HomeMy WebLinkAboutItem 6d - Annual Water Supply and Demand Assessment and Rescinding of Emergency Drought Declaration Item 6d
Department: Utilities
Cost Center: 6001
For Agenda of: 5/16/2023
Placement: Consent
Estimated Time: N/A
FROM: Aaron Floyd, Utilities Director
Prepared By: Nick Teague, Water Resources Program Manager
SUBJECT: ANNUAL WATER SUPPLY AND DEMAND ASSESSMENT AND
RESCINDING OF EMERGENCY DROUGHT DECLARATION
RECOMMENDATION
1. Receive and file the City’s 2023 Water Supply and Demand Assessment; and
2. Adopt a Draft Resolution entitled, “A Resolution of the City Council of the City of San
Luis Obispo, California, rescinding Resolution No. 11353, returning the City of San
Luis Obispo to the Monitor Stage of its Water Shortage Contingency Plan .”
REPORT-IN-BRIEF
Results of the state-mandated 2023 Water Supply and Demand Assessment (Attachment
A, Reading File) and the City’s Water Projection Model show that the City has more than
ten years of water available under a drought scenario1 with current water supply and
demand conditions and future predictions. Monthly water supply surpluses signify that the
City would not need to enter a water shortage emergency in any month during the Current
Year2 (2023) or during a following hypothetical Dry Year3,4. Record breaking rainfall during
the winter of 2022-2023 has replenished reservoir storage locally and throughout most of
California, leading Governor Gavin Newsom to terminate most drought-related Executive
Orders. Because the City’s reservoirs are currently full and the State no longer requires
the City to be in Stage 2 (“Watch Stage") of its Water Shortage Contingency Plan, staff is
recommending the City adopt a resolution (Attachment B) rescinding Resolution No.
11353 (2022 Series) and returning the City to the “Monitoring Stage.” Efforts to promote
voluntary water conservation to extend the availability of existing water resources will
1 A “drought scenario” is a period when rainfall is less than normal for several weeks, months, or years, the
flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells
increases.
2 The Current Year for this Water Supply Assessment covers the twelve months from July 2022 through
June 2023.
3 A “Dry Year” is one in which precipitation is as low as the driest year on record.
4 The Current Year and Dry Year periods for this Water Supply Assessment are concurrent with the City’s
2023 and 2024 Fiscal Year periods, respectively.
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Item 6d
continue to be promoted by staff as the City remains focused on long-term conservation
goals.
POLICY CONTEXT
The City’s Water Supply and Demand Assessment was prepared in accordance with
General Plan Water and Wastewater Element (WWE) Program A5.3.15 and meets WWE
Goal A.5.1.26 and the State’s reporting requirements (Water Code §10632.1)7. The Water
Supply and Demand Assessment provides an update on the City’s current water supply
and water demands and assesses the potential of a water supply shortage for a
hypothetical dry year.
DISCUSSION
Background
The City’s Water Supply and Demand Assessment provides an update on the City’s
current water supply and water demands and assesses the potential of a water supply
shortage for a hypothetical dry year. This report summarizes the results of that
assessment, provides detailed information on the City’s current water supply and
demands, and provides projections for the City’s long-term water supply reliability.
Current Water Supply Status
The City’s three water supply reservoirs (Nacimiento, Salinas, and Whale Rock) are
located in different local watersheds in northern San Luis Obispo County and along the
north coast (Figure 1, Map of Reservoirs and Rain Gauge Locations). Having
geographically diverse reservoirs allows the City to maximize the capture of rainfall at
various locations within San Luis Obispo County (Figure 1 and Table 1). As shown in
Table 1 below, during Fiscal Year 22-23 (FY 2023)8, all of the watersheds that provide
water to City’s reservoirs received rainfall that was significantly greater than average
exceeding historic records.
Reservoir storage volumes as of March 31, 2023 are shown below in Table 2. All of the
City’s reservoirs are at or near storage capacity. During the extreme precipitation event
on January 9, 2023, storage in Salinas Reservoir exceeded 100 percent of capacity and
water began to flow over the spillway. Salinas Reservoir remain s above 100 percent of
capacity as of the writing of this report. The volume of water in Whale Rock Reservoir
exceeded 100 percent of capacity on March 10, 2023, and water flowed over the spillway
through mid-April.
5 WWE Program 5.3.1: An update on water supply accounting and demand projections will be presented to
the City Council as part of the annual Water Resources Status Report.
6 WWE Goal A.5.1.2: Accurately forecast future water demand for planning purposes.
7 Water Code §10632.1 directs urban water suppliers to evaluate their water supply reliability for the current
year and one dry year.
8 For the purposes of this report Fiscal Year is defined as the period July 1 through June 30. Fiscal Years
are named using the calendar year at the end of the period (e.g. Fiscal Year 2023 is July 1, 2022 through
June 30, 2023).
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Item 6d
Table 1: Rainfall during the 2022 and 2023 Fiscal Years (in inches)
Rainfall
Measurement
Location
Watershed Annual
Average
Rainfall1
FY 2022
Total Rainfall
FY 2023
Total
Rainfall2
Rocky Butte Nacimiento
Reservoir
34 29 96
Hwy 46 W 7 Mile Whale Rock
Reservoir
17 12 NA3
SLO Reservoir San Luis
Obispo
Creek
16 13 51
Salinas Dam Salinas
Reservoir
16 13 52
Notes:
1. Calculated using data from fiscal years 2013 through 2022.
2. Fiscal Year (FY) 2023 rainfall data as of April 1, 2023.
3. Instrument error resulting in incomplete data set for FY 2023.
Figure 1: Map of reservoirs and rain gauge locations.
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Item 6d
Table 2: Current Reservoir Volumes and Change in Volume from Fiscal Year 2022
Reservoir Total Volume
(acre-feet)
Available
City
Allocation
(acre-feet)1
Total
Percent
Capacity
Change from FY 2022
Acre-feet Percent of
Total
Capacity
Nacimiento 353,665 4,459 94% 248,415 +66%
Whale Rock 38,967 20,350 100% 9,165 +24%
Salinas 24,661 22,661 103% 9,754 +41%
Notes:
1. As of April 1, 2023.
As shown in Table 3, the City’s FY 2022 demand was 5,263 acre -feet. The per-capita
demand during this period was 99 gallons per capita per day (GPCD). Eighty-five percent
(85%) of this demand was supplied by Nacimiento Reservoir, 10% was supplied by Whale
Rock and Salinas Reservoirs, and 5% was supplied by recycled water. The volume of
water used from Nacimiento Reservoir in FY 2023 was greater than any previous year,
helping to accomplish the City’s strategy to utilize first this annually allocated resource to
preserve water in Whale Rock and Salinas Reservoirs, which provide long-term storage.
Table 3: City Water Supply Used by Source during Fiscal Year 2022
(in Acre-feet1 and Percent of Annual Demand)
Nacimiento
Reservoir
Whale
Rock
Reservoir2
Salinas
Reservoir
Recycled
Water Groundwater3
Total City
Water
Demand
4,460 100 426 277 0 5,263
85% 2% 8% 5% 0% 100%
Notes:
1. Values are rounded.
2. Water delivered to Cal Poly State University is excluded from the City’s water demand, as Cal Poly
has its own water storage and water diversion rights in Whale Rock Reservoir.
3. Groundwater was not used for potable purposes during FY 2022.
Available Supply
Water Resource Availability is calculated based on WWE, Section 3 Water Resource
Availability. Using this method, the water resource availability for FY 2023 is 10,183 acre-
feet (refer to Table 4, below), which includes 5,482 acre-feet of dependable yield from
Nacimiento Reservoir, 4,910 acre-feet of safe annual yield from Salinas and Whale Rock
Reservoirs, 291 acre-feet of Recycled Water (2022 calendar-year usage9) and subtracts
500 acre-feet due to estimated reservoir capacity losses from siltation (WWE Policy
A4.2.2, Accounting for Future Siltation).
9 WWE Policy A 7.2.2: Accounting for Recycled Water. The City will add total recycled water usage from
the prior year to the City’s water resource availability on an annual ba sis.
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Item 6d
Per WWE, Section 5, the City accounts for water supplies necessary to meet three
specific community needs:
Primary water supply – the amount of water needed to serve the City’s current
and future residential and non-residential water demand.
Reliability reserve – the buffer for future unforeseen or unpredictable long-term
water supply impacts.
Secondary water supply – the amount of water needed to meet peak water
demand periods or short-term loss of City water supply sources.
Table 4: Fiscal Year 2023 Annual Water Supply Availability (in acre -feet)
Total Water
Availability
Primary Water
Supply
Reliability
Reserve
Secondary Water
Supply
10,183 7,496 1,249 1,438
Water Supply Disruptions
High streamflow in the Salinas River corresponding to a large precipitation event on
January 9, 2023 exposed and damaged the pipeline that delivers water from Nacimiento
Reservoir to the City, disrupting delivery of water to the City. At the date that thi s report
was published, deliveries of water from Nacimiento Reservoir to the City are expected to
resume in September 2023; repair of the pipeline is under jurisdiction of the County of
San Luis Obispo. This disruption in delivery of water from Nacimiento Reservoir has
required greater than anticipated utilization of water from Whale Rock and Salinas
Reservoirs to meet water demands. The Water Supply and Demand Assessment
provides details on how the City will meet estimated demands without exceeding the saf e
annual yield of Salinas and Whale Rock Reservoirs; ensuring that the reservoirs remain
a reliable long-term water supply.
Water Demand
During FY 2022 the City registered 4,743 acre -feet of water use at metered locations
(Table 5). The largest demand for water in FY 2022 was for residential use (63%) and the
second largest demand for water was for commercial, industrial, and institutional uses
(22%). Demand for potable irrigation, non-potable (recycled water) irrigation, and recycled
water for construction purposes were each less than 10% of the total demand. About 500
acre-feet of water (9 percent of the City’s water supply) was lost to distribution system
leaks and other distribution system processes. The City’s water loss is less than the
national average of about 15%. Year-to-date (July-February) metered data for FY 2023
shows similar demand patterns as FY 2022. The breakdown of metered water use in the
City by sector is as follows:
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Item 6d
Table 5: City Water Demand by Sector During the 2022 and 2023 Fiscal Years
(in acre-feet)
Fiscal
Year
Residential Commercial,
Industrial,
Institutional
Landscape
Irrigation
(Potable)1
Landscape
Irrigation
(Recycled)
Construction
(Recycled)
Total
Metered
Use
FY 2022 63% 22% 8% 5% 1% 4,743
FY 2023
(year-to-
date)2
64% 24% 7% 5% <1% 2,917
Notes:
1. Landscape irrigation represents potable water use measured at dedicated landscape meters for
multi-family, commercial, industrial, and institutional properties.
2. July 2022 through February 2023.
Water Shortage Assessment
The City utilizes a Water Projection Model to test both hypothetical and actual water
demand scenarios and to forecast how long water supplies will sustain the community
under specific conditions. The Water Projection Model accounts for the storage in the
City’s surface water reservoirs, other available resources, current and projected
demands, and climate data. The model uses historical hydrologic information (rainfall,
evaporation, inflow) based on the average for the worst drought period (2012 to 2014).
Per the City’s 2020 Water Shortage Contingency Plan (WSCP), the Water Supply and
Demand Assessment utilizes the Water Projection Model to determine current demand,
future demand, and any associated water shortages. Additionally, Water Code Section
10632.1 requires the City to evaluate water supply and demand on a monthly basis for
the current fiscal year (FY 2023, Current Year) and a hypothetical dry year (Dry Year) so
that potential seasonal water shortages are highlighted and accounted for.
Results of the Water Projection Model show that the City has more than ten years of water
available, and the results of the Water Supply and Demand Assessment show that the
City has monthly water surpluses under a drought scenario with current water supply and
demand conditions. Therefore, the City does not expect to enter a water shortage
emergency in any month during the Current Year or following, hypothetical Dry Year.
Drought Executive Order N-5-23
In response to the recent Statewide drought, Governor Gavin Newsom signed Executive
Order N-7-22 on Monday March 28, 2022, ordering the State Water Resources Control
Board (Water Board) to consider water use restrictions. Order N-7-22 directed the State
Water Resources Control Board to adopt emergency regulations that include d a
requirement that each urban water supplier enact water shortage response actions for a
shortage level of up to twenty percent. . Water use restrictions were implemented by the
Water Board on May 24, 2022, which required the City to enter Stage 2 of the WSCP
(“Watch Stage”). Per Stage 2 of the WSCP, the City increased programs that encourage
voluntary water conservation, examined available alternative water so urces, and
implemented time of use irrigation restrictions (only allowed 7:00 PM – 7:00 AM).
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Item 6d
In response to the historic precipitation events this winter, the Governor signed Executive
Order N-5-23 on Friday March 24, 2023, terminating specific provisions of several State
of Emergency Proclamations and Executive Orders relating to drought dated between
April 21, 2021 and March 10, 2023. The Order eases some drought measures while
maintaining others. Most importantly, Order N-5-23 terminates Order N-7-22.
Accordingly, staff are recommending that the City Council rescind Resolution No. 11353
(2022 Series), which designated the City as being in Stage 2 of its Water Shortage
Contingency Plan. Rescinding this resolution will affirm that the City is no longer
experiencing any type of water shortage (greater than 5 years of available water supply10)
and that all water conservation regulations will revert back to those identified in the
“Monitor Stage” of the WSCP. Under the “Monitor Stage”, the City maintains existing
water conservation staffing levels and budget that supports meeting internal water
efficiency goals and regulatory requirements for water conservation, including ongoing
public outreach.
Continued Communication Related to Weather Extremes and Local Conditions
The Utilities Department continues to revise its communication related to water supply
conditions to provide succinct information that is easily accessible to the community.
While the wet winter has provided the City with full reservoirs, it is important to ensure
that the community is aware of local water supply conditions and that water conservation
is equally important in wet or dry years to ensure that water supplies are available to meet
current and future demands.
Previous Council or Advisory Body Action
On August 16, 2022, the Council adopted Resolution No. 11353 (2022 Series) entitled,
“A Resolution of the City of San Luis Obispo, California, declaring that the City enter into
Stage 2, the “Warning Stage”, of its 2020 Water Shortage Contingency Plan.” This
resolution authorized staff to implement water demand reducing measures outlined within
Stages 1 and 2, the “Warning” and “Watch” stages, of its WSCP.
Public Engagement
The City will provide communications regarding current water supply conditions and the
results of the Water Supply and Demand Assessment by posting information and
documents on the Utilities Department website. Additionally, this information will be
incorporated into future public communications material (social media posts, radio ads,
and Farmers Market handouts) and into future water supply planning. A copy of this report
and the Water Supply and Demand Assessment will be sent to the City Planning
Commission upon receival by City Council.
ENVIRONMENTAL REVIEW
The 2023 Water Supply and Demand Assessment is not a "project" under the California
Environmental Quality Act (CEQA), because the action does not involve any commitment
10 The City’s 2020 Water Shortage Contingency Plan directs the City to remain in the “Monitoring Stage” as
long as there are greater than 5 years of available water supply.
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Item 6d
to a specific project which may result in a potentially significant physical impact on the
environment, as defined by State CEQA Guidelines, Section 15378.
Rescinding Resolution No. 11353, which would return the City to the “Monitor Stage” of
its WSCP, is categorically exempt from environmental review pursuant to State CEQA
Guidelines Section 15307 (Actions by Regulatory Agencies for Protection of the
Environment) because: the action is consistent with State Executive Order N -5-23 that
rescinds specific authorities related to drought mitigation measures based on the current
status of drought conditions in the State; the City would remain compliant with the WSCP
based on the State Executive Order and the status of the City’s water supply as described
above; and, water conservation measures identified for the “Monitor” stage of the WSCP
would remain in effect including maintenance of existing water conservation staffing levels
and budget that supports meeting internal water efficiency goals and regulatory
requirements for water conservation and ongoing public outreach. The monitoring and
maintenance of the City’s water supply (a natural resource) and compliance with the
WSCP, which identifies specific procedures for protection of the environment, is therefore
statutorily exempt from CEQA.
FISCAL IMPACT
There are no fiscal impacts associated with the recommended action.
ALTERNATIVES
1. Council could decide not to receive and file the 2023 Water Supply and Demand
Assessment and provide direction to staff on desired modifications. Staff does
not recommend this alternative as the report was prepared in compliance with General
Plan, Water and Wastewater Element Policy A5.3.1 and satisfies the requirements of
California Water Code §10632.1.
2. Council could direct changes or request additional information and Staff could
return to a future meeting date.
3. Council could decide not to adopt the Draft Resolution entitled “A Resolution
Rescinding Resolution No. 11353, Returning the City of San Luis Obispo to the
Monitor Stage of its Water Shortage Contingency Plan”. Staff does not
recommend this alternative as the City’s water supplies are estimated to provide
greater than ten years of water to the community and the facts therefore sufficient to
warrant a declared water shortage, outside of the state requiring such action.
ATTACHMENTS
A - 2023 Water Supply and Demand Assessment
B - Draft Resolution rescinding Resolution No. 11353 (2022 Series)
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2023 Water Supply and Demand Assessment
For the Time Period July 1, 2022, through June 30, 2024
Whale Rock Reservoir and Spillway.
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 2
I. INTRODUCTION
California Water Code (CWC §10632.1.)1 directs urban water suppliers (Suppliers) to conduct an Annual
Water Supply and Demand Assessment (Water Supply Assessment) for the purpose of (i) evaluating its
water supply reliability for the current year and one subsequent dry year and (ii) generating and
submitting an Annual Shortage Report by July 1 every year starting July 1, 2022. The procedures for
conducting a Water Supply Assessment shall include the following:
(A) The written decision-making process that an urban water supplier will use each year
to determine its water supply reliability.
(B) The key data inputs and assessment methodology used to evaluate the urban water
supplier’s water supply reliability for the current year and one dry year, including all of
the following:
(i) Current year unconstrained demand, considering weather, growth, and other
influencing factors, such as policies to manage current supplies to meet demand
objectives in future years, as applicable.
(ii) Current year available supply, considering hydrological and regulatory conditions in
the current year and one dry year. The annual supply and demand assessment may
consider more than one dry year solely at the discretion of the urban water supplier.
(iii) Existing infrastructure capabilities and plausible constraints.
(iv) A defined set of locally applicable evaluation criteria that are consistently relied upon
for each annual water supply and demand assessment.
(v) A description and quantification of each source of water supply.
The City’s 2023 Water Supply Assessment was prepared in accordance with the General Plan, Water and
Wastewater Management Element, Policy A5.3.1.2 The methods for calculating water supply and water
demand have been modified to match the reporting requirements of the Water Supply Assessment and
are described below.
II. DECISION MAKING PROCESS
The CWC does not specify the type of year the Suppliers should use to do the Water Supply Assessment
(Calendar or Fiscal). However, the California Department of Water Resources (DWR) recommends that
the one Dry Year begin in July.3 For this Water Supply Assessment, which will be submitted by July 1,
2023, the Dry Year will therefore cover the twelve months from July 2023 to June 2024. Each subsequent
Water Supply Assessment will define the Dry Year period as July 1st of the Water Supply Assessment year
through June of the next calendar year. The Current Year for this Water Supply Assessment will cover
1 Cal. Water Code §10632.1. can be accessed at:
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=WAT§ionNum=10632
2 The City’s General Plan, Water and Wastewater Element is available at:
https://www.slocity.org/home/showdocument?id=6649
3 The State of California’s Water Supply and Demand Assessment Draft Guidance states “Characteristic of a dry year
is at the discretion of the Supplier, but it should be adequately defined and ideally align with one of the WSCP water
shortage levels. The assumed Dry Year conditions are often based on a previous historic dry year, such as the driest
year on record. Suppliers presented their defined historic Dry Year in their UWMP Table 7 -1. For the purpose of this
Guidance, the Dry Year data will be applied over the twelve-month period beginning July 1st (the due date of the
current Annual Shortage Report).”
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2023 Water Supply and Demand Assessment
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the twelve months from July 2022 through June 2023. The Current Year and Dry Year periods for this
Water Supply Assessment are concurrent with the City’s 2022 and 2023 Fiscal Year periods, respectively.
The City utilizes a Water Projection Model to test both hypothetical and actual water demand scenarios
and to forecast how long water supplies will sustain the community under specific conditions. The Water
Projection Model accounts for the storage in the City’s surface water reservoirs, in conjunction with other
available resources (i.e., groundwater and recycled water), needed to meet the City’s water demand.
The model uses historical hydrologic information (rainfall, evaporation, inflow) based on the average for
the worst drought period (2012 to 2014). Other data included in the model are:
a. Water entitlement
b. Current reservoir levels/storage
c. Average gallons per capita per day community water demand
d. Rainfall
e. Temperature
f. Evaporation
g. Existing population
h. Estimated population growth
Utilizing the Water Projection Model as part of its water supply management strategy, the City can
foresee whether a water supply shortage is anticipated in any given year and the severity of a shortage
based on the availability of the City’s different sources of supply and water demand trends. The City uses
the Water Projection Model to study the potential impacts of various intensities of drought conditions,
including increased air temperature and evaporation rates, along with decreased precipitation. Per the
City’s 2020 Water Shortage Contingency Plan, the Water Supply Assessment will utilize the Water
Projection Model to determine current demand, future demand, and any associated water shortages.4
Water supply and demand are presented in the units of acre-feet (AF). Annual available supply is
determined using existing methods (General Plan Water and Wastewater Management Element
(WWME), Section 3).5 Annual demand for the purposes of estimating Current Year and Dry Year demand
is determined using a modification of the methods described in the City’s method for determining
Primary Water Supply (WWME, Section 5) as described below. Current Year monthly demand is
determined using actual metered data when available; however, for the months when metered data
have not been collected, demand is calculated using the methods described in this report.
III. WATER SUPPLY REALIABILITY EVALUATION
Description and Quantification of Each Water Supply Source
Per the General Plan Water and Wastewater Management Element, Policy A2.2.1, the City uses multiple
water sources to meet its water supply needs.6 The City has four primary water supply sources:
Nacimiento Reservoir, Whale Rock Reservoir, Salinas Reservoir, and recycled water. The City prioritizes
using contractual water supply from Nacimiento Reservoir first, with Whale Rock Reservoir and Salinas
Reservoir used as needed to meet the City’s overall potable water demand, while recycled water is used
4 The City’s Water Shortage Contingency Plan is available at:
https://www.slocity.org/home/showpublisheddocument/30334/637575513697770000
5 The City’s General Plan, Water and Wastewater Element is available at:
https://www.slocity.org/home/showdocument?id=6649
6 General Plan, Water and Wastewater Management Element, Program A 2.2.1, states “The City shall utilize
multiple water resources to meet its water supply needs.”
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2023 Water Supply and Demand Assessment
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as a non-potable source for irrigation and construction purposes within City limits. A comprehensive
upgrade to the City’s Water Resource Recovery Facility (WRRF) is currently underway and will increase
the volume of recycled water available for use in the future. Additionally, groundwater serves as the
City’s fifth supplemental water source. Substantial work efforts are being made to better understand the
City’s groundwater supplies and how they may be fully utilized in the future.
Nacimiento Reservoir
In 1959, the San Luis Obispo Flood Control and Watershed Protection District (San Luis Obispo District)
entered into an agreement with Monterey County Flood Control and Water Conservation District (now
Monterey County Water Resources Agency) to secure rights to 17,500 AF of water per year (AFY) from
Nacimiento Reservoir. Nacimiento Reservoir is located entirely within San Luis Obispo County, California
(County), and was built by Monterey County Flood Control and Water Conservation District who
continues to control reservoir ownership and operations. Nacimiento Reservoir has a storage capacity of
377,900 AF and serves the purpose of abating seawater intrusion in the groundwater aquifers of the
Salinas River Valley, while also providing flood protection and groundwater recharge for the Salinas
Valley. Of the San Luis Obispo District’s entitlement, 1,750 AFY have been designated for uses around
the lake, leaving 15,750 AFY for allocation to other areas within the County of San Luis Obispo. Water is
delivered via a 45-mile pipeline from Nacimiento Reservoir to participating agencies and cities.
The “dependable yield” from Nacimiento Reservoir is the contractual amount of water that the City has
rights to from Nacimiento Reservoir. The City’s original amount contracted for was 3,380 AFY.
Engineering studies, environmental impact reports, dependable yield analyses, and preliminary design
reports were completed to ensure water needs within the County were met. In 2004, the County
requested interested agencies to approve the contractual agreements for participation in the Nacimiento
Project. The four initial project participants included the cities of San Luis Obispo and Paso Robles, the
Atascadero Mutual Water Company, and the Templeton Community Services District. All of these
agencies executed participation agreements with San Luis Obispo County for entitlements of water which
totaled 9,630 AF. In 2004, the County Service Area 10A in Cayucos became a project participant securing
25 AFY. On June 29, 2004, the San Luis Obispo City Council authorized participation in the Nacimiento
Water Project for the delivery of the original 3,380 AF of water. In 2004, the County Service Area 10A in
Cayucos became a project participant (25 AFY).
In March 2016, the City Council approved the addition of 2,102 AFY from Nacimiento Reservoir to the
City’s water supply. This addition brought the City’s total Nacimiento Reservoir allocation to 5,482 AFY.
With uncertainty of future climatic conditions, regulation, and aging infrastructure, the additional supply
of Nacimiento water to the City’s portfolio reduces pressure on the use of water supplies in the Whale
Rock and Salinas reservoirs, extending these stored supplies during future critical water shortages.
During the worst-case drought on record in the region (2012 to 2014), Nacimiento Reservoir remained a
resilient water supply capable of providing a consistent and reliable source of water for San Luis Obispo
County. To confirm the prior analysis with more recent data, the City reviewed rainfall and inflow data
from 2013 which was the driest year on record. Over that year, Nacimiento Reservoir received 35,000
acre-feet of inflow. Though this is significantly below the average inflow into the reservoir, the San Luis
Obispo District’s entitlement could still be met if inflow remained at this level due to the District’s primary
rights.
High streamflow in the Salinas River corresponding to a large precipitation event on January 9, 2023,
exposed and damaged the pipeline that delivers water from Nacimiento Reservoir to the City, disrupting
delivery of water to the City. At the date that this report was published, deliveries of water from
Nacimiento Reservoir to the City were expected to resume in September 2023. This disruption in delivery
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of water from Nacimiento Reservoir is accounted for later in this report and points to the importance of
the City having a multi-source supply portfolio.
Whale Rock Reservoir
Whale Rock Reservoir is located
on Old Creek Road
approximately one-half mile
east of the community of
Cayucos, California. The project
was planned, designed, and
constructed under the
supervision of the California
State Department of Water
Resources (DWR). Construction
took place between October
1958 and April 1961. The
reservoir is jointly owned by the
City of San Luis Obispo, the
California Men's Colony, and the California Polytechnic State University at San Luis Obispo (Cal Poly).
These three agencies form the Whale Rock Commission which is responsible for operation and
administration of the reservoir and associated water deliveries. Day-to-day operation is provided by the
City.
Whale Rock Reservoir is formed by an earthen dam and had capacity to store an estimated 40,662 AF of
water at the time of construction. The dam is 266 feet tall with a crest length of 850 feet and crest width
of 30 feet. The top of dam elevation is 232.2 feet. The Reservoir covers an area close to 600 acres. In
2022, the maximum storage capacity is 38,967 AF. The City owns 55.05 percent of the water storage
rights at the reservoir (22,364 AF). The remaining water storage rights are apportioned between the two
State agencies with Cal Poly owning 33.71 percent and the California Men’s Colony owning 11.24 percent.
Over the life of the Whale Rock Reservoir and dam, the lake has filled to capacity and the spillway has
been used 13 times, most recently spilling in March 2023.
The Whale Rock pipeline is approximately 17 miles long, connecting the reservoir to the member
agencies, and terminating at the City's Water Treatment Plant. The design capacity of the pipeline is
18.94 cubic feet per second (approximately 8,500 gallons per minute). The line consists of modified pre-
stressed concrete cylinder pipe at most locations. Cement mortar lined steel pipe is used at creek
crossings and junctions.
Salinas Reservoir
The Salinas Reservoir (also known as Santa Margarita Lake) is located on the upper Salinas River,
approximately nine miles southeast of the community of Santa Margarita. The project was originally built
by the War Department to ensure an adequate water supply for Camp San Luis Obispo, as well as the
City of San Luis Obispo. The dam and appurtenances were declared surplus by the War Department on
April 14, 1947 and the U.S. Army Corps of Engineers assumed responsibility for the facilities. On July 11,
1947, the Corps entered into an agreement with the San Luis Obispo District for the operation and
maintenance of the dam and related facilities. The City has an agreement with the Corps for use of the
reservoir, as well as a water right permit to divert water from the Salinas River for storage within the
reservoir. Salinas Reservoir is formed by a concrete arched dam. Immediately following construction, the
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 6
reservoir had an estimated storage capacity of
24,000 AF with a surface area of 793 acres,
and a drainage area of 112 square miles.
Safe Annual Yield, or the maximum amount
that could be withdrawn each year without
drawing the reservoir below its minimum pool
constraint, for Whale Rock and Salinas
reservoirs was updated in 2018 following the
addition of data from the most recent drought
that ended in 2016 and analysis of three
independent climate change models by the
U.S. Environmental Protection Agency (EPA),
San Luis Obispo Council of Governments
(SLOCOG) as part of the 2014 Regional
Transportation Plan, and Nature
Communications. As a result of siltation since
the original construction, the reservoir
capacity has been reduced and accounted for
in the Safe Annual Yield for Whale Rock and
Salinas reservoirs.
Water is conveyed from Salinas Reservoir
through 48,700 feet (9.2 miles) of 24-inch
diameter reinforced concrete pipe to a three
million gallon regulating reservoir at the Santa
Margarita booster pump station near the northerly base of Cuesta Grade adjacent to Highway 101. The
pipeline is designed to flow by gravity from the Reservoir to the regulating reservoir when the lake level
is above the elevation of 1,267 feet. A booster pump station at the base of the dam, consisting of two
horizontal centrifugal pumps, is capable of maintaining the rated flow of 12.4 cubic feet per second
(approximately 5,565 gallons per minute) when the water surface elevation falls below 1,267 feet.
Accounting for Siltation
Siltation at reservoirs is a natural occurrence that can reduce the storage capacity over long periods. The
reduction of available storage reduces the safe annual yield of the reservoirs. Siltation at reservoirs varies
depending on factors such as rainfall intensity and watershed management practices. Climate change
could have an impact on future water availability in the form of increased siltation in reservoirs resulting
from wildland fires which could affect the safe annual yield of the City’s reservoirs. Numerous studies
and reports addressing siltation at Salinas Reservoir have been completed. The latest study, conducted
by the County of San Luis Obispo in 1990, indicated that the siltation rate is on the order of 40 AFY.7
The Whale Rock Reservoir Bathymetric Survey and Volumetric Study was completed in May 2013. The
study concluded that sedimentation has reduced reservoir capacity by 4.2% in 52 years, but this impact,
considering 52 years of sedimentation is relatively minimal. The City has policies and programs in the
WWME to anticipate the loss of storage at Whale Rock and Salinas Reservoirs. WWME Policy A 4.2.2
7 A summary of the results of the siltation study done at Salinas Reservoir can be found in the City’s General Plan,
Water and Wastewater Element, Section 4 at: https://www.slocity.org/home/showdocument?id=6649
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 7
relates to Accounting for Future Siltation.8 The policy states “The City will account for estimated safe
annual yield losses at Salinas and Whale Rock Reservoirs through 2060 by deducting 500 acre-feet of
available water supplies to account for these future losses.” The siltation rate will be updated as
information becomes available from subsequent siltation analyses. Accounting for siltation of reservoirs
contributes to the overall reliability of the City’s water supply portfolio as it ensures that the City is
planning for this occurrence. Siltation at Nacimiento Reservoir does not need to be accounted for in The
City’s water supply portfolio calculations because the contractual right for San Luis Obispo County
agencies is not dependent on reservoir capacity.
Recycled Water
The City’s Water Resource Recovery Facility (WRRF) produces over 3,200 AF of disinfected tertiary-
treated effluent per year. A minimum of 1,810 AF is discharged to San Luis Obispo Creek annually to
provide satisfactory habitat and flow volume for fish species (steelhead trout) within the Creek
environment. The balance makes up the City’s available recycled water resource which is available for
approved uses. A consistent flow of wastewater to the WRRF enables the City to produce a volume of
recycled water that exceeds current seasonal demand for landscape irrigation. The distribution and
delivery of recycled water is via a pump station located within the WRRF. The pump station does not
have backup power during a power outage. However, because power outage events have been
infrequent, the City’s recycled water supply is considered a reliable, non-potable water supply.
The primary use of recycled water in
the City is for landscape irrigation
with 75 percent of the City’s recycled
water demand occurring from May
through October. The City began
issuing annual construction water
permits in July 2009. Permit holders
have access to recycled water for
dust control and compaction on
construction sites in the City. The City
has four metered wharf head
hydrant filling stations located
throughout city limits. During
calendar year 2022, 291 AF of recycled water was used for landscape irrigation and construction water.
The City has identified a “seasonal surplus” of recycled water available in excess of required discharge to
San Luis Obispo Creek (4.96 AF per day as required by the National Oceanic and Atmospheric Association,
National Marine Fisheries Service in 2005) for landscape irrigation. As only a limited amount of landscape
irrigation takes place from November to April (seasonal off-peak period), more than 4 AF per day of
recycled water is available during the seasonal off-peak period. An upgrade of the WRRF is underway,
which will accommodate the City’s buildout and maximize recycled water production. These upgrades
will enable the City to maximize beneficial use of recycled water, including consideration of either direct
or indirect potable reuse in the future. Until potable reuse is implemented, the City is focused on
expanding the use of recycled water within City limits to help offset potable water use. Per the City’s
2017 Recycled Water Master Plan, recycled water use is projected to increase by 10 AF per year.
8 The City’s General Plan, Water and Wastewater Element is available at:
https://www.slocity.org/home/showdocument?id=6649
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 8
Groundwater
Although the City suspended using groundwater for potable purposes in April 2015, the City has
maintained its groundwater wells in an operable, stand -by position should the use of groundwater be
needed. In July of 2020, the City received a nearly $2 million planning-phase grant, funded through
Proposition 1, to study Tetrachloroethylene (PCE) contamination of the groundwater basin. This study
aims to provide a more detailed understanding of the extent of PCE contamination and to identify
potential remediation options for the City to fully utilize it’s groundwater pumping opportunities. The
planning phase of the project was completed in 2022 and an additional $5.9 million implementation-
phase grant was awarded in 2023. The implementation phase will result in the construction or outfitting
of at least two new production wells with treatment systems to provide the City with an additional source
of potable water, while simultaneously removing contaminated groundwater from the groundwater
basin. Several new monitoring wells planned for installation in the implementation phase will provide an
understanding of changing groundwater conditions resulting from renewed groundwater pumping.
In January 2022, the City and the County of San Luis Obispo, acting as Groundwater Sustainability
Agencies, submitted a draft of the Groundwater Sustainability Plan (GSP) for the San Luis Obispo Valley
Groundwater Basin to the Califo rnia Department of Water Resources (DWR). The GSP was a result of
several years of work conducted to better understand the hydrology of the basin and will be
instrumental in guiding sustainable use of groundwater in the basin, including the City’s utilizat ion of
groundwater as a source of supply. The GSP estimates a groundwater surplus (recharge minus
withdraws) of approximately 700 AFY for the portion of the groundwater basin underlying the City .
Assessment Methodology: Locally Applicable Evaluation Criteria
Water supply reliability is the City’s ability to meet the water needs of its customers under varying
conditions. The City estimates annual Water Supply based on Water and Wastewater Management
Element, Section 3. The City’s fiscal year 2022-2023 water supply that was estimated using this method
is shown in Table 1. This method incorporates Safe Annual Yield from Salinas and Whale Rock Reservoirs
as determined through the City’s Safe Annual Yield Model, the City’s contractual amount of water from
Nacimiento Reservoir (Dependable Yield), the prior Calendar Year volume of Recycled Water utilized by
the City, and reduction in reservoir storage caused by siltation as directed in WWME Policy A 4.2.2. The
values shown in Table 1 are preliminary estimates that can change with regulatory variability, climate
conditions, and other factors that may affect the City’s water supplies and customer water uses.9 As
described in Chapter 6 of the City’s 2020 Urban Water Management Plan (UWMP), the City assesses
water supply reliability by analyzing the hydrological variability of the City surface water reservoirs
(Salinas, Whale Rock, and Nacimiento). This analysis is done using the City’s Water Projection model and
applies worst-case drought conditions according to guidelines set forth in the UWMP plan
documentation.
9 The City’s 2020 Urban Water Management Plan can be accessed from the California Department of Water
Resources, WUEdata Portal at: https://wuedata.water.ca.gov/uwmp_plans.asp?cmd=2020
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 9
Table 1: Estimated Fiscal Year 2022-2023 Annual Water Supply
Water Resource Acre-Feet Description
Nacimiento Reservoir 5,482 Dependable Yield 1
Salinas & Whale Rock Reservoirs 4,910 Safe Annual Yield 2
Recycled Water 291 2022 Annual Usage 3
Siltation from 2010 to 2060 (500) WWME Policy A 4.2.2 4
10,183 Total Availability5
NOTES:
1. Dependable Yield is the contractual amount of water the City has rights to from
Nacimiento Reservoir.
2. The City’s Safe Annual Yield model was updated in 2018.
3. The quantity of recycled water included (291 AF) is the actual prior year’s usage
(calendar year 2022) per General Plan Water and Wastewater Management Element
Policy A 7.2.2.
4. Reservoir siltation is a natural occurrence that reduces storage capacity over long
periods, resulting in the reduction of safe annual yield.
5. Preliminary estimate that can change with regulatory variability, climate conditions, and
other factors that may affect the City’s water supplies and customer water uses.
The City accounts for annual demand, or the water supplies necessary to meet community needs, using
the methods detailed in the General Plan Water and Wastewater Management Element (WWME),
Section 5.10 The amount of water needed to serve the City’s future residential and non-residential water
demand is termed the primary water supply. The primary water supply is calculated using the build-out
population identified in the General Plan, Land Use Element (2014) and the maximum allowed per capita
water use under Senate Bill X7-7, which is 117 gallons per capita per day (GPCD).11 For this Water Supply
Assessment, Current Year population (2022) and Dry Year population (Current Year population plus one
percent) are used in lieu of the build-out population when calculating total annual demand. When
utilizing the Water Projection Model to estimate future water supply and demand, GPCD decreases in
accordance with the 2020 Water Shortage Contingency Plan (WSCP). For example, water demand is
calculated using an initial value of 117 GPCD and decreases by ten percent (corresponding to a ten-
percent decrease in water use) to 105 GPCD when available supply is less than 5-years of estimated
annual demand. This ten percent reduction is in alignment with the demand reduction that the City
projects it would achieve from conservation measures outlined in the WSCP.
The annual water supply and demand volumes calculated using the methods described above are
converted to monthly volumes for the purposes of this Water Supply Assessment so that potential
seasonal water shortages are highlighted. Monthly supply and demand volumes are calculated using
average monthly demand as a percent of average annual demand for the seven-year period 2016-2022;
the period following the previous drought (2015-2017) and including the most recent drought. These
monthly average demand percentages are then applied to the annual supply and demand to provide
monthly volumes.
10 The City’s General Plan, Water and Wastewater Element is available at:
https://www.slocity.org/home/showdocument?id=6649
11 Senate Bill No. 7 – Water conservation, is available at:
https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=200920107SB7
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 10
Current Year Precipitation and Reservoir Storage
Current Year precipitation in the City is above average, leading to increased reservoir storage volumes
(Table 2). Average annual precipitation for the previous ten-year period (2012-2021) at the SLO Reservoir
station was 16.23 inches (in.). Precipitation is generally greatest in the winter months, November through
April, and can be absent in the summer months, May-September. As of March 31, 2023, the Current Year
precipitation is 41.87 inches, with 39.37 inches falling between December 1, 2022 and March 13, 2023.
For that same December through March period, reservoir storage volumes increased 268,600 AF in
Nacimiento Reservoir, 13,072 AF in Salinas Reservoir, and 11,575 AF in Whale Rock Reservoir12. During
the extreme precipitation event on January 9, 2023 storage in Salinas Reservoir exceeded 100 percent
capacity and water flowed over the spillway. Salinas Reservoir remained above 100 percent capacity
through the month of March. The volume of water in Whale Rock Reservoir exceeded 100-percent
capacity on March 10, 2023 and water flowed over the spillway.
Table 2: Precipitation Measured at the SLO Reservoir Station1
(in inches)
Water Year Accumulation
(in inches)
2012 12.36
2013 8.50
2014 10.51
2015 19.02
2016 35.14
2017 13.08
2018 26.56
2019 15.59
2020 11.54
2021 10.01
2012-2021 Average 16.23
2022 (October-March) 41.87
Notes:
1. Precipitation data measured at the SLO Reservoir – P (749) station can be found at:
https://wr.slocountywater.org/site/?site_id=27&view=51a30d03-3991-46af-9d23-7bc0f56a118f.
Current Year Water Supply and Demand Assessment
Analysis of the supply and demand data from the previous year allows for a better understanding of how
annual demand is met with the available water supplies. As shown in Table 3, the City’s 2021-2022 Fiscal
Year demand was 5,263 AF. The per-capita demand, including recycled water, during this period was 99
GPCD. Eighty-five percent (85%) of this demand was supplied by Nacimiento Reservoir, 10% was supplied
by Whale Rock and Salinas Reservoirs, and 5% was supplied by recycled water. The volume of water used
from Nacimiento Reservoir in Fiscal Year 2022 was greater than any previous year, helping to accomplish
the City’s strategy to utilize an annually allocated resource to preserve water in Whale Rock and Salinas
Reservoirs, which provide long-term storage.
12 Increases in reservoir storage do not account for inflow to the reservoir that was subsequently released from the
reservoir for flood protection or beneficial uses.
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City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 11
Table 3: City Water Supply by Source during the 2021-2022 Fiscal Year1
(in acre-feet)
Nacimiento
Reservoir
Whale Rock
Reservoir 2
Salinas
Reservoir
Recycled
Water Groundwater 3 Total City Water
Demand
4,460 100 426 277 0 5,263
85% 2% 8% 5% 0% 100%
Notes:
1. Values are rounded.
2. Water delivered to Cal Poly State University at San Luis Obispo (Cal Poly) is excluded from the City’s water demand, as Cal
Poly has its own water storage and water diversion rights in Whale Rock Reservoir.
3. Groundwater was not used for potable purposes during Fiscal Year 2021-2022.
Current Year available water supply is 8,962 AF; 6,498 AF potable water and 2,464 AF non-potable water
(Table 4). In the Current Year the City planned to utilize its water sources similarly to Fiscal Year 2021-
2022 by prioritizing water from Nacimiento Reservoir to preserve or increase storage volumes in Whale
Rock and Salinas Reservoirs. However, the damage to the Nacimiento pipeline, previously detailed in this
report, is estimated to prevent the City from using water from Nacimiento from mid-January, 2023 until
September, 2023. The City’s Current Year water supply (Table 4) summarizes actual supply volumes
delivered to the City’s distribution system for the period July 2022 through February 2023 and estimated
supply volumes for March through June 2023. The estimated potable water supply volumes reflect the
absence of Nacimiento Reservoir and the increased utilization of water from Whale Rock and Salinas
Reservoirs to meet anticipated demands. Should the actual supply volumes from Whale Rock and Salinas
reservoirs match the estimated values, the total volume utilized from those reservoirs would be equal to
the safe annual yield. Utilizing a volume less than or equal to the sustainable yield helps to ensure that
the reservoirs remain a reliable long-term water supply. The subtraction of 41.67 AF for March through
June 2023 represents the City’s methods to account for siltation in the reservoirs (500 AFY evenly divided
among twelve months) and ensures that the volume of water used from Whale Rock and Salinas
Reservoirs is in alignment with the General Plan Water and Wastewater Management Element (WWME),
Section 5.
The Current Year estimated potable demand is 6,245 AF. This value is the demand calculated using the
2022 population of 47,653 and per-capita daily demand of 117 GPCD.13 The actual Current Year demand
shown in Table 5 (5,603 AF) is lower than the estimated demand because of more efficient water use (93
GPCD calculated using actual data for the period July 2022 through February 2023) and variations in
water needs caused by annual climate variations. Therefore, the monthly values estimated in Table 5 are
likely conservative estimates of demand that overestimate the actual demand.
13 Population estimate for the City website at: of San Luis Obispo is from the California Department of Finance
website at: www.dof.ca.gov/Forecasting/Demographics/Estimates/e1/
Page 137 of 1165
Table 4: Current Year 2022-23 Water Supply, in acre-feet
Potable Water Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Nacimiento Reservoir 395 311 369 395 306 275 46 0 0* 0* 0* 0* 2,097
Salinas and Whale Rock Reservoirs 79 164 78 54 70 125 296 354 793* 816* 854* 885* 4,568
Groundwater 0 0 0 0 0 0 0 0 0 0 0 0 0
Siltation from 2010 to 2060 - - - - - - - - (41.67) (41.67) (41.67) (41.67) (167)
Total by Month (Potable) 474 475 447 449 376 400 342 354 751* 774* 812* 843* 6,498
Non-Potable Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Recycled Water for non-potable use 36 39 30 27 13 6 3 4 10* 18* 33* 39* 258
Recycled Water available for use 87 87 124 162 137 229 527 272 224* 165* 114* 78* 2,206
Total by Month (non-potable) 123 126 154 189 150 235 530 276 234* 183* 147* 117* 2,464
Notes:
1. * Denotes estimated values.
2. Values are estimated assuming an annual potable water supply of 7,608 acre-feet.
3. Values are estimated assuming an annual non-potable water supply of 1,917 acre-feet.
Page 138 of 1165
City of San Luis Obispo
2023 Water Supply and Demand Assessment
Page 13
Table 5: Current Year 2022-23 Water Supply and Demand, in acre-feet
Potable Water Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Unconstrained Demand 474 474 446 448 375 400 343 351 478* 561* 610* 643* 5,603
Total Water Supply2 474 474 447 449 376 400 343 354 832* 857* 899* 934* 6,839
Surplus/Shortage 0 0 0 1 1 0 0 3 354 296 289 291 1,236
% Surplus/Shortage 0% 0% 0% 0% 0% 0% 0% 1% 74% 53% 47% 45% 22%
State Standard Shortage
Level 0 0 0 0 0 0 0 0 0 0 0 0 0
Non-Potable Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Unconstrained Demand 36 39 30 27 13 6 3 4 10* 18* 33* 39* 258
Total Water Supply3 87 87 124 162 137 229 527 272 224* 165* 114* 78* 2,206
Surplus/Shortage 51 48 94 135 124 223 524 268 214 147 81 39 1,948
% Surplus/Shortage 142% 123% 313% 500% 954% 3,717% 17,467% 6,700% 2,140% 817% 245% 100% 755%
Notes:
1. * Denotes estimated values.
2. Values are estimated assuming an annual potable water supply of 7,608 acre-feet.
3. Values are estimated assuming an annual non-potable water supply of 1,917 acre-feet.
Page 139 of 1165
Thanks to a history of collaboration
between the City and its community
members, community-wide water
conservation has resulted in more efficient
water use over the last 15 years. This water
conservation ethic is supported by City
programs such as the water conservation
rebate program, school education
program, community outreach program,
customer water audits, and the retrofit
upon sale program. Additionally, the City is
improving the water efficiency of its
operations by identifying and repairing
leaking infrastructure, annually testing and upgrading water meters, and supplying parks with non-
potable recycled water. The City will conduct regular assessments of the water conservation program to
ensure the most effective use of City resources to provide the greatest water savings.
Current Year water supply and demand data are shown on a monthly time-step in Table 5. The values
demonstrate the seasonal differences in demand and the supplies needed to meet those demands. As
demonstrated by a water surplus (supply greater than demand) in each month, the City is not anticipating
entering into a water shortage emergency at any point in the Current Year. Monthly potable surpluses
range from 289 to 354 AF, or 45% to 74% of monthly demand. This surplus is a result of drought resilient
water supply sources and community-wide water conservation efforts. Additionally, the City makes
projections of future water demand using a conservative per capita potable water use rate of 117 GPCD
which is the City’s SB X7-7 target, while actual water use within the community is currently less than 100
GPCD and not anticipated to increase beyond minor year-to-year variations over time. The difference
between projected demand and actual demand provides a water supply source that acts as a buffer
against unexpected changes in supply or demand.
The Current Year non-potable demand is 258 AF. This represents recycled water used for irrigation and
construction purposes and acts to offset potable water use. The Current Year non-potable supply and
demand assessment shows large surpluses for every month and a total annual surplus of about 1,948 AF.
The total non-potable supply includes the total volume of water treated at the City’s WRRF minus 4.9 AF
per day creek discharge requirement. The non-potable supply and demand assessment provides insight
on seasonal fluctuations in non-potable water supply and will assist the City in determining the ability to
meet increases in future demands for irrigation and the volume of water available for potable reuse
projects. Large non-potable supply volumes in December 2022, January 2023, and February 2023 are the
result of above average precipitation and the resulting increase in influent to WRRF.
Dry Year Water Supply
The City’s estimated Dry Year water supply is 10,895 AF (potable supply plus recycled water for non-
potable reuse in Table 6). The Dry Year water supply is equivalent to the Fiscal Year 2022-2023 supply,
and reflects a return to normal operations, namely restoration of water supply from Nacimiento
Reservoir once repairs are scheduled for completion in September 2023. The City is confident including
the full dependable yield from Nacimiento Reservoir in the Dry Year water supply budget because, as
mentioned previously in this report, studies and recent drought-period data show that even during
extended periods of below average rainfall inflows to Nacimiento Reservoir are sufficient to meet the
Citys annual entitlement. The City’s potable and non-potable water supplies are shown on a monthly
time-step in Table 6.
Page 140 of 1165
Table 6: Dry Year 2023-24 Water Supply, in acre-feet
Water Supply
Source
Additional
Detail on Water
Supply
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Annual
Water
Supply
Nacimiento
Reservoir
From dependable
yield
0 0 521 501 447 371 346 410 467 481 503 522 4,569
Salinas and
Whale Rock
Reservoirs
From safe annual
yield
944 1,001 338 325 290 241 224 266 303 312 327 339 4,910
Groundwater Supplier-produced - - - - - - - - - - - - -
Other Decrease in
available supply
from siltation in
reservoirs
(41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (41.7) (500)
Total Potable 902.3 959.3 817.3 784.3 695.3 570.3 528.3 634.3 728.3 751.3 788.3 819.3 8,979
Recycled Water
for non-potable
reuse
For irrigation and
construction uses
43 42 36 31 20 10 5 10 10 18 35 40 300
Recycled Water
available for use
Produced by the
WRRF that is not
allocated for non-
potable reuse or
creek discharge
requirements
50 52 92 128 110 151 249 205 224 165 113 77 1,616
Total Non-Potable 93 94 128 159 130 161 254 215 234 183 148 117 1,916
Page 141 of 1165
Dry Year Unconstrained Demand
The Dry Year estimated potable demand is 6,937 AF (Table 7). This value is the sum of the metered
demand (calculated using the estimated 2023 population of 48,130 and per-capita daily demand of 117
GPCD) and water loss (estimated as 10% of monthly metered demand). As was seen in the Current Year
demand shown in Table 5, actual Dry Year demand will likely be lower than the estimated demand
because of more efficient water use and variations in water needs caused by annual climate variations.
Most of the City’s potable demand is for single-family residential use (42%), followed by muti-family
residential (19%), and commercial (19%). Demands for industrial, institutional, and dedicated landscape
are each below ten percent of the total annual demand. Single-family and multi-family residential
demands are greatest during the period May through October when precipitation is generally low. This
suggests that residential demand is driven by outdoor irrigation and the increased demand for irrigation
during dry periods. Non-potable water is estimated to offset about 340 AF of potable demand during the
Dry Year.
Existing Infrastructure Capabilities and Plausible Constraints
The utilization of water from three separate reservoirs provides the City with operational flexibility to
meet water demands while maintaining optimal storage volumes in each reservoir; however
environmental factors can inhibit reservoir storage or prevent utilization of stored water by degrading
water quality. While inflow to Nacimiento has proven to be sufficient during the worst drought in recent
history, it is conceivable that in the most extreme drought, when precipitation is near zero, that inflow is
less than the City’s contractual amount. The City has not typically experienced significant water quality
issues with water stored in its reservoirs, but extreme heat and low reservoir levels associated with
drought conditions are ideal conditions for biological processes that can impair water quality, including
growth of algae, which can lead to secondary water quality complaints related to taste and odor. The
City’s water treatment plant is capable of producing water that meets all state and federal standards,
even as water quality is deteriorated by ongoing drought.
Currently the City satisfies demand without utilizing the full dependable yield from Nacimiento Reservoir
because pipeline capacity constraints and treatment operation only allow for the delivery and treatment
of approximately 4,500 AFY. Projects are being developed to allow for the full utilization of dependable
yield from Nacimiento Reservoir in preparation for future periods when demands require the full
available water supply. Should the City need to utilize its full entitlement to Nacimiento for any reason,
it could modify plant operation to accommodate this need. Because the City relies primarily on water
supplied by its reservoirs, disruptions in delivery of water from a reservoir could be caused by damage
to existing infrastructure. While temporary disruptions in water supply availability can be mitigated
through utilization of water from the other available reservoirs, prolonged disruptions could result in
water shortages.
The City is expanding its groundwater program and considering potable reuse of recycled water to
provide water supply redundancy and increased operational flexibility in extreme drought scenarios and
during disruptions in delivery of water from reservoirs. Additionally, the City produces recycled water
that can be used to offset potable demand and during disruptions of water supply. To further increase
potable demand offset, recycled water use could be temporarily expanded to meet irrigation needs
beyond the current scope. Ultimately the City proactively pursues projects that help gain a better
understanding of potential issues that may threaten its water supply and how to mitigate them.
Page 142 of 1165
Table 7: Dry Year 2023-24 Unconstrained Demand, in acre-feet
Water Use
Projected Monthly Water Demand1 Total
Annual
Demand
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Demands Served by Potable
Supplies
Single Family 273 288 275 272 235 204 204 198 203 243 265 275 2,935
Multi-Family 104 110 115 120 107 100 108 100 102 111 111 108 1,296
Commercial 123 126 116 118 106 105 104 98 101 107 109 121 1,334
Industrial 19 20 18 17 12 10 9 9 9 13 15 18 169
Institutional/Government 5 5 5 5 4 4 4 4 4 4 4 5 53
Landscape 67 70 62 54 37 20 13 21 20 37 55 63 519
Water Loss 59 62 59 59 50 44 44 43 44 52 56 59 631
Total by Month (Potable) 650 681 650 645 551 487 486 473 483 567 615 649 6,937
Demands Served by Non-Potable
Supplies2
Landscape 39 39 32 25 15 7 5 9 9 20 34 39 273
Golf Course Irrigation 5 7 4 3 1 1 0 1 1 3 4 6 36
Construction 4 4 3 4 3 1 1 2 1 2 3 5 33
Total by Month (Non-Potable) 48 50 39 32 19 9 6 12 11 25 41 50 342
Notes:
1. Estimated values.
2. Non-potable water treated to tertiary level.
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IV. SUPPLY AND DEMAND ANALYSIS
Using the Water Projection Model described above, the City has more than ten years of water available
under a drought scenario with current water supply and demand conditions. Analysis of supply and
demand data at a monthly timescale shows that the City has ample supply to meet monthly demands for
the Current Year and a subsequent Dry Year (Table 8). This is why the City does not expect to enter a
water shortage emergency in any month during the Current Year and following hypothetical Dry Year.
Monthly potable surpluses range from 54 to 263 AF, or 11% to 54% of monthly demand. Annually, the
City is expecting to have a potable water supply surplus of about 2,037 AF (29% of annual demand).
This analysis provides valuable insight on the primary uses of water in the City and also highlights periods
when disruptions in delivery of water from one or more of the City’s reservoirs would be most impactful
to the City’s ability to meet demand. Monthly demands show that water supply is used primarily to meet
residential demands. Additionally, monthly demands show the seasonal variation associated with the
need for more water in the hot, dry summer months and the need for less water during the cool, wet
winter months. Ultimately, the data show that water use within the City is driven by residential use during
the dry, summer months, likely in response to outdoor irrigation needs. Because of this, water
conservation programs that target reduction in outdoor irrigation may provide the greatest water
savings.
The supply and demand analysis assumes reliable delivery of available water supplies during drought
conditions similar to those experienced in recent history. More extreme drought conditions may present
issues that decrease the volume of available water in storage or degrade the quality of water in storage.
Available water supply may also be less than estimated because of disruptions in the delivery of available
water supplies, whether temporarily caused by minor issues or prolonged disruptions caused by
catastrophic events.
V. PLANNED SHORTAGE RESPONSE ACTIONS
The City does not plan to implement a water shortage response in the Current Year or following Dry Year;
however, the City’s Water Shortage Contingency Plan (WSCP) provides a framework for responding to
water shortages when necessary.14 The City’s water shortage response is dependent on the ability to
temporarily augment supply and/or reduce water demand. The goals of the WSCP are to extend the
City’s available water resources long enough to gain another winter rainfall period which could serve to
add to reservoir storage. Extending available water resources through water demand reductions provides
time for the City to bring on supplemental water supplies to meet demand. The City’s water shortage
response would combine a variety of strategies including outreach, indoor water efficiency regulations,
and outdoor irrigation restrictions, each increasing in intensity as the shortage persists and the City’s
water supplies are further restricted. If necessary, implementation of these restrictions is critical to
conserve the City’s water supply for the greatest public benefit regarding domestic use, sanitation, and
fire protection.
14 The City’s Water Shortage Contingency Plan is available at:
https://www.slocity.org/home/showpublisheddocument/30334/637575513697770000
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Table 8: Dry Year 2022-23 Water Supply and Demand, in acre-feet
Potable Water Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Anticipated Unconstrained
Demand 650 682 649 645 551 487 488 473 483 567 616 650 6,941
Anticipated Total Water Supply 819 871 837 803 713 584 542 649 746 769 807 838 8,978
Surplus/Shortage 169 189 188 158 162 97 54 176 263 202 191 188 2,037
% Surplus/Shortage 26% 28% 29% 24% 29% 20% 11% 37% 54% 36% 31% 29% 29%
State Standard Shortage Level 0 0 0 0 0 0 0 0 0 0 0 0 0
Non-Potable Water Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Anticipated Unconstrained
Demand 49 50 39 31 19 9 6 12 10 24 41 50 340
Anticipated Total Water Supply 93 94 128 159 130 161 255 216 234 183 148 117 1,918
Surplus/Shortage 44 44 89 128 111 152 249 204 224 159 107 67 1,578
% Surplus/Shortage 90% 88% 228% 413% 584% 1,689% 4,150% 1,700% 2,240% 663% 261% 134% 464%
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The City reads water meters monthly to ensure water consumption data is collected for tracking and
analysis, as well as meeting state reporting requirements. Monitoring and reporting water use metrics
are fundamental to water supply planning and management. Monitoring is essential in evaluating the
effectiveness of expected response actions and identifying the need for new actions. While compliance
tracking helps to ensure the effectiveness of enforcement programs. To monitor the functionality of the
WSCP and ensure effectiveness, staff will track community response to water demand reduction
measures, public outreach, enforcement, and other administrative actions at each water shortage
response stage. This will include a review of monthly water consumption data for each customer class
and evaluation of associated revenue and expenditure impacts. Based on these analyses, staff will
recommend program refinements to the City Council as water shortage stages progress.
VI. SUMMARY
Based on the findings from this Water Supply Assessment, the City does not expect to enter a water
shortage emergency and will not need to implement water shortage response actions between July 1,
2023 and June 30, 2024. In fact, the Water Supply Assessment shows that the City will have a water
supply surplus on an annual and monthly timestep. The City will continue to monitor its supply and
demand using its Water Projection Model to ensure that any water shortage emergencies may be
identified well in advance so that programmatic and operational changes can be made to mitigate their
effects. Finally, this Water Supply Assessment assumes reliable delivery of available water supplies during
drought conditions similar to those experienced in recent history. Decreases in water availability caused
by extreme drought conditions or disruptions in the delivery of available water supplies may create
unexpected water shortage emergencies. If such water shortage emergencies arise, the City is prepared
to implement its WSCP to extend the City’s available water resources long enough to gain additional
winter rainfall periods which could serve to add to reservoir storage or to bring on supplemental water
supplies to meet demand.
In summary, the City maintains a robust water supply portfolio that can meet current and future
demands, including during dry periods. To plan for potential future dry years, the City has secured a
multi-source supply that provides reliability and operational flexibility. The City’s estimates of water
supply and demand account for both current and future build-out demands to ensure adequate water
supply, and the use of conservative estimates provides a buffer that reduces the potential for water
shortages even during unexpected disruptions in water supply or greater than expected increases in
demand. This buffer is in part to the long-standing history of water conservation by the City and its
community members, making water conservation a reliable component of the City’s water shortage
mitigation strategy. Additionally, the City is working to expand the use of recycled water within its limits
to offset additional potable water use and to develop groundwater and potable reuse programs to
provide supplementary sources of potable water supply that provide further operational flexibility during
disruptions in water deliveries from reservoirs.
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R ______
RESOLUTION NO. _____ (2023 SERIES)
A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF SAN LUIS
OBISPO, CALIFORNIA, RESCINDING RESOLUTION NO. 11353,
RETURNING THE CITY OF SAN LUIS OBISPO TO THE MONITOR
STAGE OF ITS WATER SHORTAGE CONTINGENCY PLAN
WHEREAS, the State of California received record-breaking rainfall during the
winter of 2022-2023; and
WHEREAS, on May 24, 2022, the California State Water Board adopted an
emergency regulation mandating increased restrictions on water use across the state;
and
WHEREAS, on August 19, 2022, pursuant to Municipal Code Section 13.07.030,
the City of San Luis Obispo City Council enacted Resolution 11353 declaring that the City
enter into Stage 2, the “Warning Stage”, of its Water Shortage Contingency Plan and
ordering water reducing measures; and
WHEREAS, on March 24, 2023, Governor Newsom signed Executive Order N-5-
23, terminating specific provisions of several State of Emergency Proclamations and
Executive Orders relating to drought dated between April 21, 2021 and March 10, 2023;
and
WHEREAS, the City’s total water use is within all water use requirements
established by the State of California; and
WHEREAS, the City’s water supplies are estimated to provide greater than ten
years of water to the community, and are therefore sufficient as to warrant reversion to
the “Monitor” stage of the Water Shortage Contingency Plan.
NOW, THEREFORE, BE IT RESOLVED by the Council of the City of San Luis
Obispo that:
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Resolution No. _____ (2023 Series) Page 2
R ______
SECTION 1. Declaration. In compliance with State of California water
conservation regulations, the City of San Luis Obispo hereby declares that it rescinds the
2022 Resolution No. 11353, returning the City to the “Monitor Stage”, of its 2020 Water
Shortage Contingency Plan. Water Shortage Response Stages, attached hereto as
Exhibit A.
Upon motion of Council Member ___________, seconded by Council Member
___________, and on the following roll call vote:
AYES:
NOES:
ABSENT:
The foregoing resolution was adopted this _____ day of _______________ 2023.
___________________________
Mayor Erica A. Stewart
ATTEST:
______________________
Teresa Purrington
City Clerk
APPROVED AS TO FORM:
______________________
J. Christine Dietrick
City Attorney
IN WITNESS WHEREOF, I have hereunto set my hand and affixed the official seal of the
City of San Luis Obispo, California, on ______________________.
___________________________
Teresa Purrington
City Clerk
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Resolution No. _____ (2023 Series) Page 3
R ______
Exhibit A: Water Shortage Response Stages
STAGE
WATER
SUPPLY
STATUS1
CITY ACTIONS
Monitor
5+ years of
available water
supply
City maintains existing water conservation staffing levels and budget that
supports meeting internal water efficiency goals and regulatory
requirements for water conservation, including ongoing public outreach.
Watch
< 5 years of
available water
supply
(up to 10% water
shortage)
City increases programs that encourage voluntary water conservation
including public outreach, rebate programs, and water efficient fixture
giveaways. City examines available alternative water sources
(groundwater expansion, recycled water filling stations, water purchase
agreements, etc.), City modifies internal operations to focus on decreasing
water loss and prepares for subsequent WSCP stages. City ceases any
short-term outside-City water sales/leases.
Warning
< 4.5 years of
available water
supply
(up to 20% water
shortage)
City implements time of use irrigation restrictions (7:00 PM – 7:00 AM).
City increases staffing, budget, and outreach to achieve additional
voluntary conservation savings while preparing for Alert-Critical stages.
Alert
< 4 years of
available water
supply
(up to 30% water
shortage)
City requires mandatory conservation measures including outdoor
irrigation restrictions (four day a week watering) and considers a Water
Offset Program for new connections.
Severe
< 3.5 years of
available water
supply
(up to 40% water
shortage)
City implements Water Allotment Program. Water Offset Program for
new connections may be increased (1.5:1 or 2:1 offset ratio). Allowable
irrigation reduced to three days per week.
Extreme
< 3 years of
available water
supply
(up to 50% water
shortage)
City continues to implement a Water Allotment Program with reduced
allotment levels. Water Offset Program for new connections may be
increased (1.5:1 or 2:1 offset ratio). Allowable irrigation reduced to two
days per week with optional additional measures limiting turf and spray
irrigation.
Critical
< 2.5 year of
available water
supply
(>50% water
shortage)
City continues to implement a Water Allotment Program at further
reduced levels (minimum for public health and safety). Irrigation no
longer permitted. Water Offset Program to cease and no new connections
permitted.
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