Providing a reliable water supply for California and restoring the Sacramento-San Joaquin Delta ecosystem: Can we achieve the co-equal goals?

Background/Question/Methods: Societies throughout the world are wrestling with the dual challenge of meeting water supply needs and protecting biodiversity. The California Delta ecosystem (Delta) is one prominent example where difficulties in balancing water supply needs and sustaining biodiversity exist. The Delta is the heart of the largest water supply system in the world. The Delta provides water for ~25 million California residents, irrigates about one million hectares of farmland, and is home to ~ 60 threatened or endangered species. Critical issues and drivers of change in the Delta include climate variability, water quality, land subsidence, sea-level rise, seismicity, invasive species, human population growth, and climate change. New California legislation addressing these challenges mandates “coequal goals” for the Delta. "Coequal goals” is defined as “providing a more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem.” Key scientific issues are 1) adaptive management, 2) ecosystem restoration, 3) water quality, 4) flow criteria, and 5) climate variability and change.

Results/Conclusions: Adaptive management for the Delta is mandated in the legislation. The legislation defines adaptive management as “a framework and flexible decision-making process for ongoing knowledge acquisition, monitoring, and evaluation leading to continuous improvements in management planning and implementation of a project to achieve specified objectives.” Successfully protecting, restoring, and enhancing the Delta ecosystem involves restoring aquatic habitats that have been largely lost from the landscape. These include seasonally flooded off-channel habitats, riparian zones, freshwater tidal marshes, and brackish water tidal marshes. Major water quality issues in the Delta include salinity, nutrients, pesticides, mercury, and selenium. Flow criteria include setting river inflows, Delta outflows into San Francisco Bay, and exports from the Delta for cities and farms. Resolving the conundrum between optimizing flow conditions for a healthy Delta ecosystem and providing a reliable water supply involves the amount of flows, the timing of flows, the duration of high and low flow conditions, the frequency of various types of flows, and rates of change when flows are increasing or decreasing. California has the most variable precipitation regime in the US, and climate change is manifested in sea-level rise, earlier snowmelt, and more rain and less snow. Effectively addressing competing goals to achieve the coequal goals in the Delta must rely on the ability of scientists, policy makers, planners and decision makers to put current and emerging scientific knowledge to work in protecting, restoring, and enhancing this remarkable California landscape.