Integrated analysis of Geophysical Data of Ponnaiyar river basin using Arcview GIS Software Ruby.D 1, Chitra.C 1, Vasantha.A 1, Ramasubbulakshmi.T 1, Manivel.M 2 1 Research Scholar, Department of Geology, School of Geosciences, Bharathidasan University, Tiruchirappalli 24 Tamil Nadu 2 Professor and Head, Department of Geology, School of Geoscience, Bharathidasan University, Tiruchirappalli 24 Tamil Nadu rubyasha@gmail.com ABSTRACT A model of aquifer geometry of Ponnaiyar River basin is simulated with in agreeable degree of accuracy. The Vertical Electrical Sounding (VES) together lithologs forms the data base in the determination of depth, thickness and spatial distribution of overburden, weathered rock, fractured rock and bed rock and the corresponding themes are shown as surface plot, Contours, 3D plot and cross section with the effluent use of GIS packages Arc View. There exist close correspondence between the pattern of drainage and the aquifer dimension. Along the rivers and parts of the foothills region, deep weathered and/ or fracturing is noticed. Themes of topsoil, weathered rock, deep weathered rock and fractured rock are integrated digitally in order to obtain the places where thickness of all the three are more, thus suitable for artificial recharge (RWS). The results generated from this research will be of great help in various numerical solutions and GIS analysis pertaining to this basin. The technique of resistivity method proved to be successful where the data analyzed in group for specific area reveled satisfactory results in characterizing the aquifer geometry, although the utility of this technique for locating water well sites in hard rock areas cost doubt in certain cases. Keywords: GIS studies, Ponnaiyar river, 3Dplot, VES technique. 1. Introduction A model of aquifer geometry of ponnaiyar basin is simulated with an agreeable degree of accuracy. The vertical electrical sounding (VES) together with borehole lithogs forms the database in the determination of depth, thickness and spatial distribution of overburden, weathered rock, fractured rock and bed rock: and the corresponding themes are shown as surface plot, contours, 3D plot and cross section with the efficient use of GIS package Arc View. There exist close correspondence between the pattern of drainage and the aquifer dimension. The sedimentary crystalline contact as well as the probable presence of buried channel/ old river course in the eastern alluvial areas is also brought out through this analysis. Along the rivers and parts of the foothills region, deep weathering and /or fracturing is noticed. Themes of topsoil, weathered rock and fractured rock are integrated digitally in order to obtain the process where thicknesses of all the three are more, thus suitable for artificial recharge (RWH). The results generated from this research will be of great help in various numerical solutions and GIS analysis pertaining to this basin. This technique of resistivity method proved to be successful 456
where the data analyzed in group for specific area revealed satisfactory results in characterizing the aquifer geometry, although the utility of this technique for locating water well sites in hard rock areas cast doubt in certain cases. 2. Aim and Objectives 1. To delineate thickness, spatial distribution of top soil, weathered rock, fractured rock and fresh rock with the help of GIS Software. 2. To create 3D plot cross section of the area. 3. To analyze the hydrological data of the basin separately in the GIS environment. 4. To analyze the groundwater quality basin through integrated analysis of all the thematic maps of aquifer maps of aquifer geometry in GIS environment, to obtain suitable groundwater recharge area. 3. Scope of Study The results generated from this research will be of great help in various numerical solutions and GIS analysis pertaining to this basin. The technique of resistivity method proved to be successful where the data analyzed in group for specific area revealed satisfactory results in characterizing the aquifer geometry, although the utility of this technique for locating water well sites in hard rock areas cast doubt in certain cases. 4. Study Area Figure 1: Location of Vertical Electrical Sounding Sites(VES) in Ponnaiyar River Basin Ponnaiyar river basin extends over approximately of 11,441 sq. km, VES area covers 9119km 2 and Hill area covers 23.49km 2 and lies between 11 0 35 and 12 0 35 N latitudes and 77 0 45 and 79 0 55 E longitudes. This river basin is drained by ponnaiyar as well as its tributaries Pambar, Vaniar, Turinjalar etc., Triuvannamalai is situated in the northern side, Cuddalore and Villupuram in east and Dharmapuri and Hosur in western side. 457
5. Methodology A variety of techniques can be employed for groundwater targeting and delineation of aquifers in areas of complex geological setting, especially in hard rock terrains. However, surface investigations of groundwater are seldom more than partially successful as the results usually leave hydro geological picture incomplete. In such situations, an integrated approach, employing a combination of hydro geological, remote sensing and selected geophysical techniques, has been found to yield optimum results (Singhal et al., 1988). Traditional methods for characterizing aquifer layers include test hole drilling and analyses of log, with the objective being to characterize thickness and/or lateral extent of the aquifer layers. 5.1. Hydrogeology The basin approximately 11,441 km2 has tropical, semi arid climatic conditions. The ground water level follows the topography, where the groundwater flows toward east with a gentle hydraulic gradient. In general, the area commonly called as hard rock, is underlain predominantly by granite gneiss, charnockite and hybrid gneiss. The average annual rainfall of this basin ranges from 1000 to 1100 mm per annum. The average pre monsoon water level of this basin ranges from 5 to 9 m bgl. The groundwater quality of this basin is generally good to moderate with an average TOS of 500 to 1000 mg/l. However along the alluvial coastal zone the quality of groundwater may be saline at depths due to seawater intrusion. Respective maps discussed in this paragraph are available in UNDP, 1986. 5.2. Geophysical Survey through Vertical Electrical Sounding The field curves are interpreted by the well known method of curve matching with the aid of a computer code suited for analyzing the data of Wenner configuration. A majority of the VES curves indicate a four layered sub surface in the area, corresponding to the topsoil, weathered rock, fractured rock and basement. The information thus obtained along with that of the borehole litho logs were used as attributes in the GIS environment for the creation of thematic maps depicted as surface plots/contours/3 D plot/cross section showing the spatial and/or vertical distribution pattern of topsoil, weathered rock, fractured rock and fresh rock of the basin. 5.3. Geo Physical Method Geophysics as the name itself implies the study of the physical properties of the earth or physics as applied to geology. Hence a geophysicist should have a sound knowledge of geology, physics and to certain extend mathematics with the recent developments, and he should also have some acquaintance with electronics and instrumentation. Geophysical methods utilize certain physical properties of subsurface materials in arriving at the nature and composition of the certain subsurface. Depending on the physical properties of the field measured there are four methods of prospecting, viz., 458
Gravity, Magnetic, Seismic and Electrical. 5.4. Gravitational Method The name gravitational exploration is derived from the Latin word 'Gravis' meaning heavy. Some mineral deposits and rocks have higher or lower densities compared to the average density of the rock formations surrounding them. The aim of the gravitational prospecting is to detect underground structures by means of the changes or anomalies they produce at the surface in the gravitational field. 5.5. Magnetic Method Most of the rocks contain a small amount of Ferro magnetic materials like Magnetite, Hematite and Pyrrhotite and possess some induced magnetism. This magnetization field to an extent that can be detected by measurements on the surface using magnetic instruments. The unit of magnetic intensity is the Gauss named after the German mathematician Gauss. Another unit is Oersted, named after the Danish physicist 'Oersted'. 5.6. Seismic Method This method is based on the property of rocks to transmit seismic wave with different velocities. In the seismic method, an elastic pulse is created at the earth's surface by a dynamite explosive and the resulting ground motion at nearby points at known distance are measured by what are called Geophones. 5.7. Electrical Resistivity Prospecting Methods Electrical resistivity is widely used in ground water investigation works. This study provides a Method for subsurface exploration by means of electrical measurements taken at the surface of the earth. This study is useful where there is no outs crop or well cuttings available. In this method, four electrodes separated by certain distance are stumped. Electrical current either D.C or low frequency A.C from a power source battery two of these outer electrodes and the resulting voltage drop produced by this current in the earth is measured across the inner electrodes. It can be stated that electrical resistivity study can be tried to Locate high or low resistivity subsurface materials. Locate fault zones, which serve as Channel for ground water movement. Locate areas of weathered rocks and thickness of such rocks, Estimate the depth of occurrence of fresh rocks. Demarcate fresh and salt water contact and Determine the sequence of high and low resistivity zones saturated with 459
groundwater. Use Of Electrical Resistivity Method Some of the geographical investigations that can done by the electrical resistivity method for ground water studies are: Correlating lithology and drawing geophysical sections. Bed rock profile for subsurface studies. Fresh water salt water interface by constant separation profiling. Contact of geological formations. Water quality in shallow aquifers and ground water pollutions as in oils field brine pollution, pollution by irrigation waters and pollution by sea water intrusion, which cause change in electrical conductivity. 5.8. Wenner Method In the Wenner method, the 4 electrodes are laid out at Equal Intervals along a line. The purpose of this arrangement as said earlier, is to measure the resistance offered by the earth (designated as pa) can be calculated for the Wenner arrangement by the formula 21taR.If the subsurface is non uniform the earth's resistivity will no longer be the true or absolute resistivity, but only apparent. Hence, it is called apparent resistivity and designated as pa. If the D.C current is used, measurements are made both in the direct and reverse directions and their average is taken as the apparent resistivity. The apparent resistivity data so derived is analyzed to arrive at the true resistivity values of the different layers. 5.9. Field Procedures, Preparation Of Graphs And Interpretations Two field procedures of the electrical resistivity survey are in common use profiling and sounding. In profiling the electrode spacing 'a' is held constant during successive readings and the entire spread is moved as a unit from place to place. Moreover, profiling is used to detect sub surface change in a horizontal direction, as for instance in knowing the extent of an aquifer of a fault zone, fresh water/saltwater boundaries, extent of dykes etc., 6. Result and discussion The resistivity method is carried out to solve more problems of groundwater in the types of alluvium and other hard formation aquifer as an inexpensive and useful method. However, when resistivity methods are used, limitation can be expected if ground inhomogeneties and anisotropy are presented (Lashkaripour, 2003). The key to success of any geophysical survey is the calibration of the geophysical data with hydro geological and geological ground truth information. Though the. formation resistivity of this basin 460
cannot be defined perfectly, the approximate range of resistivity of water bearing formation of topsoil, weathered rock, fractured rock, fresh rock and alluvium/sandstone can be generalized as 20 100 n m, 50 200 n m, 150 350 n m, >350 n m and 20 150 11 m respectively. Figure 2: Composite map showing the areas where top soil, weathered rock, and fractured rock thickness are more in ponnaiyar river basin Figure 3: Litholgical cross section of Ponnaiyar river basin 461
Figure 4: A 3D view of depth to bottom of fractured rock of Ponnaiyar river basin Figure 5: Drainage map of Ponnaiyar river basin 462
The formation resistivity may be very less (5 30 n m) along the coast, in the areas of seawater intrusion. Because of the wealth of VES and borehole litholog data available for Ponnaiyar basin, the simulation of aquifer geometry seems to be most appropriate. t is well known that aquifer dimension alone is always not effective in groundwater prospecting, if used in isolation. Adequate analysis of aquifer properties (T, K, and S), hydro geological data like water level, water quality, recharge, and discharge conditions should necessarily be considered, particularly integrated with GIS tool in order to obtain realistic picture of potential aquifer zone, which is beyond the scope of this particular analysis. Even though resistivity method gives satisfactory results in the determination of interface saline water and freshwater, this research is not focused in that direction to the zones close to the sea (coastal area in the east). The basic classification adopted within each layer/theme if changed or a different classification may certainly give a rather different picture; however a compromise is needed to concise the analysis. Dominance of weathering and/or fracturing along the rivers and some parts of foothills are noticed while reviewing the themes of depth to these zones. The land use pattern of this basin cannot be correlated much with the aquifer layers unless a clear picture of the areas of groundwater fed irrigation in this basin is known, however the dominance of return flow is correlatable. Rather poor drainage density generally suggests the dominance of less runoff as well as dominant recharge to groundwater. 7. Conclusion It can be concluded that the possibility of tapping groundwater resources in this basin is bright even though some additional exercise pertaining to integrated analysis is lacking. In this study, though various themes of relevance are not digitally integrated, the difficulty is overcome by appropriate comparisons made visually. Strong correlation exists between the layers determined from this analysis and various other themes of this basin viz. drainage, geomorphology and satellite imagery, which suggests the reliability of the results brought out through this analysis. The thick zones of weathered and/or fractured rock are favorable for construction of bore wells. Though the study has given credible results, any drilling for groundwater based on this may require adequate field verification or any large scale planning require adequate sample test verification. The simulation of aquifer dimension will be of immense help in the hydrologic study, particularly for the mathematical modeling exercise carried out for flow and solute transport simulation, GIS analysis for identifying areas of potential groundwater resources and for identifying favorable locations for artificial recharge (RWH). Due to artificial recharge Increases form income as a result of augmented & dependable water supplies the zones identified through integrated analysis are suitable for carrying out recharge measures. The possibility of lesser weathered rock thickness is expected in the regions of shallow topsoil and greater drainage density, similarly the shallower fractured rock areas coincides with the shallow weathered rock areas and vice versa; although no claim is 463
made about the proper form of the weathering and fracturing function, or that the results reported here will generalize to all domain geologies. Dominance of weathering and/or fracturing along the rivers and some parts of foothills are noticed. The sedimentary crystalline contact as well as the probable presence of buried channel/old river course in the eastern alluvial areas is also brought out through this analysis. Creation of such a database in GIS environment also enables to obtain any number of litho logical cross sections along any profile of interest quite simply as well as rather quickly, which would be of immense help in water resources planning and management. The resistivity data/information at greater density proved to be reliable and much helpful in hydro geological study while analyzed in group for specific area, although it is mostly a game of chance in the process of site selection for drilling for groundwater in hard rock areas (Banks and Skarphagen, 1994). The need for more work is the direction of successful identification of deep fracture horizons employing resistivity method with an acceptable degree of accuracy as pointed out by Ballukraya, et al. (1983) and Ballukraya (2001) is also emphasized. 8. References 1. Allukraya, P.N., Sakthlvadlvel, R. and Baratan, R., 1983. Breaks in resistivity sounding curves as indicators of hard rock aquifers. Nordic Hydrology, Vol.14, pp. 33 40. 2. Ballukraya, P.N., 2001. Hydrogeophysical investigations in Namagiripettai area, Namakkal District, Tamilnadu. Jour. Geol Soc. India, VoL58, pp. 239 249. 3. Banks, D. and Skarphagen, E.R.H., 1994. Groundwater resources in hard rock: Experiences from Hvaler study, southeastern Norway. Applied Hydrology, Vol.2, pp.33 42. 4. Environmental System Research Institute (ESRI), 1997+. User guide Arcinfo, ArcView The Geographical Information System software, Redland, CA: ESRI, Inc. 5. Institute for Water Studies (IWS), 2004. Micro level study. Tamiraparani river basin report, IWS, Public Works Department, Water Resources Organisation, Govt. of Tamilnadu, Chennai 113, Vol I. 6. Kalinski, R.J., Kelly, W.E., and Bogardi, S., 1993. Combined use of geoelectrical sounding and profiling to quantify aquifer protection properties, Ground Water, Vol.31, pp. 538 544. 7. Lashkarlpour, G.R., 2003. An investigation of groundwater condition by geoelectrical resistivity method: A case study in Korin aquifer, southeast Iran. Journal of Spatial Hydrology, Vol.3, No.1, pp. 1 5. 464
8. Singhal, D.C., Sri Nlwas and Singhal, B.B.S., 1988. Integrated approach for aquifer delineation in hard rock terrains A case study from Banda distt., India. Journal of Hydrology, Vo1.98: pp. 165 183. 9. United Nations Development Programme, 1986. Water resources assessment of Ponnaiyar river basin, Strengthening the Institute for Water Studies, Madras, Tamilnadu;.Government of Tamilnadu, Public Works Department, Institute for Water Studies, Madras 600113, Volume I & II. 465