ESTUARINE OCEANOGRAPHY OF THE VEMBANAD LAKE PART I: THE REGION BETWEEN PALLIPURAM (VAIKOM) AND THEVARA (COCHIN)

Abstract

The paper gives the results pertaining to the region between Pallipuram
(Vaikom) and Thevara (Cochin) of a detailed estuarine-oceanographic study
attempted on the Vembanad lake from Pallipuram in the south to Azhikode in the
north. The study was aimed primarily at classifying to what type of estuary the
lake belongs. As the two factors almost equally influencing the lake, namely the
incursion of salt water from the Arabian sea and fresh water from the rivers,
both being by far governed by the monsoon, the major classification was attempted
on a seasonal basis.
This southern stretch of the lake, from Pallipuram to Thevara, is found to
be distinctly different in character from the northern stretch, from Cochin to Azhikode,
almost throughout the year, evidently due to its distinct circulation pattern,
induced in turn by the greater and varied river runoil received into this region.
During the monsoon, as a result, this region of the lake is a highly stratified Saltwedge
type of estuary; but during both the pre- and postmonsoon periods it
changes partly over to the Partially mixed type and partly to the Vertically homogeneous
type, the latter occurrine at the shallowest stations Perumbalam and
Pallipuram.
The incursion of upwelled waters into this region and the mixing process
like entrainment during monsoon are discussed. A future line of work for continuous
salinity and velocity measurements, which will be highly helpful in understanding
the mixing process, is indicated.