Effects of Drought and the Emergency Drought Barrier on the Ecosystem of the California Delta

Abstract

In 2015, the fourth year of the recent drought, the California Department of Water Resources installed a rock barrier across False River west of Franks Tract to limit salt intrusion into the Delta at minimal cost in freshwater. This Barrier blocked flow in False River, greatly reducing landward salt transport by decreasing tidal dispersion in Franks Tract. We investigated some ecological consequences of the Barrier, examining its effects on water circulation and exchange, on distributions of submerged aquatic vegetation (SAV) and bivalves, and on phytoplankton and zooplankton. The Barrier allowed SAV to spread to areas of Franks Tract that previously had been clear. The distributions of bivalves (Potamocorbula and Corbicula) responded to the changes in salinity at timescales of months for newly settled individuals, to 1 or more years for adults, but the Barrier's effect was confounded with that of the drought. Nutrients, phytoplankton biomass, and a Microcystis abundance index showed little response to the Barrier. Transport of copepods-determined using output from a particle-tracking model-indicated some intermediate-scale reduction with the Barrier in place, but monitoring data did not show a largerscale response in abundance. These studies were conducted separately and synthesized after the fact, and relied on reference conditions that were not always suitable for identifying the Barrier's effects. If barriers are considered in the future, a modest program of investigation should be undertaken that includes adequate replication and ensures that suitable reference conditions are available to allow barrier effects to be distinguished unambiguously from other sources of variability.

The Use of Stable Isotope-Based Water Age to Evaluate a Hydrodynamic Model

“…Water year 2014 was classified as critically dry in the Sacramento Valley [33]. For this reason, salinity conditions were fairly static during the simulation period with a slow increasing trend ( Figure 5).…”

How to Respond? An Introduction to Current Bay–Delta Natural Resources Management Options

“…As previously noted, the historic drought of 2012-2106 resulted in major challenges in preventing salinity intrusion into the Delta (Kimmerer et al 2019). Extended low flow conditions led to salinity intrusion into the Delta, putting the state's water supply at risk.…”

“…Water managers took the remarkable step of installing a temporary rock barrier during 2015 in False River, one of the key corridors through which salinity enters the central Delta ("Drought Barrier"; Figure 1). Kimmerer et al (2019) concluded that the barrier successfully prevented landward intrusion of salt by reducing tidal dispersion in Franks Tract, a flooded island that affect Delta water quality and hydrodynamics.…”

Drought and the Sacramento–San Joaquin Delta, 2012–2016: Environmental Review and Lessons

“…The extreme 2012-2016 drought again brought attention to salinity barriers, although the required studies, permitting, and vetting were not in place until 2015 (AECOM 2015). However, several thoughtful studies were implemented to examine barrier effects on changes in the salinity field, water quality, food web dynamics, and invasive clam distribution (2015 presentation by E. Ateljevich, unreferenced, see "Notes";CDWR 2017;Kimmerer et al 2019). These studies provide reasonably good evidence for the effectiveness of the drought barrier, and provide a model of rapid implementation of hypothesis-driven drought science.…”

“…Salinity Barriers. The temporary salinity barrier at False River was effectively implemented with supporting analysis and hypothesis-based monitoring, and was perhaps the best example of pairing management action and scientific study during the 2012-2016 drought (CDWR 2017;Kimmerer et al 2019). The barrier helped stabilize water quality in the southern Delta and was combined with scientific inquiries.…”