Restoration of Koggala lagoon: Modelling approach in evaluating lagoonwater budget and flow characteristics
Gayan Lakendra Gunaratne , Norio Tanaka , Prasanna Amarasekara , Tilak Priyadarshana , Jagath Manatunge
DOI:
Received October 31, 2009,Revised December 25, 2009, Accepted , Available online
Volume 22,2010,Pages 813-819
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Groyne system modification is described related to restoration e orts to Koggala lagoon, Sri Lanka.The large-scale unplanned sand
removal at the lagoon mouth shifted the formation of sand bar towards the lagoon and made adverse e ects on its ecosystem. After the
removal of the natural sand bar, groyne system was constructed to avoid sand deposition in the lagoon and to protect the highway bridge
(across the lagoon outlet channel) from the wave attack. The existing groyne system resulted the lagoon mouth being permanently open
to sea which in turn led to many environmental problems. Groyne system modification is proposed in this study to reduce the sea water
intrusion.Water budget and two-dimensional depth averaged hydrodynamic model were developed for understanding the hydrologic
and flow characteristics of the lagoon. Numerical experiments was performed at lagoon mouth area for two cases: (1) existing condition
and (2) proposed rubble mound groyne system condition. Comparison of results was obtained for both cases to describe flow pattern at
lagoon mouth. Results further showed, the width should be reduced to a maximum of 40 m. Proposed mouth width (40 m) pushed the
salting factor towards 0.5 from 0.68. Salting factor reduction with the groyne modification may result a predominant influence of fresh
water which may in turn lead lagoon to a fresh water ecosystem.
