Abstract
AbstractThe existence of morphodynamic equilibria of double‐inlet systems is investigated using a cross‐sectionally averaged morphodynamic model. The number of possible equilibria and their stability strongly depend on the forcing conditions and geometry considered. This is illustrated by considering a rectangular double‐inlet system forced by M2 tidal constituents only. Depending on the M2 amplitudes and phases at both entrances, no equilibrium, one equilibrium or multiple morphodynamic equilibria may exist. In case no equilibrium is found, the minimum water depth becomes zero somewhere in the system, reducing the double‐inlet system to two single‐inlet systems. In the other cases, the location of the minimum water depth and the direction of the tidally‐averaged sediment transport, as well as their actual values, depend strongly on the M2 tidal characteristics. Such parameter sensitivity is also observed when including the residual and M4 forcing contributions to the water motion, and when allowing for width variations. This suggests that, when considering a specific system, the number and stability of morphodynamic equilibria, as well as the characteristics of these quantities, can only be assessed by investigating that specific system in detail. As an example, the Marsdiep‐Vlie inlet system in the Dutch Wadden Sea is considered. It is found that, by using parameter values and a geometry characteristic for this system, the water motion and bathymetry in morphodynamic equilibrium are qualitatively reproduced. Also the direction and order of magnitude of the tidally‐averaged suspended sediment transport compare well with those obtained from a high‐complexity numerical model.
Highlights
A large part of the world's coastline can be characterized as barrier coasts (Mulhern et al, 2017), consisting of barrier islands, back-barrier basins and tidal inlets connecting the back-barrier basins to the open sea, with shape and size varying significantly from location to location (Glaeser, 1978; Stutz & Pilkey, 2011)
In the numerical experiments presented the influence of the forcing conditions and geometry on morphodynamic equilibria is presented
With the water motion forced by one tidal constituent, the full bifurcation diagram indicates that for most parameter values, either one unique stable equilibrium or no morphodynamic equilibrium may exist in a system with the two inlets connected together
Summary
A large part of the world's coastline can be characterized as barrier coasts (Mulhern et al, 2017), consisting of barrier islands, back-barrier basins and tidal inlets connecting the back-barrier basins to the open sea (de Swart & Zimmerman, 2009), with shape and size varying significantly from location to location (Glaeser, 1978; Stutz & Pilkey, 2011). Barrier coasts are highly dynamic, in part due to the complex nonlinear interactions among water motion, sediment transport and morphological evolution, as well as to their sensitivity to changes in external conditions caused, for example, by increased storm frequency and intensity, sea level rise and human interference (McBride et al, 1995; van der Spek, 1997). They are very important from an ecological and economical point of view. They are of importance for coastal safety (Glaeser, 1978)
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