BOARD01926

• Board Meeting Date: 1/27/2004
• Description: ISF Section - Instream Flow Appropriations - West Antelope Creek
• Board Meetings - Doc Type: Memo

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Survey methods used to collect these data are described in Harrelson et al (1994). The
students involved with the survey include: Gretchen Moran, Chad Bowdre, Tim
Brethauer, Brian BePm, Jason Eliassen, Charles Kieser, Tom Mills, and Andrew
Lockman. We thank Art Hayes (BLM) for his support and assistance.

Establishment of Benchmarks

Three benchmarks were established for survey purposes. The benchmarks are 1.5 foot
section of rebar that were driven into the ground to about 3 inches above the mineral soil
surface. Each benchmark is capped with a metal plate that labeled with the benchmark
number (BM I, II or III), the letters WSC (for Western State College) and the date the
benchmark was established (Figure 4). Locations of benchmarks relative to the channel
are shown on Plate 1 (plan map of the stream). Pictures of the locations of benchmarks I
and II are shown in Figures 5 and 6. Benchmark I was assigned an elevation of 100
meters. All other elevations reported in this survey are relative to Benchmark 1. For
example, the elevation of Benchmark II is 98.906 m and the elevation of Benchmark III
is 101.968 meters.

Channel Cross Sections

Three channel cross sections were'surveyed (designated as I, II, III) and the location of
each is shown on Plate 1. Photos of cross sections are shown in Figures 7, 8, and 9. Data
for these cross sections are given in Appendix 1. Plots of cross sections are shown in
Figures 10, 11, and 12, Note that the horizontal and vertical scales of all plots are
identical so that the profiles can be directly compared.

Cross-section I (labeled XSI in data) is located in the center of the survey reach and
approximately 15 m downstream of a breached beaver dam. The bankfull surface is
poorly defined but was interpreted as a low, flat surface with willows on the right bank
(Figure 2). Bankfull-derived parameters are listed in Table 1. Slopes are calculated from
channel bottom slopes within immediately where the stream crosses the longitudinal
profile_

Cross-section II (labeled XSII in data) is located downstream in the survey area (see map)
in a reach where it appeared that the stream was not in the lowest part of the valley.
Cross-section II profile is shown in Figure 11 which illustrates that, indeed, the lowest
part of the valley not in the active channel but is rather at station 21.5 m which has an
elevation of 95.763 m. This compares to the average water surface elevation in the
channel (for the day of the survey) of 96,023 m and the minimum channel bottom
elevation of 95.875 m. In the area around the active channel, bankfull elevation is
approximately 96.104 m (see Table 1). Figure 13 shows the abandoned channel at station
21.5 m. Figure 14 shows a second, probably older, abandoned channel at station 40.0 m.
This second abandoned channel (at 40.0 m) extends along the right side of the valley,
upstream to an older beaver dam that is barely discernible on the floodplain and can be
seen in Figure 7.

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