Making a significant “deposit” for the next dry spell

When it comes to being prepared for unforeseen circumstances, you might be wise in putting money away for a rainy day.  In our case, the Santa Clara Valley Water District puts water aside for a non-rainy day.

Since 1997, the water district has participated in a groundwater banking program with the Semitropic Water Storage District in Kern County, near Bakersfield. Groundwater banking allows us to send excess water imported from the Sacramento-San Joaquin Delta to Semitropic during wet years when supplies are plentiful, and to withdraw it during dry years. The water district is one of several partners with the Semitropic Water Storage District.

The water district expects to bank over 60,000 acre-feet of water this year, the first time since 2011 we will bank such a large amount. One acre-foot of water is roughly as much water used in a year by two families of five.

Groundwater banking allows us to have a reserve of water to draw upon during dry years and to protect our local groundwater aquifers from the threat of over-pumping and subsidence, or sinking of the land. Our total storage capacity in the Semitropic bank is 350,000 acre-feet, or about 114 billion gallons of water. During the recent historic drought, from 2012 through 2015, the water district withdrew nearly 143,000 acre-feet of water.

After a much improved rain season in 2016, the water district stored over 8,000 acre-feet in the Semitropic bank. Last year the water district focused on using the welcomed precipitation in a full-scale program to replenish our aquifers through our countywide percolation ponds. Now that our groundwater levels are healthy, we can afford to send greater amounts of water to the Semitropic bank, especially after this last wet season.

While we are sending almost 7 times more this year, it’s not a record. The most water banked in a year was about 80,000 acre-feet, back in 2005. But this year’s deposit will be good insurance for the future, and should bring our storage balance back up to approximately 250,000 acre-feet. “It’s a significant amount of water and goes a long way to protecting us against future droughts,” said Senior Water Resources Specialist Dana Jacobson.

Groundwater banking also helps save the district money during droughts when water is both scarce and can be extremely expensive to acquire. In 2015 the cost to withdraw an acre-foot of water from the Semitropic bank was about $200 per acre-foot, while the cost to purchase the same amount of water and transfer it from north of the Delta was approximately $1,000 per acre-foot. The cost of storing water is nearly consistent during normal or dry years at approximately $100 per acre-foot.

The Semitropic bank is currently the water district’s only banking operation outside of the county. However, technically speaking, we’ve operated a local banking effort here in Santa Clara County since 1929, when the district was formed to manage the region’s groundwater resources. We import about half of our water supply from outside the county, much of which is stored in local aquifers, and supplements our local water supplies which we draw upon on a regular basis.

The historic drought taught us how important it is to diversify our water supply sources to protect us during difficult times. In this sense, the Semitropic bank has proven to be an invaluable resource. The water district is also exploring options with regional partners to develop additional water supply sources and potential storage opportunities to ensure Silicon Valley has safe, clean water for years to come.

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