Salmon River below Yankee Fork
General Information
The study reach is near the Geological Survey (USGS) gage 13296500 (Salmon
River below Yankee Fork near Clayton, ID) in the Salmon - Challis National Forest. The
site is about 0.25 miles downstream of the remains of the sunbeam dam and about 0.125
miles downstream of the mouth of the Yankee Fork Salmon River. The site is on land
administered by the Forest Service at an elevation of about 5,900 ft. The drainage area
upstream of this location is 811.1 mi2 and the geology of the watershed consists
predominantly of mixed volcanics, igneous intrusions and glacial deposits.
Sediment transport measurements were made by US Geological Survey
personnel during the spring snowmelt flows of 1999 and 2000. Additional measurements
at this site include a survey of the stream reach, pebble counts of the surface material and
core samples of the surface and subsurface material.
Streamflow records are available for this gage for water years 1922 to 1991 and
2001. Average annual streamflow (Qa) for the period of record is 983 ft3/s and the 1.5
year return interval discharge is estimated at 4,170 ft3/s. The highest flow recorded was
10,500 ft3/s on June 17, 1974.
Cross-Section
Figure 1 shows the cross-section at the USGS cableway, 50 ft upstream from the
gage. The average gradient for the study reach is 0.0034 ft/ft. All sediment transport
measurements were made at the cableway.
15
Elevation, ft
Salmon River below Yankee Fork
10
Q1.5
5
Qa
0
1982 survey
-5
-10
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
Distance, ft
Figure 3. Cross-section of the Salmon River below Yankee Fork.
Channel Geometry
The station geometry relationships for the cross-section at the cableway are
shown in Figure 2. All discharge note information for 1938 through 1990 for cableway
measurements without ice effects were used to develop the power relationships with
discharge. Over the range of discharges when sediment transport was measured (1,360 to
5,070 ft3/s) estimated stream width, estimated average depth and estimated average
velocity varied from 98.4 to 123.1 ft, 4.08 to 6.39 ft, and 3.4 to 6.4.1 ft/s, respectively.
The average reach slope is 0.0034 ft/ft.
10
1000
Top Width
0.170
y = 28.834x
2
R = 0.95
100
Average Velocity, ft/s
Width and Depth, ft
Salmon River below Yankee Fork
Average Velocity
0.489
y = 0.100x
2
R = 0.96
10
Average Depth
0.341
y = 0.348x
2
R = 0.92
1
10
100
1000
1
10000
3
Discharge, ft /s
Figure 2. Width, average depth, and average velocity versus stream discharge at
the cableway cross-section on the Salmon River below Yankee Fork.
Channel Material
Surface pebble counts were made at three cross-sections and three cores of
surface and subsurface material were collected, one at each cross-section, in July 2000.
The D50 and D90 for the combined pebble counts were 104 mm and 396 mm, respectively
(Figure 3). About 6% of the surface material was sand (2 mm) size or smaller. The D50
and D90 for the combined surface cores were 138 mm and 182 mm, respectively. The
average D50 and D90 for the subsurface material are 25 mm and 133 mm, respectively. .
100
Salmon River
below Yankee Fork
90
80
Percent Finer
70
60
50
40
30
20
2000 Pebble Counts
10
2000 Subsurface Cores
2000 Surface Cores
0
0.1
1
10
100
1000
10000
Particle Size, mm
Figure 3. Particle size distribution for surface and subsurface material samples
for the Salmon River below Yankee Fork.
Sediment Transport
The bedload and suspended load measurements in water years 1999 and 2000
were all made from the cableway. The sediment transport data includes 60 measurements
of bedload transport and 30 measurements of suspended sediment. Sediment transport
measurements spanned a range of stream discharges from 1,360 ft3/s (1.37Qa) to 5,070
ft3/s (5.12Qa). Bedload transport ranged from 0.111 to 328 t/d and suspended transport
ranged from 17.0 to 4,730 t/d. Over the range of measured discharges, suspended
transport accounts for the majority of the material in transport with approximately an
order of magnitude greater suspended transport (Figure 4).
10000
Salmon River below Yankee Fork
Sediment Transport, tons/day
1000
100
10
Suspended
3.315
y = 5.089E-10x
2
R = 0.84
BCF=1.25
1
Total Bedload
3.851
y = 4.205E-13x
2
R = 0.72
BCF=1.549
Suspended
Total Bedload
0.1
100
Qa
Q1.5
1000
10000
3
Discharge, ft /s
Figure 4. Bedload and suspended load transport rate versus discharge.
The bedload transport rates by size class (Figure 5) show that at discharges up to
about 0.8 of the 1.5 year recurrence discharge the largest rates are associated with
material 0.5- 2 mm diameter. At higher discharges, the larger transport rates are
associated with 8-32 mm and > 32 mm material. Ten of the bedload samples contained
material larger than 32 mm diameter and these were at discharges of 2,890 ft3/s and
larger.
1000
Salmon River below Yankee Fork
Bedload Rate, tons/day
100
<0.5mm
2.939
y = 9.878E-11x
2
R = 0.71
10
0.5-2mm
3.065
y = 9.108E-11x
2
R = 0.62
1
2-8mm
4.514
y = 2.198E-16x
2
R = 0.63
0.1
8-32mm
4.598
y = 1.229E-16x
2
R = 0.44
0.01
>32mm
2.918
y = 4.808E-10x
2
R = 0.44
0.001
100
<0.5mm
0.5-2mm
2-8mm
8-32mm
>32mm
Qa
Q1.5
1000
Discharge, ft3/s
Figure 5. Bedload transport rate versus discharge for selected size classes.
10000
The D50 for the bedload samples ranged from 0.49 to 38.87 mm. At discharges
less than the 1.5-year discharge, the median diameter is usually sand size. At discharges
larger than the 1.5-year discharge, the median diameter exceeds sand size. The largest
median diameter was associated with a discharge of 4,380 ft3/s.
1000
Salmon River below Yankee Fork
D50 for three
surface pebble counts
Bedload Size, mm
100
D50 for three
subsurface cores
10
R2 = 0.34
1
Median Size
Largest Particle
0.1
100
Q1.5
Qa
1000
10000
3
Discharge, ft /s
Figure 8. Median size of the bedload sample versus stream discharge for the
Salmon River below Yankee Fork.