SFPUC Design Drought Workshop
Peter Drekmeier & Dave Warner: Tuolumne River Trust
Chris Shutes: California Sportfishing Protection Alliance August 23, 2022
1 “The San Francisco Bay-Delta is an
ecosystem in crisis.”
-Felicia Marcus, Former President, State Water Board
A Reminder Why We’re Here
2 The Design Drought Is Not
Based on Modeling or Projections
Source: SFPUC
It was created in response to the 1987-92 (6-year) drought – the worst on record. We have a lot more information now. 3 The SFPUC has the longest drought scenario
of California’s major water districts
4 Much Has Changed Since the
Design Drought Was Conceived
Water demand peaked at 290 mgd in 1987.
It has been under 200 mgd for the past 8 years.
Source: SFPUC
5 Much Has Changed Since the
Design Drought Was Conceived
Water demand peaked at 290 mgd in 1987. It has been
under 200 mgd for the past 8 years.
In response to the 1987-92 drought, the SFPUC
adopted the “Water First” policy, prioritizing water supply over hydropower generation.
The Long-Term Vulnerability Assessment (LTVA)
analyzed water supply vulnerability using tree ring data and 25,000 model runs based on simulated historical
data.
5 Source: SFPUC, 1993
The SFPUC Planned for Much
Higher Demand
6 Why Length of Drought
Planning Matters
Longer drought planning requires more water or
greater rationing.
Overbuilding alternative water supplies leads to
unnecessary rate hikes.
Storing water for an extremely unlikely drought
starves the Tuolumne River and Bay-Delta.
The Design Drought adversely influences other policy
decisions: instream flows, rationing, water supply
planning, water rates, Bay Delta Plan.
7 8
“According to climate projections and expert
elicitations, there is a central tendency of
warming of + 2°C and + 4°C by 2040 and
2070 (Representative Concentration
Pathway [RCP] 8.5), respectively, with no
clear direction of change in mean annual
precipitation over the planning horizon.”
Source: LTVA, p. xxii
9 NGO Questions/Requests
1) Produce model runs using current demand
and
incorporating the Bay Delta Plan
instream flow requirement.
2) What is the return period (likelihood of
occurrence)
of the Design Drought?
3) How will earlier runoff impact the SFPUC’s
w
ater entitlements on the Tuolumne River?
Letters sent on November 5, 2021 and January 19, February 4, March 4, June 8, June 13, June 21, and June 28, 2022.
10 Source Demand
(mgd)
Difference from Current
Actual Demand
SFPUC Annual
Report FY 2020/21
195 --
LTVA Baseline 227 +16%
Threshold (269 TAF) 240 +23%
LTVA Demand Figures
Sources: Data = SFPUC; Table = TRT
11 “Climate change is not the single most
important driver of vulnerability for the RWS.
Under current RWS infrastructure
conditions, either state-amended WQCP
for additional IFR on the Tuolumne River
or an increase in demand by 15% have
significant impacts on the RWS
performance that are equivalent to a
decrease in mean annual precipitation of
around 15%.”
Source: LTVA, p. 250
12 Source: LTVA, Figure 3-26
-1500
Design Drought
The Design Drought Is Much More
Severe Than Any Known Drought
Drought Storage Used
(TAF)
1976/77 517
1987-92 797
2012-15 752
Design
Drought
1,309
Total Useable SFPUC
Storage = 1,350 TAF
13 The LTVA’s Most Severe Drought
Used 1,200 TAF of Storage
Source: LTVA, Figure 3-29
Design Drought (1,309 TAF)
14 Drought Return Periods
How likely are droughts to occur?
Numbers represent how many years might be expected to
pass between droughts as severe as those listed.
The LTVA did not include a return period for the Design Drought.
Source: LTVA, p. 157
15 Chart taken from figure 5-11 in the LTVA
Source: LTVA, Figure 5-11
Drought Probability Chart from the LTVA
Explaining the Chart
Uses demand of 240 mgd
(269 TAF/year).
Chart plots amount of
storage used (x-axis)
against drought frequency
measured as 1-in-x years
(y-axis).
Note y-axis is logarithmic,
meaning droughts
become very rare as
severity increases.
The three vertical lines
represent recent droughts.
The Design Drought uses
~1,300 TAF of storage.
16 Design Drought return period = 70,000 years with 95% confidence interval ranging from 40,000 to 150,000 years.
17 Drought Return Periods
On a Linear Scale
1976-77
100
1987-92
420
7.5 Yr Design
Drought
10,000
8.5 Yr Design
Drought
70,000
-
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
400 600 800 1000 1200 1400
Return Period (years)
Drought Severity (storage used in TAF)
Return Periods and Drought Severity (storage used)
using demand of 269 TAF/240 mgd
Dashed line represents
1000 year return period
7.5-year drought return period = 10,000 years with 95% confidence interval ranging from 8,000 to 13,000 years. Source: TRT : Derived from Figure 5-11 and T able 5-1 of the LTVA 18 Probability of Droughts Beginning in Any
Given Year
Drought Return Period Likelihood
1976/77 100 1.00%
1987-92 420 0.24%
7.5 Year Drought 10,000 0.01%
8.5 Year Drought 70,000 0.0014%
19 “…leading to 1) a reduced spring runoff
volume and magnitude and 2) an increase
in winter flows. The spring runoff is also
expected to occur earlier in the season.”
“At +4°C, the shift in timing would be closer
to 20 days prior to baseline conditions.”
Source: LTVA, p. 147
Runoff Will Come Earlier in the Season
20 Source: SFPUC, 2/5/2021
In Dry Years SFPUC Entitlements Will Improve
21 In Dry Years SFPUC Entitlements Will Improve
Gain
21 In Dry Years SFPUC Entitlements Will Improve
Gain
Loss
21 Three Week Shift in Runoff
Total SFPUC Gain = 237 TAF
FY 2020/21 Demand = 219 TAF/y
Source: TRT
22 Obligations = Design Drought with 265 mgd demand.
Demands = Design Drought with 236 mgd demand.
Source: SFPUC
23 Drought Demand Earlier Deficit
Length (mgd) Run-off (mgd)
(years) (mgd)
Reasonable decisions enable the SFPUC to pass a 7.5 year Design Drought stress test with the Bay Delta Plan flows in place.
Conclusion
8.5 236 0 84
7.5 236 0 59
7.5 200 0 23
7.5 200 +31 -8
24 Recommendation
Shorten the Design Drought by one year.
25 Because the Design Drought planning model influences so many key policy decisions, it’s vitally important to get it right. Shortening it would be a safe, reasonable and prudent measure. Ratepayers, housing advocates, and
the fish will thank you. Plus, it will be much easier to settle the Bay Delta Plan lawsuit if the perceived impact isn't so great.
1 SFPUC Water Planning for Customer
Demands and the Environment
The Design Drought
August 23, 2022
Hetch Hetchy Regional Water System
Water Supply Facts
• We rely almost exclusively on Tuolumne River and local surface water supplies. • Our junior water rights on the Tuolumne mean we get to divert plenty of water in we
t years but little to none in dry years. SFPUC’s local surface water supplies are not very productive in dry years.
• Storage reduces the impact of multi-y ear droughts, and we must rely on the amount of water that can be carried over year-to-year in storage through a drought.
• Some wholesale customers, e.g., the Alameda County Water District, have s
ubstantial groundwater and other surface water supplies available to them, but we and many other wholesale customers do not. Even those with other supplies often find them to be less reliable than our system.
2 Environmental Obligations and Commitments
• Stipulations with Federal agencies exist related to releases from Cherry, Eleanor a
nd O’Shaughnessy Dams in the Sierra Nevada.
4 • Permit conditions (Lower Crystal Springs and Calaveras) and voluntary commitments (Pilarcitos) exist related to releases from Bay Area dams.
Environmental Obligations and Commitments
• Downstream of Hetch Hetchy Project facilities, we have co-c reated and committed to the Upper Tuolumne River Ecosystem Program with the National Park Service and other stakeholders.
5 • On Alameda Creek, we were a founder of the Alameda Creek Fisheries Work Group, which has led to dam removals, fish passage improvements and instream flow objectives for the benefit of fisheries.
Environmental Obligations and Commitments
• Below Don Pedro Dam, environmental obligations exist through the Irrigation Di
stricts’ FERC Don Pedro license. The Districts and San Francisco have already signed a Memorandum of Understanding with the US Fish and Wildlife Service to spend $4,000,000 on fishery habitat improvements prior to issuance of the FERC re- license.
• The State Water Board’s Bay-De lta Plan Amendments would increase flow obligations substantially with no requirements for non-flow measures. • San Francisco and the Irrigation Districts have proposed a Tuolumne River Voluntary A
greement with flow and non-flow measures being negotiated with the State as an alternative to the Bay-Delta Plan Amendments.
• Either way, the SFPUC’s and the District’s investment in habitat and the c
ommitment of increased flows to the Lower Tuolumne River will occur. 6 Purpose of Design Drought
• The Design Drought is not a prediction. It is a stress test. Its purpose is to examine the
system under stress - so that water system managers can make informed decisions including consideration of all obligations, both water supply and environmental.
• The consequences of being wrong and running out of water for water supply and/or the
environment are enormous.
• Recurrence intervals are descriptive NOT predictive and as a result are not useful for a
water manager during a drought.
• It doesn’t pay off at any time to assume the next year or two will be wet. We must a
ssume they will be dry. If they are wet, we have a beneficial addition to storage. • The Design Drought stress test was not chosen ba sed on likelihood of occurrence.
Again, it’s a stress test so we are prepared for worse droughts than we have seen and is necessary for careful planning.
7 Planning for Drought
• 1987-19 92 is the worst drought on record; but recent history shows that extreme 2-year droughts could happen at virtually any time.
• Planning for a 6-y ear drought that did occur with a 2-year cushion allows for operational decisions that better prepare us for surviving the next 6-year drought, and more.
8 January 1991
Planning for Drought
• No one will step in to help San Francisco in an extreme drought. • We c an protect ourselves from an extended drought and still provide benefits to the Lower Tuolumne River fishery. However, the Turlock and Modesto Irrigation Districts must be involved because ALL water from our upcountry system flows into Don Pedro, and New Don Pedro is their dam and reservoir. • At all times, we maintain flows downstream of our dams and invest in ecological studies, projects and programs to support native species and the environment. • However, because of uncertainty, we cannot assume that our existing supplies will c
ontinue to be sufficient. We must continually plan for Alternative Water Supplies in the future and implement them prudently.
9 Water Bank Operation Through A Drought
2012-2016
10 Water Bank Operation Through A Drought
2020 - ????
11 Timing and Volume of Tuolumne River Runoff
• Climate change will change runoff – but i t is not known exactly how • In som e years it will increase, and in some it will decrease. The changes will be in both timing and volume.
• For example, increased evaporation and soil dryness could absorb more water, r
educing runoff.
• Water Years 2021 and 2022 had similar snowpacks.
• 2021 snowmelt and runoff was in a dry environment.
• We got 57,000 AF from the Tuolumne
• 2022 snowmelt and runoff was in a wet environment.
• We got 201,000 AF from the Tuolumne
• And now the State is warning of a 10% reduction in water supply by 2040. 12 Consequences of Being Wrong
“When considering all the factors associated with the City’s entitlements to water, its physical system and the dire consequences of just being wrong in the forecasting of the length of drought that may hit the City, I can not agree with any comment that the City’s operation rule is overly conservative.”
Anson Moran, January 1994
13 Summary
• The reliability of our Reg ional Water System relies on storage, not direct diversions because of our water entitlements.
• The fu ture is uncertain. The certainty will be its unpredictability. • It is entirely prudent to plan for worse droughts in our future because the consequences of not doing so (and being wrong) are enormous. Hence, the 8.5- year design drought
• Regardless of the length of any drought, operationally, we need to p lan for the subsequent two years to be dry.
• With the existing design drought and operational planning approach, we can fulfill o
ur responsibilities to our customers and the environment. • At the same time, we must continue to plan for Alt ernative Water Supplies and be prepared to implement them.
14 Planning for Drought
Having a reliable water supply isn’t just about what rain or snow fell recently. It’s a multi- year process that strikes a balance — protecting natural habitats while ensuring there is water when you turn on the tap.
The Hetch Hetchy Regional Water System operated by the San Francisco Public Utilities Commission provides water to 2.7 million residents and businesses in the Bay Area. It relies on the Tuolumne River; local watersheds in Alameda, Santa Clara and San Mateo Counties; groundwater; and alternative water supplies. Droughts are part of living in California. Planning for them is critical to ensuring we continue to support the environment while delivering water every day. With almost 3 million people relying on us, failure is not an option.
How Much New Water Will be Available Next Year? No One Knows.
There is no way to reliably predict future snow or rainfall. We must remain prepared for dry conditions at any time. They could even worsen in the years to come. Our Tuolumne River watershed precipitation records go back 100 years, with numerous dry years and droughts. Beyond that, tree ring studies indicate that California is periodically subject to severe droughts. Climate change appears to be making this situation worse.
Average
Precipitation Dry Years Worst Drought Experienced Prudent Planning Most Dire Many years we
have plenty of
water
Some years we have
little to no new water
available to us.
The 1987-1992 drought is the worst
drought of the last 100 years for the
Hetch Hetchy system.
We also continue to experience
severe two-year droughts.
Preparedness means
planning for droughts
to be even worse in the
future.
0 Rain or Snow
Water Rights and Water for Us
The Tuolumne River is the source of 85% of the Hetch Hetchy Regional Water System’s supply. When there is a lot of rain and snow in the Sierra Nevada, there is plenty of water. In dry years, there may not be any runoff water available to us because our water rights are junior to those of the Modesto and Turlock Irrigations Districts, which also draw from the Tuolumne River.
Multi-Year Storage
In dry years, we rely on water stored in prior years. By storing water in wet years when there is lots of snow and rain, our system can deliver water even during multiple dry years.
However, just like a savings account, this storage can only last so long if it is not regularly replenished, and there is no guarantee of when that would happen.
As an Independent System, No One Will Bail
Us Out
Water systems in California are rarely interconnected. Our system is not part of the large state or federal water projects, and our physical connections to other water systems are limited and not a long-term drought solution. We must be prudent, because no one is coming to our rescue if we run out of water during a drought.
Water Conservation, Demand Management
We continuously focus on managing our customer demands
for water now and into the future through water conservation programs and recycling or reusing water. San Francisco’s per capita water use is already among the lowest in the state.
However, conservation cannot reduce our water demand
to zero.
Protecting the Environment
At all times, we maintain flows downstream of our dams and invest in ecological studies, projects and programs to support native species and the environment.
None of these projects are done alone; we partner with the U.S. Forest Service, National Park Service, San Joaquin Tributaries Authority, and Modesto and Turlock Irrigation Districts, among others.
Prudent Planning for Today and the Future
Running out of water is not an option. Prudent planning dictates we examine our supplies and operations under severe stress.
A prudent utility must understand and plan for a worst-case scenario.
Seasonal flooding
of Poopenaut
Valley below
O’Shaughnessy
Dam is part of the
Upper Tuolumne
River Ecosystem
Program.
0 500,000
1,000,000
1,500,000
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4,000,000
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Runoff Wat er Ava ilable by Year to Our Regional Water System Whether wet or dry, we always release water downstream to protect the natural ecosystems of our watersheds. Being deliberate in our drought planning ensures we can continue to support downstream ecosystems even during prolonged droughts. The Turlock and Modesto Irrigation Districts, who own and operate Don Pedro Reservoir, are essential partners in managing the river below Don Pedro Reservoir.
The ‘Design Drought’ - A Stress Test
Droughts can occur at any time and their length cannot be predicted. As a water supplier for over
2.7 million Bay Area residents, we must plan for the worst-case scenario. To prepare our system and examine how limited precipitation can affect our operations and water storage, we have created a ‘design drought’ for planning purposes.
The ‘design drought’ does not predict a given precipitation or drought sequence. It is essentially a stress test of our ability to deliver water under extreme drought circumstances. It is similar to examining your personal finances to determine how much savings you would need to weather a serious illness or losing your job.
Operationally, we must assume that any given year may be a drought, so that in a wet year, the assumption is that the next year is the beginning of a drought. In a dry year the assumption is that the next year is the continuation of a drought.
Our ‘design drought’ reflects our experience, our nearly exclusive reliance on surface water diversions and carryover storage, and our water rights relationship with the Modesto and Turlock Irrigation Districts under the 1913 Raker Act.
Extreme two-year droughts can happen at virtually any time. Recently they’re happening even more frequently. Our design drought takes our worst drought on record, the 1987-1992 drought, and then adds on two years of extremely dry conditions. This allows us to model how our storage and system would behave. We plan for an eight-year severe drought so we are prepared before it happens.
Some Years Our System Has Little to No New Water Available A Simulated Drought During the 1987-1992 drought, it was assumed each year that the drought would continue for the next two years. Our ‘design drought’ stress test is based on learning from those six years.
The ‘design drought’ utilizes the drought of
record: 1987 to 1992
Extended by two years and assumes the
most severe historically experienced two-
year sequence (1976-77) will recur
Acre-feet
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Updated August 1, 2022
SFPUC Water Supply Planning Introduction and Review White Paper Updated August 2022
This document was originally created as an introduction of information for the Commission’s March 26, 2021 workshop and review of some of the important concepts presented to the Commission in recent years regarding management of our water supply.
1. San Francisco’s entitlements on the Tuolumne River as expressed in the 1913 Raker Act
The Raker Act allocated 2,350 cubic feet per second (cfs) of the natural daily (unimpaired) flow of the Tuolumne River to the Modesto and Turlock Irrigation Districts and 4,000 cfs during the 60-day period from April 15 to June 13. Any flows above those volumes are San Francisco’s entitlement for diversion, referred to as Water Available to the City from the Tuolumne River. The graph below depicts Unimpaired Flow at La Grange (blue line), the Irrigation Districts’ entitlements (black dashed line), and annual Water Available to the City in Acre-Feet (in the green boxes) for Water Years 2011 – 2017. The graph shows the great variability from year to year in Unimpaired Flow and Water Available to the City (Annual SF Entitlement). Most years we are entitled to more water than we need; some years we are entitled to less than we need; and in very dry years we get almost nothing. The result of this is that we operate a unique system that prioritizes carryover water storage. We must store water in wet years to meet demand over a series of multiple dry years.
This also means that in years when we get very little entitlement, our instream flow requirements (for example, Bay-Delta Plan) have to be met by releasing water from our reservoirs rather than reducing the amount of water diverted.
1,992,610 172,116 176,619 27,765 50,077 645,957 3,274,879 0 5,000
10,000
15,000
20,000
25,000
30,000
10/1/2010
10/1/2011
10/1/2012
10/1/2013
10/1/2014
10/1/2015
10/1/2016
10/1/2017
cubic feet per second (cfs)
Unimpaired Flow at La Grange and Raker Entitlements
Unimpaired Flow at La Grange
Entitlement Delineation
Annual SF Entitlement (AF)
Updated August 1, 2022
2. Environmental Commitments and Obligations
Below its dams and guided by its Water Enterprise Environmental Stewardship Policy, SFPUC has existing and long-standing instream flow and environmental commitments. These include stipulations with Federal agencies related to Cherry, Eleanor and O’Shaughnessy Dams in the Sierra Nevada as well as permit conditions (Lower Crystal Springs and Calaveras) and voluntary commitments (Pilarcitos) related to Bay Area dams.
Downstream of Hetch Hetchy Project facilities, the SFPUC has co-created and committed to the Upper Tuolumne River Ecosystem Program with the National Park Service and other stakeholders.
https://uppertuolumneriver.wordpress.com/
On Alameda Creek, the SFPUC was a founder of the Alameda Creek Fisheries Work Group, which has led to dam removals, fish passage improvements and instream flow objectives for the benefit of fisheries.
Below Don Pedro Dam, environmental obligations exist through the Irrigation Districts’ FERC license. The Districts and San Francisco have already signed a Memorandum of Understanding with the US Fish and Wildlife Service (in 2021) to spend $4,000,000 on fishery habitat improvements prior to issuance of the re-license of the Don Pedro Hydroelectric Project. The State Water Board’s Bay- Delta Water Quality Control Plan, Phase 1 Amendments, would increase flow obligations substantially with no requirements for non-flow measures. San Francisco and the Irrigation Districts have proposed a Tuolumne River Voluntary Agreement (TRVA) with flow and non-flow measures to be negotiated with the State as an alternative to the Bay-Delta Plan Amendments.
3. Demand projection updates
Every 5 years we update demands as part of the State-required Urban Water Management Plan (UWMP). These represent the demands for water that we would experience if our service area was successful in meeting its development goals and mandates.
Our 2020 UWMP demand projections as well as most other agencies around California are lower than those projected for the 2015 Urban Water Management Plan.
The new UWMP demand projections on the Regional Water System (RWS) in million gallons per day (MGD) are:
2020 2025 2030 2035 2040 2045
Retail 66.5 67.2 67.5 68.6 70.5 73.7
Wholesale* 132.1 146.01 147.87 151.9 156.31 162.76
Total 198.6 213.2 215.4 220.5 226.8 236.5
*Includes San Jose and Santa Clara, 4.5 MGD each
Updated August 1, 2022
4. The Supply Assurance
Applies to the Wholesale Customers only, excluding San Jose and Santa Clara. It was established in 1984 and is a contractual obligation to meet demand up to 184 MGD in perpetuity. It does not expire but is subject to reduction due to drought, scheduled maintenance and emergencies.
The Supply Assurance is not a demand projection. However, if the Wholesale Customers have disruption in their other supplies, this contractual obligation to meet additional demands can fall on us (subject to a contractual requirement that retail and wholesale customers use best efforts to develop their own water supplies to the maximum extent feasible.). Development of new water supplies would be necessary to deliver the Supply Assurance together with our obligations to San Francisco on a sustained basis. The Wholesale Customers don’t project their SFPUC purchases to reach 184 MGD in the next 25 years. They project 162.76 MGD, but only 153.76 excluding San Jose and Santa Clara.
5. The Water System Improvement Program (WSIP) Water Supply Levels of Service SFPUC’s undertaking of the WSIP and the subsequent expense borne by the retail and wholesale customers came with a commitment to:
Meet average annual water demand of 265 MGD from the SFPUC watersheds for retail and wholesale customers during non-drought years for system demands through 2018 while limiting rationing to a maximum 20 percent system-wide reduction in water service during extended droughts. o 265 MGD is the 184 MGD Supply Assurance plus the non-binding retail allocation of 81 MGD.
The Level of Service is not a demand projection.
We project retail demand on the RWS to reach 74 MGD in the next 25 years.
6. Design Drought
The Design Drought is a stress test used for water supply planning. Operations are guided by the amount of water available for delivery and power generation based on storage targets tied to the Design Drought.
The Design Drought is a stress test analogous to the concept of a design load in structural engineering, or a design flood in dam design. These are the maximum stresses that the structure or dam are designed to withstand, and a stress greater than the design level would break the structure. The total duration of the SFPUC Design Drought is 8 ½ years; it uses the drought of record (1987-92) plus two very dry years which act as insurance against a drought worse than that experienced to date.
The development of the Design Drought is not based on the frequency or likelihood of occurrence of specific droughts.
Updated August 1, 2022
The RWS is managed in the computer simulations of the Design Drought so that there is no water left in storage at the end of the period. The RWS would never be managed to zero storage in real-world operations. It is informed by history and our experience.
7. Firm Yield
Firm Yield is the average amount of water supply that can be provided to the service area from the RWS during the Design Drought while bringing usable system storage to zero at the end of the Design Drought. It is the average annual amount of actual water that can be delivered without reduction over the Design Drought.
The firm yield of the RWS can be increased by adding water transfers and water supply projects that contribute water supply during the Design Drought.
The firm yield can be reduced by adding instream flow requirements that reduce the water supply available for delivery to the RWS service area during the Design Drought. Changing the Design Drought would also result in a change in the Firm Yield.
8. Reliability Standard (Rationing Policy)
SFPUC adopted a reliability standard (or rationing policy) as part of the WSIP (SFPUC Resolution 08-200 states “Meet dry-year delivery needs through 2018 while limiting rationing to a maximum 20 percent system-wide reduction in water service during extended droughts."). It was studied and publicly discussed in the WSIP Programmatic Environmental Impact Report analysis:
o In the 8 ½ year Design Drought we would face 3 years of 10% rationing and 3 ½ years of 20% rationing at a demand of 265 MGD.
9. Total System Yield
The amount of water that can be delivered, with rationing included, during the Design Drought.
Total System Yield is calculated by adding the Firm Yield and the Reliability Standard (Rationing Policy).
It is greater than the Firm Yield by the amount of rationing included in the Reliability Standard (Rationing Policy).
It can be thought of as the amount of "reliable" supply available to meet various demands.
10. The Fourth Agreement
It established the terms for our participation in the New Don Pedro Project. It established the Water Bank at 570,000 acre-feet of storage and gave the City access to an additional 170,000 acre-feet of seasonal flood encroachment storage.
It relieved the City of flood control responsibility on the Tuolumne River.
Updated August 1, 2022
It obligates the City to provide 51.7% of any new instream flows ordered by FERC if the Districts’ water entitlements are being adversely affected. The agreement does not expire.
The graph below depicts Unimpaired Flow at La Grange (blue line), the Irrigation Districts’ entitlements (black dashed line), and the Water Bank Account Balance in Acre-Feet (green line). The graph shows how the Water Bank Account was drawn down in the series of Water Years from 2012 – 2015 to meet the Irrigation Districts’ entitlements and thus protecting our water supply. The second graph shows the same effect in the 2020-2022 drought and with the drought projected to continue into 2023.
Updated August 1, 2022
The result of the Fourth Agreement obligations coupled with the Raker Act entitlement requirements means that we could be obligated to deliver water down the Tuolumne River by releasing water from our previously stored supplies in dry years because we have no rights to any of the natural flow of the River in those years.
The graph below depicts the Unimpaired Flow at La Grange (blue line), the Irrigation Districts’ entitlements (black dashed line), and annual Water Available to the City in Acre-Feet (in the green boxes) plus the San Francisco Share of the Bay-Delta Plan Amendments flow requirement (red line) and the annual San Francisco Share of the Bay-Delta Plan Amendments flow requirement in Acre-Feet (in the red boxes).
1,992,610 172,116 176,619 27,765 50,077 645,957 3,274,879 0 95,725 123,596 92,640 69,981 257,763 0
0 5,000
10,000
15,000
20,000
25,000
30,000
10/1/2010
10/1/2011
10/1/2012
10/1/2013
10/1/2014
10/1/2015
10/1/2016
10/1/2017
cubic feet per second (cfs)
Unimpaired Flow at La Grange, Raker Entitlements
and Bay-Delta Plan Contribution
Unimpaired Flow at La Grange
Entitlement Delineation
Annual SF Entitlement (AF)
SF Share of Bay-Delta Flow Requirement
Annual SF Share of Bay-Delta Plan (AF)
Water must be
released from
storage
Updated August 1, 2022
11. 1995 Side Agreement
In 1995, a Settlement Agreement was reached to implement additional flows on the Lower Tuolumne River as part of the current FERC Don Pedro Hydroelectric Project license.
The Districts and San Francisco entered into a Side Agreement in which the Districts would provide all of the water associated with the Settlement Agreement in exchange for an agreed amount of money from San Francisco. The Side Agreement is in place until a new license for the Don Pedro Project is issued by FERC.
San Francisco and the Districts are in discussion regarding an extension of the Side Agreement upon issuance of the re-license of the Don Pedro Project, but no extension has been agreed to yet.
Without the Side Agreement in place, San Francisco could be required to provide 51.71% of the Settlement Agreement flows in addition to any additional flows associated with the TRVA or Bay-Delta Plan Amendments, if these flows are adopted as part of a new license for Don Pedro by FERC under the Clean Water Act Water Quality Certification Process.