Varahanadhi

The main river Varahanadhi originates from the Northern part of Pakkammalai hills at an elevation of 566 m above m.s.l, in the Western slopes past of Gingee Taluk. It has two arms. The left arm originates from Melmalayanur while the right arm originates from Pakkammalai hills and they join together near Thenpalai village and forms the main river Varahanadhi and flows in an Easterly direction. On its way, the river Varahanadhi receives a number of small streams and rivulets. The total area of the basin is 2564 Sq.Kms. The river runs in Easterly direction up to Kodukkur and South-Easterly direction alternately in Tami Nadu and Pondichery states. The total length of Varahanadhi up to its outfall into Bay of Bengal, a little South of Pondichery state, is about 78.50 km.

Major portion of the basin area (84%) comprises of hard crystalline rocks of Archaean groups viz. granulite, biotite, shattered gneiss, magnetite quartzite, pyroxene granulite and charnockite. The general foliation of the rocks are in NNE to NE direction with dip towards SSE to SE direction with an angle of 55° to 80°. The remaining portion of the basin area (16%) consists of sedimentary formation. The marine sediments existing along the coastal area comprises of tidal flats, mudflat and beach/sanddune deposits.