Dames & Moore, 1999 - USDA Forest Service

3.2.1 Streamflow Suweys
Streamflow surveys were conducted during the April, MayIJunt?, July, and SeptemberlOctober 1997 and
May 1998 sampling events. However, the April 1997 sampling event included the survey of Railroad
Creek only due to the presence of snow cover, which precluded access to the other water bodies noted
above.
The streamflow survey consists of flow measurements in Railroad Creek, Copper Creek and selected
tributaries and out of basin streams. A flow measurement was attempted each time a surface water
quality sample was collected, and during periods of high and low flow to characterize flow variability.
Referring to Figures 3.2-1 and 3.2-2, and Table 3.0-1 under "Surface Water," streamflow measurements
were made at RC-1, RC-2, RC-3, RC-4, RC-5 (and RC-SA), RC-6, RC-7, RC-10, and RC-I I in Railroad
Creek, CC-1 and CC-2 (combined) in Copper Creek. CC-Dl (Copper Creek diversion) and in the portal
drainage at P-1 and P-5.
Flow measurements were made in several tributaries (Holden Creek, Big Creek, and Ten Mile Creek) that
were sampled and at all aquatic habitat sampling locations in Railroad Creek (see Section 3.9) and three
locations (Bridge Creek, South Fork Agnes Creek, and Company Creek) outside the Railroad Creek
watershed north of the Site. At stations RC-4 and RC-2, water levels were consistently monitored to
develop stage-discharge rating curves (graphs which allow one to determine flow rate from a water height
measurement) for these two stations. Flow data from the USFS (1996) was incorporated into the ratings
for both of these stations. The rating curves developed for Railroad Creek stations RC-2 and RC-4 are
discussed in Section 4.3.3.2.
A low flow or baseflow survey was completed during the September 1997 field program. The objective
of the baseflow survey was to measure the groundwater inflow component to Railroad Creek adjacent to
the Site. The baseflow survey was completed during a time of historical, steady low flow conditions
(September 22, 1997) and consisted of measuring flow at all of the Railroad Creek stations (RC-4, RC-7,
RC-2 and RC-5) adjacent to the Site. Tributary flow was also measured from Copper Creek (CC-I), the
Copper Creek diversion (CC-Dl), and SP-21 (located to the east of tailings pile 3, noted on Figure 3.3-2
and Table 3.0-1 under "seeps"). In October 1998, additional baseflow measurements were collected in
Railroad Creek between stations RC-I and RC-4 to further characterize an apparent flow loss that was
observed in 1997. The additional survey was designed to characterize the flow loss and to evaluate the
specific locations of the loss.
The streamflow measurements were made using standard USGS methods and equipment at each station
(Rantz et al., 1984). The stream depth and velocity were measured by wading into the stream when depth
and velocity were low enough to allow the hydrologist to enter the stream safely. Width was measured
from a tagline (tape measure) strung across the channel section. During periods of higher flow when a
wading measurement could not be accomplished, flow measurements were made from those stations that
could be measured from a bridge; these stations included the footbridge (station RC-4), Svens bridge
(station RC-2) and at Lucerne (station RC-3).
Rating curves were developed for the RC-4 and RC-2 gauging stations using the discharge and staff gage
measurements at these locations. The rating curve provides a means to estimate streamflow from gage
heights, and also averages errors associated with the discharge and staff gage measurements. The rating
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17693-00Jbl9Uuly 19. 1999;2:07 PM;DRAFT FINAL RI REPORT