Environmental Assessment
Volume E-3.9
Tailings Facility
Oceanography
Ambatovy Project
117
January 2006
to have been further compromised by subsistence fishing activities, increased
turbidity and ENSO-related coral bleaching in that order. With this in mind, the
added effect of the marine outfall and associated effluent are likely to be
minimal. However, the outfall should be located between Recif du Sud and Nosy
Faho at a distance that would ensure minimal effect on both these reef systems so
that further cumulative disturbance on these stressed reefs is avoided. According
to the nearfield dilution modelling, effluent components are diluted to within
water quality limits by the time they reach the water surface. As such, the
proposed site is regarded as suitable. Consideration must be given to the future
improvement in the management of the reef resources in Madagascar as the
project proceeds. The effects of the pipeline must thus be minimized so that the
poor condition of the reefs is not exacerbated, nor their future recovery
compromised.
Specific conclusions arising from the nearfield dilution modelling are that an
outfall extending 975 m from the high water mark and in 20 m water depth
should provide sufficient dilution to meet environmental guideline values. The
required dilution should be achieved by nearfield (turbulent) mixing, which will
reduce sensitivity to current direction and velocity.
The commercial fishery (prawns and linefishery) as well as the small-scale
commercial hand line fishery travel considerable distances to their fishing
grounds both to the north and south of Toamasina. They therefore fish
predominantly outside of the study area and away from the proposed outfall area
in which the effluent will be discharged into the marine environment. It is
therefore very unlikely that these fisheries will be impacted by the discharge in
any way. The boats utilizing the harbour, however, may suffer from
interruptions to their usual routines during the construction phase of the pipeline.
The key fishing areas surrounding the Toamasina port and the proposed location
for the effluent discharge pipeline are utilized by the local traditional fishermen
on a regular basis. The traditional fisheries are situated closest to the proposed
discharge location and it is therefore important to monitor these areas and
fisheries as the majority of the fishermen using them are socially and
economically dependent on these fisheries for their livelihoods.
The operational impacts could be seen as longer-term effects on the marine
environment, with the most significant being the increase in turbidity and
deposition of solids such as manganese and sulphate. The greatest area of impact
would thus be an area where the effluent would not be sufficiently diluted for a
period that would exceed the tolerance limits of the majority of organisms. This
area is termed a sacrificial zone or zone of influence around the diffuser, could be
seen as the worst impacted. According to the results of PRDW, when the worst
