Headcut Migration Research Articles

Experimental Investigation of Breach Mechanism for Overtopped Cohesive and Non-Cohesive Embankments

The failure of an embankment causes loss of lives, massive damage to infrastructure and the interruption of basic facilities; it has thus drawn increasing attention from researchers. When compared to other types of embankment disasters, overtopping-related embankment breaches are much more frequent. The study of the breach mechanism of embankments due to overtopping is becoming more and more essential for developing evacuation plans, early warning systems and damage assessment. To recognize the breach activities of embankments, it is necessary to find out discrete breach considerations like breach depth, breach initiation, breach width, etc. In the present study, a total of six tests were performed in a narrow flume using an embankment model. By conducting different experiments, it was observed that embankment breaching may be described in three stages, i.e., initial erosion, headcut erosion and lateral erosion. Furthermore, erosion is a three-dimensional process that occurs during embankment breaching, with the majority of erosion movement being associated with lateral broadening. The rate of headcut migration also has an impact on the widening rate. Furthermore, it depends upon the type of fill material and dam geometry. Also, the observed effect of moisture content on breach widening proved that the rate of widening was strongly influenced by water content. A drop of about 50% in moisture content causes approximately a 20% decrease in time to failure. In the present study, it is observed that breach shape could not be assumed to be regular shape like rectangle or trapezoid, as described in the literature. The trials were carried out in a narrow flume under constant hydraulic conditions, which are two of the study’s limitations.

Headcut Migration in Earthen Embankment Induced by Varying Sub-surface and Seepage State under Overflow

Headcut Migration in Earthen Embankment Induced by Varying Sub-surface and Seepage State under Overflow

Experimental study on predicting head-cut migration rate of check dams

Head-cut erosion is the primary mechanism causing overtopping-induced breaches of check dams. Furthermore, the dam fill soil properties directly influence the head-cut migration rate. Although the fill materials of most flume model tests are cohesive soils, there are no experimental studies on loess materials with low erosion resistance. Accordingly, this study conducted 26 groups of flume model tests on the check dam head-cut migration mechanisms. Furthermore, it comprehensively analyzed the factors influencing the characteristics of head-cut migration in check dams, namely compactness, water content, inflow, and head-cut height, from the macro-and micro-viewpoints. The head-cut erosion rate models of compacted loess were developed considering multiple factors. A nonlinear multiple head-cut migration coefficient regression model was developed using the energy dissipation theory, the findings from the head-cut erosion tests, and experimental results from other studies, while considering the water content, compactness, clay content, inflow, and head-cut height as inputs. Seven sets of measured data with different erosion resistances were selected to verify the rationality and accuracy of the proposed model. In general, the sensitivity analysis results showed that the model could be used for cohesive soil with strong erosion resistance and silty sand and loess with weak erosion resistance. Its generalization and prediction accuracy have been further improved compared to other models of the same type.

Anthropogenic channel network development in forested watersheds by recent stream channelization practices in Mark Twain National Forest, Missouri Ozarks

Human modifications of stream systems often result in channel instability and sediment pulse- induced problems. While previous research explored the direct anthropogenic impacts of channelization on fluvial systems, the history of repeated channelization, their persistent impacts on headwater streams and subsequent evolution of a drainage system need further investigation. This study evaluates the spatial distribution of channel form and stability in Big Barren Creek watershed, which drains the karst dominated Ozark Highlands of southeast Missouri. The objectives of this research are threefold: (i) describe channel morphology and hydrology in undisturbed and disturbed segments based on field data, (ii) propose a conceptual model of channel modification and response to explain the patterns of channel adjustment and (iii) evaluate the history of channel disturbance using historical aerial photograph analysis. Results show that disturbed reaches have larger channel dimensions than undisturbed reaches because channelization increased stream power and shear stress, particularly for channels that are actively incising. Channelized reaches are primarily identified on private land where headcuts developed and migrated upstream to the national forestland. Sediment supply to the channel increases from both upstream incision and bank and levee collapse resulting in downstream aggradation, which forces landowners to repeat channelization for flood control. The proposed conceptual model suggests that while the disturbed segments evolve into wider and deeper channels following channelization, they exhibit the potential to become stable over time because of biogeomorphic resistance (e.g., in-channel vegetation, armored-cohesive soil) related to the ephemeral nature of the streams in this karst region. This idea is also supported by the slower average headcut migration rate of earlier channelization (2 m/yr) compared to recent channelization (6–8 m/yr). However, channel adjustment largely depends on repeated channelization that resets the evolutionary stages that preclude this fluvial system from attaining stability.

Root Distribution and Soil Properties of Gully Heads and Their Effects on Headcut Migration in the Mollisols Region of Northeast China

Previous studies have proved that root distribution along gully headwalls greatly alters soil properties and further affects the soil erodibility of gully heads. However, it is not clear whether the gully headcut migration is affected by root distribution and soil properties. Five representative gullies developed in different land uses were selected to clarify the variations of root distribution and soil properties and their effects on headcut migration in the rainy season (May to October 2021) in the Mollisols region of northeast China. Results showed that the 68.4%–93.3% of root mass density and 65.6–88.5% of root length density were concentrated in 0–30 cm soil layer of gully heads, and the roots of <2.0 mm accounted for >85%. The gullies developed in farmlands had relatively higher soil compactness, shear strength and aggregate stability, but lower organic matter (OMC), disintegration capacity and soil permeability than those developed in woodlands, unpaved roads in farmland and stable gully-beds. Changes in soil properties of gully heads were closely related to root density. The linear, areal, and volumetric migration rate of gully heads varied greatly and were 1.07–35.11 m yr−1, 28.95–562.46 m2 yr−1 and 56.82–6626.37 m3 yr−1, respectively, with the average of 9.07 m yr−1, 156.92 m2 yr−1 and 1503.02 m3 yr−1, respectively. The change in headcut migration rate was significantly affected by root density, soil properties and drainage area, of which soil texture, OMC, soil aggregate structure, and the drainage area were the critical factors influencing headcut migration in the Mollisols region of northeast China.

Application of the Limit equilibrium method to the headcut migration of levee breaching

The headcut migration describes the physical process of the levee side slope retreat and the headcut length governs the breach widening. As a typical mode of slope stability due to soil tensile failure, the limit equilibrium method was used for the calculation of the headcut length. By considering the soil tensile stress state, the Hoek-Brown failure criterion provides a reasonable description of the levee material response. Then, the headcut length was calculated by using LEM in Slope/W. The comparisons with a large scale test show that the calculated headcut length by using LEM in Slope/W has good agreements with the measured data.

A Soil Tensile Strength Based Headcut Migration Model of Breach Side Slope

The headcut migration describes the physical process of breach side slope retreat that governs the widening of the breach. Modeling the growth of a breach due to embankment failure is the first step in mapping the resulting inundation in a floodplain. As removal of soil from the toe of the headcut effectively removes physical support for the upper part, the headcut fails on the plane normal to the direction of tensile stress. This process is a typical mode of tensile failure. A numerical model of the headcut migration was established by integrating the effects of the soil tensile strength, soil permeability and embankment geotechnical characteristics. Thus, a simple analytical equation was finally obtained to predict the critical length of the headcut. Furthermore, the presented model was verified by using the limit equilibrium method (LEM) for three typical embankment scales (2, 4 and 6 m high). The comparisons between the present model and the LEM show good agreements. The present model could provide a simple method to predict the critical length of the headcut migration and easily be adopted to breach widening models.

Channel incision by headcut migration: Reconnection of the Colorado River to its estuary and the Gulf of California during the floods of 1979–1988

AbstractThe macrotidal Colorado River Delta at the northern end of the Gulf of California in Mexico is hydrologically complex. We review historical accounts, data, field notes and photographs to evaluate the hydrological processes active on the delta prior to the advent of upstream dams. We also employ satellite imagery as well as recent LIDAR data to illustrate the critical role played by headcut erosion in restoring the river's fluvial/tidewater connection during the 1979–1988 floods. Prior to human manipulation, the river's contribution of fresh water to the Gulf was periodically interrupted by natural overflowing, avulsing, and flooding into the sub‐sea level Salton Sink on the north slope of the delta plain. River flow south towards the Gulf was also subject to occasional overflow into Laguna Salada, another sub‐sea level basin. In the mid‐20th century, the Delta was disconnected from its fluvial supply following installation of upstream dams and reservoirs. A tidal sediment obstruction developed in the estuary channel, forming a final barrier to fluvial connectivity. Release of Colorado River floodwaters into Mexico between 1979 and 1988 provided a natural experiment on the hydrological response of a long‐disconnected macrotidal delta to restoration of fluvial supply.

The role of soil pipe and pipeflow in headcut migration processes in loessic soils

AbstractHeadcut formation and migration was sometimes mistaken as the result of overland flow, without realizing that the headcut was formed and being influenced by flow through soil pipes into the headcut. To determine the effects of the soil pipe and flow through a soil pipe on headcut migration in loessic soils, laboratory experiments were conducted under free drainage conditions and conditions of a perched water table. Soil beds with a 3‐cm deep initial headcut were formed in a flume with a 1.5‐cm diameter soil pipe 15 cm below the bed surface. Overland flow and flow into the soil pipe was applied at a constant rate of 68 and 1 l min−1 at the upper end of the flume. The headcut migration rate and sediment concentrations in both surface (channel) and subsurface (soil pipe) flows were measured with time. The typical response was the formation of a headcut that extended in depth until an equilibrium scour hole was established, at which time the headcut migrated upslope. Pipeflow caused erosion inside the soil pipe at the same time that runoff was causing a scour hole to deepen and migrate. When the headcut extended to the depth of the soil pipe, surface runoff entering the scour hole interacted with flow from the soil pipe also entering the scour hole. This interaction dramatically altered the headcut processes and greatly accelerated the headcut migration rates and sediment concentrations. Conditions in which a perched water table provided seepage into the soil pipe, in addition to pipeflow, increased the sediment concentration by 42% and the headcut migration rate by 47% compared with pipeflow under free drainage conditions. The time that overland flow converged with subsurface flow was advanced under seepage conditions by 2.3 and 5.0 min compared with free drainage conditions. This study confirmed that pipeflow dramatically accelerates headcut migration, especially under conditions of shallow perched water tables, and highlights the importance of understanding these processes in headcut migration processes. © 2020 John Wiley & Sons, Ltd.

An experimental study on the effects of grass root density on gully headcut erosion in the gully region of China's Loess Plateau

AbstractVegetation plays an important role in gully headcut erosion in China's Loess Plateau, but little is known about the effects of root density on gully headcut erosion. This study attempted to investigate the effects of grass root density on gully headcut erosion and morphological development of the gully head using plots with different grass root densities (with bare land as the control). The experiment was performed on plots with different grass root densities, and the rainfall intensity and inflow discharge increased throughout the experiment. The results showed that headcut migration in bare land was mainly activated by upstream flow incision, headwall erosion, and plunge pool erosion, whereas headcut migration in grassland was driven by soil‐root matrix collapse at the headcut, headwall erosion, and plunge pool erosion. The soil loss rate (SLR), gully headcut retreat distance (GRD), gully area (GA), and upstream soil loss volume (SLVU) in grassland plots with different root densities were 45.64–68.45%, 66.97–85.38%, 69.26–78.18%, and 67.89–87.02% less than those in the bare land plots, respectively. However, as root density increased, the gully depth in the grassland plots increased from 19% to 59%, and the proportion of gully head soil loss volume (SLVGH) to the total soil loss volume increased from 63.37% to 88.37%. The SLR, GRD, GA, and SLVGH showed decreasing trends as the root density increased, as described by a Hill curve. Moreover, roots with diameters of 0–0.5 mm had greater effects on soil loss and morphological evolution than roots with larger diameters. Our results provide a reference for the reasonable selection of grass root density for controlling gully headcut erosion in China's Loess Plateau.

Monitoring of avulsion channel evolution and river morphology changes using UAV photogrammetry: Case study of the gravel bed Ondava River in Outer Western Carpathians

This paper presents results from monitoring the chute cutoff in the meander bend of the Ondava River in Eastern Slovakia. An avulsion channel was formed in the central part of the meander neck during 2010 flood events, and here we describe the mechanism of evolution and post‐cutoff avulsion channel adjustment using drones, unmanned aerial vehicle (UAV) photogrammetry and field survey. Monitoring by UAV images began on 15 June 2012 with 78 processed images, followed by 259 images during April 2014 and 375 from 18 July 2014. The majority of UAV digital elevation model (DEM) errors in the study area were associated with vegetation cover, with the average vertical root mean square error (RMSE) of the UAV‐DEM on bare ground at 0.209 m compared with 0.673 m in vegetated areas. The chute cutoff was formed by floodplain headcutting during meander neck overflow and headcut migration was directed by floodplain sediment structure and land use. Although low river discharge after the 2010 floods stabilised the avulsion channel by vegetation succession, recurrent two‐yearly interval flooding increased the avulsion channel bank erosion from 36.9 m3/month (June 2012–April 2014) to 425.6 m3/month (April 2014–July 2014).

Numerical model for homogeneous cohesive dam breaching due to overtopping failure

Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive dam breaching mechanisms and we calculate the time-averaged headcut migration rate using an energy-based empirical formula. A numerical method is adopted to determine the initial scour position at the downstream slope in terms of the water head and dam height, and the broad-crested weir equation is utilized to simulate the breach flow. The limit equilibrium method is used to analyze the stability of breach slope during the breach process. An iterative method is developed to simulate the coupling process of soil and water at each time step. The calculated results of three dam breach cases testify the reasonability of the model, and the sensitivity studies of soil erodibility show that sensitivity is dependent on each test case’s soil conditions. In addition, three typical dam breach models, NWS BREACH, WinDAM B, and HR BREACH, are also chosen to compare with the proposed model. It is found that NWS BREACH may have large errors for cohesive dams, since it uses a noncohesive sediment transport model and does not consider headcut erosion, WinDAM B and HR BREACH consider headcut erosion as the breaching mechanism and handle well homogeneous cohesive dam overtopping failure, but overall, the proposed model has the best performance.

Ephemeral gully channel width and erosion simulation technology

Concentrated surface runoff, such as associated with ephemeral gully channels, increases erosion and transfers fine sediment and associated agrichemicals from upland areas to stream channels. Ephemeral gully erosion on cropland may contribute up to 40 % or more of the sediment delivered to the edge of agricultural fields, significantly threatening the health of downstream ecological services. Typically, conservation practices developed for sheet and rill erosion are also expected to treat ephemeral gully erosion, but technology and tools are needed to account for the separate benefits and effects of practices on various sediment sources. Without improved research studies, subjective observations will continue to be used to satisfy quality criteria in lieu of scientifically defensible, quantitative methods to estimate the impact of gully erosion. Ephemeral gully channels evolve by one, or combination of, complex physical process in the form of incision, headcut migration upslope, and channel sidewalls expansion (widening). This study focused on the latter, ephemeral gully channel widening relationships. The impact of various width functions on erosion can be very significant and is dependent on discharge, slope, soil properties, and management conditions. A description is provided on six ephemeral gully widening relationships, followed by recommended improvements, comparative application, and identification of future research needs. Improvements in the development of ephemeral gully width algorithms are critical to understanding the impact of conservation practices on controlling ephemeral gully erosion. Tools are needed to predict and quantify ephemeral gully erosion, including the capability to evaluate the effect of conservation practices to control erosion. An improved critical shear stress equation was developed and described that provides an approach to incorporating impacts of management practices on the resulting gully erodibility. Conservation management planning by organizations needs a systematic approach to determining the extent of ephemeral gully erosion problems on a field, watershed, or national basis, or to predict the recurring or new locations of ephemeral gullies prior to their development.

Experimental study on scour and erosion of blocked dam

This paper presents new experimental data of the erosion rate and sediment transport rate during the processes of dam break caused by overtopping. In order to study the headcut migration, the erosion coefficient was calculated and its peak value was determined near the downstream edge of the dam crest. Then the characteristics of vertical erosion during dam break processes were analyzed by dividing the dam into three regions: the upstream region, middle region, and downstream region. The three regions show different features during headcut migration, but all are exposed to the most intense erosion at the third stage of the dam break process. Finally, three relevant parameters affecting sediment transport were discussed: the length of the dam crest, the inner slope, and the dam composition. The results show that a longer dam crest and flatter inner slope reduce the peak sediment transport rate and prolong the arrival time of peak sediment transport rate; and with the increase of the non-uniformity coefficient S, the peak sediment transport rate initially increases, and then decreases.

Movable-bed coupled analysis model of overtopping failure of concrete face sandy gravel dam

The concrete face holds water in the entire overtopping-induced break process of the concrete face sandy gravel dam. Water flow discharges over the concrete face and engenders reverse vortex. The shear stress of the reverse vortex vertically erodes the dam body. Traditional decoupled mathematical models of concrete face sandy gravel dams are based on simplified conservation equations and are not applicable. A movable-bed coupled analysis model of overtopping failure of concrete face sandy gravel dam is presented in the paper. This model includes the solid–liquid two-phase turbulent flow mathematical model and the sediment incipience module. The sediment incipience module involves bed load surface normal direction, shear stress of vortex and angle of repose. The model was applied to the experiment of overtopping failure of concrete face sandy gravel dam. The model was tested against experimental data, with reasonably good agreement between numerical results and measurements. This shows that this mathematical model can simulate the entire break process of concrete face sandy gravel dams in a meticulous and accurate way, and can clearly depict head-cut migration. Therefore, it is reasonable to believe that this model can serve as an effective tool for further study on the mechanism of overtopping failure of concrete face sandy gravel dams.

Geomorphological and riparian vegetation responses following a low-head dam removal: a study based on literature review

ABSTRACTMore and more low-head dam structures have deteriorated in recent years. Unlike the large dam, the geomorphological and ecological impacts of a low-head dam removal have not been quantified with insufficient monitoring data on pre- and post-removal. Therefore, this study intends to identify the low-head dam removal impacts on geomorphology and riparian vegetation based on previous studies. The characteristics of stored sediment in the impoundment play a critical role for geomorphological responses on a low-head dam removal creating a knickpoint and promoting a headcut migration. These geomorphological changes often form a new floodplain and create enough room for riparian vegetation establishment. The river geomorphology after a low-head dam removal can be a state of quasi-equilibrium within about a decade. In this state, a newly formed floodplain tends to be colonized by riparian vegetation in many low-head dam removal cases. After a decade to several decades, the riparian vegetation in the floodplain often develops to tree plants.

Evaluating sediment transport capacity relationships for use in ephemeral gully erosion models

Abstract. On cropland, ephemeral gully erosion in the USA may contribute up to 40% of the sediment delivered to the edge of the field. Well-tested, physically- and process-based tools for field and watershed scale prediction of gully erosion are lacking due to the fact that the complex nature of migrating headcuts is poorly understood. Understanding sediment transport capacity downstream of migrating headcuts is essential, as sediment deposition often leads to temporary storage that controls downstream water elevation, which in turn affects the rate of headcut migration. Current process-based gully erosion prediction technology used by the Agricultural Research Service (ARS) is based on characterizing the headcut migration rate, which requires the deposition depth as input to the model. Alternatively, the deposition depth can be calculated if downstream sediment transport capacity can be predicted. Data collected at the ARS-National Sedimentation Laboratory were used to test existing sediment transport relationships for the five sediment size classes (clay, silt, sand, small aggregates, large aggregates) typically used in ARS soil erosion models. The results show that the transport rate can be satisfactorily predicted for sand and large aggregate size fractions using common transport relationships based on unit stream power theory. The fractional content of the sand and large aggregate size classes can be computed using standard relationships, which are based on soil texture, previously developed by ARS. The transport of clays, silts and small aggregates is detachment limited and must therefore be computed using improved soil detachment relationships for ephemeral gullies.

Experimental Investigation of the Effects of Soil Properties on Levee Breach by Overtopping

Levee failure due to overtopping during floods is a common phenomena. An experimental study was conducted in the hydraulics laboratory, University of South Carolina, to develop an understanding of the effects of soil properties on the breaching process of earthen levees. A total of eight experiments were conducted. A new methodology to measure the subaqueous breach evolution has been developed and validated. Measurements of breach width evolution and headcut migration are shown to be related to soil properties. Inclusion of noncohesive, silt size crushed silica in the levee material (45% by weight) significantly reduced the peak discharge and breach evolution time compared to a levee constructed with sand alone. Increase in kaolin clay in the levee material led to an increase in unconfined compressive strength which in turn increased resistance to levee failure. Nondimensional equations relating the breach width evolution and headcut migration to the soil properties have been developed by performing a multivariate analysis of the experimental data.

Predicting the susceptibility to gully initiation in data-poor regions

Permanent gullies are common features in many landscapes and quite often they represent the dominant soil erosion process. Once a gully has initiated, field evidence shows that gully channel formation and headcut migration rapidly occur. In order to prevent the undesired effects of gullying, there is a need to predict the places where new gullies might initiate. From detailed field measurements, studies have demonstrated strong inverse relationships between slope gradient of the soil surface (S) and drainage area (A) at the point of channel initiation across catchments in different climatic and morphological environments. Such slope–area thresholds (S–A) can be used to predict locations in the landscape where gullies might initiate. However, acquiring S–A requires detailed field investigations and accurate high resolution digital elevation data, which are usually difficult to acquire. To circumvent this issue, we propose a two-step method that uses published S–A thresholds and a logistic regression analysis (LR). S–A thresholds from the literature are used as proxies of field measurement. The method is calibrated and validated on a watershed, close to the town of Algiers, northern Algeria, where gully erosion affects most of the slopes. The gullies extend up to several kilometres in length and cover 16% of the study area. First we reconstruct the initiation areas of the existing gullies by applying S–A thresholds for similar environments. Then, using the initiation area map as the dependent variable with combinations of topographic and lithological predictor variables, we calibrate several LR models. It provides relevant results in terms of statistical reliability, prediction performance, and geomorphological significance. This method using S–A thresholds with data-driven assessment methods like LR proves to be efficient when applied to common spatial data and establishes a methodology that will allow similar studies to be undertaken elsewhere.

Arroyo channel head evolution in a flash-flood–dominated discontinuous ephemeral stream system

We study whether arroyo channel head retreat in dryland discontinuous ephemeral streams is driven by surface runoff, seepage erosion, mass wasting, or some combination of these hydrogeomorphic processes. We monitored precipitation, overland flow, soil moisture, and headcut migration over several seasonal cycles at two adjacent rangeland channel heads in southern Arizona. Erosion occurred by headward retreat of vertical to overhanging faces, driven dominantly by surface runoff. No evidence exists for erosion caused by shallow-groundwater–related processes, even though similar theater-headed morphologies are sometimes attributed to seepage erosion by emerging groundwater. At our field site, vertical variation in soil shear strength influenced the persistence of the characteristic theater-head form. The dominant processes of erosion included removal of grains and soil aggregates during even very shallow (1–3 cm) overland flow events by runoff on vertical to overhanging channel headwalls, plunge-pool erosion during higher-discharge runoff events, immediate postrunoff wet mass wasting, and minor intra-event dry mass wasting on soil tension fractures developing subparallel to the headwall. Multiple stepwise linear regression indicates that the migration rate is most strongly correlated with flow duration and total precipitation and is poorly correlated with peak flow depth or time-integrated flow depth. The studied channel heads migrated upslope with a self-similar morphologic form under a wide range of hydrological conditions, and the most powerful flash floods were not always responsible for the largest changes in landscape form in this environment.