Environmental Assessment
Volume B-3.8
Mine
Hydrology
Ambatovy Project
113
January 2006
3.8.6.2 Prediction Confidence
With the exception of evapotranspiration, regional climate variables affecting
baseline hydrology are well understood. Local climate data from the mine site is
limited and can result in uncertainty in understanding the hydrology in terms of
rainfall response and runoff generation. To improve confidence, larger climate
data bases from nearby locations have also been used to help characterize the
local hydrology. Due to the complexity of the groundwater regime, the
interaction between surface water and groundwater in the project area is not well
understood (Volume I, Appendix 7.1).
The impact ratings are based on a hydrologic model that assesses average
monthly conditions based on reasonable estimates of annual rainfall and runoff.
The prediction confidence associated with model flows is considered medium.
Management of pond releases and diversions is key in terms of prediction
confidence.
The prediction confidence associated with sediment concentrations is considered
high for normal flow conditions up to the design flow. Despite the uncertainties
related to extreme events greater than the design storm, the prediction confidence
(moderate environmental consequence) is considered moderate to high due to the
short-term duration and local extent of the occurrence.
3.8.6.3 Monitoring
There will be continued climatological and streamflow monitoring within the
affected basins to help define flow variability. The data will be used to ensure
that pond operational guidelines meet downstream needs and minimize impacts.
The pond releases and downstream flows will be routinely monitored. In
addition, regular contact with downstream users will be made to solicit feedback
on the acceptability and availability of flows.
Throughout the project, monitoring of the effectiveness of erosion control
measures, slope stability, and reclamation success will be conducted. Sediment
and other key water quality parameters released from the collection ponds will be
monitored to ensure compliance with water quality criteria. Inflowing sediment
concentrations will also be monitored to optimize flocculant dosages and to
ensure adequate settling within the clarification ponds.
