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

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 andmore » 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.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1]
  1. Stanford Univ., Stanford, CA (United States)
  2. Stanford Univ., Stanford, CA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
OSTI Identifier:
1233277
Report Number(s):
LA-UR--14-29557
Journal ID: ISSN 1546-2366
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
San Francisco Estuary and Watershed Science
Additional Journal Information:
Journal Volume: 12; Journal Issue: 4; Journal ID: ISSN 1546-2366
Publisher:
John Muir Institute of the Environment
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Contributing Orgs:
Stanford University; Los Alamos National Laboratory
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES junction dispersion; flow phasing; tidal trapping; super-tidal time scales; Delta Cross Channel