CC44 Phase III Geologic Exploration
Memorandum
General
During January 26th – 27th, 2015, staff from the Confederated Tribes of the Umatilla Indian Reservation
(CTUIR) and the Bureau of Reclamation (Reclamation) conducted geologic explorations along the
proposed channel alignment for Catherine Creek 44 (CC44) phase III. The purpose of the explorations
was to visually estimate the sizes (D85 and D100) and percent size class (sand, gravel and cobble) by
volume of in situ material in the proposed channel alignment. Exploratory auger holes/test pits
locations were primarily at proposed riffle crest locations. Two additional auger holes were located on a
vegetated bar along the right bank just off the active channel and on a berm within the floodplain
(Figure 1). Equipment used included a skid-steer with an 8-inch auger 5 feet long and a track-hoe.
Figure 1: Locations of explorations sites for CC44 Phase III.
On January 26th, explorations were conducted using a skid-steer equipped with an 8-inch auger 5 feet in
length. On January 27th, a track hoe was used to excavate test pits at proposed rifle crest locations.
Table 1 summarizes the findings using the skid-steer with the auger. Table 2 summarizes the findings
using the track hoe.
Table 1: Visual estimates (by volume) of in situ material, depth to water and thickness of overburden at riffle crest locations
along the proposed channel alignment for CC44, phase III using an auger.
Visual Estimation of Material
(by volume)
Station
% Sand
% Gravel
36+75
39+10
42+17
46+92
52+70
Bar
Berm
50
60
60
40
50
20
90
40
40
30
50
40
50
10
% Cobble
10
Trace
10
10
10
30
D85 (mm)
D100 (mm)
40-50
30-40
40-50
30-40
30-40
90-100
180-190
60-70
90-100
120-130
110-120
190-200
Depth to
Water
Seep
(in feet)
3.5
Thickness
of fine
material
(in feet)
1-2
1-2
3-4
1-2
2-3
Table 2:Visual estimates (by volume) of in situ material, depth to water and thickness of overburden at riffle crest locations
along the proposed channel alignment for CC44, phase III using a Track hoe.
Visual Estimation of Material
(by volume)
Station
% Sand
% Gravel
% Cobble
D85 (mm)
D100 (mm)
74+40
76+00
71+25
69+50
66+80
64+20
57+70
50
50
40
30
40
50
40
40
40
40
50
30
30
40
10
10
20
20
30
20
20
40-50
50-60
60-70
60-70
60-70
70-80
80-90
220-230
220-230
180-190
290-300
230-240
340-350
150-160
Depth to
Water
Seep
(in feet)
2.5
5.5
4
6
6
5
4
Thickness
of fine
material
(in feet)
1-2
4-5
2-3
3-4
2-3
1-2
2-3
Discussion
In comparing tables 1 and 2, the visual estimates of the percent of sand, gravel and cobble are similar.
However the D85 and D100 sizes, on average, are larger when the track how was used. This is due to the
inability of the auger to remove the cobble and gravel sized material from the hole. The auger holes
‘coned’ meaning that low cohesion material in the top section of the sand gravel and cobble unit
sloughed into the hole. The result was a reduction in the size of the D85 and D100 visual estimate.
Measurement of the depth to water seeps was also difficult due to the sloughing of material. When
using the track hoe, some sloughing still occurred, but the bucket was able to remove material to a
deeper depth where larger substrate exists.
Summary
Explorations results show that material at proposed riffle crests in the current active floodplain within
the CC44 Phase III footprint is fairly similar near the riffle crest locations along the proposed channel
alignment. The exposed basal layer is comprised of predominantly cobble and gravel with sand. The
deposit is upward fining with low cohesion. Areas of greater material cohesion coincided with
occasional clay lenses and iron oxidation layers. Water seeps within the exposed basal unit were
observed between depths of 2.5 and 6 feet from the surface. The basal layer is overlain by finer
material comprised of predominantly silt with medium cohesion but ranges to silty sand with gravel.
The finer material varied in thickness from 1 to 5 feet.