HomeMy WebLinkAboutCC 2025-03-25_09d Monthly Wter Supply and DemandItem 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: March 25, 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 Ac re
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 is 2,100 AF.
The monthly water use for the City in February 2025 was 123.7 AF. Attachment 3 has
been revised to show the comparison of the previous year’s use. March 2023 through
February 2024 vs. the current years use of March 2024 through February 2025. The
increase is directly related to rainfall totals over the two years.
The per capita monthly water use for February 2025 is 80 gallons per day/per person.
The residential per capita use was 62 gallons per day/per person. There was a total of
2.3 inches of rainfall in the City in February 2025.
ANALYSIS OF ISSUES:
The United States Drought Monitor, as of March 13,2025, shows San Luis Obispo County
is abnormally dry. Rainfall for the period of July 1, 2024, through March 13, 2025, is 7.75
inches at the Corporate Yard rain gauge. Lopez Lake is 93.2% as of March 13, 2025.
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Item 9.d.
City Council
Monthly Water Supply and Demand Update
March 25, 2025
Page 2
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 the threshold valve. The current
deep well index is 0.73 feet lower than October 202 4, 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 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 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 multiyear projection showing how increased downstream releases will likely
impact Lopez Lake storage levels.
Attachment 5, titled 2011 to 2024 Actual Storge 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 specific water
storage levels like spillway or maximum capacity (49,476 AF) and minimum pool (1,690
AF), or essentially no potable water.
This 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 impacts 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.
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Item 9.d.
City Council
Monthly Water Supply and Demand Update
March 25, 2025
Page 3
ADVANTAGES:
The report provides the City Council and the public with the current and projected
conditions of our water supply and demand.
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 February
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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285
1937
96
304
2067
103
0
500
1000
1500
2000
2500
Commercial Usage Portion of Production Acre Feet Production Usage (gpcd)
Previous Year Water Use Comparison
Attachment 3
Previous year use Mar 2023 to Feb 2024 Current year use Mar 2024 to Feb 2025
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