Environmental Assessment
Volume C-3.6
Slurry Pipeline
Hydrology
Ambatovy Project
59
January 2006
Table 3.6-6 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
negative
right-of-way:
negligible
watercourse
crossings:
high
hydrostatic
testing:
negligible to low
local
short-term
yes
right-of-way:
high (average
conditions)
watercourse
crossings:
low
hydrostatic
testing:
low
right-of-way:
negligible
watercourse
crossings:
moderate
(a)
hydrostatic
testing:
negligible
operation/closure negative
negligible
local
medium to
long-term
yes
high (average
conditions)
negligible
Issue: Changes in Sediment Levels In Receiving Water Bodies
construction
negative
right-of-way:
low
to moderate
watercourse
crossings:
high
hydrostatic
testing:
negligible
local
short-term
yes
high (average
conditions)
watercourse
crossings:
low
hydrostatic
testing:
low
right-of-way:
low
watercourse
crossings:
moderate
hydrostatic
testing:
negligible
operation/closure negative
negligible to low
local
medium to
long-term
yes
high (average
conditions)
negligible to low
(a)
Very short-term (hours to days).
3.6.5.2 Prediction Confidence
The prediction confidence associated with changes in flows, water levels and
sediment levels from development of the slurry pipeline is considered moderate
to high. Moderate to high changes in these characteristics are primarily
associated with construction of watercourse crossings and water withdrawals for
hydrostatic testing. In both cases, the duration will be short which results in a
maximum impact rating of moderate in terms of environmental consequence.
The prediction confidence associated with the pipeline right-of-way and
increased sediment levels is considered moderate based on erosion control
measures that are available for limiting sediment transport from disturbed areas
to receiving water bodies.
3.6.5.3 Monitoring
Routine visual inspections during pipeline construction will be conducted to
ensure the effectiveness of erosion and sediment control measures. During
instream works all control measures will be maintained and repaired as necessary
to restrict sediment transport to off-site locations. Routine inspections of the
pipeline right-of-way and watercourse crossing locations will also be conducted
during operations to monitor and evaluate the effectiveness of erosion control
measures, slope stability, stream bank stability and revegetated and reclaimed
areas, as described in Volume B, Section 6. Water withdrawal rates and
