Environmental Assessment
Volume B-3.8
Mine
Hydrology
Ambatovy Project
93
January 2006
Site-specific streamflow data was collected over the March 2004 to March 2005
period at 12 locations in the mine area, including three stations along the
Mangoro River. Discharge and water level measurements were collected
monthly by a team of technicians in order to establish a rating curve for each
location. Water levels were recorded on a daily basis by local assistants and
were used to derive a time series of streamflow for each station. Daily water
levels continue to be recorded at these locations.
3.8.3.3 Results
Long-term climate records are available near the mine site at Moramanga and at
Andasibe (Perinet), while short-term records are available for the mine site.
Derived monthly and annual precipitation for the mine is summarized in
Table 3.8-1. The mean annual rainfall is estimated to be 1,700 mm. Historical
records suggest that the annual rainfalls for 1:50 year dry and wet conditions vary
from about 40% lower to 50% higher than the mean. Maximum daily rainfall for
various return periods are shown in Table 3.8-2. Maximum daily rainfall
amounts at the mine site are based on data from Andasibe (Perinet) and reflect
the higher rainfall conditions at the mine relative to Moramanga. Maximum 24-
hour rainfall amounts (Table 3.8-3) have been estimated by applying a factor of
1.08 to the daily maximum values. This factor was derived based on the short-
term data available from the mine site.
Table 3.8-1 Derived Monthly and Annual Precipitation (mm) for the Mine
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Annual
139
275
338
273
226
84
53
57
86
80
36
56
1,700
Table 3.8-2 Maximum Daily Rainfall
Maximum Daily Rainfall (mm) for Various Return Periods
(a)
2-yr
5-yr
10-yr
20-yr
50-yr
100-yr
113
168
214
266
346
419
(a)
Andasibe (Perinet) rainfall data 1963-1973.
Table 3.8-3 Maximum 24-Hour Rainfall Amount
Maximum 24-hour Rainfall (mm) for Various Return Periods
(a)
2-yr
5-yr
10-y
20-yr
50-yr
100-yr
122
181
231
287
374
453
(a)
Maximum daily precipitation at Andasibe (Perinet) adjusted by a factor of 1.08 to convert to
maximum 24-hour values.
