ALMOST all the rivers that originate near the Arabian Sea flow eastward into the Bay of Bengal because of the peninsular tilt. One river that deviates from the norm is the Cauvery, which suddenly turns southwards before-heading east again. Geologists believe the Cauvery is actually two rivers that were joined together by an upsurge of land mass that occurred after the peninsular slant was established (Current Science, Vol 63, No 7).

Originating at Talakaveri in the Western Ghats, the Cauvery meanders through the fertile plains of Mysore. The meandering - a trait associated with the final stage of rivers - is maintained till Shivasamudram, where the northern extension of the Biligirirangan hills blocks the river's flow.

At this point, the Cauvery suddenly changes character. It splits into several channels, loses height rapidly and flows with enormous power through narrow, straight channels marked by abrupt bends.

At Hogenakal, the river virtually leaps into Tamil Nadu and flows southwards to Mettur on a straight and narrow course. After capturing the river Bhavani near Erode, the Cauvery once again heads east and branches into two beyond Tiruchi - as the Kolladarn to the north and as the Cauvery to the south.

The theory that the Cauvery is a composite river arises because of the changes in the direction, latitude and elevation of the river. The presentday Palar river from Vaniambadi onwards is considered the original course of the upper Cauvery (the part over the Mysore plateau). The exitence of a wide river bed near Vaniambadi is believed to be that of a major river usurped by its tributary, the Palar. The several right-angled turns the Cauvery makes after Shivasamudrain are because of the repeated capture of many rivers and their tributaries.

The hill ranges between Shivasamudram and Vellore are land masses that were pushed up, cutting the upper Cauvery into two. One segment was diverted south. to become the lower Cauvery and the other dwindled eastwards into an insignificant stream.