Centre for Remote Sensing, Bharathidasan University
Khajamalai Campus, Trichirappalli-620 023. Tamil Nadu, India
Email: [email protected]
The growth of the population is increases year by year more stress on agriculture sector for increasing the food grain production, which consequently increased deforestation and demand for more water. Trochirappalli environs, Tamil Nadir, are chronically drought prone and faces acute water scarcity not only drinking purposes but also agriculture purposes. The available surface water resources are inadequate to meet the entire water requirement for different purposes. So the demand for under ground water has increased each and every year.
In general, surface water are more pollution when compare to groundwater. Hence, groundwater serves as a very important source of water for various purposes not only urban development but also rural habitations improvements. In the hard rock terrain exploration groundwater studies are carried out using various conventional methods. In recent years extensive use of satellite remote sensing has made it easier to define the spatial distribution of different groundwater potential zones based on the geomorphology and it’s associated features (Prithvi Raju, 1980; Sankar et.al. 1993). In numerous earlier investigations (Bedi and Bhan, 1978; Karanth and Seshu Babu, 1978; Moore, 1978; Bhattacharya et.al 1979; Raju et.al 1985; Sinha et.al 1990; Satyanarayana 1991; Rao, 1991; Prakash and Mishra, 1991; Tiwari and Rai 1996; Palanivel et.al 1996; Ravidran and Jeyaram , 1997; Pradeep, 1998; Kumar et.al 1999 have been applied for remote sensing techniques for groundwater studies. The interpretation of satellite data in conjunction with sufficient ground truth information makes it possible to identify and outline various ground features such as geological structures, geomorphic features and their hydraulic characters (Das et.al 1997), that may serve as direct or indirect indicators of the presence of groundwater ( Ravindran and Jeyaram (1997).
The area under study Trichirappalli environs central part of Tamil Nadu State. It lies between north latitudes of 9° 45′ to 11° 15′ and east longitudes 78° 15′ to 80° 30′ covers an areas about 9000 sq.km. The major river Cauvery is ephemeral nature through the area from east to west. The average annual rainfall in the area is 95 cm. In the study area, falls under the rocks age group of Achaeans, Cretaceous groups, Tertiary sedimentary formations and an isolated pockets of Gondwanas. More than sixty percentage of area covered by hard rocks while the sedimentary formations occupy the rest.
Physiography and hydrogeology:
In this study area is plain but gently sloping towards the east and southeast. The elevation of the area is in general ranges from 300 – 500 m above MSL. The area is drained by Cauvery River and its tributaries as well as Amaravathi and Bhavani rivers. Groundwater occurs underwater table conditions especially in the weathered and fractured portions of the crystalline formations. The depth of groundwater table ranges from a few m to thirty m below ground level. In the sedimentary areas groundwater occurs under semi-confined conditions, water level ranges from a few m to 20 m below ground level.
Drainage is mostly dendritic to sub-dendritic patterns controlled by fracture and joints are exists in the hard rock areas where as sedimentary areas, parallel to sub parallel pattern is well developed in the east, northeast and southeastern part of the study area. Data used
IRS 1A LISS I (Path 24 and Row 61) imagery for visual interpretation Survey of India toposheets Nos.56J/9,10,11,13,14,15,12&16 and 58N/1,2,3,4 and 80/1.
The IRS IA LISS I (false colour composite) has been visually interpreted by using standard interpretation keys such as colour, tone, texture, pattern of drainage, shape and topography etc., to prepare geomorphological maps. All the conventional information such as geological, hydrogeological, well inventory data and also the information collected during the field checks was used in the finalization of the hydro-geomorphological maps.
Results and discussion:
Geologically, Trichirappalli environs falls under both hard crystalline and sedimentary formations. The hard rocks include hornblende biotite gneisses, charnockites, granitic gneisses and anorthosites of Archaean age. The pegmatite / quartzite’s vein is present in the intrusive bodies, which act as good groundwater barriers to store groundwater (Karanth et.al. 1992; Scuba Rao, 1992). A number of structural features like antifoam folds, conform folds and overturned folds are found (Fig.1). The sedimentary formations beds overlie the crystalline formations in the areas of northeastern, eastern and southeastern parts. Sedimentary rocks comprised of laterite uplands, sandstone (Tertiary age), an isolated pocket of durry crust (Cretaceous formations) and patches of Gondwana formations. The boundary between crystalline and sedimentary units lies east of Senkipatti and north of Alathur. The major rock types are encountered in the sedimentary areas sandstone, clay, laterites, sands shale, kankar, limestone and fossiliferous limestone etc.,
Well inventory was conducted by open well observing the well cross sections and lithology of the various bore wells and dug wells information was collected from the well owners and drillers. Well depth, water level below ground level, water level fluctuations and yielding capacities of the individual wells are given in the Table 1.
The geological, structural, well inventory, hydrological data was integrated with the remote sensing technology information for the preparation of hydro-geomorphological maps (Fig.2)
Structural hills are the linear or arcuate hills exhibiting definite trend lines and charnockites formations. These hills are structurally controlled with complex folding, faulting, criss-crossed by numerous joints/fractures which facilitate some infiltration and mostly act as run off zones. These are found to be north to northwestern parts of the study areas. The structural trend of the hills ranges in the southwest to northeastern direction with slight deviation towards the western part. The slope of the hills ranges from 2 degree to 4 degree. In this unit groundwater prospects is very poor.
Denudational hills and residual hills:
Denudational hills are marked by sharp to blunt crest lines with rugged tops indicating that the surface run off at the upper reaches of the hills has caused rill erosion. They are mostly exposed to the south to southwest. Denudational hills comprised of charnockites, hornblende biotite gneisses, and anorthosites/ quartzites. These are found to be south-central to southwest. A few pockets of denudational hills exist in the northwestern parts of the study area are mostly covered with forest leaving no common tonal characteristics for their identification. But that could be interpreted from their massive size and dotal to elliptical shape. The rugged topography of this region is due to the erosion of the denudational hills to the plain region, leaving the rock exposed. The groundwater potential is moderate to poor.
Residual hills are the end products of the process of pediplanation, which reduces the original mountain masses into a series of scattered knolls standing on the pediplains (Thornbury, 1990). The hills more resistant formation standing out prominently differential erosion and weathering. It’s occurring as isolated patches are found at lower altitudes complex to the denudational hills. In spite of their isolated occurrence, their continuity in a linear or curvilinear fashion gives indication that they are structurally controlled. The shape of the residual hills, controlled by the different lithological composition, distribution and spacing of joints and fractures. In the imageries dark grey tone and coarse texture in block and white images and dark reddish colour in false colour composite with radial drainages pattern (Gupta 1980). Groundwater prospects are beloved to be poor in the areas.
In this unit developed as a result of continuous processes of pedimentation. The altitudinal variations is relatively high for rolling plain and is about 5 -10 m. In this horizon are exists irregular dissected portions with a number of gully are present. The pediplain with sedimentary rocks exposures (Upper Cretaceous formations) are to be found in the north-eastern part of the area. This formed due to intensive weathering under semi arid climatic conditions, representing final stage of the cyclic erosion (Knig, 1950 and Sparks, 1960). These are identified in the imageries grey tone on false colour composite (Ghose, 1993). Groundwater prospects in this unit good due to the moderate thickness (15-20 m) weathering materials (Prakash and Mishra 1993). Pedipalin are also found in the western part of the area.
Pediment is isolated residual hillocks being remnants of weathering and denudation. Inselbergs are mostly barren, rocky, usually smooth and rounded small hills. This unit occurs in the northern, north-western and south-western parts of the study areas. From this groundwater point of these are all treated neither containing nor transmitting of waters i.e. aquifuge nature. Mostly acts as run off zones.
This unit is basically pediments zone and various soil types cover over the pediment materials. This unit is very low weathering thickness of the materials up to 5 m . These units characterized by very high runoff zone and poor groundwater recharge horizons. These units are found to be north, north-western, central, south and south-western parts of the study area.
Buried pediments (medium):
This units is moderately weathered with a thickness varies from 5-20 m . The groundwater prospects in these units are moderately good. In this zone are found close of the Cauvery River, south-central, southwest and southern parts of the study areas.
Buried pediments (deep):
These units mainly due to highly weathering of the hornblende biotite gneisses under semi-arid climatic conditions. In this unit infiltration is moderately good. The thickness of weathered zone varies from 10-20m and favours a good amount of water to circulate within this zone before reaching the deeper fracture zone. Groundwater potential zone is very good and this unit is suitable for dugwell, dugcumbore wells and bore wells. Buried pediments are found detached pockets of the entire study area.
This is the youngest geological unit and including various landforms formed by fluvial action. This consists of sand, silt and clays and facilities channel bed infiltration. It is a highly permeable zone helping in partial bank recharge and subsurface flow groundwater occurs under semi-confined to perched water table conditions with shallow water levels. Groundwater prospects in flood plains are almost invariably found to be good (Sharma and Jugran 1992). In this units are exists all along the Cauvery river courses.
Deltaic plain is the major geomorphic unit in the area, and is under intensive cultivation. It is occupy about twenty percentage of the area and is comprised of finer loosely packed sediments. Within the deltaic plain some localized low lying areas, affected by water logged and soil salinity or alkalinity are found. The water logging and salinity problems may be due to the rising the water level, low lying topography and seepage from canals etc., This zone are found to be southeast, east, north-eastern parts of the study area.
Paleochannels or old river courses, buried by subsequent sedimentation, are generally potential reservoirs for groundwater and hence useful for groundwater exploration. In addition to that, the paleochannel identification useful in flood mitigation. In the identification of paleochannel contrasting dark tone in a characteristics winding fashion in association with cropping pattern and linearly oriented vegetation.
Several paleochannel are found to be deltaic region of the Cauvery river delta filled with sands. Soils in this region more moisture content as compared to the surrounding areas due to the groundwater flow zones. The paleochannels are observed mainly in the south eastern and eastern parts of the study area especially deltaic region of the Cauvery River. This areas falls under the low-lying topography. The origin of the paleochannels may be due to the frequent changes in the river of Cauvery.
Groundwater prospects in buried channel are excellent because of hydrophilic nature of alluvial and colluvium deposits, retention of foot waters, location of contiguous to the river mainly responsible for recharge.
Lateritic uplands/ sandstone:
Lateritic uplands/Sandstone are developed over early Pleistocene to Recent age groups. The thickness varying from 10-15m and its characterized by moderate to good infiltration from rainfall and considerable water table fluctuations. Groundwater prospects in this unit are moderate to good in this zone because of the aquifer horizons sand. A number of laterite uplands are found to be northeastern, eastern and southeastern parts of the study areas.
A lineament is defined as a large-scale linear feature, which expresses itself in terms of topography, which is in itself, an expression of the underlying structural features. From the groundwater point of view such features may include, valleys controlled by faulting and jointing, hill ranges and ridges, displacements and abrupt truncation of rocks, straight streams and right angles off setting of stream courses etc., (Merh et.al., 1989 and Ramesh, 1990). A lineament is a regional scale linear or curvilinear feature, pattern or changes in pattern that can be identified in a data set and attributed to a geologic formation or structure (Qureshy and Hinze,1989). The linear features can be measured and treated quantitatively like measurements of other geological properties, but it is necessary to use formal statistics that reflect the circular nature of the directional data (Cheeney, 1983; Gaile and Burt, 1980 and Gambel et al 1953; Mardia 1972). Lineaments are linear fractures commonly associated with dislocation and deformations. They provide the pathways for groundwater movement and are hydrogeologically very important Sankar et.al 1996. Lineaments are important in rocks where secondary permeability and porosity dominate and inter-granular characteristics combine in secondary openings influencing weathering, soil water and groundwater movements. The fracture zone forms an interlaced network of high transmissivity and serve as groundwater conduits in massive rocks in inter-fracture areas. The lineament intersection areas are considered as good groundwater potential zones. The combination of fractures and topographically low grounds can also serve as the best aquifers horizons (Karanth, 1989; Subba Rao, 1992). A numerous lineaments were marked in this study area. The lineaments are trending in the directions of northeast to southwest, north to south. A few of them east-west direction also. The distribution of lineaments is maximum in the western part where as minimum are found to be eastern part. The length of the lineaments a few km to several kilometres ( Fig.3).
Finally, Trichirappalli environs has been classified into three zones on the basis of their groundwater potential zones such as low, moderate and good after integrating well inventory, yield characteristics along with geological, geomorphological and hydrogeological informations (Fig.4).
Summary and conclusion:
Visual interpretation of IRS 1A Satellite imageries provided information related to the geology, geomorphology, lineaments interpretation was helpful in knowing the nature and water potentiality of different geomorphic units. The composition of materials of landforms, and there from inferred rechargebility and other hydrogeomorphic characteristics aid in identifying the groundwater potential zones.
Geologically, the area is occupied both hard and sedimentary formations. The hard rocks include hornblende biotite gneisses, granitic gneisses, charnockites, anorthosites, quarzites, and pegmatites. In the sedimentary formations comprised of sandstone, shale, clay, limestone, shell limestone and kankar etc. The majority of the fractures patterns northeast to southwest, southeast to northeast and east to west directions.
Hydrogeomorphologically, the investigated areas occupied by denudational hills, Residual hills, structural hills, Pediments, Pediplains, flood plains, buried pediments shallow, medium, deep and deltaic plians. By studying the hydrogeomorphological conditions of the area, it is possible to deciper the groundwater potentiality. Most part of the area moderate to good, while rest of the area buried pediments medium, pediplains having moderate groundwater potential zones. In this area dug wells are recommended. In the shallow pediments, pediments areas dug-cum-bore wells are recommended because, the water level will lower during pre-monsoon period. Bore well are recommended the lineaments and intersections areas. In addition to that electrical resistivity survey is required for to locate the exact location of good bore wells/tube wells sites in the areas.
In the investigated area has undergone successive tectonic activities and is traversed by a number of lineaments whose analyses from IRS 1A satellite imageries interpretation provides useful information about tectonics and the structure of the area. Acknowledgement:
The author is grateful to The Director, Centre for Remote Sensing, Bharathidasan University, Khajamalai Campus, Trichirappalli 620 023, for providing the work facilities and permitting to carry out the research work.
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