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Title: Environmental impact assessment for coastal modification and construction of a causeway between Hoan’dehdhoo and Madaveli, Gaafu Dhaalu Atoll
Authors: Land and Marine Environmental Resources Group
Keywords: Coastal modification
Causeway construction
Existing environment
Existing beach environment
Existing marine environment
Existing terrestrial environment
Existing socio-economic environment
Constructional impacts
Socio-economic impacts
Mitigation measures
Environmental monitoring program
Environmental impact assessments
Issue Date: Oct-2016
Citation: Land and Marine Environmental Resources Group. (2016). Environmental impact assessment for coastal modification and construction of a causeway between Hoan’dehdhoo and Madaveli, Gaafu Dhaalu Atoll. Male': Maldives
Abstract: The non-technical summary outlines the findings of the Environmental Impact Assessment for the construction of a causeway of length 441m, linking Hoan‟dehdhoo and Madaveli and the reclamation of 3.5ha of land area in Madaveli in Gaafu Dhaalu Atoll in the South of Maldives. This project was earlier addressed through another EIA submitted in 2012 (SEAMARC, 2012), though due to delays in implementation of the project, the EIA period is now void. Furthermore, design of the causeway and changes to other components of the project, requires submission of a second EIA for the project, prior to commencement. The project proponent of the proposed project for coastal modification and construction of causeway between Hoan‟dehdhoo and Madaveli is Ministry of Housing and Infrastructure while the contractor for the project is Maldives Transport and Contracting Company Plc.The project includes two components: 1. Construction of a causeway linking the islands of Hoan‟dehdhoo and Madaveli. The proposed causeway has a total length of 441m and width of 15m. The causeway between the two islands will be constructed in two parts connected by the uninhabited island of Haadhoo which lies in the shallow lagoon area between the two islands. Construction of the causeway will be through reclamation of land area between the islands, whereby stretch of land between Madaveli to Haadhoo is proposed to have a length of 261m, while that between Haadhoo and Hoan‟dehdhoo is proposed to have a length of 180m. The area will be reclaimed to a height of 1.4m above Mean Sea Level (MSL) and protected through construction of a sand cement bag revetment along the whole length of both sides of the causeway. Concrete culverts at 50m apart will be placed along the length of the causeway to allow tide flow. The length of the culverts is equal to the width of the causeway (15m) and 6m wide. 2. The second component of the project is the reclamation of 3.5ha of land at the southeastern side of Madaveli. Reclamation of the land will be to a height of 1.3m above MSL, using sand sourced from the lagoon area. Proposed borrow area for the project is located at the eastern side lagoon between the two islands. A total of 73,500m3 of sand is required for this work and the recommended borrow area is proposed to be dredged to a depth of -3m from the seabed.Impacts on the environment from various activities of the project (both during construction and operation) have been identified through interviews with the project management team, field data collection and surveys and are also based on past experience of consultant in similar development projects. Impacts which have been identified were analysed with the aid of a Leopold Matrix, which gives numerical assessment of the magnitude and importance of an impact. The proposed project involves construction of a causeway between Madaveli and Hoan‟dehdhoo and reclamation of 3.5ha of land area on the southeastern side of Madaveli. The main construction stage impact associated with the project is due to dredging and reclamation works, which have the potential to greatly impact the marine environment through direct habitat loss and indirectly through sedimentation. Impacts discussed are;  Direct loss of habitat due to dredging and reclamation work  Sedimentation impact due to dredging and reclamation work  Mobilization of equipment and labor  Impact on vegetation due to causeway and road construction  Noise, vibration and disturbance to nearby residents  Impact on vegetation  Pollution of natural environment due to possible spillage, solid waste, disposal of untreated waste water  Risk of accidents and pollution on workers and local population The proposed borrow area is located at the eastern side of the reef between the two islands. Dredging works is proposed to be undertaken using excavator and transported using interim bonds. Dredging works at the borrow area will create sediment plume and expected to flow eastwards (tidal currents). Sand bund is proposed around the periphery of dredging area hence spread of fines will be reduced. The causeway construction works will close the aperture between Madaveli/Haadhoo/Hoan‟dehdhoo and stop flow of water. The culverts will be laid after connecting the islands, hence sediment plume will be minor and only depend on tidal currents (west to east on the eastern side of causeway). Impacts of sedimentation during causeway reclamation are therefore categorized as moderate and short termed. Significant negative impact on western side (southern side bay area of both islands) shoreline and immediate land area adjacent to proposed causeway is envisaged in the operational phase. In the event of storm surge (udha), water will pile up at the western side bay area causing rise of water level consequently causing flooding. Even at present, periodic flooding is experienced during SW monsoon due to storm surge. Therefore protection against storm surge is thought to be less and negative impacts high due to current design of the causeway. Mitigation measures for the various components which are expected to have impacts, have been proposed in the report, including the recommendation to revise the current design of causeway and include revetment at the southern side of reclamation area. Given that this project is developed specifically for these two islands, an alternative location is not considered. Alternatives for the project have been considered for the following;  Design of the causeway  Materials used to construct the revetment  Borrow location  Reclamation design The no-project scenario is also considered, the environmental impacts which arise due to the project such as change to hydrodynamics and loss of marine habitat and possible increase in surge related flooding can be avoided. However, should this option be chosen, this means that the social benefits (increased employment opportunities, easier travel between islands, better public services and increased housing plots) provided by the project will be cancelled. Hence given the high positive impact on the socioeconomic environment, discontinuation of the project is not seen to be a feasible option. Although this may be the case, the current causeway design is envisaged to increase surge related flooding hence this component is not feasible and needs to be revised. Details of the various alternatives considered and the selected alternatives are shown in Section 10 of the report. The consultant concludes that the proposed project component, especially the causeway with current design which lacks coastal protection measures in the vicinity of the causeway on either island is likely to cause significant environmental damage (specifically coastal flooding) at both islands. It is therefore recommended that an alternative design for the causeway should be considered.
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