Thompson Creek
General Information
Thompson Creek is a tributary of the Salmon River near Clayton, ID. The study reach is
a 420 ft length of stream located upstream of the confluence with Pat Hughes Creek about 2.7
miles upstream of the existing USGS gaging station (13297330, Thompson Creek near Clayton,
ID). The elevation of the study reach is about 5,700 ft. The drainage area above the USGS gage
is 29.5 mi2 and above the study reach is 21.8 mi2. The geology of the watershed is
predominantly sedimentary.
In 1994 and 1995, personnel of Case Western Reserve University established a stream
gage and measured sediment transport and streamflow at this site. Additional information
collected at the site include a survey of the stream reach, pebble counts of the substrate surface in
1994, core samples of surface and subsurface substrate in 2000 and transport distance of painted
rocks during high flows in 1995. Figure 1 shows a photograph of Thompson Creek looking
downstream.
Figure 1. Downstream view of Thompson Creek.
Streamflow records are also available for the downstream USGS station since water year
1972. Discharge at the study reach is estimated as 95.7% of the discharge of the USGS station.
Estimated average annual streamflow for the stream is at the study reach is 15.8 ft3/s and the
estimated bankfull discharge is 87.6 ft3/s. Stream discharge in 1994 was very low and the largest
mean daily discharge and instantaneous peak discharge were only 31.6 ft3/s and 34.0 ft3/s,
respectively. In 1995 the largest mean daily discharge and instantaneous peak discharge were
120 ft3/s and 135 ft3/s , respectively, on June 4, well above bankfull discharge.
Channel Profile and Cross-Section
Figure 3 shows the longitudinal profile for the channel bed in the center of the channel,
the water surface elevations along each bank at the time of the survey and bankfull flow
elevations (floodplains). The average gradient for the study reach is 0.0153 ft/ft. Cross-sections
of the channel were surveyed at four locations. Discharge and sediment transport measurements
were made at cross-section 1 (XS1) and the movement of painted rocks during the spring and
early summer snowmelt flows in 1995 were measured at two transects about 13 and 28 ft
downstream of XS1.
165
Elevation, ft
Thompson Creek
XS2
160
Water Surface Elevation Left Edge
Center of Channel Bed Elevation
Water Surface Elevation Right Edge
Bankfull Elevation Left Side
Bankfull Elevation Right Side
XS1
Painted Rock
Transects
XS5
XS4
155
0
50
100
150
200
250
300
350
400
Distance, ft
Figure 2. Longitudinal profile of the study reach in Thompson Creek.
450
500
170
Thompson Creek
Elevation, ft
Cross-section 1
165
Qb
Qa
160
155
0
10
20
30
40
50
60
70
80
90
Distance, ft
Figure 3. Cross-section of Thompson Creek at the sediment transport measurement site.
Channel Geometry
Figure 3 shows the cross-section at the sediment transport measurement site, crosssection 1. The channel geometry relationships for this cross-section are shown in Figure 4. All
data collected in 1994 and 1995 were used to develop the displayed power relationships with
discharge. Over the range of discharges when sediment transport was measured (8.15 to 124
ft3/s) estimated stream width, estimated average depth and estimated average velocity varied
from 14.2 to 22.1 ft, 0.51 to 1.22 ft, and 1.1 to 4.6 ft/s, respectively. The average reach slope is
0.0153 ft/ft.
100
10
Thompson Creek
Width
0.162
y = 10.129x
2
R = 0.95
Average Velocity
0.515
y = 0.384x
2
R = 0.99
Velocity, ft/s
Width and Depth, ft
10
Average Depth
0.322
y = 0.258x
2
R = 0.97
1
0.1
1
10
100
1
1000
3
Discharge, ft /s
Figure 4. Width, average depth, and average velocity versus stream discharge
at the sediment transport measurement cross-section.
Channel Material
Pebble counts were made near cross-section 1 in June 1994 and at four cross-sections in
July 2000. The D50 and D90 for the pebble counts in 1994 were 66 mm and 130 mm, respectively
(Figure 5). The D50 and D90 for the combined 2000 pebble counts were 59 mm and 140 mm,
respectively, and about 5% of the surface was sand size and smaller material. In July 2000, three
core samples were also collected in the reach. The D50 and D90 for the combined surface and
combined subsurface cores were 135 mm and 228 mm and 43 mm and 164 mm, respectively.
100
Thompson Creek
90
80
Percent Finer
70
60
50
40
1994 Pebble Counts
2000 Pebbles Counts
2000 Surface Cores
2000 Subsurface Cores
30
20
10
0
0.1
1
10
100
1000
Particle Size, mm
Figure 5. Particle size distribution for surface and subsurface material samples
in Thompson Creek.
Sediment Transport
The sediment transport data include 84 measurements of bedload transport and 24
measurements of suspended sediment transport. Sediment transport measurements spanned a
range of stream discharges from 8.15 ft3/s (0.52Qa; 0.09Qb) to 124 ft3/s (7.85Qa; 1.42Qb).
Bedload transport ranged from 0.000627 to 22.0 tons/day and suspended transport ranged from
0.154 to 63.7 tons/day. 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 at the lowest discharges and about three times as much at the highest
discharges during which sediment transport was measured (Figure 6).
100
Thompson Creek
Suspended
2.478
y = 0.000258x
2
R = 0.93
BCF=1.081
Sediment Transport, tons/day
10
Total Bedload
3.275
y = 2.085E-06x
2
R = 0.89
BCF=1.522
1
0.1
0.01
0.001
Qa
Qb
Total Bedload
Suspended
0.0001
1
10
100
1000
Discharge, ft3/s
Figure 6. Bedload and suspended load transport rate versus discharge.
The bedload transport rates by size class (Figure 7) shows that the larger rates are
associated with material in the 0.5 to 2mm diameter size class. No curve fitting was done for
sediment >32mm diameter since only one of the samples contained this size class of material.
100
Thompson Creek
Sediment Transport, t/day
10
<0.5 mm
2.963
y = 2.166E-06x
2
R = 0.92
1
0.5 - 2 mm
3.307
y = 1.031E-06x
2
R = 0.88
0.1
2 - 8 mm
3.546
y = 6.186E-08x
2
R = 0.71
0.01
0.001
8 - 32 mm
3.056
y = 2.873E-07x
2
R = 0.23
0.0001
Qb
Qa
<0.5 mm
0.5 - 2 mm
2 - 8 mm
8 - 32 mm
>32 mm
0.00001
1
10
100
1000
3
Discharge, ft /s
Figure 7. Bedload transport rate versus discharge for selected size classes.
The size of the largest particle in the bedload sample increased with discharge (Figure 8).
The largest particle measured in a bedload sample was 68.5 mm at discharges of 85.4 and 89.0
ft3/s. At discharges near or greater than bankfull discharge (87.6 ft3/s), the largest particle often
exceeded 30 mm. There is a tendency for increasing median size of the bedload sample with
increasing discharge. The D50 for most of the bedload samples was in the sand size, 0.5 to 2.0
mm. The largest median diameter of a bedload sample was 7.1 mm. The information on the
largest particle in the bedload sample and observations of painted rock movement suggest that
discharges at, or slightly above, the bankfull discharge are capable of moving the median
diameter particles on the channel surface.
1000
Thompson Creek
Largest Painted
Rock Moved in
1995
Particle Diameter, mm
100
D50 Surface
Substrate 1994
R2 = 0.75
10
R2 = 0.20
1
Qa
Qb
Median Diameter
Largest Particle
0.1
1
10
100
1000
Discharge, ft3/s
Figure 8. Median size of the bedload sample and the largest particle size versus
stream discharge for Thompson Creek.
Painted Rock Transport
A total of forty painted rocks were placed across two transects (twenty per transect) on
April 25, 1995. Daily mean discharge on the day of rock placement was 18.2 ft3/s. The size of
the rocks ranged from 41 to 131 mm diameter (b-axis) which represents the D14 up to the D91 of
the surface particle size distribution measured at cross-section 1. Transport of the rocks as of
July 31, 1995 are shown in Figures 9 and 10.
300
Thompson Creek
Painted Rocks
Transect 1
Downstream Distance Moved, ft
250
200
150
Particle B-axis, mm
100
50
114 131 114 101
95
55
89
98
82
M
113
63
M
M
7.4
8.2
63
79
98 124
72
82
M
99
M
68
51
M
0
0
0.8
1.6
2.4
3.3
4.1
4.9
5.7
6.5
9
9.8 10.6 11.5 12.3 13.1 13.9 14.7 15.6
Distance across stream, ft
Figure 9. Transport distance of painted rocks at transect 1.
250
Thompson Creek
Painted Rocks
Transect 2
Downstream Distance Moved, ft
200
150
100
Particle B-axis, mm
50
56 115
74
46
M
84
128
99
3.3
4.2
5.2
6.2
7.2
104 119
68
M
86
M
70
94
9.2 10.2 11.1 12.1 13.1 14.1 15.1 16.1
17
18
19
20
113 126
97
58
41
M
96
83
0
1.3
2.3
8.2
Distance across stream, ft
Figure 10. Transport distance of painted rocks at transect 2.
Thirty of the forty rocks were found. Of those found, only three had not moved. The
maximum transport distance was 250.9 ft for a 51 mm diameter rock and the average was
transport distance was 50.1 ft. The largest daily mean discharge during the period when painted
rock movement was studied was 119.6 ft3/s on June 4, 1995 and the largest instantaneous
discharge was 129 ft3/s.