Investigating the impacts of infrastructure on ecology and coastal livelihoods

Location: Jaffna, Sri Lanka. 24th Sep 2015

Scientists from Jaffna University in Sri Lanka have undertaken a small grant project whose impacts are widespread and long-term. The results of their research have given new life to an important lagoon in the northern part of the country, enhancing biodiversity and opening doors for more productive fisheries and better opportunities for eco-tourism.

Editor's note: This story is a follow up to an earlier story, Revitalizing Thondamanaru Lagoon.


The Thondamanaru Lagoon is an important brackish water body in Jaffna. During the rainy season the lagoon covers an area of approximately 78  sq km  with an average depth of 1.5 meters.  In 1953, the Irrigation Department established a barrage with sluice gates about 0.4 km from the mouth of the lagoon. The idea of the barrage was to prevent the entry of sea water into the lagoon and retain the rain water which drains into the lagoon — ultimately transforming the brackish water body to a fresh water body.  

Those who conceived this brackish to fresh water lagoon project anticipated that the fresh water will slowly leach out or reduce the accumulated salt in the area and eventually a significantly large area of land will be less saline to the level suitable for crop production. Furthermore, availability of water for irrigation is also considered as a plus.  

As envisaged, a gradual decline in salinity of the lagoon and adjacent well water was observed during the period 1963 -1969.  With the changes in salinity, fauna and flora around the lagoon also changed.  The annual lagoon catch before the installation of the barrage was approximately 150 tons of fish and it plummeted to 35 tons.  The number of species of fish also reduced from 47 (1968) to 15 (1978). The pros and cons of this change from salt water to freshwater was debatable, but further scientific research in the lagoon had to be halted due to the civil unrest that prevailed for nearly 30 years.   

Then in July 2014, assisted by the Mangroves for the Future (MFF) programme, a team of scientists from the Department of Zoology, University of Jaffna undertook a study to access the current situation. The purpose was to identify livelihood options for the Thondamanaru Lagoon area in the post-conflict era.  The team looked at the faunal and floral compositions of the lagoon. They studied physical and chemical parameters of lagoon water and also collected socio-economic data. With the collected information a number of ideas for future land use for the lagoon started emerging. Although the study will go on till mid-2015, their findings and observations over a 10 month period drew the attention of many including the provincial and district authorities including the staff planning water resources and livelihoods.

As such, the research findings and suggestions on the management of the lagoon were presented to Senior officials of Government Departments in Jaffna on 16 May 2015 at the auditorium of Karaveddy Divisional Secretariat in Jaffna, for consideration.  The event was led by the District Secretary of Jaffna, Mr   N. Vethanayahan.  Divisional Secretaries of Point Pedro, Karaveddy and Kopay (representing the divisions covering the Thondamanaru Lagoon), Dean of the Faculty of Science, University of Jaffna, two retired Civil Engineers with historical knowledge on the barrage and a highly respected retired scientist,   Prof K. Chitravadivelu were among the participants.    

The team recommended a two pronged approach for the future land use of Thondamanaru Lagoon area. It included allowing sea water to enter the lagoon so that the changes to the ecology and impact on lagoon fishery that require salt water, is minimal. At the same time they proposed to enhance the area available for cultivation by creating sand bunds. In summary the recommendations are:

  • Sea water to be allowed to enter into the lagoon through the barrage
  • Sand bund bordering the lagoon to be in place to minimize salt water intrusion to the land    
  • Sandbar with gate in place at Vallai Bridge (inner border) to keep water in the lagoon during dry season.
  • Growing mangroves and flora which inhabits tidal  flats to be encouraged in the lagoon- Avicennia sp., Suweda etc


For more information on the project, please visit the page, Baseline analysis of development opportunities for Thondamanaru Lagoon

Thondamanaru Lagoon

Thondamanaru Lagoon , Thondamanaru Lagoon © Kumudini Ekaratne, IUCN, 2014

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