HomeMy WebLinkAboutFive Mile Creek Hydroelectric Project Hydrology Report - Feb 2020 - REF Grant 7091226polarconsult alaska, inc.
1503 West 33rd Avenue, Suite 310
Anchorage, Alaska 99503-3638
Phone: (907) 258-2420
FAX: (907) 258-2419
MEMORANDUM
DATE: February 28, 2020 (Revision 2 — June 30, 2020)
TO: David Brailey, Project File
FROM: Joel Groves, PE Polarconsult Project Manager
SUBJECT: Hydrology Memo for Five Mile Creek Hydroelectric Project - Chitina, Alaska
REVISION 2
Prior memo versions have been revised to:
1. Address CEI and AEA review comments.
1.0 INTRODUCTION AND BACKGROUND
Chitna Electric, Inc. (CEI) is developing a hydroelectric project at Five Mile Creek approximately
five miles north of the community of Chitina, Alaska. As part of the development process, CEI
conducted a hydrology study from 2008 to 2010 to characterize the resource potential at Five
Mile and guide project design. CEI's consultants previously developed 65-percent design plans
and completed partial permitting efforts for the project (CRW 2012, CRW 2014). CEI retained
Polarconsult Alaska, Inc. (Polarconsult) in 2019 to advance design and permitting for the hydro
project. Polarconsult had previously been involved in the project through 2010, and
contributed to the original hydrology study.
Review of currently available information found no published record of the original primary
hydrology data at Five Mile.' The existing published hydrology analysis (Clifton 2011) includes
a 14-month period of record at Five Mile and record extension to a basin with significantly
different characteristics (Gulkana River, USGS gauge #15200280). The Clifton analysis
acknowledged significant limitations these factors impose on hydrology study conclusions.
To address these limitations and support project design and permitting, Polarconsult reviewed
the available data resources listed in Table 1 to provide a summary of primary hydrology data at
Five Mile and additional data analysis to supplement prior findings.
Table 1: Available Data Resources
CRW Conceptual Design Report and relevant Clifton Lab appendices (CRW 2012, CRW 2014)
Polarconsult file archives (Polarconsult 2019)
AEA SharePoint File Server (AEA 2019)
Personal files provided by Daniel Hertrich (Hertrich 2019)
Polarconsult's review identified an additional six months of data (March through August 2010)
for the upper weir gauging station that was not used in the prior analysis. This memo
documents prior analysis and provides current analysis of all available data.
2.0 SUMMARY OF FINDINGS
Review identified additional upper weir stage data from March 2, 2010 to August 20, 2010 that
was not included in prior analyses. These data are used to develop updated rating curves for
the upper gauging station and updated hydrograph based on all available data for the site.
1 'Primary' hydrology data includes information such as the stage record, documentation of stage record
adjustments, direct flow measurements, manual stage measurements, and related information that is typically
documented so the quality of the hydrology study results can be evaluated by interested parties.
200630-FIVEMILE HYDROLOGYREPORT REV 2.DOC
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
These data were analyzed to develop the following information for project design and
permitting:
1. Correlation and record extension to characterize long term Five Mile Creek hydrology.
Analysis of regional gauges by Brailey Hydrologic concluded that there are no suitable
record extension candidates for Five Mile Creek. Regional hydrology and meteorological
records were reviewed to conclude that the 2008 — 2010 hydrology record at Five Mile
Creek is expected to be reasonably representative of resource hydrology.
2. Flood frequency analysis to provide guidance for design flood for project works.
3. Resultant record characterizes Five Mile Creek hydrology with two seasons of quantitative
winter flow data (January to May, 2008 and December to May, 2009 - 10), one season of
estimated quantitative summer flow data (May to August, 2010), and two seasons of
qualitative non -winter flow data (visual observations, May to October, 2017 and 2019).
3.0 HYDROLOGY DATA
3.1 Creek and Basin Description
Five Mile Creek is a minor creek that drains a north-west facing mountainous basin located in
the northerly periphery of the Chugach Mountains north of the Gulf of Alaska. The total basin
measures 15.38 square miles in area (Figure 1). The basin's westerly divide consists of several
mountain summits and interconnecting saddles and ridges at 4,500 to 5,500 foot elevation.
The upper 1/3rd of the basin is alpine tundra, and the lower 2/3rds are vegetated by mature
spruce/alder forest. The creek exits the mountains onto the Copper River valley floor, traverses
its roughly -half -mile long alluvial fan and discharges to the Copper River at 600 foot elevation.
The local climate is transitioning from maritime characteristics along the gulf coast (wet and
moderately cool) to the continental characteristics of the Copper River Basin (dry with extreme
seasonal temperatures) with greater emphasis on interior continental characteristics and
common incursions of more moderate weather from the gulf coast. Mean annual precipitation
across the basin ranges from 15 to 40 inches and mean minimum January temperature varies
across the basin from minus 4 to minus 8°F (USGS 2003).
Figure 1: Project Location and Vicinity Map
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3.2 Available Hydrology Data
Two gauging stations were established at Five Mile Creek for this project. No prior gauging
efforts on this creek are known. Table 2 summarizes available hydrology data for both sites,
and Table 3 summarizes available stage and flow measurements.
FEBRUARY 2020 (REVISION 2 —JUNE 30, 2020) PAGE 2 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
Table 2: Summary of Hydrology Data for Five Mile Creek
Location Basin Area Elevation Latitude
Period of Record
Number of
(scl.mi.) 1 (feet) Z Longitude
Begin Date
End Date
Records (days) 3
1/7/2008
5/1/2008
8
Five Mile Creek 61°34'55"
13.58 660
12/4/2009
5/12/2010
8
Lower Weir 144026'19"
May to Oct.
2017, 2019
See Note 4
Five Mile Creek 12.11 1570 61034'42"
Upper Weir 144°28'57" 8/28/2009 8/20/2010 357
Gulkana River 1,760 1,852 62031'15" 10/1/1972 12/10/2019 7,197
(#15200280) 145031'51"
1. Basin areas interpreted from LiDAR and/or other published topographic data. The basin area for the lower
gauging station may vary as some divides proximate to the Edgerton Highway are ambiguous.
2. Approximate elevation. Interpreted from project LiDAR data.
3. The lower gauge was manually read during the indicated period of record. The upper gauge was fitted with a
data logger recording at a 15-minute interval.
4. Periodic visual observations at the culvert outlet to assess flow by Mr. Finnesand. Mr. Finnesand performed
field work for the 2008-2010 winter flow measurement study and characterized summer flows as being
comparable to winter flow (occurrences in 2017) or well above winter flow and project design flow (consistent
through 2019 season) (Finnesand 2019).
3.2.1 Lower Weir Gauging Station
The lower weir gauging station consists of a standard Cipolletti weir constructed of plywood
that can be bolted to the outlet of the culvert that passes beneath the Edgerton Highway
(Photographs 1 to 4). This weir is described in Figure 2. This weir is only suitable for measuring
low flows as the pressure on the weir during common high flows would expectedly destroy it.
The weir was installed in the late winter of 2007-08 and 2009-10. This station was never fitted
with a data logger, rather CEI personnel manually measured water stage in the pool behind the
weir about twice a month during the late winter season. No concurrent flow measurements
are known to exist at the lower weir gauging station. All 2008 to 2010 flow data was calculated
from the station's rating curve (equation 1). The weir hardware is still in good condition
(Finnesand 2019).
3.2.2 Upper Gauging Station
The upper gauging station consists of a plywood weir that was constructed across Five Mile
Creek at river mile (RM) 2.27 on August 28, 2009 (Photograph 5). The weir formed a small pool
in the creek into which a pressure transducer (PT) was installed. A data logger recorded stage
data at 15-minute intervals. No temperature data was logged at this site. The weir was
destroyed sometime between site visits on March 9, 2010 and August 20, 2010. Review of
stage data suggests the weir most likely failed during high flows on May 27, 2010. The broken
weir remains in place (Photographs 6, 7, and 8).
Stage data from this station exists for the period August 28, 2009 to August 20, 2010. AEA
personnel visited the gauge to perform maintenance on March 23, 2016 (AEA 2016), but no
stage data download is known to exist from this site visit. Site photographs indicate the data
logger was missing on October 14, 2018 (BPE 2018, Photograph 7). The fate of the logger
hardware (and any on -board data) is unknown. The type of logger used had a large memory,
and could provide a useful additional hydrology record if ever recovered.
FEBRUARY 2020 (REVISION 2 —JUNE 30, 2020) PAGE 3 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
Table 3: Five Mile Creek Flow and Stage Measurements
Local Date/Time Party Measured 1 Measured OSS Concurrent PTZ Method /
Flow (cfs) Stage (feet) Reading (feet) Equipment
Five Mile Creek at Upper Weir Gauging Station
8/28/200919:00 Hertrich 17.3 2.1 2.01 CV-MM
3/9/2010 CEI NM 1.22 3 1.14 -
8/20/2010 10:00 Paulus 12.9 1.07 1.06 CV-MM 4
3/23/2016 11:00 AEA 2.55 NM 2.8 Tracer 4
Five Mile Creek at Lower Weir Gauging Station
1/7/2008 CEI 2.4 0.44 - Weir
2/6/2008 CEI 2.3 0.42 - Weir
2/20/2008 CEI 2.1 0.40 - Weir
3/5/2008 CEI 1.9 0.38 - Weir
3/31/2008 CEI 1.6 0.33 - Weir
4/14/2008 CEI 1.3 0.29 - Weir
4/24/2008 CEI 1.6 0.33 - Weir
5/1/2008 CEI 2.3 0.42 - Weir
12/4/2009 CEI 3.8 0.58 1.41 Weir
12/31/2009 CEI 3.2 0.52 1.30 Weir
2/3/2010 CEI 2.4 0.44 1.25 Weir
2/25/2010 CEI 2.1 0.40 1.24 Weir
3/25/2010 CEI 1.9 0.38 1.11 Weir
4/13/2010 CEI 1.8 0.35 1.08 Weir
5/1/2010 CEI 2.3 0.42 1.115 Weir
5/12/2010 CEI 3.6 0.56 1.306 Weir
8/20/2010 14:00 Paulus 11.9 - 1.06 CV-MM 4
Acronyms
CEI: Chitina Electric, Inc. personnel.
cfs: cubic feet per second
CV-MM: Current -velocity method using Marsh McBirney Flowmate 2000.
NM: not measured.
OSS: outside staff. The physical staff board installed at the gauging station.
PT: pressure transducer.
Tracer: 'Sudden dose' tracer method using a fluorescent dye tracer (Hudson 2005).
Weir: Flow is calculated based on a weir equation (equation 1, see report narrative). Stage is reported as the
water depth measured from the weir sill up to the water surface elevation upstream of the weir nappe.
Notes
1. All lower gauging station flow data are calculated from manual stage readings and weir equation.
2. All PT data is for the upper weir gauging station. Concurrent upper weir data is reported with lower weir data.
The time of stage readings at the lower weir was not recorded. Upper weir PT readings are representative for
the day. Days with PT reading fluctuations of more than 0.05 feet are noted. All data are unadjusted .
3. Water depth measured from the weir crest down to the water surface elevation upstream of the weir nappe.
Converted to OSS stage based on documented weir crest elevation of 2.14' in OSS datum (Polarconsult 2009a).
4. Average of two concurrent measurements is reported. The coefficient of variance between the two
measurements is less than 10% unless indicated otherwise.
5. Upper weir PT reading fluctuated from 1.10 to 1.16 on this date.
6. Upper weir PT reading fluctuated from 1.30 to 1.45 on this date.
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 4 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO
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POLARCONSULT ALASKA, INC.
Figure 2: Five Mile Creek Lower Weir Installation (Polarconsult 2007)
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2 LAYERS OF NECESSARY
1" THICK
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/ 37,
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(GLUE TO PLYWOOD)
8.5" ALL THREAD
FLAT WASHER
FEBRUARY 2020 (REVISION 2 —JUNE 30, 2020) PAGE 5 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
4.0 HYDROLOGY ANALYSIS
4.1 Station Rating Curves
4.1.1 Lower Weir Gauging Station
The rating curve for the lower weir gauging station (Equation 1) is based on the Cipolletti weir
equation and indicated weir dimensions .2 Figure 3 shows the stage -discharge curve.
Equation 1, Lower Weir Rating Curve: Quw = 8.42 x H "S
Where: QLW = flow at lower weir in cubic feet per second
H = water depth above the lower weir sill in feet.
Valid for H from 0 to 1.0.
Figure 3: Lower Weir Gauging Station Rating Curve
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4.1.2 Upper Weir Gauging Station
Review of prior reports and data indicate only a preliminary weir rating curve was prepared for
the upper gauging station. This curve was based on one flow measurement, standard weir
equations and the upper weir geometry. Equation 2 is this preliminary curve.
Equation 2, Upper Weir Preliminary Rating Curve (for reference only):
Quw = (0.479 + (0.033 x H)) x (8.03) x (50.5/12) x H "'
Where: Quw = flow at upper weir in cubic feet per second
H = water depth above the upper weir sill in feet.
2 The rating equation on Figure 2 is incorrect. Equation 1 reflects the indicated weir geometry and the Cipolletti
equation, and is consistent with prior reported hydrology data (Polarconsult 2008 at Table 2, Page 8).
FEBRUARY 2020 (REVISION 2 —JUNE 30, 2020) PAGE 6 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
All available hydrology data was reviewed and a final rating curve developed for the upper weir
station. Equation 3 is the final curve for the upper gauging station. Figure 4 shows available
stage and flow data, the preliminary rating curve, and the final rating curve #1 for this station.
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Equation 3, Upper Weir Rating Curve #1:
For H<2.05: Quw = 1.6 + 15.5 (H — 1.00) 1.15
For H>2.05: Quw=1.6+15.5(H-1.00)""+3.33x20x(H-2.05)1.s
Where: Q„w = flow at upper weir in cubic feet per second
H = water depth above the pressure transducer in feet (adjusted).
Valid for H from 0 to 2.5.
Valid from 8/28/2009 to 5/27/2010.
Figure 4: Uooer Weir Gauging Station Rating Curve #1
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1
Stage (feet, PT = 0 datum)
Equation 3 is valid prior to the assumed weir failure on May 27, 2010. Equation 4 is the
estimated rating curve after the failure. The Equation 4 rating curve is based on the data in
Table 4, and is shown in Figure 5. This curve is based on the following assumptions:
- The site's stream bed section geometry, including the weir debris, remained stable from
May 27, 2010 through August 20, 2010.
- The pressure transducer installation was not affected by the weir failure or other events.
- The calculated flow at the time of weir failure (65 cfs) is reasonably accurate. This flow is
more than 400% of the highest flow measurement used to develop rating curve #1 (eqn 3).
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 7 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
Available data suggests these assumptions are reasonable, but flow calculated from this stage
record may be significantly incorrect. Appropriate caution is warranted in use of these data.
Equation 4, Upper Weir Rating Curve #2: Quw = 1.5 + 17.8 (H-1.32) 2.1
Where: Q„w = flow at upper weir in cubic feet per second
H = water depth above the pressure transducer in feet (adjusted).
Valid for H from 0 to 2.0.
Valid from 5/27/2010 to 8/20/2010.
Figure 5: Upper Weir Gauging Station Rating Curve #2
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Table 4: Flow and Stage Measurements Used for Upper Weir Rating Curve #2
Local Date/Time Party Measured Flow (cfs) PT Stage Reading (feet, adj.) Method / Equipment
Five Mile Creek at Upper Weir Gauging Station
Point of zero flow - 0 1.12 Note 1
5/27/2010 19:00 - 65 2.87 Note 2
8/20/2010 14:00 Paulus 12.9 2.18 CV-MM 3
Acronyms: Notes:
cfs: cubic feet per second 1. Point of zero flow is estimated from available site information.
CV-MM: Current -velocity method 2. Flow is estimated from calculated flow prior to weir failure.
using Marsh McBirney Flowmate 2000. 3. Average of two concurrent measurements is reported. The
coefficient of variance between the two measurements is less
than 10% unless indicated otherwise.
FEBRUARY 2020 (REVISION 2 —JUNE 30, 2020) PAGE 8 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO POLARCONSULT ALASKA, INC.
4.2 Station Hydrographs
Adjusted stage data for the lower weir and upper weir gauging stations are presented on Figure
6. Upper station stage data is adjusted for ice effects and datum shifts per Brailey 2020.
Figure 7 presents measured flow adjusted to the upper gauging station and calculated flow
based on the adjusted stage record (Figure 6) and rating curve equations (equations 3 and 4).
5.0 CONCLUSIONS
Based on review of available data:
1. Available data indicates the 2009-2010 hydrograph based on the upper gauging station
period of record is representative of a typical year for Five Mile Creek and is appropriate
to use for project design and economic analysis.
2. Available data cannot provide quantitative estimates of expected variability in year-to-
year resource hydrology or resultant project performance.
3. Site -specific hydrology data is insufficient to generate customized flood frequency
estimates. Estimates from published regional regression methods, with consideration of
site -specific information, including the demonstrated long-term adequacy of the
Edgerton Highway culvert at Five Mile Creek installed in 1969, are recommended for
design.
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 9 OF 16
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FIVE MILE CREEK HYDROELECTRIC PROJECT
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7.0 REFERENCES
AEA 2016.
Alaska Energy Authority (AEA). Chitina Trip Report. March 23, 2016.
Anchorage, AK.
AEA 2019.
AEA. Project files on SharePoint file server. May 2019. Anchorage, AK.
BPE 2018.
Bering Pacific Engineering, LLC (BPE). Site photographs provided courtesy of
BPE. October 14, 2018.
Brailey 2020.
Brailey Hydrologic. Five Mile Creek streamflow record extension and flood frequency
analysis. Anchorage, AK. March 31, 2020.
CRW 2012.
CRW Engineering Group, LLC. Chitina, Alaska. Conceptual Design Study Report.
Fivemile Creek Hydroelectric Project. (176 pages). January 13, 2012. Anchorage, AK.
CRW 2014.
CRW Engineering Group, LLC. Chitina, Alaska. Five Mile Creek Hydroelectric
Project. 65% Design Drawings (31 sheets). August 2014. Anchorage, AK.
Finnesand 2019.
Martin Finnesand, President of Chitina Electric, Inc. Personal communication.
May 2019. Anchorage, AK.
Hertrich 2019.
Daniel Hertrich, P.E. Personal communication and digital file transfer. August
30, 2019.
Hudson 2005.
Hudson, Rob and Fraser, John. Introduction to Salt Dilution Gauging for
Streamflow Measurement Part IV. The Mass Balance (or Dry Injection) Method.
Streamline Watershed Management Bulletin. Volume 9, No. 1. Fall 2005.
Polarconsult 2007.
Polarconsult Alaska, Inc. Design Drawing 'Five Mile Creek Culvert Weir, O'Brien
Creek Design, Phase 1. Chitina AK.' November 21, 2007.
Polarconsult 2008.
Polarconsult Alaska, Inc. O'Brien Creek Hydroelectric Conceptual Design, Final
Report. March 27, 2008. Anchorage, AK.
Polarconsult 2009a.
Polarconsult Alaska, Inc. Project memo Report on weir installation on Fivemile
Creek in Chitina. September 1, 2009. Anchorage, AK.
Polarconsult 2009b.
Polarconsult Alaska, Inc. E-mail from Daniel Hertrich to Alan Fetters of AEA
conveying interim weir equation for upper weir station. October 28, 2009.
Anchorage, AK.
Polarconsult 2019.
Polarconsult Alaska, Inc. Project files associated with Five Mile Creek from prior
contracts with the Alaska Energy Authority and its contractors in 2007 through
2010. Anchorage, AK.
USGS 2003.
U.S. Geological Survey. Estimating the Magnitude and Frequency of Peak
Streomflows for Ungoged Sites on Streams in Alaska and Conterminous Basins in
Canada. Water Resources Investigations Report 03-4188. 2003. Anchorage, AK.
Curran J.H., Meyer D.F., Tasker, G.D.
NCDC 2020.
National Climatic Data Center. Daily weather data retrieved on February 27,
2020 for period of record at the following stations:
Chitina, AK (#USC00501824), Kenny Lake, AK (#USC00504567), May Creek, AK
(#USS0042M01S), McCarthy, AK (#USC00505757)
https://www.ncdc.noaa.gov/cdo-web/datatools/findstation
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 12 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO
8.0 PHOTOGRAPHS
Photograph 1. Lower weir installed at culvert outlet. CEI, January 7, 2008.
Photograph 2. Lower weir installed at culvert outlet. CEI, January 9, 2008.
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 13 OF 16
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Photograph 5. Newly completed upper weir gauging station. Polarconsult. August 28, 2009.
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Photograph 6. Upper weir gauging station after weir failure (downstream view).
Polarconsult. August 20, 2010.
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 15 OF 16
FIVE MILE CREEK HYDROELECTRIC PROJECT
HYDROLOGY MEMO
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Photograph 7. Upper weir gauging station (upstream view). Bering Pacific Engineering.
October 14, 2018.
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Photograph 8. Upper weir gauging station (downstream view). Polarconsult. June 5, 2019.
FEBRUARY 2020 (REVISION 2 -JUNE 30, 2020) PAGE 16 OF 16