Earth Surface Processes and Landforms最新文献

Bank erosion in Arctic rivers helps shape channel geometry, mobilizes carbon from permafrost and influences sediment delivery to the Arctic Ocean. On Alaska's Arctic coastal plain, rivers begin flowing during snowmelt in late spring while extensive river ice persists in channels, such that hydraulics are altered and water is kept cool. The effects of river ice on permafrost bank erosion are poorly understood, primarily due to a dearth of field observations and a lack of river ice in existing models.

To address this knowledge gap, we developed a numerical model to simulate the melt of substrate interstitial ice and bank collapse along individual permafrost river banks. We parameterize the model with field observations from riverbanks in three different channels on the Canning River delta, which are disparately impacted by river ice during snowmelt. We explore the bank erosion produced without river ice in the model and with modern river ice model scenarios that we drive with different stages and water temperature boundary conditions. We also compare predicted erosion rates to observations from satellite imagery to validate this approach.

In the model, banks are idealized as vertical profiles that rise 1–2 m above the river bed and are comprised of silt- to sand-sized sediment with dense roots in the active layer. Underneath, we generalize bank ice content underneath the active layer to represent ice-rich permafrost on the river corridor boundaries. The model predicts that these ice-rich river banks can erode by 2–6 m/yr. Scenarios without ice underpredict erosion in the distributary channels. Scenarios with varying river ice for different deltaic channels produce erosion rates similar to observations.

Our results suggest that the prolonged melt of thick river ice in a delta nonlinearly impacts permafrost bank erosion by blocking river discharge to certain branches, heightening stage across the distributary network and locally limiting river water warming. Given expected changes in air temperature and hydrology, future estimates of Arctic river bank erosion could be improved by considering river ice.

We evaluate the effectiveness of Ground Penetrating Radar (GPR), soil granulometry and geomorphometric analysis in identifying shallow variations of sandy and clayey materials in a colluvial-alluvial plain. In addition, 2D Electrical Resistivity Tomography (2D ERT) was used to provide complementary information about deeper subsurface features, beyond the resolution limit of GPR. Geophysical methods were combined with unmanned aerial vehicle (UAV) data and particle size analysis to achieve high-resolution detections of sediment variations in a colluvial-alluvial plain. A Digital Terrain Model (DTM) was derived from remote sensing data, providing topographic attributes. Two pieces of equipment were tested for acquiring GPR images: one with a 400 MHz antenna and another with dual frequencies of 250 and 700 MHz. However, GPR data were acquired using a 400 MHz antenna along 16 transects, as it provided the best balance between resolution and electromagnetic (EM) wave penetration depth. The ERT data were collected along a single profile using the dipole–dipole array. Soil cores were sampled at 0.20 m intervals to a depth of 1 m to validate the geophysical interpretations. GPR images showed two distinct patterns: one towards the footslope (West sector) and another towards the lowland (East sector). The topographic attribute LS Factor, with a maximum value of 1.55, on the footslope in the West sector, represents colluvial ramps. Mean TWI (> 10) directly related to mean MrVBF (>2) illustrates areas with higher sediment deposition and moisture accumulation in the East sector. Principal Component Analysis (PCA) and Spearman's correlation demonstrated that the depth of soil core samples is positively correlated with sand (r = 0.26) and negatively correlated with clay (r = −0.18). GPR images revealed variations in sediment composition (horizontal resolution) at depths of up to approximately 4 m (vertical resolution). The GPR efficiently mapped strong returning signals from sandy lenses and weaker signals from clay, highlighting its potential for areas with similar geomorphology. The real resistivity model revealed a resistive surface layer across the entire line, corresponding to massive migmatite gneiss. The inclusion of geomorphometric data in geophysical analyses contributes to interpreting interactions between surface morphology, soil texture and geophysical properties. Our results encourage further on-site research to characterize materials in terms of colluvial and alluvial origins.

The use of locally widened river reaches in river restoration is a common approach that aims to enhance morphological heterogeneity and dynamics and therefore increase habitat availability and quality. However, the success of some implemented locally widened river reaches is limited when there is a lack of morphodynamics, which may be related to factors such as sediment supply, channel slope and bank height, reflecting the degree of river bed incision. Therefore, this study examines the morphodynamic development of widened reaches with a moderate longitudinal slope (0.003) in mobile-bed laboratory experiments. The initial setup consisted of a channel with the adjacent floodplain on one side, measuring 30 channel widths in length and four in width. Sediment supply from upstream corresponded to a rate of 100% of the initial channel transport capacity. Sequences of bed-forming discharges and larger floods were conducted. Three experimental series were tested in which the bank height was varied from high (0.11 m = water depth at HQ₃₀), over medium (0.07 m = water depth at HQ₂), to zero (i.e. no offset between river channel and floodplain). Two-dimensional hydrodynamic numerical simulations based on the resulting bed topographies added high-resolution data on bed shear stress. The results show that morphodynamic activity, defined as the areas of erosion and deposition relative to the zones with full sediment transport, remains low for the widening with moderate slope, promoting channel stability across all three experimental series. The high-offset series experienced lateral erosion, with the main channel shifting into the floodplain and subsequently being constrained by the fixed banks. For the series with medium and no floodplain offset, stabilization in the straight channel was observed. These patterns contrast with the understanding of the influence of sediment supply on the morphodynamic activity for steeper slopes. In previous studies, the morphodynamic activity in a widened reach was high for high sediment supply conditions. Our findings from the experiments with the moderate slope (0.003) suggest that under such conditions, there are additional controlling parameters of the widening process.

A numerical model that computes the vertical distribution of different sediment sizes in riverbeds has been used to predict the formation of lenticular sedimentary structures in a flume with antidunes. The Navier–Stokes equations were solved to find the water velocities and the turbulence, and convection-diffusion equations for five different sediment sizes were used to predict the sediment concentrations. Changes in the elevations of the water surface and bed due to erosion and deposition were also included. The model includes algorithms that divide the bed into 1,000 adaptive vertical layers, each with its unique grain size distribution. The spatial resolution of the bedding and the resulting lenticular structures was thereby computed directly. The model predicted the formation of stationary and downstream-moving antidunes that occasionally would move upstream, leading to the formation of the lenticular structures. The numerical model explained the different physical processes with high spatial and temporal variation in velocity, turbulence, pressure, changes in bed sediment size fractions, together with water surface and bed movements. This is documented by detailed figures and animations in the current study.

In Northern Pakistan, gullying-related soil erosion results in severe soil degradation, detrimentally affecting the region's socioeconomic situation and environment. Gully erosion susceptibility mapping (GESM) is most effective at mitigating the negative impacts of soil erosion. Gully management strategies begin by creating suitable evaluation tools, identifying the causes of the gully and devising solutions for controlling it. This study aimed to evaluate the performance of two models, frequency ratio (FR) and information value (IV), to assess the soil erosion susceptibility of the study area. In the present study, we detected and identified 1287 inventory points of gully erosion using various satellite images, including Google Earth Pro and field surveys. This research considered topographic, geologic and climatic factors as causative parameters. The FR illustrated that a low class of soil erosion covered 21.4% of the area, and medium, high and very high classes covered 34%, 31.4% and 13.2%, respectively. The results of the variables using IV models showed that the areas covered by low, medium, high and very high classes are 28.5%, 37.6%, 15.2% and 18.7%, respectively. The models were validated using the AUC technique, revealing that the success rate curve (SRC) and predicted rate curve (PRC) for IV are 80% and 89%, respectively, whereas the SRC and PRC for FR are 86% and 93%, respectively. The validation results show that the FR model outperformed the IV model. This research is useful for assisting decision-makers and policymakers in devising a strategic plan to mitigate the adverse impacts of soil erosion in this important geographic region.

Knowledge of how the avulsion style of river, channel mobility and floodplain reworking changes under different paleoclimatic conditions, helps to understand the morphodynamics of fluvial intrinsic behaviours and its impact on shaping basin alluvial stratigraphic architecture. In order to elucidate the relationship between extrinsic factors and internal fluvial processes, here, we explored how river morphodynamics change across the mid-Pleistocene climate change. Sedimentary facies analyses in the Jiudong Basin of western-central Hexi Corridor were applied to constrain changes in channel-floodplain processes. Ten lithofacies and nine facies associations involved in general shallow lake, delta front, delta plain, overbank and channel sub-environments were identified. These data do show evidence of elevated channel mobility, floodplain reworking and avulsion style changed significantly after 0.8 Ma. Taken together with studies of erosion rate/sediment flux variability and paleoclimate evidence from the region, the most plausible explanation of these findings from the Jiudong Basin is that, sedimentary processes subjected to declining vegetation and floodplain cohesiveness, due to a dry and unstable climate, experienced accelerated channel dynamics after 0.8 Ma. In the context of climate change across the mid-Pleistocene, these findings provide an important perspective on the complex links between fluvial dynamics, floodplain reworking and climate change.

Repeating fluvial macroforms are ubiquitous. The streamwise alternation of steeper, coarse-grained, cobble/pebble bars and near-horizontal, fine-grained, sand/granule flats is characteristic of upland, single-thread, dryland channels. We have monitored the rate of formation of a bar-flat sequence by flash floods, noting the disposition and extent of each macroform as they evolve. To accomplish this, the bed material of a straight reach of the Nahal Yatir in the northern Negev Desert, Israel, was thoroughly mixed to a depth of 0.5 m with the aid of a mini excavator, obliterating a well-formed sequence of bars and flats. The ten flow events of two succeeding rain seasons were recorded, as were the changing topography and textural roughness of the bed following each complete post-flood dewatering. Embryonic flats, texturally like those present before disturbance, formed under the first flow event, occupying a fifth of the total length of the flats that had existed in the reach before experimental disturbance. Their length increased and their inclination decreased with each flow event, returning to the natural, pre-disturbed, aggregated length within two rain seasons. Restoration of the pre-disturbance bar-flat sequence was almost complete, the location of bars differing only marginally in places. Resemblance with the natural original was high, reflecting the sedimentary dynamism of desert flash floods. A mechanism that models and explains the formation and stability of these macroform sequences is developed in a companion paper.

Sources, transport mechanisms and pathways of fine sediment in river systems are dependent on a multitude of climatic, geomorphic and anthropogenic factors, resulting in geomorphic equifinality, in which it is difficult to parse how different landscape processes affect sediment transport across different spatiotemporal scales. The objectives of this study are to 1) provide a conceptual model to consider how differing spatial distributions and hydrologic timing of sediment sources, both upland and in-channel, can result in equifinal sediment transport outcomes, and 2) utilize analytical methods with widely available environmental datasets to infer sediment processes from stream gaging data. Hysteretic patterns of observed storm events were classified based on their direction and timing of peak sediment concentration, relative to streamflow, using records from 35 U.S. Geological Survey stream gages in the period between 2007 and 2023 within two different physiographic regions: the Mid-Atlantic Delaware River Basin (DRB) and the Midwestern Illinois River Basin (IRB). The DRB contains mixed forest, urban, suburban and agricultural watersheds over diverse topography, and the IRB is primarily an intensively managed agricultural watershed on flat terrain. We use principal component analysis and linear discriminant analysis to infer regional hydrologic relations with turbidity dynamics, and to identify the primary hydrologic and land surface characteristics most effective at distinguishing between hysteretic classes in each region. These analyses reveal underlying regional relations in storm event hydrodynamics and landscape characteristics that contribute to varying patterns in sediment dynamics. Incorporating these sediment dynamic relations with spatial distributions and hydrologic timing of sediment sources could help to improve process understanding and predictive capability of fine sediment transport in watersheds.

Beavers (Castor fiber, Castor canadensis) are recognized as key ecosystem engineers, influencing river hydrology and geomorphology through dam construction. While their structures are associated with positive impacts like flood attenuation, increased biodiversity and water quality improvements, beaver dams are quickly blamed for exacerbating downstream flooding following their failure during extreme rain events. This study examines two Quebec Superior Court rulings (2008 and 2017) where beaver dam failures were considered responsible for significant property damage in the Port-au-Persil watershed, located in the Charlevoix region of Quebec, Canada. Using hydrological and hydraulic modelling (HEC-HMS and HEC-RAS), we assessed the downstream impacts of beaver dam failures during extreme rainfall events caused by Hurricane Katrina (2005) and Irene (2011). The results reveal that the failure of beaver dams had minimal impact on peak discharge and water levels downstream. For the Irene 2011 event, a 1D hydraulic model showed incremental flow increases of 11–15% and water level rises of up to 0.23 m near the area affected by the damage. A revised 2D model, incorporating a hypothetical four-fold increase in dam retention volume, demonstrated only minor changes in water levels (0.05 m), confirming that the observed flooding would have occurred even without dam failure. The 2D simulations further highlight that dam height, rather than retention volume, controls downstream flood wave propagation. These findings challenge the negative perception of beaver dams and emphasize the importance of robust scientific assessments in flood-related liability cases. The legal implications of Article 105 of Quebec's Municipal Powers Act, which holds municipalities liable for flood damage caused by “obstacles” in rivers, create a risk of widespread beaver dam removal. This study advocates for evidence-based management practices and public education to recognize the ecological benefits of beaver dams while addressing concerns over their perceived flood risks.