PROJECT PERFORMANCE AND MONITORING OF A REVETMENT, COCOS BAY, EAST TRINIDAD

Charmaine O'Brien-Delpesh, Candice Gray-Bernard, Marisha Tang-Kai

Abstract


The eastern shoreline of Trinidad has been suffering extensively from erosion over the years. This coast is exposed to the Atlantic Ocean and is subjected to large swells especially during the North Atlantic winter period, storms and hurricanes. The coastal area of Cocos Bay located on the east coast of Trinidad between the Nariva and Ortoire Rivers has been undergoing severe erosion at a rate of approximately 0.5 m to 1.7 m per year. In 2005, the Ministry of Works and Transport, Drainage Division started the construction of a 2.3 km long rubble revetment (rip rap) which was completed in 2008. The function of the revetment was to control erosion and flooding thereby protecting the Manzanilla-Mayaro Road which is a major artery linking the oil and gas sector as well as several coastal villages. This revetment formed the emergency intervention phase of a three phase solution recommended along the South Cocos Bay. Conforming to the Certificate of Environmental Clearance (CEC), the Ministry of Works and Transport, Drainage Division has been monitoring the possible impacts of the structure on the beach environment from post construction to present and its structural integrity. During the last five years, the monitoring study has revealed that in the vicinity of the revetment, erosion and flooding have been mitigated; however there has been narrowing of the beach even though the gradient has remained the same.
Flanking has also been observed immediately north and south of the revetment. In regards to the structural integrity of the revetment, the armour layer which was constructed using local rock (blue limestone), 200 - 300 kg is showing signs of weathering and shearing. This has resulted in voids in the armour layer which has exposed the filter and underlayers. It is recommended that in order to maintain the functionality and structural integrity over a design life of 25 years, the armour layer be repaired with a suitable material which has historically been sourced externally. The post documents the prevailing wave climate, previous coastal evolution modelling, and the pre and post construction profile records. The shoreline response to the revetment is predicted using GENESIS and compared to the actual response based on an analysis of the beach profile monitoring records are also presented.

Keywords


coastal erosion; beach profile; revetment

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