Evaluating Freshwater Inflow Regulations in the San Francisco Bay Estuary

Fresh water flowing into California’s San Francisco Bay Estuary is highly contested and tightly managed. The current regulations for spring inflows were established in 1995, following a severe multi-year drought, lawsuits, fish population declines and several Endangered Species Act listings. These new standards were designed to provide inflows that reflected variation in hydrological conditions, prevent extreme low inflows, and protect low salinity habitat. However, since then, both fish populations and spring inflows have continued to decline. I investigated the implementation and effects of the standards. I found that, although the standards had been met in most years, they were violated or waived in many dry years. Comparison of pre-standard (1970-1994) and post-standard years (1995-2015) showed that implementation of the standards had little effect on seasonal flow amounts, although the frequency of extreme low inflows was reduced. Low salinity habitat quality and quantity showed slight improvement in some dry years, but not in the driest years when the standards were waived. Overall, this analysis suggests that the 1995 flow standards provided little if any improvement in inflow or ecological conditions in the estuary, information that should be informative for the State Water Board’s review of the standards that is currently underway.