Environmental Assessment
Volume B-4.1
Mine
Flora
Ambatovy Project
170
January 2006
compaction. Surface water will flow downstream of the mine area collection
ponds within existing channels and streams to local rice paddies and marshes,
including the Torotorofotsy Wetlands. The increase in surface water flow will
occur primarily during the wet season. No significant change in flow during the
dry season is predicted.
An increase in surface water flow is not expected to increase mean annual water
levels in local area wetlands since there are no new hydrologic inputs to the mine
site watersheds and groundwater deficits can be offset by releases of greater
volumes of excess surface runoff through active water management. Additional
water brought into the mine site from the Mangoro River by way of a water
intake pipeline, will exit the mine site completely by way of the slurry pipeline.
There may be periods during the wet season when increases in surface water flow
may result in water levels increases within local streams leading to wetlands,
including the Torotorofotsy Wetlands. Stream water level increases are
estimated to range between 1 and 9 cm during operation and post-closure periods
depending upon the particular sub-basin. Stream water level increases within the
Torotorofotsy drainage basin are predicted to have a negligible affect to the total
inflow of water to the Torotorofotsy Wetlands (Volume B, Section 3.8). Flow
levels will in part be attenuated by a runoff collection pond in the headwaters of
the Torotorofotsy River. Thus, no adverse affects are predicted for the vegetation
communities within the Torotorofotsy Wetlands; eastern Madagascar’s largest
and most intact natural marsh ecosystem.
In other local area wetlands, impacts to stream water levels are predicted to be
low (Volume B, Section 3.8). In one case (i.e., the wetlands surrounding the
Sahamarirana River, immediately south of Ambatovy) this translates to a stream
water level increase of 8 cm during operations and 9 cm during the post-closure
period. These relatively small increases in water levels at different stages of
mine development and closure are not likely to have an adverse effect on
wetlands fringe vegetation because this type of ecosystem is inherently adapted
to wet conditions. However, depending upon the tolerances of particular
wetlands species to increased water levels, there is a potential that species
composition within the wetlands communities may change by favoring certain
species over others. For instance, woody species are generally more sensitive to
deviations of seasonal and annual hydrologic cycles than herbaceous species
(Adamus and Brandt 1990). Potential effects to woody plants should not be
overstated though considering that sedge and grass species dominate these
wetlands ecosystems. In addition, because magnitude and probability of change
to the wetlands water levels are low, any potential vegetation effect is predicted
to be low as well.
