Collaborative Research: Sea-level Rise and Vegetation Controls on Deltaic Landform Evolution: A Coupled Experimental and Numerical Modeling Study

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Deltas are home for 25% of the human population (Syvitski et al., 2005). Across the world, combinations of changes in sea-level-rise rates, land use changes in the watersheds the feed deltas, and human activities on deltas themselves are causing rapid changes to delta landscapes and loss of valuable habitats and ecosystem services. Science for predicting changes in delta landscapes, ecosystems, and coastlines is now urgently required to successfully evaluate and implement plans to improve sustainability for deltas globally. However, changes on deltas are controlled by an array of interactions between coastal rivers, plants and animals, hurricanes and storms, and a range of human manipulations. The proposed study will enhance our understanding of, and ability to predict how deltas will respond to changes in climate and land-use forcing, focusing on both physical and biological aspects of delta systems using laboratory flume and computational experiments.Physical delta experiments will be conducted in the University of Texas (UT) Sediment Transport and Earth-surface Processes (STEP) basin, which allows for independent and precise controls of the major geological factors: sediment supply and relative sea level rise (RSLR). These experiments will also be the first to investigate interactions between physical and biological processes in shaping deltas. Experiments will involve seeding the delta surface with small plants (Alfalfa) at different spatial densities. The ecosystem is simplified in the experiments but still naturally coevolving with a growing and self-organizing fluviodeltaic system. Computational modeling efforts, based on the results of the physical experiments, will produce a reduced complexity model that captures the main eco-morphodynamic feedbacks under rapid relative sea-level rise over engineering and geological time scales. The resulting computational models will provide a platform for experiments addressing the ecomorphodynamic evolution of a range of delta types, under disparate sets of forcing (e.g. river vs. wave dominated) and under various scenarios of land-use and climate changes. The scientific insights to be gained through the coupled laboratory experiments and computational modeling include: 1) the fluviodeltaic system's response to RSLR, in particular, changes in avulsion (flood) frequency and shoreline roughness, 2) the self-organization of the deltaic distributary channel network that coevolves with vegetation, 3) the effects of spatial variation in vegetation density on channel avulsion location and frequency, and 4) how the feedbacks from vegetation dynamics during rapid RSLR affect deltaic landforms and resulting stratigraphy. This work will produce the first quantitative eco-morphodynamic model based on controlled laboratory experiments, allowing exploration of future changes in fluviodeltaic landscapes, channel activity, and vulnerability for a range of delta types and RSLR rates.