Hydrologic connectivity controls the lateral exchange of water, solids, and solutes between rivers and floodplains, and is critical to ecosystem function, water treatment, flood attenuation, and geomorphic processes. This connectivity has been well‐studied, typically through the lens of fluvial flooding. In regions prone to heavy rainfall, the timing and magnitude of lateral exchange may be altered by pluvial flooding on the floodplain. We collected measurements of flow depth and velocity in the Trinity River floodplain in coastal Texas (USA) during Tropical Storm Imelda (2019), which produced up to 75 cm of rainfall locally. We developed a two‐dimensional hydrodynamic model at high resolution for a section of the Trinity River floodplain inspired by the compound flooding of Imelda. We then employed Lagrangian particle routing to quantify how residence times and particle velocities changed as flooding shifted from rainfall‐driven to river‐driven. Results show that heavy rainfall initiated lateral exchange before river discharge reached flood levels. The presence of rainwater also reduced floodplain storage, causing river water to be confined to a narrow corridor on the floodplain, while rainwater residence times were increased from the effect of high river flow. Finally, we analyzed the role of floodplain channels in facilitating surface‐water connectivity by varying model resolution in the floodplain. While the resolution of floodplain channels was important locally, it did not affect as much the overall floodplain behavior. This study demonstrates the complexity of floodplain hydrodynamics under conditions of heavy rainfall, with implications for sediment deposition and nutrient removal during floods.

The elevation of natural river levees can vary considerably along the length of a river, and low‐lying features such as secondary floodplain channels allow for hydrologic exchange between a river and its floodplain over a range of discharges. This hydrologic, “river‐floodplain connectivity” plays a role in attenuating flood waves and transporting fluvial material to floodplain ecosystems. However, flood wave attenuation and transport are also limited by the available storage provided by floodplains. In this study, we explore the combined controls of river‐floodplain connectivity and floodplain width on flood wave attenuation and transport, and how those controls change as flood magnitude increases. We develop idealized river‐floodplain models based on the geometry of the lower Trinity River in Texas, USA, varying floodplain width, peak discharge, and degree of river‐floodplain connectivity, which we prescribe by varying the width of a secondary channel connecting the river to the floodplain. We show that attenuation transitions from connectivity‐limited to storage‐limited as discharge increases. Secondary channel conveyance allows for floodplain inundation at lower discharges, but also fills the floodplain faster and, for larger floods, can cause higher flood peaks downstream. Greater secondary channel conveyance and wider floodplains increase fluxes to the floodplain, but secondary conveyance allows the floodplain to drain faster while wider floodplains have longer average residence times. This study presents a framework for understanding how secondary channel conveyance and floodplain width combine to modulate lateral flow exchange, residence times, and flood wave attenuation, and can guide successful management of river systems and future restoration efforts.

Coastal areas are complex environments with diverse hydrodynamic, morphological, sedimentological, and biological contexts. Vegetation is increasingly recognized as a crucial agent that shapes the geomorphology and hydrology of coastal and riverine systems by inducing a hydraulic roughness that influences flow velocities, inundation, erosion, and deposition. At the same time, vegetation growth depends on the environmental habitat conditions, which it modifies continuously, resulting in a biophysical feedback-loop. This loop between plant growth and the physical environment is inherently dynamic, meaning they both vary spatiotemporally through their interactions; however, these dynamics are currently excluded from most hydro-morphodynamic models that predict long-term coastal change. We present the DYnamic COastal VEgetation model DYCOVE: an open-source, process-based vegetation model that simulates dynamic coastal marsh vegetation by representing key ecological processes such as seed dispersal, establishment criteria, growth curves, and mortality rules. Vegetation dynamics are governed by species-specific thresholds for inundation, desiccation, bed level change, and flow conditions while age-dependent stress tolerance enables realistic transitions from seedlings to mature plants of multiple species. Based on literature-derived parameterizations of ecological thresholds, DYCOVE reproduces realistic vegetation distributions and zonations both in tidally- and fluvially-impacted coastal environments with an F1 score above 0.8 and species distribution with a total accuracy of 70 %. DYCOVE’s flexible, species-agnostic framework allows exploration of how various vegetation types influence coastal hydrodynamics, sediment transport, and land-building, representing a crucial advancement in process-based eco-hydro(morpho)dynamic modelling.

Coastal areas are complex environments with diverse hydrodynamic, morphological, sedimentological, and biological contexts. Vegetation is increasingly recognized as a crucial agent that shapes the geomorphology and hydrology of coastal and riverine systems by inducing a hydraulic roughness that influences flow velocities, inundation, erosion, and deposition. At the same time, vegetation growth depends on the environmental habitat conditions, which it modifies continuously, resulting in a biophysical feedback-loop. This loop between plant growth and the physical environment is inherently dynamic, meaning they both vary spatiotemporally through their interactions; however, these dynamics are currently excluded from most hydro-morphodynamic models that predict long-term coastal change. We present the DYnamic COastal VEgetation model DYCOVE: an open-source, process-based vegetation model that simulates dynamic coastal marsh vegetation by representing key ecological processes such as seed dispersal, establishment criteria, growth curves, and mortality rules. Vegetation dynamics are governed by species-specific thresholds for inundation, desiccation, bed level change, and flow conditions while age-dependent stress tolerance enables realistic transitions from seedlings to mature plants of multiple species. Based on literature-derived parameterizations of ecological thresholds, DYCOVE reproduces realistic vegetation distributions and zonations both in tidally- and fluvially-impacted coastal environments with an F1 score above 0.8 and species distribution with a total accuracy of 70 %. DYCOVE’s flexible, species-agnostic framework allows exploration of how various vegetation types influence coastal hydrodynamics, sediment transport, and land-building, representing a crucial advancement in process-based eco-hydro(morpho)dynamic modelling.

Geomorphic transitions—such as the interface between rivers and floodplains—are critical zones controlling water, sediment, and nutrient transport. River–floodplain connectivity often occurs through secondary channels that convey fluxes into the floodplain. In other cases, connectivity is created or amplified by human interventions. But is higher connectivity in a landscape always beneficial?In this talk, we examine the role of connectivity—both structural and functional—in shaping flood wave attenuation and long-term land change. We draw on two contrasting landscapes. First, in the Trinity River (Texas), rivers and floodplains are connected via floodplain channels. Using an idealized model, we show that attenuation transitions from connectivity-limited to storage-limited as discharge increases. Secondary channel conveyance promotes early floodplain inundation and attenuation at lower flows, but at higher flows it can fill storage rapidly and even increase downstream flood peaks. Greater conveyance and wider floodplains increase fluxes to the floodplain, yet conveyance shortens residence times while wider floodplains prolong them.Second, we examine coastal Louisiana: the sediment-rich Wax Lake Delta, which is gaining land, and the sediment-starved Terrebonne Bay, which is losing land. Here, connectivity plays opposite roles—enhancing resilience and land growth in one system while accelerating degradation in the other.This work shows that connectivity is not universally “good”: it can attenuate floods and build land under some conditions, but under others it transfers risk or drives loss. Understanding these dynamics is critical for designing floodplain reconnection and managing landscapes under climate change.

Coastal areas are complex environments with diverse hydrodynamic, morphological, sedimentological, and biological contexts. Vegetation is increasingly recognized as a crucial agent that shapes the geomorphology and hydrology of coastal and riverine systems by inducing a hydraulic roughness that influences flow velocities, inundation, erosion, and deposition. At the same time, vegetation growth depends on the environmental habitat conditions, which it modifies continuously, resulting in a biophysical feedback-loop. This loop between plant growth and the physical environment is inherently dynamic, meaning they both vary spatiotemporally through their interactions; however, these dynamics are currently excluded from most hydro-morphodynamic models that predict long-term coastal change. We present the DYnamic COastal VEgetation model DYCOVE: an open-source, process-based vegetation model that simulates dynamic coastal marsh vegetation by representing key ecological processes such as seed dispersal, establishment criteria, growth curves, and mortality rules. Vegetation dynamics are governed by species-specific thresholds for inundation, desiccation, bed level change, and flow conditions while age-dependent stress tolerance enables realistic transitions from seedlings to mature plants of multiple species. Based on literature-derived parameterizations of ecological thresholds, DYCOVE reproduces realistic vegetation distributions and zonations both in tidally- and fluvially-impacted coastal environments with an F1 score above 0.8 and species distribution with a total accuracy of 70 %. DYCOVE’s flexible, species-agnostic framework allows exploration of how various vegetation types influence coastal hydrodynamics, sediment transport, and land-building, representing a crucial advancement in process-based eco-hydro(morpho)dynamic modelling.