Introduction

The Cuddapah basin is a significant tectonic and orogenic belt of the unfossiliferous Precambrian rocks of Peninsular India. The study area forms a part of the crescent-shaped Cuddapah basin (King 1872; Pascoe 1950; Wadia 1957; Dutt 1966; Krishnan 1968; Crawford and Compston 1973; Murthy et al. 1979; Krishnaswamy 1981) located at the southwestern boundary. Vaidyanadhan (1962, 1967), based on the landforms in the Cuddapah Basin and over the Eastern Ghats, concluded that the Eastern Ghats were heaved up a little due to cymatogenic upwarp during the Mid-Tertiary. Janardhana Raju et al. (1994) have demarcated potential zones for developing groundwater in an adjacent area in the Cuddapah district, based on integrated geological, hydrological and geophysical (electrical resistivity) surveys. In order to ascertain the potential for locating groundwater, the study area has been demarcated into different zones based on geomorphology. The results so obtained have been further corroborated through hydrogeological and geophysical data. The electrical conductivity of groundwater was also measured and areas demarcated to determine its suitability for general use.

Methodology

The satellite data (IRS-1B, LISS–II FCC) at 1:50,000 scale was visually interpreted to delineate various geomorphological units based on structural trends, lineaments, soil tones, vegetative cover and relief linearity. The water-level fluctuation in dug wells was monitored for pre- and post-monsoon seasons from a network of 107 wells uniformly spread over the area during 1996–1997. Representative wells in shale, quartzite, limestone and alluvium were selected, and a few aquifer tests were performed. A total of 112 vertical electrical soundings (VES) were conducted, using the Schlumberger method of electrode configuration. Groundwater quality was determined through a study of electrical conductivity (EC). A combined map of the features (geomorphology, water levels and resistivity) was prepared to correlate them with groundwater availability in different zones.

Study Area

The study area (latitudes 14°29′04″ to 14°39′51″N and longitudes 78°19′12″ to 78°41′32″E) covers an area of about 480 km2 (Fig. 1). The Proterozoic formations of south India occupy a large part of Andhra Pradesh and are designated as the Purana Formations. The Puranas consist of the Cuddapah and Kurnool systems of sedimentary rocks, mainly composed of shales, limestones and quartzites (Table 1). The Pageru River is an ephemeral stream and culminates in the east of the study area into the Papaghni River. The Pageru River basin enjoys a semi-arid climate with temperatures between 24 and 44 °C and an average annual rainfall of 581 mm. The Pageru River basin is a fairly well-drained basin (Fig. 2) with a high drainage density (2.61 km/km2) in the western region and a low drainage density (1.04 km/km2) in the east.

Fig. 1
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Location of Pageru River basin

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Table 1 Stratigraphic succession. After Murthy et al. (1979)
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Fig. 2
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Drainage pattern of Pageru River basin

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The youngest rock formations of the study area are classified as the Cuddapah Super group and the Kurnool group (Fig. 3). The oldest are the Tadipatri formations, belonging to the lower Cuddapah Super group, and are essentially composed of slaty shales with interbedded thin layers of siliceous limestone, quartzite, and basic intrusive sills (Narayanaswami 1966). The formations trend generally NNE–SSW with a gentle dip of about 10°east (Fig. 3). The Tadipatri formation is overlain by the rocks of the Kurnool group, which include quartzite, limestone and shale (Table 1). A distinct angular unconformity separates the Cuddapah formations from the Kurnool rocks, and occurs as horizontal beds over the tilted Cuddapah rocks. An alluvial geomorphic unit of Holocene and Recent age is a more or less stratified deposit of gravel, sand, silt and clay that occurs all along the course of the streams. The alluvium at the confluence of the Rivers Pageru (flowing eastwards) and Papaghni (flowing northwards) near Putlampalli was found to be comprised sand of variable thickness and composed of sandy aquifers occupying the easternmost part of the study area (Sreedevi et al. 2001).

Fig. 3
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Geology of Pageru River basin

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Hydrogeomorphology

Water is an important agent in the formation of landforms (Scheidegger 1973). The satellite images were examined based on visual interpretation and the study area was divided into several geomorphological units such as valley fills, flood plains, alluvial plains, shallow buried pediplains, moderately buried pediplains, pediments and structural landforms (Fig. 4).

Fig. 4
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Hydrogeomorphology of Pageru River basin

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Valley fills were identified along the Pageru River course in the south. Flood plains and alluvial plains (Fig. 4) were demarcated at the confluence of River Pageru (Fig. 2) and River Papaghni (not shown as it is located at the eastern tip of Fig. 2) in the east (Lokesh and Narayana Shenoy 1996; Pandey et al. 2002). The depth to the water table is 2 m below ground level (b.g.l.) in these landforms. The average yield from bored wells varies from 19,200 to 25,200 l/h.

The denuded landforms are the result of weathering and erosion caused by different exogenetic geomorphic agents to form pediments and pediplains, etc. Pediments with a weathered zone thickness of less than 2.5 m predominantly occur in and around Turakapalle and Nallalingayapalle, and as isolated patches in the north-central region in and around Niduzuvvi and Valsapalle (Fig. 1). Generally, these areas are not favourable for groundwater exploration (Krishna Murthy and Srinivas 1995; Sarfaraz Ahmed and Nagi 1999). The water table varies from 4 to 6 m b.g.l. during the pre- to post-monsoon season with average yields ranging from 840 to 2,100 l/h.

Shallow buried pediplains (BP-S) occur along the sloping foothills and are covered by Tadipatri shale, Auk shale, Narji limestone, Koilkuntla limestone and Nandyal shale. The thickness of the weathered zone is less than 5 m and is covered with soil. The water table varies from 2 to 6 m b.g.l. Moderate yields (3,120–5,160 l/h) occur along the fracture zones and bedding planes (Krishna Murthy and Srinivas 1995; Palanivel et al. 1996; Gowd et al. 1998).

Moderately buried pediplains (BP-M) are gently sloping, flat and smooth on the surface of the Tadipatri shale, Auk shale, Narji limestone, Koilkuntla limestone and Nandyal shale, which is weathered to a depth of 15 to 20 m. The groundwater prospects are moderately high in these areas (Krishna Murthy and Srinivas 1995; Srinivas Rao et al. 1997; Gowd et al 1998). The water table varies from 2 to 6 m b.g.l. The average yield from wells ranges from 5,640–11,340 l/h.

The structural landforms identified in the study area are mesas/buttes, Cuesta hill, structural hill and linear ridges. Mesas/buttes are composed of quartzite formations, which are found on the western side of Uppaluru and the northwestern side of Vomikonda villages.

Cuesta hills are gently sloping surfaces, underlain by hard and compact Banaganapalle quartzite, which are nearly parallel to the dip of the bedding planes with escarpments cutting across the bedding planes. This type of landform with a limited horizontal area is observed in the eastern and central parts of the study area.

The structural hills are exposures of linear to acute hills exhibiting definite trends composed of varying lithology. They mostly occupy the western part of the basin. They are mainly composed of the Tadipatri formation. The trend of the structural hills ranges from northwest to southeast. The run-off is high with negligible infiltration, making them poor aquifers (Raju et al. 1989; Gowd et al. 1998). The water levels are below 6 m b.g.l. The average yield ranges from 800 to 1,680 l/h. Linear ridges (LR), observed in the southern region, and composed of basic intrusives, are narrow, and have low relief and generally no vegetative cover. The ridges are mostly strike controlled.

Lineaments

The lineaments in the Precambrian shield areas extend into the sedimentary rocks overlying them and exert their influence in the tectonic history of the younger formations (Vaidyanadhan 1971). It has been suggested that south India has been subjected to certain epeirogenic uplifts since the Jurassic (Vaidyanadhan 1967). The lineaments of the study area have been traced from the satellite data of IRS 1B-LISS II imagery of false colour composite (FCC). A number of mega- and micro-lineaments are identified from the satellite imagery, further checked by field studies, and demarcated at a 1:50,000 map scale. A few faults with clearly visible displacements have been identified running parallel to the trends of regional features (river drainage, lineaments, strike of formations, etc.) with some in a transverse direction to these trends (Fig. 5). The ridges of the crystalline quartzites (adjoining Uppaluru) are marked by faulting with fractures in a NW–SE direction.

Fig. 5
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Distribution of lineaments

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The three lineament sets (NE–SW, NW–SE and latitudinal) exist all over the Precambrian region in India although the actual orientation with respect to the azimuth might differ from place to place by a few degrees (Vaidyanadhan et al. 1971). The lineaments are of varying dimensions and orientations, trending NW–SE and are roughly parallel to the trends of geological formations. A few lineaments strike E–W along the river course. The perfect linearity of the second- and third-order streams also indicates that drainage is controlled by the structural trends of these features. Thus, the Pageru River drainage pattern in general, and tributaries in particular, are controlled by the structures present in the area. The study also indicates that the maximum compressional deformation occurred in the western margin of Cuddapah basin. The interpretation of satellite data also indicates that the rocks appear to have been deformed repeatedly.

Lineament Density

After preparing 2x2-cm grids, the total length of lineament within each grid (1 km2) was measured by a similar method as used by Haridas et al. (1994). These were plotted on the respective grid centres. These values were joined by isolines to prepare a lineament density map (Fig. 6). Quite often it was found that groundwater seepage was along certain prominent lineaments and that this property could be utilised in the search for groundwater (Vaidyanadhan et al. 1971). Lineaments are the main features that control the occurrence of groundwater in the study area. Secondary porosity is imparted by joints and fractures in the areas of higher lineament density. The lineament-density map reveals the variations in the potential for obtaining groundwater in the basin. Stephen Mabee et al. (1994), from a study of regional-scale lineament analysis for fractured bedrock aquifers, concluded that wells located on or near fracture-correlated lineaments are generally more transmissive. Although the majority of the area is underlain by Tadipatri shales, the potential for locating groundwater is moderate (central part), but there are certain significant pockets with a high density of fractures that have a comparatively high potential. There are also medium lineament-density patches with limited areal extent, indicating a moderate potential distributed mostly in the central part and as small patches in other parts of the basin. A large part of the basin area, however, has a low lineament density indicating a poor potential. Based on lineament density, it is inferred that the groundwater prospects are poor in a large part of the study area.

Fig. 6
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Demarcation of lineament density

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Hydrogeology

The hydrogeological condition of the study area is controlled by the lithology, structure and geomorphology. The area is mainly divided lithologically into quartzites, shales and limestones. The groundwater in all the rock formations occurs in unconfined and semi-confined aquifers (Janardhna Raju et al. 1994). The permeabilities of all the formations depend on secondary porosity, except for alluvium where the porous material (gravel and sand) is highly permeable. Alluvium mainly occurs along the river and stream courses and the groundwater is unconfined.

The water-level fluctuations in dug wells were monitored during the pre- and post-monsoon seasons from a network of 107 wells uniformly spread over the study area in 1996–1997. The fluctuations in water levels vary from 1.7 to 7.0 m b.g.l. with a mean water level of 2.03 m b.g.l. Table 2). The total depth of dug wells ranges from 8–15 to about 30–70 m b.g.l. in bored wells.

Table 2 Groundwater occurence in different lithologic/hydrogeomorphological units, Pageru river basin
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Since it was not possible to conduct pumping tests on a large number of wells, the average seasonal fluctuations in water levels was determined to evaluate potential zones for obtaining groundwater, and to also consider the specific yield on a qualitative basis.

Pumping tests have been conducted in four different geological formations (Fig. 5), the details of which are included in Table 3.

Table 3 Results of pumping tests
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Groundwater quality was determined from water samples collected from dug wells and bored wells. The electrical conductivity (EC) variations (post-monsoon measurements) for the entire basin were determined and classified into three categories, as shown on Fig. 7.

Fig. 7
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Distribution of electrical conductivity values

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Geophysical Investigations

Although indirect, the geophysical methods provide information on aquifer geometry that is useful in conceptualization of the aquifer system. A vertical electrical sounding (VES) method was used and a good resistivity contrast was measured between weathered rock containing water and the hard rock without water. Thus, 112 vertical electrical soundings were carried out covering the entire study area, using the Schlumberger method of electrode configuration. Quantitative interpretation of the electrical resistivity data was made by considering the variation in the apparent resistivity for each electrode separation, keeping the place of observation constant. Master curves depicting different geological sections for two, three and four layers with various ratios of absolute resistivities are available and were fitted with field curves to obtain absolute resistivities for the different layers. This method can provide a lot of freedom and has low ambiguity. If the subsurface consists of three layers with varying thicknesses, there will be four possible configurations for their resistivities and corresponding sounding curves (Sreedevi et al., 2001). These are:

$$ \begin{aligned} & {\text{H}}\;{\text{type}} = \rho _{1} > \rho _{2} < \rho _{3} \\ & {\text{K}}\;{\text{type}} = \rho _{1} < \rho _{2} > \rho _{3} \\ & {\text{A}}\;{\text{type}} = \rho _{1} < \rho _{2} < \rho _{3} \\ & {\text{Q}}\;{\text{type}} = \rho _{1} > \rho _{2} > \rho _{3} \\ \end{aligned} $$
(1)

Similarly, for four layers, there could be different configurations. A further ‘A’ type followed by an ‘H’ type is common in three-layer cases and ‘KA’ types followed by ‘HA’ and ‘HH’ types are common in four-layer cases. The depths to the basement derived from the sounding interpretations were in good agreement with the actual depth obtained from the lithologic data collected during the fieldwork from dug wells, dug-cum-bored wells and bored wells. This interpretation has helped us to understand the subsurface layering, degree of saturation and depth to basement of these aquifers.

Discussion and Conclusion

The geomorphology, hydrogeology and resistivity interpretations were integrated to make a map of the potential zones for obtaining groundwater (Fig. 8). The map portrays three zones as poor, moderate and good. The area where the depth to solid rock is very shallow and the saturated zone is thin is characteristic of the entire massive limestone area and is demarcated as the poor zone, which occurs at the northern and southern borders of the basin.

Fig. 8
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Demarcation of the potential of zones for obtaining groundwater

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The zone of moderate potential occurs in the central portion of the basin between the northern and southern basin boundaries, which is occupied by poor zones in massive limestone, and also at the northeastern boundary. Almost the entire moderate zone is in shale.

The good potential zones occur mainly as two isolated patches at the northwestern portion of the basin in Tadipatri shales, near Kolavali and Vontigaripalle within the moderate zone, and a third good zone is near Payasampalle at the southeastern portion of the basin.

Remote sensing data have been used to identify zones in landforms suitable for groundwater prospecting. Groundwater development in the various geomorphic units is promising in flood plains, alluvial plains and valley fills, which are associated with thick alluvium and weathered material that has high porosity and permeability. However, only a small part of the studied area is occupied by these landforms and, hence, favourable zones for obtaining groundwater are very limited in this basin area. A large part of the area is occupied by pediments, pediplains, structural hills, and mesas and buttes that do not favour much infiltration and, hence, are generally not favourable for groundwater exploration. Irrigation suitability, based on EC and SAR (Fig. 9), shows that many of the samples fall in doubtful to unsuitable classes.

Fig. 9
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Specific conductance and percent sodium relationship for irrigation waters

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Based on the geophysical surveys, the study reveals that a large part of the area has high-resistivity layers indicating poor potential for obtaining groundwater. The potentially productive groundwater zones are identified as isolated patches located in the north-western and south-eastern parts of the region. Generally, the massive limestone and quartzite areas are demarcated as poor zones whereas the areas underlain with shale have moderate to good potential.