HomeMy WebLinkAboutThayer Lake Hydropower Project - Lower Watershed Environmental Studies - Jul 2015 - REF Grant 7040038Angoon Hydroelectric Project
Thayer Creek, Alaska
2013/2015
Lower Watershed Environmental studies
Submitted to:
Alaska Power & Telephone Company
193 Otto Street
P.O. Box 3222
Port Townsend, Washington 98368
Submitted by:
Shipley Group
32 North Main Street
Farmington, Utah 84025
July, 2015
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TABLE OF CONTENTS
Section I – Lower Thayer Creek Drainage Stream Habitat
Overview ………………………………………………………………… I-1
Thayer Creek Anadromous Reach …………………………………… I-2
Physical Channel Description ……………………………………………………….I -3
Large Woody Debris (LWD) …………………………………………… I-11
Stream Profiles and Channel Morphology ……………………………. I-17
Anadromous Reach Substrate Assessment …………………………… I-28
Thayer Creek Gorge Characteristics ………………………… I-36
Summary of Gorge Features ……………………………………………………… I-46
Tributary Flows into Thayer Creek Gorge …………………… I-47
Thayer Creek Reach Above the Gorge ………………………….. I-56
Potential Hydro Project Impacts to Stream Habitat ……. I-69
Section II - lower Thayer Creek Drainage Water Resources
Overview ……………………………………………………………….. II-1
Thayer Creek Streamflow Assessment …………………………. II-1
Thayer Creek water and air temperatures …………………. II-21
Local Weather Conditions ………………………………………… II-25
Tributary flows into the Thayer Creek Gorge ………….. II-26
iii
Section III - Lower Thayer Creek Drainage Fisheries Surveys
Overview ……………………………………………………………….. III-1
2013 Fish Sampling Results …………………………………………………….III-2
2014 Fish Sampling Results …………………………………………………….III-8
2015 Fish Sampling Results ………………………………………… III-12
Adult Fish Escapement Surveys …………………………………………….… III-13
Section IV - References…………………………………………………. IV-1
Appendices:
Appendix I-1 Thayer Creek stream profile video records
(on DVD disk)
Appendix I-2 Thayer Creek anadromous reach substrate
¼ m2 quadrat video records (on DVD disk)
Appendix II-1 Solinst datalogger temperature and
water depth records above the gorge
on Thayer Creek 4-20-2013 through
4-9-2014 (on DVD disk)
Appendix II-2 Solinst datalogger temperature and
Water depth records above the gorge on
Thayer Creek 4-10-14 through 4-8-15 (on
DVD disk)
iv
Appendix II-3 Calibration curve and depth/cfs conversion
table for Thayer Creek above the gorge
Appendix III-1 Summary of fisheries catch data for 2013
Permit SF 2013-037
Appendix III-2 Alaska Department of Fish and Game
Thayer Creek trip report, August 5-6, 2014
Appendix III-3 Summary of fisheries catch data for2014
Permit SF 2014-234
Appendix III-4 Summary of fisheries catch data for 2015
Permit SF 2015-072
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List of Figures
Section I – Lower Thayer Creek Drainage Stream Habitat
Figure I-1. Lower Thayer Creek drainage studied by the Shipley Group.
Six reaches, 3 tributaries, and 4 major barrier were initially identified
and used to define the reaches. ……………………………………………………………… I-2
Figure I-2. Study zones established within the anadromous reach. …………………………… I-3
Figure I-3. Physical features at the mouth of Thayer Creek. ………………………………………. I-4
Figure I-4. The upper end of the anadromous reach showing major LWD
and channel features. …………………………………………………………………………. I-6
Figure I-5. Lower section of anadromous reach showing reach showing
major LWD and channel features. ……………………………………………………………… I-7
Figure I-6. West bank of Thayer Creek in zone IV, showing bedrock outcrops
in the foreground. …………………………………………………………………………………….. I-8
Figure I-7. West shoreline of Thayer Creek showing duff layer and timber on
top of bedrock. …………………………………………………………………………………….. I-9
Figure I-8. East shoreline of Thayer Creek showing the erosion resistant
root/duff layer sloughing into the creek as the underlying alluvium
is washed away. …………………………………………………………………………………….. I-10
Figure I-9. Active area of alluvial erosion on the east shoreline. …………………………… I-11
Figure I-10. Extensive undercutting of rootmat without callpse of the mat. ……. I-11
Figure I-11. Cluster of LWD on west bank in zone I. ………………………………………………….. I-13
Figure I-12. Cluster of LWD and exposed roots on the east bank. Note the
flat terrain behind the stream bank. ………………………………………………….. I-13
Figure I-13. LWD with root wad attached. At higher water flows this tree is
at the waterline. The old side channel begins in this area. …………………………… I-14
Figure I-14. Cluster of LWD in zone II. Note the steep bank of the stream. ……. I-15
Figure I-15. LWD blowdown from the winter of 2013 in zone IV. Note the
bedrock exposure along the west bank. ………………………………………………….. I-15
Figure I-16. LWD on the east bank enhancing the undercut bank habitat value. ……. I-16
Figure I-17. A small LWD log lying adjacent to undercut bank in zone III. ……………….. I-16
Figure I-18. Profile of Thayer Creek at the bottom of Zone I and top of Zone II. ……. I-19
Figure I-19. Bottom of Zone I looking at west bank from middle of stream. ……. I-19
Figure I-20. Profile of the middle region of Zone II. ………….………………………………………. I-20
Figure I-21 . Middle of Zone II looking towards the east bank. …………………………… I-20
Figure I-22. Profile of the bottom of Zone II, top of Zone III. …………………………… I-21
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Figure I-23. Bottom of Zone II looking to the west bank. ………………………………………. I-21
Figure I-24. Profile of the middle of Zone III. …………………………………………………. I-22
Figure I-25. View of profile at the middle of Zone III looking towards the
west bank. The tree on the bank is a recently felled tree from the
powerhouse site. ……………………………………………………………………………………. I-22
Figure I-26. Profile of the top of Zone IV, bottom of Zone III. ………………………….. I-23
Figure I-27. Upstream view to the top of Zone IV profile showing gravel and
cobble beach on east bank. ………………………………………………………………………… I-23
Figure I-28. Profile of the middle of Zone IV, the same location where water
flow data is collected. ………………………………………………………………………… I-24
Figure I-29. Middle of Zone IV profile viewed from the east bank. ………………………….. I-24
Figure I-30. profile of the bottom of Zone IV, east bank, side channel and south
channel to the midstream Island. …………………………………………………………….. I-25
Figure I-31. View of the Zone IV bottom profile from the midstream island
looking towards the east bank. …………………………………………………………….. I-25
Figure I-32. Profile of the west channel of the bottom of Zone IV. ………………………….. I-26
Figure I-33. View from the midstream island to the west bank on the bottom
of Zone IV profile. ……………………………………………………………………………………. I-26
Figure I-34. Bottom of Zone IV profile viewed from the west bank. ………………. I-27
Figure I-35. Percent composition of particles in zone I. ……………………………………... I-30
Figure I-36. Percent composition of particles in zone II. ……………………………………… I-30
Figure I-37. Percent composition of particles in zone III. ……………………………………... I-30
Figure I-38. Percent composition of particles in zone IV. ……………………………………... I-30
Figure I-39. Weight percent composition of particles in zone I. ………………………….. I-31
Figure I-40. Weight percent composition of particles in zone II. ………………………….. I-31
Figure I-41. Weight percent composition of particles in zone III. ………………………….. I-31
Figure I.42. Weight percent composition of particles in zone IV. ………………………….. I-31
Figure I-43. Representative photo of zone I substrate. ……………………………………… I-32
Figure I-44. Representative photo of zone II substrate. ……………………………………… I-32
Figure I-45. Representative photo of zone III substrate. ……………………………………… I-32
Figure I-46. Representative photo of zone IV substrate. ……………………………………… I-32
Figure I-47. Cumulative percent composition comparison of the anadromous
reach zones. ……………………………………………………………………………………………….. I-33
Figure I-48. Comparison of weight percent composition of particles < 60 mm
in each zone. ……………………………………………………………………………………………….. I-35
Figure I-49. Comparison of number of particles > 90mm in each zone. ………………. I-36
vii
Figure I-50. streamflow records for 2 years on Thayer Creek (2013/2014
and 2014/2015) recorded near the dam site. Two year annual
average stream flow was 350 cfs. …………………………………………………………….. I-37
Figure I-51. Aerial view of Thayer Creek showing the affected stream in the
project area from the dam site/pond location downstream to tidewater.
Significant tributary flows enter the gorge in segments 2 and 4. See
Table I-5 for a description of the physical characteristics of each
stream segment. …………………………………………………………………………………… I-39
Figure I-52. Aerial view of the gorge area of Thayer Creek showing the
approximate locations of major fish barrier features within the gorge.
There are 8 falls of near or greater than 10 ft height in the gorge and
two major velocity barriers. In addition there are two cascade falls
areas identified. …………………………………………………………………………………… I-40
Figure I-53. Section of the gorge near the upper end of segment 1 showing
the narrow bedrock Delimited channel of Thayer Creek and the top
end of a narrow pool at the bottom of the photo. Water flows at this
time were measured at 65-101 cfs. ……………………………………………….. I-41
Figure I-54. Velocity barrier above anadromous barrier falls near bottom
of gorge (Map A location). The pool is about 8 ft deep and is scoured
bedrock with some cobble and gravel patches near the edges of the pool.
Rapids in the background flow over bedrock through a 30 ft gap. ……………. I-42
Figure I-55. A 10+ ft falls below Tributary T-1 in the gorge (Map D location)
showing the deeply incised bedrock delimited stream channel. ……………. I-43
Figure I-56. gravel area in stream Above T-1; water flows approximately
100cfs. …………………………………………………………………………………………….. I-43
Figure I-57. View looking down Thayer Creek several hundred feet above the
anadromous falls (Map B location). A 10+ft falls occurs just around
the bend in the stream. ……………………………………………………………………… I-44
Figure I-58. View downstream looking at a velocity barrier near tributary
T-1 in gorge. Channel narrows down to about 30 ft as it flows
around bend over bedrock. …………………………………………………………………….. I-47
Figure I-59. View looking downstream at the anadromous barrier falls from
the gorge (Map B location). Two of the three falls at this location can
be seen in this photo. …………………………………………………………………….. I-47
Figure I-60. Identified tributaries contributing flow to the Thayer Creek gorge.
Areas B-1 and B-2 lie below tributary T-2, and area B-4 is between
Tributaries T-2 and T-3. ……………………………………………………………………… I-51
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Figure I-61. Mouth of tributary T-2. ……………………………………………………………………… I-53
Figure I-62. Tributary T-3 about 300 ft from Thayer Creek. …………………………………… I-53
Figure I-63. One of the streams at tributary T-1. ………………………………………………. I-54
Figure I-64. A large tributary in area B-2 on the west side of Thayer Creek. …………. I-54
Figure I-65. A large tributary in area B-4 on the west side of Thayer Creek. …………. I-55
Figure I-66. A small tributary less than 2 ft wide in area B-4. ………………………. I-56
Figure I-67. A small tributary in area B-2 on the west side of Thayer Creek. ………... I-57
Figure I-68. Upstream area of Thayer Creek (Reach 6) included in the
environmental studies showing the 3 major segments in this reach. ………… I-59
Figure I-69. Bottom end of large pool at the dam site in Segment A. The
dark portion of the stream channel is exposed bedrock. ………………………. I-60
Figure I-70. Top end of the large pool above dam site. The main channel
comes into the pool from the left; the channel in the background
carries intermittent flows except during high water flow periods. ……………. I-60
Figure I-71. Segment A showing the mouth of a small north tributary
entering Thayer Creek in an area with extensive undercut grassy banks. …… I-61
Figure I-72. A portion of Thayer Creek below the logjam showing extensive
overhanging brush cover adjacent to the sinuous creek channel. ……………. I-61
Figure I-73. A deep pool and run just above the large pool . The Solinst
datalogger is located at the overhanging tree in this pool. ………………………… I-62
Figure I-74. Large logjam in segment A viewed from segment B. ………………………… I-62
Figure I-75. Upstream view of segment B viewed from the logjam at the top
of segment A. …………………………………………………………………………………… I-63
Figure I-76. Lower end of segment B undercut bank and deep channel on
left side, shallow gravel slope on right side; root wad and fallen
tree in foreground. …………………………………………………………………………………… I-63
Figure I-77. Segment B in August showing grass cover on right bank and
overhanging vegetation on the left undercut bank. …………………………………….. I-64
Figure I-78. View across the lower end of segment B towards riparian/wetland
grassy area. The bank on the far side is sandy and silty fines. ……………… I-64
Figure I-79. Lower end of segment C showing bedrock on south bank and
midstream channel morphology. …………………………………………………………….. I-65
Figure I-80. Rapids with pocket pool adjacent to the south bank just below
the S bend in Thayer Creek. ………………………………………………………………………… I-65
Figure I-81. Rapids at the top end of Segment C at the start of the S bend.
Both banks are exposed bedrock at this bend. …………………………………….. I-66
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Figure 82. Deep run in Thayer Creek below the S bend in the stream. The banks
are comprised of bedrock and boulders overlying bedrock …………………………… I-66
Figure I-83. Percent composition of spawning gravels in the mainstem of
Thayer Creek above the gorge. …………………………………………………………….. I-67
Figure I-84. Typical gravel substrate in Thayer Creek above the dam site. ………………. I-68
Section II - lower Thayer Creek Drainage Water Resources
Figure II-1. Location of the datalogger at the mouth of Thayer Creek. ……………… II-2
Figure II-2. Location of the datalogger above the dam site on Thayer Creek. …………… II-2
Figure II-3. Twelve month hydrographic record for Thayer Creek 2013/2014. ………… II-4
Figure II-4. Twelve month hydrographic record for Thayer Creek 2014/2015. …………. II-4
Figure II-5. Predicted annual hydrograph for Thayer Creek from the EIS for
the Angoon Hydroelectric Project (USDA, FS, 2009). …………………………… II-5
Figure II-6. 30-minute flows recorded April 24/25, 2013 compared to the
daily average flow for April 24, 25, and 26. ………………………………………………….. II-10
Figure II-7. 30 minute flows recorded over 42 hours from 1-13-14 through
1-15-14 compared to daily average flow for those 3 days. …………………………… II-11
Figure II-8. Water velocity profiles at the dam site under different stream
flow conditions. …………………………………………………………………………………….. II-12
Figure II-9. Stream profile at the dam site; channel width is 104 ft. ……………….. II-13
Figure II-10. Dam site profile location; gravel can be clearly seen in background.
The darker streambed in the foreground is bedrock. …………………………… II-13
Figure II-11. Water velocity profiles at the mouth of Thayer Creek under
different stream flow conditions. ……………………………………………………………… II-14
Figure II-12. Stream profile at the mouth of Thayer Creek, channel width
is approximately 109 ft. ………………………………………………………………………….. II-15
Figure II-13. Stream profile location at the mouth of Thayer Creek viewed
from the east bank. …………………………………………………………………………………….. II-15
Figure II-14. The barrier falls at the top of the anadromous reach at a stream
flow rate of 1025 cfs ( October, 2014). ………………………………………………….. II-16
Figure II-15. The barrier falls at the top of the anadromous reach at a stream
flow rate of 223 cfs ( August, 2014). ……………………………………………………………… II-17
Figure II-16. The barrier falls at the top of the anadromous reach at a stream
flow rate of 100 cfs ( April, 2013). …………………………………………………………….. II-18
Figure II-17. Average daily flows in Thayer Creek sorted by average volume
per day. ………………………………………………………………………………………………. II-21
x
Figure II-18. Annual average daily water temperature record for the dam site
on Thayer Creek. …………………………………………………………………………………… II-24
Figure II-19. 30 minute interval annual temperature records for the dam
site on Thayer Creek. …………………………………………………………………………………… II-24
Figure II-20. Comparison of 30 minute interval water and air temperature
data for the month of August. …………………………………………………………… II-26
Figure II-21. Comparison of 30 minute interval water and air temperature
data for the month of June. ………………………………………………………………………. II-26
Figure II-22. 30 minute interval annual air temperature record for the mouth
of Thayer Creek. ………………………………………………………………………………….. II-27
Figure II-23. Comparison of 30 minute interval annual water and air
temperature records. ………………………………………………………………………. II-27
Figure II-24. Barometric pressure record from the mouth of Thayer Creek. ………….. II-28
Figure II-25. Tributaries contributing water flows to the Thayer Creek gorge.
T-1, T-2 and T-3 contribute 74% of the water flow. …………………………………….. II-30
Figure II-26. Barometric pressure record from the mouth of Thayer Creek,
2014/2015. ……………………………………………………………………………………………….. II-31
Figure II-27. Tributaries contributing water flows to the Thayer Creek gorge.
T-1, T-2 and T-3 contribute 74% of the water flow. ……………………………………. II-34
Section III - Lower Thayer Creek Drainage Fisheries Surveys
Figure III-1. Lower Thayer Creek drainage showing the areas sampled by Shipley
Group in 2013 and 2014. The upper portion of the gorge is inaccessible
and was not sampled. ………………………………………………………………………… III-2
Figure III-2. Dolly Varden captured in Thayer Creek above the gorge. ………………. III-4
Figure III-3. Cutthroat Trout captured above the gorge in Thayer Creek. ………………. III-4
Figure III-4. Rainbow Trout (~106 mm) captured in the anadromous reach
in April, 2013. ………………………………………………………………………………………………… III-5
Figure III-5. Cutthroat Trout (~110 mm) captured in the anadromous reach in
April 2013. ………………………………………………………………………………………………… III-5
Figure III-6. Coho or Cutthroat Trout fry (< 40 mm long) observed in Thayer
Creek in early August 2013. …………………………………………………………………………. III-6
Figure III-7. A Cutthroat Trout caught above the gorge in August 2013 on an
artificial dry fly. …………………………………………………………………………………….. III-7
Figure III-8. Area fished with a dip net in 2014. ………………………………………………….. III-9
xi
Figure III-9. Coho Salmon (60 mm) captured below zone IV in Thayer Creek
August 11, 2014. …………………………………………………………………………………….. III-10
Figure III-10. Cutthroat Trout (<40 mm) captured below zone IV in Thayer Creek
August 11, 2014. …………………………………………………………………………………….. III-11
Figure III-11. Cutthroat Trout (<40 mm) captured below zone IV in Thayer Creek
August 11, 2014. …………………………………………………………………………………….. III-11
Figure III-12. Dolly Varden (51 mm) captured below zone IV in Thayer Creek
August 11, 2014. …………………………………………………………………………………….. III-11
Figure III-13. Pink Salmon lying in the run in Zone IV in early August 2013
when water flows were 100 cfs. The rope on the right side of the
photo is the water profile location near the mouth of Thayer Creek. ……………. III-15
Figure III-14. Pink Salmon in zone I, just below the plunge pool in August
2013 when water flows were 100 cfs. ………………………………………………….. III-16
Figure III-15. Pink salmon carcasses littering the shoreline of the stream in
August. ………………………………………………………………………………………………... III-17
Figure III-16. A Chum Salmon carcass on the streambank in zone III. ……………….. III-18
Figure III-17. Water conditions in Zone III in September 2014; water flows
are within a few inches of bankfull conditions. ………………………………………. III-19
Figure III-18. Barrier falls on Thayer Creek at a flow rate of 1,025 cfs in
October, 2014. …………………………………………………………………………………….. III-19
Figure III-19. Pink Salmon attempting to jump barrier falls in early August 2014.
Water flow at this time was approximately 260 cfs. ………………………….. III-20
xii
List of Tables
Section I – Lower Thayer Creek Drainage Stream Habitat
Table I-1 . Anadromous reach large woody debris (LWD) ……………….. I-12
Table I-2. clustered substrate data from the anadromous zone. …….. I-28
Table I-3. Spawning Gravel Preferences of Salmonids. ………………………… I-34
Table I-4. Average Particle counts for m2 area by size class (mm)
in each zone. ………………………………………………………………………… I-35
Table I-5. Major physical features of the Thayer Creek gorge and
Anadromous reach. ……………………………………………………………….. I-46
Table II-6. Summary of Tributary Flows to the Thayer Creek
Gorge. …………………………………………………………………………………… I-52
Section II - Lower Thayer Creek Drainage Water Resources
Table II-1. The four highest and lowest 30 minute flows recorded
for Thayer Creek in 2013/2014 compared to the daily
average flows for these days. ……………………………………………………… II-5
Table II-2. The four highest and lowest 30 minute flows recorded
for Thayer Creek in 2014/2015 compared to the daily
average flows for these days. ……………………………………………………… II-6
Table II-3. Short term changes in flow during high and low flow
periods. ………………………………………………………………………………….. II-6
Table II-4. Comparison of minimum and maximum flows from the
EIS and Shipley Group data. ……………………………………………………... II-8
Table II-5. Monthly and quarterly average, maximum and minimum
flows based on 24 months of average daily flows data
(April 10, 2013 through April 8, 2015). ………………………………….. II-20
xiii
Table II-6. Analysis of spill days and volume by month for a power
plant operation at 100 cfs. …………………………………………………. II-22
Table II-7. Average monthly rainfall and snowfall records compiled
for Angoon, Alaska. …………………………………………………………… II-32
Table II-8. Summary of Tributary Flows to the Thayer Creek
Gorge. ………………………………………………………………………………. II-36
Section III - Lower Thayer Creek Drainage Fisheries Surveys
Table III-1. Summary of fish catches by location in Thayer Creek for
all collection methods in 2013. ……………………………………………………. III-6
Table III-2. Angling success in area R-4 above the gorge in 2013………….. III-7
Table III-3. Summary of fish catches by location in Thayer Creek
for all collection methods in 2013. ………………………………………….. III-10
Table III-4. Summary of fish catches by location in Thayer
Creek in 2015. ……………………………………………………………………….. III-13
Table III-5. Total fish counts for Thayer Creek anadromous
reach, 2013. ……………………………………………………………………….. III-16
Table III-6. Pink Salmon counts by segment in the Anadromous
reach, 2013. ……………………………………………………………………….. III-17
Table III-7. Total fish counts for Thayer Creek anadromous
reach, 2014. ……………………………………………………………………….. III-21
Table III-8. Pink Salmon counts by segment in the Anadromous
reach, 2014. ………………………………………………………………………… III-21
Section I – Lower Thayer Creek Drainage Stream Habitat
Overview
The Angoon Hydroelectric Project EIS has provided a general description of the Thayer Creek
drainage region USDA, USFS, 2009). The EIS described the anadromous reach as composed of
two channel types, an estuarine process group- large estuarine channel (ES4), and a large
contained process group – moderate gradient contained narrow valley channel (LC2). The
estuarine channel was 620 ft. long with a dominant substrate of gravel to cobble. The upper
moderate gradient contained narrow valley channel was 1020 ft. long and contained a
dominant substrate of small to large cobble. Bankfull width was described as 80-90 ft., with a
stream gradient varying form <1 to <2%. The anadromous reach had only one qualifying pool at
the base of the barrier falls and considered overwintering of adult fish in the riffles and runs
unlikely. Large woody debris was limited with only 8 key pieces in the reach. The quality of
spawning habitat was described as moderate for Pink and Chum salmon, and poor for other
species.
The EIS described the gorge as a deeply incised contained channel (MC3) approximately 7,500
ft. long, with a stream gradient less than 4%. The channel width was listed as less than 66 ft.
Dominant substrate was listed as small gravel to bedrock. Above the gorge the stream was
described as a wide, low gradient floodplain channel (FP5) with a stream gradient less than 2%.
Stream width was listed as less than 66 ft., and dominant substrate as sand to cobble. Harza
Northwest(1995) provided additional comments on the habitat in the gorge and described it as
relatively poor, with extremely limited spawning, rearing, and holding habitat.
The assessment of stream habitat in the anadromous reach, and the reach above the gorge,
was based on limited field work within these two reaches. The assessment of the gorge was
largely based on observations from the upper slopes of what can be seen in the gorge. Actual
instream field work is lacking in the gorge reach. Our work was initiated to provide more
specific measurement of stream and habitat characteristics through these stream reaches to
verify and extend observations and conclusions already reached. We initially divided the lower
drainage into 6 specific reaches (Figure I-1). However, once we got into the gorge, comprised
of reaches 2-5, the gorge was treated as a single reach. Reaches 2-4 were accessible from
several side slope locations and the T-2 tributary drainage. The T-3 drainage ended in a cliff at
least 25 ft. high. No access was found to the stream north of tributary T-2. However, the
uppermost cascade/falls was reachable by carefully hiking along the west bank slope
downstream to the top of the falls. Reach 6 extended from the dam site upstream to the first
major bend in the stream. We extended the anadromous reach to include the lowermost island
at the mouth of the creek. The high tide MHHW level lies near the upstream tip of this island.
I-1
Figure I-1. Lower Thayer Creek drainage studied by the Shipley Group. Six reaches, 3
tributaries, and 4 major barriers were initially identified and used to define the reaches.
Thayer Creek Anadromous Reach
The anadromous reach was subdivided in 5 zones (Figure I-2). A 300 ft. long tape was used to
establish the length of each zone, except for zone I where a rangefinder was used to establish
the 500 ft. boundary. Zones II, III and IV were then measured using the tape to set the
Reach 6
End of study
area
I-2
boundaries. At the lower boundary of zone IV, the tape was again used to set a 500 ft. zone,
which happened to coincide with the bottom of the island at the mouth of the stream. Zone I,
at the top end of the anadromous reach, was 500 ft. long; zones II, II, and IV were each 250 ft.
long; and zone V was 500 ft. long. The proposed powerhouse is located at the upper end of
zone II on the west bank. The bottom of zone IV was in the vicinity of MHHW, while zone V is
all intertidal habitat. Zone V was only used for adult fish escapement and juvenile fish trapping
studies.
Figure I-2. Study zones established within the anadromous reach.
Physical Channel Description
Major physical features of the mouth of Thayer Creek are shown in Figure I-3. The MHHW mark
is near the boundary of zone IV above the island at the mouth of the creek. Fishery studies
Zone I- 500 ft.
Zone II- 250 ft.
Zone III- 250 ft.
Zone IV- 250 ft.
Zone V – 500 ft.
I-3
conducted in zone V show that both spawning of pink salmon and rearing habitat for Coho
salmon, Dolly Varden, and Cutthroat Trout occurs at least 200 ft. downstream into the intertidal
zone. A deep holding pool extends downstream from the bottom tip of the island until the
beginning of a gravel shoal at the mouth of the stream. A gravel bar exists at the mouth
approximately in line with major reef formation on the north and south sides of the mouth of
the creek. At low tide the gravel bar is about a foot under water, and the pool is more than 3 ft.
deep. The reef areas are exposed at middle high-tide conditions, but completely covered by
high tides.
Figure I-3. Physical features at the mouth of Thayer Creek.
Gravel bar
at mouth
Deep holding
pool at mouth
Zone IV lower
boundary
Confirmed intertidal
rearing habitat; pink
salmon spawning
habitatreef
reef
I-4
Zones I through IV of the anadromous reach are depicted in Figures I-4 and I-5. The top of the
anadromous reach is bounded by a barrier falls, which actually consists of a series of 3 falls
within a 50 ft. linear section of the creek. The lowermost falls is 8-9 ft. high, while the second is
at least 10 ft. high, and the third, again 10+ ft. Above the third falls is a 15-20 ft. cascade that
drops about 8 ft. The lowest falls flows into a large plunge pool which was measured to a depth
of 12 ft. under the main section of the falls (Figure I-4). Water flows out of the plunge pool in
two channels, a major channel on the east side and a smaller one on the west side. These two
channels are separated by a bar or riffle depending on the water flow. At low water flows it is a
bar while at flows higher than 125-150 cfs it is a riffle. Below the bar/riffle the two channels
come together into a long run with deep water along the east bank and shoaling out to the
west bank. The deep run continues on into zone II, while some of the water flows towards the
west bank and reestablishes a channel along that shoreline. The banks throughout zone I are
all exposed bedrock or a thin duff layer covering bedrock. The stream ranges form 90-110 ft.
wide. Large woody debris (LWD) occurs at the plunge pool and along the west bank. At the
bottom of zone I on the east bank is a cluster of 5 logs, while on the west side is a small sandy
island built on an old log jam. A small high water sandy channel exists on the shore side of the
island.
The cluster of 5 logs extends into zone II on the east bank, along with several more logs that lie
completely in zone II (Figure I-4). The run tails out at the top of zone II and a flow of water
begins cross-channel towards the west bank and the deep channel that forms at the bottom of
zone I. An old, overgrown side channel begins along the east bank in zone II and runs south
along the base of the mountains. The deep channel along the west bank moves into the middle
of the stream and established a strong midstream flow through the rest of zone II. The channel
is about 100 ft. wide through zone II.
The stream takes a slight dogleg bend in zone III (Figure I-5). A bar extends at an angle across
the stream from the bottom of zone II to the bottom of the dogleg bend in zone II. Under low
flows water is pushed to the west bank of the stream as a result of this bar. At high flows it has
no effect on direction of water flow. Most of zone III is riffle, with a shallow run established
along the east bank and a deeper narrow run along the west bank after the dogleg bend. A
considerable amount of logs have accumulated along the west bank in the area of the bend.
One long log lays adjacent to the shore midway through the zone. The stream narrows in the
zone to 83 ft.
In zone IV the stream widens substantially from 83 ft. to 110 ft. and ultimately 192 ft. at the
downstream boundary. A run exists about 1/3 way across the stream from the west bank
through the upper zones. This run shallows out and then bends south as it approaches the
I-5
Match line
Z-I
Z-II
110 ft.
Bar/
riffle
Plunge
pool
run
Vegetated island and
sandy side channel built
up on old logjam
Logjam with emergent
vegetation and
accumulating fines
run
logs
run
Zone I is 500 ft.
long from plunge
pool to Zone II
boundary
Figure I-4. The upper end of the anadromous reach showing major LWD and channel
features.
I-6
Figure I-5. Lower section of anadromous reach showing reach showing major LWD and channel
features.
Match line
Sand/gravel beach
Grassy wetland
fringe
Z-IV
192 ft.
Z-IV
mid
Z-III
Z-IV
83 ft.
99 ft.
Z-III
Z-II
Zones II, III, and IV each 250
ft. long. Anadromous reach
1250 ft. long.
logs
riffle
run
riffle
rapids
110 ft.
riffle
run
I-7
island at the mouth of the stream. The main flow of the stream follows the east channel
around the island. Large woody debris is present on both sides of the creek at the mouth.
The shoreline on the west side of the creek is exposed bedrock with boulders and cobbles, or
bedrock covered by a shallow duff layer (Figures I-6, I-7, and I-11). There is little undercut
bank development on this shoreline with the banks generally being steep slopes or cliffs along
the shore. In zone IV the banks are 3-10 ft. high, and get higher as you move upstream. In zone
I banks are cliffs of 50-90 ft. in height. An alluvial, sand, gravel and cobble layer covers bedrock
at the mouth of Thayer Creek, but bedrock is exposed at the shoreline of the creek.
The east side of Thayer Creek is exposed bedrock or duff covered bedrock only in zone I. Below
zone I the mountains fall away from the creek allowing the formation of a relatively flat, heavily
forested landscape extending to the beach. Along the east shoreline an exposed alluvial layer
of sand, gravel, and cobble bounds the water line, covered by a well-developed root and duff
zone of vegetation (Figures I-8 and I-9). The duff/root layer tends to resist erosion while the
underlying alluvium is washed away by high water events. As a consequence, the east shore
Figure I-6. West bank of Thayer Creek in zone IV, showing bedrock outcrops in the foreground.
I-8
Figure I-7. West shoreline of Thayer Creek showing duff layer and timber on top of bedrock.
has an extensive amount of undercut banks along zones II, III, and IV. LWD tends to lie parallel
to shore enhancing habitat value of undercut banks as well. The root mat is so sturdy that
undercutting can extend several feet under the stream bank (Figure I-10). The east bank
appears to be a major source of gravels to the lower stream.
I-9
Figure I-8. East shoreline
of Thayer Creek showing
the erosion resistant
root/duff layer sloughing
into the creek as the
underlying alluvium is
washed away.
I-10
Figure I-9 Active area of alluvial erosion on the east shoreline.
Figure I-10. Extensive undercutting of rootmat without callpse of the mat.
Large Woody Debris (LWD)
There is a large amount of large woody debris (LWD) in the anadromous reach, but of variable
quality. The EIS identified 8 key pieces of LWD (USDA, USFS, 2009). We found a considerable
number of LWD in the stream, many in clusters acting as one key unit (Table I-1). We identified
6 clusters of LWD spread between all four zones, with 5 of them judged to be key LWD (Figures
I-11 to I-14). In one case three trees were blown down in the winter of 2013 on the west bank
I-11
(Figure I-15), but they were not judged to be important at this time. In fact, the parts of two of
them, that were in the water, disappeared by the end of summer in 2014. LWD on the
Table I-1. Anadromous reach large woody debris (LWD)
Location Coordinates Description Log size(s)
Zone IV, right
bank, at MHHW
boundary
08 V 0522311
6381844
Cluster (9) of wind fall logs,
mostly out of water, root
wads present but tips of
fallen trees in water,
branches still present on
trees.
Trees up to76 ft. long,
15-35 inch diameters
Zone III, at
dogleg bend on
west bank
# 1:08 V 0522321
6381928
# 2: 08 V 0522329
6381921
# 3 and # 4: 08 V
0522353 6381935
# 5: 08 V 0522396
6381963
Series of 5 logs angled from
the bank into the water
following the bend in the
stream
# 1: 114 ft. long, 36”
diameter
#2: 31.5 ft. long, 15”
diameter
#3: 37 ft. long, 24”
diameter
#4: 42 ft. long, 16”
diameter
#5: 126 ft. long, 36”
diameter with rootwad
Top of Zone II,
deep run, west
bank
08 V 0522438
6382018
Multiple logs in logjam
partially angled into water
from bank
Not measured
Top of Zone II
east bank
08 V 0522450
6382004
Log, with root wad, running
parallel to undercut bank in
shallow riffle
55 ft. long; 4-8”
diameter
Bottom of Zone
I, west bank
08 V 0522483
6382031
Logjam of 7 logs near bank
both above and below the
water
Largest tree 35 ft. long,
30” diameter
Bottom of Zone
I, east bank,
bottom of deep
run
08 V 0522486
6382049
Cluster of 5 trees parallel to
shore, one log with rootwad
in the water
Trees 60-120 ft. long,
15-35” diameters
Plunge pool top
of Zone I, east
bank
08 V 0522507
6382022
logjam of 8 trees on the bank
and in the water in plunge
pool and at top of deep run
Not measured
I-12
Figure I-11. Cluster of LWD on west bank in zone I.
Figure I-12. Cluster of LWD and exposed roots on the east bank. Note the flat terrain behind
the stream bank.
I-13
Figure I-13. LWD with root wad attached. At higher water flows this tree is at the waterline.
The old side channel begins in this area.
east bank tend to lie parallel with the current, and close to the bank (Figures I-16 and I-17).
This orientation typically enhances habitat value of undercut banks in the stream regardless of
size of LWD.
I-14
Figure I-14. Cluster of LWD in zone II. Note the steep bank of the stream.
Figure I-15. LWD blowdown from the winter of 2013 in zone IV. Note the bedrock exposure
along the west bank (arrows).
I-15
Figure I-16. LWD on the east bank enhancing the undercut bank habitat value.
Figure I-17. A small LWD log lying adjacent to undercut bank in zone III.
I-16
Stream Profiles and Channel Morphology
Stream profiles were collected from the top, middle, and bottom of each of the four
anadromous stream zones. Video records of each profile transect are contained in Appendix
I-1. Unfortunately, high water precluded getting profiles from the middle and top of zone I. The
single profile from the bottom of zone I is shown in figures I-18 and I-19. The profile shows the
remnants of the strongly developed deep run on the east bank and the beginning of a deeper
water channel on the west bank. The west bank is shown in Figure I-19.
Just a few feet downstream from this profile is one from the top of zone II (Figures I-20 and I-
21). This profile shows the development of two runs, one on each side of the stream. The
channel on the west side is the dominant channel in the stream at this point and remains so all
of the way downstream to the middle of zone IV. This is likely due to the influence of the
exposed and shallow bedrock running along the west bank of the stream. The one on the east
side weakens, shallows, and becomes intermittent as it progresses downstream. Note the
extensive amount of LWD on the east bank.
The next profile is at the bottom of zone II and the top of zone III (Figures I-22 and I-23). At this
point the run has disappeared on the east bank, with a new shallow run starting to develop
adjacent to the bank. The main run has now moved near the west bank. A single low value
LWD log can be seen next to the west bank (Figure I-23). The next profile is from the middle of
zone III (Figures (I-24 and I-25). The well-developed channel on the west side has broadened
out, and the ridge traversing the stream is noticeable in the middle of the stream. The tripod
in Figure I-25 sits on top of the ridge. At low water this ridge directs flows towards the main
channel on the west bank. The next profile is from the bottom of zone III and the top of zone IV
(Figures I-26 and I-27). The datalogger near the mouth of Thayer Creek lies along this profile at
the boulder on the west side. The channel on the west side has broadened out and the ridge is
now near the east bank. Note in the picture the gravel/cobble beach on the east bank due to
the dogleg that exists in this section of the stream.
The next profile is from the middle of zone IV below the dogleg at the water flow measurement
station on the creek (Figures I-28 and I-29). The channel is now broad and rather flat in the
middle of the stream. Note the low energy environment near the east bank and the large
amount of fines present on the streambed. Just past this profile the stream channel moves to
the east across the flats as it approaches the island in the middles of the stream below zone IV.
As it moves east it redevelops into a narrow, high velocity east channel. The last profile is from
the bottom of zone IV (Figures I-30 to I-34). This is the longest profile stretching 196 ft. across
the stream and crossing 2 islands and three stream channels. The profile is at the approximate
MHHW mark on the creek.
I-17
From the large island in the middle of the stream the east channel is the main flow of water
from the stream (Figure 30) and is a deep rapids along the entire east side of the island in zone
V until it reaches the holding pool below the island.. However a small amount of water
separates into a side channel adjacent to the east shoreline. The bank is quite steep at this
location but terminates in a marine grass wetland with another bank beyond it at the edge of
the trees. The west channel is a high velocity channel that is relatively flat or shallow and ends
at the west bank just below the last surface bedrock exposure. Below the tip of the island
bedrock exposure is no longer visible along the west bank. A small, slightly deeper channel
runs close to the west bank. The west channel becomes very narrow and high velocity rapids as
it move s downstream along the west side of the island. A view of the entire profile is shown in
Figure I-34 from the west bank.
I-18
Figure I-18. Profile of Thayer Creek at the bottom of Zone I and top of Zone II.Figure I-19. Bottom of Zone I looking at west bank from middle of stream.West bankEast bankI-19
Figure I-20 . Profile of the middle region of Zone II. Figure I-21. Middle of Zone II looking towards the east bank.East bank West bankI-20
Figure I-22. Profile of the bottom of Zone II, top of Zone III.Figure I-23. Bottom of Zone II looking to the west bank.West bankEast bankI-21
Figure I-24. Profile of the middle of Zone III. West bankEast bankFigure I-25. View of profile at the middle of Zone III looking towards the west bank. The tree on the bank is a recently felled tree from the powerhouse site. I-22
Figure I-26. Profile of the top of Zone IV, bottom of Zone III. Figure I-27. Upstream view to the top of Zone IV profile showing gravel and cobble beach on east bank.East bank West bank East I-23
Figure I-28. Profile of the middle of Zone IV, the same location where water flow data is collected. West bank East bank Figure I-29. Middle of Zone IV profile viewed from the east bank. I-24
13579111315171921232527293133353739414345474951535557596163656769717375777981838587899193959799101Figure I-30. Profile of the bottom of Zone IV, east bank, side channel and south channel to the midstream Island. East channelSide channelEast bank Figure I-31. View of the Zone IV bottom profile from the midstream island looking towards the east bank. I-25
Figure I-32. Profile of the west channel of the bottom of Zone IV. West channelWest bankFigure I-33. View from the midstream island to the west bank on the bottom of Zone IV profile.I-26
Figure I-34. Bottom of Zone IV profile viewed from the west bank. West channelEast channel Side channel Midstream island island I-27
Anadromous Reach Substrate Assessment
Substrates in the stream were analyzed by zone using 1/4m2 quadrat counts of the armor layer
of the stream. A total of 5 quadrats were collected from each zone. Number and weight data
were collected for larger particles and fine gravel and sands were only weighed as a group. The
data was then normalized to a representative meter square streambed for each zone. Data was
then presented as percent composition and weight percent composition. However, due to
high water, zone I quadrats all came from the bottom end of this zone. Appendix I-2 contains
video records of quadrats in each zone.
Percent composition of substrate from each zone is presented in Figure I-35 through I-38. The
percent composition for each zone were all similar with zones I, II, and II having D50 values of
16 mm particles, while zone IV had a D50 value of 22.5 mm. In terms of highest composition
11.3 mm was the highest in zones I, II, and III, 16 mm in zone IV. Fine gravel and sand made up
less than 5% in all zones. Weight- Percent composition is shown in figures I-39 through I-42.
On a weight percent basis zones I, III, and IV had D50 values of 90 mm, while zone II had a D50
value of 128 mm. However, the graphs were all unique from one another. Zone IV was the
only zone that had a significant percentage (11%) of > 362 mm particles. All four zones had
substantial percentages of 256 mm particles (11-24%). In terms of visual appearances (Figures
I-43 through I-46) zone I appeared to have the largest particles, while zones II and IV had the
least. Finally, when each zone was compared on a cumulative percent composition basis
(Figure I-47) zone II had the greatest percentage of smaller particles with 80% less than 128
mm, while zone I had the least at 57% less than 128 mm. Zone IV had the greatest percentage
of large particles with 20% greater than 256 mm. Zones II, III, and IV had nearly identical
particle size distributions below 90 mm.
Table I-2 clusters data into larger groupings of particles sizes. Fine gravel and sands were
lowest in Zone I, but was similar in the other three zones. The same pattern was exhibited with
particles smaller than 32 mm with zone I having half as much of this size category as the other
zones. Zone I also showed the same pattern for less than 90mm and less than 128 mm
particles. However, for the size class greater than 128 mm, zone I had the highest cumulative
weight percentage as well as number of particles greater than 128 mm. This data on particle
sizes from the table compares well with the visual assessment of particles sizes in each zone
(Figure I-43 to I-46).
I-28
Table I-2. Clustered substrate data from the anadromous zone.
fine
gravel-
sand
cum wt %
< 32 mm
Cum wt %
< 90 mm
cum wt % >
90 mm
cum wt % <
128 mm
cum wt % >
128 mm
number of
particles/m²
> 128 mm
Z-I 2.4 7.7 31.9 68.1 56.9 43.1 6
Z-II 4.7 16.7 50 50 81.2 18.8 2
Z-III 3.9 13.8 42.1 57.9 63.6 36.4 4
Z-IV 4.7 18.9 56.2 43.8 74.5 25.5 3
I-29
Figure I-35. Percent composition of particles in zone I.Figure I-36. Percent composition of particles in zone II.Figure I-37. Percent composition of particles in zone III.Figure I-38. Percent composition of particles in zone IV.I-30
Figure I-39. Weight percent composition of particles in zone I.Figure I-40. Weight percent composition of particles in zone II.Figure I-41. Weight percent composition of particles in zone III.Figure I.42. Weight percent composition of particles in zone IV.I-31
Figure I-43. Representative photo of zone I substrate.Figure I-44. Representative photo of zone II substrate.Figure I-45. Representative photo of zone III substrate.Figure I-46. Representative photo of zone IV substrateI-32
0
10
20
30
40
50
60
70
80
90
100
zone I
zone II
zone III
zone IV
Figure I-47. Cumulative percent composition comparison of the anadromous reach zones.
Particle size distributions can also be compared relative to quality of gravels as spawning
substrate for salmonids. In general, salmonids show a preference for particles sizes less than
10% of the body length (Kondolf and Wolman, 1993) and most species prefer particles less than
100 mm in diameter (Lotspiech and Everest, 1981). The maximum sizes of salmonids in Alaska
reported by Mecklenburg, et.al. (2002) is shown Table I-3. All of the salmonids prefer clean
gravels with less than 5% fine gravels and sands.
%
I-33
Table I-3. Spawning Gravel Preferences of Salmonids.
Species Maximum size Spawning gravel
preference
Closest equivalent
Wolman gravel size
class
Pink salmon 76 cm < 76 mm < 60 mm
Chum/Coho Salmon 109 cm < 109 mm < 90 mm
Cutthroat Trout 99 cm < 99 mm < 60 mm
Steelhead Trout 122 cm < 122 mm < 90 mm
King Salmon 160 cm <160 mm < 128 mm
The data from the ¼ m2quadrats was used to construct a particle count for each zone for a
typical m2 surface area (Table I-4). Size classes above 90 mm interfere with optimal spawning of
salmonids and reduce the quality of the spawning habitat. The weight-percent composition of
each zone for particles smaller than 60 mm is shown in Figure I-48, and the total number of
particles greater than 90 mm is shown in Figure I-49. Zone I has half the weight percent of
small particles compared to the other 3 zone. Zone I also has twice the number of large
particles compared to the other 3 zones (Figure I-49). These data suggest that zone I has the
poorest salmonid spawning habitat within the anadromous reach. The amount of spawning
habitat available in the anadromous reach is approximately 157,000 ft2 if we assume 90% of the
stream remains wetted throughout the winter. At an assumption of 75% that spawning habitat
value would drop to 131,000 ft2. Based only on the numbers and sizes of oversized particles in
each zone a potential reduction in available spawning area of up to 45% can be expected in
zones I and IV , while a potential reduction in available spawning habitat of up to 20% can be
expected in zones II and III. The impact of a few large particles present in the spawning
grounds is evident in the zone IV area where the presence of one particle larger than 362 mm
has doubled the potential reduction in spawning area within that zone. Overall these data
suggest that zones II and III are the most important spawning areas in the anadromous reach
based only on substrate quality. However, if the amount of available spawning habitat is
factored into each zone a different conclusion is reached. Zone I contains 41% of available
spawning habitat, and zone IV, 24%. Zones II and III both have about 17% of available spawning
habitat. Applying the potential substrate interference to the available spawning habitat in each
zone results in zone containing 23% of available spawning habitat, , zones II and III 14%
respectively, and zone IV 13%. This means that there could be as much as a 36% reduction in
useable spawning habitat due to large particles sizes on the spawning grounds. Regardless of
I-34
the quality of the spawning gravels in Thayer Creek, it is still capable of supporting runs of +/-
60,000 pink, chum, and Coho salmon per year, as well as successful spawning of Dolly Varden,
Cutthroat Trout, and Rainbow/Steelhead Trout.
Table I-4. Average Particle counts for m2 area by size class (mm) in each zone.
Particle
size class Zone 1 Zone 2 Zone 3 Zone 4
> 362 0 0 0 1
362 1 0 0 0
256 3 2 1 2
180 2 0 3 0
128 12 6 6 6
90 16 8 13 15
60 15 20 26 31
45 25 40 54 80
32 60 91 86 121
22.5 83 160 142 221
16 227 294 158 350
11.3 266 301 364 0
0
5
10
15
20
25
30
35
40
zone 1 zone 2 zone 3 zone 4
Wt % < 60 mm/m²
Figure I-48. Comparison of weight percent composition of particles < 60 mm in each zone.
I-35
0
2
4
6
8
10
12
14
16
18
20
zone 1 zone 2 zone 3 zone 4
number of particles > 90 mm/m²
Figure I-49. Comparison of number of particles > 90mm in each zone.
Thayer Creek Gorge Characteristics
The Thayer Creek hydro project would divert about 80 cfs of water from the creek above the
gorge to generate hydropower near the mouth of the creek. The water would be returned to
the anadromous portion of the creek to maintain present fishery values in the creek. However,
during February and March flows in the creek approach 100 cfs and may get as low as 75 cfs for
one or more hours. At these times flows in the creek could be reduced to the minimum release
requirement for short periods of one to several hours during the day. For the remaining 10
months 25 - 350+ cfs of water would flow through the gorge, in addition to any tributary flows
into the gorge from the surrounding drainage. Currently all water flows through the gorge
amounts to less than 100 cfs during dry periods to more than 900 cfs during rainy periods. The
hydrograph for the period April 21, 2013 through April 8, 2015 (Figure I-50) shows a flow range
of 90 to 920 cfs. However, prior to the collection of flow data a low flow of 65 cfs was recorded
on April 4, 2013, and an estimated high flow of 1,025 cfs was measured on October 4, 2014.
Under normal operating conditions the gorge would still experience seasonal flows greater than
400 cfs for at least 4 months of the year.
I-36
May Jun Jul AugSep Oct Nov Dec Jan Feb MarcfsFigure I-50. Streamflowrecords for 2 years on Thayer Creek (2013/2014 and 2014/2015) recorded near the dam site. Two year annual average stream flow was 350 cfs. 2013/2014 2014/2015 I-37
The stream is shown in figures I-51 and I-52 from the diversion dam to tidewater. It has been
divided into six segments, the anadromous reach at the mouth (1,400 ft.) and five gorge
segments covering 5,900 ft. The anadromous reach is 80-100 ft. wide, while the gorge is
typically 30-40 ft. wide in segments 1-3 (Figures I-53 and I-54), and 50-100 ft. wide in segments
4 and 5. The shoreline in the gorge is deeply incised, exposed bedrock from the anadromous
fish barrier falls up to the dam site (Figure I-54, I-55, I-56). The stream is inaccessible in
segments 3 and 4 due to cliffs 15+ ft. in height. Likewise, the streambed is scoured bedrock and
large boulders over most of that distance, except for a 200-300 ft. section of streambed
between tributaries 1 and 2, where the bedrock is overlain by a shallow layer of boulders,
cobbles and gravels (Figure I-57). Small pockets of gravels and sands also occur covering the
bedrock along the edges of pools near the high water mark throughout the gorge, especially
where eddies occur in the pools. Rapids are relatively flat or ridged bedrock features within
the streambed, while pools are deep depressions in the bedrock between the shallow, flat
bedrock sections. Wading is restricted to the rapids sections during low flow periods (less than
125 cfs).
Large woody debris is limited in occurrence in the stream. In many places LWD is non-
functional because fallen trees cross the gorge above the water (Figures I-55 and I-56) due to
the narrow channel and steep banks. In other locations, large woody debris lies in the water
oriented downstream and close to the banks (Figure I- 53 and I-54). Due to the high water
flows large woody debris has few branches remaining on the portions of the trees in the water.
Only one root wad was observed within the gorge in a pool in segment 1.
The locations of major features in the gorge are shown in Figure I-51, while a description of
each segment of the gorge is listed in Table I-5. At least 8 waterfalls of approximately 10 ft. or
greater height occur within the gorge and are located in all segments except segment 5
adjacent to the dam site. The barrier falls at the bottom of the gorge is composed of a series of
3 falls 9-12 ft. high, within a 50 ft. linear distance (Figure I-59). However, segment 5 has the
greatest slope of any of the segments averaging 12.6%. The slopes of the other segments range
from 2.4 to 7.7%, with an average of 3.1%, except for waterfall and cascade features (Table I-5).
Under all flow conditions the 8 waterfalls and two cascades are barriers to upstream movement
of fish and fragment the gorge habitat. At flows greater than 200-300 cfs velocity barriers also
occur at numerous places in the gorge causing further fragmentation of habitat (Figures I-54
and I-58). However, two major velocity barriers exist in segments 1 and 2 in the gorge. Water
flows in the gorge currently are less than 200 cfs only 20% of the year.
I-38
Figure I-51. Aerial view of Thayer Creek showing the affected stream in the project area from
the dam site/pond location downstream to tidewater. Significant tributary flows enter the
gorge in segments 2 and 4. See Table I-5 for a description of the physical characteristics of each
stream segment.
Anadromous reach
Gorge segment # 1
Gorge segment # 2
Gorge segment # 3
Gorge segment # 4
Gorge segment # 5
Dam site
Pond
Tributary
complex T-1
Tributary T-2
Tributary T-3
I-39
Figure I-52. Aerial view of the gorge area of Thayer Creek showing the approximate locations of
major fish barrier features within the gorge. There are 8 falls of near or greater than 10 ft.
height in the gorge and two major velocity barriers. In addition there are two cascade falls
areas identified.
Cascades Falls
Falls
Velocity
barrier (E)
Velocity
barrier (A)
B
C
D
Falls
I-40
Figure I-53. Section of the gorge near the upper end of segment 1 showing the narrow bedrock
delimited channel of Thayer Creek and the top end of a narrow pool at the bottom of the
photo. Water flows at this time were measured at 65-101 cfs.
Pool
I-40
I-41
Figure I-54. Velocity barrier above anadromous barrier falls near bottom of gorge (Map A
location). The pool is about 8 ft. deep and is scoured bedrock with some cobble and gravel
patches near the edges of the pool. Rapids in the background flow over bedrock through a 30
ft. gap.
I-42
Figure I-55. A 10+ ft. falls below Tributary T-1 in the gorge (Map D location) showing the deeply
incised bedrock delimited stream channel.
Figure I-56. View looking down Thayer Creek several hundred feet above the anadromous falls
(Map B location). A 10+ft falls occurs just around the bend in the stream.
I-43
Figure I-57. Gravel area in stream Above T-1; water flows approximately 100cfs.
In 2013 an effort was made to identify significant tributary flows into the gorge below the dam
site. A total of 3 significant tributaries (Figure I-51) were identified, along with another two
dozen smaller ones. The three major tributaries contribute 74% of the tributary flows to the
gorge. Tributary T-1 is a complex of small flows from the slope on the east side of the creek. It
was estimated that these flows collectively may contribute up to 5 cfs to the creek. Tributary T-
2 is a well-defined stream that drains a muskeg/beaver pond complex. Flows from this stream
were measured at 3-5 cfs. Tributary T-3 is a well-defined, relatively steep stream much larger
than T-1 and T-2 that drains a wetland/lake complex further up-slope. It has a channel width of
8-15 ft. and high water depth of 1.5 ft. Flows in this tributary were measured at 5-8 cfs, but
channel characteristics indicate flows could easily reach or exceed 15 cfs. Smaller identified
flows collectively contribute another 2-3 cfs. In total, tributary flows typically contribute from
10-16.5 cfs or more to the gorge under normal weather conditions. During extended dry
periods these tributary flows could decrease to 5-6 cfs.
Bedrock
I-44
The only spawning habitat occurs in a small segment 200-300 ft. long between tributaries T-1
and T-2 (Figure I-56). However, currents are very strong in this area presenting a hostile
environment to any fry potentially emerging from gravels. Quiet water refugia, that could help
keep fry in this rea after emergence, were absent as well.
A fish trapping effort was conducted in the gorge in April 2013. A total of 18 baited fish traps
were fished in segments 1 and 2 of the gorge overnight for a total effort of 432 hours. Only
segments 1 and 2 were fished because segments 3 and 4 were inaccessible. Only one juvenile
Cutthroat trout (160 mm) was caught in that effort. After travelling down about 5,000 ft. of
the gorge this fish appeared lethargic and showed several areas of scale loss on the body and
numerous fin tears and ragged fin edges. It did not appear to be in the same healthy condition
as juvenile fish caught in the anadromous reach using the same trapping methods. This fish
was caught in the only root wad we observed in the stream during our survey of the gorge.
The area at the dam site in segment 5 was also fished with 18 baited traps. Numerous Dolly
Varden and Cutthroat Trout were caught, along with two three-spine sticklebacks, in 48 hours
of fishing, all in excellent condition. Later in the summer several fish were seen in the stream at
the upper end of segment 5. These fish were estimated to be in the range of 4-6 inches. When
spooked all of these fish swam upstream back to the pool area at the top of the gorge.
The configuration of the stream at the top of the gorge consists of a large pool and bends in the
stream, followed by a rapid flat water section flowing over smooth bedrock. This section
gradually increases in slope from less than 1% to over 12% in a distance of 250 ft. Fish entering
the top segment of the gorge experience the increasing velocity of the water and are able to
swim back upstream and avoid entering the gorge. In fact, fish have been observed doing this
when wading in this segment of the gorge. However, part way down segment 5 the current will
become too swift for fish to overcome and swim back upstream. At this point the current will
force the fish to go over the cascade at the top of segment 4 and travel downstream through
the gorge. In contrast, a hydroelectric diversion structure will provide a differing hydraulic
environment. The structure will provide a low velocity environment until just a few feet from
the spillway, at which point the velocity will increase rapidly. Once a fish gets too close to the
spillway, it will be forced over the spillway into the gorge.
The lack of fish in the gorge was not surprising given the poor quality of habitat to support
them, and the lack of refugia under all flow conditions. We did not find suitable holding or
rearing waters in the gorge. What we did find was a narrow (40 ft.) bedrock bounded stream
and an extremely fragmented habitat with 11 barriers (falls and velocity barriers) within a 5,900
ft. section of stream. Benthic resources would be very limited due to the extensive amount of
bedrock, lack of gravels on the stream bottom, and limited cover. Pools, runs, riffles, and
rapids were all bedrock delimited, except between T-1 and T-2, where for 200-300 ft. a thin
layer of gravels existed. Fish would be dependent on food resources falling into the water or
I-45
drifting downstream. The fast water flows would require considerable energy expenditure by
fish for whatever resources were available in the water column. As fish search for suitable
habitat and food they would encounter numerous fish barriers that would force them further
downstream, eventually ending up in the anadromous reach. The high water flows of 400 –
1000+ cfs would also flush the fish entering the gorge downstream until they arrived at the
anadromous reach. The condition of the one fish captured in the lower end of the gorge
indicates that travelling over the falls and through the velocity barriers is physically challenging
for them. At this time we would have to conclude that there is no resident population of fish in
the gorge; and fish entering the gorge are at best short-term transients travelling through the
gorge that integrate into the fish population in the anadromous reach.
Table I-5. Major physical features of the Thayer Creek gorge and anadromous
reach.
Distance from
mouth of creek
Segment
Length (ft.)
Elevation
change (ft.)
Average
slope (%)
accessibility
Anadromous reach
(0- 1,400 ft.)
1,400 10 0.7 Accessible but difficult
or impossible to cross at
flows greater than 400
cfs
Gorge section 1
(1,400 - 1,450 ft.)
Anadromous barrier
50 30 60 inaccessible
Gorge section 1
(1,400- 3,450 ft.)
2,050 50 2.4 Accessible at flows less
than 150 cfs
Gorge section 2
(3,450 – 5,200 ft.)
1,750 50 2.9 Accessible at flows less
than 150 cfs
Gorge section 3
(5,200 – 6,400 ft.)
1,200 50 4.2 inaccessible
Gorge section 4
(6,400 – 7,050 ft.)
650 50 7.7 inaccessible
Gorge section 4
(6,775 - 6,825 ft.)
50 40 80 inaccessible
Gorge section 5
(7,050 – 7,300 ft.)
250 30 12 accessible at flows less
than 400 cfs
I-46
Figure I-58. View downstream looking at a velocity barrier near tributary t-1 in gorge. Channel
narrows down to about 30 ft. as it flows around bend over bedrock.
Figure I-59. View looking downstream at the anadromous barrier falls from the gorge (Map B
location). Two of the three falls at this location can be seen in this photo.
I-47
Summary of Gorge Characteristics and Habitat Values
The gorge is currently poor quality fish habitat lacking the structure and substrate to provide
adequate food, shelter, and spawning substrate for establishment of a resident fish population.
This is primarily due a variety of factors including:
o Fluctuating high water flows in excess of 350 cfs, and as high as 1,000 cfs or
more, for 6-7 months of the year
o Extensive bedrock substrate delimiting the stream channel
o Narrow stream channel, typically 30 – 40 ft. wide in segments 1-3 generating
high current velocities as flows increase.
o Fragmented, discontinuous habitat from twelve known fish barriers within
segments 1-4 of the gorge over a distance of 5,900 ft. There are 8 falls in the
gorge near or greater than 10 ft. height, 2 bedrock cascades ~50-100 ft. long, and
numerous velocity barriers formed by narrow channel configurations at water
flows greater than 200 cfs
Gorge section 1- 4 falls ; 1 major velocity barrier
Gorge section 2 – 1 major velocity barrier; 1 falls
Gorge section 3 – 2 falls; 1 major cascade
Gorge section 4 – 1 falls; 1 major cascade
Gorge section 5 – 12% grade
less than 200 cfs < 20% of time
average annual flow ~ 360 cfs
flushing flows exist for 6 months of the year
2.5 months of the year flows low enough to support some fish habitat
use
8 months of the year excess water >250 cfs will be flowing down gorge
o The condition of the one Cutthroat trout captured in the gorge indicates it is a
high stress environment
Lethargic condition
Abrasions (lost scales)
Torn and ragged fins
o Periodic excess water flows in excess of 350 cfs for 6-7 months of the year will
maintain the status quo of current fish use and habitat values in the gorge.
I-48
Tributary Flows into Thayer Creek Gorge
The EIS had recommended a bypass flow of 20-40 cfs in the Thayer Creek gorge to maintain
wintering habitat, maintain pool depths, provide greater stream connectivity, and decrease
harmful icing conditions on overwintering fish (USDA, USFS, 2009). These recommendations
were based on assumptions that fish overwintering occurs in the gorge and some minimal
population of resident fish exists in the gorge year-round. Our investigation of the gorge
indicates that there is no resident population of fish in the gorge; fish are transient occupants
moving downstream through the gorge to the anadromous reach; and that spawning, rearing
and overwintering habitat in the gorge is lacking as well. While a few fish occur in the gorge,
they appear to be transients moving through the gorge after moving downstream and passing
over the first barrier falls below the dam site, and not residing in the gorge for any significant
period of time (see the fisheries section). Operation of the hydro project under the most robust
operations scenario would result in minimum bypassed water flows (ranging from 0 -75 cfs) for
one or more days over a period of up to 4 months during the year. Stipulated bypass flows,
and tributary flows, would be the major sources of water in the gorge on those days of reduced
flow.
A total of 28 contributing tributary streams were identified within the Thayer Creek gorge
(Figure I-60). Three of them (T1, T2, and T3; Figures I-61, I-62 and I-63) contribute 74% of the
water flow, and the remaining 25 contribute 26% of the water flow. Observed flows, and
maximum and minimum estimated water flows from these 28 streams is summarized in Table I-
6. In April 2013 observed flows contributed 10-16.5 cfs to the gorge. This was a period of
frequent precipitation, and occasional heavy rainfall. Low flows were estimated from
observations in the summer during a period of relatively dry weather. Maximum flows were
based on stream bankfull conditions and monthly rainfall totals.
Only 3 tributaries contribute substantial flows to the gorge. Tributary T-3 (Figure I-62) is the
most important contributing 40% of the water flow. The stream is 8-15 ft. wide and has a bank
full depth of 18-24 inches. It is a well- defined deeply incised stream channel that carries
substantial sediment, including cobble sized particles. Maximum water flows were estimated at
more than 15 cfs, but flows of less than 1 cfs have been observed in the stream. During normal
weather conditions flows are expected to be in the range of 3-5 cfs.
Tributary T-2 is a perennial flow that drains a beaver pond complex (Figure I-61). There is a
substantial thalweg flow in this small stream. Observed surface flows were in the range of 2-3
cfs at the beaver ponds. High flows were estimated to be in the range of 5 cfs. Tributary T-1
(Figure I-63) is a complex of 3 small streams on the east side of the creek. Each appears to
contribute about 1 cfs. These streams cascade down the slope into the creek without a clear
I-49
channel formed near the stream. The remaining streams fall into two categories, those with
channel widths greater than 2 ft. (Figures I-64 and I-65), and those smaller than 2 ft. (Figures I-
66 and I-67). The small streams with larger channels showed flows ranging from 0.1 to 0.5 cfs.
The smallest channel streams showed flows of 0.1 to 0.3 cfs. Generally highest water flows
would occur during rainfall events. Cumulatively, during dry spells water flows may be on the
order of 5-6.5 cfs, but under normal weather conditions flows of 10+ cfs can be expected.
I-50
Figure I-60. Identified tributaries contributing flow to the Thayer Creek gorge. Areas B-1 and B-2 lie below tributary T-2, and areaB-4 is between Tributaries T-2 and T-3. T-1T-2 T-3 B-4 B-1/B-2 I-51
Table II-6. Summary of Tributary Flows to the Thayer Creek Gorge.
Tributary Description Observed flows Estimated low
flow
Estimated max
flow
T-1 3 streams within 100 ft.
of each other flowing
down slope
1-2 cfs in each
stream
< 3 cfs 6-8 cfs
T-2 Stream drains wetland
beaver pond complex;
deeply incised channel
below beaver ponds,
lots of large and small
woody debris in
channel, channel width
3-8 ft.
2-3 cfs < 1 cfs 5+ cfs
T-3 Well-developed channel
8-15 ft. wide, sand,
gravel, cobble present in
channel; flows over
bedrock in some
locations
3-5 cfs < 1 cfs 15+ cfs
B-1/B-2
area
9 small tributaries,
channels less than 2 ft.
wide
Cumulative 1-1.5
cfs
Cumulative < 0.5
cfs
Cumulative 2-3
cfs
B-4 area 13 small tributaries
channels range from < 2
ft. up to 4 ft. wide
Cumulative 3-5
cfs
Cumulative < 1
cfs
Cumulative 7-9
cfs
Cumulative
flows
All 28 tributaries 10-16.5 cfs < 6.5 cfs 35-40 cfs
I-52
Figure I-61. Mouth of tributary T-2.
Figure I-62. Tributary T-3 about 300 ft. from Thayer Creek.
I-53
Figure I-63. One of the streams at tributary T-1.
Figure I-64. A large tributary in area B-2 on the west side of Thayer Creek.
I-54
Figure I-65. A large tributary in area B-4 on the west side of Thayer Creek.
I-55
Figure I-66. A small tributary less than 2 ft. wide in area B-4.
I-56
Figure I-67. A small tributary in area B-2 on the west side of Thayer Creek.
I-57
Thayer Creek Reach Above the Gorge
Thayer Creek originates from Thayer Lake and travels through a broad valley for approximately
8 miles until it reaches the gorge. The lake and stream are both prime Cutthroat Trout habitat
and support a trophy sport fishery. The sport fishery is operated from a lodge located on
Thayer Lake. Sport fishing is limited to the lake and only the upper end of Thayer creek that is
easily reached from the lodge on day trips.
Field studies were conducted on Thayer Creek in the vicinity of the proposed dam site above
the gorge. The area of study is shown in Figure I-68. It was divided into 3 segments. Segment
A extended from the dam site to the upstream logjam. Segment B extended from the logjam
upstream approximately ¼ mi until the channel began to narrow. Segment C extended
upstream from that point to the beginning of the “S” bend in the stream. Segment A is a
complex riparian/wetland area, with multiple channels, oxbow ponds, and prone to flooding
during high water (Figures I-69 through I-74). There are several high island areas colonized by
mature trees, as well as lower lying areas with alder brush and grass. Extensive wetland grass
areas also occur. Multiple channels exist at different elevations, some only carrying water
during high flow events, and others that are interconnected during low flow events. Most
channels are active, with extensive brush covered and undercut banks (Figures I-72 and I-73).
Most pools are small and separated by short runs or riffles. LWD is limited in occurrence and
most prevalent at the large pool before the gorge and near the upper logjam area at the top of
this segment (Figure I-76). The streambed is mostly gravel and excellent spawning habitat. An
extensive logjam blocks the stream at the upper end of this segment.
Segment B is a straight, broad section of stream channel that begins at the logjam and gradually
narrows upstream after about a ¼ mile (Figures I-75 and I-76). At the lower end it is more than
100 ft. wide, while the upper end is less than 75 ft. The entire active channel is high quality
spawning gravel with a few scattered boulders. The south bank is sandy substrate merging into
a grassy low lying wetland towards the bottom of the channel, and is tree lined at the upper
end (Figures I-77 and I-78). Undercut banks occur throughout this segment, but particularly on
the west bank where a 2-3 ft. deep channel runs parallel to shore. Most of the main channel is
gravel and excellent spawning habitat, particularly at the lower end of segment B.
Segment C is less than a ¼ mile long. The channel narrows rapidly in the section and there is an
increase in boulder and cobble substrate (Figure I-79). The shoreline is exposed bedrock, or
bedrock overlain by a thick root/duff layer supporting tree growth to the edge of the stream or
exposed bedrock (Figures I-80, I-81, and I-82). With the narrowing of the channel, water also
becomes much deeper and supports midstream main channel morphology. At the upper end a
series of rapids in the midstream and pocket pools on the south side develop, with the north
I-58
shore all exposed bedrock (Figures I-81 and I-82). At the upper end of segment C the stream is
40-50 ft. wide. Spawning gravels are limited in occurrence in segment C.
Figure I-68. Upstream area of Thayer Creek (Reach 6) included in the environmental studies
showing the 3 major segments in this reach.
Dam site
Segment C: Bedrock exposure, cobbles,
heavily treed shoreline with bedrock
exposure, boulders in stream, limited gravel
substrate, rapids and small pools present
Segment B: Broad gravel riffles, a few small
pocket pools and boulders, extensive
undercut banks, deep channel next to bank,
grassy banks, some LWD
Segment A: Multiple channels, undercut
banks, heavy brush and tree cover, deep
pools, convoluted channels, lots of LWD,
logjam across stream, extensive grassy
riparian/wetland flats
I-59
Figure I-70. Top end of the large pool above dam site. The main channel comes into the pool
from the left; the channel in the background carries intermittent flows except during high water
flow periods.
Figure I-69. Bottom
end of large pool at the
dam site in Segment A.
The dark portion of the
stream channel is
exposed bedrock.
I-57
I-60
Figure I-71. Segment A showing the mouth of a small north tributary entering Thayer Creek in
an area with extensive undercut grassy banks.
Figure I-72. A portion of Thayer Creek below the logjam showing extensive overhanging brush
cover adjacent to the sinuous creek channel.
I-61
Figure I-73. A deep pool and run just above the large pool. The Solinst datalogger is located at
the overhanging tree in this pool.
Figure I-74. Large logjam in segment A viewed from segment B.
I-62
Figure I-75. Upstream view of segment B viewed from the logjam at the top of segment A.
Figure I-76. Lower end of segment B undercut bank and deep channel on left side, shallow
gravel slope on right side; root wad and fallen tree in foreground
I-63
Figure I-77. Segment B in August showing grass cover on right bank and overhanging
vegetation on the left undercut bank.
Figure I-78. View across the lower end of segment B towards riparian/wetland grassy area. The
bank on the far side is sandy and silty fines.
I-64
Figure I-79. Lower end of segment C showing bedrock on south bank and midstream channel
morphology.
Figure I-80. Rapids with pocket pool adjacent to the south bank just below the S bend in Thayer
creek.
I-65
Figure I-81. Deep run in Thayer Creek below S bend in stream. The bank is boulders over
bedrock.
Figure I-82. Rapids at the top end of Segment C at the start of the S bend. Both banks are
exposed bedrock at this bend.
I-66
The substrate in Thayer Creek above the gorge is substantially different than what is found in
the anadromous reach (Figure I-83). Less than 3% of the gravels are larger than 60 mm, and
none larger than 128 mm. The D50 value is 22.5 mm which is similar to the D50 values in the
anadromous reach. However, the upper stream shows a more symmetric distribution of
particle sizes around the D50 value, while in the anadromous reach the particles sizes are
skewed towards the larger particles. The absence of larger particle sizes is most evident in the
photo of typical gravels in the stream (Figure I-84).
0
2
4
6
8
10
12
14
16
18
20
22
24
> 362 362 256 180 128 90 60 45 32 22.5 16 11.3 8 5.7 4
Figure I-83. Percent composition of spawning gravels in the mainstem of Thayer Creek above
the gorge.
%
D50 value
I-67
Figure I-84. Typical gravel substrate in Thayer Creek above the dam site.
Potential Hydro Project impacts to stream Habitat
Diversion infrastructure
A hydroelectric diversion structure will provide a differing hydraulic environment from the
current stream flow into the gorge. The structure will provide a low velocity environment until
just a few feet from the spillway, at which point the velocity will increase rapidly. Once a fish
gets too close to the spillway, it will be forced over the spillway into the gorge. Encountering
the fish diversion structure is a one-time experience for the fish and forces them to move
downstream through the gorge to the anadromous reach. As long as water is spilling over the
diversion structure it will provide an opportunity for fish to leave a high quality fish habitat area
to pass through a high stress, poor quality habitat until they reach the anadromous reach of the
stream.
I-68
Excess water flows for 8 months of the year that is not used by the power project will allow fish
to continue to move downstream during operations as they have in the past without the
project operating. Providing fish passage at the diversion structure will extend that opportunity
to 12 months, and may negatively enhance the downstream movement of fish from the lake
environment at the dam site into the gorge as fish cruise the lake shoreline and feed along the
lake edges.
Stipulated bypass flows
Stipulated flow releases of 20-40 cfs will not have a significant effect on maintaining or
improving the quality of fish habitat in the gorge, or contribute to establishing a resident
population of fish in the gorge. However it will maintain continuity of water flow through the
gorge at a rate of 20-40 cfs on those days when no spill over the dam occurs.
Tributaries contribute 6.5 to 40 cfs to the gorge depending upon local rainfall events. These
flows supplement the stipulated bypass flow releases of 20-40 cfs in the gorge.
Operation of the hydro project under the most robust operations scenario would result in
minimum bypassed water flows for about 20-30 days in the February/March timeframe. At
that time stipulated bypass flows and tributaries would be the major sources of water flow
through the gorge.
Impoundment
Most of segment A above the gorge would be flooded by the project impoundment. The area
would resemble a flooded beaver pond complex with a mixed grass and shrub shoreline. Large
trees within the impoundment boundary in segment A would likely not survive the saturated
and flooded soils after filling of the impoundment.
Impounded water may back up into the lower end of the stream extending into segment B and
reduce current velocities at the interface of these two segments. There may be some buildup
of fine sediments infiltrating the gravels at the interface of segment A and B due to the
localized reduction current velocities.
Tailrace discharge
The powerhouse site is located approximately 500 ft. downstream from the barrier falls in the
anadromous reach. Fish spawning occurs throughout the anadromous reach up to the barrier
falls. If the tailrace discharge point into the creek is located more than 100 ft. downstream
from the barrier falls there may be a loss of productive spawning habitat due to low water
I-69
conditions that would occur in the February/March timeframe relative to the higher water
flows available to fish during the spawning season.
I-70
Section II - Lower Thayer Creek Drainage Water Resources
Overview
Water resources data is very limited for Thayer Creek. HDR collected streamflow measurements
over 3 years on Thayer Creek from 1999 to 2001 (HDR, 2003). However, the EIS for the Angoon
Hydroelectric project used records from Hasselborg Creek, a similar drainage on Admiralty
Island, to predict water flows in Thayer Creek (USDA, USFS, 2009). Their analyses indicated that
Thayer Creek flow would be approximately 14% higher than flows recorded for Hasselborg
Creek. The hydroelectric project is essentially a run-of-river design involving a small diversion
dam at the top of the gorge, a pipeline to transport water to a power plant located below the
gorge, discharge of the water back into the stream, and transmission of power to Angoon. A
small 10-20 acre pond would be formed behind the dam on the stream above the gorge. Excess
water, not used to generate power would be spilled over the dam and continue through the
gorge to the anadromous section of the stream. The proposal is to generate approximately
1MW of power from the power plant.
In 2013 Shipley Group began year-round monitoring of temperature and flow in Thayer Creek
at two locations, one at the proposed dam site, and the other at the mouth of Thayer Creek
using Solinst dataloggers. Barometric pressure is also being continuously monitored at the
mouth of Thayer Creek with a Solinst Barologger. The site at the mouth of Thayer Creek was
near the west bank in a deep run in the middle of Zone IV (Figure II-1). The datalogger was
cabled to a tree and then wrapped around a boulder in the stream. Tethering the meter to
shore proved problematic with the meter being moved from its position after 3 months of
deployment most likely by river otters. The meter was redeployed by anchoring the datalogger
to the boulder in the stream with a cable. The meter is still in position and we hope to get a
year-long record collected by the summer of 2015. The second site was located above the
gorge near the dam site. It was positioned in a deep pool by an overhanging tree (Figure II-2).
This meter was cabled to the overhanging tree and secured in place by a fence stake driven into
the streambed adjacent to the tree. Two years of data has been successfully collected at this
site. The temperature and depth records for 2013/2014 and 2014/2015 are shown in
Appendices II-1 and II-2. A calibration curve and conversion table for stream depth versus
stream flow (cfs) is contained in Appendix II-3.
Thayer Creek Streamflow Assessment
Stream flow records were collected from April 20, 2013 through April 8, 2015 (Figures II-3 and
II-4). Data (temperature and pressure) was continuously collected and averaged over 30
minute intervals. Pressure was then converted to submerged depth of the datalogger. The
II-1
calibration curve and conversion table in Appendix II-3 were used to convert depth of the meter
to water flow in cubic feet per second (cfs). A total of 5 flow measurements were collected at
the dam site in 2013, ranging from 100 to 700 cfs, and used to construct the calibration curve.
Most notable in the two records is the absence of a spring runoff peak in the spring of 2015 due
to the abnormally low snowfall accumulations in the winter of 2014/15. The late spring and
summer were wetter in 2015 than 2014 and also shows up in the hydrographic record. The fall
and winter patterns between the two hydrographs were generally similar for the two years.
The annual average streamflow for Thayer Creek was 370 cfs in 2013/2014 and 322 cfs in
2014/2015.
Figure II-1. Location of the datalogger at the mouth of Thayer Creek.
II 2
Figure II-2. Location of the datalogger above the dam site on Thayer Creek.
II-3
Figure II-3 Twelve month hydrographic record for Thayer Creek 2013/2014. Ann. ave. flow 370 cfs Ann. ave. flow 322 cfsFigure II-4. Twelve month hydrographic record for Thayer Creek 2014/2015.II-4
The four highest and lowest recorded flows for a 30 minute interval in 2013/2014 are shown in
Table II-1 compared with the average daily flow for that date. The minimum flow recorded was
80cfs, while the maximum was 919 cfs. In some cases the data shows a large variation in the 30
minute and daily flow values, while in others they are very similar for both high and low flows.
In 2013/2014, 30 minute high flows were greater than the average daily flows by 8-177 cfs;
while variations in 30 minute low flows versus daily average flows were lower by 5 to 44 cfs.
The four highest and lowest recorded flows for a 30 minute interval in 2014/2015 are shown in
Table II-2 compared with the average daily flow for that date. The pattern between the two
years is similar but the magnitude of variations in 30 minute versus daily flows was smaller. In
2014/2015, 30 minute high flows were greater that the average daily flows by 40-162 cfs; while
variations in 30 minute low flows versus daily average flows were lower by 7-22 cfs. However,
in both years the highest and lowest 30 minute flows did not match up with the highest and
lowest average daily flows.
Looking at the same dataset as shown in Table II-1, the minimum flow period recorded can be
compared to the maximum (Table II-3). The data for both years has been integrated and
organized from highest to lowest daily average flow values for these dates. The maximum daily
fluctuation in streamflow ranged from 16 to 461 cfs for high flows, and from 10 to 87 cfs for low
flows. The difference represents the magnitude of short term changes in flow which can also
be expressed as a percentage of the average flow for that day. Again a high variability occurs
from small to large percentages of flow in high and low flow periods. However, on two of the
events low flows changed by more than 100% in 24 hours. Under high flow conditions the
greatest percentage change was only 68% in 24 hours. This indicates extent of impacts from
short-term variations in daily rainfall on stream flow in this creek.
Date
30 minute high
flow (cfs)
Daily average flow
(cfs)date
30 minute low flow
(cfs)
Daily average low
flow (cfs)
5/15/2013 776 768 3/2/2014 80 124
10/14/2013 876 750 3/1/2014 85 110
1/14/2014 919 742 2/28/2014 95 103
10/9/2013 750 643 2/27/2014 100 105
Table II-1. The four highest and lowest 30 minute flows recorded for Thayer
Creek in 2013/2014 compared to the daily average flows for these days.
II-5
Table II-2. The four highest and lowest 30 minute flows recorded for Thayer
Creek in 2014/2015 compared to the daily average flows for these days.
Date
30 minute high
flow (cfs)
Daily average flow
(cfs)date
30 minute low flow
(cfs)
Daily average low
flow (cfs)
1/21/2015 924 762 2/9/2015 103 110
1/22/2015 802 762 3/5/2015 93 108
1/23/2015 829 760 2/11/2015 83 105
1/24/2015 829 748 2/12/2015 89 103
Table II-3. Short term changes in flow during high and low flow periods.
Date
Daily average
flow (cfs)
30 minute high
flow (cfs)
30 minute low
flow (cfs)
Maximum 24 hr
fluctuation in
flow (cfs)
Percentage change in
24 hours
5/15/2013 768 776 760 16 2
1/21/2015 762 924 613 311 34
1/22/2015 762 802 710 92 11
1/23/2015 760 829 708 121 15
10/14/2013 750 876 585 291 33
1/24/2015 748 829 687 142 17
1/14/2014 742 919 458 461 50
10/9/2013 643 750 497 253 34
3/2/2014 124 167 80 87 52
3/1/2014 110 155 85 70 45
2/9/2015 110 122 103 19 16
3/5/2015 108 123 93 30 24
2/11/2015 105 138 83 55 40
2/27/2014 105 110 100 10 9
2/28/2014 103 110 95 15 14
2/12/2015 103 113 89 24 21
The mean daily stream flows calculated for Thayer Creek from the EIS (USDA, USFS, 2009) and
the record collected by Shipley Group are shown in Figure II-5 and figures II-3 and II-4,
respectively. In general, the two hydrographs are similar in appearance, but flows are greater
in the winter in Figure II-5, and the peaks in the spring and fall are higher, than in the predicted
hydrograph. The minimum and maximum values from both hydrographs are compared in Table
II-4 by yearly quarter. Minimum values collected by Shipley Group are higher in the 1st, 2nd, and
4th quarters, while the predicted EIS data is higher in the 3rd quarter. Maximum flows collected
by Shipley Group are higher in the first 3 quarters, while the EIS predicted value is higher in the
II-6
4th quarter. In general terms, there is more water flowing in 3/4 of the year than predicted by
the EIS hydrograph, and less water in ¼ of the year.
The predicted extreme minimum flow in the EIS (USDA, USFS, 2009) was 26 cfs. The minimum
30 minute flow recorded by Shipley Group was 78 cfs which is approximately 3 times higher
than the extreme minimum flow predicted in the EIS. However, the daily average minimum
flow was even higher at 103 cfs.
Figure II-5. Predicted annual hydrograph for Thayer Creek from the EIS for the Angoon
Hydroelectric Project (USDA, USFS, 2009).
II-7
Table II-4. Comparison of minimum and maximum flows from the EIS and
Shipley Group data.
1st Quarter
Jan-Mar
2nd Quarter
Apr-Jun
3rd Quarter
Jul-Sep
4th Quarter
Oct-Dec
EIS- minimum flow 115 145 250 250
Shipley minimum flow
2013/2014 103 105 122 266
Shipley minimum flow
2014/2015 103 155 181 138
EIS maximum flow 315 660 500 785
Shipley maximum flow
2013/2014 743 768 595 750Shipley maximum flow
2014/2015 762 415 623 668
The EIS also predicted an extreme maximum flow of 2,530 cfs for Thayer Creek (USDA, USFS,
2009). We observed near bankfull flow conditions at an estimated 1,025 cfs, and the recorded
30 minute high flow for the year was 919 cfs. At those flow rates the stream was fully
contained within its normal flow channel. The equivalent water depth over the meter at a flow
of 919 cfs was 4.52 ft. If the depth for a flow of 2,530 cfs is extrapolated from the calibration
curve, it would increase the water depth over the meter by 3.5 ft. to a depth of 9ft. While this
depth would be contained within the stream channel at the dam site, we believe it would cause
flooding in the anadromous reach on the east side of the stream. There is evidence of an old
stream channel along the base of the mountains on the east side that extends over a distance
of at least ½ mile. While this channel was dry at the observed flow estimated at 1,025 cfs, the
entrance to the channel at the stream was not 3.5 ft. higher than the surface of the water at
that flow. In fact, the water level was within inches of flooding into this channel. The west
bank of Thayer Creek in the anadromous reach would easily contain flows of 2,530 cfs.
Water levels also change rapidly during the day. Figures II-6 and II-7 depict hourly flows for two
different periods of rapid water level change. In figure II-6 the flows at midnight on 4-24-13
were 250 cfs, but rose to 599 cfs in 26 hours, and then leveled off at 558 cfs on 4-26-13.
However, the average daily flow on the 25th was only 352 cfs. In the second example the daily
average water flow was 397 cfs on 1-13-14, but in 24 hours water flow had risen to 919 cfs.
However, the daily average on 1-15-14 was only 711 cfs. By 1-16-14 daily flows averaged 685
cfs. These dramatic changes are related to extreme rainfall events, but reflect the rapid change
in stream flows with no apparent lag effect from Thayer Lake. The lake effect seems to be
II-8
exhibited in an extension of higher stream flows following an extreme rainfall event. In other
words, stream flow rises fast and tails off slowly.
Streamflow current velocities and profiles are shown in Figures II-8, II-9, II-11, and II-12 for the
Thayer Creek dam site and mouth locations; while photos of each site are shown in figures II-10
and II-13, respectively. At the dam site high velocity water follows the south shoreline and
bedrock substrate in the stream, with water velocities reaching 5 feet per second as flows
approach 700 cfs. The gravels on the north side show evidence of extensive transport with
higher flows, but consistently cover 35-40 ft. of the north side streambed. Bankfull water
height appears to be near 1.8 ft. above the streambed on the north bank. At the mouth
location the channel is approximately 109 ft. wide and high flows are found in mid-channel 25-
60 ft. from the west bank. Peak flows of 4-4.8 feet per second occur from 30-55 ft. in mid-
channel. Bedrock exposure at this location is confined to the west bank. Bankfull water height
appears to be about 4.5 ft. above the streambed on the west bank.
The most dramatic differences in stream flows are exhibited at the barrier falls. The barrier falls
is shown in Figures II-14, II-15, and II-16 at flows of 1,025 (est.), 223, and 100 cfs, respectively.
At the highest flow the second falls extends almost to the first falls. At low flows a bar appears
below the plunge pool separating the stream into two channels, one on the east and the other
on the west side of the creek.
II-9
0:01:511:01:512:01:513:01:514:01:515:01:516:01:517:01:518:01:519:01:5110:01:5111:01:5112:01:5113:01:5114:01:5115:01:5116:01:5117:01:5118:01:5119:01:5120:01:5121:01:5122:01:5123:01:510:01:511:01:512:01:513:01:514:01:515:01:516:01:517:01:518:01:519:01:5110:01:5111:01:5112:01:5113:01:5114:01:5115:01:5116:01:5117:01:5118:01:5119:01:5120:01:5121:01:5122:01:5123:01:51Figure II-6. 30-minute flows recorded April 24/25, 2013 compared to the daily average flow for April 24, 25, and 26. II-10
18:01:5119:01:5120:01:5121:01:5122:01:5123:01:510:01:511:01:512:01:513:01:514:01:515:01:516:01:517:01:518:01:519:01:5110:01:5111:01:5112:01:5113:01:5114:01:5115:01:5116:01:5117:01:5118:01:5119:01:5120:01:5121:01:5122:01:5123:01:510:01:511:01:512:01:513:01:514:01:515:01:516:01:517:01:518:01:519:01:5110:01:5111:01:5112:01:51Figure II-7. 30 minute flows recorded over 42 hours from 1-13-14 through 1-15-14 compared to daily average flow for those 3 days. II-11685 ave. 1-16-14
Figure II-8. Water velocity profiles at the dam site under different stream flow conditions.II-12
0369121518212427303336394245485154576063666972757881848790939699102Figure II-9. Stream profile at the dam site; channel width is 104 ft. bedrockgravelFigure II-10. Dam site profile location; gravel can be clearly seen in background. The darker streambed in the foreground is bedrock. II-13
Figure II-11. Water velocity profiles at the mouth of Thayer Creek under different stream flow conditions II-14
Figure II-12. Stream profile at the mouth of Thayer Creek, channel width is approximately 109 ft. West bank East bank Figure II-13. Stream profile location at the mouth of Thayer Creek viewed from the east bank. II-15
Figure II-14. The barrier falls at the top of the anadromous reach at a stream flow rate of 1025 cfs (October, 2014).II-16
Figure II-15. The barrier falls at the top of the anadromous reach at a stream flow rate of 223 cfs (August, 2014).II-17
Figure II-16. The barrier falls at the top of the anadromous reach at a stream flow rate of 100 cfs (April, 2013).II-18
Although the current design of the hydro project is now focused on a 1 MW run-of-the-river
project using up to 100 cfs of water, alternatives were considered that encompassed water uses
as high as 400 cfs. Based on the data presented in Figures II-3 and II-4, flows of 100+ cfs would
be available most of the year except for February and March when stream flows drop below
100 cfs for brief periods of time. The situation is more complex when considering potential
power generation alternatives utilizing up to 400 cfs. Stream flow data has been summarized
by month and quarter for average, maximum, and minimum flows in Thayer Creek (Table II-5).
Based on the two year record the annual average flow is approximately 350 cfs. However,
average flows in February and March are less than 200 cfs; and in April, July and August they
are less than 300 cfs (Table II-5). When minimum daily flows are considered, during 10 months
of the year daily flows of less than 300 cfs occur. On a quarterly basis, flows are less than 200
cfs in the first and third quarters; and between 200 and 300 cfs in the second and fourth
quarters.
These statistics indicate that a high variability in daily flows may be contributing to the monthly
summary statistics confounding interpretation of higher flow occurrences on Thayer Creek.
Therefore, we analyzed the hydrologic data on a daily basis (Figure II-17). This analysis
indicated that flows greater than 400 cfs were only available 32% of the time; while 300 cfs or
more would be available 50% of the time. While average daily flows in the two year record
exceeded 100 cfs all of the time, there were 18 days when short-term, 30 minute flows
dropped below 100 cfs, with the lowest 30 minute flow being 78 cfs. This data indicates that a
run-of-the-river design is reasonable with a small storage capacity to level out day to day, short-
term, low flow variations that occur on Thayer Creek. Incorporation of larger storage capacity
reservoirs would be required to support power projects that require more than 100 cfs water
flows for power generation.
The daily average flow data was then analyzed with respect to frequency of spill over the dam,
that is, days when more water is flowing in the creek than can be used by the power plant
operating at a capacity of 100 cfs (Table II-6). Based on the data in Table II-3, the variation in
daily, 30 minute, low flows averages approximately 27 cfs. Therefore, if it is assumed that the
power plant will use 100 cfs, then any daily average flow days less than approximately 127 cfs
could result in a no spill event for a portion of the day. Based on the two year hydrographic
record, approximately 18 days in February and March, a no spill event could occur lasting one
or more hours, but less than 24 hours. Approximately 85% of the year at least 75 cfs will be
spilling and flowing through the natural channel course in Thayer Creek. Spill flows ranging
from 25 - 75 cfs could occur in the natural channel 13% of the time (up to 92 days), most likely
in the months of February, March, July and August.
II-19
month
average flow
(cfs)
Maximum flow
(cfs)
Minimum flow
(cfs)
January 474 752 270
February 193 381 103
March 188 339 108
April 267 383 189
May 487 591 334
June 379 510 273
July 264 418 173
August 281 397 177
September 370 580 199
October 521 709 372
November 355 504 239
December 337 489 202
12 month annual average
flows 343 504 220
First Quarter average flows 285 491 160
Second Quarter average
flows 378 495 265
Third Quarter average flows 305 465 183
Fourth Quarter average
flows 404 567 271
Table II-5. Monthly and quarterly average, maximum and minimum flows based
on 24 months of average daily flows data (April 10, 2013 through April 8, 2015).
II-20
0
50
100
150
200
250
< 120 > 120 < 200 >200 < 330 > 330 < 410 > 410 < 550 > 550
CFS
Figure II-17. Average daily flows in Thayer Creek sorted by average volume per day.
II-21
Month
Average stream
flow (cfs)
2013/2014 2014/2015 2013/2014 2014/2015 2013/2014 2014/2015
January 31 31 0 0 0 4 474
February 24 23 4 5 12 16 193
March 25 27 6 4 14 17 188
April 23 30 7 0 6 3 267
May 31 31 0 0 0 0 487
June 30 30 0 0 0 0 379
July 31 31 0 0 2 0 264
August 30 31 1 0 31 0 181
September 30 30 0 0 4 0 370
October 31 31 0 0 0 0 521
November 30 30 0 0 0 0 355
December 31 31 0 0 0 0 337
Number of potential spill
days
Number of potential
no-spill days
Number of potential spill
days < 75 cfs
Table II-6. Analysis of spill days and volume by month for a power plant
operation at 100 cfs.
II-22
Thayer Creek water and air temperatures
The Solinst dataloggers measure water temperature at the same time as pressure.
Temperature is averaged for 30 minute blocks of time and recorded in in the datalogger. Air
temperature at Thayer Creek was recorded along with barometric pressure about 300 ft.
upstream of the mouth of the creek.
Average daily water temperatures for the dam site on Thayer Creek are shown in Figure II-18.
Temperatures begin rising in April, and continue until June. Temperatures begin falling in
September, and continue to fall until November. Water temperatures are typically above
freezing (1-
summer. The temperature profile is shown in Figure II-19 in 30 minute intervals. This
projection shows the amount of daily temperature variation that occurs, since both high and
low temperatures (and everything in between) are displayed). The summer high temperature
This temperature data indicated that daily temperature variations are greatest in the spring and
summer, and least in the fall and winter. Daily temperatures fluctuations of 3-
less.
II-23
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
17.5
18
18.5
19
4/16/2013 5/16/2013 6/16/2013 7/16/2013 8/16/2013 9/16/2013 10/16/2013 11/16/2013 12/16/2013 1/16/2014 2/16/2014 3/16/20144-16-13 5-16-13 6-16-13 7-16-13 8 -16-13 9-16-13 10-16-13 11-16-13 12-16-13 1-16-14 2-16-14 3-16-14
Daily water temperaturein Thayer Creek April 2013 through March 2014
Figure II-18. Annual average daily water temperature record for the dam site on Thayer Creek.
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
19.00
20.00
4/16/2013 5/16/2013 6/16/2013 7/16/2013 8/16/2013 9/16/2013 10/16/2013 11/16/2013 12/16/2013 1/16/2014 2/16/2014 3/16/2014
30 minute dam site water temperature
measurements, April 2013 -March 2014
Figure II-19. 30 minute interval annual temperature records for the dam site on Thayer Creek.
II-21
II-24
Short term temperature records are shown in Figures II-20 and II-21. The temperature record
for August, 2013 is compared with the air temperature record for the same period in Figure II-
20. The daily oscillation in water temperature is quite obvious in the figure, with daily water
temperatures ranging from 15.5 to 19.2 C and changes of 2.8-
temperatures show a similar pattern that generally follows that of water. However, air
temperatures are cooler that those in the water. This is thought to be due to lake effect on the
stream. Thayer Lake has a large surface area and can capture considerable heat which is
dissipated on a different timeframe than being measured here on a daily basis. The net effect
of this is generally elevated water temperatures through the summer compared to local air
temperatures near the beach. The 30 minute water and air temperature records for the
month of June 2013 are shown in Figure II-21. In this case a strong correlation exists between
air and water temperature, with both following the same trajectory and range of temperatures.
However, in mid-June the two records begin to grow apart as lake effect warming starts
influencing the water temperature record and push it higher than those of the coastal air. Daily
oscillations are also subdued in the June record compared to those shown in August.
The 30 minute air temperature record is shown in Figure II-22. Below zero temperatures are
recorded from November through April. Temperatures as low as -14 to -16 C (3-
during this timeframe. High temperatures of 17--
months. The air temperature for 2014/2015 is shown in figure II-23. The summer
temperatures are similar to those in 2013/2014. However, the winter temperatures from
November through March indicate that the winter of 2013/2014 was much colder than the
while for the same period in 2013/2014 it was -
When the water and air temperature records are overlapped (Figure II-24) the lake effect
shows up clearly. Air temperature is the major influence on water temperature in the spring.
Lake effect influences on water temperature occurs in the summer. As air temperatures begin
to drop in the fall the lake effect produces a lag in water temperature keeping it higher than air
temperatures. In the winter lake effect damps out any significant cooling from super-cold air
temperatures.
II-25
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
17.5
18
18.5
19
19.5
20
Water temperature record for August 2013
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
average water flow
100 cfs
Figure II-20. Comparison of 30 minute interval water and air temperatures for August.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Water Temperature record for June 2013
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Average water
flow 560 cfs
Figure II-21. Comparison of 30 minute interval water and air temperatures for June.
C
C
II-26
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Air temperature April 2013 to April 2014
APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR
Figure II-22. 30 minute interval annual air temperature record for Thayer Creek, 2013/2014.
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Figure II-23. 30 minute interval annual air temperature record for Thayer Creek, 2014/2015.
C
II-27
Air temperature April 2014 to April 2015
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
18
20
air temp
water temp
Figure II-24. Comparison of 30 minute interval annual water and air temperature records.
Local Weather Conditions
Both air and barometric pressure data was collected at the mouth of Thayer Creek. In addition
historical weather records collected at the Angoon power plant were used to supplement the
temperature and pressure data. Temperature data was presented in the previous section. In
ds frequently -8 to -
barometric pressure is shown in Figure II-25 for 2013/2014. The annual average pressure is
1013 mbar, and ranges from 975 to 1038 mbar. The record shows roughly 13 high pressure
systems (greater than 1025mbar) and a dozen low pressure systems (less than 995mbar)
occurred during the year. The strongest lows occurred in September and the winter months,
while the strongest highs occurred in April, May, October, and the winter months.
Local barometric pressure for 2014/2015 is shown in figure II-26. The annual average pressure
was 1012, and ranged from 974 to 1044, similar to the previous year. The record showed
roughly 11 high pressure systems (greater than 1025mbar) and 10 low pressure systems (less
II-28
than 995 mbar), again similar to 2013/2014. In contrast to 2013/2014, the record in 2014/2015
showed an extended low pressure system (less than 995 mbar) from October 17th to 22nd and
an extended high pressure system (greater than 1020 mbar) from February 20 to March 3rd.
The strongest lows occurred in September, October and February, while the strongest highs
occurred in November, January and February.
II-29
Figure II-25. Barometric pressure record from the mouth of Thayer Creek, 2013/2014. II-30
Figure II-26. Barometric pressure record from the mouth of Thayer Creek, 2014/2015. II-31
Precipitation records for the area were constructed from 9 years of records (2010, 2006, 2005,
2004, 2003, 1960, 1959, 1958, and 1957) to gather at least 5 records for each month of the year
(Table II-7). The data was then averaged to produce monthly values for rainfall and snowfall.
Based on this compilation of historical records (Source: NOAA Historical database for Alaska-
Angoon Powerhouse) the average annual Angoon rainfall precipitation is 38.3 inches. The
average annual snowfall precipitation is 25 inches. However, Angoon exists in a local rain
shadow, so these values might be lower than the amounts of precipitation received at Thayer
Creek which is 7 miles north of Angoon. Generally more than 3 inches of rain falls each month
from September through January. The lowest rainfall occurs from April through June when less
than 2 inches falls each month. Based on these rainfall records, the high stream flows measured
in May are largely due to spring thaw and snowmelt, not rainfall.
The snowfall records are highly variable and range from zero in each month to as high as 36.1
inches in any given year. The maximum snow values may be a more realistic projection of
snowfall conditions at Thayer Creek than the annual average values, which would indicate
substantial snowfalls can be expected to occur in any given year from December through
March.
Table II-7. Average monthly rainfall and snowfall records compiled for Angoon,
Alaska.
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Ave
Rainfall
(inches)
3.23 1.65 2.44 1.71 1.65 1.78 2.26 2.68 5.14 5.9 5.99 3.83
Ave
Snowfall
(inches)
13.8 2.4 2.9 0 0 0 0 0 0 0.4 0.8 5.1
Max
snowfall
(inches)
36.1 9.5 13.1 2.2 1.8 13.1
II-32
Tributary flows into the Thayer Creek Gorge
The EIS had recommended a bypass flow of 20-40 cfs in the Thayer Creek gorge to maintain
wintering habitat, maintain pool depths, provide greater stream connectivity, and decreasing
harmful icing conditions on overwintering fish (USDA, USFS, 2009). These recommendations
were based on the assumptions that fish overwintering occurs in the gorge and some minimal
population of resident fish exists in the gorge. While a few fish occur in the gorge, they appear
to be transients moving through the gorge after moving downstream and passing over the first
barrier falls below the dam site, and not residing in the gorge for any significant period of time
(see the fisheries section). Based on existing fall and winter water flows, October to January
maximum daily flows of 630-920 cfs, and average daily flows of 445-660 cfs, the extensive
occurrence of scoured bedrock substrate, and numerous falls and velocity barriers, there is no
overwintering habitat or resident fish population within the gorge. That aside, there are
additional water flow contributions occurring within the gorge that contribute to stream flows,
and would contribute to a base flow during the four months when little or no water is
bypassed by the project (see earlier discussion in the streamflow assessment subsection). A
total of 28 contributing tributary streams were identified within the Thayer Creek gorge (Figure
II-27). Three of them (T1, T2, and T3) contribute 74% of the water flow, and the remaining 25
contribute the remaining 26%.
II-33
Figure II-27. Tributaries contributing water flows to the Thayer Creek gorge. T-1, T-2 and T-3 contribute 74% of the water flow. T-1T-2 T-3 Dam siteBarrier falls II-34
Observed flows, and maximum and minimum estimated water flows from these 28 streams is summarized in
Table II-8. In April 2013 observed flows contributed 10-16.5 cfs to the gorge. This was a period of frequent
precipitation, and occasional heavy rainfall. Low flows were estimated from observations in the summer
during a period of relatively dry weather. Maximum flows were based on stream high bankfull conditions and
monthly rainfall totals. Only 3 tributaries contribute substantial flows to the gorge. Tributary T-3 is the most
important contributing 40% of the water flow. The stream is 8-15 ft. wide and has a bank full depth of 18-24
inches. It is a well- defined deeply incised stream channel that carries substantial sediment, including cobble
sized particles. Maximum water flows were estimated at more than 15 cfs, but flows of less than 1 cfs have
been observed in the stream. During normal weather conditions flows are expected to be in the range of 3-5
cfs. Tributary T-2 is a perennial flow that drains a beaver pond complex. There is a substantial thalweg flow in
this small stream. Observed surface flows were in the range of 2-3 cfs at the beaver ponds. High flows were
estimated to be in the range of 5 cfs. Tributary T-1 is a complex of 3 small streams on the east side of the
creek. Each appears to contribute about 1 cfs. These streams cascade down the slope into the creek without
a clear channel formed near the stream. The remaining streams fall into two categories, those with channel
widths greater than 2 ft., and those smaller than 2 ft. The small streams with larger channels showed flows
ranging from 0.1 to 0.5 cfs. The smallest channel streams showed flows of 0.1 to 0.3 cfs. Generally highest
water flows would occur during rainfall events. Cumulatively, during dry spells water flows may be on the
order of 5-6.5 cfs, but under normal weather conditions flows of 10+ cfs can be expected.
II-35
Table II-8. Summary of Tributary Flows to the Thayer Creek Gorge.
Tributary Description Observed flows Estimated low
flow
Estimated max
flow
T-1 3 streams within 100 ft.
of each other flowing
down slope
1-2 cfs in each
stream
< 3 cfs 6-8 cfs
T-2 Stream drains wetland
beaver pond complex;
deeply incised channel
below beaver ponds,
lots of large and small
woody debris in
channel, channel width
3-8 ft.
2-3 cfs < 1 cfs 5+ cfs
T-3 Well-developed channel
8-15 ft. wide, sand,
gravel, cobble present
in channel; flows over
bedrock in some
locations
3-5 cfs < 1 cfs 15+ cfs
B-1/B-2
area
9 small tributaries,
channels less than 2 ft.
wide
Cumulative 1-1.5
cfs
Cumulative < 0.5
cfs
Cumulative 2-3
cfs
B-4 area 13 small tributaries
channels range from < 2
ft. up to 4 ft. wide
Cumulative 3-5
cfs
Cumulative < 1
cfs
Cumulative 7-9
cfs
Cumulative
flows
All 28 tributaries 10-16.5 cfs < 6.5 cfs 35-40 cfs
II 36
II-36
Section III - Lower Thayer Creek Drainage Fisheries Surveys
Overview
Fishery habitat, fish distributions and potential hydro project impacts have been analyzed and
presented in the Angoon Hydroelectric project EIS (USDA, USFS, 2009). However, much still
remains unknown about fishery values and uses in the lower Thayer Creek drainage. The
anadromous section of Thayer Creek covers less than 2,000 ft. of stream from tidewater to a
fish barrier upstream. The anadromous reach is variously described as 1,000 to 1250 ft. long
from the upper end of a tidal island at the mouth of the stream to the barrier falls. Limited
fisheries data is available for the anadromous reach, with the ADFG Anadromous Catalog listing
Pink and Chum Salmon in Thayer Creek. USFS sampling of the anadromous reach in 2004
indicated the presence of Coho Salmon and juvenile Steelhead trout in the creek (USDA, USFS,
2009). Based on these species presence, the USFS concluded it was likely that spawning and
rearing is likely for Chum, Pink, and Coho salmon, and Dolly Varden; and seasonal rearing
habitat use by Steelhead, Cutthroat Trout and Coho salmon occurs. There has been no fishery
sampling in the gorge, but assessment of the gorge by both the USFS and Harza (1995) from the
upper slopes concluded that habitat was poor and extremely limited for rearing and holding
habitat. However, a small resident population might exist in the gorge. Upstream of the gorge
the primary species present is Cutthroat Trout originating from Thayer Lake (USDA, USFS,
2009).
In 2013, Shipley Group began fishery studies within the lower Thayer Creek drainage to expand
information on fish occurrence and use of the anadromous reach; assess the habitat, residency,
and use of the gorge by fish; and assess the resident fish population potentially affected by the
hydro project immediately above the gorge. Fish sampling using small and large minnow traps,
oval fish traps, dip nets, and hook and line techniques were conducted throughout the
anadromous reach, within the lower portion of the gorge, and above the gorge to the first
major bend in the stream (Figure III-1). Approximately 2,000 ft. of the gorge immediately
below the proposed dam site is inaccessible due to cliffs and extremely steep slopes. The rest
of the gorge could be accessed when water flows were less than approximately 125 cfs using
ropes to traverse the slopes to the stream and then moving along the shoreline adjacent to the
creek or crossing the stream at riffles and moving along the opposite shoreline. However, at
higher flows crossing the stream would not be possible and access to the stream channel would
be treacherous. Adult fish escapement surveys were also conducted in the anadromous reach
in August, September, and October for the past 2 years.
III-1
2013 Fish Sampling Results
A total of three separate fishing efforts were conducted at Thayer Creek in 2013. Fish surveys
were completed in April, June, and August. The anadromous reach was fished on multiple
occasions, the gorge once, and the area above the gorge on multiple occasions (Figure III-1).
Minnow trapping, oval fish traps and angling techniques were used in the April survey, while
only angling was used in June. The August survey used angling techniques and dip nets. The
trapping effort in April was conducted using commercially prepared salmon roe to bait large
and small minnow traps, as well as oval fish traps. Angling was conducted using flies and lures.
A dip net was used in August to collect fry observed along the shoreline in the anadromous
reach of the stream. No fry were observed in Thayer Creek above the gorge in June or August
surveys. A summary catch report for 2013 is contained in Appendix III-1. All fish were
identified and released back into Thayer Creek in the areas where they were captured.
Figure III-1. Lower Thayer Creek drainage showing the areas sampled by Shipley Group in
2013 and 2014. The upper portion of the gorge is inaccessible and was not sampled.
III-2
A summary of the catch data is shown in Table III-1 by area. A total of 68 fish were captured
during the 3 surveys. We could not access the upper 2,000 ft. of the gorge area of the creek in
reach R-3 due to extensive cliffs and near vertical slopes on the north side of the creek. The
Coho salmon reported in the anadromous reach were all captured with a dip net, and were
tentatively identified as either newly emerged Coho salmon fry or Cutthroat Trout fry. All of
the fry were less than 40 mm in length and very easy to catch. A specific sampling effort was
planned for the summer of 2014 to positively identify these fry (see the next section- 2014 Fish
Sampling Results).
A total of 5 Dolly Varden were captured in traps above the gorge in a small tributary creek
flowing into Thayer Creek from the north side (Figure III-2). These are from a landlocked
population of Dolly Varden that has not been reported as present in Thayer Creek before.
These fish ranged in size from 85 to 152 mm. One Dolly Varden was also caught in Thayer
Creek using angling techniques in the June survey near the dam site. Trapping in Thayer Creek
upstream to the first major bend in the stream only yielded Cutthroat Trout. A total of 6
Cutthroat Trout were also caught in traps in April in this tributary creek. Another 23 Cutthroat
Trout were caught above the gorge in Thayer Creek in June and August by angling methods
(Figure III-3). The largest was 13 inches (330 mm) long. Three-spined Sticklebacks were also
found in Thayer Creek and the tributary creek on the north side above the gorge.
In the anadromous reach a total of 14 rainbow trout (Figure III-4), 10 coastrange Sculpin, one
Cutthroat trout (Figure III-5), and 4 Coho salmon were captures. In early August, we also found
fry in the anadromous reach which were sampled with a dipnet. Pictures taken in the field
were ambiguous so the fish were tentatively identified as either late emerging Coho salmon fry
or cutthroat trout fry (Figure III-6). All of the fry were less than 40 mm long.
Although extensive trapping was conducted in the lower gorge area, only one Cutthroat trout
was captured at a location near the bottom of the gorge. It was caught in a submerged root
wad, one of only two we found in the gorge, and showed signs of abrasion with missing scales,
and several tears in its fins. Trapping occurred in the lower gorge from just above the
anadromous barrier at the top end of reach R-1, up to the T-2 tributary at the top of the lower
reach of the gorge, a distance of over 4,000 ft. The gorge was inaccessible above this point.
III-3
Figure III-2. Dolly Varden captured in Thayer Creek above the gorge.
Figure III-3. Cutthroat Trout captured above the gorge in Thayer Creek
III-4
Figure III-4. Rainbow Trout (~106 mm) captured in the anadromous reach in April, 2013.
Figure III-5. Cutthroat Trout (~110 mm) captured in the anadromous reach in April 2013.
III-5
Figure III-6. Coho or Cutthroat Trout fry (< 40 mm long) observed in Thayer Creek in early
August 2013.
Table III-1. Summary of fish catches by location in Thayer Creek for all collection
methods in 2013.
species R-1 mouth of
creek to gorge
R-2 lower
gorge
R-3 upper
gorge
R-4 above
gorge
Total catch
Cutthroat
Trout
1 1 - 29 31
Rainbow
Trout
14 0 -0 14
Dolly Varden 0 0 - 6 6
Coho Salmon 4 0 -0 4
Coastrange
Sculpin
10 0 - 0 10
Three-spined
Stickleback
0 0 - 3 3
Total catch 29 1 -38 68
The results of angling are shown in Table III-2. A total of three sampling efforts were conducted
above the gorge in the reach known to contain Cutthroat trout. No fish were captured in April,
III-6
but moderate numbers were captured in the other two periods in mid-summer (Figure III-7).
Angling also occurred in the anadromous reach at the mouth of the creek in April. Two rainbow
trout were captured during that effort, both in the plunge pool at the barrier falls.
Within the 7,300 ft. long gorge there are at least 6 falls greater than 10 ft. in height. The top of
the gorge is a long cascading falls over bedrock (50-75 ft. long) with a slope of 80%; and the
bottom end of the gorge is a 50 ft. length of stream containing 3 large falls, with an average
slope of 60%. In addition there are numerous velocity barriers that occur during high water
flow events. Most of the upper gorge in reach 3 (2,000 ft. long) is cliffs of more than 25 ft. on
the north side of the creek and near vertical slopes or cliffs on the south side. If access to the
creek is achieved, you cannot move up or downstream from that access location. The lower
gorge is not much better than the upper gorge. However, we were able to access more than
half of the gorge from three access points on the north side when water flows were less than
125 cfs. At higher stream flows access in the lower gorge would be minimal, as well.
Table 2. Angling success in area R-4 above the gorge in 2013.
Date Dolly Varden Cutthroat trout
April 4, 2013 0 0
June 30, 2013 1 8
August 11, 2013 0 15
Accessible habitat in the gorge is dominated by scoured bedrock pools separated by short
rapids flowing over bedrock, and occasional deeper runs over bedrock. Boulders and large
Figure III-7. A Cutthroat
Trout caught above the
gorge in August 2013 on an
artificial dry fly.
III-7
cobble occur in slower moving sections of the stream, mostly near bends and eddy areas.
Gravels and sands are limited to deposits in the higher littoral areas and in back eddy areas of
pools. Although large amounts of large woody debris are present along the sides of the stream,
little of it is actually in the water, and what is in the water has most branches and bark stripped
away. Root wads, when present provide the best habitat, but only two were observed in the
water. The only fish captured in the gorge was caught in a root wad at the edge of a deeply
scoured pool. Cobble and gravel substrate in the creek bed is only present over a distance of
600-800 ft. in the area of the gorge between T-2 and T-1, a relatively low gradient (3%) portion
of the gorge. This area was trapped with no success in April.
During high water flows there would be little, if any, habitat to sustain a resident fish
population within the gorge. The pools, runs and riffles in the creek bed were all scoured
bedrock, except in the one section noted above. Our observations in the gorge were made in
April at flows less than 125 cfs, but we measured flows above the gorge in October at 676 cfs,
and the highest flows recorded by our stream gages were near 1,150 cfs. Since the gorge is also
deeply incised, with near vertical slopes the stream channel is very narrow and does not
increase substantially with increased flows. The scoured streambed is evidence of the strong
velocities reached in the stream under high water flows. Overall, the gorge was rated as poor
habitat to support any long term residency of fish. Fish in the gorge would be short term
transients moving downstream into the gorge, and present only in the summer (July/August)
and winter (March/April) low flow periods. However, since a single fish was caught near the
bottom of the gorge in April it indicates that fish are able to pass through the gorge to the
anadromous reach at the mouth of the stream.
2014 Fish Sampling Results
Two fishing efforts were conducted in 2014, the first one in early August in conjunction with
ADF&G staff, and the second one in October. The August survey consisted of electrofishing in
the anadromous reach and above the gorge in the north tributary and mainstem of Thayer
Creek by ADF&G, and dip netting in the anadromous reach by the Shipley field crew. The
report by ADF&G staff on their sampling effort is included in Appendix III-2. In addition, Shipley
conducted a fall minnow trapping survey of the anadromous reach. A summary of catch data
for 2014 is contained in Appendix III-3. Due to high water conditions encountered in October
(near bankfull water flows) only the south shoreline in zones II, III, and IV of the anadromous
reach were sampled.
In reach R-4 the electrofishing effort was concentrated in a small tributary stream flowing into
Thayer Creek from the north just above the proposed dam site where both Dolly Varden and
Cutthroat trout had been captured in 2013. A total of 6 Cutthroat Trout and 7 Dolly Varden
were caught in this small tributary (Table III-3). In addition one Cutthroat Trout was captured in
III-8
Thayer Creek. In the anadromous reach a total of 14 fish were captured (Table III-3). These
included 10 Cutthroat Trout and one Coho Salmon.
At the same time in in the anadromous reach, Shipley conducted a dipnet sampling effort along
the south shoreline in a back channel between the small island straddling the downstream
boundary of zone IV (Figure III-8). A total of 19 fish were captured in this side channel
consisting of 3 Dolly Varden, 2 Coho Salmon, and 14
Figure III-8. Area fished with a dipnet in 2014.
Cutthroat trout (Table III-3). The 2 Coho
Salmon were both 60 mm long (Figure III-9),
while the Cutthroat Trout were all less than
40 mm (Figures III-10 and III-11). We used a
small plastic aquarium to suspend fish in
stream water after capture which facilitated
recognition of key features for positive
identification. Based on the fry observations
in 2014 the fry observed in 2013 (see Figure
III-6) were Cutthroat Trout and not Coho
salmon fry. The Dolly Varden captured by
dipnet were approximately 51 mm long
(Figure III-12). Fish were captured both
within and below zone IV. Most of these
fish were young of the year (Figures III-9 to
III-12). All of these fish were captured below
MHHW in the intertidal zone indicating that
the stream below zone IV is used as rearing
habitat by juvenile fish in Thayer Creek.
III-9
Table III-3. Summary of fish catches by location in Thayer Creek for all collection
methods in 2014.
species R-1 mouth of
creek to gorge -
August
(electrofish*)
R-1 mouth of
creek to gorge -
August
(Dipnet)
R-1 mouth of
creek to gorge
– October
(minnow trap)
R-4 above
gorge - August
(electrofish*)
Total
catch
Cutthroat
Trout
10 13 18 7 48
Rainbow
Trout
0 0 11 0 11
Dolly
Varden
0 2 0 7 9
Coho
Salmon
1 2 19 0 22
Coastrange
Sculpin
2 0 0 0 2
sole 1 0 0 0 1
Total catch 14 17 48 14 93
III-9
Figure III-9. Coho Salmon (60 mm) captured below zone IV in Thayer Creek August 11, 2014.
III-10
Figure III-10. Cutthroat Trout (<40 mm) captured below zone IV in Thayer Creek August 11,
2014.
Figure III-11. Cutthroat Trout (<40 mm) captured below zone IV in Thayer Creek August 11,
2014.
Figure III-12. Dolly Varden (51 mm) captured below zone IV in Thayer Creek August 11, 2014.
III-10
III-11
Based on the two years of fish sampling in Thayer Creek Cutthroat Trout are the most abundant
fish above the gorge, but there is also a small population of landlocked Dolly Varden in the
Creek. Also present are three-spined stickleback. Unless there is a fish barrier in Thayer Creek
below Thayer Lake and the gorge there is no reason why the Dolly Varden would not also be
found throughout the entire upstream drainage above the gorge. The gorge from the barrier
falls upstream to the entry of the T-2 tributary was fished in the spring of 2013. Only one fish
was captured in this section of the stream. The habitat in this section was considered generally
poor, capable of supporting transient fish moving downstream, but not able to support long
term residency of fish. Most of the stream is scoured riffles, pools and runs over bedrock with a
few boulders, cobble and large woody debris. There are numerous falls and velocity barriers
throughout the gorge.
The anadromous reach supports a variety of fish that use the stream as spawning and rearing
habitat including Cutthroat Trout, Rainbow/steelhead Trout, Dolly Varden, and Coho Salmon.
Based on juvenile fish capture in traps, Rainbow/steelhead Trout appear to be the most
abundant fish in the stream. However, based on fry observations, Cutthroat Trout would
appear to be the most abundant species in the stream. However, juvenile Cutthroat Trout are
not showing up in the trap data, with only one fish captured so far in the anadromous reach.
Finally, rearing habitat extends at least to MHW at the mouth of the creek.
2015 Fish Sampling Results
An early spring juvenile fish sampling effort was conducted April 8-11, 2015 in the anadromous
reach and above the gorge on Thayer Creek. Emphasis was placed on identifying juvenile fish in
the anadromous reach since only one Cutthroat Trout (110 mm long) was identified in the
previous April survey in 2013 (Figure III-5). This could have been due to misidentification of
small Cutthroat Trout which can be very hard to distinguish from Rainbow Trout when they are
less than 100-120 mm in length (Pollard et. al., 1997).
The results of the 2015 survey are summarized in Table III-4. A total of 27 fish were captured in
three days of fishing, two above the gorge and one day in the anadromous reach. The trapping
effort was extended by 24 hours due to a weather delay that prevented us from recovering the
traps after 24 hours of fishing effort above the gorge. As in the past, both Cutthroat Trout and
Dolly Varden were captured in Thayer Creek above the gorge. The Cutthroat trout were
captured in a small tributary stream while the Dolly Varden were captured in Thayer Creek.
III-12
Table III-4. Summary of fish catches by location in Thayer Creek in 2015.
Species Above Gorge Anadromous
reach
Total catch
Cutthroat Trout 4 15 19
Dolly Varden 2 - 2
Rainbow Trout - 3 3
Coho Salmon - 3 3
Total catch 6 21 27
In the anadromous reach juvenile Coho Salmon, Rainbow Trout, and Cutthroat Trout were
captured. Cutthroat Trout comprised 71% of the catch, while Rainbow Trout and Coho Salmon
each represented 14.5% of the total catch. In 2014 59% of the juvenile fish in the anadromous
reach were Cutthroat Trout, while 14% were Rainbow Trout, and 27% Coho Salmon. Based on
these results, it is probable that some of the 14 Rainbow Trout identified in the 2013 surveys in
the anadromous reach were, in fact, small Cutthroat Trout.
Adult Fish Escapement Surveys
Adult fish escapement surveys have been conducted for the past two years on the anadromous
reach of Thayer Creek. The creek is locally referred to as “Humpy Creek” by Angoon residents
(Gabriel John, personal communication). Angoon residents occasionally fish for halibut, and
troll for King Salmon and Coho Salmon in the vicinity of Thayer Creek. We were also told by
several residents of Angoon that one of the local fishing guides has occasionally guided
fishermen on the creek in May fishing for Steelhead. We have looked for Steelhead in the
stream in April surveys in 2013, 2014, and 2015, but have not seen any yet.
Escapement surveys in 2013 were conducted in August and October (Table III-5). The
anadromous reach varies from 80-100 ft. over most of its length. However, near MHHW the
stream broadens out to more than 190 ft. wide. Water flow conditions were generally low
and clear in August (flows near 100 cfs,) making for excellent observation conditions (Figures III-
13 and III-14). However, in October flows were high and observation conditions were difficult
since the water was deep and the stream could not be waded.
III-13
The 2013 survey occurred during a high return year for Pink salmon (Table III-6), with more than
58,000 counted in the 5 surveys completed on the stream. . Pink Salmon were present in high
numbers throughout the anadromous reach, as well as in the intertidal portion of the stream
(Table III-6). The August Pink salmon survey counts ranged from 9,458 to 16,371, while in
October the count had dropped to 638 fish. However, Chum, Coho, King, and Sockeye salmon
were also present in small numbers (Table III-5). A few Cutthroat trout were also seen in the
stream in August. Overall, Pink salmon accounted for 99.8% of the fish, and all others
collectively, 0.2%. Both Pink and Chum salmon carcasses were seen in the stream during the
surveys (Figures III-15 and III-16).
III-14
Figure III-13. Pink Salmon lying in the run in Zone IV in early August 2013 when water flows
were 100 cfs. The rope on the right side of the photo is the water profile location near the
mouth of Thayer Creek.
III-15
Figure III-14. Pink Salmon in zone I, just below the plunge pool in August 2013 when water
flows were 100 cfs.
live dead live dead live dead live dead live dead live dead
13,305 131 7 2
9,458 333 10 1 6 1 1
15,995 498 3 1 6 35
16,371 756 2
638 646 32
55,767 2,364 20 2 40 8 1 1 35
Cutthroat Trout Total Count
13,445
Pink Salmon Chum Salmon Coho Salmon
Sockeye
Salmon King SalmonDate
10-Aug-13
12-Aug-13
27-Aug-13
20-Aug-13
58,238total count
9,810
16,538
6-Oct-13 1,316
17,129
III-16
Table III-5. Total fish counts for Thayer Creek anadromous reach, 2013.
Table III-6. Pink Salmon counts by segment in the Anadromous reach, 2013.
live dead live dead live dead live dead live dead live dead
3,150 4 3,915 30 1,714 26 3,830 28 696 43 13,305 131
3,041 5 2,417 58 1,847 82 1,683 52 470 136 9,458 333
4,162 32 2,856 183 2,614 116 2,978 32 3,385 135 15,995 498
3,742 110 3,328 112 2,982 138 3,422 183 2,897 213 16,371 756
28 0 168 10 288 340 74 242 80 54 638 646
14,123 151 12,684 393 9,445 702 11,987 537 7,528 581 55,767 2,364total count
segment 1
zone I
Segment 2
Zone II
Segment 2
Zone II
Segment 4
zone IV
Segment 5
intertidal total countDate
6-Oct-13
10-Aug-13
12-Aug-13
20-Aug-13
27-Aug-13
Figure III-15. Pink salmon carcasses littering the shoreline of the stream in August.
III-17
Figure III-16. A Chum Salmon carcass on the streambank in zone III.
Escapement surveys in 2014 were conducted in September and October (Table III-7). In
contrast to 2013, water flows in 2014 all appeared to be in excess of 500 cfs during the surveys
(Figure III-17), and were measured at 1025 cfs (near bankfull conditions) on the October 4th
survey (Figure III-18). Due to the high water conditions it was not possible to survey more than
about the lower 100 ft. of zone I at the top of the anadromous reach, so no counts were
obtained of fish near or at the plunge pool and barrier falls. However, in early August several
hundred Pink salmon were seen in the creek, and observed jumping at the barrier falls (Figure
III-19). It was also not possible to wade into the creek during the surveys, so all observations
were made by walking the south bank which made observations in mid- and far-channel areas
impossible under these high flow conditions.
III-18
Figure III-17. Water conditions in Zone III in September 2014; water flows are within a few
inches of bankfull conditions.
Figure III-18. Barrier falls on Thayer Creek at a flow rate of 1,025 cfs in October, 2014.
III-19
Figure III-19. Pink Salmon attempting to jump barrier falls in early August 2014. Water flow at
this time was approximately 260 cfs.
In contrast to 2013, Pink Salmon returns were low in 2014 (Table III-7). We had also scheduled
surveys to cover September and October, rather than August and October as conducted in
2013, with the October survey specifically targeting Coho Salmon. Pink Salmon were observed
in the stream in early August. A few hundred fish were estimated to be in the stream, but no
counts were made. Small schools of 6-20 Pink Salmon were seen throughout the anadromous
reach; and fish were commonly seen attempting to jump the barrier falls (Figure III-20). At the
same time in 2013, 13,000 pink salmon were estimated to be in the stream (see Figure III-13).
Two Sockeye Salmon were also observed in the Creek in early August, 2014, but were not seen
in the September surveys. Pink Salmon, as in 2013, still accounted for 99% of the fish
observations on the stream; with Coho Salmon making up the remaining 1%. Pink Salmon
were also distributed throughout the anadromous reach even though the numbers were very
low (Table III-8). Notably, no Chum Salmon were seen in the 2014 surveys. They may be
present only in the early part of the run in August (as in 2013) and had already spawned by the
time counts were initiated in 2014.
III-20
Table III-7. Total fish counts for Thayer Creek anadromous reach, 2014.
live dead live dead live dead live dead live dead live dead
88 10
131 46 1
0 14 1
2 0 1
221 70 3
Date Cutthroat Trout Total Count
30-Aug-14 98
Pink Salmon Chum Salmon Coho Salmon
Sockeye
Salmon King Salmon
294
12-Sep-14 178
29-Sep-14 15
4-Oct-14 3
Table III-8. Pink Salmon counts by segment in the Anadromous reach, 2014
live dead live dead live dead live dead live dead live dead
20+ 1 21 2 23 3 18 2 6 2 88 10
40 11 22 13 13 6 38 12 18 4 131 46
2 1 3 6 2 0 14
1 1 2 0
60+ 14 43 16 37 12 57 20 24 8 221 70
Segment 5
intertidal total count
Segment 2
Zone II
Segment 2
Zone II
Segment 4
zone IV
29-Sep-14
4-Oct-14
30-Aug-14
12-Sep-14
Date
segment 1
zone I
total count
The anadromous reach of Thayer Creek supports a robust population of Pink Salmon in odd
numbered years of spawning. In even numbered years the pink salmon run appears to be at
least an order of magnitude smaller. In addition, a small number of Chum and Coho salmon
spawn the stream every year. Both King and Sockeye salmon have been observed in the river
as well, but we have seen no evidence that they spawn in Thayer Creek. The main run of Pink
salmon appears to occur in August and tails off after that. Chum salmon also appear to spawn
in August. Coho Salmon appear to spawn in September and October. Although the
anadromous reach was casually surveyed for Steelhead during field efforts in April of 2013 and
2015, Steelhead were not seen in the creek. Smaller fish, probably adult Cutthroat or Rainbow
Trout, have been observed in the creek during the same timeframe.
III-21
Section IV - References
Harza Northwest, Inc., 1995. Thayer Creek field survey preliminary fish habitat assessment:
Angoon Hydroelectric Project engineering field trip report Angoon Hydroelectric
Project, geologic and geotechnical engineering field trip report (G. Gilmour, A. Liou, and
N. Dbaibo). October 18, 1995.
HDR Alaska, Inc. 2003. Thayer Creek Station water years 1999, 2000, 2001 streamflow
analysis. Prepared for Kootznoowoo Inc. June, 2003.
Kondolf, G. M., and M. G. Wolman. 1993. The Sizes of Salmonid Spawning Gravels. Water
Resources Research. Vol. 29, no. 7: 2275-2285. July, 1993.
Lotspiech, F. P., and F. H. Everest. 1981. A New method for Reporting and Interpreting
textural Composition of Spawning Gravel. USDA Forest Service, Pacific Northwest Forest
and Range Experiment Station, Research Note PNW-369. January 1981, 11 pp.
Mecklenburg, C. W., T. A. Mecklenburg, and L. K. Thorsteinson. 2002. Fishes of Alaska.
American Fisheries Society, Bethesda, Maryland. 1037 pp.
USDA Forest Service. 1992. A Channel Type Users Guide for the Tongass National Forest,
Southeast Alaska. (By: Paustian, S. J., K. Anderson, D. Blanchet, S. Brady, M. Cropley, J.
Edgington, J. Fryxell, G. Johnejack, D, Kelliher, M. Kuehn, S. Maki, R. olson, J. Seesz, and
M. Wolanek). USDA Forest Service, Alaska Region, R10, Technical Paper 26. April, 1992.
USDA Forest Service. 2009. Angoon Hydroelectric Project Final Environmental Impact
Statement. Tongass National Forest, Admiralty island National Monument, Juneau,
Alaska. Tongass National Forest, R10-MB-628, February, 2009.
IV-1
APPENDIX II-3
CALIBRATION CURVE AND DEPTH/CFS CONVERSION TABLE
FOR THAYER CREEK ABOVE THE GORGE
ftcfsdate meter depth measured cfs8/11/2013 1 120.34/21/2013 1.42 206.6 4/20/2013 1.44 222.6 4/10/2014 1.78 352.86/30/2013 1.92 385.2 10/5/2013 2.94 676.1
Calibration table for meter at dam site above gorge
Matrix data in cfs; X/Y in depth (ft)
0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69
5.60 1155
5.50 1135 1137 1139 1141 1143 1145 1147 1149 1151 1153
5.40 1115 1117 1119 1121 1123 1125 1127 1129 1131 1133
5.30 1095 1097 1099 1101 1103 1105 1107 1109 1111 1113
5.20 1070 1073 1075 1078 1080 1083 1085 1088 1090 1093
5.10 1050 1052 1054 1056 1058 1060 1062 1064 1066 1068
5.00 1030 1032 1034 1036 1038 1040 1042 1044 1046 1048
4.90 1005 1008 1010 1013 1015 1018 1020 1023 1025 1028
4.80 980 983 985 988 990 993 995 998 1000 1003
4.70 960 962 964 966 968 970 972 974 976 978
4.60 935 938 940 943 945 948 950 953 955 958
4.50 915 917 919 921 923 925 927 929 931 933
4.40 890 893 895 898 900 903 905 908 910 913
4.30 870 872 874 876 878 880 882 884 886 888
4.20 845 848 850 853 855 858 860 863 865 868
4.10 825 827 829 831 833 835 837 839 841 843
4.00 805 807 809 811 813 815 817 819 821 823
3.90 780 783 785 788 790 793 795 798 800 803
3.80 760 762 764 766 768 770 772 774 776 778
3.70 735 738 740 743 745 748 750 753 755 758
3.60 715 717 719 721 723 725 727 729 731 733
3.50 695 697 699 701 703 705 707 709 711 713
3.40 675 677 679 681 683 685 687 689 691 693
3.30 650 653 655 658 660 663 665 668 670 673
3.20 625 626 630 633 635 638 640 643 645 648
3.10 605 607 609 611 613 615 617 619 621 623
3.00 585 587 589 591 593 595 597 599 601 603
2.90 560 563 565 568 570 573 575 578 580 583
2.80 535 538 540 543 545 548 550 553 555 558
2.70 515 517 519 521 523 525 527 529 531 533
2.60 495 497 499 501 503 505 507 509 511 513
2.50 475 477 479 481 483 485 487 489 491 493
2.40 450 453 455 458 460 463 465 468 470 473
2.30 425 428 430 433 435 438 440 443 445 448
2.20 405 405 409 411 413 415 417 419 421 423
2.10 385 387 389 391 393 395 397 399 401 403
2.00 360 363 365 368 370 373 375 378 380 383
1.90 340 342 344 346 348 350 352 354 356 358
1.80 320 322 324 326 328 330 332 334 336 338
1.70 295 298 300 303 305 308 310 313 315 318
1.60 270 273 275 278 280 283 285 288 291 293
1.50 250 252 254 256 258 260 262 264 266 268
1.40 230 232 234 236 238 240 242 244 246 248
1.30 205 208 210 213 215 218 220 223 225 228
1.20 185 187 189 191 193 195 197 199 201 203
1.10 165 167 169 171 173 175 177 179 181 183
1.00 140 143 145 148 150 153 155 158 160 163
0.90 120 122 124 126 128 130 132 134 136 138
0.80 95 98 100 103 105 108 110 113 115 118
0.70 70 73 75 78 80 83 85 88 90 93
0.60 50 52 54 56 58 60 62 64 66 68
0.50 35 37 39 41 43 45 47 49 51 53
0.51 0.52 0.53 0.54 0.55 0.56 0.57 0.58 0.59
Y
X
APPENDIX III-1
SUMMARY OF FISHERIES CATCH
DATA FOR 2013
Permit SF 2013-037
APPENDIX III-2
ALASKA DEPATMENT OF FISH AND GAME
THAYER CREEK TRIP REPORT
AUGUST 5-6, 2014
MEMORANDUM State of Alaska
Department of Fish and Game
Division of Habitat
TO: Jackie Timothy DATE: August 13, 2014
Southeast Regional Supervisor
THRU: SUBJECT: Thayer Creek Trip Report
August 5-6, 2014
FROM: Nicole Legere PHONE NO: (907) 465-6979
Habitat Biologist
The City of Angoon is located within Admiralty Island National Monument. Electricity in Angoon is
produced by diesel powered generators creating high costs for the residents. Kootznoowoo, Inc.
proposes to develop a hydroelectric facility on Thayer Creek, Stream No. 112-17-10500, to supplement
the use of diesel generators. Thayer Creek drains from Thayer Lake and is located six miles northwest
of Angoon within the National Monument and Kootznoowoo Wilderness.
On August 5, 2014 Fish and Wildlife Technician Rick Hoffman and I met with Dr. Paul Rusanowski
and Mr. Marcus Blood from the Shipley Group, in Angoon. The Shipley Group has been conducting
research in Thayer Creek for past several years so we took the opportunity to learn more about the
hydroelectric project and to collect fish and stream data to update the Anadromous Waters Catalog.
We traveled to Thayer Creek by boat and hiked a well-established trail up the west side of the creek
towards the proposed dam site. The channel becomes deeply incised 1250 feet upstream from the
mouth. The trail follows the rim of the gorge with very few creek access points. There are a few small
tributaries along the trail. We stopped at one tributary that flows into the gorge. According to Mr.
Blood, this tributary is the largest contributor of water to Thayer Creek below the proposed dam site.
There was low flow, gravel cobble substrate, and minimal fish habitat (Figure 1). Dr. Rusanowski said
there was a barrier waterfall downstream of this location. He retrieved a water level logger in the creek
that was out of the water due to low flows.
We arrived at the proposed dam site just above the upper section of the gorge. This section of the creek
is wide open with gravel and cobble substrate and minimal gradient change. The next tributary we came
to was immediately upstream of the proposed dam site (Figure 2). We electrofished the tributary for 100
yards upstream and caught seven cutthroat trout and six Dolly Varden char. Most of the fish were
young of the year. We took a water flow measurement, 88 feet wide and 261 cfs, in Thayer Creek
immediately upstream of the mouth of the tributary (Figure 3). We walked upstream to install a rope
across the creek for a geological team that will take samples to determine the best site to build the dam.
Thayer Creek Trip Report August 5-6, 2014 2 August 13, 2014
Figure 1.Tributary below proposed dam site. Figure 2.Tributary immediately upstream of proposed
dam site what contained resident cutthroat trout and
Dolly Varden char.
On August 6, 2014 we returned to the lower section of Thayer Creek to take flow measurements and
sample for fish. We took flow, 96 feet wide and 223 cfs, on a fixed line across Thayer Creek
downstream of the waterfalls (Figure 4). We electrofished two rearing coho salmon (Figure 5), 10
cutthroat trout, one sole, and two sculpin. Dr. Rusanowski and Mr. Blood caught two rearing coho
salmon and about 10 cutthroat trout using at small dipnet in the intertidal water of Thayer Creek.
Approximately 1250 feet upstream the channel becomes narrow and there is a series of three waterfalls
(Figure 6). In the past Dr. Rusanowski and Mr. Blood measured the first waterfall to be 12 feet and
plunge pool at the base to be at least 20 feet deep. Due to safety concerns we did not attempt to confirm
these measurements. We saw several salmon attempting to jump the waterfall with no success (Figure
7). We saw several pink salmon and one pair of sockeye salmon swimming in the jump pool. Mr.
Hoffman was able to get to the other side of the creek to look at the second waterfall (Figure 8). He
estimated the fall to be 14 feet with no plunge pool at the bedrock base. Mr. Rusanowski and Mr. Blood
said there is another waterfall around the corner of the second fall but it is difficult to access. According
to the Anadromous Fish Block guide from the Alaska Forest Resources & Practices Regulations
handbook1 the first waterfall is a barrier to all anadromous fish except steelhead and the second waterfall
is a barrier to all anadromous fish.
I have submitted a route correction and species addition to the Anadromous Waters Catalog to reduce
the length of the current anadromous section on Thayer Creek and to add rearing coho salmon and
sockeye salmon presence to the catalog (Attachment 1).
1 Alaska Forest and Resources Practices Regualtions, 2007, 11 AAC 95.265. Classification of surface water bodies, subpart
(g), Table A: Anadromous Fish Blockage.
Thayer Creek Trip Report August 5-6, 2014 3 August 13, 2014
Figure 3.Upper flow site in Thayer Creek above
proposed dam site.
Figure 4.Lower flow site in Thayer Creek downstream
of the waterfalls.
Figure 5.Coho salmon caught below waterfalls in
Thayer Creek.
Figure 6.First and second waterfalls in Thayer Creek.
Figure 7.Salmon attempting to jump the first waterfall
in Thayer Creek.
Figure 8.Second waterfall in Thayer Creek.
Thayer Creek Trip Report August 5-6, 2014 4 August 13, 2014
Attachments: Thayer Creek nomination to the Anadromous Waters Catalog submitted on August 13,
2014.
Email cc:
Al Ott, ADF&G Habitat, Fairbanks
Biologists, ADF&G Habitat, Juneau
Dan Teske, ADF&G Sporfish, Juneau
Dave Harris, ADF&G Commfish, Juneau
Shawn Johnson, ADF&G Sportfish, Juneau
Brad Palach, ADF&G Wildlife, Anchorage
Paul Rusanowski, The Shipley Group, Utah
ATTACHMENT
THAYER CREEK CORRECTION
Water body name: Thayer Creek Survey date: 8/6/2014
Water body number: 112-17-10500 Species & Lifestage: CHp, Pp
Watershed: Fishery Creek-Frontal Chatham Strait MTR: C049S067E Quad: Sitka C-2
Findings: The lower section of Thayer Creek is gravel and cobble substrate. We had visual
observations of several adult pink and one chum salmon in the stream. There is a series of water
falls approximately 1 upstream from the mouth of the creek that we determined are
anadromous fish passage barriers. We caught four rearing coho salmon downstream of the
waterfalls and saw several pink and one pair of sockeye salmon swimming in the plunge pool
below the falls. Upstream of the waterfall the creek flows through a bedrock gorge for
approximately one mile then opens up to a low gradient stream with gravel and cobble substrate.
We surveyed a tributary in this area and caught resident cutthroat trout and Dolly Varden char.
Recommendations: Correct the anadromous section of Thayer Creek in the AWC to represent
the actual extent of anadromy. Add rearing coho salmon and sockeye salmon presence to the
AWC.
Table 1.-Thayer Creek survey data.
Waypoint Latitude Longitude Notes Sample Effort Sample Results
837 57.5935 -134.6217 Tributary on river right. This
tributary provides the most
water to Thayer Creek.
845 57.5939 -134.6178 Stopping here, habitat
continues.
846 57.5931 -134.6165 Mouth of tributary.
849 57.5929 -134.6227 Small tributary into gorge.
850 57.5776 -134.6275 Mouth of Thayer Creek. HN 2 CO, 10 CT
851 57.5785 -134.6276 EF, Visual 2 CT, 1 CH
852 57.5785 -134.6273 EF 3 CT, 1 flat fish
853 57.5795 -134.6263 EF 1 CO ~ 75 mm
854 57.5799 -134.6251 EF 3 CT
855 57.5798 -134.6244 EF 1 CO ~ 80, 2 CT
856 57.5803 -134.6236 16 yds away from base of a
series of three waterfalls. Too
deep and steep to get any
closer. The first fall is
approximately 12 ft.with at least
20 ft. deep plunge pool. Visual
of salmon trying to jump the falls
with no success. The second
fall is the approximately 14 ft.
bedrock substrate, no plunge
pool, and higher velocity. We
did not have a visual of the third
falls but there is confirmation it
exists.
Visual 2 adult S, several
adult P
Figure 1.Coho salmon caught below waterfall in
Thayer Creek.
Figure 2.First
pool.
Figure 3. Figure 4.Rick Hoffman walking upstream from
the mouth of Thayer Creek.
Figure 5.Thayer Creek route correction map.
APPENDIX III-3
SUMMARY OF FISHERIES CATCH
DATA FOR 2014
Permit SF 2014-234
APPENDIX III-4
SUMMARY OF FISHERIES CATCH
DATA FOR 2015
Permit SF 2015-072