annexc - Newmont Mining Corporation

Annex C4 – Water Resources Supplemental Information C4 - 5
SW-21 (PRA-1): Pra River at Praso Kuma (drainage area = 875 km 2 )
� Feb-June 2004 flow measurements = 0.066 to 3.66 m 3 /sec
� Minimum flow in May 2007 was zero m 3 /sec
� Peak flows in September 2007 = 60 m 3 /sec, with sustained flows >10 m 3 /sec
� Calculated bankfull discharge = 62 m 3 /sec
SW-27 (PRA-2): Pra River at Ofoase-Praso Bridge (drainage area = 2,045 km 2 )
� 1991-1999 flow measurements = 0 to 107 m 3 /sec
� Minimum flow in May 2007 was zero m 3 /sec
� Peak flows in September-October = 80 m 3 /sec, with sustained flows >20 m 3 /sec
� Calculated bankfull discharge = 94 m 3 /sec
Mamang River
The Mamang River watershed covers an area of approximately 475 km 2 . Mean monthly
flows based on flow measured for the Pra River at Ofoase-Praso (2,045 km 2 ) were
calculated by the area-ratio method for five locations within the Mamang basin, assuming the
Pra and Mamang River basins have similar watershed characteristics. Mean monthly flow
estimates for the Mamang River at three monitoring sites are summarized in Table C4-3.
Using these monthly averages, mean annual discharge for the Mamang River at its mouth
(SW-25, 475 km 2 watershed area) is 2.9 m 3 /sec.
TABLE C4-3
Mean Monthly Flow Calculated for Mamang River and Tributaries
Mean Monthly Flow (metre3/second) Surface Water Site &
Watershed Area Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Mean
SW-25: Mamang River
at Kotokuom (475 km2) 0.42 0.32 0.49 0.93 1.37 5.04 6.64 4.06 4.71 6.08 2.78 1.14 2.90
SW-24: Mamang River
at Nkwanten (384 km2) 0.34 0.26 0.39 0.75 1.11 4.07 5.37 3.28 3.81 4.92 2.25 0.92 2.35
SW-28: Mamang River at Mamanso
(98 km2) 0.09 0.07 0.10 0.19 0.28 1.03 1.36 0.83 0.97 1.25 0.57 0.23 0.60
Adenkyerensu stream (10 km2) 0.01 0.01 0.01 0.02 0.03 0.11 0.15 0.09 0.10 0.13 0.06 0.02 0.06
Afosu stream (7.4 km2) Source: SGS 2004g.
0.01 0.01 0.01 0.01 0.02 0.08 0.1 0.06 0.07 0.09 0.04 0.02 0.05
In April-May 2007, two continuous recording stream gauging stations were installed on the
Mamang River by Clear Creek Consultants (2008b) at SW-28 (MAM-1, upstream) and SW-
24 (MAM-2, downstream). Figures C4-4 and C4-5 are hydrographs for these stations
showing flow measured in 2007, and some individual flow measurements in February-June
2004 and May-December 2007. The following are selected flow data for these two stations
(Clear Creek Consultants 2008b):
Akyem Gold Mining Project November 2008 FINAL EIS