Erosion Width Research Articles

UAV AERIAL SURVEY IN MONITORING OF COASTAL GEOSYSTEMS IN THE SOUTHERN IRKUTSK AMPHITHEATRE

Estimating the dynamics of exogenous geological processes and understanding their controlling factors is an urgent task faced by many regions of the world. One of the methods of its solution is monitoring. The paper presents the UAV monitoring results for short-term dynamics of complex exogenous processes at five key sites in the coastal zone south of the Bratsk reservoir. The study area is a part of the platform structure in the south of the Irkutsk amphitheater, which is considered to be relatively stable in terms of geodynamics. There has been developed a methodical scheme for obtaining data series on the dynamics of complex exogenous geological processes in the coastal geosystem. A flight altitude of 50–60 m is optimal to obtain orthophotos with a resolution of 1.1–2.2 cm/px, sufficient to estimate the areal dynamics of the processes, and a DEM with a resolution of 2.6–5.4 cm/px to estimate the volumetric dynamics.The eroded coastal area at the Rassvet site was measured to be 6900 m2, which corresponds to an average erosion width of 3.45 m per linear meter of coastal length with maximum values of up to 6.51 m. A high rate of coastal erosion in the period 2021–2022 is related to the maximum water level in the Bratsk reservoir, close to the normal headwater level. The assessment of the volumetric dynamics of the coastal gullies yielded negative values, as most of the gully mouths were eroded. The secondary valley-bottom gullies (Mamontov and Barany sites) and coastal gullies (Khadakhan site) are characterized by positive dynamics both in area and volume growth (12–20 m2 and 1.3–35.0 m3, respectively). At the Khadakhan site, the volumetric growth of new and previously observed suffusion sinkholes was 0.45 m3.The obtained areal and volumetric rates of the exogenous processes can serve as a basis for their modern assessment and prediction of their development in order to prevent and reduce socio-economic risks.

Experimental Study on Gully Erosion Characteristics of Mountain Torrent Debris Flow in a Strong Earthquake Area

In recent years, as the frequency of debris flow outbreak in strong earthquake areas has increased and the scale has been expanding, in order to explore the erosion characteristics of debris flow, a lateral erosion flume model experimental device has been designed, and 18 groups of incomplete orthogonal experiments have been carried out, with a unit weight of debris flow of 1.6~2.0 g/cm3, a content of fine particles in the accumulation of 0~28.82%, and a longitudinal slope gradient of the gully of 8°~20° as variables. The results show that the erosion width, erosion depth, and erosion volume decrease with the increase in fluid bulk density and increase with the increase in gully slope. When the longitudinal slope of the gully was 16°, the sediment with 11.40% fine particles had the strongest erosion effect, indicating that more or less fine particles are not conducive to the occurrence of lateral erosion of the gully. Finally, through multi-factor variance analysis, it was found that the order of the three factors on the gully lateral erosion degree from strong to weak is: debris flow unit weight, gully slope, and accumulation grading. The analysis results further showed that the unit weight of debris flow has the greatest impact on the erosion degree of the side slope, which is consistent with the experimental results. The research results have important reference significance for revealing the mechanism of lateral erosion and improving the level of debris flow disaster prevention in strong earthquake areas.

A Study on the Influence of Sand Median Grain Size on the Short-Term Recovery Process of Shorelines

Recently, the impacts of short-term erosion caused by storm waves on coastal damages are increasingly recognized as social issues, compared to those of long-term erosion from climate change or coastal development. The erosion caused by the storm wave has an episodic characteristic that the shoreline recovers gradually after retreating for a short-term. Furthermore, if shoreline changes caused by longshore sediment transport are not taken into consideration, the shoreline position is determined by following two physical parameters based on the bulk response model. The beach response factor determines converging ultimate erosion on the assumption that incident waves constantly affects a beach, which can be estimated according to the concept of Dean’s profile. On the contrary, the beach recovery factor affects the velocity of the shoreline retreat and recovery. Therefore, the parameter plays an important role to predict the peak erosion due to the storms. However, there are still insufficient researches to utilize it as an engineering design for erosion reduction. In this study, the two methodologies (i.e., approximation formula and statistical analysis) that estimates peak erosion width caused by the storms are compared to extract the beach recovery factor. During the process, it is confirmed that peak wave height has little impact on the beach recovery factor. Instead, it is mainly determined by the median grain size. Also, the beach recovery factor is estimated as a function of median grain size based on the shoreline and sand survey data conducted over ten years. Among the 41 surveyed sites along the east coast, 11 sites of straight-type shorelines that directly react to the incident waves were applied to consider only the short-term recovery process. To prove validity, the estimated applied into the real sea and then the results were compared to the shoreline data extracted from CCTV images. Using these results, the peak erosion width for a target wave event can be predicted with only median grain size. These study results are expected to be used as a concrete and practical means to manage the coast, in preparation for the current and future shoreline erosion threats.

Simulation of Bay-Shaped Shorelines after the Construction of Large-Scale Structures by Using a Parabolic Bay Shape Equation

Among the various causes of coastal erosion, the installation of offshore breakwaters is considered the main cause that influences the most serious changes in shorelines. However, without a proper means for predicting such terrain changes, countries and regions continue to suffer from the aftermath of development projects on coastal land. It has been confirmed that the parabolic bay shape equation (PBSE) can accurately predict shoreline changes under the wave climate diffracted as a result of such development projects. This study developed a shoreline change model that has enhanced the previous shoreline change models by applying PBSE to shoreline changes into bay-shaped features. As an analytical comparison with the second term of the GENESIS model, which is an existing and well-known shoreline change model, a similar beach erosion width was obtained for a small beach slope. However, as the beach slope became larger, the result became smaller than that of the GENESIS model. The validity of the model was verified by applying it to satellite images that demonstrated the occurrence of shoreline changes caused by breakwaters for seaports on the eastern coast of Korea; Wonpyeong beach, Yeongrang beach, and Wolcheon beach. As a result, each studied site converged on the static equilibrium planform within several years. Simultaneously, the model enabled the coastal management of the arrangement of seaports to evaluate how the construction of structures causes serious shoreline changes by creating changes to wavefields.

A Novel Method for River Bank Detection from Landsat Satellite Data: A Case Study in the Vietnamese Mekong Delta

River bank (RB) erosion is a global issue affecting livelihoods and properties of millions of people. However, it has not received enough attention in the Vietnamese Mekong Delta (VMD), i.e., the world’s third largest delta, compared to salinity intrusion and flooding. There have been several studies examining RB and coastal erosion in the VMD using remotely sensed satellite data, but the applied methodology was not adequately validated. Therefore, we developed a novel SRBED (Spectral RB Erosion Detection) method, in which the M-AMERL (Modified Automated Method for Extracting Rivers and Lakes) is proposed, and a new RB change detection algorithm using Landsat data. The results show that NDWI (Normalized Difference Water Index) and MNDWI (Modified Normalized Difference Water Index) using the M-AMERL algorithm (i.e., NDWIM-AMERL, MNDWIM-AMERL) perform better than other indices. Furthermore, the NDWIM-AMERL; SMA (i.e., NDWIM-AMERL using the SMA (Spectral Mixture Analysis) algorithm) is the best RB extraction method in the VMD. The NDWIM-AMERL; SMA performs better than the MNDWI, NDVI (Normalized Difference Vegetation Index), and WNDWI (Weighted Normalized Difference Water Index) indices by 35–41%, 70% and 30%, respectively. Moreover, the NDVI index is not recommended for assessing RB changes in the delta. Applying the developed SRBED method and RB change detection algorithm, we estimated a net erosion area of the RB of –1.5 km2 from 2008 to 2014 in the Tien River from Tan Chau to My Thuan, with a mean erosion width of –2.64 m and maximum erosion widths exceeding 60 m in places. Our advanced method can be applied in other river deltas having similar characteristics, and the results from our study are helpful in future studies in the VMD.

Reliability and Change in Erosion Measurements by High-resolution Peripheral Quantitative Computed Tomography in a Longitudinal Dataset of Rheumatoid Arthritis Patients.

The aim of this multireader exercise was to assess the reliability and change over time of erosion measurements in patients with rheumatoid arthritis (RA) using high-resolution peripheral quantitative computed tomography (HR-pQCT). HR-pQCT scans of 23 patients with RA were assessed at baseline and 12 months. Four experienced readers examined the dorsal, palmar, radial, and ulnar surfaces of the metacarpal head (MH) and phalangeal base (PB) of the second and third digits, blinded to time order. In total, 368 surfaces (23 patients´ 16 surfaces) were evaluated per timepoint to characterize cortical breaks as pathological (erosion) or physiological, and to quantify erosion width and depth. Reliability was evaluated by intraclass correlation coefficients (ICC), percentage agreement, and Light k; change over time was defined by means ± SD of erosion numbers and dimensions. ICC for the mean measurements of width and depth of the pathological breaks ranged between 0.819-0.883, and 0.771-0.907, respectively. Most physiological cortical breaks were found at the palmar PB, whereas most pathological cortical breaks were located at the radial MH. There was a significant increase in both the numbers and the dimensions of erosions between baseline and follow-up (P = 0.0001 for erosion numbers, width, and depth in axial plane; P = 0.001 for depth in perpendicular plane). This exercise confirmed good reliability of HR-pQCT erosion measurements and their ability to detect change over time.

Prediction model of the collapse of bank slope under the erosion effect of wind-induced wave in the Three Gorges Reservoir Area, China

During the storage period of the Three Gorges Reservoir, the bank erosion caused by wind-induced wave is getting more serious, especially for the crushed stone soil bank. The continuous wave scouring and erosion destabilize the bank slope and even induce the occurrence of landslides. Based on the energy conservation theory, the bank slope will reach a stable state after continuous wave erosion. Regarding this, this paper derives the prediction formula of the stable slope angle and erosion width when the wave erodes the crushed stone soil bank slope. Model tests on bank slopes with different dry densities and different crushed stone contents under the action of waves were conducted to observe the erosion process of wave-induced crushed stone soil bank slope and verify the proposed prediction formula. The results show that under the action of wave erosion, erosion ridge and collapse steep angle would form at the upper edge of the bank slope and the controlling factors of this process are the dry density of the crushed stone soil and the wave energy. When the content of crushed stone soil gradually increases, the ability of the bank slope to resist wave erosion weakens at first and then gradually strengthens. Comparing the erosion stable slope angle obtained from the model tests with the calculated results using the proposed prediction formula, a linear relationship could be observed, indicating that the proposed prediction formula is reliable for further analysis.

A new one-dimensional numerical model for unsteady hydraulics of sediments in rivers

This paper presents the model UMHYSER-1D (Unsteady Model for the HYdraulics of SEdiments in Rivers 1-D), a one-dimensional hydromorphodynamic model capable of representing water surface profiles in a single river or a multiriver network, with different flow regimes considering cohesive or non-cohesive sediment transport. It has both steady and unsteady flow and sediment modules. For steady gradually varied flows, UMHYSER-1D uses the standard step method to solve the energy equation and the “NewC” scheme for the de St Venant equations. For sediment transport, UMHYSER-1D uses two methods: for long-term simulation, the unsteady terms of the sediment transport continuity equation are ignored, and a non-equilibrium sediment transport method is used. For short-term simulation, the convection–diffusion equation, with a source term arising from sediment erosion/deposition is solved using the fractional step method. The equation without the source term is solved with an implicit finite-volume method, then the equation with source term is solved. Internal boundary conditions, such as time-stage tables, rating curves, weirs, bridges, and gates are simulated. Incorporated is the active layer concept, which allows selective erosion, enabling the simulation of bed armoring. Non-cohesive sediment transport equations and cohesive sediment physical processes are applied to calculate the sediment deposition and erosion. Finally, UMHYSER-1D empirically accounts for bed geometry adjustments by using a relationship between erosion width and flow rate, an angle of repose condition for bank stability and three minimization theories. The presented validation and application cases show UMHYSER-1D’s capabilities and predicts its promising role in solving complex, real engineering cases.

Erosion Control Line (ECL) Establishment Using Coastal Erosion Width Prediction Model by High Wave Height

Erosion Control Line (ECL) Establishment Using Coastal Erosion Width Prediction Model by High Wave Height

Riverbank Stability Assessment under River Water Level Changes and Hydraulic Erosion

The dominant mechanism of riverbank cantilever failure is soil erosion of the bank toe and near bank zone. This paper demonstrates that the shape of the riverbank cantilever failure depends on the properties of the soil and the fluctuation of the river water level (RWL). With a stable RWL, a riverbank with higher resistance force leads to failure with larger and deeper overhang erosion width. When RWL rises, a less cohesive soil bank will be eroded over a larger width and riverbank failure will occur earlier. With a low rate of rising RWL, riverbank failure may happen in a type of mass failure. With a high rate of rising RWL, a riverbank will fail in a type of overhang riverbank failure, with the soil erosion rate being the main affected factor.

Calculation Model of Soil Dam Wash-Away Due to Overflow

Water flow over soil dam crest causes its fast failure. Break-through wave being formed in dam ebb side leads to drastic economic and social consequences. Accuracy in calculation of the break-through wave parameters depends on the accuracy of discharge hydrograph construction in the dam erosion site. A calculation scheme for soil dam wash-away due to overflow has been devised on the basis of the experimental data. Wash-away process is divided in two stages in accordance with the devised scheme. Wash-away of the downstream toe occurs at the first stage. The crest level from the side of upstream edge remains constant. Intensive crest lowering is observed at the second stage. The eroding body is considered to have a shape of a round-crested weir. In such a case the washed-away massif has a form of nappe-shaped crest profile. A mathematical model has been developed on the basis of this scheme and according to this model equations of deformation and flow motion are considered simultaneously. The model is consistent in a good way with physical erosion pattern during fast flood rise and when the erosion width is known; the model is recommended for calculation of breaching sections in reserve water outlets. In general case and when the width is unlimited (three-dimensional problem) calculation formulae have one more unknown variable that is flow width within the erosion site. The paper describes peculiar features in physiccal erosion pattern for such case and a number of the known formulae for determination of the erosion have been given and analyzed in the paper. The equation which fits in a good way in the proposed mathematical model has been chosen, and it provides the possibility to adapt the model for three-dimensional erosion conditions. Calculations made in accordance with the proposed methodology make it possible to construct discharge hydrograph in the dam erosion site.

Definition for Rheumatoid Arthritis Erosions Imaged with High Resolution Peripheral Quantitative Computed Tomography and Interreader Reliability for Detection and Measurement.

High-resolution peripheral quantitative computed tomography (HR-pQCT) sensitively detects erosions in rheumatoid arthritis (RA); however, nonpathological cortical bone disruptions are potentially misclassified as erosive. Our objectives were to set and test a definition for pathologic cortical bone disruptions in RA and to standardize reference landmarks for measuring erosion size. HR-pQCT images of metacarpophalangeal joints of RA and control subjects were used in an iterative process to achieve consensus on the definition and reference landmarks. Independent readers (n = 11) applied the definition to score 58 joints and measure pathologic erosions in 2 perpendicular multiplanar reformations for their maximum width and depth. Interreader reliability for erosion detection and variability in measurements between readers [root mean square coefficient of variation (RMSCV), intraclass correlation (ICC)] were calculated. Pathologic erosions were defined as cortical breaks extending over a minimum of 2 consecutive slices in perpendicular planes, with underlying trabecular bone loss and a nonlinear shape. Interreader agreement for classifying pathologic erosions was 90.2%, whereas variability for width and depth erosion assessment was observed (RMSCV perpendicular width 12.3%, axial width 20.6%, perpendicular depth 24.0%, axial depth 22.2%; ICC perpendicular width 0.206, axial width 0.665, axial depth 0.871, perpendicular depth 0.783). Mean erosion width was 1.84 mm (range 0.16-8.90) and mean depth was 1.86 mm (range 0.30-8.00). We propose a new definition for erosions visualized with HR-pQCT imaging. Interreader reliability for erosion detection is good, but further refinement of selection of landmarks for erosion size measurement, or automated volumetric methods, will be pursued.

Critical caving erosion width for cantilever failures of river bank

The cantilever failure is one of the typical bank failures, in which the lateral caving erosion at the bottom of the bank plays an important role. When the caving erosion width is larger than a certain value, the cantilever failures such as shear, toppling and stress failures may occur. In order to understand the condition of the cantilever failure, the collapse mechanisms of the cantilever failures are studied based on the bank stability theory and flume experiment. According to the bank stability equation with the lateral erosion, the critical caving erosion width (CCEW) formulas for the shear and toppling failures of simple slope bank were derived in this paper. The formulas show that the CCEW increases as the overhanging soil thickness and soil cohesion increase, and decreases as the crack depth on the bank surface and the slope angle of the bank increase. And these formulas were tested with experimental data, which shows the predicted values are good agreement with experimental data. The paper reveals a quantitative expression on the process of the river cantilever failure.

Automated three-dimensional registration of high-resolution peripheral quantitative computed tomography data to quantify size and shape changes of arthritic bone erosions.

To monitor size and shape changes of bone erosions and changes in BMD in the vicinity of the erosion and in the periarticular trabecular compartment of patients with RA using high-resolution peripheral quantitative CT (HR-pQCT) imaging and to compare an automated three-dimensional (3D) image processing technique with manual measurements of erosion width and depth. The shape of 40 bone erosions and composition of bone around the erosions were analysed in the MCP joints of 22 RA patients both manually and by semi-automated 3D image processing at two different time points. Periosteal segmentation was performed using volume growing and morphological operations. Image registration was applied for transfer of baseline segmentations to follow-up datasets. Eight erosions decreased in size, 6 increased and 28 remained stable. Increasing erosions were more spherical and smaller at baseline compared with decreasing or stable erosions. BMD in the vicinity of shrinking erosions increased, while it decreased next to expanding erosions. There was moderate agreement in the determination of erosion volume between semi-automated and manual measurements, but agreement was poor when assessing changes in volume over time. Longitudinal changes in erosion size and shape and of BMD in the vicinity of an erosion can be measured. BMD changes are associated with progression and regression of erosions. However, the semi-automated and manual approaches did not classify longitudinal changes of erosion volume in the same way. Further research is necessary to define the nature of these differences.

Effect of soil composition on piping erosion of earthen levees

ABSTRACTInternal erosion processes due to piping in an earthen levee built in a laboratory flume are reported in this paper. Different sand, silt and clay mixtures are used for constructing the levee. An image processing technique using an edge-detection algorithm is successfully applied to track the erosion process from the recordings of both side and bottom views. The change in the depth of erosion during the piping phenomenon for different soil composition is studied. The results show that small changes in clay content in the soil mixtures significantly affect the erosion rate. The average depth is approximately equal to the average bottom width of erosion in the piping zone. An exponential equation to estimate the depth of erosion as a function of time and the coefficient of soil erodibility is presented. Results for the critical shear stress and the coefficient of soil erodibility agree well with those obtained from the hole erosion test but not with those obtained from the jet erosion test.

Experiment and Simulation of Earthen Embankment Breach

Many studies of earthen embankment failure from overtopping flow have been conducted in various aspects. Most of them focused on the mechanism of breach, depth and width of erosion, and breach hydrograph. The results were obtained either from both physical and numerical modeling and/or coupling techniques. However, a physical hydraulic model of the effect of breach mechanism under three types; overtopping, beneath structure and piping hole have not been studied. Fixed embankment slopes with scale of 1:8.5 were employed to perform the experiment. It was found that the piping hole case at the toe of embankment was the most severe damage. The iRIC Nays2D numerical model shows a good performance of simulated results in both water flow and breach morphological characteristics, indicating that the model simulation is reasonable.

Effect of raindrop splash and transversal width on soil erosion: Laboratory flume experiments and analysis with the Hairsine–Rose model

The parameter consistency of the one-dimensional Hairsine-Rose (H-R) erosion model under conditions of significant rainfall splash was examined. To account for the splash characteristic length scale and its interaction with the transverse erosion width, experiments were carried out using erosion flumes of the same length (6 m), but different widths, with sediment concentrations measured at the flume exits. Total sediment concentration and the concentration of seven size fractions ( 1000 µm) were measured at high rainfall intensity (60 mm/h) and with a gentle slope (2.2%). The conditions employed ensured that erosion was predominantly precipitation-driven. The experimental results showed that raindrop splash affected particularly the sediment breakthrough from the wider flumes (flumes 1 and 2, 1- and 0.5-m wide, respectively). However, the raindrop splash effect was less significant in observed sediment concentrations from the narrower flumes (flumes 3 and 4, both 0.25-m wide). For these flumes, the detached sediment was affected by the transversal width of the flume in that an amount of detached sediment adhered to the barriers instead of being removed in the overland flow. The one-dimensional H-R model was fitted to the experimental results and good agreement was found, in particular for the finer size classes. The data for the coarser grain sizes were more scattered, suggesting sediment motion by mechanisms other than as a suspension in the overland flow (e.g., rolling along the soil surface). The optimized parameters indicated that the shield layers (where the shield consists of redeposited eroded sediment) of the wider flumes (1 and 2) developed within 5-10 min from the start of the experiment, whereas in the narrower flumes (3 and 4) they never fully developed. The optimized detachment rates were consistent with previous findings, but the estimated thickness of the deposited layer was too small to provide complete protection of the original soil against raindrop detachment, indicating that the shield was not uniform. The experimental design allowed us to investigate directly the effect of flow non-uniformity on soil erosion by inclusion of an offset drainage point in flume 4. The observations taken during and after the experiment, as well as surface elevation data, confirmed the noticeable impact of non-uniform flow on the erosion process.

Ability of ultrasound imaging to detect erosions in a bone phantom model

ObjectivesThe authors examined the validity, interobserver reliability and interscanner variation in detecting bone erosions with ultrasonography using a custom-made phantom.Methods21 bovine bones were used. Artificial erosions were made into 15...

PHYSICAL MODELING OF OVERTOPPING EROSION AND BREACH FORMATION OF COHESIVE EMBANKMENTS

The formation process and timing of a dam embankment breach caused by flood overtopping can dramatically impact the rate at which water is released from a reservoir and directly impacts the hazard to life and property downstream of a breached dam. Therefore, dam embankment erosion processes and the rate of breaching from overtopping events are important to both engineers and planners alike, who must predict impacts on local communities and surrounding areas affected by flooding. There is a distinct difference between the erosion processes of non-cohesive and cohesive embankments during overtopping. The USDA-ARS has conducted seven large-scale overtopping failure tests on cohesive embankments ranging in height from 1.5 to 2.3 m. The purpose of this study is to: (1) establish a better understanding of the erosion process of overtopped cohesive embankments, and (2) provide detailed data for future numerical model development, validation, calibration, and testing. Three soils were tested, two non-plastic SM silty sand materials and a CL lean clay. A four-stage breach erosion process was observed for cohesive embankments. The primary erosion processes observed and reported in this article for cohesive embankments during stages 2 and 3 were headcut migration and erosion widening. The rate of these two processes was observed to vary by several orders of magnitude and was observed to be strongly dependent on the soil material properties.

IMAGE–BASED EROSION MEASUREMENT TECHNIQUE

Two and three dimensional analysis using closerange digital photographs can be very useful in measuringchanges in erosion on the landscape. Computer software exists for conducting photographic analysis but it is often either costprohibitive or very labor intensive to use. This article describes a simple 2D imagebased technique used to conduct simplemeasurements photographically using software that would typically already be in use in an engineering office (i.e. CAD,image editing, and spreadsheet programs). The technique is very repeatable and results in reliable measurements whencompared to actual physical measurements. The accuracy of using these measurements was evaluated by comparingphysically measured distances and photographically measured distances between parallel ropes on the landscape. Thestandard error was 17 mm with a coefficient of determination of 1.0 for the linear regression. The overall mean absolutedeviation of residuals was 18 mm and the maximum absolute residual was 52 mm. The application selected for this articleis the documentation of the extent and width of erosion during an embankmentovertopping test. This technique wasdemonstrated to be an effective method for measuring distances and locations on the landscape.