Formation of coastal deltas under varying morphodynamic conditions

Abstract:

Delta morphology has been primarily classified qualitatively through visual analysis of coastal landforms, leading to the development of qualitative ternary diagrams indicating the degree of fluvial-, tidal-, and wave-influence on delta morphology. Recently, global datasets have quantified the degree fluvial-, tidal-, and wave-influences for 51 of the world’s largest and most populated deltas. Here, we develop and validate numerical morphodynamic models that simulate the formation of coastal deltas for the full range of fluvial and marine influences in global datasets, filling the parameter space more completely. Model input parameters such as delta plain area, bathymetric slope, incoming sediment size and concentration are used to define the modeling domain and initial model conditions. Fluvial discharge, tidal amplitude, and wave height are varied according to the published parameter ranges. Models for each type of delta (fluvial-, tidal-, and wave-dominated) are validated by comparing model output parameters, including the length of the main river stem, number of distributary channels, water depth reached by sub-aqueous clinoform, and total width of distributary channels along the shoreline, to observations in global datasets. Our models permit examination of how fluvial, tidal, and wave forces shape delta topography at higher resolution than global datasets, and examination of the extreme cases where only one type of fluvial or marine influence dominates. Understanding the how parameters vary according to delta type can be used to determine how projected shifts in morphological forcings may impact highly populated and environmentally productive deltaic landscapes.