Atmospheric cold fronts are frequently occurring perturbations to the northern Gulf of Mexico coastal region. Given the low-lying elevations in this region and the connectivity between distributary channels and deltaic wetlands, the nonlinear interplay between the cold frontinduced storm surge and tidal oscillations are likely important hydrodynamic processes regulating circulation and sediment dynamics. This study uses the Delft3D Flexible Mesh numerical modeling suite to assess the water level fluctuations resulting from the non-linear interaction between cold front induced storm surge and tidal oscillations in Wax Lake Delta (WLD) between December 2022 and January 2023. The WLD is a small, dynamic sub-delta located in Louisiana, USA, known for its ongoing progradation. The primary focus of this study lies on analyzing two cold fronts that approach from the northwest direction. The results illustrate that within the shallow, vegetated wetland interiors with spatially-variable inundation, the water level fluctuations resulting from non-linear interaction can exceed four times the water depth, while the variations relative to the water depth in the relatively deep primary channels are insignificant. Analysis for two cold fronts from the northwest and further numerical experiments revealed that the water level variation response to the non-linear interaction between the cold front storm surge and tides is predominantly influenced by the intensity of the cold front and the magnitude of the tidal range. This study emphasizes the notable impact of the non-linear interaction between cold front and tide on water level variation, which, in turn, influences inundation extent, sediment transport, and ecological factors in the WLD. AGU 2023, H51N-1280, San Francisco Link: https://agu.confex.com/agu/fm23/meetingapp.cgi/Paper/1293693

River deltas are dynamic ecosystems in which seasonal vegetation dynamics mediate flow and sediment transport timescales and channel-network evolution, yet most delta models either omit vegetation or hold it static. We couple the Delft3D Flexible Mesh (DFM) hydro-morphodynamic solver with the NBSDynamics vegetation module via the Basic Model Interface (BMI), using four representative freshwater vegetation types and three coupling scenarios to estimate the influence of seasonal vegetation dynamics and morphological development on water age and connectivity in an idealized river delta. We find that the vegetated deltas elongate, whereas unvegetated systems expand laterally. Channel water-age distributions are predominantly unimodal and tightly coupled to sedimentation, while island interiors exhibit multimodal distributions and a weaker water age–deposition coupling. System connectivity is largely discharge-driven in unvegetated deltas; however, in vegetated systems, connectivity control becomes state-dependent, shifting between hydrodynamic forcing during low biomass and vegetation dominance during peak canopy growth. Within this dynamic, seasonal vegetation emerges as a transitional regime between the static and no-vegetation endmembers across three network connectivity metrics. A Water-Age-Weighted Sedimentation Index (WAWSI) consolidates these signals into a seasonal fingerprint of vegetation-mediated connectivity, in which long-age and high-deposition zones form laterally in island interiors near the delta front. The results imply that the effectiveness of sediment diversions and marsh creation for sea-level-rise adaptation and land-loss mitigation depends on the phenological state of the vegetation species present and on antecedent morphological reworking, providing a process-based foundation for nature-based restoration in dynamic deltaic environments.