HomeMy WebLinkAboutCC 2025-07-22_09k Monthly Water Supply and Demand UpdateItem 9.k.
MEMORANDUM
TO: City Council
FROM: Bill Robeson, Assistant City Manager/Public Works Director
BY: Shane Taylor, Utilities Manager
SUBJECT: Monthly Water Supply and Demand Update
DATE: July 22, 2025
RECOMMENDATION:
Receive and file the Monthly Water Supply and Demand Update.
IMPACT ON FINANCIAL AND PERSONNEL RESOURCES:
Approximately two (2) hours of staff time are required to prepare the report.
BACKGROUND:
The City of Arroyo Grande’s water entitlements are calculated on a water year that began
April 1, 2025. The current water supply for water 2025/2026 includes.
2,290 Acre Feet (AF) from Lopez Lake Reservoir/Lopez contract entitlement.
The current modeled, safe yield is 357 AF of groundwater from the Santa Maria
River Groundwater Basin, with an entitlement of 1,323 AF.
An additional 160 AF of groundwater is available from the Pismo formation from
the existing City well system.
In addition to the annual Lopez La ke Reservoir contract entitlement, the City will have
689.69 AF of stored Lopez water, which is unused entitlement from water year 2024/2025.
The City also accepted an offer to purchase 470.33 AF of surplus Lopez water. The
surplus water cost is $55,146.74 or $117.14 per Acre Feet (AF).
The total supply from Lopez Lake Reservoir for this water year is 3,450 AF. The predicted
water use for the 2025/2026 water year is 2,200 AF. The monthly water use for the City
in June was 190.7 AF.
The supply of the additional 1,160.02 AF of Lopez water will be used first to prevent losing
it due to a potential 100% capacity Lopez Lake Reservoir spill over that occurred in 2023
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Item 9.k.
City Council
Monthly Water Supply and Demand Update
July 22, 2025
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and 2024. This allows for maximum banking of unused entitlement for this water year.
Attachment 6 details the stored and surplus water for water year 2024/2025.
ANALYSIS OF ISSUES:
The United States Drought Monitor, as of Ju ly 11, 2025, shows San Luis Obispo County
is abnormally dry. Rainfall for the Fiscal Year period of July 1, 2024, through June 30,
2025, is 9.35 inches at the Corporate Yard rain gauge. Lopez Lake is 88.0% as of July
11, 2025.
The deep well index for the 2nd quarter of 2025 was completed on April 14, 2025, and is
12.07 feet above sea level, which is 4.57 feet above the threshold valve. The current deep
well index is 0.17 feet lower than January 2025, and 1.74 feet lower than April 2024.
On January 15, 2025, in response to a preliminary injunction issued by the United States
District Court to the County of San Luis Obispo, Lopez Lake downstream releases were
increased from 2.0 million gallons per day to 5.1 million gallons per day, or 5,800 AF per
year (AFY). These releases are required until the lake is drawn down to 20,000 AF, after
which the releases will drop to 4,300 AFY, even though the “safe yield” is 4,200 AFY. The
County has prepared an updated projection that reflects the increased release rate. The
impact on Lopez Lake storage with this release level is shown in Attachment 2.
The increased release rate does not impact the City’s contract entitlement (how much
water the City receives) from Lopez Lake. The month -to-month comparisons at this time
show a negligible reduction due to Lopez Lake’s high volume during the dry season. The
City will continue working with the County to develop a multi-year projection showing how
increased downstream releases will likely impact Lopez Lake storage levels.
Attachment 5, titled 2011 to 2024 Actual Storage vs. Pred icted Storage model, provides
past annual water storage information from 2011 to 2024. The blue “Actual Storage (AF)”
line on the graph shows the water storage levels in Lake Lopez over 13 years. The dark
orange line shows what water storage levels would have been if the current court-ordered
release rates were in effect during the period. The dashed lines denote specific water
storage levels, such as spillway or maximum capacity (49,476 AF) and minimum pool
(1,690 AF), or essentially no potable water.
The model shows:
Out of the 13 years, 9 of those years would activate the Low Reservoir Response
Plan (LRRP) – below 20,000 AF, which limits water consumption.
Approximately 3 years of significant water quality issues.
Approximately 2 years of no potable water.
The County appealed the preliminary injunction. The City and all other Zone 3 contractors
will continue to work with the County to assess and report the impact on our water supply
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Item 9.k.
City Council
Monthly Water Supply and Demand Update
July 22, 2025
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from Lopez Lake until litigation is resolved. However, the costs of this litigation will be
shared by the City and Zone 3 member agencies.
ALTERNATIVES:
The following alternatives are provided for the Council’s consideration:
1. Receive and file the report, or
2. Provide other directions for staff.
ADVANTAGES:
The report provides the City Council and the public with the current and projected water
supply and demand conditions.
ENVIRONMENTAL REVIEW:
No environmental review is required for this item.
PUBLIC NOTIFICATION AND COMMENTS:
The Agenda was posted at City Hall and on the City’s website in accordance with
Government Code Section 54954.2.
ATTACHMENTS:
1. Monthly Operations Report for June
2. Lopez Lake Reservoir Storage Projection
3. Previous Year Water Use Comparison
4. Deep Well Index Levels for 2nd Quarter
5. 2011 to 2024 Actual Storage vs. Predicted Storage
6. 2024-2025 End of Water Year Stored Project Water and Surplus Water Generated
(April 2024 – March 2025)
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Attachment 6
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