HomeMy WebLinkAboutFive Mile Creek Hydroelectric Project Reconnaissance Trip Report - Oct 2019 - REF Grant 7091226polarconsul t alaska, inc.
1503 West 33rd Avenue, Suite 310
Anchorage, Alaska 99503-3638
Phone: (907) 258-2420
FAX: (907) 258-2419
M E M O R A N D U M
191021M-JUNE4-7TRIPREPORT.DOC
DATE: October 21, 2019
TO: Martin Finnesand, Chitina Electric, Inc. (CEI)
FROM: Joel Groves, PCA
SUBJECT: Fivemile Creek Trip Report June 4 to 7, 2019
CC: Jeff Doty (CEI);
Ed Herndon, Chitina Native Corporation (CNC);
Betsy McGregor, Alaska Energy Authority (AEA)
INTRODUCTION AND SUMMARY OF FINDINGS
Polarconsult engineers Joel Groves and Gary Paulus mobilized from Anchorage to Chitina June 4
to 7 to conduct field investigations for the Fivemile Creek hydro project. This report describes
field activities, initial findings, and action items for the project.
Several alternate project layouts were identified that are believed to have significant technical
and cost advantages relative to the 2014 designs.
1 These include:
A bedrock intake site ~250 feet downstream of the 2014 intake site.
A penstock route that reduces penstock length by ~2,000 feet relative to the 2014 route.
Several alternate powerhouse sites that appear to be technically and/or economically
favorable to the 2014 powerhouse site.
1. LOGISTICS AND MEETINGS
Mr. Groves and Mr. Paulus traveled by road from Anchorage to Chitina and stayed at the
Wrangell View RV Park adjacent to Chitina Electric, Inc. (CEI)s diesel power plant and the
Chitina Airport. The RV park is a convenient base of operations for access to the project site.
Chitina Native Corporation (CNC) provided an ATV to facilitate project access. The existing jeep
trail was in good condition, with no downed trees or significant mud holes. At the time of our
visit the jeep trail was passable for four wheel drive vehicles up as far as the cleared route to
the 2014 intake site. Downed beetle killed spruce make some cross country travel in the
project area difficult, but all areas of the project were accessible on foot and proposed
alignments were hiked during this field visit.
Weather throughout the visit was generally sunny, with daytime highs in the mid to upper 60s
and overnight lows in the low 40s. Afternoon thunder cells brought some intervals of rain but
precipitation was not significant. Vegetation was very dry. The forest floor, generally a thick
bed of mosses / lichens, was completely dry under foot pressure. There was no remaining
snow pack in the project area, and all vegetation was fully leafed out.
During the course of the site visit Mr. Groves and Mr. Paulus met with Mr. Martin Finnesand
and Mr. Jeff Doty of CEI, and Mr. Pete Peschang of Ahtna Inter Tribal Resource Commission.
Mr. Finnesand and Mr. Peschang hiked portions of the project with Polarconsult personnel on
June 6
th, and initial findings were reviewed with Mr. Finnesand on the afternoon of June 6
th.
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2. PROJECT LAYOUT ACTIVITIES AND INITIAL FINDINGS
To facilitate communication and stakeholder understanding of the project, Polarconsult has
included the following sheets of the project site showing 2014 and current design alternatives.
Sheet W 1, a plan and profile of Fivemile Creek from its mouth on the Copper River up
beyond the proposed hydro diversion sites. Stationing along the creek thalweg is provided
both in feet and river miles (RM) above the mouth. Key features are annotated.
Sheets P 1 and P 2, showing plan and profile of the proposed new penstock route(s) from
the new intake at RM 2.22 down to four alternate powerhouse sites. The 2014 project
layout is also shown on these sheets for reference.
The following narrative uses mileage / stationing on these sheets to describe project locations.
2.A. Diversion / Intake Sites
The existing intake site at RM 2.27 has exposed bedrock on both edges of the canyon floor but
unconsolidated deposits to a maximum depth of ~30 feet in the middle ~40 foot width of the
canyon floor.
2 These deposits complicate design, construction, and operation of the diversion
structure for the following reasons:
Increased likelihood that some surface flow may pass through this stratum and not be
directed into the hydro project.
Increased potential for foundation scour, requiring additional attention to this hazard
during design, construction, and long term monitoring of the diversion structure.
More complicated structural design and costly construction, requiring both spread
footings / gravity structure on alluvium and footings on bedrock.
To avoid these issues, the creek below RM 2.27 was hiked to see if alternate intake sites exist.
The first exposed bedrock sill across the creek occurs at RM 2.22, about 250 feet downstream
of and 25 feet lower than the 2014 intake site. At this location the entire creek flows through a
rock chute approximately 15 feet wide (Photograph 16). Both banks are exposed bedrock. The
creek bed was obscured by flowing water but site conditions suggest it is also bedrock.
Exposed bedrock sills across the creek bed are common downstream of RM 2.22, but the creek
canyon also becomes more deeply incised, making it increasingly difficult and costly for a
penstock to exit the canyon from prospective downstream diversion sites. Lower diversion
sites also provide less head and power for the hydro project.
Initial review indicates moving the intake from RM 2.27 down to RM 2.22 would allow the
intake structure to be fully founded on bedrock, avoiding or reducing the design, construction,
and operational issues listed above. The technical requirements to exit the canyon from this
site appear to be substantially similar to those for the original site at RM 2.27.
1 The 2014design and project elements refer to the 65% plans issued in Sept. 2014 (CRW 2014).
2 Based on approximate bedrock surface compiled from GPR surveys and depicted on sheet C502 (CRW 2014).
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2.B. Penstock / Access Routes
The penstock and access routes from both the 2014 design and potential alternates were
reviewed during this site visit in an effort to:
Reduce the amount of rock cuts required for construction.
Avoid access grades over 20% to improve year round access to project features.
Reduce length and overall cost of project improvements.
Reduce length of penstock within the AK DOT Edgerton Highway right of way.
Key findings follow.
1. Preferred Upper Penstock Route (for all project alternatives)An approximately 3,550 foot
long alternate penstock and diversion access route was identified this visit that is preferred
over the 2014 route. The alternate route starts at the RM 2.22 alternate diversion site, then
travels overland at grades to 15%, joining the jeep trail and 2014 penstock route at mile (MP)
0.85 (2014 penstock station 44+50). It then follows the 2014 route down to jeep trail MP 0.25
(sheet P 1). This route, combined with the alternate intake site, is approximately 900 feet
shorter than the 2014 route at a loss of 25 feet of head. This route can be developed with
maximum access grades of approximately 15%, and would bypass a 20% grade along the 2014
route at jeep trail MP 1.14. This route would also avoid several areas of shallow or exposed
bedrock along the jeep trail MP 0.85 to 1.17.
2. Alternate access routes that may be preferred depending on powerhouse siting.
Old Edgerton Highway road bed.A portion of the abandoned Edgerton Highway road bed
parallels the current highway from MP 28.03 to 28.26, just north of Fivemile Creek. This feature
could be useful for penstock construction if the hydro powerhouse is sited along Fivemile Creek
at sites B, C, or D. The old road bed is approximately 100 feet east of and 40 feet lower than
the current highway. It crosses in and out of the current highway ROW.
Old Jeep Trail road bed.An abandoned portion of the original Fivemile mine trail runs from the
east side of the Edgerton Highway at MP 27.83 for approximately ½ mile down towards the
north bank of Fivemile Creek. This route may be favorable for access to a powerhouse sited on
the north side of Fivemile Creek in the vicinity of the RV park (alternate site B). The first
approximately 0.15 miles of this route is located on a native allotment (Lot 2, USS 11725), and
the remaining 0.29 miles are on CNC land. Access across or around the native allotment would
need to be determined. Maximum grade along this abandoned road bed is approximately 23%
at MP 0.28, but it appears this could be reworked to about 15%.
3. Alternate corridors reviewed this visit that are not preferred. A more direct penstock route
following the jeep trail from MP 0.85 to MP 0.50, then heading overland directly to the
Edgerton Highway just north of Fivemile Creek (Sheet P 2, route E).This corridor would
reduce the length of the penstock to powerhouse alternate sites A or D by approximately 300
feet. However, this route was found to have unfavorable topography, with several incised
valleys that the penstock would need to navigate. The sideslopes of these valleys feature
bedrock outcroppings, indicating that routing the penstock through this area may be relatively
costly. Lastly, this corridor ends at a 50 to 75 foot tall road cut above the Edgerton Highway
which the penstock would need to descend to reach any powerhouse site. For these reasons,
route Edoes not warrant further consideration.
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2.C. Powerhouse Sites
The 2014 powerhouse site is adjacent to (east of) the existing diesel powerhouse, with a 300
foot tailrace returning water to Fivemile Creek just downstream of the highway. This location is
favorable with regard to flood hazards, fish habitat permitting, operations and maintenance,
and electric and controls connections. It is unfavorable with regard to penstock and tailrace
length/ cost, project head, and possible encroachment on the existing adjacent lease lot.
Four alternate powerhouse sites were identified this site visit (Sheet P 2). Initial review
indicates all four sites may offer significant advantages relative to the 2014 site. Further
analysis is needed to identify the best site. A discussion of each site follows.
Alternate Site A Above the Edgerton Highway.
There is sufficient room on the upstream side of the Edgerton Highway for a hydro
powerhouse. The site would be tight, but a driveway off the Edgerton can be constructed to
DOT standards and the powerhouse building sited on CNC land adjacent to the highway ROW.
The site would need to be built up for access and protection from flood hazards. Rock blasting
could be useful both to expand the site and generate rip rap to armor slopes along the creek.
This site is comparable to the 2014 site with regard to fish habitat. It is superior to the 2014
powerhouse site with regard to penstock length. Combined with other penstock modifications
described in this memo, the total penstock length to Site A would be approximately 8,600 feet,
almost 2,000 feet shorter than the 2014 route. This site would eliminate a highway penstock
crossing, and would reduce the length of penstock in the highway ROW from approximately
2,200 feet to 600 feet. It is inferior to the 2014 site with regard to finished floor elevation
(about 40 feet higher) and electric and controls tie in (about 700 foot long primary electric
extension would be required).
Alternate B north of Fivemile Creek near the RV Park.
This site is on uplands adjacent to the alluvial fan north of the RV Park and Fivemile Creek.
Benefits of this site include increased project head (44 feet more than the 2014 site), reduced
penstock length (8,100 feet total, including approximately 400 feet at 35% grade from the
Edgerton Highway crossing down to the powerhouse) and low risk of flood damage to the
powerhouse.
This site would require approximately 700 feet of primary electric/controls extension. Access
could be either from the south via a new ~600 foot long access road starting at the Airport
Road with a bridge crossing over Fivemile Creek, or from the north via restoration of the ~1/2
mile long abandoned jeep trail that starts at Edgerton Highway MP 27.83 and a 200 foot long
road extension to the site. The 0.15 mile segment of the abandoned jeep trail on a native
allotment could be avoided with approximately 500 feet of new road on CNC land.
This site would return water to about RM 0.35 on Fivemile Creek. If necessary, a 250 foot long
tailrace ditch could return water to RM 0.40, or a penstock tap and small diameter pipeline
could provide a minimum seasonal flow at the culvert outlet. The permit requirements with
regard to fish habitat would need to be determined through discussions with ADFG.
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Alternate C south of Fivemile Creek near the RV Park.
Alternate C is similar to Alternate B, but on the south side of Fivemile Creek downstream (east)
of the RV park. The main advantage relative to alternate B is eliminating about 500 feet of
primary electric, road and a vehicle bridge across Fivemile Creek. The tradeoff is 533 feet of
additional penstock and a pipe bridge or buried pipe crossing of Fivemile Creek. Also, this site is
relatively less sheltered than Site B from erosion or flood hazards from Fivemile Creek.
Alternate D south of Fivemile Creek downstream of Edgerton Highway.
Alternate D is similar to the 2014 powerhouse site, but moved closer to Fivemile Creek to
reduce penstock and tailrace lengths and avoid encroaching on the clinic lease lot.
2.D. Tailrace / Discharge Sites
Alternate powerhouse site A would return water to Fivemile Creek at RM 0.56, just above the
Edgerton Highway culvert. Alternate site D would return water to Fivemile Creek at RM 0.52,
just below this culvert. Both discharge points are upstream of the understood upper possible
limit of anadromous fish habitat (at the highway culvert outlet at RM 0.52) and are not
expected to generate any concerns with regard to fish resources.
Alternate powerhouse sites B or C would return water to Fivemile Creek around RM 0.35, which
is 0.17 miles downstream of the understood upper possible limit of anadromous fish habitat.
Consultation with ADFG would be required to determine what if any implications this tailrace
location would have on ADFG permit terms and conditions. Potential permit terms could
include a seasonal in stream flow reservation imposed at the diversion site or culvert outlet, or
other off site mitigation measures. A minimum seasonal flow at the culvert outlet could be met
with a penstock tap and small diameter line run from the powerhouse to the culvert outlet.
Tailrace discharge from powerhouse site B could also be directed into the lower reaches of a
left lateral tributary of Fivemile Creek. This tributary appears to have better fish habitat than
the main channel of Fivemile Creek, and this might be a viable mitigation option for the project.
2.E. Observations of Downstream Reach of Fivemile Creek
Fivemile Creek downstream of the highway culvert was hiked to review stream morphology.
This reach of Fivemile Creek flows for 0.52 miles down the northerly periphery of the creeks
alluvial cone, ending at its mouth on the bank of the Copper River. The creek is confined to this
corridor by rip rap armored slopes along approximately 200 feet of the right bank from RM 0.52
to 0.48. Downstream, the creeks active flood channel is 50 to 300 feet wide, generally of
natural character, and does not currently abut engineered slopes. The airport road prism is
located 25 to 350 feet south of the current right bank meander. Should the creek encroach on
the airport road prism, it is expected AK DOT would protect the road by further armoring the
road prism and/or channelizing the creek. The RV Park is the only existing development
between the Airport Road and the creek in this reach.
Channel morphology through this reach is predominately a continuous riffle running at a 6.2 to
3.2% gradient, steepest upstream and progressively flatter as it progresses down the alluvial
cone. There are very few main channel pools, side channels, or channel braiding at the
observed flow condition, but dry side channels are present through most of the reach, and are
likely active at high water conditions. The creek shows significant sign of active meander and
bank scour, with active cut banks in several areas.
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Stream substrate in this reach includes small boulders, cobble, gravel, sand and silt.
Predominant substrate size decreases downstream, with large cobble predominant at the top
of this reach and large gravel predominant at the mouth on the Copper River.
No fish were observed anywhere along Fivemile Creek during this visit. A tributary discharging
to Fivemile Creek from the north (river left) at RM 0.27 appears to have pools and low velocity
areas that may be more favorable fish habitat than the main stem of Fivemile Creek. This
tributary also appears to be better protected from flood events than the main stem. This
tributary is on the far bank and was not observed in detail.
Photographs 1 through 10 provide representative depictions of this reach of Fivemile Creek.
Photograph captions provide approximate location on the creek (river mile) and orientation of
the field of view. A plan and profile of the creek thalweg is provided as Sheet W 1.
2.F Material Sites
A significant portion of the material needed for project road and trail construction can likely be
sourced from on site borrow identified/produced within the project footprint during
construction. Where additional material is required, it could be sourced from existing small
material sites along the jeep trail and/or existing established quarries in the project vicinity.
The type and volume of material available from the small borrow pits along the jeep trail is
unknown. Also, this corridor is located within a conservation easement on CNC land. Obtaining
small volumes of borrow from these pits may be feasible, but the feasibility of expanding these
pits to meet the hydro projects needs is unknown.
Depending on the volume and type of material required, it may be most cost effective to obtain
material from existing established pits in the project vicinity.
2.G Review of LiDAR topo
Qualitative review of topography generated from LiDAR data indicates LiDAR accurately depicts
the existing ground surface in most areas. No gross errors were evident due to vegetative
canopy masking. Extremely rugged terrain in the canyon is not accurately depicted, with most
steep rock outcrops smoothedinto adjacent terrain. Such errors are typical of LiDAR
topographic products. Limited ground based topo surveys at specific sites within the canyon
may be warranted prior to final design to better characterize these exposed rock surfaces.
3. HYDROLOGY
The creek was visually estimated to be flowing at approximately 75 +/25 cubic feet per second
(cfs), and the flow rate appeared stable throughout the visit. Because wading conditions were
marginally safe, there are no current gauging station data loggers in place, and the flow was far
higher than the project design flow (~5 cfs), quantative flow measurements were not taken
during this visit. The flow rate appeared uniform during the visit, and is likely sourced from
ongoing snow melt in the higher portions of the basin above the project intake.
3.1 Upper Gauging Station
The data logger and pressure transducer were removed from the upper gauging station prior to
October 14, 2018 (Photograph 17). The stilling tube, outside staff board, data logger stand, and
solar panel were still present in June 2019. The solar panel and mounting bracket were
salvaged during this site visit to protect from future damage or theft. They can be reinstalled or
replaced should the upper station be returned to service. Two large pieces of the wood weir
installed in August 2009 are still wedged into the creek in a general V orientation pointed
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downstream. The broken weir is backfilled with boulders and cobbles and the section appears
quasi stable.
3.2 Lower Gauging Station
The brackets used to mount the weir at the lower gauging station were submerged during this
visit so their condition could not be directly assessed. The culvert had a freefall outlet
(waterfall) dropping ~7 feet into a bedrock plunge pool ~5 feet deep (Photographs 9, 10).
4. SITE CONTROL
Several ROW boundary monuments adjacent to the project footprint were found during this
site visit. These can be surveyed during future field work to verify their position and provide
local survey control for the project.
5. DIESEL POWERHOUSE
Cursory inspection of the exterior of the diesel powerhouse was completed this trip.
Information needed for electrical and control tie in designs can be obtained in the future from
as built drawings and future inspection of the diesel plant switchgear.
6. ACTION ITEMS
Before the project can be advanced, the general layout needs to be finalized. The major open
question is the optimal powerhouse location. Polarconsult is currently conducting a high level
comparative economic analysis of the four powerhouse sites described in this report. The
findings will be presented to CEI and AEA for review and comment. Once the powerhouse
siting is refined, then the following actions are recommended:
1. Engage with key agencies (AK DOT and ADFG) to solicit feedback on the recommended
project layout and identify any significant regulatory hurdles.
2. Finalize scope and schedule of pending DOE analysis of the project. Polarconsult will work
with CEI, CNC, and DOE on this item.
7. REFERENCES
CRW 2012. CRW Engineering Group, LLC.Chitina Alaska, Conceptual Design Study Report,
Fivemile Creek Hydroelectric Project. January 13, 2012. 176 pages.
CRW 2014. CRW Engineering Group, LLC.Chitina Alaska, Fivemile Creek Hydroelectric
Project, 65% Design Drawings. September 2014. 34 sheets.
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8. PHOTOGRAPHS
To the extent practical, photographs have been organized starting at the creek mouth on the
Copper River (RM 0.0) and proceeding upstream to the 2014 intake site (RM 2.27).
Photograph 2.Upstream view of Fivemile
Creek at RM 0.25, below project reach. Note
active cut banks and recently deposited
large woody debris. June 6, 2019.
Photograph 1.Overview of Fivemile Creek and existing
improvements looking downstream from terrain above the
Edgerton Highway. Creek reach from RM 0.0 up to 0.5 is
visible in this photograph. June 6, 2019.
Copper River
RM 0.5
Culvert Outlet
ClinicRM 0.0 Mouth of Fivemile Creek Edgerton
Highway
Airport Diesel Power PlantRV Park
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Photograph 3.Downstream view of Fivemile
Creek at RM 0.25. Note riffle morphology
and cobble gravel substrate. Mouth of a
small tributary is visible on left (far) bank in
distance. June 6, 2019.
Photograph 4.Upstream view of
Fivemile Creek substrate at RM 0.30.
Small cobbles dominate with
significant fractions of large cobble
and gravel also present. June 6, 2019.
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Photograph 5.Upstream view of Fivemile Creek at RM
0.30. Note recently formed channel, active cut banks, and
large woody debris. Recent flooding is also evident in
upland forest south of creek (photo left). June 6, 2019.
Photograph 6.Upstream view of Fivemile
Creek at RM 0.40. Note cobble bar and
active cut bank beyond. June 6, 2019.
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Photograph 8.Downstream view of Fivemile
Creek at RM 0.50, Riffle below highway
culvert plunge pool. June 4, 2019.
Photograph 7.Downstream view of
Fivemile Creek at RM 0.40. Note
active cut bank. June 6, 2019.
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Photograph 9.Upstream view of
Fivemile Creek at RM 0.50, highway
culvert outlet. June 4, 2019.
Photograph 10.Upstream view through Fivemile
Creek highway culvert barrel from RM 0.50. Culvert
is 10 foot diameter and rests on/near bedrock.
Waterfall is ~6 to 7 feet high. June 4, 2019.
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Photograph 11.View of Fivemile Creek
at RM 0.55, highway culvert inlet.
June 4, 2019.
Photograph 12.Upstream view of
Fivemile Creek at RM 0.55, highway
culvert inlet. June 4, 2019.
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Photograph 14.Upstream view of
Fivemile Creek from RM 0.58. Reach
immediately upstream of alternate
powerhouse site A.June 4, 2019.
Photograph 13.Downstream view of
Fivemile Creek alternate powerhouse site
Afrom north canyon rim above RM 0.61.
June 5, 2019.
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Photograph 16.Downstream view of
Fivemile Creek at RM 2.22, proposed
intake site. Note exposed bedrock on both
sides of creek channel. June 5, 2019.
Photograph 15.Upstream view of Fivemile
Creek and lower canyon viewed from
north rim. Reach from approximately RM
0.65 to RM 0.75 is visible. June 5, 2019.
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Photograph 18.Upstream view of
Fivemile Creek from RM 2.27, upper
stream gauging station and 2014
intake site. June 5, 2019.
Photograph 17.Upstream view of Fivemile Creek at RM
2.27, upper stream gauging station and 2014 intake site.
Condition of weir remains appeared unchanged during
June 2019 site visit. Photograph courtesy of Bering
Pacific Engineering, LLC. October 14, 2018.