Modelling floodplain sedimentation using particle tracking

Both climate change and river rehabilitation projects induce changes in floodplain sedimentation. Notably along the lower River Rhine, the sediment deposition patterns and rates are subject to change. To assess the magnitude of these changes, we developed the MoCSED model, a floodplain sedimentation model within a geographical information system for the lower Rhine River. We based MoCSED on the ‘method of characteristics’ (MoC), a particle tracking method that minimizes numerical dispersion. We implemented the MoCSED model in the PCRaster dynamic modelling language. The model input comprises initial suspended sediment concentrations, water levels, flow velocities, and longitudinal and transverse dispersivities. We used a combination of the Krone and Chen concepts to calculate the subsequent sedimentation (SED routine). We compared the model results with sediment trap data for the Bemmel floodplain along the Dutch Waal River during the 2003 inundation. This comparison showed that MoCSED was able to simulate the pattern of sediment deposition. In addition, the model proved to be an improvement in comparison with a conventional raster‐based floodplain sedimentation model for the lower River Rhine. In future, MoCSED may serve well to study the impact of a changing discharge regime due to climate change and floodplain rehabilitation plans on deposition of sediments. Copyright © 2006 John Wiley & Sons, Ltd.     

Geomorphic controls on floodplain sediment and soil organic carbon storage in a Scottish mountain river

River floodplains constitute an important element in the terrestrial sediment and organic carbon cycle and store variable amounts of carbon and sediment depending on a complex interplay of internal and external driving forces. Quantifying the storage in floodplains is crucial to understand their role in the sediment and carbon cascades. Unfortunately, quantitative data on floodplain storage are limited, especially at larger spatial scales. Rivers in the Scottish Highlands can provide a special case to study alluvial sediment and carbon dynamics because of the dominance of peatlands throughout the landscape, but the alluvial history of the region remains poorly understood. In this study, the floodplain sediment and soil organic carbon storage is quantified for the mountainous headwaters of the River Dee in eastern Scotland (663 km²), based on a coring dataset of 78 floodplain cross-sections. Whereas the mineral sediment storage is dominated by wandering gravel-bed river sections, most of the soil organic carbon storage can be found in anastomosing and meandering sections. The total storage for the Upper Dee catchment can be estimated at 5.2 Mt or 2306.5 Mg ha^-1 of mineral sediment and 0.7 Mt or 323.3 Mg C ha^-1 of soil organic carbon, which is in line with other studies on temperate river systems. Statistical analysis indicates that the storage is mostly related to the floodplain slope and the geomorphic floodplain type, which incorporates the characteristic stream power, channel morphology and the deposit type. Mapping of the geomorphic floodplain type using a simple classification scheme shows to be a powerful tool in studying the total storage and local variability of mineral sediment and soil organic carbon in floodplains. © 2019 John Wiley & Sons, Ltd.     

Dynamics of phosphorus compounds in a lowland river system: Importance of retention and non-point sources

Intensive measurements of the fluxes of phosphorus (P) and of P retention were carried out in a Danish lowland watershed (Gjern Å) during two hydrological years (June 1987 to May 1989). Seasonal and short-term variations of P concentrations were measured by intensive automatic sampling covering P fluxes from the entire Gjern Å watershed and two subcatchments: the Gelbæk and Lake Søbygård. Moreover, infrequent sampling was performed in all major tributaries of the river system. Transport of P compounds (dissolved and particulate P) exposed a seasonal pattern which was highly affected by flow conditions, instream processes, as well as point and non-point sources. Stormflow P transport during the two study years (1987-8 and 1988-9) constituted 56 and 61% in the Gelbæk, respectively, compared with 25 and 23% in the Gjern Å, respectively. Particulate P transport in the Gelbæk constituted 56 and 75% of annual total P transport during the two years compared with 77 and 75% in the Gjern Å. The magnitude of monthly baseflow and stormflow total P loads was significantly correlated with the mean monthly discharge during baseflow and stormflow in the Gelbæk, whereas only stormflow loads were correlated to discharge in the Gjern Å. In situ measurements of retention showed that the maximum amount of P stored in the Gelbæk during summer (June to August) was 22gPm^?2 (1988) compared with 27gPm^?2 (1987) in the Gjern Å. Lake Søbygård was a P source during summer but a P sink during winter and on an annual basis the net P released was 810 and 1420 kg, which corresponded to 7 and 20% of the annual P export from the watershed, respectively. Retention constituted about 30% of gross P transport in the Gelbæk during summer compared with 20% in the Gjern Å. Resuspension of retained P during stormflows in September 1987 constituted 94% of the stormflow P transport and 54% of the total P transport. Monthly total P and dissolved reactive P (DRP) mass balances for the main channel of the Gjern Å revealed a significant DRP retention over 17 months (p < 0.05) caused by P adsorption on sediments and biological uptake. On an annual basis the main channel was a sink of DRP (1220 and 1660 kg P) but a source of total P (3440 and 1000 kg P). implying that the channel is an important source of particulate P. Bank erosion proved to be a significant P source in the main channel of Gjern Å, whereas P delivery from soil erosion was possibly of minor importance. The annual non-point P export from two intensively sampled catchments was significantly higher (0.89 and 0.45 kg Pha^?1 yr^?1) than from the five extensively sampled subbasins (0.43 and 0.17 kg Pha^?1 yr^?1). No significant relationship could be established between non-point P export and the proportion of arable land and soil type. Only for the wet year of 1987-8 was a significant relationship established between non-point P export and the P load from scattered dwellings outside sewage areas in five subbasins.     

Modelling sediment and total phosphorus export from a lowland catchment: comparing sediment routing methods

Bank erosion is the main source of suspended sediment (SS) and diffuse total phosphorus (TP) in many lowland catchments. This study compared a physically based sediment routing method (Physical method), which distinguishes between stream bed and bank erosion, with the original sediment routing method (Original method) within the Soil and Water Assessment Tool (SWAT) version 2009, for simulating SS and TP losses from a lowland catchment. A SWAT model was set up for the lowland River Odense catchment in Denmark and calibrated against observed stream flow and phosphate (PO₄) loads. On the basis of an initial calibration of hydrological and PO₄ parameters, the SWAT model with the Original method (Original model) and the SWAT model with the Physical method (Physical model) were calibrated separately against observed SS and TP loads. The SWAT model simulated daily stream flow well but underestimated PO₄ loads. The Physical model simulated daily SS and TP better than the Original model. The simulated contribution of bank erosion to SS in the Physical model (99%) was close to the estimated contribution from in situ erosion measurements (90–94%). Compared with the Original method, the Physical method is not only more conceptually correct but also improves model performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Overbank sediment deposition patterns for straight and meandering flume channels

Experiments with the 10 m Flood Channel Facility at HR Wallingford, UK, indicate a fundamental dependency of the overbank deposition pattern of channel suspended sediments on channel planform. Two experiments (100 and 140 l s^?1) in a 1·95 m wide straight channel showed deposition concentrated in a berm along the channel bank. Little sediment was transferred further onto the floodplain. For the larger flow, the berm formed further from the channel. A single experiment (103 l s^?1) with a 1·31 m wide meandering channel showed deposition across the entire floodplain tongue between successive meanders. Maximum deposition occurred on the downstream side of the meander, just past the bend apex. These generalized flume results complement the real‐world but site‐specific data of field studies. Copyright © 2002 John Wiley & Sons, Ltd.     

Modelling wetland connectivity during overbank flooding in a tropical floodplain in north Queensland,Australia

Hydrological connectivity between floodplain wetlands and rivers is one of the principal driving mechanisms for the diversity, productivity and interactions of the major biota in river–floodplain systems. This article describes a method of quantifying flood‐induced overbank connectivity using a hydrodynamic model (MIKE 21) to calculate the timing, the duration and the spatial extent of the connections between several floodplain wetlands and rivers in the Tully–Murray catchment, north Queensland, Australia. Areal photogrammetry and field surveyed stream cross data were used to reproduce floodplain topography and rivers in the model. Laser altimetry (LiDAR)–derived fine resolution elevation data, for the central floodplain, were added to the topography model to improve the resolution of key features including wetlands, flow pathways and natural and artificial flow barriers. The hydrodynamic model was calibrated using a combination of in‐stream and floodplain gauge records. A range of off‐stream wetlands including natural and artificial, small and large were investigated for their connectivity with two main rivers (Tully and Murray) flowing over the floodplain for flood events of 1‐, 20‐ and 50‐year recurrence intervals. The duration of the connection of individual wetlands varied from 1 to 12 days, depending on flood magnitude and location in the floodplain, with some wetlands only connected during large floods. All of the wetlands studied were connected to the Tully River for shorter periods than they were to the Murray River because of the higher bank heights and levees on the Tully River and wetland proximity to the Murray River. Other than hydrology, land relief, riverbank elevation and levee banks along the river were found key factors controlling the degree of connectivity. These variations in wetland connectivity could have important implications for aquatic biota that move between rivers and off‐stream habitats during floods. Copyright © 2011 John Wiley & Sons, Ltd.     

A sediment budget for a cultivated floodplain in tropical North Queensland,Australia

Sugarcane is grown on the floodplains of northern Queensland adjacent to the Great Barrier Reef lagoon. Sediment and nutrient loss from these sugarcane areas is considered a potential threat to coastal and marine ecosystems. To enable sugarcane cultivation, farmers have structured the landscape into different elements, comprising fields, water furrows, ‘headlands’ and drains. In order to apply appropriate management of the landscape and reduce export of sediment, it is important to identify which of these elements act as sediment sources or sinks. In this study erosion and deposition rates were measured for the different landscape elements in a subcatchment of the Herbert River and used to create a sediment budget. Despite large uncertainties, the budget shows that the floodplain area is a net source of sediment. Estimated sediment export varies between 2 and 5 t ha^?1 y^?1. The relative importance of the landscape elements as sediment sources could also be determined. Plant cane is identified as the most important sediment source. Water furrows generate most sediment, but are a less important source of exported sediment due to their low connectivity. Headlands and minor drains act as sediment traps. Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling the long‐term sediment trap efficiency of small ponds

A numerical model (sediment trap efficiency for small ponds—STEP) is developed to simulate sediment deposition in small ponds (i.e. <1 ha) and to calculate the sediment trap efficiency (STE). The algorithms are kept simple to allow the model to simulate larger time periods (i.e. several years). Eight runs with an experimental pond were executed to test the model. The STEP model produces reasonable predictions of STE as well as the shape and magnitude of the effluent sediment concentration graph. The model efficiency of STEP for the prediction of STE equals 0·38 and the root mean square error equals 4·7%. Similar models, such as DEPOSITS and CSTRS, were inefficient in predicting the experimental results. The STEP model was used to simulate the long‐term (33 years) STE of small retention ponds in central Belgium using 10‐min rainfall data. For a typical pond (1000 m²) with a catchment area of 25 ha, annual STE can vary from 58 to 100%, with a long‐term STE of only 68%. Copyright © 2001 John Wiley & Sons, Ltd.     

Channel and floodplain sediment dynamics in a reach of the tropical meandering Rio Beni (Bolivian Amazonia)

The study investigates interactions, water and sediment exchanges, between a rapidly migrating meander and its associated floodplain at fine temporal and spatial scales. The Beni River, an Amazonian free meandering river, makes the transition between Andean ranges and Amazonian lowlands. For the period 2002–2006, an assemblage of tools and methods (water and sediment discharges, topometric and bathymetric surveys, sedimentation rate estimations from unsupported ²¹⁰Pb and sediment trapping system) was used to jointly analyse the influence on the sediment budget of external factors (mainly water and sediment discharge) and the inherent behaviour of the system. The main issue addressed is the investigation of the complex relationship between ‘morphological conditioning’ of fluvial landform and process. The first part of the study was undertaken with the aim of linking erosion–deposition in an active meander with water and sediment fluxes. The three inter‐annual evolutions are characterized by very unequal sediment budgets; the first two intervals underwent predominant erosion, and the latter slight accumulation. Digital elevation models, evaluated for the active meander, demonstrate that sedimentation on the point bar depends more on external factors than erosion of the concave bank, which fluctuates slightly. The second part of the study, focusing on water and sediment exchanges between active bend and floodplain, examines the respective parts played by overbank flow and by an abandoned channel on the diffusion and sequestration of sediment. The association of short‐ and long‐term estimation of sedimentation rates suggests that floodplain construction is associated with two different processes and rhythms of sediment transportation. Finally, a sediment budget is proposed for the Beni River in the upper part of the Amazonian lowlands. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling sediment (dis)connectivity across a river network to understand locational-transmission-filter sensitivity for identifying hotspots of potential geomorphic adjustment

Rivers act as ‘jerky conveyor belts’ that transmit fluxes of flow and sediment downstream. This transmission of fluxes can be highly variable within a drainage basin resulting in either abrupt or gradational sediment (dis)connectivity patterns and processes. This study assesses sediment (dis)connectivity across a basin as a means to understand the locational, transmission and filter sensitivity properties of a fluvial system. Drawing upon the case study of Richmond River Catchment, New South Wales, Australia we use the concepts of effective catchment area and buffers, along with graph theory and an empirical sediment transport model CASCADE (Catchment Sediment Connectivity and Delivery), to assess (1) the degree to which modelled sediment cascades along the river network are connected or disconnected (2) how the position, pattern and configuration of (dis)connection facilitates or restricts geomorphic adjustment in different parts of a catchment, and (3) use the findings as a basis to explain the locational-transmission-filter sensitivity of the catchment. We use this analysis to segregate supply limited and transport limited reaches and identify various controls on sediment dynamics: in-stream sediment storage units, junctions between different geomorphic river types, tributary confluences and sediment storage units within partly confined floodplain units. Such analysis lays the foundation for network scale identification of potential hotspots of geomorphic adjustment.     

大渡河龚咀水库泥沙特性与淤积

龚咀水库库容3.1×10~8m~3,是大渡河上最大的水库,从1971年蓄水以来的15年间,淤积量达2.2096×10~8m~3,占库容的71.3％。淤积可分蓄水初期,三角洲发展和淤积接近平衡三个时期,其淤积率分别为83.5％,53％和2.9％。淤积物的平均粒径从1.82mm增加为3.38mm。卵砾推移质移动至坝前。淤积量变化过程即为输沙能力调整恢复过程。     

Interaction between meander dynamics and floodplain heterogeneity in a large tropical sand‐bed river: the Rio Beni,Bolivian Amazon

The evolution of meandering river floodplains is predominantly controlled by the interplay between overbank sedimentation and channel migration. The resulting spatial heterogeneity in floodplain deposits leads to variability in bank erodibility, which in turn influences channel migration and planform development. Despite the potential significance of these feedbacks, few studies have quantified their impact upon channel evolution and floodplain construction in dynamic settings (e.g. locations characterized by rapid channel migration and high rates of overbank sedimentation). This study employs a combination of field observations, geographic information system (GIS) analysis of satellite imagery and numerical modelling to investigate these issues along a 375 km reach of the Rio Beni in the Bolivian Amazon. Results demonstrate that the occurrence of clay‐rich floodplain deposits promotes a significant reduction in channel migration rates and distinctive styles of channel evolution, including channel straightening and immobilization of bend apices leading to channel narrowing. Clay bodies act as stable locations limiting the propagation of planform disturbances in both upstream and downstream directions, and operate as ‘hinge’ points, around which the channel migrates. Spatial variations in the erodibility of clay‐rich floodplain material also promote large‐scale (10–50 km) differences in channel sinuosity and migration, although these variables are also likely to be influenced by channel gradient and tectonic effects that are difficult to quantify. Numerical model results suggest that spatial heterogeneity in bank erodibility, driven by variable bank composition, may force a substantial (c. 30%) reduction in average channel sinuosity, compared to situations in which bank strength is spatially homogeneous. Copyright © 2015 John Wiley & Sons, Ltd.     

Recent increase of river–floodplain suspended sediment exchange in a reach of the lower Amazon River

We analyzed variation of channel–floodplain suspended sediment exchange along a 140 km reach of the lower Amazon River for two decades (1995–2014). Daily sediment fluxes were determined by combining measured and estimated surface sediment concentrations with river–floodplain water exchanges computed with a two‐dimensional hydraulic model. The average annual inflow to the floodplain was 4088 ± 2017 Gg yr^?1 and the outflow was 2251 ± 471 Gg yr^?1, respectively. Prediction of average sediment accretion rate was twice the estimate from a previous study of this same reach and more than an order of magnitude lower than an estimate from an earlier regional scale study. The amount of water routed through the floodplain, which is sensitive to levee topography and increases exponentially with river discharge, was the main factor controlling the variation in total annual sediment inflow. Besides floodplain routing, the total annual sediment export depended on the increase in sediment concentration in lakes during floodplain drainage. The recent increasing amplitude of the Amazon River annual flood over two decades has caused a substantial shift in water and sediment river–floodplain exchanges. In the second decade (2005–2014), as the frequency of extreme floods increased, annual sediment inflow increased by 81% and net storage increased by 317% in relation to the previous decade (1995–2004). Copyright © 2017 John Wiley & Sons, Ltd.     

Seasonal fluxes and sediment routing in tropical catchments affected by nickel mining

An important gap in the management of land erosion in mining-affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining-affected Santa Cruz and Pamalabawan catchments in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub-catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub-catchments, with as little as 10–22% of relative disturbance area being enough to generate four-fold to eight-fold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub-catchments with > 10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km⁻² d⁻¹) compared with sub-catchments with < 10% disturbance (3.6 ± 17.7 t km⁻² d⁻¹) and undisturbed catchments (2.0 ± 5.7 t km⁻² d⁻¹). We also show that sediment flushing predominantly occurs in the most disturbed sub-catchments at the onset of the wet season. A small number of flood events transports the bulk of the sediment, with hysteresis effects being most pronounced in disturbed areas. Lastly, we show that floodplain sediment recycling exerts a key control on sediment delivery at both reach and catchment scales, with the relative contribution of floodplain sources to the sediment budget becoming dominant in the latter stages of the wet season- up to 89% of the total sediment export per storm event. This study highlights the importance of both degree of disturbance and sediment pathways in controlling sediment transport in mining-disturbed areas, and that considering the entire sediment routing system including intermediate stores is crucial to optimizing existing and future measures against siltation and potential contamination of trace metals and metalloids downstream of mining areas.     

Modelling scour and deposition in harbours due to complex tsunami-induced currents

In this paper, a set of models responsible for hydrodynamics, sediment transport, and morphological evolution are introduced with their theoretical backgrounds, and it is explained how they are fully connected through a two-way coupling to yield an integrated sediment transport model applicable to tsunami cases. In particular, a fully nonlinear Boussinesq model with bottom shear-induced rotational terms is chosen for the hydrodynamic model in order to provide a better physical approximation of tsunami-related, near-bed hydrodynamics in the nearshore. A finite-volume scheme, stable and suitable for phase-resolving model runs longer than 10 simulated hours, is adopted in the numerical discretization. The accuracy and applicability of the developed model are investigated through numerical tests on various sediment problems in the shallow region. Calculated results agree well with existing experimental records. Finally, an ocean-wide, field-scale simulation of the 2011 Tohoku-oki tsunami is attempted, with a focus on the localized effects of tsunami-induced morphological changes at Crescent City Harbor and Santa Cruz Harbor (USA). Consistent with the reported observations, strong and vortical velocity fields are generated through the model and result in significant changes in morphological configurations. Depth variations and areas of scouring and deposition are compared between modelled and observed records, and the results are discussed. © 2019 John Wiley & Sons, Ltd.     

引水结构变化对天津于桥水库磷滞留的影响分析与生态水量估算

2014年南水北调中线一期工程通水后,天津市的水源结构发生变化,由单一滦河水源变为双水源.引水结构变化导致于桥水库入库水量变化,从而影响水库的总磷(TP)滞留.一般认为,入库总磷负荷随入库水量减少而降低,且水力停留时间越长,将越有利于总磷滞留,从而水库TP浓度降低.但根据统计数据发现,南水北调通水后于桥水库入库水量降低,TP负荷反而升高,水库TP浓度升高.何种TP滞留机制造成了这样的结果?本文通过分析2001-2018年间入库水量(W_IN)、入库总磷负荷(TPL_IN)在南水北调通水前后的变化规律,采用Vollenweider模型推求水库TP浓度和磷滞留量(R_P),探讨水力停留时间(T)对库区总磷滞留量的影响机制,并估算双水源新情势下控制于桥水库磷滞留量的生态水量.结果表明:TPL_IN随W_IN呈先降低后升高趋势;引水期τ与R_P之间存在显著的正相关关系,随着τ增加,正相关性下降,但同时考虑非引水期和引水期τ时,R_P受较小的TPL_...     

Relationship between texture and fractions of inorganic phosphorus in the surface sediment of a reservoir

Inorganic P was fractionated into three categories (NaOH-, BD- and HCI-extractable) for 30 surface sediment samples in La Minilla Reservoir (Sevilla, Spain). The amount of reactive P extracted with NaOH (NaOH-RP) and with HCI (HCI-RP) correlated in a multivariate regression with the clay and sand content of the sediment. This multivariate function should aid in predicting the amount of phosphorus available to the sediment organisms, and it can also contribute to the knowledge of the phosphorus budget of the reservoir.Supported by a Grant from CSIC-CONICET.     

Modelling the decadal dynamics of reach-scale river channel evolution and floodplain turnover in CAESAR-Lisflood

Sedimentary deposits provide records of environmental change quantifying erosion fluxes conditioned by natural and anthropogenic disturbances. These fluxes are lagged by internal storage, particularly within floodplains, complicating reconstruction of environmental changes. The time sediment remains in storage underpins the interpretation of sedimentary records and accurate monitoring of pollutant fluxes. Turnover time is a measure of the timeframe to erode every floodplain surface. CAESAR-Lisflood is used to simulate fluvial evolution at reach scale, providing a basis for quantifying environmental changes on the timescales of sediment storage. We evaluate the accuracy of CAESAR-Lisflood simulations of channel changes and turnover times for alluvial floodplains using historical channel changes reconstructed for 10 reaches in northern England to quantify model accuracy in replicating mean annual erosion, deposition and channel lateral migration rates, alongside planform morphology. Here, a split-sample testing approach is adopted, whereby five of the reaches were calibrated and the resulting parameter values were applied to the other reaches to evaluate the transferability of parameter settings. The lowest overall integrated error identified the best-fit simulations and showed that modelled process rates were within ~25–50% of rates from historical reconstructions, generally. Calibrated parameters for some reaches are widely transferable, producing accurate geomorphic changes for some uncalibrated sites. However, large errors along some reaches indicate that reach-specific parameterization is recommended. Turnover times are underpinned by the assumption that areas of floodplain previously unvisited by the channel are reworked. This assumption has been challenged by studies that show floodplain (re)occupation rates vary spatially. However, this limitation is less important for the short-duration simulations presented here. The simulations reconstruct floodplain turnover times estimated by mapped rates mostly successfully, demonstrating the potential applicability of calibrated parameters over much longer timescales. Errors in the form of under-predicted erosion rates propagated, resulting in over-predicted turnover times by even greater magnitudes. © 2020 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Seven decades of hydrogeomorphological changes in a near-natural (Sense River) and a hydropower-regulated (Sarine River) pre-Alpine river floodplain in Western Switzerland

Hydropower alteration of the natural flow and sediment regime can severely degrade hydromorphology, thereby threatening biodiversity and overall ecosystem processes of rivers and their floodplains. Using sequences of aerial images, we quantified seven decades (1938/1942–2013) of spatiotemporal changes in channel and floodplain morphology, as well as changes in the physical habitats, of three floodplain river reaches of the Swiss pre-Alps, two hydropower-regulated and one near-natural. In the Sarine River floodplain, within the first decades of hydropower impairment, the magnitude and frequency of flood events (Q₂, Q₁₀, Q₃₀) decreased substantially. As a result, the area of pioneer floodplain habitats that depend on flood activity and sediment dynamic, such as bare sediments, decreased dramatically by approximately 95%. However, by 2013 vegetated areas had generally increased in comparison to the pre-regulation period in 1943, indicating general vegetative colonization. Between 1943 and 2013, the active channel underwent essential narrowing (up to 62% width reduction in the residual flow reach) and habitat turnover rates were very low (5% of the total floodplain area changed habitat type five to six times). In contrast, from the 1950s onwards, the near-natural floodplain of the Sense River experienced recurrent narrowing and widening, and frequent changes between bare and vegetated areas, reflecting the shifting habitat mosaic concept typical for natural floodplains. In the three reaches investigated, we found that the active floodplain width and erosion of vegetated areas were primarily controlled by medium to large floods (Q₁₀, Q₃₀), which combined with reduced time intervals between ordinary floods ≥ Q₂ most likely mobilized streambed sediments and limited the ability of vegetation to establish itself on bare gravel bars within the parafluvial zone. These findings can contribute to restoration action plans such as controlled flooding and sediment replenishments in the Sarine and other floodplain rivers of the Alps. © 2020 John Wiley & Sons, Ltd.