Central Ground Water Board, Ministry of Water Resources, Government of India, North Central Region, Bhopal , Geophysical studies

GEOPHYSICAL STUDIES - Geophysical Surveys for Groundwater Exploration

GEOPHYSICAL SURVEYS FOR GROUNDWATER EXPLORATION

The role of geophysical methods in Groundwater Exploration is vital. Its chief aim is to understand the hidden subsurface hydrogeological conditions accurately and adequately. Since the base of any geophysical methods is the contrast between the physical properties of the target and the environs, the better the contrast or anomaly, better would be geophysical response and hence the identification. So, the efficacy of any geophysical techniques lies in its ability to sense and resolve the hidden subsurface hydrogeological heterogeneities or variation. Hence for groundwater exploration a judicious application or integration of techniques is most essential to become successful in exploration, technologically as well as economically. It is to be clearly conceptualized that groundwater can not be detected directly by any one of the geophysical methods and therefore the interpretation is contextual and a broad understanding of the subsurface hydrogeological condition is prerequisite.

The systematic geophysical surveys for groundwater exploration have been done in the part of Morena, Bhind, Dewas, Jabalpur, Jhabua, Khandwa, Mandsaur, Sagar, Sidhi, Hosangabad, Guna, Shivpuri, Sheopurkala, Ratlam, etc districts of Madhya Pradesh. These surveys were conducted during the period of year 1983-2003 and are being discussed here.

Morena District:

Due to canal irrigation in Morena district, a serious problem of water logging in low lying areas of upper reaches and non availability of water in tail ends of the canal system is being faced. To combat the situation World Bank had launched a plan to construct a number of augmentaion tubewells in district with association of CGWB. In this context the systematic geophysical surveys were also conducted in Chambal-Kunwari Doab area of Morena district during year 1983-84. The alluvium sediments consisting of clay, silt, sand and gravels cover the surveyed area. The alluvium overlies the irregular Vindhyan basement comprising shale and sand stone. These deposits are in continuation of the Indo-Gangatic alluvium accumulated in the drainage basins of the Chambal and Sindh (Kunwari is tributary of Sindh). In total 54 spot VES were conducted in about 200 Sq.Km. area. The objective of the geophysical surveys was to delineate the bedrock topography in the area and to determine the nature of alluvium in terms of sandy and clayey horizons depth wise etc. The study area is almost a flat topography with a general elevation varying between 150m and 173 m above mean sea level and has a gentle slope towards east.

The resistivity sounding carried out in the area generally reveal two to three layers before bedrock is indicated. The resistivity of the alluvium formation is in the range of 20 ohm-m. The bedrock, generally indicated in all the sounding curves, has the resistivity of the order of 50-500 ohm-m at varying depths. It is observed that the depth to bed rock in the area varies from 50 to 170 mbgl. The depth of the bedrock is shallow towards south western and are deeper in northern and eastern part.

The two sets of resistivity values have been inferred for bedrock:

50-150 ohm-m resistivity, probably indicative of Shelly sandstone, occupying mostly western and southern part of the area.

ii) 150-500 ohm-m resistivity probably indicative of limestone/sandstone mostly occupying eastern part and few local patches in western area.

Bhind District:

Bhind district forms a part of the Indo-Gangetic alluvium comprising of fine sediments, i.e. clay, silt and sand. This alluvium is deposited over the Vindhyan basement. It is observed that the deeper aquifer resting over doleritic formations having poor quality of water. In this regard geophysical surveys were planned to see the possibility of aquifers below doleritic formationand also to estimate the thickness of alluvial formations .

In this context twenty three vertical electrical soundings covering 17.8 line km., were observed along three regional traverses of the district during FSP 87-88. Fourteen VES were conducted along Bhind-Lahar section, 3 VES were conducted along Bhind-Mehgawan section and 6 VES were conducted along Mehgawan-Mau section.

In FSP 98-99, 21 VES were conducted in between the parts of Jhilmil and Besli river. The objective of investigation was to delineate the thickness and extension of doleritic formation in an area affected by inland salinity. The basement topography on which the alluvium has been deposited and interface of fresh/saline groundwater in the area has been deciphered.

Dewas District:

Dewas, a very fast growing industrial township of western Madhya Pradesh, situated over a basaltic formation of Cretaceous to Eocene age . Due to irregular rainfall and over exploitation of groundwater, it faces acute shortage of water during the summer season.

To combat the situation, an integrated approach of various scientific methods including geophysics have been applied over an area of 150 sq.Km. to select suitable areas for groundwater exploration by state Government. The study area constitutes a part of Malwa plateau and comprises Deccan trap basalt and Recent alluvium soils. In this area the zones of interest have been scanned through remote sensing study followed by surface and sub-surface geophysical study. Thirty VES using Schlumberger configuration have been conducted during FSP 1990-91

Apart from these the detailed geophysical investigations have been conducted in Chhoti Kali Sindh and Nagda watershed of district.

Jabalpur District:

Jabalpur district is located in the central part of the state. The systematic geophysical surveys conducted in the district were limited in parts of Kundam, Shahpura, Murwara and Barwara blocks. The areas of these blocks are covered by different kinds of hard and soft rock formations and have different types of depositional environment. The prime objective of the surveys was to identify the different litho-units and granular zones occurring at different depths at selected sites for groundwater exploration. The other objectives include to estimate the thickness of alluvium formation, demarcation of different aquifer systems and to study the groundwater potential of Deccan Traps, Lametas and other metamorphic rocks.

The resistivity surveys comprising VES and Gradient Resistivity Profiling (GRP) were conducted at villages Bairagi, Mahgawan and Harduli Kalan in Kundam block during FSP 94-95 and at villages Bijana, Bharatpur, Kalon(Kodori), Patti Chargawan and Kohli in Shahpura block during FSP 95-96. During FSP 97-98 geophysical surveys were conducted in Murwara and Barwara blocks of the district. The surveyed areas are mainly along Murwara-Jabalpur, Murwara-Bilheri-Rithi, Murwara-Barwara-Shahdol, Barwara-Barhi roads and link roads of these roads joining to various villages. The important villages covered by resistivity surveys in Murwara and Barwara blocks are Lakhakhera, Rohania, Basari, Pipariya kalan, Vilayat kalan, Loharwara, Devri Hatai, Chandan, Gubradhari, Kaudia, Pahari, Niwar, Jhinjhari, Gulwara, Bilehri, Bandha, Nitara etc.

Apart from these 6 VES were conducted in Bargi block during FSP98-99 to assist the groundwater exploration progremme.

Jhabua District:

Under Technology Mission in Jhabua district 12 spat VES (Schlumberger, AB=100 to 1200m) were observed near 5 existing borehole sites for correlation of geo-electric parameters of VES and borehole lithology. Four VES were conducted near proposed sites for tubewell construction. After processing and analyzing the VES data three suitable sites were recommended for drilling and borehole drilling yielded satisfactory discharge.

Mandsaur District:

In the Chambal sub-basin, Mandsaur district is apart of Malwa plateau in western M.P. It is a leading district of the state for the cash crop production. The water requirements for agriculture and drinking, mainly depend upon its groundwater potential. The depleting groundwater reserves, declining water level, increasing water demands and unexpected occurrence of brackish to saline groundwater at places give an alarming threat of groundwater drought situation in the district. To combat the situation, systematic geophysical surveys were conducted to identify the depth of occurrence of potential aquifer zones within the area proposed for exploratory drilling on hydrogeological consideration by CGWB viz Akiya, Ajaypur, Junapai, Kukdeswar, Rewa-Dewra, Kharauda, Barkhera-Gangesa, Bhanpura, Chhoti Patlasi, Risthal and Nayagaon etc. Additional sites viz Pipliya Mandi, Diken, Nahargarh, Nagari, Suhasra, Shamgarh, Malargarh were also taken for investigations. In order to achieve above objectives sixty three VES were conducted at different locations of district.

Apart from these the detailed geophysical investigations have been conducted in Tumar watershed of district.

Sagar District:

The surface resistivity surveys were conducted in Sonar sub-basin of Sagar and Damoh districts during January-March, 1994 with objective of identification and delineation of potential limestone aquifers. The study area covers the part of survey of India Toposheet No.55 I within north latitudes 23^o 40' and 23 ^o 55' and east longitudes 79^o 00' and 79^o 25'. Geologically alluvium, Lametas and Vindhyan formation cover the area. The Vindhyan rocks occupy major portion of the study area. The upper Vindhyan consist of Kaimur series, Rewa series and Bhander series.

In total 42 VES were conducted to achieve the objective, most of them were deep soundings with maximum current electrode separation of 1400 m. The surface resistivity measurements were made with DC resistivity meter GGA-30 which have the power output of 60 watts. The VES curves obtained in the area are generally of H,HK,HA,HKH type. The interpreted layer parameters of VES are presented in table 5.2.8 The layer parameters reveal 3-4 geo-electrical layers sequence. The geological and hydrogeological characteristics of the different layers have given rise to variation in the resistivity values which form the basis to distinguish the sub-surface lithology with respect to different layers.

Khandwa District:

The geophysical investigations comprising deep vertical electrical soundings (VES) (Electrode separation AB=200 m to 1400 m) were conducted in an area of about 150 Sq.Kms. in Burhanpur block of Khandwa district during the months of Jan-Feb, 1997. In total 25 nos. of VES were conducted in and around Burhanpur township area. The objective of survey was to estimate the thickness of alluvial cover overlying Deccan traps for ground water exploration program.

The results of the surface geophysical study reveals that the thickness of alluvium has wide range (0-350 m) of variation from place to place in the area. It is observed that the thickness of alluvium formations is increasing towards north-west of Burhanpur town and it is maximum (more than 300 m) near Khooni Bhandara.

Besides these 5 numbers of VES were also conducted at different locations namely Khaknar, Bargaon, Nepa-Nagar, Taklikalan villages & Khandwa town, for ground water exploration program by selecting the suitable location for exploratory drilling in the area. At Khaknar current electrode separation was 400 m. But VES could be interpreted for a depth 5 m only due to thick layer of massive basalt. At Borgaon the current electrode separation was same as above but the information could be obtained down to depth of 7 m. At Nepa Nagar with 400 m current electrode separation, information could be inferred up to 10 m only due to thick massive basalt at shallow depths. However at Takli Kalan with the same current electrode separation the information could be obtained down to 81.0 m bgl which matches with the drilling results. The VES conducted at Khandwa could reveal the information down to 36.0 m only.

Sidhi District:

During year 1991, 40 shallow and deep VES (Schlumberger) were conducted in Sidhi district with the objective to select some favorable locations for groundwater exploration. The surveyed area covers about 2500 sq km area over Gondwana formation of the district. The important locations covered by surveys include Deori, Pathraula, Bitkhuri, Baharwar, Amha, Dhumadol, Majhgawan, Bastua, Kota, Nagpokhar, Kundaur, Chamordol, Tala, Majhauli, Chuhiya, Tamsar, Chokari, Kusmi, Nauriha, Mahgawan, Parasi, Keslar, Songarh, Sarai, Bhaiatola, Dongri, Dauhani, Gannai, Sajapur, Rajmilan, Singrauli and Bargawan. The current electrode separation varies between 400 to 1400 m. The VES results indicated 4 to 5 geoelectrical layer sequence of Gondwana shales and sandstone. Because of wide variation in elevation due to hilly terrain the results of VES could not be correlated properly in space, but few geo-electrical sections have been prepared.

A geoelectrical cross-section across Gopad river between Kundaur and Dauhani over Gondwana formation is drawn. Topographically the area on both the sides of river is on higher elevation. The top geo-electrical layer with 100 ohm-m resistivity extends on either side of the river. Below this, a layer with 300 ohm-m resistivity, is restricted to the south-west side of the river. The layer with the resistivity value of 175 ohm-m extending on either side of river is representative of upper Gondwana formation comprising sandstone and shale. This layer overlies a highly resistive and compact sandstone layer (resistivity more than 1000 ohm-m). The layer with 175 ohm-m of resistivity may be favorable for artificial recharge by making a sub-surface structure across the river, in case of any depletion of water table in the area.

Hosangabad:

About 29 VES were conducted during FSP 2000-2001 and FSP 2001-2002 in Hosangabad district. The investigation was confined to Hosangabad- Timarni road and Babai Farm area. The investigations clearly delineated the alluvium thickness in the area. It also characterizes the nature of different horizons in terms of resistivity.

Guna:

To assist the groundwater exploration programm in district about 43 VES and 2.7 line-km GRP were conducted in the district during FSP 2002-2003. The investigations were mainly concentrated around Mungawali and Chanderi town. The combination of VES and GRP has successfully delineated the saturated fractures in the area.

Shivpuri:

To assist the groundwater exploration programm in district about 8 VES and 0.32 line-km GRP were conducted in the district during FSP 1999-2000. The investigations were mainly concentrated around Mungawali and Chanderi town. The combination of VES and GRP has resulted good response.

Sheopur:

About 28 VES and 2.4 line km GRP were conducted in district. The concentration of investigation was in forest area of Kuno-Palpur. The objectives of investigation was to identify the suitable area for making groundwater structures to meet the drinking water requirements of 1400 families displaced from Kuno-Palpur reserve forest to rehabilitated area under Asiatic Gir Lion rehabilitation project.

Chhindwara:

About 14 VES and 0.164 line km GRP were conducted around Jhilmili village in district. The investigation delineated the weathered Basalt and Red bole at shallow depths. The productive layers occurring at deeper depth could not be identified through VES.

Ratlam:

About 12 VES were conducted for pinpointing the suitable location for drilling of boreholes for augmenting water supply to Hussain Tekri, Jaora. Investigation suggested the presence of deeper aquifers around Hussain Tekri.

GEOPHYSICAL INVESTIGATION FOR ACCELERATED
EXPLORATORY DRILLING PROGRAMME UNDER DROUGHT

Sagar, Damoh, Panna & Chhatarpur district of Madhya Pradesh were affected by drought. Due to this, these districts are facing acute shortage of potable water. To mitigate the situation and to the ground water potential CGWB has taken up accelerated exploratory drilling programme in drought-affected area of these districts during AWP 2000-2001.

In this content, the geophysical survey comprised of VES and GRP were planned to pin point the suitable sites in hydrogeologically feasible areas of the districts. About 20 spot VES and 2.6 line km GRP were conducted in selected villages of Sagar, Damoh, Panna and Chhatarpur districts.

GEOPHYSICAL SURVEYS IN SPECIAL PROJECT STUDIES:

In the State, a comprehensive programme of geophysical surveys for ground water resources was started in 1976 by an Indo-British Betwa project. Subsequently, the Regional office took up the geophysical surveys for ground water exploration, short term investigation and artificial recharge. The results are being discussed separately for each.

In Madhya Pradesh, two special water resources evaluation projects, the Narmada project and Betwa project were completed before formation of North Central region. In Narmada project, mainly the sub sub-surface geophysical logging were conducted to correlate the various lithological formation forming the different aquifer system. No systematic surface geophysical surveys were conducted in this project. The geophysical surveys conducted during Betwa project are described below.

Betwa Project:

The project area, the surface geophysical investigations, initiated in November, 1976, were carried out employing resistivity, seismic, magnetic, VLF (e.m.) and induced polarization methods in order to select the suitable geophysical methods which are likely to give more useful results in the project area. This was followed by detailed surveys in February, 1977 employing gravity method in addition to the above methods in Deccan basalt and Vindhyans. Finally in the last phase, detailed surveys employing resistivity surveys, seismic refraction, and VLF (e.m.) methods were undertaken in granitic area near Lalitpur in UP.

The objectives of the geophysical surveys for Betwa project project area were:

(a) to determine the response of the formations occurring in the Betwa catchment to different geophysical techniques.

(b) to asses the results in terms of their relevance to hydrogeological studies and drilling results in hard rock areas with regard

(i) to delineate the zone of fractured or jointed rocks occurring at depth in the top flow (shallow aquifer) which is likely to be associated with higher yields,

(ii) to indicate the occurrence of deeper aquifers which are likely to have high yield and

(iii) to delineate Trap/ Vindhyan contact at depths.

GEOPHYSICAL SURVEYS FOR SHORT-TERM WATER SUPPLY INVESTIGATIONS

Central Ground Water Board is taking up short-term surveys for augmenting water supply to various government, non - government organizations, industries etc. on payment basis. In this connection, a number of geophysical investigations have been conducted at places to identify suitable location point for drilling of borehole for water supply scheme. The list of geophysical surveys conducted for short-term water supply investigation are given below:

1. Forest Research Institute, Jabalpur

2. Cantonment Area, Jabalpur

3. Central Ordinance factory, Jabalpur

4. Vehicle Factory, Jabalpur

5. Industrial Area, Mandideep, Raisen

6. Western Coal field, Chirmiri,Sarguja

7. NABARD Quarters, Bhopal

8. MP Scouts and guide, Gandhi Nagar, Bhopal

9. Ordinance factory, Khamaria, Jabalpur

10. Working women hostel, University campus, Bhopal

11. Central plastic research institute, Bhopal

12. Eastern Circuit Ltd, Pilukheri, Rajgarh

13. BDA defence Colony, Bairagarh, Bhopal

14. Anant Spining mills, Mandideep, Raisen

15. Lal Bahadur Shastri Institute, Solsinda, Indore

16. Pahwa Rubber Ltd, Mandideep, Raisen

17. Model Airport, Indore

18. OPTEL telecommunication, Mandideep, Raisen

19. Bhopal Airport Authority, Bhopal

20. CPWD general pool residential quarter, Bhopal

21. GSI Campus Bhopal

22. Naval Selection center, Bhopal

23. MHOW cantonment, Indore.

24. Sukhi-Sewaniwa Firing range, Bhopa.

25. Military Farm area, Bhopa.

26. Central Warehouse Corporation, Khandwa.

27. MP Council of Science ant technology, Obedullahgaj, Bhopal.

28. Indian meteorological department, Bhopal.

29. National Law Institute, Bhopal.

30. Bhopal Development Authority, Bhopal.

31. Sports Authority of India, Bhopal.

32. Military Engineering Services, Gwalior.

33. Air Force Center, Gwalior.

34. Indian Institute of Soil Sciences, Bhopal.

35. Central Institute of Agriculture Engineering, Bhopal.

36. Power Grid corporation, Khandwa.

RESISTIVITY SURVEYS FOR ARTIFICIAL RECHARGE OF GROUNDWATER

Apart from groundwater exploration work, geophysical surveys have also been conducted for other purposes like artificial groundwater recharge, watershed development studies and pollution studies. We know that water is the basic need for most of activities in a watershed and today groundwater is being considered as much more valuable resource than it was in the past. Hence, groundwater exploration, exploitation and management are coming to merit the geo-scientific techniques. Due to increased demand and over-exploitation of groundwater in watershed area, the search for potential groundwater zones and its augmentation through various artificial recharge structure is imperative. The basic considerations for understanding the sub-surface behavior of a watershed are characteristics of soils, overburden thickness, direction of groundwater flow, sub-surface basement topography, nature of watershed fills, presence of fracture/micro-fracture in the watershed, geology and geological structures. These basic considerations can be easily obtained through geophysical techniques for selecting areas, zones and locations for the desired sustainable development of the watershed.

The resistivity surveys conducted in Chhoti Kali Sindh watershed of Dewas district, Jabera watershed of Damoh district and Tumar Watershed of Mandsaur district for siting suitable locations for artificial recharge of ground water are being discussed below:

Chhoti Kali Sindh Watershed, Dewas District

Chhoti Kali Sindh watershed is situated in Dewas/Tori Kalan block of Dewas district between north latitudes 22o52'10" to 24 o04'40" and east longitude 76o02'06" to 76o08'22" (Survey of India toposheet 55 A/4 and 55 B/1). The total geographical area of watershed is about 982km and there are 21 villages in this watershed. There are three water supply schemes namely Siya complex, Bilawali area and Amlawati area having 18 operational wells supplying water to Dewas township. A large number of irrigation wells are also present in this watershed.

Chhoti Kali Sindh is covered by Deccan trap basaltic rock formation overlain by thick alluvium cover. Due to thick piles of lava flows, the nature and morphology of the pre-volcanic setting have remained obscured and pose different hydrogeological situations and problems. The indiscriminate use of groundwater resource is a serious problem being faced in such geological terrain. The over-exploitation of this valuable groundwater resource has led to many intractable that need immediate attention. Due to heavy withdrawal of groundwater the decline of groundwater levels, dwindling yield of bore wells and sometimes failure of borewells are being observed in recent years. The necessity of augmenting the existing water resources in the area through artificial recharge of groundwater and water conservation measure is felt.

Realizing the difficulties in groundwater situation systematic hydrogeological and geophysical survey were planned to find out the feasibility for artificial recharge of groundwater and water conservation measures. The resistivity surveys comprising Vertical Electrical Sounding (VES) were conducted at about 35 locations covering the area of watershed during FSP 96-97.

Jabera Watershed, Damoh District

Jabera, a fast growing township of Damoh district, is surrounded by Vindhyan hills from all sides and forming a closed valley watershed. To obtain the subsurface hydrogeological condition of watershed area for artificial recharge of groundwater and conservation of rainwater in watershed area, an integrated approach of hydrogeology and geophysics have been applied. The zone of interest has been scanned through hydrogeological surveys followed by surface resistivity soundings. Twenty-seven VES using Schlumberger configuration have been observed. The subsurface hydrogeological condition beneath the area has been presented through geoelectrical cross-section, iso-resistivity map and iso-pach map. It has been found that the thickness of alluvium/unconsolidated formation varies from 5 to 40 mbgl in watershed area.

On the basis of resistivity surveys and hydrogeological conditions prevailing in the watershed area an exploratory borehole is recommended for drilling near Munderi village down to the depth of 120 mbgl. To restrict the groundwater flow subsurface dyke structure is recommended near Banshipuri.

Tumar Watershed, Mandsaur distririct

The watershed area is occupied by Deccan Trap and overlain by alluvial formation. To plan the various watershed development and management strategies , integrated hydrogeological and geophysical investigations have been conducted in Tumar watershed area. About 79 VES were conducted covering whole watershed area. Based on geoelectrical parameters, the shallow subsurface hydrogeological conditions of the watershed area have been presented in the form of geo-electrical cross sections and fence diagram. It is observed that the surface resistivity soundings are very much useful in estimating thickness of porous permeable beds and basement topography of watershed. These informations have been used in identifying / confirming locations for construction of percolation tank, stop dams, subsurface dykes etc. for conservation of rainwater through artificial recharge of groundwater for sustainable watershed development and management. Here, the study presents judicious approach of geophysical investigations for deciphering the hidden sub-surface hydrogeological conditions of watershed area to perform the developmental and management activities.

RESISTIVITY SURVEYS FOR CONSERVATION OF GROUNDWATER

The increased demands of domestic drinking water, irrigation and industrial requirements have drawn the attention of planner towards the conservation of water in the basin itself through artificial recharge of groundwater. Now a days conservation of groundwater is essential component of water resources management. For this purpose construction of various surface and subsurface structures are in practice to artificially regulate the flow of groundwater and induce the recharge effectively in the area. The basic consideration for siting surface and subsurface structures are direction of groundwater flow, overburden thickness, subsurface basement topography, nature of basin fills, presence of fractures/micro-fractures in the basin and geological structures/lineaments. These considerations can be achieved by geophysical methods accurately and rapidly.

Central Ground Water Board, North Central Region has taken up some special studies program for suggesting some suitable sites for making groundwater conservation structures to the State Government Agencies in different parts of M.P. The four locations namely Barwan Kalan in Rajgarh district, Khunpur Pipliya in Dewas district, Tharod in Mandsaur district and around Burhanpur town in Khandwa district had been selected to make subsurface dyke structures across the nalas/rivers flowing in that area. The individual case studies are being discussed below.

Barwan Kala village, Rajgarh district

For this purpose Resistivity surveys were conducted around Barwan Kala village in Rajgarh district to estimate the alluvium thickness for construction of subsurface dyke. Thirteen VES with maximum current electrode separation (AB = 50 to 200 m) were conducted between Khankar Gandhi and Angadpur villages covering an area of about 7 sq. km. The nature of VES curves (mostly H type) clearly indicates that the alluvium cover present in the entire study area. The study reveals that the thickness of alluvium/weathered cover varies from 6 to 25 m. The geoelctrical cross-section indicates that in southern part of the area i.e, near Angadpur, alternate occurrence of low and high resistivity value layer, below 5.0 mbgl down to a depth of 25.0 mbgl has been deciphered which indicate the presence of next basaltic flow. The lowest alluvium/ weathered thickness of about 6.0 m is picked up in NW part of the study area at VES location and recommended for making sub surface dyke at this location.

Londri river bed, Dewas district

Resistivity surveys were conducted in and around the bed of Londhri river in Dewas district to know the sub-surface topography surrounding the river bed to select the suitable site for constructing sub-surface dyke across the river. An east-west trending geoelectrical cross section along the bed of Londhri river reveals the presence of three major geo-electrical layers. It is observed that the thickness of top unsaturated alluvium layer varies between 1.0 and 4.0 m. The second layer having the resistivity of the order of 2 to 5 ohm-m represents the saturated alluvium layer with thickness varying from 3 to 25 m bgl. The Thickness of the alluvium layer is maximum in eastern part of the section near village Mangariya and is minimum in the central part near village Khunpur Pipliya. The third layer having the resistivity of the order of 40 to 110 ohm-m is representing hard rock formation, which may be basalt. On the basis of geophysical results, a structure for conservation of ground water was recommended near Khunpur Pipliya village.

Tharod village, Mandsaur district

In order to recharge the phreatic aquifer, a site was proposed for construction of sub-surface dyke near village Tharod in Mandsaur district, where the deeper aquifer are holding poor quality of groundwater. Resistivity surveys comprising 11 VES have been conducted in south-east part of village Tharod with objective to assess the alluvium/weathered thickness overlying the Basaltic rock formation and also to find the variation in ground water quality for deciding the location, height and other designed parameters of sub-surface dyke structure. The study reveals that the thickness of alluvium/ weathered cover overlying basalt varies from 2 to 20 m. It is observed that the thickness of alluvium/weathered formation increases towards the east direction near the railway bridge. Survey results also indicate that another low resistivity formation (may be weathered/fractured basaltic formation) is underlying the hard rock formation. On the basis of hydrogeological and geophysical consideration the location of sub-surface dyke recommended across the nala near railway bridge located in south-eastern part of the village.

Burhanpur area, Khandwa district

A site proposed for construction of sub-surface dyke in a alluvium tract of Tapi river around Burhanpur township in Khandwa district has been investigated by resistivity surveys. The objective of the investigation was to assess the alluvium/ weathered thickness along the nala flowing in western side of Mohamdpur village and estimation of thickness of calcareous bed overlying clay bed in the area to decide the location, height and other design parameters of sub-surface dyke structure for artificial recharge of ground water. Eleven VES with maximum current electrode separation of 50 to 1000 m were conducted across the nala in western side of Mohamdpur village and around Chinta Haran.

A east-west trending geo-electrical cross-section along village Biroda and Kala Chabutra clearly presents the sub-surface lithological conditions. The thickness of the upper calcareous bed underlying the top unsaturated layer is estimated for study area.

Two parallel E-W trending geo-electrical cross-sections along the nala flowing toward south in western side of village Mohamadpur indicate the presence of three to four geoelectrical layer sequence. On the basis of resistivity surveys two locations ie. western side of Mohamadpur village and around Khuni Bhandara area have been selected for construction of sub-surface dyke for artificial recharge of ground water.

RESISTIVITY SURVEYS FOR POLLUTION STUDY

Pollution of the shallow aquifers by the industrial waste effluents throughout their journey from the source, is alarming in several parts of the state, mainly in soft rock terrain where they have better path for transport. Groundwater pollution studies though quite a young discipline, face the challenge. Geophysics can make a humble contribution in its success. Electrical and electro-magnetic can be employed to demarcate the affected areas in terms of enhanced electrical conductivity of groundwater. The techniques are already in practice in other parts of the country. A detailed study have been conducted for detection of spatial distribution of the level of contamination in terms of conductivity and monitoring the lateral and vertical movement of the pollution concentration in Pithampura industrial area of Dhar district.

Schlumberger VES and Wenner resistivity profiling have been conducted to map the subsurface resistivity. The pseudo section of Wenner resistivity profile identified the path of pollutant movement. VES conducted in different seasons indicated the influence of groundwater recharge on the intensity of groundwater pollution. The VES conducted in the month of May (Pre monsoon) indicated the apparent resistivity value of the order 60 ohm-m in shallower region while it is in the range of 90 ohm-m in deeper region. The VES conducted at the same location in the month of October (Post monsoon) have resistivity value of the order of 10 ohm-m in shallower region and 120 ohm-m in deeper region. The variation in pre and post monsoon resistivity value revealed that lowering of resistivity in sallow part is due to groundwater saturation in shallow aquifer where as the increase in apparent resistivity of deeper zone is due to improvement in groundwater quality of deeper aquifer due to increase in water saturation. The VES conducted in the month of December indicate that the shallow aquifer is being de-saturated and pollution in deeper aquifer is increasing.