On-Farm Recharge: Acceptance and use by farmers and water managers in the San Joaquin Valley, California
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Decades of groundwater depletion in California is recognized as a threat to the reliability and quality of water available to farms, communities and the environment. The new California Sustainable Groundwater Management Act (SGMA) requires local Groundwater Sustainability Agencies (GSAs) to develop plans to manage groundwater supplies to ensure long-term sustainable yields. Replenishing depleted groundwater supplies will be essential to achieving this balance. The current default for groundwater recharge – dedicated recharge basins – is costly, and requires the purchase and retirement of many acres of productive land in order to capture the infrequent but large flood flows needed to achieve balance.On-farm recharge is an innovative solution to get water into the ground without taking agricultural land out of production. It can be implemented quickly using existing irrigation surface canals during heavy floodwater conditions without investing in costly new infrastructure. Accelerating the replenishment of groundwater supplies through on-farm recharge can also reduce the extent to which GSAs may need to restrict groundwater pumping. The success of this new practice will depend on acceptance of the strategy by individual farmers and GSA managers.This presentation will present the findings of interviews and surveys with farmers who have experimented with applying floodwater on working cropland in excess of their crop’s water demand. In response to four years of drought and concerns about declining groundwater, farmers on over 100 fields with highly permeable soils volunteered to accept flood flows during the 2015-2016 flood season to accelerate groundwater recharge. In the absence of rigorous scientific data about the tolerance of crops on sandy soils to periodic over application of water, farmers growing 10 different crops as well as fallow ground were asked about the management decisions they make regarding acceptable timing and duration of water for recharge. The acceptable quantity of water applied in excess of crop demand also provides a starting point for determining the potential of this practice to address basin wide groundwater depletion under different cropping systems.The acceptance of this strategy also depends on acceptance by GSAs who must weigh the financial and social costs and benefits of alternative groundwater management methods. The presentation will compare the costs of on-farm recharge with dedicated recharge basins in terms of construction and operation expenses as well as potential incentives that may be needed to achieve widespread use. Unlike traditional recharge basins, on-farm recharge places individual farmers at greater risk of crop damage while their voluntary actions benefit all groundwater users in the basin. Information and decision support tools about the feasibility of on farm recharge will enable GSAs to consider on-farm recharge as a cost-effective and immediate option to include as part of their Groundwater Sustainability Plans..This presentation addresses the social and economic dimensions of on-farm recharge and complements presentations by other collaborators that address hydrologic infiltration potential, the effect on nitrate management and groundwater quality, and crop health. All these issues must be more fully understood before this strategy is promoted at scale to achieve groundwater sustainability goals.