MODELING BACKBARRIER AND SEA LEVEL CONTROLS ON TIDAL PRISM DYNAMICS IN TRANSGRESSIVE SYSTEMS

Along barrier island chains, tidal exchange between the backbarrier and the coastal ocean supports unique saltwater and brackish ecosystems and is responsible for exporting sediment and nutrients. The volume of the reversing tidal flow (tidal prism), basement controls, and the wave and tidal regime of the coast dictate the size and number of tidal inlets and the volume of sand sequestered in ebb-tidal deltas. The inlet tidal prism is a function of bay area, tidal range, and secondary controls, including flow inertia, basinal hypsometry, and frictional factors. Global sea- level rise (SLR) is threatening coastal environments by causing mainland flooding, changes in sediment supply, and conversion of wetlands and tidal flats to open water. These factors are impacting basinal hypsometry, resulting in enlarging tidal prisms, increased dimensions of tidal inlets and ebb-tidal deltas, and erosion along adjacent barrier shorelines. Although the effects of SLR on coastal morphology are difficult to study by field observations alone, physics-based numerical models provide a sophisticated representation of coastal processes over decadal time-scales, offering opportunities to link process causation to long term development. Modeling provides a numerical laboratory to test hypothesis related to SRL. Here, we use a numerical model that includes the relevant features in the barrier/tidal basin system, linking marsh degradation, inlet and ebb-delta growth to barrier erosion through long-term hydrodynamics and morphology simulation. Sediment exchange and process interactions are investigated using an idealized domain resembling backbarrier basin in the East Coast of the US, so that the sensitivity to varying SLR rates, marsh loss, sediment supply, and wave climate can be more easily analyzed. Results explore the processes over geologic time scales, demonstrating the vulnerability of backbarrier systems to projected SLR and marsh loss, demonstrating early to middle stages of barrier disintegration and initiation of transgressive systems worldwide.