Dames & Moore, 1999 - USDA Forest Service

The GZF is the depth relative to the staff gage at which flow would be zero. ' The GZF for RC-4 agrees with
channel cross-section data at the measurement section. However, the GZF for RC-2 appears to be too low
to be physically realistic. This indicates that the rating for RC-2, although useful for the purposes of this
project, may not be appropriate for long term use. Assuming a realistic value for GZF, determined from
physical channel measurements, would yield a rating for RC-2 of:
where:
GZF = -0.8
Discharge = 20.1 (G-GZF)"2.835 (4-3)
Equation 4-3 was not used for the RI, but should be used in the fitture if data extrapolation is required. This
equation can be verified and updated if more flow data is collected at RC-2. For the purposes of this study,
however, equation 4-2 was used to estimate flow at RC-2 in order to yield the highest accuracy for flow
estimates in 1997.
4.3.3.3 Railroad Creek
Channel Geomorphology
Overview
Referring to Figure 4.3-2, Railroad Creek flows approximately 18 miles from its headwaters at Lyman
Glacier near the Pacific Crest to Lake Chelan. Approximately 13 tributary streams with watersheds greater
than 1 square mile enter Railroad Creek along its length. The largest,tributaries include Big Creek, Copper
creek, Tenmile Creek, Klone Creek and Tumble Creek. Copper Creek enters Railroad Creek at the Site.
The locations of the streams and the stream gradients were determined based on existing topographic maps
of the watershed (USGS, 1967a and 1967b).
Upstream of Site to Tenmile Creek
Upstream of the Site, the stream gradient is steepest near the headwaters betiveen Lyman Glacier and Crown
Point Falls, just below Lyman Lake (Figure 4.3-3). Between Crown Point Falls and Hart Lake, the stream
gradient averages 3 to 3.5 percent. The gradient steepens again for a short reach below Hart Lake, and then
levels off again in the vicinity of the Site.
From approximately one mile upstream of the Site to one mile downstream of the Site, the stream gradient is
nearly the flattest in the basin (other than immediately downstream of the Tenmile Creek confluence),
averaging between 1 to 2 percent. In this reach, glacial sediments can be observed in occasional cutbanks
with thicknesses in excess of 20 feet in some places.
The stream channel for this segment of stream exhibits bar development, occasional braiding, and a
developed floodplain except in the reach adjacent to the tailings piles. Within the approximate one mile
reach from the vehicle bridge west of Holden Village to the west end of tailings pile 1 (Figure 4.3-3a), the
channel is confined by riprap andlor cribbing along its south bank, and in some areas confined by a steep
embankment along the road on the north bank. Within this confined reach, the channel is relatively straight
17693-00S-d19Vuly 19. 1999:4:51 PM:DRAFT FINAL RI REPORT