Influence of Back‐Barrier Basin Geometry on Multiple Tidal Inlet Systems: The Roles of Resonance and Bottom Friction

Observations of barrier coasts around the world suggest that some systems do not conform to the O'Brien‐Jarret law. Here we explain this by investigating how resonance and bottom friction affect the response of tidal inlets to variations in basin geometry. Therefore, we develop a morphodynamic barrier coast model that is based on the stability concept of Escoffier for the morphological evolution of the inlets, coupled with an idealized hydrodynamic model that describes the water motion in the outer sea, inlets and arbitrarily shaped backbarrier basin. We find that the total tidal prism through all inlets is predominantly determined by the (cross‐shore) width of the basin and {identify three regimes for this}. First, a linear regime for narrow basins (i.e. basin width ≪ tidal wavelength) where a larger basin leads to a linear increase in total tidal prism. Second, a resonant regime for basins with a width around the resonant condition in which the total tidal prism reaches a peak. This resonance condition is a quarter tidal wavelength for basins without friction, which shifts to narrower basins as friction becomes stronger, down to 0.15 tidal wavelength. Third, a dissipative regime for {wide} basins (i.e. the cross‐shore basin dimension or basin width ≪ resonant condition) with sufficiently strong bottom friction in which the total tidal prism does not change for wider basins, because the tidal wave completely dissipates in the basin.