Water balance and renewal time of rekawa lagoon, Sri Lanka; a restorative approach

Abstract

Rekawa Lagoon is a chocked and shallow coastal water body located in the southern coast of Sri Lanka. It is relatively unusual in that the major freshwater input, Kirama-oya river connects through the constricted channel much closer to the inlet at seaward end. A causeway was constructed, around 700 m from the lagoon inlet to the inland, across the constricted channel with an effort to link a secluded Kapuhenwala village with the rest of the area which in turn greatly reduced the volume and speed of water entering and leaving the lagoon system. Construction of the causeway led to many environmental problems with poor flushing efficiency and hampering to and fro movement of the prawns in the lagoon. The aim of this study was to evaluate the present situation and propose alternative management scenarios for improvement of water flow and lagoon ecosystem. The implications of different development stages of the causeway were discussed in terms of field measurements supported by modeling to describe the water balance and the water renewal time. The alternative of modifying the existing causeway was proposed to increase the free water flow at the inlet that favors recruitment of juvenile shrimp species.