While driving south on I-5 from San Francisco to Los Angeles through the Central Valley, it’s hard to ignore that this is the agricultural heartland of the state. All tucked away in the dry golden hills and dusty ravines surrounding the San Joaquin Valley is a verdant plethora of orchards and fields, sometimes punctuated by the not-so-sweet smells of industrial livestock feedlots.
On a recent trip along this corridor, I had the chance to visit the Kern Water Bank. Just like a bank enables people to save their money for rainy days, the Kern Water Bank enables farmers to store groundwater in the aquifer beneath their facilities for when the rainy days are over.
California has been dealing with extremes in the hydrological cycle for decades. Historically, surface water reservoirs have enabled water managers to even out the fluctuations of water availability and demand. However, the high capital costs for surface water reservoirs, limited suitable land for constructing new reservoirs, and increasing concerns of evaporative losses in a changing climate, hint that alternative methods for securing water for California are necessary.
A promising alternative method for securing water in California is groundwater banking. Groundwater banking is a process by which excess surface water is stored in an aquifer as groundwater. Water is “recharged” when it is available by allowing it to percolate into the ground and is pumped out or “recovered” during dryer periods, enabling water managers to achieve the same function as surface water reservoirs of moderating hydrological extremes.
While the Kern Water Bank’s main goal is to provide a reliable water supply for its customers – mostly farmers – it also serves the purpose of maintaining nearly 20,000 acres of wildlife habitat.
The San Joaquin Valley wasn’t always an agricultural haven. Before farming, the region was a regularly inundated wetland environment providing a home to a variety of species and an oasis for migratory birds. Over the last 150 years, more than 95% of those wetlands have been lost to agricultural reclamation and development of communities throughout the Valley.
The Kern Water Bank is now home to 77 new species, some being either endangered or sensitive species. This has largely been aided by the Kern Water Bank’s serendipitous proximity to surface water, enabling them to access water to recharge their aquifer from the Kern River, State Water Project and Central Valley Project.
When water is available in the surface water running past their doorstep, the Kern Water Bank pump water from into 7,000 acres of shallow ditches to create ponds that recreate a wildlife habitat. The water in the ponds then percolates through the porous soil beneath the root zone and is stored as groundwater at a rate of 0.3 feet per day. The Kern Water Bank has even improved the water quality for downstream users of the Central Valley Project, since groundwater pumped out during the recovery process is lower in dissolved organic carbons and salts, which effectively dilutes the Central Valley Project water streaming pass their facilities.
The 7,000 acres of recharge pond space at the Kern Water Bank have recharged over 1.7 million acre-feet and recovered 0.9 million acre-feet as of May 2011. This leaves about 0.8 million acre-feet of water available in storage, which is nearly half of the 1.5 million acre-feet of accessible storage space in total. That is the amount of water that could sustain 3 million families over a year.
It has cost approximately $260 million to purchase farmland for the Kern Water Bank facilities and $35 million in infrastructure (wells, canals, pumps stations, and pipelines) costs. But when we compare this to the proposed expansion of the Shasta Reservoir, California’s largest surface water reservoir (4.5 million acre-feet), by increasing the height of the dam by 18.5 feet to acquire 636,000 acre-feet of additional storage space, the cost is $1.07 billion.
That’s $197 per acre-foot to store groundwater at the Kern Water Bank versus $1,682 per acre-foot to store water additional water at Shasta.
Economics aside - there are certainly benefits and limitations in both surface and groundwater storage. For example, surface water reservoirs have the potential for hydropower generation that can offset the capital costs. But tradeoffs include inundating existing habitats and communities. Whereas groundwater recharge pond facilities that store groundwater can strengthen natural wildlife habitat, but require access to surface water and the right geology to store the water under the earth.
Despite their differences, both surface and groundwater reservoirs require careful management and a reliable supply of water from rain or snowmelt to refill them. California’s future depends on it.