Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

Abstract

This paper, part of the collection of research comprising the State of Bay-Delta Science 2016, describes advances during the past decade in understanding flow dynamics and how water-quality constituents move within California's SacramentoSan Joaquin River Delta (Delta). Water-quality constituents include salinity, heat, oxygen, nutrients, contaminants, organic particles, and inorganic particles. These constituents are affected by water diversions and other human manipulations of flow, and they greatly affect the quantity and quality of benthic, pelagic, and intertidal habitat in the Delta. The Pacific Ocean, the Central Valley watershed, human intervention, the atmosphere, and internal biogeochemical processes are all drivers of flow and transport in the Delta. These drivers provide a conceptual framework for presenting recent findings.The tremendous expansion of acoustic and optical instruments deployed in the Delta over the past decade has greatly improved our understanding of how tidal variability affects flow and transport. Sediment is increasingly viewed as a diminishing resource needed to sustain pelagic habitat and tidal marsh, especially as sea level rises. Connections among the watershed, Delta, and San Francisco Bay that have been quantified recently highlight that a landscape view of this system is needed, rather than consideration of each region in isolation. We discuss interactions of multiple drivers and information gaps.

Ecosystem variability along the estuarine salinity gradient: Examples from long‐term study of San Francisco Bay

“…As a result, patterns of water properties and biota along the estuarine axis from freshwater to sea seldom represent the simple passive mixing of two water sources. Here, we examine the nature of and reasons for patterns along the salinity gradient of San Francisco Bay, “…a classic example of a coastal plain estuary in which terrestrial freshwater mixes with salt water entering the estuary from the ocean” (Schoellhamer et al ).…”

“…. .a classic example of a coastal plain estuary in which terrestrial freshwater mixes with salt water entering the estuary from the ocean" (Schoellhamer et al 2016).…”

The Future of Sediment Transport and Streamflow Under a Changing Climate and the Implications for Long‐Term Resilience of the San Francisco Bay‐Delta

“…A study by Sankey et al (2017) suggests that an increase in wildfires and burned area in the watersheds and above reservoirs will mobilize more sediment in the watershed and cause more dam sedimentation problems. Sensitivity analyses have shown that increases in storm frequency and magnitude will lead to increases in streamflow, suspended sediment concentration, and sediment discharge (Stern et al, 2016), which logically extends to a hypothesis that sediment supply could increase if (1) more precipitation falls as rain rather than snow, causing greater runoff in winter and less in spring, (2) storm intensity and frequency increases, (3) there are no changes in reservoir trapping efficiency, and (4) no more post‐hydraulic mining geomorphic adjustments occur (Schoellhamer et al, 2016). Annual variability of precipitation is higher in California than the rest of the United States, and the wettest 5% of wet days contribute about a third of the annual precipitation and two‐thirds of the variance (Dettinger, 2016).…”

Patterns, pace, and processes of water‐quality variability in a long‐studied estuary

“…Therefore, Outflow plays an important role in the annual variability of SPM in the estuary, and the long-term trend of decrease results from the 50% reduction of sediment supply from the Sacramento River since the 1950s. That loss was a result of sediment retention behind dams and gradual removal by storms of the sediments deposited in the river system during the 19 th century (Schoellhamer et al 2016).…”