Environmental Assessment
Volume C-3.6
Slurry Pipeline
Hydrology
Ambatovy Project
50
January 2006
Site-specific streamflow data were collected at 12 pipeline watercourse crossing
locations along the route. Discharge measurements were taken during September
and October 2004 to characterize late dry-season flows.
3.6.2.3 Results
The slurry pipeline route is about 195 km long and runs between the ore
preparation plant at the mine and the process plant at the coast. The first 30 km
of the route descends from the highlands to the coastal plain, with mean annual
temperatures along this section increasing from about 17 to 22°C. The remaining
portion of the route runs from the base of the escarpment, across the coastal plain
and finally to the plant. Mean annual temperatures along this portion of the route
are above 24°C.
Mean annual precipitation along the pipeline route was estimated from isohytes
(lines on a map connecting places receiving equal rainfall) provided in Chaperon
et al. (1993). The variation in precipitation is shown in Figure 3.6-1.
For the purpose of this assessment, rainfall intensities along the pipeline corridor
were assumed to be similar to those at the mine or tailings facility, depending on
location and the amount of rainfall that is characteristic of the area. Maximum
rainfall statistics derived for the tailings area are assumed to be applicable to the
majority of the pipeline length as it crosses the coastal plain. For the first 30 km
of the pipeline route, however, maximum rainfall amounts will vary from those
derived for the mine site to those derived for the coast. Maximum 24-hour
rainfall amounts have been estimated by interpolating between the mine and
tailings amounts based on the mean annual rainfalls at the sites (Table 3.6-1).
Runoff volumes depend on the basin size for each stream as well as the runoff
per unit area. Estimates of monthly runoff along the route are provided in
Table 3.6-2 for the early dry, late dry, and wet seasons. These monthly and
extreme daily values are derived from observed streamflows over the 2004-2005
monitoring season.
A summary of the discharge measurements taken at watercourse crossings along
the pipeline route is provided in Table 3.6-3.
