Lagoons of Sri Lanka: From the Origins to the Present E. I. L. Silva, J. Katupotha, O. Amarasinghe, H. Manthrithilake and Ranjith Ariyaratna Lagoons of Sri Lanka: From the Origins to the Present E. I. L. Silva, J. Katupotha, O. Amarasinghe, H. Manthrithilake and Ranjith Ariyaratna The authors: Professor E.I.L. Silva is a Visiting Professor at the Limnology/Zoology Department of the University of Sri Jayawardenapura, Sri Lanka, and at the University of Ruhuna, Sri Lanka; Professor J. Katupotha is at the Department of Geography, University of Sri Jayawardenapura, Sri Lanka; Professor O. Amarasinghe is at the Sociology Department, University of Ruhuna, Sri Lanka; Dr. H. Manthrithilake is Head, Sri Lanka Development Initiative at the International Water Management Institute (IWMI), Colombo, Sri Lanka; and Mr. Ranjith Ariyaratna is a Consultant with IWMI, Colombo, Sri Lanka, and was Benchmark Basin Coordinator with the Institute at the time this report was prepared. Silva, E. I. L.; Katupotha, J.; Amarasinghe, O.; Manthrithilake, H.; Ariyaratna, R. 2013. Lagoons of Sri Lanka: from the origins to the present. Colombo, Sri Lanka: International Water Management Institute (IWMI). 122p. doi: 10.5337/2013.215 / coastal lagoons / hydrology / hydrography / ecosystems / biodiversity / fauna / mangroves / marshes / salinity / geomorphology / species / poverty / fisheries / governance / institutions / legislation / Sri Lanka / ISBN 978-92-9090-778-7 Copyright © 2013, by IWMI. All rights reserved. IWMI encourages the use of its material provided that the organization is acknowledged and kept informed in all such instances. Photos: Cover photo by Prof. J. Katupotha showing fishermen engaged in fishing in the Negombo Lagoon. All photos in the text are by Prof. O. Amarasinghe. Please send inquiries and comments to: [email protected] ii Acknowledgements This study was conducted with the financial support of the International Water Management Institute (IWMI), Colombo, Sri Lanka. The authors acknowledge the contribution and support of the staff of the Department of Fisheries and Aquatic Resources, Sri Lanka, other local officials around the country, fishermen, the army personnel during the field visits for the data collection, the reviewers who helped improve the report by providing constructive comments and Samanmalee Thanuja Fernando of Central Environmental Authority, Sri Lanka for painstakingly doing line drawings of maps and the calculations therein under the supervision of Prof. J. Katupotha. They also thank the IWMI personnel, Pavithra Amunugama, Manager, Publications, for the prompt liaising with the authors and those who contributed to the publication of this paper, Sumith Fernando, Layout Specialist, for the excellent layout work and Kingsley Kurukulasuriya, Senior Consultant Editor for the outstanding editing of this paper. iii Contents Executive Summary ................................................................................................................................1 Chapter 1. Introduction ...........................................................................................................................3 Chapter 2. State of Knowledge ..............................................................................................................5 Present Knowledge ...........................................................................................................................5 Benchmark Study .............................................................................................................................6 Chapter 3. Origin, Formation and Evolution .......................................................................................12 Introduction ....................................................................................................................................12 Distribution of Lagoons .................................................................................................................18 Geomorphology ..............................................................................................................................28 Chapter 4. Hydrology and Hydrography ..............................................................................................30 Hydrology ....................................................................................................................................30 Hydrography ...................................................................................................................................33 Chapter 5. Ecosystems and Biodiversity ..............................................................................................41 Lagoon Flora and Fauna ................................................................................................................41 Lagoon Fauna .................................................................................................................................45 Ecological Significance ..................................................................................................................50 Natural and Anthropogenic Pressures ............................................................................................51 Chapter 6. Socioeconomic Relevance ..................................................................................................55 Social and Economic Values of Lagoons ......................................................................................55 Current State of Utilization of Lagoons ........................................................................................58 Misuse of Lagoon Ecosystems and the Threats ............................................................................63 Present Status of Resources ...........................................................................................................73 Chapter 7. Governance and Management ............................................................................................75 Evolution of Fisheries Governance and Management in Sri Lanka .............................................75 Institutions and Legislation ............................................................................................................77 The Present Lagoon Management Regimes ..................................................................................79 Lagoon Resources and Human Well-Being ...................................................................................81 Way Forward ..................................................................................................................................85 Chapter 8. Conclusions .........................................................................................................................86 Definition and Classification .........................................................................................................86 Development and Consequences ...................................................................................................92 Values ....................................................................................................................................92 References ....................................................................................................................................93 Annexes ..................................................................................................................................103 v Executive Summary Sri Lanka, an island in the Indian Ocean, has lagoons along 1,338 km of its coastline. They experience low-energy oceanic waves and semidiurnal microtidal currents. The Sri Lankan coastal lagoons are not numerous but they are diverse in size, shape, configuration, ecohydrology, and ecosystem values and services. The heterogeneous nature, in general, and specific complexities, to a certain extent, exhibited by coastal lagoons in Sri Lanka are fundamentally determined by coastal and adjoining hinterland geomorphology, tidal fluxes and fluvial inputs, monsoonal-driven climate and weather, morphoedaphic attributes, and cohesive interactions with human interventions. Most coastal lagoons in Sri Lanka are an outcome of mid-Holocene marine transgression and subsequent barrier formation and spit development enclosing the water body between the land and the sea. This process has varied from one coastal stretch to another due to wave-derived littoral drift, sediment transport by tidal fluxes, fluvial inputs and wave action or, in other words, sea-level history, shore-face dynamics and tidal range as the three major factors that control the origin and maintenance of the sandy barrier, the most important features for the formation and evolution of coastal lagoons with their landward water mass. In certain stretches of Sri Lanka’s coastline, formation of the barrier spit was very active due to shore-face dynamics that resulted in chains of shore parallel, elongated lagoons. They are among the most productive in terms of ecosystem yield and show some similarities to large tropical lagoons with respect to sea entrance, zonation, biodiversity and ecosystem services. However, some of them become seasonally hypersaline due to lack of freshwater input and high evaporation. Functions and processes of some of these water bodies are fairly known. There are a fair number of small back-barrier lagoons of different shapes and sizes whose origin goes back to sea-level history. They are located on low-energy coasts with