Dear Supriti,

There are many literature on this issue. I may provide you some.

Tidal environments are characterized by complex networks of tidal channels and bars. Tidal-current action is, usually, much stronger than river flow at this location, and produces a series of mutually evasive tidal channels, separated by straight, elongate tidal bars. There are dominant and subordinate currents in a tidal channel at the same time. When there is tidal flood intruding into the channel, the river flow is still flowing to the sea. Other than the river flow, a large amount of tidal flow is passing upward and during ebb tide it is coming back. When next tides come, the additional flow may not exit from the system. So, tidal channel morphology splits the channel into two separate paths, where one is for flood tide and other is for ebb tide.  The dominant current is responsible for the obliquely down-current migration of the point bars. While, the subordinate current is stronger on the point-bar surface than it is on the cut-bank side of the channel.

For better understanding you may go through the paper of Robert W. Dalrymple, and Kyungsik Choi, 2007. Morphologic and facies trends through the fluvial–marine transition in tide-dominated depositional systems: A schematic framework for

environmental and sequence-stratigraphic interpretation.

Earth-Science Reviews 81 (2007) 135–174

Cheers

Jakia

Thanks Jakia for sharing this resource. Pardon me, perhaps I couldn't explain what I want to know exactly. I want to know about why the neighboring channel has  flood tidedominated side on opposite side.Suppose, in a tide-dominated delta, every channel has flood tide dominated side and ebb tide dominated side. Should this flood dominated side on same side of every channel? If not, why?Is it geomorphologic characteristics of the respective channel or something else?

Dear Supriti, Yes. It is a geomorphologic characteristics of the tide dominated channel. I am working on Bangladesh delta and of course Meghna estuary which is a tide dominated delta. Along with this I have observed that all of the estuaries to the Bay of Bengal have both channels. If you ever go to a tide dominated channel, you will also see flood tide and ebb tides are passing simultaneously in opposite direction. 

If you go through the said paper, you will get all of your answers deeply. BTW, do you have the paper?

Yes this is determined by the channel shape in easy terms, the tide will flow on the outer side of a bend with the slower tide on the inner side, so two channels could easily be different

Dear Supriti, the wider the channel the more effect you will see because of the Coriolis force, which will act more strongly  for diurnal and longer tidal components. . Gibraltar is an example the out going tide (going west) is pushed to the north Spanish coast, and vice versa for the inflow towards the N. African coast.  Also if you have tributary rivers entering up channel on the outgoing side their additional surface volume added to the outflow and make the sea level slightly higher and the tidal range greater, and vice versa, except effects due to shoreline complications inside and outside of the channel. 

Dear Supriti,

When entering shallow coastal areas and tidal channels, the tide interacts in a non-linear way with the topography, river outflows, density gradients. This makes it difficult to pint-point a single simple reason for differences in the ebb/flood dominance and make generalizations.

I can think of a couple of reasons for differences in ebb/flood dominance within one channel. In shallow areas, the ebb/flood asymmetry can be due to the sum of the main tidal constituent (M2, for example) and its higher harmonic (M4) which is generated by nonlinear interactions with itself (due to the topography, for example). The ebb or flood dominance depends on the relative phase lag of the two constituents, and this phase lag will highly depend on the bathymetry (i.e. the shape of the tidal channel).

Second, Zimmeman (Topographic generation of residual circulation by oscillatory (tidal) currents, 1978) showed that the Coriolis force and frictional torques acting on an oscillatory current over and irregular bottom topography produce a small scale vorticity field that is transferred to the mean field. In other words, the interaction of the tide with the bathymetry generates a residual circulation. In many tidal channels, this residual circulation has the shape of a tidal eddy having velocities in the direction of the flood on one side of the channel and in the direction of the ebb on the other side of the channel. This generates, a difference between both sides of the channel.

I hope this helps.

Hello Supriti,

since hydrodynamics are the active force and the sea bottom the responding one, Thomas is quite right to give the Coriolis force credit for the existence of flood and ebb channels by provoking a shift in the direction of currents thus leading to a diversion between flood and ebb channels. But it does not fully explain the phenonema, since e. g. in tidal inlets there are sometimes flood channels on both sides of the ebb channel which is only explainable due to interactions of currents and and bottom topography. This has been excellently described by van Veen in 1950; his contribution was transferred into English by Ad van der Spek, Marcel Stive and Tjerk Zitaman and published 2005 in the Journal of Coastal Research. You will find the full text on the RG-page of Tjerk Zitman.

Hi Supriti!

I agree with Hanz and Thomas that the Coriolis force is responsible for the frequently observed ebb- or flood-dominance on opposite sides of a tidal channel. As pointed out by Hanz this does not, however, apply to the existence of separate flood channels on opposite sides of ebb-tidal deltas. These form as a result of the fact that the ebb current in an inlet is still quite strong when the water level begins to rise with the oncoming flood tide. As a consequence, the flood tide pushes past on both sides of the ebb flow, thereby excavating flood channels. Generally, the flood channel on the side from where the tidal wave approaches is larger and better developed than the one on the opposite side. This phenomenon explains why one observes the water level near an inlet within tidal basins to be rising, even though the water is still flowing in the ebb direction. As a consequence, the turn of the tide (rising water level) does not coincide with the turn of the current.

Regards, Burg Flemming

The importance of the Coriolis force on the asymmetry of the flow in a tidal channel scales with the width of the channel relative to the Rossby radius of deformation.  I think that the across-channel variation in the magnitude of the bottom stress/depth is likely to be the dominant mechanism in most tidal channel (most are narrow relative to the barotropic Rossby scale).  The fundamental of the dynamics are discussed in a paper by Li and O'Donnell (1997), see http://onlinelibrary.wiley.com/doi/10.1029/97JC02330/abstract.

When the effects of density variations are included the dynamics are more complex.  The bottom line is that in most estuarine channels there is no simple answer.  The details of the bathymetry, channel curvature  and bottom type, the river discharge, the length of the river,  and the distance form the ocean all influence the pattern of the mean flow and the pattern of current fluctuations.

Thanks to all of you.  

Dear All, if possible please show some mathematical calculation for defining a flood channel and Ebb channel. Calculation should be carried out based on tidal constituents, cross section properties, suspended sediment concentration, hydrodynamics etc. You all copy and paste some hypothesis from the previous research. I think we need some mathematical justification to distinguish the flood channel and Ebb channel. Otherwise, scientific community will not believe us.

Kind Regards

Saiful

Dear Prusiti

The issue of flood- or ebb-dominance is closely linked to the morphology and morphodynamics of tidal channels. A good kick-off for understanding this problem is the attached paper by Lanzoni & Seminara (2002; and citations therein), and the chapter by Friedrichs (2010, especially section 3.9 on tidal asymmetry), both also providing the mathematical basis that you request.

Best regards,

Burg Flemming