Flooding farm fields may replenish California groundwater



Groundwater is  underground water moving through geologic formations called aquifers and is stored in open spaces in the soil. Groundwater depletion is a term used to describe water declines caused by groundwater pumping, particularly in the long-term. Warming temperatures across California has led to less annual snowmelt and farmers have gotten increasingly concerned about the dwindling groundwater supply.

Dan Theobald, or “Wastewater Dan” as he is known, proprietor of Environmental Services (www.esdlt.com), is a professional wastewater and safety consultant/trainer. In an guest article on Water Online, Dan Theobald explains that groundwater depletion can lead to damaging effects such as lowering the water table which leads to more well drilling or deepening of wells, increased costs of water to the user, reduced water in lakes and streams, land subsidence which leads to loss of support below ground and soil can collapse, compact, and drop, and deterioration of water quality.

Don Cameron, the general manager of Terranova Ranch, southwest of Fresno, Calif. did something innovative. Six years ago, he seized an opportunity to open an  irrigation gate when a nearby river was running high due to recent rain and flooded hundreds of acres of vineyards from February until May. According to NPR, “his idea was pretty simple: Flood his fields and let gravity do the rest. Water would seep into the ground all the way to the aquifer”.

To put things in perspective, California can use more than half of the stored groundwater for irrigation in dry years. In general, the state lets these groundwater basins be replenished naturally at irregular rates by rainwater or seepage from rivers and lakes. As agricultural farmers pump groundwater basins to keep their crops alive in drought, many of these basins have difficulty delivering a steady water supply.

California crops being irrigated (Photo courtesy of AP Images)


Cameron’s unconventional method of replenishing groundwater has led to several studies. UC Agriculture and Natural Resources (UC ANR), “researchers are working on a new approach to replenish these critical underground supplies once the rains return: using farm fields as recharge basins during winter months.” Groundwater recharge is done by flooding water on open farm land and letting it percolate into the aquifers. Researchers at UC Davis say there is much potential in groundwater recharge. It would effectively use aquifers as surface reservoirs.

Data shows that there are 3.6 million acres of agricultural land in California that has good potential for this process to be successful. However, certain factors need to be explored before agencies and farms are brought into this service. For example, what crops can tolerate standing water for weeks or months, soil fertility and salinity need to be taken into account, as well as building infrastructure and city codes needing to be revised or adapted to the procedure.

The field test conducted by UC Davis involved watering 10 acres of alfalfa crops with more than twice the amount of water it would get in a year and the results were promising. According to the study, the water percolated into the ground easily and did not drown the crops, as alfalfa is known to do. Another study is to do a field test on almond fields is scheduled this year.

Other known ways of artificially replenishing groundwater include rain gardens or rainwater harvesting, which according to Dan Theobald, rain garden advantages include:

  • Improvement of water quality by filtering pollutants
  • Pleasing appearance to the building
  • Preservation of native vegetation
  • Storm water and flood control
  • Attraction of bees, birds, and insects
  • Easy maintenance
  • Groundwater recharge

However, the drawback of rainwater harvesting is it can only be done in areas it rains and only during the rains. Another method is using injection wells to push water into aquifers but this method is energy intensive.


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