Study region: The Fort St. Philip (FSP) crevasse on the Mississippi River Delta, Louisiana, USA, represents a dynamic sediment diversion system connecting the river to the Breton Sound Basin. This region is characterized by rapid subsidence, tidal influence, and vegetation-hydrology interactions that shape deltaic land building. Study focus: This study quantifies the morphodynamic evolution of the FSP crevasse splay between 2013 and 2019 and evaluates the relative roles of vegetation, tides, waves, and diverted sediment in controlling land building. We applied a Delft3D-FM morphodynamic model validated using satellite-derived elevations generated through a Random Forest machine-learning approach. The model incorporates site-specific sediment properties, subsidence rates, and seasonal vegetation dynamics. New Hydrological Insights for the Region: Results show that vegetation and diverted riverine sediment were the dominant positive drivers of splay growth, while tides and waves acted as erosional forces. Vegetation increased splay volume above 0.00 m NAVD88 by 77 % in comparison to the simulation without vegetation, whereas tidal and wave processes produced substantial net erosion. Hydroperiod analysis reveals persistent inundation in distal and medial zones, enhancing sediment receiving and retention, while proximal areas remain strongly controlled by seasonal river discharge. The integration of machine-learning-derived topography with process-based modeling provides a transferable framework for assessing sediment diversion performance and wetland resilience in river-dominated deltas worldwide.

A high-resolution numerical model of hydrodynamics to simulate salinity conditions in the lowermost Mississippi River was utilized to analyze the salt wedge propagation. Extensive upriver propagation occurred during 2022-2024 with discharge conditions between 5,000 and 8,500 cms, which are below long-term seasonal averages but above historically defined severe drought thresholds. Our analysis reveals that while sea level rise and deepening of the navigation channel contribute to upstream wedge movement excessive water loss through a series of lateral crevasses was a primary cause of the upriver wedge propagation distance. When the lateral crevasses (during drought events) are closed in the simulation using native sand material, it results in significant reduction of the salt wedge propagation upriver. The model also demonstrated that an underwater sand sill presently utilized in low events to limit propagation of the wedge upriver movement, if moved further downstream enhances its function and effectiveness. Overall, this model may serve as a vital tool for public risk communication and co-production, fostering informed decision-making for water management in the Lower Mississippi River.

Anthropogenic activities have driven the Mississippi River Delta (MRD) to retrograde above and below sea level, a fate shared by many large coastal river deltas. However, the role of seasonal sediment dispersal to the coastal ocean in shaping the delta remains unclear. Here we present oceanic dispersal and seabed deposition patterns and quantity for the river’s total fine-grained sediment load. Using 7 Be as a seasonal tracer of fluvial sedimentation, we share a mass-balance sediment budget for ~ 3000 km 2 of the subaqueous MRD for the year 2025. Findings show that 7 Be sediment deposition rates (SDR) depend on oceanographic conditions and seabed morphology as well as sediment supply. A bypass zone exists on the northeast shelf despite the local opening of multiple large passes and hydrologic backstepping of the river. Additionally, SDR patterns indicate that fine-grained sediment from these passes is advected southwestward towards Pass a Loutre and South Pass where it is deposited, highlighting oceanic dispersal processes in overall delta evolution. While 7 Be SDRs show sediment deposition across the delta front, plume sedimentation alone is not enough to continue delta front progradation. Findings will be used to improve predictions of the evolution of the MRD and aid future management.

Mangrove ecosystems in the Beibu Gulf, China, underwent severe deforestation before the 2000s. However, the influence of the deforestation event on sedimentary organic carbon (OC) biogeochemistry has not been reported in this region yet. Based on the 210Pb chronology of four sediment cores sampled in the Beilun River Estuary National Nature Reserve, this study analyzed soil texture, bulk OC, stable and radiocarbon isotopes, and lignin biomarkers to reconstruct historical changes in OC storage and accumulation rate over the past half-century. Before the National Nature Reserve establishment in 2000, the stage of pre-establishment I (Pre-EST I, before 1970) was characterized by an average TOC of 1.24 f 0.14 % with finer particles (76.2 f 6.2 %), older (6406 f 362 BP) terrestrial sources (72.2 f 6.6 %). After significant transitional changes of all the parameters in Pre-EST II(1970-2000), the average TOC became lower (0.68 f 0.15 %) with mainly younger (1357 f 147 BP) marine-derived OC (52.8 f 11.0 %) with coarser particles (59.4 f 4.7 %) in Post-EST stage after 2000. The lignin concentration Sigma 8 also decreased from 0.61 f 0.12 mg 100 mg-1 sediment in Pre-EST Ito a half value of 0.32 f 0.11 mg 100 mg-1 sediment in Post-EST. The three-stage changes were attributed to deforestation before the National Nature Reserve establishment in 2000. As a result, the remnant sedimentary OC in mangrove sediments indicated not only the source change of OC, but also a decrease in carbon accumulation rate by 14.5 %, a decrease in carbon density by 30.2 % and a decrease in carbon storage by 54.0 % in Beibu Gulf, China. If the mangrove recovery rate was kept the same as in the study, the global mangrove carbon storage may increase by 1.2 Tg C till the end of this century under good protection.

Effective streamflow monitoring networks are crucial for flood mitigation planning and water management operations. In Louisiana, USA, extreme rainfall, flat topography, and coastal-inland interactions necessitate enhancements to the sparse existing monitoring resources. This study introduces a stakeholder-driven approach to designing a streamflow monitoring network by integrating local expertise with geospatial process-based criteria. Our approach combines stakeholder input, gathered via web-based geospatial applications, with an automated scoring system. The system is based on hydrologic and geomorphic factors to prioritize gage placements while balancing regional needs and resource constraints. Implemented as part of the Louisiana Watershed Initiative (LWI), the network design addresses monitoring gaps, particularly in ungauged large watersheds and streams with complex flow regimes. The study highlights the importance of incorporating local knowledge into technical designs to support flood mitigation planning, real-time flood forecasting, and hydrodynamic model calibration. This framework can be adopted by other flood-prone regions worldwide to enhance flood monitoring and mitigation planning efforts.

Wetlands in deltas across the globe have been severely affected by climate change-induced sea level rise. One strategy to mitigate these impacts is to engineer large river sediment diversions. In this study, we use a morphodynamic model to simulate and quantify the depositional footprint of the 80-day Caernarvon crevasse event that occurred during the Great Mississippi Flood of 1927 in Breton Sound Basin, Louisiana, USA, as an analog to engineered diversions. We examine the effects of river sediment load by modeling the same crevasse splay formation under the past, current-day, and future projected sediment load decline of the Lower Mississippi River. To assess the model's performance, we compared crevasse formation to field-measured deposition thickness and mass per area. The model shows that under current sediment loads, a flood discharge comparable to the 1927 event would build 70% less land was it to occur today. Further, silt falling velocity and clay flocculation percentage are the two key factors controlling splay footprint and deposition. The model also demonstrates the effects of sediment supply decline on the land-building potential of engineered sediment diversions. These sediment diversions, designed to mimic natural crevasse splay formation, are being pursued as a coastal restoration strategy in the Mississippi Delta. The analysis presented here emphasizes key attributes of engineered diversions and their relevance to the successful implementation of these restoration strategies, including flow capacity, ability to distribute sediment in the receiving area, and the extent to which they would induce marsh inundation.

Vertical land motion is one of the main factors contributing to increased flood risk in coastal communities. Here, we use satellite interferometric synthetic aperture radar (InSAR) data to detect and measure previously undocumented land motions in Greater New Orleans (GNO), Louisiana. Although most of New Orleans is generally stable, rapid elevation loss occurs in parts of the city (up to -20 millimeters per year) and on flood protection walls constructed following Hurricane Katrina (up to -28 millimeters per year). This work provides unprecedented spatial coverage of land motion rates in GNO, including wetlands and the flood protection system previously lacking data, which allows a more detailed examination of ground deformation patterns and insight into underlying drivers. In the broader context, this work shows the potential of InSAR for measuring localized land motion in New Orleans and similar communities, particularly where the presence of wetlands complicates its application.

The Breton Sound Estuary, located within the Mississippi River Delta, has experienced significant wetland loss over the past century due to a combination of natural and anthropogenic factors. This study examines the patterns and mechanisms driving wetland change in the upper Breton Sound Basin and focuses on the impacts of riverine isolation, hydrological alterations, and human activities. Prior to human interventions, the basin received regular large riverine input via overbank flooding and crevasse channels. Levee construction began in the 18th century, but it wasn’t until the great Mississippi River flood of 1927 that continuous levees were built that completely isolated the river from the upper Breton Sound Basin. The reduction of riverine input led to replacement of fresh and low salinity marshes by more salt-tolerant species. Sediment introduced during this single 1927 event created a 130 km2 crevasse splay still visible in marsh cores more than 10 km from the levee breach. Higher levees built afterward as part of the Mississippi River and Tributaries Project (MR&T) have almost completely isolated this basin from the river. A small river diversion was constructed in 1991 to divert river water into the basin, but its impact has been minimal compared to the historical crevasse channels. Starting the 1970s, wetlands in the upper basin began to deteriorate and was dramatic during the passage of Hurricanes Katrina and Rita in 2005, and wetland loss was much higher in some areas. For example, some wetlands in the path of diverted water had loss rates of about 7% per year during the passage of the hurricanes compared to <1% per year for most of the rest of the upper basin. Here we describe patterns of wetland change and analyze factors responsible for the loss. There have been pervasive changes in hydrology of the upper Breton Sound Basin due to flood control levees. But dredging of an extensive canal network is mostly responsible for the majority of wetland loss in the central part of the upper basin. Marshes facing the open waters of Breton Sound had low loss rates and receive sediments and nutrients from resuspended seafloor materials and Mississippi River water discharged to open waters of Breton Sound. Nutrients played a negligible role in causing wetland loss. Sediment introduction is likely the most effective restoration strategy for mitigating further wetland loss, and specific recommendations are provided that are tailored to the unique conditions of different zones within the Basin. Understanding the complex interplay of factors influencing wetland dynamics in the Breton Sound Estuary is crucial for developing effective restoration and management strategies in the face of ongoing environmental changes.

Coastal ecosystems are complex and often support a broad spectrum of functions with competing objectives. In addition to their ecological value, they offer socio-economic benefits (i.e., ecosystem services) to coastal com-munities. One potential way to help address this complexity is to use decision support systems to help natural resources managers understand system dynamics and evaluate strategies to maintain the health and integrity of these ecosystems. This paper presents a roadmap and detailed application of co-production strategies where managers and researchers are fully engaged in a collaborative manner in the design of a decision support tool for coastal ecosystems. It also emphasizes the importance of capturing end-users' (i.e., natural resource managers) priorities to refine the conceptual design of the decision support tool, while maintaining a sound scientific and modeling framework. The case study presented here centers on the Northern Gulf of Mexico, but the concept can be exported globally to other systems. This effort highlights foundational co-production strategies, including transdisciplinary team assembly, a knowledge sharing workshop, Toolbox Dialogue Initiative workshops to facilitate working across disciplines, core team and focus group meetings, and design charrettes. Further, this paper articulates the benefits and difficulties of executing a co-production process through virtual collaborations.

The Mississippi River channel from New Orleans to the Gulf of Mexico (GOM) is a key deep draft navigation channel and an active deltaic lobe. Natural and engineered lateral exits from this reach into adjacent receiving basins historically has provided mineral sediment for wetland accretion in the face of rising relative sea level and supported estuarine-coastal food webs. However, our analysis indicates water losses from the channel have increased by 25% since 2004 due to (1) bank failures during large floods since 2012 that have created several large exit channels downriver of the flood protection levee, and (2) the opening of an engineered diversion at West Bay in 2004. This has resulted in a 60-80% loss in stream power in the lowermost navigation channel that is accompanied by net shoaling between 2012 and 2022 and an increased dredging need. Our 2022 survey in the GOM exit passes indicates that only 20% of the freshwater, 5% of the total suspended sediment (2% of the sand) at New Orleans now reaches the GOM: this supports previous research indicating the delta front is retreating after centuries of progradation. Together these results indicate that (1) river containment and the sustainability of the navigation channel is threatened, (2) sediment load reaching the seaward end of the delta may be insufficient to avoid major degradation, and (3) the increased freshwater flux into adjacent shallow coastal water bodies has unknown implications for coastal hypoxia and food webs, including commercial species (e.g., oysters) and marine mammals. Future acceleration in sea level rise rates and tropical storm frequency/intensity likely will worsen these trends.

Land‐surface subsidence is a major contributor to land loss in many river deltas. New approaches yielding high‐resolution data are needed to parse the relevant driving forces. In 2016, we established a novel “subsidence superstation” ∼2 km from the Mississippi River in coastal Louisiana (USA) to measure compaction in a global reference frame as a function of depth in Holocene sediments and deeper subsidence. The site features three borehole optical fiber strainmeters to obtain continuous records of displacement between ∼1.3 m below the surface and depths of ∼11, 25, and 38 m. These data are complemented by an adjacent station providing hydrologic data and near‐surface compaction. We also installed three GPS antennas, one of which is mounted to a rod cemented into the Pleistocene basement. A core from one of the boreholes provides insight into the sediment properties of the entire Holocene succession. Five years of records reveal the compaction rate in the material between 1.3 and 38 m is likely less than 0.25 mm/yr. The GPS records yield a subsidence rate of 2.5 mm/yr regardless of the depth of the anchor, thus corroborating the low compaction rates observed by the strainmeters. The new instrumental records show that current subsidence at this location is governed mostly by deformation of the Pleistocene or underlying strata rather than compaction of Holocene material, with the exception of the uppermost meter. The methodology represents an important new approach to mapping subsidence rates at varying depths, providing insight into the mechanisms governing delta subsidence.

A description of historical and ambient water quality conditions is often required as part of navigational studies. This paper describes a series of tools developed by the USGS that can aid navigation managers in developing water quality assessments. The tools use R, a statistical software program, and provide methods to retrieve historical streamflow and water quality data, summarize observations, model concentrations and fluxes, and estimate seasonal, annual, and decadal trends. The utility of these tools is demonstrated by providing an analysis of the seasonal variability and long-term trends of nitrate plus nitrite, orthophosphate, and suspended sediment concentrations and fluxes at nine sites in the Mississippi River Basin. Trends in annual mean concentration and flux showed fairly stable nitrate plus nitrite at most of the nine sites, with increases in the Upper Mississippi and Missouri Rivers and decreases on the Illinois River over a 40-year period beginning in 1980. Orthophosphate concentration or flux increased at almost all sites over a similar time period. Conversely, a concurrent steady decline in suspended sediment concentrations and fluxes was noted at sites throughout the basin.

Dune-scale cross-beds are a fundamental building block of fluvial-deltaic stratigraphy and have been recognized on Earth and other terrestrial planets. The architecture of these stratal elements reflects bed-form dynamics that are dependent on river hydrodynamic conditions, and previous work has documented a multitude of scaling relationships to describe the morphodynamic interactions between dunes and fluid flow. However, these relationships are predicated on normal flow conditions for river systems and thus may be unsuitable for application in fluvial-deltaic settings that are impacted by nonuniform flow. The ways in which dune dimensions vary systematically due to the influence of reach-averaged, nonuniform flow, and how such changes may be encoded in dune cross-strata, have not been investigated. Herein, we explored the influence of backwater flow on dune geometry in a large modern fluvial channel and its implications for interpretation of systematic variability in dune cross-strata in outcrop-scale stratigraphy. This was accomplished by analyzing high-resolution channel-bed topography data for the lowermost 410 km of the Mississippi River, which revealed that dune size increases to a maximum before decreasing toward the river outlet. This spatial variability coincides with enhanced channel-bed aggradation and decreasing dune celerity, which arise due to backwater hydrodynamics. An analytical model of bed-form stratification, identifying spatial variability of cross-set thickness, indicates a prominent downstream decrease over the backwater region. These findings can be used to inform studies of ancient fluvial-deltaic settings, by bolstering assessments of proximity to the marine terminus and associated spatially varying paleohydraulics.

Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change, and now is the time to document, understand, and mitigate their impacts.

Fluvial bedforms generate a turbulent wake that can impact suspended‐sediment settling in the passing flow. This impact has implications for local suspended‐sediment transport, bedform stability, and channel evolution; however, it is typically not well‐considered in geomorphologic models. Our study uses a three‐dimensional OpenFOAM hydrodynamic and particle‐tracking model to investigate how turbulence generated from bedforms and the channel bed influences medium sand‐sized particle settling, in terms of the distribution of suspended particles within the flow field and particle‐settling velocities. The model resolved the effect of an engineered bedform, which altered the flow field in a manner similar to a natural dune. The modelling scenarios alternated bed morphology and the simulation of turbulence, using detached eddy simulation (DES), to differentiate the influence of bedform‐generated turbulence relative to that of turbulence generated from the channel bed. The bedform generated a turbulent wake that was composed of eddies with significant anisotropic properties. The eddies and, to a lesser degree, turbulence arising from velocity shear at the bed substantially reduced settling velocities relative to the settling velocities predicted in the absence of turbulence. The eddies tended to advect sediment particles in their primary direction, diffuse particles throughout the flow column, and reduced settling likely due to production of a positively skewed vertical‐velocity fluctuation distribution. Study results suggest that the bedform wake has a significant impact on particle‐settling behaviour (up to a 50% reduction in settling velocity) at a scale capable of modulating local suspended transport rates and bedform dynamics. © 2020 John Wiley & Sons, Ltd.

The authors regret that we unknowingly used erroneous bulk density data in Figs. 4 and 6 (panels b,c,e) that affected results in Fig. 7.

A distinct suite of sand bedforms has been observed to occur in laboratory flows with limited sand supply. As sand supply to the bed progressively increases one observes sand ribbons, discrete barchans and, eventually, channel spanning dunes; but there are relatively few observations of this sequence from natural river channels. Furthermore, there are few observations of transitions from limited sand supply to abundant supply in the field. Bedforms developed under limited, but increasing, sand supply downstream of the abrupt gravel–sand transition in the Fraser River, British Columbia, are examined using multi‐beam swath‐bathymetry obtained at high flow. This is an ideal location to study supply‐limited bedforms because, due to a break in river slope, sand transitions from washload upstream of the gravel–sand transition to bed material load downstream. Immediately downstream, barchanoid and isolated dunes are observed. Most of the bedform field has gaps in the troughs, consistent with sand moving over a flat immobile or weakly mobile gravel bed. Linear, alongstream bedform fields (trains of transverse dunes formed on locally thick, linear deposits of sand) exhibit characteristics of sand ribbons with superimposed bedforms. Further downstream, channel spanning dunes develop where the bed is composed entirely of sand. Depth scaling of the dunes does not emerge in this data set. Only where the channel has accumulated abundant sand on the bed do the dunes exhibit scaling congruent with previous data compilations. The observations suggest that sediment supply plays an important, but often overlooked, role in bedform scaling in rivers.

The Mississippi River and its delta and plume provide insights into research-informed approaches to managing river-dominated coastal zones.