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Lateral variability of subtidal flow at the mid‐reaches of a macrotidal estuary
Author(s) -
Ross Lauren,
ValleLevinson Arnoldo,
Sottolichio Aldo,
Huybrechts Nicolas
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012504
Subject(s) - advection , estuary , geology , oceanography , outflow , current (fluid) , flow (mathematics) , spring (device) , hydrology (agriculture) , geotechnical engineering , mechanics , mechanical engineering , physics , engineering , thermodynamics
Abstract Transverse variations of tidal and subtidal flow were investigated in a macrotidal and convergent estuary. This was accomplished by combining data analysis of current velocities and water density with numerical modeling at the mid‐reaches of the Gironde Estuary (France). Nonlinear mechanisms responsible for overtide generation and hence subtidal flows were found to vary across the estuary and from neap to spring tides. Subtidal flows were driven by a combination of internal asymmetry, tidal advective accelerations, nonlinear effects of water level variations, quadratic friction, and river discharge. The quarter‐diurnal overtide band (D4) in the flow was generated by internal asymmetry and tidal advective accelerations during neap tide. The ratio of quarter‐diurnal to squared semidiurnal bands (D4/D2 2 ) was largest (>0.3) in sections of the channel showing subtidal outflow. River discharge increased from neap to spring tides causing a subsequent increase of seaward subtidal currents. During spring tide, D4 was generated by tidal advective accelerations and quadratic friction combined with river discharge, rather than by internal asymmetry. The sixth‐diurnal overtide (D6) in the flow was comparable to D4 for both neap and spring tides. Largest D6/D2 3 ratios were found in the shallowest cross‐channel locations during both neap and spring tides.