Circulation Within The Curved Channel Of The North Passage In The Changjiang River Estuary Using A Vorticity Approach: Data Analysis And Mathematical Modeling

To further understand the physics of circulation within the Curved Channel of the North Passage in the Changjiang River estuary,based on a vorticity approach,both in situ observational data analysis and mathematical modeling have been used.Firstly,vessel mounted 300 kHz ADCP measurements were made of tidal currents along the cross sections AD3,AD5 and AD6 within the Curved Channel of the North Passage in the Changjiang River estuary,on 23 to 24 February?neap tide/dry season?and 28 February to 1 March 2014?spring tide/dry season?,respectively.Secondly,lateral secondary flows,which have?two-layer‘structures separated by irregular interfaces,are present along the three cross sections AD3,AD5 and AD6:?a?they display flood/ebb and neap/spring tidal variability;?b?the structures of lateral secondary flows do not vary significantly,while their magnitudes,directions and distributions are similar from the first flood/ebb tidal cycle to the second one;?c?overall distributions of velocities appear to be intermittent;?d?the discontinuous interfaces and structures vary spatially;?e?lateral secondary flows can intermittently occur at the low slack water,early flood,maximum flood,high slack water,early ebb,and maximum ebb.Thirdly,calculated semi-Lagrangian residual flows show:?i?along the three cross sections AD3,AD5and AD6,longitudinal circulating semi-Lagrangian residual flows at the surface layer are seaward and at the bottom layer landward during the neap tide;but longitudinal semi-Lagrangian residual flows at both the surface and bottom layers are seaward during the spring tide.?ii?along the cross section AD3,lateral circulating semi-Lagrangian residual flows at the surface layer are toward the Northern Dikes and at the bottom layer toward the Southern Dikes during the neap tide,while at the surface layer toward the Northern or Southern Dikes and at the bottom layer toward the Southern or Northern Dikes during the spring tide.?iii?along the cross sections AD5 and AD6,lateral circulating semi-Lagrangian residual flows at the surface layer are toward the Northern Dikes and at the bottom layer toward the Southern Dikes during both the neap and spring tides.?iv?the magnitudes of longitudinal semi-Lagrangian residual flows range from-0.2 to 0.7ms^-1 and those of lateral semi-Lagrangian residual flows from-0.15 to 0.2 ms^-1.?v?apparent lateral variability of longitudinal semi-Lagrangian residual flows is present.Furthermore,analyses of the major factors affecting the circulation within the Curved Channel show:?1?longitudinal baroclinic pressure gradient,the internal friction induced mixing and the bottom friction induced mixing seem to be the primary factors affecting longitudinal flows while the lateral redistribution of along-channel momentum the secondary one,the centrifugal force and the Coriolis force can be neglected.?2?lateral baroclinic pressure gradient and the internal friction induced mixing are the primary factors affecting lateral secondary flows while the centrifugal force,the Coriolis force,and the bottom friction induced mixing the secondary ones.?3?estuarine circulation??[]??is 6.85×10^-2 s^-1 and 7.10×10^-2 s^-1 along the cross section AD5 within the curved channel of the North Passage on a neap/spring tide in the dry season,respectively,while tidally averaged?the lateral redistribution of along-channel momentum?????is-2.89×10^-6 s^-2 and-5.38×10^-6 s^-2,respectively,thus lateral circulation can weaken estuarine circulation via the lateral redistribution of along-channel momentum.Finally,modeled results from the three-dimensional model TELEMAC show:?i?the primary factors affecting modeled lateral and longitudinal circulations are the same with those of measured data at1000 m,1500 m,2000 m and 2500 m,respectively,from the starting point P5 along the cross section AD5;?ii?estuarine circulation??[]??within the Curved Channel of the North Passage is always positive,while tidally averaged?the lateral redistribution of along-channel momentum?????is always negative along the cross sections AD3,AD5 and AD6 on a neap/spring tide in the dry season,thus lateral circulation may weaken estuarine circulation via the lateral redistribution of along-channel momentum and this effect seems to be stronger on a spring tide than on a neap tide.