By Scott Hamilton, President, Hamilton Resource Economics
The San Joaquin Valley faces a critical water shortage. If nothing is done, potentially one million acres, 20% of the cultivated land in the San Joaquin Valley, could be fallowed. With existing reservoirs and river flows fully committed to meeting annual demands, there has been a call to build more surface reservoirs to reregulate flood flows. Currently the California Water Commission is pursuing three surface water storage programs under its Water Structure Investment Program: an expansion of Los Vaqueros Reservoir in the East Bay area, Pacheco Reservoir on the west side of the San Joaquin Valley and Sites Reservoir on the west side of the Sacramento Valley.
Surface reservoirs play an important role in water management but have their problems. California typically experiences very wet years and very dry years and not so many “average” years. To complicate water planning further, the wet and dry years typically come in cycles as exaggerated by climate change. During very wet years, surface reservoirs are only successful in capturing a small proportion of the water that is available. During a drought cycle, surface reservoirs can quickly run dry. These circumstances make surface reservoirs poorly suited to deal with the cyclical nature of California’s hydrology. Surface reservoirs are very expensive. Now that state and federal governments are leaning towards only supporting the public benefit component of water projects, it has become much harder to complete surface reservoir projects. And new surface storage often raises environmental concerns as valleys are flooded and fish habitat and migration routes are impacted.
That is not to say that certain surface reservoir projects are not without their benefits. Surface reservoirs have an essential role to play in providing water for high value uses, recreation, flood protection and water for emergencies. And surface reservoirs are a critical element in reregulating winter and spring precipitation to meet summer irrigation demands. But such re-regulation is not an essential element in achieving groundwater sustainability. For that, more water needs to be recharged into groundwater basins than is pumped out of them–and the timing of that recharge is not critical. Conjunctive use, the practice of storing water in aquifers during wet periods for recovery using groundwater wells in dry periods, has been utilized by water districts throughout the Valley for many decades. It is fundamental to the way that many water districts operate. Water is diverted to recharge ponds where it infiltrates through sandy soils until it reaches and supplements the water table. Conjunctive use projects have their advantages. Evaporation losses are small relative to the quantity of water recharged and the storage capacity is very large. The Kern Water Bank has stored as much as 1.3 million-acre feet on its 20,000 acres and in 2017 alone recharged 560,000-acre feet of water – more than the capacity of Lake Isabella. While infiltration rates frequently diminish through the recharge season, recharge can continue indefinitely while surface water is available. During droughts, farmers and water districts can draw on that stored water. Groundwater storage has other significant benefits beyond surface storage. Although still expensive, it is far cheaper to build recharge facilities than it is to build new surface reservoirs. Groundwater recharge facilities can also be designed to provide environmental benefits—restoring seasonal wetlands that were once abundant throughout the Valley – see Groundwater-recharge-guidelines-checklist_07-spreads.pdf (edf.org).
Like surface storage, groundwater recharge is not without its challenges. If not properly located and managed, groundwater recharge can distribute fertilizers and contaminants to the groundwater. Many areas do not have the geologic conditions suited for groundwater recharge. Even if soils appear sandy on the surface, clay lenses below the surface can restrict infiltration rates. New technology, aerial electro-magnetic surveys, while not cheap, allow examination of geologic conditions hundreds of feet below the surface.
In the end, economics becomes a determining factor. Somebody has to pay for the private benefits of water storage and that typically is the end user––the communities and farmers that benefit. In the southern Valley, Temperance Flat, a 1.26-million-acre foot proposed reservoir upstream of Friant dam on the San Joaquin River, was one of the best hopes for new surface storage in the San Joaquin Valley. That project is now on hold. Aaron Fukuda, General Manager of Tulare Irrigation District cites funding and environmental issues as key impediments.
While increased groundwater storage represents a fundamental component of achieving groundwater sustainability in the San Joaquin Valley, current recharge capacity within the region is vastly short of what is needed. The Water Blueprint for the San Joaquin Valley, an initiative intended to bring more water into the region, estimates another 7,500 cubic feet per second (CFS) of recharge capacity will be needed to achieve sustainability. This represents an enormous undertaking possibly comprising 60,000 acres or more.
There is still time to make investments in water infrastructure. Water districts throughout the region are working to build more recharge capacity and innovative options for recharging aquifers are being explored that would reduce the cost of groundwater recharge. Further investment in groundwater recharge has the potential to provide benefits for wildlife, communities, and industry in the San Joaquin Valley. But it will take sustained water user support to make that potential a reality.
