Project Overview and ObjectivesOur research aims to assess the feasibility, risks and costs associated with opportunistic agricultural groundwater banking - the intentional diversion of flood flows in the winter (November-March) onto fallow or dormant agricultural fields for infiltration and groundwater replenishment. To assess the feasibility we are conducting field experiments in conjunction with surface water - groundwater modeling, GIS analyses, and agronomic calculations that will lead to the development of feasibility indices and decision support tools to:
- determine suitable locations within the Central Valley that can be used to intentionally replenish groundwater from diverting flood flows in the winter onto those sites,
- quantify the availability of flood flows from rivers and reservoir releases during the winter month (Nov.-Apr.),
- quantify the capacity of water conveyance systems to deliver flood flows to recharge sites,
- provide recommendations on farming practices that support winter recharge activities,
- assess the impact of intentional groundwater recharge on water quality (nitrate, salt and pesticide movement),
- quantify the risk and costs of winter water application on crop production for selected crops (e.g., alfalfa and irrigated pasture),
- quantify the economic benefits and costs of agricultural groundwater banking.
A methodological goal is to develop a web-based knowledge database designed for a wide range of users including growers, consultants, agronomists, farm advisors, government agency staff, scientists and educators. The web-based knowledge database will serve as an information and decision support system to i) synthesize the research findings from this project as interactive maps and risk/cost calculators; ii) explain the developed suitability indices and their use, and iii) serve as a platform for the future development and discussion of agricultural and water resources issues related to groundwater recharge and banking. The three specific objectives of our research are:
Objective 1 – Physical feasibility:
Agricultural areas are seen as the most probable locations for groundwater banking because of the available acreage, wide distribution, proximity to water supply systems, availability of high infiltration capacity soils, and connection to aquifer systems. However, there exists uncertainty regarding the physical constraints of this concept, in particular, the agricultural groundwater banking opportunities in relation to the cropping season, water sources for recharge, practical feasibility of storm/flood water conveyance onto fields, recoverability of banked water, and water quality risks. To address these issues we will combine field research, GIS analyses and surface and groundwater modeling to develop a decision support tool for stakeholders to assess their site-specific groundwater recharge potential based on the site’s soils, climatic, water supply and water-infrastructure properties.
Objective 2 – Crop feasibility:
Maintaining or improving crop yields is essential for the successful adoption of agricultural groundwater banking among stakeholders. Much research has been done to optimize crop irrigation in relation to yield, however, crop-specific data on the flooding tolerance in relation to soil hydraulic properties, farming practices and hydro-climatic conditions is sparse. Stakeholders will remain hesitant to adopt agricultural groundwater banking concepts as long as the risks and costs for crop production remain unknown. We will estimate the risks and costs using alfalfa and irrigated pasture as test crops. We will establish a knowledge database on the crop physiological performance for different flooding durations, crop stages (growing stage, age of stand), soils (soil type, hydraulic conductivity, infiltration rate, soil compaction), climatic (air and water temperature) and biogeochemical conditions. Based on this knowledge we will develop crop-specific and soil-landscape specific management guidelines and flooding suitability indices to assist stakeholders in mitigating the risk of yield loss due to agricultural groundwater banking.
Objective 3 – Farm-economic feasibility:
In times of great uncertainty of agricultural water availability due to increasing demand and climate change, policy makers must consider alternative ways to expand the benefits of available water resources. Groundwater banking comprises a storage that is envisioned to improve water supply reliability in California. However, successful implementation of groundwater banking on agricultural fields depends on the farm-economic and legal feasibility of diverting surface water outside the growing season onto fields using existing irrigation infrastructure. We will develop a decision support tool that allows estimation of on-farm costs of agricultural groundwater banking (e.g. costs associated with yield loss/gain, energy, labor, water permits, and management practices). This tool will be used to promote the benefits of agricultural groundwater banking among stakeholders, to estimate the need for economic incentive tools to acknowledge the service to the community, and to develop guidelines for growers to integrate agricultural groundwater banking activities with local water/irrigation districts and district customers.