Abstract:
A field observation was conducted on 22nd November 2011 to estimate the present state of
density stratification of Koggala lagoon. Vertical variation of salinity, water temperature and dissolved
oxygen were measured with neap and ebb. The same measurements were taken from inflow streams.
The observations indicate that main water body of the lagoon is salinity stratified despite the strong or
partial mixing at the mouth. Particularly, strong saline stratification is prominent in the deep central part of
the lagoon. Firstly, the current hydraulic state and then bulk parameter of Koggala lagoon is analysed.
The relationship between the mixing state and the values of parameters of Koggala lagoon agree with
Fisher’s plot. The effects of modification of lagoon mouth are discussed based on these parameters.
Temporal and spatial complexities of lagoon mouth affect transport and mixing of saline water and
intrusion into the lagoon. In future, a modified bulk parameter will be needed for better understanding of
stratification behaviour of the Koggala lagoon.
