Environmental Assessment
Volume B-3.8
Mine
Hydrology
Ambatovy Project
112
January 2006
Table 3.8-13 Residual Impact Classification for Hydrology
Phase
Direction
Magnitude
Geographic
Extent
Duration
Reversibility
Frequency
Environmental Consequence
Issue: Changes in Streamflows and Water Levels in Receiving Water Bodies
construction/
operations
negative
wet season:
moderate to
5 km; low to negligible
beyond 5 km
dry season:
negligible
mean:
moderate to 1.5 km; low to
negligible beyond 1.5 km
local
local
local
medium-term
yes
high (average conditions)
wet season:
low (to 5 km); low to negligible
(beyond 5 km)
dry season:
negligible
mean:
low (to 1.5 km); low to negligible
(beyond 1.5 km)
closure
negative
Ambatovy (south) basins:
moderate to 5 km; low to
negligible beyond 5 km
Analamay (north) basins:
moderate (to 1.5 km); Low
(1.5 to 5 km); negligible
(beyond 5 km)
local
local
long-term
no
high (average conditions)
Ambatovy (south) basins:
low (to 5 km); Low to negligible
(beyond 5 km)
Analamay (north) basins
low to negligible (beyond 1.5 km)
Issue: Changes in Sediment Levels in Receiving Water Bodies
(a)
construction/
operations
negative
low to moderate
local
short-term
yes
low
operations
negative
for design conditions:
low to moderate
for extreme events:
moderate to high
local
medium-term
short-term
yes
high (average conditions)
low
low
moderate
closure
negative
negligible to low
local
long-term
no
high (average conditions) low
Issue: Changes in Torotorofotsy Wetlands Hydrology and Sediment Levels
construction/
operations
negative
flows:
negligible
sediment:
low for typical conditions;
moderate to high for extreme
events
(b)
local
medium-term
medium-term
short-term
yes
high (average conditions
high (average conditions)
low
negligible (flows) to low (sediment)
for typical conditions
negligible to moderate for extreme
events
closure
negative
flows:
negligible
sediment:
low
local
long-term
no
high (average conditions) negligible to low
(a)
Changes in sediment levels immediately downstream of the runoff collection ponds; sediment levels in receiving streams will decrease with increasing distance downstream due to dilution from
tributary water.
(b)
High magnitude change is based on worst-case assumption; data collection and modeling are currently being conducted to improve understanding of sediment levels under
extreme events.
