California's recent (and ongoing) record-breaking drought has been a reminder of how vulnerable we are to a changing climate and what may be becoming a 'new normal' of frequent droughts. As California strives to build and restore a reliable and resilient future for its water in accordance to the 2014-2018 Water Action Plan, it is of utmost importance that we optimize California's water system by integrating flexible water storage solutions that will help ensure a more reliable and resilient water supply for our future.

Storage projects need to be selected carefully to maximize the benefit of limited funding available for water infrastructure [1]. Last week, our paper titled "Benefits and Economic Costs of Managed Aquifer Recharge in California" was published in the open-source peer-reviewed journal San Francisco Estuary & Watershed Science [2]. For the first time ever, our study investigated the benefits and economic costs of groundwater recharge and storage - known as managed aquifer recharge (MAR). Our analysis found MAR projects in California to have a median cost of $410 per acre-foot (the amount of water that fits on an acre of land covered in 1 foot of water) and achieve a whole range of public co-benefits.

When compared to the cost of other water management strategies, MAR projects are on the same order of magnitude as conservation actions, but 5 times cheaper than surface water projects ($2,100 per acre-foot median cost). Despite the cost-effectiveness of MAR, only 6% of the total $23 billion awarded under all past water bonds released since 1970 went towards MAR projects. The demand for MAR projects hasn't been the issue as less than 50% of the 248 applications submitted for past state funding were awarded, indicating that the demand for MAR projects across the state far outstrips available funds [3].

In our study, we also found MAR projects to exhibit a wide degree of flexibility to integrate multiple water source types (surface water, urban stormwater, and treated wastewater) and achieve a range of co-benefits (Figure 2). In a follow-up survey we conducted with projects awarded state funds, MAR projects that diversified their water portfolio by integrating multiple water source types were more resilient and able to still perform during the most recent drought. The flexibility of incorporating co-benefits into MAR projects also enabled local water agencies to achieve public benefits such as ecosystem improvements, water quality improvements, flood control, emergency response, and recreation. Aside from conjunctive management, flood control was a common co-benefit for MAR projects as it allowed local agencies to convert a local risk into a resource.

Figure 2. Co-benefits reported for MAR projects in California

As local agencies work to achieve sustainability in their groundwater basins through the implementation of California's new groundwater legislation, the Sustainable Groundwater Management Act of 2014 (SGMA), MAR projects will become an increasingly important water management strategy to bring groundwater basins into balance. Unlike in the past, SGMA now gives agencies more confidence that MAR projects will be respected and protected from basin pumping since local agencies will be able to monitor and regulate nearby pumping activities. In addition, MAR projects can also be used to help prevent adverse impacts to environmental beneficial uses and users, such as groundwater dependent ecosystems. In our analysis, we found that some local agencies are already using MAR projects to restore, replenish and repurpose native habitat to improve water quality, achieve flood control, increase water quality, and enhance local recreation by building trails (Figure 3).

Figure 3. MAR strategies for enhancing natural habitat while achieving groundwater basin water quantity and quality benefits.

As California works towards building a resilient and reliable water supply for its future, water storage will remain one of the many solutions needed but is still not a silver bullet. Limitations in the amount of available surface water remaining (state water use allocations are more than 5x the amount of available water!) place an upper limit on how much water we can fill our reservoirs and groundwater basins. Integrating urban stormwater and treated wastewater can help alleviate water supply concerns, but conservation strategies need to complement these efforts.

For more info on the study read a summary in Stanford News.

References

1. Hanak, E., B. Gray, J. Lund, D. Mitchell, C. Chappelle, A. Fahlund, K. Jessoe, J. Medellín-Azuara, D. Misczynski, J. Nachbaur, R. Suddeth. 2014. Paying for Water in California. San Francisco: Public Policy Institute of California

2. Perrone, D. and M. M. Rohde. 2016. Benefits and Economic Costs of Managed Aquifer Recharge in California. San Francisco Estuary & Watershed Science 14(2).

3. Perrone, D. and M.M. Rohde. 2014. Storing water in California: What Can $2.7 Billion Buy Us? Stanford University: Water in the West. Available with this link.