Progress in coupling models of coastline and fluvial dynamics

The morphology and depositional history of wave-influenced deltas reflects the interplay between the fluvial and coastal domains. Here we present initial results of the coupling of stand-alone coastal and terrestrial models within the Community Surface Dynamics Modeling System (CSDMS) Component Modeling Tool (CMT), applied to study the evolution of wave-influenced deltas. The coastal domain is modeled using the Coastline Evolution Model (CEM), which simulates plan-view shoreline evolution due to wave-driven alongshore sediment transport, with fluvial influence incorporated by adding sediment along the coastline. The first application involves one-way coupling of the climate-driven hydrological transport model HydroTrend with CEM to investigate how fluctuations in sediment input rates due to climate change may affect the plan-view delta morphology and evolution. Simulations reveal that sediment discharge variability can have a significant effect on delta morphology if fluvial delivery of sediment temporarily exceeds the capacity for alongshore sediment transport to remove sediment from regions proximal to the river mouth. The second application involves two-way coupling of CEM with a river with multiple active distributary channels. In this case, changes to the coastline affect the apportionment of discharge flowing out of coeval distributaries through a two-way feedback. Model simulations where distributary length affects sediment discharge demonstrate how the dynamics of one distributary can control the sediment discharge of another. Wave-influenced deltas exhibiting strong channel feedbacks may prograde delta lobes faster than those without feedback. These preliminary model experiments demonstrate the capability of CMT to bidirectionally couple models that represent different process domains and were developed and designed independently (i.e. without the intentions of such coupling), offering the potential for further numerical studies of interactions taking place at the intersection of different process realms.