HomeMy WebLinkAbout6.16.22 Board Correspondence - FW_ Dam Safety Compliance Report submitted in FERC P-803-000 by Pacific Gas and Electric Company,et al. (2)
From:Paulsen, Shaina
To:BOS
Subject:Board Correspondence - FW: Dam Safety Compliance Report submitted in FERC P-803-000 by Pacific Gas and Electric Company,et al.
Date:Thursday, June 16, 2022 9:22:55 AM
Please see Board Correspondence below.
Shaina Paulsen
Associate Clerk of The Board
Butte County Administration
25 County Center Drive, Suite 200, Oroville, CA 95965
T: 530.552.3304 | F: 530.538.7120
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Subject: Dam Safety Compliance Report submitted in FERC P-803-000 by Pacific Gas and Electric Company,et al.
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On 6/16/2022, the following Filing was submitted to the Federal Energy Regulatory Commission (FERC), Washington D.C.:
Filer: Pacific Gas and Electric Company
Pacific Gas & Electric Company (as Agent)
Docket(s): P-803-000
Lead Applicant: Pacific Gas and Electric Company
Filing Type: Dam Safety Compliance Report
Description: Pacific Gas and Electric Company submits 2017 Probable Maximum Flood Study & Spillway Rating Curve Analysis,
Response to FERC Comments for the DeSabla-Centerville Hydro Project under P-803.
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245 Market Street
tƚǞĻƩ DĻƓĻƩğƷźƚƓ
San Francisco, CA 94105
Mailing Address:
Mail Code N11D
P.O. Box 770000
San Francisco, CA 94177
June 15, 2022
Via Electronic Submittal (E-File)
Frank L. Blackett, P.E., Regional Engineer
Federal Energy Regulatory Commission
Division of Dam Safety and Inspections
San Francisco Regional Office
100 First Street, Suite 2300
San Francisco, CA 94105-3084
RE: DeSabla-Centerville Hydroelectric Project, FERC No. 803-CA
Round Valley Dam, NATDAM No. CA00346
2017 Probable Maximum Flood Study and Spillway Rating Curve Analysis
Comment Responses
Dear Frank L. Blackett:
This letter presents to the Federal
the probable maximum flood (PMF)
study and spillway rating curve (SRC) analysis for Round Valley Dam, which is part of
DeSabla-Centerville Hydroelectric Project, FERC No. 803.
in a letter dated August 10, 2021.
2021 letter included general comments, as well as several technical
comments specific to the PMF study and SRC analysis for Round Valley Dam. PG&E
initial plan and schedule to respond
to the remaining technical comments in a letter to FERC dated February 28, 2022. PG&E
responses technical comments are enclosed with this letter (Enclosure 1).
Should you have technical questions concerning this matter, please contact Dr. Abbas
Dorostkar, senior dam safety engineer for PG&E, at (415) 973-8117. For general questions,
please contact Jackie Pope, license coordinator for PG&E, at (530) 254-4007.
Sincerely,
Robert O. Ellis, P.E., G.E.
Deputy Chief Dam Safety Engineer
Enclosure:
1. Responses to FERC Comments Regarding
and Spillway Rating Curve Analysis
ENCLOSURE 1
Enclosure 1
DeSabla-Centerville Hydroelectric Project, FERC No. 803-CA
Round Valley Dam, NATDAM No. CA00346
Responses to FERC Comments Regarding 2017 Probable Maximum Flood Study
and Spillway Rating Curve Analysis
In a letter to Pacific Gas and Electric Company (PG&E) dated August 10, 2021 the
Federal Energy Regulatory Commission (FERC) provided comments regarding the
2017 probable maximum flood (PMF) study and spillway rating curve analysis for Round
Valley DeSabla-Centerville Hydroelectric Project, FERC
No. 803. and provided our plan and
schedule to respond to the remaining technical comments in a letter dated February 28,
2022. technical comments are copied below, followed by
Technical Comments
Spillway Rating Curve
Comment 1:
Submit the HEC-RAS model files used to develop the spillway rating curve
analysis.
PG&E is preparing the original HEC-RAS model files used to develop the
spillway rating curve for submission to FERC and will submit the files by April 30,
2023.
Comment 2:
Please update Drawings 342313 (Discharge Rating Curve Round Valley
Reservoir) and 440225-2 (Exhibit Drawing L-1), and any other applicable
drawings related to the spillway rating curve and elevation information from the
LiDAR survey. Relevant drawings should be updated or included in the next
update of the dam STID.
PG&E is updating the supporting technical information document (STID) for
Round Valley Dam to include the updated spillway rating curve and elevation
information. PG&E will provide an update STID to FERC by April 30, 2023.
Comment 3:
As stated in the report Summary and Discussion, the rating curves should be
reviewed if observational flow/stage information become available to allow
verification of the model results and updated (if necessary) with observed data.
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Enclosure 1
Currently, there are no flow monitoring gages downstream of Round Valley Dam
to verify the discharge rating curve. Industry-standard methods and engineering
judgement were used to develop representative rating curves for the spillway.
Potential modifications and improvements to incorporate observational flow/stage
data
improvement program (SAIP) for Round Valley Dam.
schedules regarding the SAIP have been communicated in separate
correspondence.
Probable Maximum Flood Study
Comment 4:
Section 2.0 references that the spillway can discharge up to 1,800 cfs at zero
freeboard. This is incorrect based on the Spillway Rating Curve analysis (stated
as 1,365 cfs) submitted along with the PMF report. Clarify this apparent
discrepancy.
Section 2.0 of the PMF report will be updated to reflect the spillway capacity at
zero freeboard based on the Spillway Rating Curve Analysis. PG&E will provide
an updated PMF Report to FERC by May 31, 2023.
Comment 5:
The Round Valley Dam PMF report utilizes watershed information and analyses
from the Probable Maximum Flood Estimate Revisions for Selected Dams in the
Feather River Watershed (FRW) report, developed by HDR in 2015 but never
submitted for our review. However, the 2015 PMF study for the FRW was revised
by a 2017 PMF study and accepted by the FERC in February 2021. Please
evaluate if the Round Valley Dam PMF should be revised based on the most
recent PMF revision for the FWR and update the references using the accepted
PMF study. Please also resubmit the revised modeling files (e.g., HEC-1) and
update the Round Valley Dam PMF estimates, as necessary.
PG&E will evaluate changes to the calibration results used in the PMF study
based on the 2017 FRW PMF study and update the Round Valley Dam PMF
study and modeling as needed. Based on the results of the evaluation, PG&E will
update the PMF report and model as needed and provide to FERC by May 31,
2023.
Comment 6:
As noted in Chapter 8 of the FERC Engineering Guidelines, the ratio R/(TC + R)
tends to be approximately constant for hydrologically similar drainage basins in a
region. According to Table 4-1 of the PMF report, which shows the calibrated unit
hydrograph parameters used for your regression analysis to estimate TC and R
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Enclosure 1
for the Round Valley watershed, the above ratios that are computed using the
calibrated parameters vary significantly from 0.42 to 0.97. Rather than using all
the calibrated USGS gages to perform your regression analysis, consider using
only the gages that represent watersheds with similar basin shape factors (i.e.,
could also be back-calculated using an average R/ (TC + R) ratio for the
calibrated gages with similar shape factors and the TC for the Round Valley
parameters. This approach may indirectly account for other hydrologic
parameters that R is dependent on (e.g., impervious area), while a direct
estimating TC and R or further justify your selected approach.
PG&E will review the United States Geological Survey (USGS) calibration gages
used to perform the regression analysis to estimate T and R values to ensure
C
that only gages that represent watersheds that are hydrologically similar to the
Round Valley watershed were used. Based on the results of the evaluation,
PG&E will update the PMF report as needed and provide to FERC by May 31,
2023.
Comment 7:
We understand that an update to the GIS dataset (e.g., terrain, grid size) for
-137, 1061, 2130-CA) had an impact on
hydrologic parameters, such as the longest flowpaths and basin shape factors,
which affected the PMFs for the projects. Please verify that the GIS dataset for
the Round Valley watershed and other underlying source data are up to date. If
revisions are needed, explain the effects on the associated hydrologic
parameters and resultant PMF.
PG&E will review and, if necessary, update the GIS dataset used for Round
Valley Dam. Based on the results of the evaluation, PG&E will update the PMF
report as needed and provide to FERC by May 31, 2023.
Comment 8:
Section 7.0 It is our understanding that except for the April general storm, the
antecedent reservoir level was assumed to be empty and the low-level outlet was
assumed to be open for other critical (October-March) period simulations. Based
on our review of the most recently submitted DSSMR, this condition may not
always be the case. Please evaluate the reservoir conditions against historical
operational reservoir data and provide additional supporting information for
starting reservoir elevations (e.g., reservoir data, guidance from the FERC
Engineering Guidelines Chapter 8). Otherwise, please re-run all the simulations
using normal pool conditions.
3
Enclosure 1
PG&Ewill review current operating procedures based on the most recentDam
Safety Surveillance and Monitoring Report (DSSMR) for Round Valley Dam.
Historical data will be used to confirm whether the antecedent reservoir
conditions comply with standard operating procedures and reservoir data.
Operational assumptions related to antecedent reservoir level and lower-level
outlet will be updated as needed and validated in the report. Based on the results
of the evaluation, PG&E will update the PMF report as needed and provide to
FERC by May 31, 2023.
Comment 9:
Evaluate the reliability of the low-level outlet during a flood event to remain
operational if impacted by debris. Please consider the historical reservoir cycling,
debris history/debris buildup in the watershed, lack of telecommunications, etc. in
the evaluation. Provide supporting justifications if deemed operational.
PG&E will conduct sensitivity runs to evaluate the impact of the low-level outlet
on the computed PMF. Based on the results of the evaluation, PG&E will update
the PMF report as needed and provide to FERC by May 31, 2023.
Comment 10:
Section 9.0 Wind Wave Analysis Per the USBR Design Standards No. 13-
Chapter 6 Section B.4.1, the wave height statistic used to compute wave runup
should be selected based on the ability of the crest and downstream slope to
withstand overtopping by wave action. According to this section, when the crest
and downstream slope are adequately protected against erosion or will not
slough or soften excessively, or when public traffic will not be interrupted, a wave
height equal to the average height of the highest 10 percent of the waves (1.27 x
height of significant wave) should be used to compute wave runup. Please
provide the selection criteria/justification for the selected ratio H/Hs of 1.0 which
is associated with a wave height equal to the average height of the highest 33.3
percent of the waves.
PG&E will review the current wind wave analysis based on methodologies
provided in United States Bureau of Reclamation (USBR) Design Standard 13
(June, 2021) to address the parameters mentioned in Comment 10, above.
Based on the results of the evaluation, PG&E will update the PMF report as
needed and provide to FERC by May 31, 2023.
Comment 11:
Section 11.0 This section described a 15-percent increase in PMF inflow in
comparison to the values used in the 2014 dam break analysis. Upon finalization
and acceptance of the Round Valley PMF Report, please provide a plan and
schedule to update the Round Valley Dam break analysis and updating the
inundation maps for the EAP.
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Enclosure 1
By May 31, 2023, PG&E will provide a plan and schedule to update the Round
Valley Dam break analysis and inundation maps.
Comment 12:
We will accept the use of HEC-1 software for this iteration of the Round Valley
PMF study and revisions resulting from comments in this enclosure. However,
please note the U.S. Army Corps of Engineers (USACE) no longer supports the
HEC-1 software. In future submittals, PG&E should develop HEC-HMS
simulations (either new or using imported HEC-1 data) for hydrology and flow
routing analyses.
PG&E acknowledges this comment.
Comment 13:
For future submittals utilizing HEC-HMS, the Exponential Loss Method should
not be used for continuous simulations because it is a function of cumulative
infiltration and does not include any type of recovery (HEC-
Instead, future models should use the Initial and Uniform Loss Method (which is
the preferred method described in Chapter 8 of our Engineering Guidelines) or
the Soil Moisture Accounting Method for continuous simulations with multi-peak
rainfall events.
PG&E acknowledges this comment and will adopt the industry accepted
hydrological modeling parameters in future modeling efforts.
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