Dames & Moore, 1999 - USDA Forest Service

Discharge in Railroad Creek was monitored on a continuous basis at station RC-4 immediately upstream of
the tailings piles at the Site. Additionally, water level and discharge was monitored closely at station RC-2
immediately downstream of the tailings piles. Other stations where discharge was frequently measured
were station RC-1 upstream of the Site (considered to be a background station) and RC-3 at Lucerne. All of
these stations could be measured from a bridge or log at relatively high flows. Stations RC-5, RC-SA, RC-
6, and RC-7 were measured less frequently because of the difficulty in wading and measuring at higher
flows.
The hydrograph of streamflow in Railroad Creek at RC-4 is shown on Figure 4.3-4 and includes flow from
April 16 to October 4, 1997. Also on Figure 4.3-4, flow measurements from the other stations are plotted.
RC-2 flows plotted on the hydrograph were estimated from the rating equation for that station
(Appendix H). The hydrograph illustrates the seasonal variability of flows during spring, summer and fall
of 1997. In general, the flow pattern is similar to the long term average for the period of record at Lucerne,
with the highest flows occurring in May and June, followed by a gradual decline, and low flows in fall and
early spring.
Com~arison of Stations
The hydrograph also illustrates the comparability and relationship between flows at all stations. Comparing
Figure 4.3-4 with the hydrograph for the Stehekin River for the same time period (Figure 4.3-5) indicates
that the flow measurements at the two stations were very similar; however, the peak flow at each station
occurred at a different time. The comparison of flows indicates similar general climatic conditions and
basin response, and the difference in peak timing probably indicates micro-climatic and storage differences
between the two basins, and differences in basin aspect which impact the snowmelt characteristics.
Flow relationships between stations was evaluated by comparing measured flows at stations RC-1, RC-2,
RC-3, RC-4 and CC- 1 (the primary tributary between RC- 1 and RC-2) in relation to reference stations RC-2
and RC-4. RC-2 and RC-4 were chosen as the reference stations because they had the most usable and
available data; rating curves were developed for both stations. The rating curves provide a smoothing or
averaging of the measurement error inherent in the flow measurements and stage readings. The flow
relationships were evaluated as ratios of station flow to reference flow computed from the ratings.
Table 4.3-4 presents the results of this analysis. The flow ratios relative to RC-2 and RC-4 were statistically
averaged to provide the most reliable values.
Table 4.3-4 indicates that the rating estimates at RC-4 averaged 2 percent lower than the measured values
for that station, and the rating at RC-2 results in a 3 percent greater estimated flow value compared to the
measured flows. Averaging this error by normalizing the flow ratios for the other compared stations by
negative 2 percent for RC-4 and positive 3 percent for RC-2 (dividing each station ratio by the ratio of each
reference), indicates that gain between stations RC- 1 and RC-4 averages between negative one (indicating a
loss of flow) and zero percent. In contrast, the gain measured between RC-4 and RC-2 averages 12 to 15
percent, of which 12 percent is accounted for by inflow from Copper Creek. The measured gain between
RC-2 and RC-3 averages 79 to 101 percent.
Referring to Figure 4.3-3% the flow ratios between RC-1, RC-4 and RC-2 appear to have seasonal
variability; however, given the potential measurement error, the magnitude of the seasonal variability cannot
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17693-005-019Uuly 19.1999:4:51 PM;DRAFT FWAL RI REPORT