Cauvery Delta is the fifth major Indian delta is quite unusual in its morphology. It has practically no protuberance. Distributaries start diverging some 125 km west of the coast. However, a more striking point of distribution of streams occurs at Yanjore, c. 80 km inland. The delta extends for 125 km from the Caleroon mouth in the north to near Mutupet in Palk Strait. It is an unusually symmetrical delta. It is something like an isosceles triangle. The north-south sea shore-base of this triangle is about as large as the perpendicular bisector of this base.
The Cauvery delta is devoid of seaward projection, which is regarded as an essential condition of a delta. There is only slight seaward protuberance, which occurs in the section south of Porto Novo. This projection is only 8 km and this too is in a straight line, not arcuate, which is characteristic of a normal delta. This abnormal straightness of the delta face is believed to result from the dominance of marine action, which produces bars on the mouth of the river.
“The barriers (100 to 1,000) m wide) check the spread of sediment on the shelf beyond the bar into a protuberance.” Guilcher thinks that such a case is no longer a delta but this view is not correct. A delta is generally a triangular plain at the mouth of a river falling into the sea. The triangular shape is due to divergent distributaries, which have been occasioned by large amount of sediments that cannot be quickly discharged by the channels of extremely low gradient in an aggrading region. The channels are raised and choked by their own sediments. Consequently, crevassing or breaching of channels across their levees is common. All these phenomena characterize Cauvery delta.
The only wanting thing is the lobate seaward face because of the strong opposing power of the N.E. monsoon, which is almost orthogonal to the coast here. The extensive Bay provides a vast fetch. The delta face of the Cauvery is marked by sand hills and beach ridges, which have been largely built out of the sediments excavated from the offshore shelf to be piled up into barriers by the strong waves generated by the N.E. monsoon.
The structural base of the Cauvery is similar to that of the Krishna. The gneissic shield was submerged below the sea during Cretaceous and Tertiary as shown by the marine beds of the time, now tilted seaward. Elevation after marine deposition gave rise to the coastal plain over which the Cauvery has deposited its sediment in Pleistocene and Recent times.