Valley ‘in crisis’ from water imbalance

Friant Water Authority (FWA) released recently a brochure summarizing the water imbalance issue in the San Joaquin Valley, and it stated that even after a drought-ending wet season last year, the combined effects of prolonged drought and increasing regulations on water resources have placed the Valley in a severe state of overdraft — meaning groundwater is being pumped out faster than it can be replenished.

The brochure states that groundwater overdraft in the San Joaquin Valley is estimated at 1.8 million acre feet (MAF) per year on average — nearly 22 Success Lakes at full capacity. Simple numbers, complex problem The historical “demand” for water in the San Joaquin Valley is 13.3 MAF, which is primarily used by agriculture, but includes cities like Fresno and dozens of disadvantaged communities that support the agricultural economy.

To meet that demand, the Valley receives surface water from several sources. Each year, 10.4 MAF of surface water flows into the Valley from the Sierra Nevada mountains, but almost 4 MAF is taken from that in water exports to the Bay Area and San Joaquin River outflow, which is tightly managed and driven largely by regulatory requirements that are becoming more stringent for all of the rivers that flow to the Delta.

The Valley receives 4.1 MAF of imported water each year from the Sacramento-san Joaquin River Delta, and about .9 MAF in annual precipitation.

The resulting water deficit is filled by pumping groundwater, and is being extracted at rates that exceed replenishment, hence the term “over” draft.

The San Joaquin Valley can expect further reductions in surface water in the form of state regulations. California’s State Water Resources Control Board (Water Board) is considering increasing outflow requirements for the San Joaquin River to 40 percent of natural inflow, and imports from the Delta are subject to future reductions as species decline and aquatic ecosystems have been failing.

With less water coming in from the Delta and more water leaving via the San Joaquin River, the imbalance in the Valley would increase to 2.9 MAF per year in the near future.

Effects of sustained overdraft Sustained overdraft leads to significant problems such as the de-watering of wells, as experienced in East Porterville and other Valley communities in 2016. De-watered wells can leave communities and farmers without any dry-year water supplies and result in a race to drill deeper and deeper wells.

Another effect is land subsidence — where the voids that previously contained water in aquifers physically collapse. Land subsidence can permanently reduce the holding capacity of aquifers, and the physical displacement of the terrain can damage roads, bridges and canals.

In the past two years alone, segments of the Friant-kern Canal have subsided almost three feet; these segments now convey less than 40 percent of their designed operating capacity.

The Friant Division, which includes the Friantkern and Madera canals, has delivered surface water from the San Joaquin River to support crops and cities in the southern San Joaquin Valley for the past 50 years. It was designed with the expectation that groundwater would serve as a backup during dry conditions, and that heavy surface water deliveries in wet years would allow the regional groundwater to replenish.

However, changes in recent decades have eroded the previous stability of the Friant Division. In addition to record-setting drought, a reduction in water supplies to restore salmon below Friant Dam and sustained groundwater overdraft have impacted the ability of the Friant Division to serve the eastside of the San Joaquin Valley.

Possible solutions FWA identifies two general strategic approaches that can reduce this deficit and protect the groundwater of the San Joaquin Valley: reducing groundwater use, and/or increasing surface water recharge. They feel that a combination of these strategies will be needed.

Reducing groundwater use Of the methods for reducing groundwater use, the FWA identifies three approaches as most relevant in managing the demand for groundwater in the Valley.

Water recycling, including using treated wastewater that would otherwise flow into the rivers, may help depending on timing. If recycling of water occurs when it would be needed to meet flow requirements in the rivers, it would likely result in a need to increase releases from upstream surface storage reservoirs.

Water conservation can also be an important tool, especially during droughts, but it provides no net benefit to the groundwater overdraft problem unless it is accompanied by a reduction in the acreage of irrigated crops or lawns, known as land use changes or land retirement.

In most cases, changing the use of irrigated land to reduce groundwater overdraft can help. Although it varies, land retirement can reduce groundwater overdraft between 2 and 5 acre-feet per acre of land retired.

But the impacts of land retirement are significant, as reduced agricultural activity directly affects State and local economies. Agriculture jobs also tend to be concentrated in disadvantaged communities, where few alternatives for employment exist, placing these communities at an elevated risk.

Increasing surface water use Additional surface water can be used to help groundwater recharge by either ponding it and allowing the water to infiltrate into the ground, or by reducing groundwater pumping and instead using a like amount of additional surface water. This second method, known as “in-lieu recharge,” is the most effective way to immediately reduce overdraft without retiring land.

But capturing additional surface water to help with the problem presents its own challenges. The only new surface water that can be captured from the Valley is that which is not required to flow out to meet regulatory requirements. Such water is only available during wet years, which occur three or four years out of every 10 years on average.

There are many ways to capture and convey this surplus water for groundwater recharge. Studies have shown that the maximum amount of additional surplus surface water that could be captured this way is between 100 to 400 thousand acre-feet per year. To capture the higher end of that range would require a significant increase in surface storage on the San Joaquin River above Millerton Lake.

Another answer is to get more surface water from the Delta. Current water delivery obligations from the Delta are approximately 7.4 million acre-feet. However, the current annual average delivery is only projected to be 4.1 million acre-feet.

The proposed California Waterfix tunnels are intended to deliver water more effectively south of the Delta and could increase reliability of Delta imports by as much as 1 million acre-feet, of which about 0.5 million acre-feet would remain to the San Joaquin Valley.

The only other way to increase this reliability is by changing regulations that have required more water to flow past the pumps in the Delta for environmental reasons. FWA feels Federal legislation could increase the reliability of Delta water deliveries by approximately 1 million acre-feet per year without significantly impacting Delta wildlife.