HomeMy WebLinkAbout2018 Seasonal Flood Control Outlet Gate Closure Plan for Lake Oroville Menchaca, Clarissa
From: Bennett, Robin
Sent: Tuesday, April 17, 2018 8:30 AM
To: Menchaca, Clarissa
Cc: McCracken, Shari
Subject: FW: Project Safety Compliance Report submitted in FERC P-2100-000 by Department of
Water Resource,et al.
Attachments: 04-16-2018 Oro Dam Spillway- 2018 Seasonal Gate Closure Plan
20180417-5D37(32830847).pdf
See the attached 2018 Seasonal Flood Control Outlet Gate Closure Plan for Oroville Dam Spillway.
Robin Bennett,
Executive Assistant
(530) 872-6304 rbennett@buttecounty.net Butte County Supervisor's Office Supervisor Doug Teeter, Board of
Supervisors, District 5
747 Elliott Road
Paradise, CA 95969
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Sent:Tuesday,April 17, 2018 6:07 AM
Subject: Project Safety Compliance Report submitted in FERC P-2100-000 by Department of Water Resource,et al.
On 4/17/2018,the following Filing was submitted to the Federal Energy Regulatory Commission (FERC),Washington
D.C..
Filer: Department of Water Resource
California Department of Water Resources (as Agent)
Docket(s): P-2100-000
Lead Applicant: California Department of Water Resources
Filing Type: Project Safety Compliance Report
Description: The Department of Water Resource under P-2100. submits Oroville Emerg. Recovery-Spillways,2018
Seasonal Flood Control Outlet Gate Closure Plan.
To view the document for this Filing, click here
http:Helibrary,FERC.gov/idmws/file_list.asp?accession_num=20180417-5037
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of warFR��
STATE OF CALIFORNIA
_f y DEPARTMENT OF WATER RESOURCES
OROVILLE EMERGENCY RECOVERY -SPILLWAYS
4 OF CALSF�
OROVILLE EMERGENCY RECOVERY — SPILLWAYS
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
April 16, 2018
Table of Contents
Introduction...................................................................................................................... 2
PrimaryObjectives .......................................................................................................... 2
Strategy...........................................................................................................................2
Upper Feather River Basin Hydrology............................................................................. 3
Precipitation Variability....................................................................................................3
Snow Water Content Variability.......................................................................................4
ReservoirInflows.............................................................................................................5
ReservoirStorage ........................................................................................................... 9
Historical 2017 Operations............................................................................................ 10
Historical 2018 Operations............................................................................................ 10
Forecasted 2018 Operations......................................................................................... 11
Construction Considerations ......................................................................................... 14
Seasonal FCO Gate Closure Date ................................................................................ 15
Contingency .................................................................................................................. 16
Conclusion..................................................................................................................... 16
ATTACHMENT A—Technical Memorandum SRT-FCO-DOC-12 (CEI I)....................... 16
Oroville Emergency Recovery—Spillways
2098 Seasonal FCO Gate Closure Plan for Labe Oroville
Introduction
During normal flood operations, Lake Oroville's Flood Control Outlet (FCO) spillway was
damaged on February 7, 2017. Reacting to that, DWR elected to deviate from the 1970
U.S. Army Corps of Engineers (USACE) water control manual (WCM) for Lake Oroville.
The WCM gives the Director of DWR authority to modify operation temporarily during
emergency situations such as when dam safety is a concern. DWR coordinated this
deviation with USAGE, and USACE concurred. DWR reduced—and then halted---
reservoir releases in the gated spillway. With continued reservoir inflow due to storm
runoff, the reservoir pool level rose to elevation 901 ft. This led to the first-ever
emergency spillway release. Flow down the unlined emergency spillway slope caused
erosion and scour, raising concern about dam safety. Following the incident in February
2017, repairs were made to both the FCO spillway and emergency spillway.
In October 2017, a plan for operating the partially restored FCO spillway from
November 2017 through April 2018 was developed to maintain dam safety and manage
flood risk. The Lake Oroville 2017-2095 Flood Control Season Operations Plan
(Operations Plan) was developed to address the interim FCO spillway flow limitations.
The Operations Plan outlined operational strategies that limited the FCO spillway design
release to 100,000 cubic feet per second (cfs). The Operations Plan ensured dam
safety, provided downstream flood protection, and met the existing USACE flood control
requirements set forth in the WCM. DWR also targeted lower lake elevations than
required by the existing WCM.
This Seasonal FCO Gate Closure Plan (Plan) details the near-term operation plan for
Lake Oroville including final FCO spillway gate operations for this season and with a
preliminary look at anticipated operations and forecasted lake elevations through the
end of November. This Plan incorporates actual and forecast snowpack information and
technical analyses that will support the final FCO gate closure with the intent to
maximize the 2018 construction season.
Primary Obaectives
DWR, in order to manage the risks for public safety, developed two primary objectives
governing this Plan for Lake Oroville and they are:
1. Lengthen the construction window as much as feasible to ensure
recovered spillway flow capabilities are achieved prior to next winter
2. Begin FCO demolition at the earliest date for which risk of emergency
spillway use has become negligible.
Strategy
In recognition and management of risks associated with hydrologic uncertainties such
as significant late season precipitation events and the passage of an appropriate
2
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
volume of snowmeit prior to the final FCO gate closure, along with any unscheduled
outages pertaining to the use of Hyatt Powerplant (Hyatt) and its appurtenances, this
Plan must be adaptive and flexible to be successful. Real-time conditions create a
dynamic environment and this Plan must accommodate these changing circumstances.
Upper Feather River Basin Hydrology
California hydrology varies widely by region with Northern California receiving the most
precipitation. The highest monthly volume of precipitation occurs in the months of
November through March. Conversely, the months of June to September produce
almost zero precipitation volume. Runoff in the months of April, May, and June are
primarily a function of snow accumulated through April 1. The hydrology not only varies
by region and time of year, but it also varies widely from year to year as seen in Figures
1 and 2, which are discussed below in more detail.
Precipitation Variability
The Northern Sierra Precipitation 8-Station Index covers the major watersheds in the
northern Sacramento Valley (Figure 1) and shows that water year 2016-2017 set a new
record for total annual precipitation of 94.7 inches, compared to water year 1982-1983,
which had been the wettest on record, with an annual total of 88.5 inches (Table 1).
Conversely, Figure 1 shows the 8-Station Index for water year 2017-2018, to date, has
been tracking well below the 1966-2015 historical average. As of April 11, the
cumulative precipitation for water year 2017-2018 is only about 37 inches compared to
about 87 inches for the same period during the 2016-2017 water year.
Table 1: Comparison of Northern Sierra Precipitation 8-Station Index values.
Cumulative Water Year Total Percent of an Average
Water Year Precipitation as of (Inches) Water Year
April 11 (Inches)
1983 79 88.5 171%
2017 90 94.7 183%
2018 37 37' 71%1
1 Total inches and percent average as of April 11, 2018
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Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
North Sierra Precipitation: 8-Station Index,April 11,2018
100 6 - �., ��, --�rsWa-sla0Ty�— – ---
5hosta oam Percent of Average for this Date:SS%
Mineral
9$ Ar Qaiac 94.7 i
BrushCrookE
9D 201fi-2D17 Dail Precip(wettest)
SleriavilleRS -_... ....... .... . . .. Y
s Blue canyon 1982-1983(2nd wettest) 88.5 !
Pacific House - -
s ,,: 1997-1998 62.4
80
e y
75
70
0 65
a 60
Z
iv 55 CL
50.x. r„_.. n; E3�3�=-7ri�} �•t..
45 m
a, urrent Daily Precip:37.
-” 40
2014-2015 Daily Precip M
37.2
35
S 301 i r°
3
201
1976-1977(2nd driest&driest thru Aug) 19.0
151
10€
E
51
0
Oct 1 Nov 1 Dec 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1
Water Year(October 1 -September 30)
Figure 1: The 8-Station Index plot of precipitation shows that 2018 has been below the 1966-2015
historical average.
Snow Water Content Variability
The current snow water content is a stark contrast to water year 2016-2017, when
snowpack in the northern Sierra was about 150% of the April 1 average for this same
time period, as shown in Figure 2. The snow water content for 2016-2017 peaked
around mid-April 2017 and the snowmelt for that water year lasted well into July.
As of April 10, 2018, the snow water content for the northern Sierra (Figure 2) was 34%
of the April 1 average. The snow water content in the northern Sierra seems to have
peaked around 50% of the April 1 average and has now started to decline.
4
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
California Snow Water Content,April 10,2018,Percent of April 1 Average
250 T
Norah - Percent Of Average forth 6%ls bate:J
200 1982-1983(max)
2016-2017
150
100
50 ;".2cfd,i;c
1975-
34
DEC JAN FEB MAR APR MAY JUN JUL
Figure 2: Below average snow water content to date for 2018 is close to other dry years like 1976-
1977 and 2014-2015.
Reservoir Inflows
Lake Oroville inflows can be divided into three distinct seasons. During the months of
November through March reservoir inflows are primarily a function of direct runoff from
precipitation falling in those wettest months. Reservoir inflows in the months of April
through June are primarily a function of snow melt runoff from the accumulated snow
pack as of April 1 each year. Reservoir inflow in the months of July through October are
primarily a function of releases from upstream reservoirs operated by Pacific Gas and
Electric. Historically the direct runoff months produce the highest reservoir inflows
followed by the snow melt months at a distant second. Inflows during the summer
period are inconsequential.
Figure 3 illustrates actual inflows into Lake Oroville from April 15, 1980 to April 14,
2017. The highest peaks occurred in December through March from runoff due to
atmospheric river storm events. From April to June, runoff from major precipitation
events taper off and runoff becomes increasingly dominated by snowmelt. From June to
November 1, historical inflows were significantly lower than the capacity of Hyatt.
5
Oroville Emergency Recovery--Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
Actual Oroville Inflows(1980-2017)
3(AOM
)50'aw
Z.
lu�na�
Mg
'a
C I.
it
i
1Cr1,R0.J yj
o 4u..•- �r? �r
F5-AIM A-hn: 24 3,,� 12 5^V LNa• ?i t)c 9 fel M Ma-
Figure 3:Annual distribution of historical daily inflows into Oroville shows high variably of winter
precipitation and low variability in the summer.
Table 2 shows a comparison of the April to July runoff forecasts for 2017 and 2018, as
of April 1 for each year, along with the average April to July runoff for the historical
period 1966 to 2015. Runoff forecasts are unimpaired (full natural) flows which
represent the natural water production of the river basin, unaltered by upstream
diversion, storage, or export or import of water to or from other watersheds.' In the
table, the 50% exceedance is the projected median runoff forecast for April to July
(1,090 TAF) and it can be seen that 90% of the projected runoff forecasts will likely only
exceed 800 TAF. Even under wetter assumptions as illustrated by the 10%
From B-120 Water Supply Forecast Update Summary(posted on 03/15/18 14:05),
http://cdec.water.ca.gov/bl20up,html
6
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
exceedance forecast the projected runoff of 1,340 TAF is well below the historical
average (1,704 TAF).
Table 2: Comparison of April to July runoff forecasts.
Year Apr—July((TAF)Runoff Ruun Forecast percent of Average
2017 2,790 164%
2018(90% exceedance) 800 47%
2018(50% exceedance) 1,090 64%
2018(10% exceedance) 1,340 79%
Historical Average 1,704 100%
'April through July forecast of runoff as of April 1 for each year
2 Historical average for 1966-2015 period
The National Weather Service (NWS) California-Nevada River Forecast Center
(CNRFC) produces forecast ensembles (f=igure 4) which overlay 59 years of historical
events onto the current conditions in the basin and forecast the Lake Oroville inflows up
to one year. The current conditions include snowpack conditions and soil moisture, on
which forecasts of future precipitation, wind, and temperature are applied.
The NWS ensemble forecast predictions incorporate the following:
1. Days 1 to 3, NWS meteorologist forecasts incorporates current temperature,
precipitation, freezing temperatures, and watershed conditions.
2. Days 3 to 15, NWS's Global Ensemble Forecast System weather model.
3. Day 15 and beyond, climatology (applying historical temperature and
precipitation inputs).
7
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
NWS-CNRFC Ensemble Traces for Oroville Inflow
350000
300400
250000
200000
0
_ 150400
100000 ; 66;
S
50400
0 0 0 0 o a o 0 0 0 a 0 0
6% 0
Figure 4: NWS-CNRFC ensemble traces of potential Oroville inflow from April 11, 2018 to April 11,
2019 indicate reducing inflows into summer, but potential for high inflow going into the winter.
The ensembles traces depicted in Figure 4 include actual conditions beginning on April
11, 2018 along with forecasted inflows to Lake Oroville through April 11, 2019. The
forecast of inflows indicates reducing inflows into summer, but potential for high inflow
starting early November and going into the winter. Similar to actual inflows shown in
Figure 3, peak inflows occur from December through February with mainly lower flows
occurring June through October with one notable exception2.
Z The so called"Columbus Day Storm" occurring in 1963 was considered a 250-year event for October.
8
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
Reservoir Stora-ge
Reservoir inflows vary not only during the year, but from year to year, as well. This
inflow variation translates directly to variances in water storage from year to year. As
shown in Figure 5, during water year 2016-2017, storage in Lake Oroville significantly
exceeded the storage in 2017-2018. Currently, storage is tracking about 695 thousand
acre feet less than last year at this time. In addition, as noted previously, the below
average snowpack will not provide the same refill potential during the April through July
runoff period as it typically does.
Lake Oroville Storage Comparison
9W 3,538
Water year 2016-2017 §
i
t
aso z,eoa
800 2.192
C m
o �U p
m
n
R
750 0 1,678
Water year 2017-2018
1,255
t
650 E 992
Oct Nov pec Jan Feh Mar Apt May Jun Jul Aug Sep
Figure 5: Lake Oroville water year 2016-2017 and 2017-2018 elevations.
9
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
Historical 2017 Operations
Since the February 2017 incident, the FCO spillway has been used three times with
each cycle ranging from 11 to 29 days. The decision to use the FCO spillway was
based upon projected inflow hydrology and storage levels and the stable condition of
the FCO. The last cycle the FCO spillway gates operated was from May 10 — 19, 2017.
Demolition of the FCO spillway chute began on May 20, 2017 when the lake was at 835
feet. Outflow from the lake was released in such a manner to meet downstream needs
with the final objective of reaching elevation of 700 feet by November 1. Figure 5 and
Figure 6 both show the 2017 elevation drawdown of the lake to meet the November 1
target.
Historical 2018 Operations
Following November 2017, the lake elevation slowly increased as the winter season
progressed, but at no time during the November 2017 to April 2018 period did the lake
reach an outflow trigger elevation as outlined in the 2017-2018 Operations Plan
(Figure 6).
For most of the winter, the below average precipitation, snowpack, and inflows resulted
in releases to the Feather River that have been made to meet both minimum instream
and Bay-Delta requirements while conserving storage for future releases to meet
downstream needs. One exception was a significant increase in releases in early April
to moderate elevation gains from peak inflows associated with a warm precipitation
event occurring early in the month. This dramatic fate winter hydrologic change
complicated planning efforts as action was taken to avoid rapid elevation gain to
elevation 830 feet and potential use of the FCO during the month of April. This action
was successful and risk of reaching elevation 830 feet before late in the month has
been abated. Since that early month precipitation event, the storage elevation gains
have stabilized and the releases to the river are being ramped back down.
10
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
2017-2018 Winter Operations Plan
900.0 3538
850.0
2808
.......................
Elev. M
86 ft.FCO Spil laa
,y Sill E levat'jo0j.-
800.0 .............................................................. 2192
0
Enhanced Flood Pool Elevation Target
Out 11--NEY.or EI-6-=U-6""
............
1678
— — — — — — — — — — — — — — — — — — —-
750.0
700.0 1255
650.0 912..
S 0 N 0 j F M A M 1 I A
- - ExIsthl;FCFA FCD dry ground —Z)dning FCM FCD was ground ElewlonUggeM 17-'IR DamSalety Pool Target + Elevadon
Figure 6: Lake Oroville elevation, beginning September 2017 through April 11, 2018,showing
drawdown of lake to 700 feet by November 1,2017 and the increase of storage at the end of the
winter season.
Forecasted 2018 Operations
Using HEC-ResSim, DWR has performed analyses assessing near-term reservoir
elevations using the ensemble inflow forecast provided by the CNRFC through the next
thirty days. The latest analysis, (performed April 12, 2018) shown in Figure 7, indicates
that the reservoir is likely to top out below elevation 830 feet by mid-May. There is still a
potential for lake elevations to rise to nearly 850 feet although the probability appears
low.
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for lake Oroville
880
870 . . . . .
860-
850-
840-
830
60850640
---------
620-
810-
4,
20 810
800
60,000-
40.000-
30,000
0,00040000-30,E
3
20 MO
10,0130 r
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 1 2 1 3 4 1 5 6 1 7 8 1 9 10
Apr2018 I May2018
Figure 7: Lake Oroville projections of elevations and releases through May 10,2018 following May
8, 2018 gate closure.
Figure 8 shows the variance of maximum pool elevation by month from the HEC-
ResSim analysis. This figure indicates that May has the potential for higher maximum
lake elevations compared to April.
12
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
870 _..._..__.._._.___...___..____.....__._......___..._._............
_.._.._. ..__...�.
Legend
Maximum
860
9
3rd quartile
Mean
Median
8501ist quartile
rn I
Minimum 3
0
V � ;
Z 840 i
c �
0
> 830 : 3
cis !
o
0 I I
a i
820
3
810 e
3
800 '
April 12-15 April 16-30 May 1-11
Forecast Period
Figure 8: Variance of maximum pool elevation by month from analysis of ensemble forecast.
Table 3 shows the maximum pool elevation and release percentiles by forecast period
based on the analysis. The table shows a simulated gate closure on May 8, 2018
combined with inflows from the ensemble forecast may result in a maximum pool
elevation of only 848 feet and maximum release of only 10,000 cfs. The table also
shows that 90% of the simulations had a maximum pool elevation of 830 feet or less
with a maximum release of 10,000 cfs or less.
13
Oroville Emergency Recovery-Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
Table 3. Ensemble maximum pool elevation and release percentiles by forecast period
Maximum pool elevation (ft)for Maximum release(cfs)for forecast
Statistic' forecast period period
April April May April April May
12-15 16-30 1 -11 12 -15 16-30 1 -11
Maximum 805 834 848 10,000 9,000 9,000
10% 804 824 830 10,000 7,500 5,000
exceedence
20% 804 818 825 10,000 7,500 5,000
exceedence
xc
e 804 815 818 10,000 7,500 5,000
exceedence
40% 804 813 815 10,000 7,500 5,000
exceedence
50% 804 812 814 10,000 7,500 5,000
exceedence
60% 804 811 812 10,000 7,500 5,000
exceedence
70% 804 810 811 10,000 7,500 5,000
exceedence
80% 804 809 810 10,000 7,500 5,000
exceedence
90% 804 808 809 10,000 7,500 5,000
exceedence
Minimum 804 807 807 10,000 7,500 5,000
' For example, 10%exceedence means the maximum pool elevation was 804 ft or greater in 10%of the
simulations (approximately 6 out of 59 ensemble members) during the period of April 12 through April 15.
Each spring and fall there is a Hyatt penstock outage for routine maintenance. During
the spring 2018 outage, the April 16 through May 11 Hyatt capacity will be at 5,000 cfs.
However, in the event additional outflow capacity is needed, the River Valve Outlet
System (RVOS) can be put into service and provide an additional 4,000 cfs of capacity.
Beginning May 11, Hyatt is expected to have five units available with a capacity of about
13,000 cfs. The ensemble runs have taken these outage assumptions into account.
Construction Considerations
As discussed previously, the HEC-ResSim analyses have indicated there is a potential
for lake elevations to rise to nearly 850 feet. Although the probability of this occurring
appears small (1 in 59 or 2%), extensive coordination with Kiewit has led to the
conclusion that water behind the FCO gates would not pose a significant impact on
safety or construction schedules. DWR has prepared Technical Memorandum (TM)
SRT-FCO-DOC-12 confirming the minimal risks to construction activities and public
safety should the lake reach these elevations, along with applicable remediation
measures, and included as Attachment A to this Plan. Topics discussed in the TM
14
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
attachment include stability of the FCO headworks structure, construction sequencing,
and seepage and groundwater conditions.
Seasonal FCO Gate Closure Date
In preparation for the spillway repairs, DWR plans to establish a seasonal closure date
for the FCO gated spillway of May 8, 2018. Beyond this date the availability of Hyatt and
the RVOS will ensure that reservoir inflows produced by late season precipitation and
snowmelt can be adequately released.
The May 8 date is twelve days earlier than the final seasonal gate closure date of last
year. The earlier closure date for this year is justified given this year's subpar snowpack
is projected to be largely exhausted by early May.
An outflow trigger elevation of 830 feet will be employed for the months of May and
June to trigger increased Hyatt releases of up to 10,000 cfs. This outflow action should
be achievable without undue risk being placed on the Hyatt generating units. As shown
previously in Figure 5, an FCO gate seasonal closure on May 8 with a potential lake
elevation near 830 feet would be comparable to the conditions of 2017. As experience
has shown from 2017 operations, a lake elevation around 830 feet at the time of the
FCO gate closure did not have significant impacts on safety or construction. A lake
elevation of 830 feet can also be drawn down to the FCO sill elevation of 813 feet in a
short period (approximately two weeks), further facilitating safety and construction
needs if necessary.
Although it is unlikely that elevation 830 feet will be reached this season, this elevation
is also well below the elevation for which the reservoir can be easily managed back
down to a reasonably low level by the fall. Under some scenarios as a result of
significant but rare late season precipitation events the reservoir elevation may increase
above elevation 830 feet. However, this will not pose any risk to reservoir management
this spring nor will it pose any challenges to the draw down to reasonably low levels
next fall.
Beginning no later than July 1, Lake Oroville storage will be drafted to meet local water
deliveries, flow and salinity obligations in the Sacramento-San Joaquin Delta, and
deliveries to State Water Project water supply contractors south of the Delta. Releases
will be made on a pattern that meets these beneficial needs and achieves an end of
September storage elevation of 710 feet. This target will be completely within the control
of the Project operators considering additional reservoir inflows are negligible during the
summer period. Into the fall, it is anticipated that additional drafting of the lake will occur
and the lake elevation will be below 700 feet by the construction milestone of November
1, 2018.
15
Oroville Emergency Recovery—Spillways
2018 Seasonal FCO Gate Closure Plan for Lake Oroville
This low elevation will also provide a desirable buffer of vacant storage should the
completion of the FCO spillway be delayed coupled with any unusually early start to the
2018-2019 rainy season.
As stated earlier, Hyatt capacity is sufficient to manage expected inflows into the fall.
However, it is important to look at possible draw down forecasts for the lake elevation to
ensure reasonably low lake elevations are achieved prior to next winter.
DWR will continue to provide bi-weekly reports until the spillways construction is
completed. In the June 1 bi-weekly report, DWR will provide the operation forecast
which will guide the lake drawdown to the September 30, 2018 target of 710 feet, similar
to the reports that were submitted during the summer in 2017.
Contingency
The River Valve Outlet System (RVOS) will be available to pass flow at a rate of at least
4,000 cfs as a contingency in the event additional outflow capabilities are required
during the 2018 FCO construction season. The RVOS, will only be used as a
contingency in the event of an unexpected loss of capacity at Hyatt or for temperature
management in the late summer into early fall. Prudent management of the cold water
pool is critical for the survival of fish species later in the summer and fall and is therefore
essential that this cold water pool be conserved earlier in the year.
Conclusion
Peak accumulation of snowpack on April 1, 2018 was one-third the accumulated
snowpack the year prior and is expected to be largely exhausted by early May. In
preparation for the spillway repairs in a manner that is consistent with the objectives of
this Plan, DWR plans to establish a seasonal FCO gate closure date of May 8, 2018.
Beyond this date the availability of Hyatt and the RVOS will ensure that reservoir inflows
produced by late season precipitation and snowmelt can be adequately released and a
reasonably low reservoir elevation will be achieved by the fall.
ATTACHMENT A —Technical Memorandum SRT-FCO-DOC-12 (CEII)
16