Valley Voices

Groundwater storage isn’t sexy, but it beats Temperance Flat

Robert Merrill
Robert Merrill

During the past decade, most discussions regarding solutions to California’s water problems have centered on increased surface water storage with new dams. Valley politicians, farmers and some newscasters seem singularly focused on so-called “new water,” and building dams to hold back water they refer to as “water lost to the ocean.”

Perhaps one reason Valley congressmen fail to win passage of their bills to increase water storage, mainly by building Temperance Flat Dam on the San Joaquin River, is that their proposals have changed little each year. Maybe it’s time to examine other solutions for water storage to survive droughts. Could a bill emphasizing increased groundwater recharge instead of surface storage make the Valley more drought resistant?

California and the San Joaquin Valley have a water crisis for many reasons, but let’s examine four main underlying problems.

1. Both agricultural and urban growth demands for water keep increasing.

2. Groundwater storage receives far less attention than surface storage.

3. Construction time and costs of surface (dams and reservoirs) and subsurface (groundwater) storage projects are neither thoroughly investigated nor compared.

4. The impact of climate change on precipitation and snowpack has been overlooked or denied until recently.

First, we need to acknowledge that water is a finite resource although its availability varies in time and location. “New water” is a fantasy. Thus, unlimited growth in demand by urban users and agriculture is mathematically impossible. Under state allocation policy, urban users have priority over agricultural users when surface-water supplies are stressed.

Such policies result in intense competition between agriculture and the environment/ecosystems for the remaining water. This has caused overdrafting of groundwater and the one-dimensional solution of demanding more surface storage.

A good analogy of water availability is a bank account. Surface water is the checking account and groundwater is the savings account. Another dam would add slightly to our checking account, but the reservoir must be managed for both storage and flood control.

Under certain circumstances, such as a sudden snowmelt, water must be released in a controlled manner to make room in the reservoir, thereby preventing uncontrolled flooding.

Capturing these controlled flood releases and depositing them into a groundwater savings account would enhance our overall water storage, while leaving part of the flood releases for a fragile salmon population.

Second, the Legislature has finally moved to manage groundwater with the Sustainable Groundwater Management Act, highlighting the San Joaquin Valley as a critically overdrafted groundwater region.

Critical to complying with the SGMA are sustainable practices that prevent further decline in our water table, but SGMA timelines take effect too far in the future. More recharge basins are needed now.

To rebuild our groundwater supply, it is necessary to build additional recharge basins in areas with appropriate geologic and soil conditions. Construction of new and enlarged conveyance structures like canals would also be required to capture and transport flood releases to new recharge facilities.

Without these groundwater recharge infrastructure investments, we would lose the ability to capture those floodwaters and add them to our groundwater savings account. It is our groundwater supply that will get us through the drought years.

Third, additional groundwater recharge infrastructure could be constructed for about one-third the cost of the proposed Temperance Flat Dam, and it can be built in two to three years rather than the 10 years likely required for building the dam.

Combining adequate groundwater recharge and storage capacity with the existing Friant Dam will likely make Temperance Flat unnecessary. Consider also, reservoirs suffer high evaporative losses in summer, while groundwater storage has zero evaporative losses.

Fourth, drought protection is essential, as California’s past 11,000 years of climatic/geologic record is dominated by droughts with short intervals of flooding. Climate-change models suggest that Central California will experience longer drought periods punctuated infrequently by El Niño years.

Meanwhile the central Sierra Nevada snowpack is forecast to decline; more of its precipitation will fall as rain. This means less natural snowpack storage, and when major storms arrive, reservoirs must release much of that water as a flood-protection measure. Capturing much of these flood releases and sending them to expanded recharge facilities would help us adapt to climate change by rebuilding groundwater storage.

Climate change will increase the probability of droughts by altering precipitation patterns. Building Temperance Flat to capture small amounts during infrequent flood years is unlikely to significantly improve sustainability. But, expanding groundwater recharge capacity will undoubtedly create a sustainable water supply for future generations.

Robert Merrill is a Fresno State emeritus professor of geology.