Dames & Moore, 1999 - USDA Forest Service

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was discovered that Howe Sound Company likely conducted limited mineral exploration in the Holden
Creek watershed). Stream flow measurements and other relevant data collected during the RI are presented
in Appendix H.
. Streamflow monitoring stations on Copper Creek include CC- I upstream of the tailings piles (established by
PNL and the USFS), CC-2 near the confluence of Copper Creek and Railroad Creek (also established by
PNL and the USFS), and CC-DICC-Dl, which is the Copper Creek diversion (established at the request of
the Agencies). CC-DtCC-Dl flow is diverted from Copper Creek upstream of CC-l and routed through the
hydroelectric plant (Figure 4.3-3a). Flow from CC-DICC-Dl is also diverted for water use at Holden
Village. Flow was also monitored in the portal drainage at stations P-l (where the drainage flows from the
mine portal) and P-5 (upstream of the confluence with Railroad Creek).
Staff gages for measuring water levels are located at stations RC-2, RC-4 and RC-6 in Railroad Creek.
Additionally, a continuously recording water level recorder (Troll) was installed in the stilling well at RC-4
on May 24, 1997. The Troll was removed during the winter due to the low water levels and freezing
temperatures. A staff gage is also located behind the weir which controls flow out of the hydroelectric plant
in the Copper Creek diversion.
Accuracy of Measurements a
The accuracy of strearnflow measurements in Railroad Creek is dependent on several factors, including the
method of measurement, the irregularity of the cross-section, and the degree of turbulence in the water at the
cross-section. Under ideal conditions, discharge measurements with the equipment used (Price AA or
equivalent SWOFFER meter, wading rod and/or bridge board and sounding reel) is assumed to be accurate
to within 2 percent of the actual flow (Rank et al., 1982). However, all of the stations measured at the Site
exhibit highly irregular cross-sections due to the cobble- to boulder-size substrate material. Based on
professional judgment and experience, the irregular cross-section reduces accuracy to within 5 percent of the
actual flow. In addition, using the bridge board and reel is less accurate than wading due to difficulties in
measuring depth and maintaining stable position for the velocity meter; the bridge board is used at higher,
much more turbulent velocities when wading is not possible. Thus, bridge board measurements are
assumed to reduce accuracy by another 5 percent.
Based on the above, wading measurements which, based on experience, can be safely accomplished in
Railroad Creek at the Site when RC-4 river stage levels are approximately 1.5 feet or lower, have an
assumed accuracy within 5 to 7 percent of the actual flow. Bridge board measurements have an assumed
accuracy within 10 to 12 percent of the actual flow.
Stage measurements observed on staff gages installed at RC-2, RC-4 and RC-6 also have a finite accuracy.
During higher flows, staff gage readings have an assumed accuracy of 0.05 foot due to waves and
turbulence disturbing the water level at the gage. This accuracy is based on site-specific experience reading
the gages. At lower flows, less turbulence and waves allow for more accurate gage reading, and is assumed
to be on the order of 0.02 foot. As noted above, a continuous water level recorder (Troll) was installed in a
stilling well at RC-4. The accuracy of the pressure transducer in the data logger is reported by the
manufacturer to be 0.0 1 foot.
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17693-005-019Uuly 19.1999;4:51 PM;DRAFT FINAL RI REPORT