PALMDALE — Water suppliers will rely on water stored underground during wet years to ensure adequate supplies for the Valley during dry years, according to a plan presented Tuesday.
The Antelope Valley-East Kern Water Agency, a water wholesaler which supplies State Water Project water to providers across the Valley, detailed its projected demand and supplies for the next 25 years in the Urban Water Management Plan.
The plan is required by the state to be updated every five years, and is accompanied by a Water Shortage Contingency Plan that may be updated more frequently.
“This plan supports long-term water supply planning for the agency and also provides framework for conservation and drought response,” AVEK Assistant General Manager Matt Knudson said.
Providers such as Los Angeles County Waterworks and the Quartz Hill Water District use AVEK in addition to their groundwater supplies to provide for customers.
In 2020, AVEK supplied approximately 42,000 acre-feet of treated and untreated water to customers and an additional 7,000 acre-feet was stored underground in the aquifer, according to the plan.
AVEK is allotted 144,800 acre-feet of water from the State Water Project; however, it seldom receives a full allotment. As of 2020, the long-term average received was 58% of the allotment. This number is projected to decrease to 52% by 2040, according to the plan and based on data provided by the state Department of Water Resources.
With the current drought conditions, the state has said this year’s allocation will be 5%.
An acre-foot is 325,851 gallons, or approximately the amount of water a typical Antelope Valley household used in one year, before the most recent drought-reduced usage.
Using data from the Southern California Association of Governments and Kern Council of Governments, plan consultants Water System Consulting calculated that the population within the agency’s boundaries will increase from about 320,000 in 2020 to 447,000 in 2045, a rate of about 1.3% annually, Water Systems Consulting engineer Rob Morrow said.
This will lead to a corresponding increase in AVEK water demand from approximately 44,440 acre-feet in 2025 to 57,590 acre-feet in 2045, according to the plan’s projections. These projections take into account factors such as continuing conservation efforts.
“The per capita demand is probably the toughest thing we’re all trying to estimate across California right now,” Morrow said. “We haven’t had a ‘normal’ few years of supply and demand and it’s tough to say what normal water use it.”
In addition to State Water Project water brought through the California Aqueduct, AVEK’s water supplies include groundwater, based on a court-ordered apportionment of local aquifer. This amounts to about 4,350 acre-feet per year.
Additional supplies are available as a result of an agreement with Los Angeles County Waterworks to provide a reliable water source for any new construction within AVEK’s boundaries. New projects must secure an outside source of water that is then made available through AVEK to meet the additional demand, Knudson said.
In a normal year, the plan projects AVEK water supplies totaling 91,000 acre-feet to serve a demand of 44,440 acre-feet in 2025, climbing to 97,010 acre-feet to serve a demand of 57,590 acre-feet in 2045.
Excess State Water Project water can be sent into the agency’s water banks, the largest of which currently has a total capacity of 150,000 acre-feet. At the start of 2021, that water bank held approximately 90,000 acre-feet of water, thanks to storing surplus in recent wet years, Knudson said.
In a single dry year — like 2021 — when State Water Project deliveries are very low, that stored water will be used to make up the supply difference.
To calculate the effects of multiple dry years, consultants used the allocations from the stretch of five driest years, from 1988 to 1992, to calculate supply needs and estimated the agency would need to target capacity of about 97,000 acre-feet in 2025 to nearly 133,000 acre-feet in 2045.
Knudson said the agency expects to use about 22,000 to 23,000 acre-feet of stored groundwater this year to serve its customers.
The agency is in the design phase of another water bank, which is expected to begin receiving water in 2023, Knudson said. It will ultimately have a capacity of 280,000 acre-feet, with annual recharge and recovery rates of 70,000 acre-feet.
AVEK Director Frank Donato questioned whether the agency’s current stored water capacity and the ability to add water to it would be enough to weather several dry years, especially as it is currently limited by the infrastructure available to extract and distribute the stored water for use.
“When we do get a wet year, we’re going to have to flood this basin as much as we can” to meet the target levels of stored water, he said.
Any year the agency receives more than a 30% allocation, it can add to the water bank storage, Morrow said.
In addition to the underground water banks, the agency may also store some surplus State Water Project water in the San Luis Reservoir in the San Joaquin Valley.