Earth Surface Processes and Landforms最新文献

Rivers are fundamental water bodies supporting a wide range of ecosystem services. However, during the last century, river dynamics have been considerably modified by human engineering, notably channelized and dyked to prevent floods. In many Alpine rivers, this has led to the formation of a complex of alternate bars, gradually colonized by vegetation. Therefore, assessing spatial and temporal dynamics over large extents of these alternate bar systems represents a challenge to better understand the functioning of ecosystems in Alpine river and eventually to prevent flood risk. The three objectives of this study were 1) to create a database characterizing bars along a 30 km segment of the River Arc, in the French Alps, 2) to create a bar typology and to compare it to expert point of view, and 3) to assess the dynamics of the system after a 10-year return period flood event that occurred in June 2013. High-resolution LiDAR data and aerial photographs were used to localize major bed evolutions through a DEM of Difference (DoD), and to delineate and characterize gravel bars, including their volume, between two dates covering the flood event (in Sept. 2010 and Nov. 2013, respectively). Other river parameters such as sinuosity and river width were also calculated. A hierarchical clustering applied to the whole dataset revealed some bar morphological patterns, with three types of bars, depending in their functioning and age: large old vegetated bars with no mobility, very young, small and low elevated free bars without vegetation, and less mobile and more elongated bars, mostly corresponding to hybrid alternate bars. The results also highlight strong sediment dynamics resulting from the June 2013 flood. Bars were indeed statistically slightly thinner and shorter in 2013 than in 2010, corresponding to an enlargement of the main channel. Finally, these results proved the strong potential of remote sensing data—especially LiDAR data—to characterize sediment bars in channelized river over large extents.

Extreme precipitation events can rapidly reshape mountain landscapes, even in tectonically inactive regions like the Southern Appalachians. Here, we illustrate how discrete storm events drive rapid geomorphic change with a repeat-lidar analysis of impacts from Hurricane Helene (September 2024) in the Hickory Nut Gorge, North Carolina, USA. Airborne lidar collected before and after Helene reveals characteristic patterns of landslide initiation, sediment delivery, and river channel evolution. Our observations augment the current understanding of landslide reactivation, highlight debris flows as a key process of coarse sediment transport, and demonstrate how episodic flooding can reshape river channel geometry and roughness. Geomorphic signatures of extreme events quickly obscure as vegetation regrows and infrastructure is repaired, underscoring the need for both pre-event and rapid postevent lidar to detect and quantify change. Together, these insights clarify how infrequent, high-intensity storms drive both immediate landscape change and long-term geomorphic evolution in steep mountain terrain.

The Tibetan Plateau, known as the ‘Third Pole’ of the Earth, has become a hotspot for landform classification studies due to its young tectonics, complex terrain and diverse landforms. Strong internal and external forces have shaped highly distinctive landscapes, posing significant challenges to landform classification. Previous studies mainly focused on landform morphology, whereas classifications that integrate morphology and genesis remain limited. Existing genetic classifications of the Plateau are based mainly on visual interpretation, hardly meeting the demand for large-scale automated landform classification. To address this issue, this study selected plains within the Tibetan Plateau as the study area and developed an automated classification method for plain genetic types by integrating multisource data. The results show that: (1) plains account for 25% of the Tibetan Plateau, with a mountain-to-plain ratio of about 3:1. (2) Fluvial and periglacial processes are the dominant external forces shaping the plains, with fluvial and periglacial plains comprising 51.73% and 26.07% of the total plain area, respectively, followed by lacustrine plains (10.55%), arid plains (7.55%), aeolian plains (3.21%) and loess plains (0.89%). (3) Accuracy evaluation results indicate that the classification accuracy for different genetic types of plains ranges from 75% to 91.89%, with an overall classification accuracy of 85.33%. Comparison with the 1:1 000 000 Geomorphological Atlas of China confirms that the overall distribution patterns are consistent, and the results of this study provide finer detail. The proposed hierarchical classification strategy and multisource data fusion framework provide a transferable approach for landform genetic classification in complex geomorphic regions.

Many estuaries worldwide face increasing sediment loading caused by catchment land use change and intensification, creating subsequent adverse effects on estuarine ecosystems. Extreme weather events can disproportionately alter sediment pathways and loading. Although storm-driven sediment exchange has been widely examined at open coasts and inlets, key transport mechanisms within constricted, sheltered estuaries remain understudied.

This study presents an observational dataset capturing the impact of a 99th percentile water-level event (based on 20 years of records) on sediment transport pathways in a sheltered, barrier-enclosed estuary. This event, driven by a 3-day storm surge (>0.5 m) combined with a spring tide, was recorded during a 3-week field campaign.

Sediment transport pathways and riverine contributions were analysed, and observations revealed substantial changes in suspended sediment concentrations increasing from 18 mg/l to 70 mg/l during the event. The elevated water levels and resulting pressure gradient at the constricted study site entrance caused by the storm surge increased local flood dominance. Combined with higher flow velocities and resuspension, the storm led to a sixfold increase in sediment import at the estuary entrance and a 600-fold increase in sediment flux to the upper estuary.

The decoupling of peak suspended sediment concentrations from streamflow indicates that the resuspension of estuarine legacy sediment, rather than catchment inputs, dominated the system's response.

These findings challenge assumptions about estuarine sediment budgets and emphasise that incorporating high water-level surge events into models can enhance the prediction of long-term estuarine evolution. Given projected increases in storm frequency under climate change, understanding these episodic but highly consequential sediment pulses can support the assessment of wetland resilience and inform estuarine management strategies.

Understanding floodplain wood transport, deposition and storage is necessary to fully close wood budgets in river corridors (the channel, floodplain and hyporheic zone). However, most work on wood in river corridors has focussed on in-channel wood. Here, we review current understanding of wood dynamics in floodplains using a floodplain wood budget to highlight the processes that change floodplain wood storage. We discuss autochthonous and hillslope recruitment to the floodplain, floodplain wood decay and burial/exhumation, controls on lateral wood fluxes between the floodplain and the channel, and fluvial wood transport within the floodplain itself. We compile wood load data for floodplains and channels in locations in which data on floodplain wood loads exist, finding that floodplains are an important storage location for wood within the river corridor across diverse environments. We briefly review the impacts of floodplain wood on physical and ecological processes and then summarise important knowledge gaps that limit understanding of floodplain wood dynamics. We emphasise that future research should address methods to determine wood piece source location and track wood within the river corridor; mechanistically explore coupled flow-sediment-vegetation-wood processes across spatial and temporal scales; extend observations of floodplain wood loads and storage characteristics and explore multiple size classes of organic matter; and work to inform management decisions related to floodplain wood. Because it may be less likely to be transported downstream and interact with infrastructure, floodplain wood may be less hazardous than in-channel wood but can still provide ecological benefits and enhance physical complexity. Improving our understanding of wood dynamics on floodplains is thus important for supporting river management.

Shoreline erosion and coastal flooding are two major hazards causing significant losses of life and property in a warming climate. To enhance coastal resilience against climate change, this study offers an integrated assessment of long-term shoreline erosion (the combined shoreline retreats driven by ambient dynamics and sea level rise) and potential flooding risk (PFR, quantified by the annual cumulative exceedance hours of extreme sea levels) along China's sandy beaches. We further examine the concurrent coastal hazard (CCH) of shoreline erosion and PFR, and evaluate the associated exposure of physical assets and population. Our findings suggest that under the high emission scenario SSP5–8.5, China's sandy beaches are projected to experience intensified erosion and elevated PFRs, primarily attributable to rising mean sea levels. Moreover, shoreline erosion is proportionally more prevalent along the southern coasts. Coastlines projected to experience fewer PFR hours tend to exhibit higher severity, and vice versa. As a result, more than 65% of sandy shorelines are threatened by CCH, and over 80% of coastal physical assets and populations along sandy beaches are exposed to CCH. Among the cities in China's Greater Bay Area, Hong Kong and Shenzhen are projected to face the highest levels of exposure for both physical assets and population. This study identifies future hotspots of shoreline erosion and coastal flooding along China's sandy coastlines and provides scientific evidence to support adaptation strategies aimed at mitigating climate-induced coastal hazards.

Floods are one of the most critical environmental threats in Central Europe. In Germany, they are responsible for more than half of the economic damage caused by environmental hazards. The magnitude of the 2021 Ahr flood has far exceeded what was forecast in previous flood hazard assessments. This was due to a significant underestimation of hazards, as the former hydrological models considered instrumental discharge records exclusively. Because the recording period only began in the second half of the 20th century, high-magnitude flood events prior to that period were not considered in flood hazard assessments. Historical flood events from written sources were also not included in official flood hazard assessments. In this study, we show the importance of geomorphological records from Ahr flood deposits for reconstructing past high-magnitude flood events. Our chemo- and lithostratigraphical analysis of four recovered cores from the Ahr floodplain shows that centennial- to millennial-scale high-energy flood deposits are not the exception but the rule. The four floodplain sediment cores record the catastrophic flood of 2021 and the two historical floods of 1804 and 1910, as well as a previously unidentified flood event dated approximately to the end of the 5th century A.D. In addition, the geomorphological analysis in combination with near-surface geophysical prospection shows that the Ahr floodplain is dominated by high-energy flood deposits and that low to medium-magnitude flood events are not preserved in the floodplain stratigraphy. The fluvial geomorphological record proves that the 2021 flood event is not an exception in the Ahr floodplain stratigraphy. In fact, at least three other flood events have been identified in the last 1,500 years that, based on lithostratigraphic parameters, had a comparable magnitude. The results document the high potential of floodplain archives for reconstructing high-magnitude flood events in Central European rivers, allowing a systematic reassessment in terms of the occurrence and frequency of high-magnitude flood events. The occurrence of the large floods in the Ahr valley does not show any clear coupling with the Central European hydroclimatic history. However, what is noticeable is that the historically documented high-magnitude Ahr floods occur during the summer season, which is in parallel with high atmospheric moisture loads.

Real-time monitoring and early warning systems for landslides are crucial for minimizing casualties and property losses. The tangential angle method, which assesses the deformation rate of the displacement–time curve at specific instances, has been successfully applied in some cases. However, this method often results in omissions, false alarms and frequent alerts due to its reliance on fixed time windows and single-point displacement measurements. Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) is an advanced deformation monitoring technology offering high frequency and accuracy. Nonetheless, it currently lacks a quantitative early warning method that fully leverages surface scene information. To address these challenges, this paper proposes a hybrid intelligent early warning approach based on surface deformation monitoring, comprising a point-based early warning (PEW) method and an area-based early warning (AEW) method. The PEW method enhances the traditional tangential angle approach by adopting a self-adaptive time window, thereby reducing warning errors associated with fixed time intervals. The AEW method facilitates early warnings by detecting landslide expansion behaviours, effectively utilizing the extensive data from surface scene monitoring. The proposed early warning system was validated through a detailed case study of the Jianshan landslide monitored by GB-InSAR. The results demonstrate that both PEW and AEW methods perform effectively within their respective scopes, although each possesses certain information blind spots. The integrated method capitalizes on the strengths of both approaches while mitigating their individual limitations, thereby achieving more accurate and reliable early warnings.

River systems are often in nonequilibrium because of changes in water and sediment inputs and channel-boundary conditions, but it remains unclear how the changes affect the trajectories of river channel-form adjustment from nonequilibrium to equilibrium. Using the data collected from a series of experiments conducted in sand-bed flumes and the generalized model of the rate law, this study presents a detailed investigation of the trajectories of channel-bed elevation adjustments from aggradation to equilibrium. For 15 runs of the experiments conducted respectively in the 2- and 4-m-wide sand-bed flumes at two flow discharges (30 and 60 L·s⁻¹) and four sediment concentrations (5, 10, 20 and 30 kg·m⁻³), the temporal variations of average channel-bed elevations at both inlet and outlet cross-sections in the 2-m-wide flume all take exponential decay trajectories and can reach equilibrium within a short period. In contrast, the temporal variations in the 4-m-wide flume take exponentially or linearly increasing trajectories in many runs, without a tendency of reaching equilibrium. Crucially, we found that under the combined influence of flow discharge, sediment concentration and channel width, the adjustment trajectories tend to shift from gradual increase to decay as the unit sediment transport rate increases. These trajectories arise from complex spatiotemporal interactions among flow conditions, sediment transport and channel-bed morphology. Further investigation is needed to identify the processes and conditions under which river channel-form adjustments evolve along nondecaying trajectories.