Bed Scour Research Articles

Flow processes near smooth and rough (concave) outer banks in curved open channels

Flow processes near the (concave) outer bank in curved river reaches are investigated in a laboratory flume, with focus on the influence of the bank roughness. An outer‐bank cell of reversed secondary flow occurs for all the investigated roughness configurations of the outer bank. The cell widens the outer‐bank boundary layer, which reduces the flow forcing on the bank, but also advects high‐momentum fluid toward the lower part of the bank, which enhances the flow forcing on the bank. Increasing the roughness of the outer bank causes a considerable widening and strengthening of the outer‐bank cell, which amplifies both effects on the flow forcing. The widening of the outer‐bank boundary layer induced by the outer‐bank cell reduces the effective width of the channel, i.e., the width where most of the discharge is conveyed, which increases significantly the sediment transport capacity in the central part of the channel. The near‐bank processes are qualitatively similar but show considerable quantitative variations around the bend. The outer‐bank cell reaches its maximum strength in the zone that is most vulnerable to bed scour and bank erosion, which corroborates its morphological relevance. The outer cell is mainly generated by reversed near‐surface gradients in the profile of the streamwise velocity. The anisotropy of the cross‐stream turbulence is the major mechanism opposed to the outer‐bank cell. Increasing roughness of the outer bank amplifies all dominant mechanisms but does not modify their relative importance. The relevance of the experimental results for natural curved river configurations is discussed.

New Type of Spur Dike at the Exit of Diversion Channel: Courter-Arc Vertical Ladder Spur Dike

Arranging spur dike at the exit of diversion channel significantly influences the safety of the downstream cofferdam and the scour of the downstream bed by changing the water velocity and turbulence. In order to compare the advantages of different arrangement of spur dike, detailed profiles of velocity and scouring are measured in laboratory flume. And water depths, surface velocity and the condition of downstream bed scouring are investigated at the exit of diversion channel at different arrangement. A new type of spur dike is designed, which is named as courter-arc vertical ladder spur dike. Through experiments on physical model, the new type of spur dike alters the direction of the outflow, decreases water speed and reduces downstream bed scouring and ensure high slope safety.

인공사석 배열에 따른 파랑에너지 저감효과 분석

현재 국내 연안에 시공된 호안구조물은 불투수성 콘크리트 재료로 이루어져 있다. 그러나 파랑에너지 감소 효과가 미미한 획일적인 형식으로 저면 세굴로 인한 구조물 붕괴, 반사파에 의한 해빈 침식으로 자갈층이 형성되는 문제점을 발생시키고 있다. 파랑의 에너지를 제어하기 위하여 다양한 형태의 투수성 구조물들을 사용하지만 구조물의 제원이 파랑에너지 저감에 미치는 영향에 관한 연구는 수행된 사례가 거의 없다. 따라서 본 연구에서는 다양한 마찰면적과 공극률을 갖는 인공사석들에 대하여 수리모형실험을 수행하여 마찰면적과 공극률이 파랑에너지에 미치는 영향을 검토해보았다. 그 결과, 마찰면적과 공극률이 증가할수록 파랑에너지 감소 효과가 커지며 사석의 배열이 파랑에너지 감소에 중요한 역할을 하는 것을 확인할 수 있었다. The locally constructed revetment structures for coastal protection are presently made of imprevious concrete materials. However, the wave energy reduction effect of present revetment structures are considerably inefficient which yields to bed scouring and thus, collapsing of the revetment structures. Studies on the analysis of the influence of riprap arrangement on the friction area and void fraction, for wave energy reduction, are insufficient. Therefore, this study analyzed the wave energy reduction effect of various artificial ripraps, made with varying friction area and void fraction, in different riprap arrangements. The results of the analysis showed that the increase of both friction area and void fraction of arranged artificial ripraps yields to a more efficient wave energy reducing material intended for revetment structures.

Effect of groin geometry on scouring of sandy river beds having 180° Bend

Groins are commonly used at the river bends for controlling erosion along the banks and protecting the adjacent infrastructure. Groins are designed to divert river flows towards its axis, thus reducing stream pressures leading to enhanced protection of river banks. The new flow pattern, however, entails the inherent risk of disturbing the established river regime leading to scouring around the groin. This research was undertaken to investigate the effect of groin geometry, represented in its length and angle of inclination, on scouring of sand bed using an experimental flume having a 180° bend. The laboratory experimental program modeled groins of four different lengths, that is, 2, 4, 6, and 8 cm, with angles of inclinations of 30, 60, 90, and 120°. Whereas, aggregation of natural sand with a median grain size, d50 = 1.6 mm was used as material of the flume bed, with discharge of 30 lit/s. The results pertaining to the effects of groin geometry on maximum scour depth were analyzed in the light of previous published data. The results further substantiated that an increase in length or inclination of groin causes a corresponding increase in the dimensions of scouring hole around it. It is also observed that increasing the groin length or its inclination leads to increase in the extent and thickness of sedimentation downstream of the groin. The results are represented by curves and equations to facilitate determination of the maximum scour depth for various groin geometry conditions. Key words: Groin, river erosion, scour depth, groin geometry, groin length, groin inclination.

Effects of submerged flexible vegetation and solid structure bars on channel bed scour

The effects of different submerged obstacle longitudinal bars with different arrangement densities on the flow profile and morphology of a scour hole were investigated under clear water conditions. Acoustic Doppler velocimetry (ADV) data were applied to plot the vertical distributions of three-dimensional velocities and turbulent contours. The experimental results indicate that arrangement density (also can represent porosity), structural material (flexible or solid), and the sidewall effect are the main factors impacting turbulent kinetic energy and the morphology of scour holes. For flexible vegetation, the maximum turbulent kinetic energy near the bed surface increased with the arrangement density. For the same structure, the depth and the magnitude of the lateral expansion of the scour hole also increased with the arrangement density. The flexible vegetation reduced the depth of the scour hole because of deflection and arrangement density. The larger volumes of scour found in the upstream and middle sections of solid structures compare well to those in flexible vegetation. The deflection of porous flexible vegetation transported the turbulent kinetic energy downstream, reduced the turbulent kinetic energy near the sediment bed, and increased the stability of the bars. Flexible vegetation bars are able to protect the bank and the bed of a river under normal conditions, making them a good alternative design in the management and restoration of rivers.

Sediment mobility and bed armoring in the St Clair River: insights from hydrodynamic modeling

ABSTRACTThe lake levels in Lake Michigan‐Huron have recently fallen to near historical lows, as has the elevation difference between Lake Michigan‐Huron compared to Lake Erie. This decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems, together with social and economic impacts on communities in the entire Great Lakes region. Results from past work suggest that morphological changes in the St Clair River, which is the only natural outlet for Lake Michigan‐Huron, could be an appreciable factor in the recent trends of lake level decline. A key research question is whether bed erosion within the river has caused an increase in water conveyance, therefore, contributed to the falling lake level. In this paper, a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the St Clair River and assess the likelihood of morphological change under the current flow regime. A two‐dimensional numerical model was used to study flow structure, bed shear stress, and sediment mobility/armoring over a range of flow discharges. Boundary conditions for the numerical model were provided by detailed field measurements that included high‐resolution bathymetry and three‐dimensional flow velocities. The results indicate that, without considering other effects, under the current range of flow conditions, the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour. However, the detailed maps of the bed show mobile bedforms in the upper St Clair River that are indicative of sediment transport. Relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition. Ship‐induced propeller wake erosion also is a likely cause of sediment movement in the entire reach. Other factors that may promote sediment movement, such as ice cover and dredging in the lower river, require further investigation. Copyright © 2012 John Wiley & Sons, Ltd.

The physical basis for anomalous diffusion in bed load transport

Recent studies have observed deviation from normal (Fickian) diffusion in sediment tracer dispersion that violates the assumption of statistical convergence to a Gaussian. Nikora et al. (2002) hypothesized that particle motion at short time scales is superdiffusive because of inertia, while long‐time subdiffusion results from heavy‐tailed rest durations between particle motions. Here we test this hypothesis with laboratory experiments that trace the motion of individual gravels under near‐threshold intermittent bed load transport (0.027 < τ* < 0.087). Particle behavior consists of two independent states: a mobile phase, in which indeed we find superdiffusive behavior, and an immobile phase, in which gravels distrained from the fluid remain stationary for long durations. Correlated grain motion can account for some but not all of the superdiffusive behavior for the mobile phase; invoking heterogeneity of grain size provides a plausible explanation for the rest. Grains that become immobile appear to stay at rest until the bed scours down to an elevation that exposes them to the flow. The return time distribution for bed scour is similar to the distribution of rest durations, and both have power law tails. Results provide a physical basis for scaling regimes of anomalous dispersion and the time scales that separate these regimes.

Water, Wind, Wood, and Trees: Interactions, Spatial Variations, Temporal Dynamics, and their Potential Role in River Rehabilitation

AbstractRecent Australian research has quantified the role of large wood (wood of any origin and length with a diameter greater than 0.1 m) in dissipating stream energy, forming pool habitats by local bed scour, protecting river banks from erosion, and damming rivers with long rafts causing avulsions. Large wood in Australian streams is sourced by a range of processes from the nearby riparian zone which has usually been degraded by post‐European settlement vegetation clearing. Large wood loadings within the bankfull channel are dependent not only on the type and quality of the riparian plant community but also on bankfull specific stream power, channel width, and the processes of large wood delivery to the stream. While bank erosion and floodplain stripping by catastrophic floods are obvious and important delivery mechanisms, treefall and trunk and branch breakage by strong winds during tropical cyclones and severe storms are also significant in the tropics. Furthermore, wood decay and downstream transport produce temporally dynamic large wood distributions. The longevity of natural large wood structures in rivers, such as rafts, debris dams, and log steps, requires determination. River rehabilitation programs need to not only include the reintroduction of large wood, but also carefully plan the spatial distribution of that wood, the most appropriate type and range of large wood structures, and, most importantly, the revegetation of the riparian zone to ensure a natural long‐term source of large wood. Exotic species management is an essential part of river rehabilitation.

黒部川における河床変動,河床材料分布,植生の変化に関する研究

The Kurobe river which is very steep river on alluvial fan yields a mass of sediments from drainage basin. Depositing sediments in dam reservoirs deteriorate a function of water storage. Therefore, the cooperating sediment flushing of Unazuki dam and Dashidaira dam is made in the latter period of floods to maintain the capacity of dam reservior water storage from 2001. After stopping gravel dredging in the downstream of Kurobe river, vegetation growth on sand bank has gradually begun. And then dense vegetation growth cause bed scouring of channel thalweg in downstream reach. The purpose of this study is to deepen the understanding of river channel change by investigating relationship between flood flows, gravel dredging, bed variations and vegetation growth over time in the Kurobe river and to conducts a proper river management.

Alluvial cover dynamics in response to floods of various magnitudes: The effect of the release of glaciogenic material in a Swiss Alpine catchment

Fluvial incision into formerly glaciated landscapes is commonly affected by the release of glaciogenic sediments from the hillslopes, via landsliding, hillslope failure and debris flow activity. These deposits typically comprise abundant block-size clasts. Here, we determine the ability of the fluvial processes to evacuate glacially derived sediments in an Alpine hanging valley blanketed by >100-m-thick glacial till. We assess along-stream profiles of basal shear stress during annual, decadal and centennial floods, by means of the hydrological model HEC-RAS. We use bed surface grain size data to: (i) evaluate the Shields stress profiles for these floods, (ii) determine at which timescale the bed undergoes significant changes, and to (iii) predict transport capacity patterns for each flood. In addition, we present digital photogrammetry-based estimates of bed elevation changes over two selected time intervals that experienced low- and high- magnitude floods, respectively. The results indicate that floods with return periods of ≤10years are capable of mobilizing the coarse fraction of the bed material, thereby substantially altering the channel geometry. The predicted near-critical Shields stress values for these floods in the area where the glacial deposits are thickest suggest a strong hillslope-channel coupling, which may have resulted in the formation of the knickzone observed in this sector. However, decadal to centennial floods are required to transport the material over long distances and scour the bed in the upper part of the inner gorge. In addition, the observed downstream trend from bed scouring to deposition in the inner gorge for these floods and the opposite trend for low-magnitude floods suggest that these patterns are not directly controlled by downstream variations of transport capacity. We propose that the supply of sediment through hillslope failure and bank collapse significantly contributes to the sediment flux for high-magnitude floods. We conclude that the morphology and the timescale of sediment transport in this glacially conditioned landscape have been substantially controlled by the hillslope-derived supply of coarse-grained material.

Accelerated overbank accumulation after nineteenth century river regulation works: A case study on the Maros River, Hungary

In the nineteenth century, the meandering rivers of the Carpathian Basin were extensively regulated, and their large (up to 100 km wide) floodplains were confined by artificial levees. On the narrow (0.5–4 km) artificial floodplains confined by these levees, overbank sedimentation has become the dominant geomorphological process, resulting in rising floodplain levels during the last century. The Maros River is an extreme example of this process, as it carries a significant amount of suspended sediment (4.6 × 10 6 m 3/y) and because its lowland reach was drastically shortened by cutoffs, resulting in bed scour and an increased sediment load. Simultaneously, a flood embankment system was constructed, reducing the floodplain width by 70–80%. The resulting accelerated overbank sediment accumulation increases the flood hazard along the river. The aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower Maros River over the last 150 years and to identify its influencing factors. The lateral slope of the protected (natural) floodplain was projected towards the present-day channel, allowing the volume (m 3) and rate (cm/y) of overbank sedimentation to be calculated using digital terrain modelling (DTM). Changes in the rate of sedimentation were determined by pollen analysis. The studied reach was divided into five sections based on the rate of aggradation: (i) the distal surface of the alluvial fan, where no sedimentation was measured, only incision; (ii) the original front of the alluvial fan (1.0 ± 0.4 cm/y); (iii) the recently formed secondary alluvial fan (1.4 ± 0.3 cm/y); (iv) the low-lying floodplain (0.4 ± 0.2 cm/y); and (v) the outlet unit (2.0 ± 0.5 cm/y). The aggradation rate was slower on elevated forms, such as the pre-regulation natural levee (0.2 cm/y), and greater on the low-lying floodplain (0.6 cm/y). The greatest accumulation rate (1.3–2.4 cm/y) was measured in cutoffs. The sedimentation rate was high during the regulation period (1.9–2.4 cm/y) but later decreased to 0.5–0.9 cm/y. The rate of aggradation was determined by the width, height and slope conditions of the floodplain, the impoundment of the main river and the land use in the area.

Erosion of glacial till from the St. Clair River (Great Lakes basin)

Variations in water level observed in Lakes Michigan and Huron during the last few decades have motivated a comprehensive study involving climatic, hydrologic and hydraulic factors organized by International Joint Commission of the Great Lakes. It has been submitted, among other possible causes, that changes in conveyance in the St. Clair River could be contributing to the lowering of the upper Great Lakes water level. Sediment transport processes, in particular bed scour and erosion, can affect significantly a river's conveyance, thus creating the need to assess the erodibility properties of the river bed. To this end, laboratory tests were performed in order to obtain the value of the critical shear stress needed to erode the cohesive fraction of the bed sediment material, known as glacial till, from the St. Clair River. Different flows with increasing velocities were run up to the point where initial sediment erosion could be observed. Through detailed near-bed velocity measurements using a laser Doppler velocimetry (LDV) system, a value of 4.2 N/m 2 was obtained as the critical shear stress for the erosion of glacial till. A threshold for the critical shear stress for erosion of similar cohesive sediments was also found and expressed in dimensionless form. These results could be used in combination with mathematical models to estimate the risk of scour and erosion at locations where the glacial till is exposed to both strong currents and flow forces induced by the large navigation vessels commonly observed along the course of the St. Clair River.

Experimental Study on Critical Flow Conditions Causing Damage of Grass-Covered Revetment

Flexible vegetations supply great effect on river bank protection. It is important to study the critical flow conditions, including bed shear stress, scour duration and frictional velocity etc, causing damage of grass-covered revetment. Laboratory experiments prove that, destruction of turf can be estimated by observing the variation of water head. The experimental shear stress above vegetation zone has nonlinear relation with velocity square, which agrees with theoretic derivation. Before the turf destruction occurring, shear stress above vegetation zone increases with the scour duration and then goes to stabilization. This mentioned Shear stress will change suddenly when local scour damage happens, or keep stabilization while affine damage is on-going. Under the same flow conditions, the critical bed shear stress of reinforced turf is larger than that of natural turf. As far as the same-form revetments are concerned, the bed shear stress at breaking point increases with the flow velocity.

Flow structure and channel morphology at a natural confluent meander bend

Previous experimental, field, and modeling studies of confluence dynamics have focused mainly on junctions formed by straight channels. In contrast, natural rivers often meander and tributaries can enter meandering rivers on the outside of bends to form a junction planform known as a confluent meander bend. In this study, field measurements of three-dimensional velocity components and bed topography at a confluent meander bend reveal a complex hydrodynamic environment that responds to changes in momentum-flux ratio, while channel morphology remains relatively stable. Flow from the tributary deflects high-velocity flow and helical motion in the curving main river toward the inside of the bend, inducing bed scour and inhibiting point-bar development. The high junction angle forces the tributary flow to abruptly realign to the orientation of the downstream channel, initiating a counter-rotating helical cell over the outer portion of the bend. Two surface-convergent helical cells persist through the downstream channel, where the combined flows accelerate as the channel cross-sectional area is constricted by a bar along the downstream junction corner, precluding flow separation. Long-term stability of its planform suggests that this confluent meander bend represents a quasi-stable channel configuration. Overall, patterns of flow and channel morphology are quite different from typical patterns in most meander bends, but are generally consistent with a conceptual model of confluent meander bends derived from previous laboratory experiments and numerical modeling.

Geometry and grain-size characteristics of the basal surface of a braided river deposit

Research Article| March 01, 2011 Geometry and grain-size characteristics of the basal surface of a braided river deposit J. Tobias Gardner; J. Tobias Gardner Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Search for other works by this author on: GSW Google Scholar Peter E. Ashmore Peter E. Ashmore Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information J. Tobias Gardner Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Peter E. Ashmore Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Publisher: Geological Society of America Received: 03 Aug 2010 Revision Received: 05 Oct 2010 Accepted: 08 Oct 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (3): 247–250. https://doi.org/10.1130/G31639.1 Article history Received: 03 Aug 2010 Revision Received: 05 Oct 2010 Accepted: 08 Oct 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. Tobias Gardner, Peter E. Ashmore; Geometry and grain-size characteristics of the basal surface of a braided river deposit. Geology 2011;; 39 (3): 247–250. doi: https://doi.org/10.1130/G31639.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Description of the three-dimensional geometry and grain-size patterns of fluvial deposits and their relationship to the morphodynamics of the river has been an elusive objective in sedimentology, hindered by limited exposure and the time scale of fluvial dynamics. In small-scale physical models the time scales are short enough to map river morphology and sedimentology during significant (and continuous) morphological development of the river and its deposits, especially for braided rivers. Using close-range digital photogrammetry, the dynamics of the river morphology, and resulting deposit geometry and sedimentology, were captured using digital elevation model differencing techniques, combined with automated grain-size mapping from image texture analysis. Using these novel methods we show the temporal development and characteristics of braided river deposit geometry, and, for the first time, map the characteristics and development of the basal surface of braided river deposits in relation to river morphodynamics and formative processes. The basal surface has considerable relief, wide variation in grain size similar to that of the river as a whole, develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages, and is only partially related to bed scour associated with laterally migrating channel confluences You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Validation of Bed-Load Transport Measurements with Time-Sequenced Bathymetric Data

Advances in bathymetric data acquisition have made it possible to explore alternative methods for measuring bed-load transport in rivers. The method validated herein consists of measuring rates of bed scour by using time-sequenced bathymetric data. The validation is performed in a laboratory flume by comparing the measured rates of bed scour with direct measurements of bed-load transport. The bed forms in the flume are dunes traveling at nearly constant speed. The shape of the dunes remains nearly constant. No suspended load is present. The ranges for Froude and Rouse numbers are 0.24–0.50 and 4.6–10.4, respectively. The study shows that under the given conditions, bed-load transport determined from time-sequenced bathymetric data is equally accurate to that determined from measurements of bed-form amplitude and speed. Obtaining bed-load transport from time-sequenced bathymetric data is often more expedient than traditional methods.

Prediction of Scour Depth in Downstream of Ski-Jump Spillways Using Soft Computing Techniques

Scour of bed in downstream of a ski-jump spillway is a critical phenomenon that can endanger the spillway stability. The present paper deals with application of soft computing techniques like classification and regression tree (CART), support vector machine (SVM) and M5 for the prediction of downstream scour of the spillways. The results of testing data set present CART model as the best among the other computing methods. The results of models showed that CART produces better prediction of the scour in the downstream of the spillway compared to other techniques. However, the other techniques are better than the available empirical relationships for the prediction of scour.

STUDY ON LOCAL SCOUR AND VARIATION OF BED COMPOSITION AROUND NON-SUBMERGED SPUR DYKE

Several studies have been made on local bed scour by movable bed experiments. Researches taking into account non-uniform sediment transport are still very few, in particular in case of the involvement of spur dykes. In this paper, we carried out movable bed experiments around an impermeable spur dyke under non-submerged condition. Both uniform and non-uniform sediment beds with similar mean diameter used and the changes of the bed configuration and bed surface composition have been considered. In addition, we used color sediment which is divided in three ranges of diameter with different colors in order to clarify the spatial differences of bed surface composition through pictures and visual observation. We focused on the relation between initial grain-size distribution and the final scour hole depth and the influence of vortices around a spur dyke on bed surface composition.

Bed scouring downstream of hydraulic structures under steady flow conditions: Experimental analysis of space and time scales and implications for mathematical modeling

Abstract Sediment transport and bed deformation in alluvial rivers are space and time dependent. The knowledge of the space and time scales can be helpful for the definition of predictive procedures of an alluvial reach response to changing boundary conditions. In this work, attention is paid to scouring process occurring downstream of the rigid basement of a hydraulic structure. The analysis is focused on transient bed profiles which are determined, under steady flow conditions, by a decrease of the upstream sediment transport rate. In particular, the paper is aimed at improving understanding of the space and time scales required by the alluvial system to reach the equilibrium conditions. For this purpose, movable-bed runs are carried out in a straight laboratory channel, for two values of the water discharge. During each run, the longitudinal bed profiles are measured at different times. Based on experimental data, spatial scale factors of the bed scouring and of the bed load transport to reach the equilibrium conditions are defined. Particularly, it is found that the scour length varies especially during the first evolution phase and then it oscillates around of a mean value that is about 40% of the channel reach interested by the phenomenon under consideration; an expression is found for the adaptation coefficient which allows the estimation of the spatial delay of the bed load transport rate. Using both the collected data and literature data an expression defining the time scale of scouring is deducted. According to this expression the non-dimensional time scale is related to Shields parameter through an exponential law. Then, by the help of a 1-D numerical model previously developed by the writer, the implications for choosing the spatial and temporal resolutions, on which numerical results depend significantly, are shortly discussed. The results show that the time and space scales, which represent physical constraints of the spatial and temporal resolutions, need to be properly defined in order to simulate the scouring process evolution.

Analysis of changes in the step-pool morphology and channel profile of a steep mountain stream following a large flood

The step-pool morphology of steep mountain streams is reorganized during large floods by the removal of steps, scouring of the channel bed and the formation of a new step-pool sequence by the re-deposition of step-forming grains. In this paper we document these changes caused by the largest recorded flood (return period ~ 50 years) in the steep mountain stream Erlenbach in central Switzerland in 2007 by comparing pre-flood and post-flood surveys of a ~ 650 m long study reach. We show that the flood led to statistically significant changes in the distributions of step height and spacing, most notably an increase in the variance of both variables. Organization at the river reach scale is not apparent, and the correlations between step properties both pre- and post-flood are generally weak. The flood led to widespread erosion of the river bed. Locally up to 2–3 m of vertical channel change was observed. At least 60% of the steps moved, even the largest ones; however they remained constrained to the parts of the study reach where landslides on the adjacent hillslopes are most active. Detailed changes in bed structure were analyzed from the pre- and post-flood profiles with a statistical scaling approach which identifies the complexity of the spatial organization of sediment in the longitudinal profile. Multiscaling found in both step and pool sequences reflects the complex spatial structure which is the result of the superposition of steps formed by the history of flood events.