Dispersion mechanisms of a tidal river junction in the Sacramento–San Joaquin Delta, California

Journal Article · Wed Dec 17 00:00:00 EST 2014 · San Francisco Estuary and Watershed Science

DOI:https://doi.org/10.15447/sfews.2014v12iss4art1· OSTI ID:1233277

Gleichauf, Karla T. ^[1]; Wolfram, Philip J. ^[2]; Monsen, Nancy E. ^[1]; Fringer, Oliver B. ^[1]; Monismith, Stephen G. ^[1]

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1. Stanford Univ., Stanford, CA (United States)
2. Stanford Univ., Stanford, CA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

In branching channel networks, such as in the Sacramento–San Joaquin River Delta, junction flow dynamics contribute to dispersion of ecologically important entities such as fish, pollutants, nutrients, salt, sediment, and phytoplankton. Flow transport through a junction largely arises from velocity phasing in the form of divergent flow between junction channels for a portion of the tidal cycle. Field observations in the Georgiana Slough junction, which is composed of the North and South Mokelumne rivers, Georgiana Slough, and the Mokelumne River, show that flow phasing differences between these rivers arise from operational, riverine, and tidal forcing. A combination of Acoustic Doppler Current Profile (ADCP) boat transecting and moored ADCPs over a spring–neap tidal cycle (May to June 2012) monitored the variability of spatial and temporal velocity, respectively. Two complementary drifter studies enabled assessment of local transport through the junction to identify small-scale intrajunction dynamics. We supplemented field results with numerical simulations using the SUNTANS model to demonstrate the importance of phasing offsets for junction transport and dispersion. Different phasing of inflows to the junction resulted in scalar patchiness that is characteristic of MacVean and Stacey’s (2011) advective tidal trapping. Furthermore, we observed small-scale junction flow features including a recirculation zone and shear layer, which play an important role in intra-junction mixing over time scales shorter than the tidal cycle (i.e., super-tidal time scales). Thus, the study period spanned open- and closed-gate operations at the Delta Cross Channel. Synthesis of field observations and modeling efforts suggest that management operations related to the Delta Cross Channel can strongly affect transport in the Delta by modifying the relative contributions of tidal and riverine flows, thereby changing the junction flow phasing.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• Contributing Organization: Stanford University; Los Alamos National Laboratory
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1233277
• Report Number(s): LA-UR-14-29557
• Journal Information: San Francisco Estuary and Watershed Science, Vol. 12, Issue 4; ISSN 1546-2366
• Publisher: John Muir Institute of the Environment
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
junction dispersion
flow phasing
tidal trapping
super-tidal time scales
Delta Cross Channel