In the midst of a historic drought, how has the Santa Clara Valley Water District been able to maintain our water supply without needing to take more extreme water conservation measures?
Since 1997, the water district has made significant investments in banking water in an underground aquifer outside the county. This groundwater banking has been an important water management tool designed to increase the water supply reliability in Santa Clara County. This decision has proven to be valuable in helping the district provide enough safe, clean water during this historic drought.
What is groundwater banking?
More than half of Santa Clara County’s water supply is imported from the Sierra Nevada range of northern and eastern California, through rivers that flow into the Sacramento-San Joaquin Delta or directly to water conveyance systems. Each year, the district is allocated water from the State Water Project and the federal Central Valley Project. These allocations are based on the Sierra Nevada snowpack, water levels in large state reservoirs like Lake Oroville and Lake Shasta and other factors.
Think of groundwater banking as putting money in a savings account. When someone has a little bit of extra money, they can put that extra money in a savings account until a time they need extra cash. The practice of groundwater banking is not that different. In a year when there’s a large Sierra snowpack and our local reservoirs are at capacity, our share of available water that year may be more than we actually need and more than we can store locally. So, with groundwater banking, we have a method to send that surplus water down the California Aqueduct to a groundwater basin near Bakersfield for safe keeping. During dry years, when we have less snowpack and local reservoirs are low, the water district is able to tap that bank of surplus water to make up for any water shortages the county may face.
There is a cost for this program, but it’s more cost effective and reliable than securing supplemental supplies in dry years. The district saves money by banking water in wet years when supplemental supplies are less expensive and withdrawing them in dry years when supplemental supplies can cost considerably more.
The water district has an agreement with the Semitropic Groundwater Storage Bank to store our surplus water. Located in Kern County near Bakersfield, it is one of the largest groundwater banking programs in the world. The water district’s agreement with Semitropic means the district can store up to 350,000 acre-feet of water, more than twice the capacity of all ten of our local reservoirs combined. In 2015, the district was able to withdraw more than 45,000 acre-feet, enough to serve 90,000 households for a year. The district’s storage balance was 190,339 acre-feet, or about 62 billion gallons of water, as of Oct. 31, 2016.
What are the benefits of groundwater banking?
By banking water, the district is able to fully use our imported water contracts in wet times, when we might have had to turn back excess water due to restricted capacity of our reservoirs. The water district’s investment in water banking has helped boost local water reliability during the last four years of drought, avoiding the need for more serious water use reduction measures.
How much does groundwater banking cost?
The cost to put, store, and retrieve water at the Semitropic Groundwater Storage Bank varies but is about $200 per acre foot. But considering that buying water from other agencies in drought years can cost significantly more, the banking program saves the district money.
How do we withdraw water from the Semitropic Groundwater Storage Bank?
The Semitropic Groundwater Storage Bank is an “in lieu” storage program, meaning that the Santa Clara Valley Water District does not pump that stored groundwater back north to Santa Clara County. Instead, the district retrieves this stored water through an exchange with other State Water Project contractors.
Again, back to the bank reference, think of it like a bank’s ATM. You can deposit money in a branch in Los Angeles and later retrieve your money from an ATM in San Jose.
All in all, our investment in this groundwater bank has benefited our community greatly during this historic drought. Without it, water managers would have had to impose more severe water use restrictions or purchased far more expensive water supplies to make up the gap between supply and demand.
Valley Water News 
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