To manage environmental impacts from dredging and reclamation works, Boskalis is implementing various mitigating measures in compliance with EIA requirements and in addition to these requirements. All of the mitigating measures are focused on reducing the spreading of sediments in the water as much as possible. To make sure these measures are helping, environmental monitoring is carried out daily to ensure water quality meets the limits set in the EIA.
Construction of a perimeter bund on the outer reef of Gulhifalhu is the main mitigating measure to reduce the spreading of sediment from the reclamation works in the waters outside Gulhifalhu lagoon. Due to the depth of the Gulhifalhu lagoon, it is not possible to construct a perimeter bund inside of the lagoon to fully enclose the reclamation area. That same depth helps sediment from the reclamation works to settle to the seabed before the currents carry it outside the Gulhifalhu reef.
To reduce sediments spreading from the bund construction itself, several mitigating measures are put in place during the construction of the bund:
Boskalis has extensive experience in using silt screens as a mitigating measure to reduce the spread of sediments in the water, including using them in the Maldives.
In the Gulhifalhu project, currents, waves and the depth of the reef flat make it very difficult to effectively and safely install silt screens on the edge of the reef flat, outside the perimeter bund. That is why they are being used inside the Gulhifalhu lagoon only, at the end of the perimeter bund, to reduce spreading of the sediment in the water column to the outside of the reef.
When dredging in the sand borrow area, a so-called green valve is used on board the dredge. This is a technical system on board the dredge, which reduces the spreading in the water of sediment brought into suspension during dredging.
The EIA requires the following:
When turbidity and/or sedimentation limit is exceeded at a monitoring location, cause is investigated and construction activities area adjusted to reduce turbidity and/or sedimentation levels to below the limits.
During bund construction, the following, much stricter process is followed to manage sediment plumes moving to Vilimale:
When a plume is seen to reach halfway across the channel to Vilimale, bund construction activities are stopped, even when water quality limits set in the EIA are met at the monitoring location on Vilimale.