Paper No. 10
Presentation Time: 10:15 AM


SIMMS, Alexander, Department of Earth Science, University of California, Santa Barbara, 1006 Webb Hall, Santa Barbara, CA 93106 and RODRIGUEZ, Antonio B., Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell Street, Morehead City, NC 28557,

Understanding the factors influencing coastline retreat rates during transgression is important for coastal planners in the face of ongoing sea-level rise. Most models of coastline response to sea-level rise focus exclusively on interactions between the rate of rise and topography, ignoring dynamic bathymetry and sedimentation. In this paper, we present a box model that shows that the upper shoreline of wave-dominated estuaries (bayhead deltas), which commonly contain populous urban and industrial centers, become stabilized and their rate of retreat decreases as they transgress across a tributary junction. Our model is based on two important observations from river valleys and estuaries across the world. First, valley cross-sectional area is conserved across tributary junctions. Second, estuarine water depth is largely a linear function of fetch in estuaries with an excess supply of fine-grained materials due to the importance of waves reworking fine-grained sediments. The decrease in retreat rate at tributary junctions is caused by a decrease in total estuarine volume accompanied by a conservation of sediment within the estuarine system as a tributary junction is transgressed. Our modeling results highlight the importance of inherited topography created during falling sea levels on shaping the nature and rate of transgression during the ensuing sea-level rise. In particular, tributary junctions act as pinning points during transgression.