Environmental Assessment
Volume E-3.8
Tailings Facility
Hydrology
Ambatovy Project
69
January 2006
Table 3.8-4 Impact Description Criteria and Numerical Scores for the Ambatovy
Project – Surface Water Hydrology
Resource
Direction
(a)
Magnitude
(b)
Geographic Extent
(c)
Duration
(d)
Reversibility
(e)
Frequency
(f)
surface water
hydrology
positive
,
negative
or
neutral
for the
measurement
endpoints
negligible
: <5%
change
low
: 5 to 10%
change
moderate
: 10 to
30% change
high
: >30%
change
local
: effect restricted
to the LSA
regional
: effect
extends beyond the
LSA into the RSA
beyond
regional
:
effect extends beyond
the RSA
short-term
:
<3 years
medium-term
:
3 to 30 years
long-term
:
>30 years
reversible
or
irreversible
low
: occurs once
medium
: occurs
intermittently (1 to
10 times per year)
high
: occurs
frequently (>10
times per year)
(a)
Direction: positive or negative effect for measurement endpoints, as defined for the specific component.
(b)
Magnitude: degree of change to analysis endpoint.
(c)
Geographic Extent: area affected by the impact.
(d)
Duration: length of time over which the environmental effect occurs. Considers a three-year construction period and a
27-year operations period.
(e)
Reversibility: effect on the resource (or resource capability) can or cannot be reversed.
(f)
Frequency: how often the environmental effect occurs.
3.8.5.4 Mitigation
To mitigate the effects on flows, water levels and sediment levels, the Ambatovy
Project will implement the following measures:
•
stage development to limit the amount of disturbed and exposed areas;
•
monitor changes in climate conditions and downstream flows and
suspended sediment concentrations;
•
implement an emergency response plan to advise downstream residents
of potential spillway releases during extreme storm conditions;
•
use erosion control measures, including the development of stable
embankment slopes and prompt revegetation (refer to Volume D,
Section 3.8 for other examples of best management practices for erosion
and sediment control);
•
return areas to natural runoff conditions through grading and
revegetation; and
•
direct streams and drainage paths to natural receiving water bodies.
3.8.5.5 Results for Key Question H-1: What Effect Will the Tailings
Facility Have on Flows and Water Levels in Water Bodies?
Development of the tailings facility will involve three operational phases, in
which tailings are deposited in one tailings basin after another. The facility will
divert water from the upper watersheds and will also intercept groundwater
downgradient of the embankments. The operational phases will be followed by
