Dames & Moore, 1999 - USDA Forest Service

After flowing through the hydroelectric power plant, water from the diversion flows to the west side of
tailings pile 1 and into Railroad Creek upstream of tailings pile 1 (Figure 4.3-3a). This water is in partial
contact with debris and some tailings material within the short reach downstream of the hydroelectric plant
before it enters Railroad Creek. A small portion of this water also flows to the outdoor sauna pool.
Streamflow
Discharge in the Copper Creek diversion is routed over a weir downstream of the hydroelectric plant. The
height of water behind the weir is measured by a staff gage, and can be converted.to flow in cfs via a weir
rating table that is kept in the hydroelectric plant. The discharge was also measured directly by Dames &
Moore in the field. During the April 1997 field program, discharge in the diversion was estimated to be
. approximately 2.8 cfs based on the staff gage height in the pool behind the weir. According to the Holden
Village operations manager, the majority of flow from Copper Creek was diverted during April to provide
power and water to Holden Village (personal communication with Mark Schmidt, 1997).
In 1997 the staff gage behind the weir was read relatively frequently, and ranged uniformly throughout the
spring, summer and fall observations. The weir table indicates the measurements correspond to flows of 6.8
to 7.1 cfs. Direct measurements at the weir indicated slightly lower flows, between 5.5 and 6 cfs. The
relatively minor difference between the rated flow and the measured flow may be due to measurement error
at the weir, or may also be partially due to loss of flow via infiltration within the diversion channel and
stilling pool behind the weir.
4.3.3.6 Portal Drainage
Channel Morphology
Referring to Figure 4.3-3% the portal drainage emerges from the 1500-level main mine portal and flows
downslope in both a man-made ditch and a natural drainage to a point approximately mid-way between
RC-I and RC-4 where it enters Railroad Creek. The drainage channel is composed of cobble and gravel,
with a millimeter or more of whitish precipitate (apparent aluminum hydroxide)'coating the bed materials
throughout its length. Flow measurements were made in the drainage at the upstream end where it emerges
from the mine portal (Station P-I), and at its downstream end just before entering Railroad Creek (Station P-
5) during each sampling round, and on a weekly basis throughout the MayIJune 1997 sampling round.
Streamflow
Flow measurements in the portal drainage at stations P-l and P-5 during 1997 are shown on Figure 4.3-7.
For two out of the three paired flow measurements, P- 1 was greater than P-5, indicating a loss of flow as the
drainage water flows downslope, probably resulting from infiltration into the channel bed. The exception
was during May when snowrnelt runoff between P-l and P-5 resulted in a higher flow at P-5. Flows ranged
from a high in MayIJune of approximately 3.5 cfs, to a low of less than 0.3 cfs in mid-September.
A weir and water level data logger (transducer or Troll) were installed at the 1500-level main portal opening
in the portal drainage in early October 1997 to collect relatively continuous water level data. The weir
consists of wood planking installed across the bottom of the portal opening, with plastic sheeting placed on
the upstream side to prevent leakage, and a V-shaped notch in the planking through which the water flows.
G:\WPDATA\OO5NEPORTSWOLDEN-2W-O.DOC
17693-00S-019Uuly 19.1999;4:SI PM:DRAFT FINAL RI REPORT