Groundwater Banking on California Croplands By ERYN WINGATE | CCA, Board Member, Western Region Certified Crop Advisers
On-farm groundwater recharge methods include winter flooding, skipped row flooding, subsurface reverse tile drainage, recharge ponds and unlined canals or irrigation ditches (photo courtesy Almond Board of California.)
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alifornia relies heavily on groundwater, with 40% of annual demand supplied by aquifers during non-drought years and upwards of 60% during dry years. Approximately 83% of people in California receive part of their annual supply from groundwater, and many communities are exclusively reliant on well water for both ag and domestic purposes3. Chronic groundwater overdraft, estimated at 2 million acre-feet per year since the 1960s, leaves California communities and farmland vulnerable to water shortages and rising surface water and pumping costs1.
Groundwater depletion also causes subsidence, or land sinkage, as dry aquifers collapse. Subsidence damages infrastructure, such as roads, powerlines, pipes and canals. The California Aqueduct’s flow capacity has reduced due to increasing subsidence rates, with some areas surrounding the infrastructure sinking almost 1.25 inches per month4. Groundwater recharge efforts have begun to reverse subsidence in some regions, but aquifer degradation and sunken land is often irreversible, and recharge efforts fail. The collapsed aquifers are irreparably damaged and can no longer store water. California experienced the worst drought on record from 2012 to 2015, 6
exacerbating groundwater pumping overdraft, water shortages and subsidence. Recharge during rainy years does not replenish the loss, and between 2010 and 2020, roughly 28% of monitored wells in California declined by 5 to 25 feet3,6,8. State officials responded by passing the Sustainable Groundwater Management Act (SGMA) in 2014 to bring pumping and recharge into balance by 2040. Local groundwater sustainability agencies, tasked with developing recharge implementation plans, will likely include Agricultural Managed Aquifer Recharge (AgMAR) to meet requirements and balance the groundwater pumping budget7. On-farm groundwater recharge methods include winter flooding, skipped row flooding, subsurface reverse tile drainage, recharge ponds and unlined canals or irrigation ditches. Traditional recharge methods like drainage basins require land dedicated solely to water percolation, limiting groundwater banking with high infrastructure construction costs and spatial constraints. Winter surface flooding on irrigated agricultural land can be implemented widely at low cost and with few infrastructure or management changes at the field level. With 5 million acres of California farmland suitable for AgMAR, groundwater banking can scale
Progressive Crop Consultant September / October 2023
up dramatically if even a small percentage of acreage can dually purpose for recharge during rainy years3,6. University research and early commercial implementation on orchards, vineyards and other crops indicate AgMAR can effectively recharge aquifers and benefit production in multiple ways3,5,6,7. AgMAR helps growers and landowners secure irrigation water availability for dry years while preventing further aquifer degradation and subsidence. When properly managed, recharge efforts can also improve soil quality by leaching excess salinity below the root zone. Well water quality also improves when clean stormwater dilutes nitrate and total dissolved solids (TDS) accumulated in the basin after years of ag chemical leaching and pumping overdraft. Better soil and irrigation water quality improve crop health and fertilizer use efficiency, leading to lower production costs or increased yield and crop quality.
Implementation
Growers and landowners implementing AgMAR must consider soil suitability for recharge, crop tolerance, water application timing and field management practices to protect both crop health and groundwater quality. Research and field studies conducted over the
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