Tunisia, and others, situated in both sedimentary aquifers and fractured formations [2]. Such wells are also not uncommon in India and have been reported from many parts of the country including the States/UTs Jammu &Kashmir, Uttarakhand, Uttar Pradesh, Bihar, Odisha, West Bengal, Rajasthan, Chhattisgarh, Kerela, Telangana, Tamil Nadu, Tripura, Arunachal Pradesh, Kerala etc [3]. Flowing wells, however, need to be controlled to prevent wastage of groundwater resources as well as reduction in lowering of artesian pressure in the aquifers.

In addition to the naturally occurring autoflow wells, there also exists a possibility of creating an artificial autoflow condition in several areas where the piezometric surface of the confined aquifers lies at a very shallow depth from the ground surface. In such areas, the opportunity of the energy advantage that is naturally offered by the wells tapping the confined aquifers can be harnessed to create an energy-free groundwater storage. Such an arrangement can suffice the irrigation water requirement of small and marginal farmers and for meeting the drinking and domestic requirements of rural households.

As per the prevalent practice, the common structures that are constructed for pumping out groundwater from the aquifers include dug wells (open wells), tube wells/borewells, and dug cum bore wells. The term tube-well is used for wells that are constructed in an alluvial or soft rock formation in which a tubular well assembly is lowered in the well. The tubular assembly contains the well-screen which is placed at the most permeable part of the aquifer. However, in the case of the hard rock formation, the well is stable on its own and hence tubular assembly is generally not lowered in the well. Such wells are known as borewells. Dug-cum-borewells are constructed mainly to increase the yield of the dug wells [4]. In this case, a bore is constructed at the base of the dug well to connect the phreatic aquifer with the underlying confined aquifer [4, 5]. Wells that are constructed in confined aquifers are known as artesian wells. In such wells, the piezometric level rises above the top level of the aquifer and in some cases can rise even above the land surface leading to autoflow well or flowing artesian well [5]. Except for the autoflow wells and the dug wells which do not require pumps for lifting water, pumps are lowered in the well for pumping out the groundwater regardless of the natural energy advantage offered by artesian wells with piezometric heads lying at very shallow depths from the ground surface.

In this paper, we present an energy-free model for groundwater extraction by creating artificial autoflow conditions (artificial autoflow wells) which is suitable for meeting the irrigation requirements of small and marginal farmers and domestic requirements for rural households. The model is suitable for areas with multi-aquifer set-up with the following conditions; (i) areas where a thick layer of surficial clay overlies the main aquifers making the area unsuitable for dugwells (ii) areas where the water level in the top unconfined aquifer (phreatic aquifer) has declined below 20 m from ground level resulting in drying up of dugwells and shallow handpumps and (iii) areas where the shallow aquifer is contaminated and not suitable for drinking and domestic uses and the deeper confined aquifers are contamination free. Though the present model appears similar in design to that of a dug-cum-borewell, it essentially differs from it both in purpose, design and the intended benefits in following ways;

Aspects	Dug cum borewell	Artificial autoflow well
Purpose	Enhancement in yield of the dug well	Using the pressure head of the artesian aquifers for creating energy-free groundwater storage
Design	Dug well is provided with an extension bore/tube at the bottom	Tubewell tapping the artesian aquifer is provided with a cemented storage tank at the surface
Benefits	• Enhanced yield of the dug well • Contribution from the extension bore can be increased by deepening the dug well zone	• Can be constructed even in areas where dug well are not suitable • No risk of cross-contamination from phreatic to artesian aquifers and vice-versa
Limitations	• If the water level of the phreatic aquifer falls below the depth of the dugwell, augmentation from extension bore will be less effective because of loss of water from dugwell storage to recharge to the shallow aquifer	• Not economically desirable in areas where the head of the artesian aquifer is deep • Not desirable for areas where the water level of the phreatic aquifer is shallow and the quality is fresh

In India, the confined aquifers are distributed across four major hydrogeological environments. Based on the various studies carried out by CGWB, a brief description of such geological environments which hosts multi-aquifer systems of the country and their geographical distribution is given below.

(i) Multi-aquifer systems in the Ganges-Brahmaputra Alluvial Province: The vast plains of the Ganga and the Brahmaputra rivers encompassing an area of about 8.5 lakh sq km are underlain by late Tertiary and Quaternary alluvium which constitutes multi-tiered aquifer system made up of alternating layers of various grades of sands, silts and clays.

(ii) Multi-aquifer systems in the Gondwana Sedimentary Province: Multi-aquifers in the semi-consolidated sandstone, shale and limestone along the Godavari, Mahanadi, Narmada, Son and Damodar valleys, western parts of Rajasthan, Kutch and Saurashtra areas and in scattered patches along the east coast belong to this group. Flowing / artesian wells have been reported from Khammam district in Andhra Pradesh and Surendranagar district in Gujarat. The lateral and vertical extent of the aquifers are limited at places by dykes and sills of trappean rocks.

(iii) Multi-aquifer systems in the Cenozoic Sedimentary Province: Aquifers in the narrow coastal plains on the Malabar and Coromandel coasts, coastal fringes on the Saurashtra and Kutch peninsulas, extensive embayment in Gujarat and Rajasthan and strongly folded rocks in eastern India belong to this group. Along the Coromandel and Malabar coasts, the seaward dipping strata contain several artesian aquifers. Multi-aquifer systems are found in the Krishna-Godavari interstream area in Andhra Pradesh and Cauvery-Paleru river interstream area in Tamil Nadu. Multi-aquifers also occur in the Cambay basin in Gujarat and Rajasthan which are underlain by sediments deposited under estuarine, deltaic and lagoonal conditions alternating with marine conditions. Folded tertiary sandstones in eastern India contain artesian aquifers that yield water by free flow to wells located in intermontane valleys.

(iv) Multi-aquifer systems in the Cenozoic Fault Basins: Quaternary valley fill deposits consisting of lenses of sand and gravel intercalated with silt and clay in three discrete fault basins along the Narmada, Purna and Tapti valleys belong to this group.

The proposed model would thus be viable in parts of the above four major hydrogeological environments where the pre-monsoon and post-monsoon piezometric heads of the deeper artesian aquifers are very shallow. Presently, the development of deeper artesian aquifers involves the construction of deep tubewells which are fitted with pumps (Fig. 1a). Though the existing practice is convenient for those who can afford the energy cost of pumping, it poses an economic burden to the small and marginal farmers particularly from the eastern parts of the country. It has been reported that the economic burden faced by small and marginal farmers for extraction of groundwater in the most prolific groundwater basin of the country, attributing it to the rising energy costs [6]. Further, the declining groundwater trend in shallow aquifers in various parts of the alluvial aquifers is likely to result in increased energy consumption and financial pressure for farmers in the near future.

The model proposed here is presented in Fig. 1b. As per this model, first, a tubewell tapping the confined aquifer is to be constructed. After construction of the well, a circular cemented storage tank with the well at the center is to be made. The well casing below the average pre-monsoon piezometric head and upto the depth of the storage tank may then be screened. This would convert the well into an artificial flowing well. However, unlike the flowing artesian well, this artificial flowing well will have a natural shut-off whenever the water level in the storage tank becomes equal to the piezometric head of the deeper confined aquifer. Further, to prevent any evaporation loss from the storage tank and any contamination of the deeper aquifers from the storage tank due to anthropogenic activities, the top of the storage tank is designed to be covered with a cemented slab featuring a manhole. The time required to fill the storage tank and ensure uninterrupted water supply from artesian aquifers will depend on the hydraulic parameters of the deeper aquifer.

The schematic diagram depicts an example from an area characterized by a deeper water level in the phreatic aquifer, however, the piezometric head of the deeper confined aquifer in the area is shallow (< 5m bgl) (Fig. 1c). If the circular storage tank is designed for a depth of 10 meters (from ground level) and a diameter of 2.5 meters, the minimum storage in the tank considering the pre-monsoon piezometric head as 5 m bgl would be approximately 25 cubic meters of water.

Wells constructed by the CGWB tapping deeper aquifers have shown autoflow conditions at several places with significant variation in the discharge. In the Alluvial Formations of Uttarakhand, specifically in Udham Singh Nagar district, the discharge of such wells have been found ranging from 17 to 3400 liters per minute (lpm) [7]. Similarly, in Bihar's Madhubani district, the discharge varies between 160 and 300 lpm [8]. The discharge of autoflow wells in Tertiary Sandstone of Tripura has been found upto 120 lpm [9]. In the Tertiary Formations of West Bengal (Birbhum and Bankura Districts), aquifers below 136 mbgl are found under autoflow condition with the discharge upto 1200 lpm [10]. Assuming a conservative discharge rate of 60 lpm, the designed storage of 25 m³ would need a refilling time of 7 hours and can meet the irrigation requirement of upto 5mm/day for an area of 0.5 hectares. The model can also be seamlessly integrated with the drip irrigation system which finds extensive application in regions with limited groundwater.

Small and marginal farmers can gainfully utilize the created groundwater storage for meeting their irrigation water requirement through use of the traditional animal powered water lifting devices like the Persian wheel or ‘raha’ which can lift water from depth upto 20m [11].

Autoflow wells provide the natural opportunity for harnessing groundwater without the expense of energy. Wide variation in discharge of Autoflow wells has been found in different parts of India which under favorable condition even reaches upto 3400 lpm. However, in addition to the natural autoflow wells, there also exists a promising prospect of creating an artificial autoflow condition which can lower the dependence on energy for groundwater extraction. Such wells are feasible in areas with multi-aquifer set-up where a thick layer of surficial clay overlies the main aquifers making the area unsuitable for dugwells; areas where the water level in the top unconfined aquifer (phreatic aquifer) has declined below 20 m from ground level resulting in drying up of dugwells and shallow handpumps and; areas where the shallow aquifer is contaminated and not suitable for drinking and domestic uses and the deeper confined aquifers are contamination free.

Artificial autoflow wells can thus provide an energy free alternative for groundwater extraction which can meet the requirement of Small and marginal farmers through use of traditional animal power water lifting devices. Another promising use of Artificial Autoflow wells can be in areas where rural water supply is dependent on deeper confined aquifers for various reasons like groundwater contamination, drying up of the shallow aquifers etc. The proposed model can be adopted in other areas with similar hydrogeological setup.

Funding- The proposed model was developed without any funding support..
Code or data availability- No original data has been generated for this paper. Instead, relevant data from various studies has been referenced and cited appropriately
Ethics approval- The research protocol for this study was reviewed and approved by the Central Ground Water Board. All procedures performed in this study were conducted in accordance with the ethical standards.
Consent to participate- Informed consent was obtained from all participants prior to their involvement in the study
Consent for publication- All authors have consented to the submission and publication of this manuscript

Author Contribution

SND-Conceptualization, Design and WritingSRC-Conceptualization, Design and WritingMS- Design and Writing

Acknowledgement

The authors extend their heartfelt gratitude to Dr. Sunil Kumar Ambast, Chairman of CGWB, and Smt. Anitha Shyam, Member (South), CGWB and Dr. Shashi Kant Singh, Scientist of CGWB for their invaluable guidance and encouragement. The authors would like to thank Shri Jai Kishan Tandon, Draughtsman, CGWB, NR, Lucknow, for his assistance during the finalization of the schematic diagram.

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Bussa, R., Rai, P., & Patel, K. (2021, December). Story of Artesian Aquifer, Udham Singh Nagar District, Uttarakhand. Bhujal Samvad. Central Ground Water Board. pp 6-8. Retrieved from https://cgwb.gov.in/cgwbpnm/public/uploads/documents/1686740180452338553file.pdf
Adyalkar, P. G. (1975) Dug-wells, dug-cum-bore wells, and tubewells Indian Farming. pp. 13-16. ISSN 0019-4786
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Ray, T.K., (2009), Hydrogeology of West Bengal in Artificial Ground Water Recharge & Aquifer Management, SWID, West Bengal. (Available at: http://117.252.14.250:8080/jspui/bitstream/123456789/5861/1/L-5%28ii%29-Hydrogeology%20of%20West%20Bengal..pdf )
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No competing interests reported.

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Opportunities for energy-free groundwater extraction through artificial autoflow well: a conceptual feasibility in Indian context

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Introduction

Feasible areas for Artificial Autoflow Well

Proposed Design and benefits of Artificial Autoflow Well

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Author Contribution

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