The Role of Sea Level Rise and in Situ Carbonate Accumulation on the Morphodynamic Evolution of a Carbonate Tidal Channel. The Case of the Bahamas Islands.

Abstract:

We explore the problem of morphodynamic evolution of carbonate tidal channels, bounded seaward by the ocean and shoaling landward, as observed in coastal lagoons and estuaries. Governing model equations are the conservation of mass and momentum for the flow, and the conservation of sediment mass in the water column and in the bed deposit. We model carbonate accumulation in terms of a specified depth-dependent carbonate “production rate” based on modern rates of carbonate accumulation rate. We further assume that 1) there is no input of clastic sediments to the system, 2) cementation processes are slow when compared to carbonate accumulation, 3) there is an absence of particles in the silt/mud range, and 4) we treat the carbonate sediments as non-cohesive particles. Governing equations are integrated with finite volume for unsteady, two-dimensional, depth averaged shallow-water flow over arbitrary topography. This method is known to capture sharp fronts accurately. We use Roe’s approximate Riemann solver for the computation of fluxes at the interfaces between one finite volume and the other. For second order accuracy we implement MUSCL (Monotone Upstream Scheme for Conservation Laws) and a predictor-corrector time stepping scheme. We validate the model at field scale by comparing the numerical results with field data collected in the Bahamas channels. The comparison is presented in terms of flow velocities, bed profiles and grain size distributions of the bed surface. Finally, we use the validated model to explore how different rates of sea level rise will affect the morphodynamic evolution of the tidal channels under different “production rate” scenarios, e.g. constant, depth dependent.