MODELING SHORE-NORMAL LARGE-SCALE COASTAL EVOLUTION

We present a model for the evolution of the shelf surface in response to marine sedimentary processes. Following morphodynamical theory, the model presupposes a characteristic configuration of the shelf surface, that in profile is a concave-up exponential curve, whose steeper inner limb is the shoreface. The profile is seen as an equilibrium response to the variables of sedimentation. The profile translates landward or seaward as sea level rises or falls, but will do so in an state of dynamic equilibrium with the shape of the profile varying according to changes in: (1) the rate of sea level change, (2) the time-averaged wave and bottom current conditions, (3) the average allochthonous sediment supply rate, and (4) the sediment grain size distribution. The governing equations for the model include an equation for time-averaged cross-shore (diabathic) sediment flux and the sediment continuity equation. Simulations of continental margin profiles show that profile adjustments affect mainly the coefficient of curvature of the profile. An increase in the rate of sea level rise straightens the profile; it decreases the slope of the shoreface, but increases the shelf slope. An increase in sediment input increases profile curvature; the shoreface steepens while the shelf floor flattens. An intensification of hydraulic climate straightens the profile in a manner similar to an increase in the sea level rise rate, while an increase in grain size increases profile curvature as does an increase in sediment input.