Study of Lineaments in Polavaram Dam Project Area, Khammam, East and West Godavari Districts, Andlira Pradeshi Dr

Study of Lineaments in Polavaram Dam Project Area, Khammam, East and West Godavari Districts, Andlira Pradeshi Dr. N.R.Ramesh Abstract Mapping of structural lineaments around the Polavaram Project, led to identification of several major faults /shear zones. The objective of the study was to aid the geotechnical investigations of the multi-purpose dam project. The methodology Involved remote sensing studies of LANDSAT MSS and TM FCC imagery and black and white aerial photographs, followed by ground validation of 73 lineaments. The major lineaments in the area trend ENE-WSW to NE-SW. Based on the study, the lineaments are classified into faults, shear zones, fractures etc. A number of faults/shears were confirmed from field evidences such as abrupt change in landforms and/ or lithology on either side of lineament and other geological and structural features. A few faults were delineated in the vicinity of the dam site, such as, the major arcuate fault situated on the left bank of the river, 12 km northeast of the dam site; ENE-WSW fault across ihe Godavari River, 3 km north of the dam site and NNW-SSE fault, east of Devipatnam. Faults were also delineated around Bhadrachalam, Ashwaraopet etc, some of which mark the contact between the basement gneisses and Gondwanas. Proximity of Bhadrachalam temple town, known for seismic activity and also presence of significant morphostructures in the Godavari delta, calls for detailed study of Quaternary geology around the Project. Thus the evaluation of lineaments in terms of Uieir status and seismic/ neotectonic significance would prove useful for the purpose of planning and safe designing of the multi-purpose Polavaram project. Introduction shown that there is a definite correlation ^ , Xbetween many earthquakes and specific Lineaments are linear eatures of the earth Godavari valley area a and include traces ol laults shear zones ^ut all ol joints and frartures. Generally rivers and ,hem are not considered significant from the streams tend to ollow the lineament. geotechnical Investigations. Lineaments are of groat significance to Many of them are not traceable on the ground geoscientists especia ly for engineering geology as they ref ect various structural „„,rt,urden, some of the lineaments features of an area. Mapping and analyses o lineaments helps us in understanding the confirmed to be stractura^tectonic frame v,ork and geological ^^^^ace traces of faults/ shears (Ramesh el setup of the area. Remote sensing techniques al 1991) have given a boost to lineament studies since identification and mapping of lineaments Lineaments are to be evaluated and their become relatively easy in the satellite significance known for the purpose of imagery/ aerial photographs, because of planning safe design of important projects or synoptic view, availability of data in different studying the safety of existing one in an area, bands and repetivity. Number of studies Detailed knowledge of active faults and the carried out in India and elsewhere, have associated seismicity is required to quantify the seismic risk. In the present study, an Kondapudi, where after the direction of the attennpt has been made to identify active river becomes south-south east till it lineaments of the Godavari valley by debouches on to coastal plains south of preparing a lineament map using satellite Polavaram. These major trends do not appear remote sensing data and aerial photographs to be controlled by structure. and correlating the same with ground evidences and associated seismicity, if any. Data base and methodology Study area The following data were used in the study: • Landsat Multispectral Scanner (MSS) / The study envisaged mapping of lineaments Thematic Mapper (TM) data (band in and around the proposed Polavaram dam products/ False Colour Composites) on project (Fig.1). The proposed multi-purpose 1:1 million/2, 50,000 scale. project envisages construction of a dam across the Godavari River, 3.5 km north of • Geological and mineral map of Andhra the Polavaram village, about 35 km upstream Pradesh on 1: 500,000 scale. of Rajahmundry. The dam is expected to • Aerial photos ( black and white) on create a reservoir spreading over a vast area 1:60,000/ 30,000 scales upto Kunavaram in the north-west. Major lineaments were mapped first from The area is bounded by lats 17° 0'-17° 45' N individual scenes of Landsat data (MSS/TM, and long 80° 45'-82° 0' E and falls in parts of FCC) on 1 : 1 million scale to make a single Khammam, East Godavari and West mosaic map. Godavari districts, Andhra Pradesh. The northern part of the area is generally rugged, The methodology involved remote sensing hilly and forested and is relatively studies of LANDSAT MSS and TM FCC inaccessible when compared to the southern imagery, bands 2, 3 & 4 of 1987 and part. interpretation of black and white aerial photographs, followed by ground validation of A major part of the area to the north is 73 lineaments. occupied by the rugged hilly terrain of the Eastern Ghats. The ground elevation which Regional geology and subsurface is 2 0 m above m.s.l. in the coastal plain in setup around the dam site the southern part rises to more than 50 m above m.s.l. in the Bhadrachalam area and The project area comprises Archaean upto 750 m above m.s.l in the hilly region, crystallines, Gondwana sedimentaries, further north. In the eastern part of the area, Deccan Trap, Rahjahmundry sandstones and Quaternary alluvium. The area to the east and the hills form inselbergs. Remnant planation southeast of Bhadrachalam is occupied surfaces are seen above 700 m to 760 m above m.s.l on either side of the Godavari predominantly by the Peninsular Gneissic River. A few stretches of floodplains occur Complex and the rocks belonging to the breaking the monotonous rugged terrain. Eastern Ghat Supergroup. To the west and south of Bhadrachalam is known for the coal The area forms the lower part of the Godavari bearing Gondwana formations. The basin, just above the delta. The meandering Gondwanas comprising both lower and upper trunk channel of the Godavari has cut deep are believed to be the result of taphrogenic gorges across the hilly terrain downstream sedimentation-the basin to be the result of (SSE) of Kunavaram. The river has a southerly trough faulting in WNW-ESE direction. The course upto Bhadrachalam from where it Gondwana sedimentaries show horizontal to takes a left turn and continues to flow in a sub-horizontal dips (except in the vicinity of roughly east south east direction upto faults). The area around Rajahmundry exposes Traps and Rajahmundry Sandstone litho-sequence comprising top soil (250 m/s (Mio-Pliocene). The Gondwana sediments to 350 m/s), sands and clayey silts (700 m/ and Rajamundry Sandstone have been s to 1,600 m/s) and compact bedrock (5000 lateritised. The Quaternary alluvium m/s). The thickness of top soil, sands and comprising both lOlderl andlNewerl alluvium clayey silts, weathered or fissured rock at is well developed along the banks of the saddle dams varies from 3-10 m, 10-20 m Godavari River and its major tributaries. and 0-20 m, respectively. Along the other alignment the thickness of top soil, sands The rock formations of the area have suffered and clayey silts, weathered/ fissured rock polyphase deformation. The regional strike of foliation in the Eastern Ghats Supergroup vary from 3-10 m, 10-40 m and 0-30 m, respectively. is NE-SW with steep south-easterly dips. In the eastern part of the area ENE-WSW In the river bed, the depth to compact foliation and axial plane trends are equally bedrock varied between 30 m and 70 m from prominent. Towards west, the rocks are folded the surface. On the other hand, the depth to into tight oppressed, isoclinal folds with south compact bed rock estimated along the easterly axial plane dips. On the other hand, alignments over the left bank and the right the eastern part is characterised by ENE- saddle dams varied between 10 m and 30 m WSW trending open folds and doubly from the surface. plunging folds. The gravity surveys along the Mallisala- The River Godavari is flowing in a rift valley of Kakinada in East Godavari district indicate 50 km width and 900 km length in a NW-SE increasing thickness of sediments towards direction. The rift valley has undergone the coast. Seismic surveys indicated shallow continuous tectonic disturbances right from depth of Trap (300 m) towards south east near the early Precambrian to the Late Tertiary Peddapuram. The traps are inferred to extend period, as evidenced by occurrence of from Katravupalle in ESE direction to sediments of all periods and also associated Gollaprolu, and further east of Gollaprolu, the with Cretaceous-Eocene volcanic activity. sediments are underlain by crystallines. Along the eastern margin of the rift valley near Further east of Kattravupalle the Traps are Venkatapur, Holocene sediments occupy a overlain by alluvium of Eleru River. The narrow strip- 1 0 km wide and 60 km long. Rajahmundry Sandstone extends upto These sediments are also associated in this Samalkot and further east it is covered by region with a high gradient of negative alluvium of Eleru River. The area north and Bouguer anomalies falling by 70 m Gal in a east are covered by the Quaternary alluvium distance of 40 km (Qureshy, 1970). (Rao et al., 1971). Refraction seismic surveys in Polavaram Lineament analyses and discussion Project area were carried out by Keshavamani, Rama Rao and Krishna Rao The lineaments in the study area mainly trend (1990) with the objective of delineating the in the following directions: bed rock topography along the proposed i) NE-SW alignments of the dam across the Godavari River, left bank saddle dam, housing the ii) ENE-WSW power block and the right bank saddle dams.

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