Avoiding Overdraft

Can groundwater recharge safeguard agricultural water supplies?


Many agricultural areas of the American West are reliant on groundwater withdrawals—and even more so in the face of drought. But many aquifers have become depleted or overdrafted over the years. And as temperatures rise with climate change and as droughts become more extreme, overdrafts are likely to increase.  To help ensure sustainable water supplies, farmers today are attempting to restore water sources beneath agricultural fields through a practice called on-farm groundwater recharge.

For decades humans have extracted water from aquifers at far greater rates than precipitation has been able to replenish them, creating a massive deficit, explains Dr. Helen Dahlke, Associate Professor of Integrated Hydrologic Sciences in the Department of Land, Air, and Water Resources at the University of California, Davis. To put this deficit in perspective, Dahlke states that, “During the period 1960–2016, we have extracted about 80 million acre-feet (MAF) beyond what is naturally replenished from rainfall. 80 MAF is 700 years of the annual water use for the District of Columbia. Another way to think about it is that the entire volume of Lake Tahoe is 120 MAF, a lake that is over 500 yards deep.”

In order to replenish groundwater sources, water must be slowed and allowed to permeate the soil surface. “On-farm groundwater recharge is putting the beaver back in the watershed,” explains Jeff Barry, principal hydrogeologist at GSI Water Solutions, of slowing water down on its journey across land.  “If you look at the history of our occupancy of land, in order to create viable agricultural spaces, we channelized farmland and took measures to promote runoff. Without pooling, ponds, and beaver dams, aquifers aren’t naturally recharged. Therefore, the need exists to slow water down as it flows.”

There are a number of different techniques for on-farm groundwater recharge. Barry is a proponent of placing recharge locations at higher positions in the water system than low-lying basins. A method that Dahlke is currently researching involves flooding agricultural fields. Dahlke and her team have conducted trials with on-farm groundwater recharge, flooding sites planted to alfalfa and almonds to evaluate impacts of excess water on crops.

The team’s research determined that when groundwater recharge is performed on soils that have high infiltration rates, there seems to be little harm to either the alfalfa or almond crops, but these flooding events must be temporary and applied with pulse irrigation to allow air to reenter the root system.  

Hydrogeologists agree that there are a number of factors to consider when selecting a site for on-farm recharge, including geography, soil type, proximity to aquifers, and crop suitability, among others. “Not all areas are connected to deeper aquifers. Where you do this, as well as the specific geology of that area, is critically important,” explains Barry. Today online tools such as the Soil Agricultural Groundwater Banking Index (SAGBI) and the Groundwater Recharge Assessment Tool (GRAT) are available to support decision-making.

Since the passage of the Sustainable Groundwater Management Act (SGMA), a three-bill policy that requires increased reporting and sustainable basin management, the agricultural community has become more invested in the protection of their water resources. Don Cameron, vice president and general manager of Terranova Ranch and an early adopter of on-farm groundwater recharge, recently told Water Deeply that the 2014 policy had a catalyzing effect.

“All of a sudden the growers started to understand what SGMA meant at the grower level, and what that meant was that in the future they may not be able to farm all of their land,” Cameron said. “They’re definitely not going to be able to pump all of the water that they’ve been pumping in the past, and to mitigate that, they’re going to have to do groundwater recharge.”

What are your impressions? Do you think that on-farm groundwater recharge offers a practical solution for agricultural water management? WE_bug_web

  • Jonathan McClelland.

    I took a look at the SAGBI link you provided, and it looks like with a few exceptions there is predominately poor soils and geological conditions to effectively facilitate on farm aquifer recharge. Based on that data, I think that the majority of funding for aquifer recharge should be directed to capturing surface water, doing the necessary purification procedures, and injecting it directly into the aquifer. This aquifer is vital to the survival of agriculture in the Central Valley, and is critically overdrafted already. A multi-faceted approach is necessary to correct the situation- nature by itself, w/o future overdraft would take 1,000+ years to restore it to its capacity as recently as 1940. What will be required includes subsurface banking of storm runoff adjacent to crop root zones, centralized collection & treatment for injection wells, changing the crop mix to grow more valuable crops that are climate appropriate and can be fallowed (with subsidy) in times of drought. It does not include expanding or constructing new surface reservoirs. The good sites for these were constructed long ago, they’ve contributed to the decimation of our fisheries and created a false sense of “water wealth” that has encouraged ranchers and farmers to be wasteful of the water allocated (at greatly subsidized rates). Besides, the irrigation season in the valley is hot and windy, leading to about 6 surface feet being evaporated. The two projects that irrigation districts are proposing currently are the Temperance Flat Dam on the San Joaquin River, which already runs dry in the summer due to the existing dams on it, and optimistic projections for yield are only available in the wettest 40% of historical years. It would also result in a net power loss, due to the inundation of 2 power plants. The other project is the Sites Off-stream Reservoir, which would lose 1/3 of its “captured” water to evaporation, and further degrade the threatened Sacramento River salmon. Do we want to put yet another “threatened” species into the “endangered” designation?

  • John Delgado.

    The comments made by Jonathan McClelland presented excellent information and comments about California’s water shortage. The altering of natures water sources and flow by man, has created the water problem California faces today. However, recharging aquifers and correcting the situation…..and only nature by itself, with out future overdraft would take years, the environmental need changes,and innovative solutions is now. That means we must implement approaches that will help Mother Nature in capturing natural surface waters by removing man made canals/reservoirs that will permit water flow to natural percolating ponds along the Sierras; doing the necessary purification procedures, by all parties, and injecting it directly into the aquifer. A multi-faceted approach, which includes wind and solar energy so as to remove damaging reservoirs and dams, is necessary to correct the situation…..nature by itself, even without future overdraft would take years to correct the water shortage. California aquifers, and for that matter in other dry areas of the country, are vital to the survival of agriculture and in the expanding communities occurring throughout the state. You would think with American technology and implementing innovative approaches that solutions to our water shortage would have begun.

  • Marie Light.

    McClelland’s principles are right on target. Long-term planning is needed to sustain the productivity of farming reliant upon finite groundwater resources. Increasing an aquifer’s volume of water in storage can be done and will take time. The advantage of storing water in an aquifer is the capacity is enormous compared to reservoirs and there is no loss to evaporation. Wells will be needed to recover the water if the point of use is not part of the recharged aquifer. Project’s removing a portion of the surface flow directed to aquifer recharge will need to include an assessment of what happens downstream to ensure an equitable use of surface water. Communities understanding their mutual benefits will be able to apply innovative technologies and develop sustainable water sources for their food. Investing in groundwater recharge is preferable to litigating who has the water right as it flows to the sea.

  • Dan Howes.

    First, comments regarding this article. Farmers in the Central Valley have been doing this for over 100 years. It is laughable by people that actually work in the irrigation industry that this “technique” is presented as new. There are numerous irrigation districts that have operated to oversupply water users surface water in spring and early summer because they do not have the reservoir capacity to store this water. Farmers over-apply to recharge the groundwater and use that groundwater later in the season. This points to the reason we need additional surface storage. The first comment was very misleading. No crops grown in the Central Valley of California consume 6 acre-feet per acre through evapotranspiration and evaporation rates are well below this level. Some crops might in the Imperial Valley (much warmer year around) but not in the Central Valley. The amount of evaporation suggested in first comment is significantly over-estimated. Deep reservoirs will store solar energy, significantly reducing the evaporation rate compared to shallow “pan” evaporation which is being used to mislead readers. The reservoirs are needed not for year to year regulation but to capture peak flows that would normally flow out of the state through the Delta at a time that does not benefit fish or people. California must invest in both groundwater and surface storage to become sustainable into the future. Believing otherwise is very short-sided.

    • Laura S.

      Dan, I really appreciate your perspective. You clearly have extensive experience in this arena. Thank you for offering such insightful comments.

  • Dr Edo McGowan.

    It will be political

    Laura, this is good. The topic is ripe for discussion, although this is an extant practice in some areas. Nonetheless, its wider practice will help slow down the demise of ag, as we have known it—- for a while. Throughout history, variously across the globe as things dried down, man’s inventiveness sprang forward to conquer adversity. A form of this is seen in rainwater harvesting which has been elaborated over time and is demonstrated by archeological findings in many ancient areas. I think it is just that the acknowledged need had not introduced itself sufficiently around here for this to become, until now, a widely discussed current topic. We had water to waste. This far exceeds the boundaries of California. One needs only to look at the High-Plains Aquifer systems.
    It will get sticky, however, as the urban-ag conflict begins to evolve. This “conflict” will be more severe in areas overlying the classic fossil aquifers that have been mined to support a growing and now highly dependent population base. I worked in a number of areas where this situation and practice was taking place and it was not without issue. The issues were political, more than technical. Politics based on misunderstanding were often the drivers.
    In Botswana, under its agricultural law, the harvesting of rain water for recharge and increased soil moisture was encouraged. This practice, however ran into direct conflict with the country’s urban laws where the need to increase runoff to dams prohibited such harvesting. Botswana is a flat country with high evaporation rate and dams have a very bad surface to volume ratio. Runoff was needed to maintain dam levels for urban demands. As the population grew, this divisional line became more important and hence more contentious. What was not considered was that the whole system was drying down and life as “usual” would need to change. This was exacerbated by the fact that satellite dependent population centers had been developing with the help of deep wells stuck down into fossil aquifers.
    To help make sure that plantings were not wasted, which depended on adequate rain, hence soil moisture banked at sufficient levels to get off a crop, some fairly sophisticated rain-tracking and estimating models were being developed for Botswana and that portion of Africa. This allowed fine tuning of the plantings, cf Cape Town.
    In Rwanda, the watershed was not protected because of deforestation and the heavy rains saw that the land was soaked. This caused land to move with massive mud avalanches taking entire sides of mountains into the valleys below. Thus, the strategy was to carefully move moisture into the underlying systems. But, often soil loss was so advanced that there was not enough soil to bank the water. This is unlikely to be an issue in California, cf, the Montecito mud-flows secondary to large fires. But, as the system dries down, the risk of large fire increases. Thus, in the future will it remain unlikely?
    We here in the western U.S. are more like Botswana and the issues will be more like theirs—an urban-ag conflict. The San Joaquin recharged off the Sierra runoff. In fact the whole of the valley is filled with deep sediments derived by eons of down-gradient materials movement via erosion. The ancient Sierra eroded into the valley fill. Then, we via our cleverness, farmed the area, pulled out more water than recharged, saw subsidence, compaction and destruction by salts. This resulted in massive areas being lost with aquifers contaminated. Nonetheless we grew cities now dependent on contaminated water. We have been moved into a time of increased drought and now hope that we can pull back on the stick to shallow out the dive so we can at least walk away from the crash.
    It is good to see efforts out there that might help. If you are going into the water, make sure your gear is up.


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