HomeMy WebLinkAboutCC 2025-04-22 Monthly Water Supply and Demand Update
Item 9.d.
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: April 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 is required to prepare the report.
BACKGROUND:
The City of Arroyo Grande’s water entitlements are calculated on a water year that began
April 1, 2024. The current water supply for water year 2024/2025 includes 2,290 Acre
Feet (AF) from Lopez Reservoir, 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.
The predicted water use for the 2024/2025 water year was 2,100 AF. The actual use
finished at 2,085 AF for water year 2024/2025.
The monthly water use for the City in March 2025 was 147.6 AF. Attachment 3 has been
revised to show the comparison of the previous year’s use. April 2023 through March
2024 vs. the current years use of April 2024 through March 2025. The increase is directly
related to rainfall totals over the two years.
ANALYSIS OF ISSUES:
The United States Drought Monitor, as of April 10, 2025, shows San Luis Obispo County
is abnormally dry. Rainfall for the period of July 1, 2024, throug h April 10, 2025, is 8.85
inches at the Corporate Yard rain gauge. Lopez Lake is 93.5% as of April 10, 2025.
The deep well index for the first quarter of 2025 was completed on January 22, 2025, and
is 10.78 feet above sea level, which is 3.28 feet above t he threshold valve. The current
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Item 9.d.
City Council
Monthly Water Supply and Demand Update
April 22, 2025
Page 2
deep well index is 0.73 feet lower than October 2024, and 1.55 feet lower than January
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. 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 currently impact on 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 Lo pez Lake’s high volume of water;
however, as Lopez Lake decreases in volume into the dry season and because of its V
shape, the comparisons will become more apparent. 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. Predicted 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 this period. The dashed lines denote specif ic water
storage levels like 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 has appealed for 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 from Lopez Lake until the litigation is resolved.
ALTERNATIVES:
The following alternatives are provided for the Council’s consideration:
1. Receive and file the report, or
2. Provide other directions to staff.
ADVANTAGES:
The report provides the City Council and the public with the current and projected water
supply and demand conditions.
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Item 9.d.
City Council
Monthly Water Supply and Demand Update
April 22, 2025
Page 3
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 March
2. Lopez Lake Reservoir Storage Projection
3. Previous Year Water Use Comparison
4. Deep Well Index Levels for 1st Quarter
5. 2011 to 2024 Actual Storage vs. Predicted Storage
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