water recharge in a vineyard
Recharge in a vineyard (Terranova Ranch Inc.)

By Scott Hamilton, President, Hamilton Resource Economics

Some of you may have seen the movie or heard the story of Dunkirk. At the start of the Second World War, British, French and Belgian armies were surrounded and cutoff by the German Army and were trapped against the French shore near the town of Dunkirk. Churchill described the event as a colossal military disaster with the “whole root and core and brain of the British Army” stranded. A disaster seemed imminent. The call went out to the British people for help–to gather whatever would float, cross the 20 miles of open water to the French coast and bring the soldiers home. Some 800 vessels–merchant and fishing boats, yachts and lifeboats, made multiple journeys across those waters. In eight days some 388,000 men were rescued. Those men lived to fight another day and eventually, with the help of some trusted allies, win the Second World War.

The San Joaquin Valley faces its own war–a water war. A war, that if lost will cost, according to Dr. David Sunding, a professor at UC Berkeley, $7 billion per year in lost income, tens of thousands of jobs, and some historic family farms. There are four elements to winning this water: capturing water that is not needed for any other purpose, conveying that water to where it is needed, recharging the local groundwater basins with the conveyed water, and an immense amount of political support. 

Figure 1. Groundwater quality over time, with and without recharge. At sites with low nitrate levels in recharge water but high legacy levels of nitrates in the soil, recharge (the blue line) could potentially worsen conditions in the short term but improve conditions in the long term compared to the no recharge condition (brown line).

If the Valley had a Churchill, he would be calling on every family farm to do what it can to achieve the third element: replenish groundwater basins by recharging surplus water. That probably makes little sense in the middle of the current drought, but eventually rain will come, and preparation is needed now. For too long the Valley has let winter and spring time water flow to the ocean because there was no home for it–there was not enough recharge capacity. 

The Water Blueprint for the San Joaquin Valley (WaterBlueprintCA.com) estimates the need for recharge to be in the order of 60,000 acres. That is a staggering amount of land. The secret to success is on-farm recharge. On-farm recharge typically refers to the practice of flooding either fallow fields or orchards and vineyards that are dormant so the water can percolate to the water table. But other alternatives exist. Dedicated ponds can be used to allow water to infiltrate to the water table. If such ponds are also designed to provide wildlife habitat, then multiple benefits can be achieved. Dry wells can be used to replenish aquifers below confining clay layers. Reverse tile drains can recharge water all year long below the root zone. On-farm recharge won’t work everywhere; some soils are too tight and won’t take the water. Some have underlying clay layers that prevent the water from reaching the water table. And some farms overlie contaminated groundwater such that recharge in the area would not be beneficial. But for many places in the Valley, particularly those on deep sandy soils, it would work very well. 

Factors to consider before implementing on-farm recharge (MAGSA)

Many farmers would naturally be concerned about what recharge would do to the health of their crops and therefore their yield. Various industry groups have been looking at this for some time. The Almond Board, for example, in a multi-year study found that recharge in dormant almond orchards didn’t negatively impact yield. Jesse Roseman at the Almond Board is taking this research and developing a guidance document for growers interested in on-farm recharge in their almond orchards. Contact him at JRoseman@AlmondBoard.com for more information. Additional information is available online. See for example Groundwater Recharge Through Winter Flooding of Agricultural Land in the San Joaquin Valley (SusCon.org) that provides information on the timing of recharge applications for perennial crops. 

Farmers in the Valley are getting creative, says Aaron Fukuda, general manager of Tulare Irrigation District. Farmers who once converted their orchards that were flood irrigated to a drip or micro sprinkler system, are now reconverting them to a dual system. When those really wet winters come, they flood their dormant fields. The rest of the time, they maximize irrigation efficiency. This clever strategy maximizes recharge when water is plentiful and dispenses it sparingly when water is short.

On-farm recharge is not without its concerns. People are concerned that on-farm recharge will distribute pesticides and fertilizer applied on the surface to the groundwater. But adverse effects can be avoided if the practice is implemented properly – see Water Sustainability at Technical Resources | Sustainable Conservation (suscon.org). General advice for protecting water quality during recharge is to coordinate with your water district manager so he or she is aware of what you are doing, especially if you are near communities with domestic wells. Have a nutrient management program and adhere to it to avoid applying more fertilizer than the crop can use, and work with the water district to monitor groundwater quality. On-farm recharge can affect operations: when and how much fertilizer should be applied given there is a chance that water for recharge may become available shortly after fertilizer application, flooded fields complicate spray applications, and some disease risks will be elevated. For more on this, see some farmers personal experiences at On-Farm Recharge Webinar: Pecans & Other Nuts – YouTube (start at 59 minutes) 

Many basins have areas with contaminated groundwater. By recharging good quality water and pumping the poorer quality water (e.g. water high in nitrogen), groundwater quality can improve over time. Figure 1 provides an illustration of how conditions can be improved compared to a no recharge situation. 

On-farm recharge is one of the most cost-effective ways of storing water. In 2016, Mr. Stacey Sullivan, Policy Director for Sustainable Conservation, compared the costs of on-farm recharge to the costs of dedicated recharge basins. “For on farm recharge, we found the costs running between $40 and $107 per acre-foot, and the range on that is very much on whether or not there’s existing flood irrigation capacity on the land, or whether you’d need to put something in,” he said. “But even with adding additional canals, it’s still cheaper than building a dedicated recharge basin at $124 an acre-foot and obviously, if we’re going to start talking about significant surface storage, those numbers go up by a factor of 10 or more.”

The water wars in the Valley are very real. Ground water basins need at least an additional two million-acre feet per year, on average. But if wet winters occur only one year in three, that means at least 6 million-acre feet need to be recharged when the water is available. That is more than three times the size of San Luis Reservoir. It is an enormous undertaking. But if on-farm recharge were to occur on hundreds of fields throughout the Valley, and with the help of some trusted allies, this battle could be won.