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1. Channel-floodplain response to changes in sediment supply and floodplain width

   Viparelli, E; Eke, E (August 2020, Taylor and Francis)

   Flow regime, sediment supply and base level control geometry and evolution of alluvial channels and floodplains. Single thread rivers subject to constant forcing can reach equi-librium conditions in which the amount of sediment deposited on the floodplain through point bar deposition and overbank sedimentation is balanced by erosion of floodplain sed-iment through channel migration. At equilibrium, floodplain slope and sediment size dis-tribution, reach-averaged channel geometry (width and depth) and channel migration rates do not change in time. In response to changes in sediment supply and floodplain width, channel geometry and migration rate, floodplain slope and size distribution are expected to evolve in space and time. Predicting this response remains an open problem for geoscien-tists and engineers. Here we use an equilibrium solution of a 1D morphodynamic frame-work of channel-floodplain evolution to investigate how equilibrium conditions change as a function of sediment supply and floodplain width. Sediment is modeled here as a mix-ture of two grain sizes, sand and mud. Channel migration rate and width are functions of near-bank flow properties and floodplain characteristics. We zero the model using input parameters based on the pre-1930 ~ reach of the Minnesota River from Mankato to Jordan, USA, where data is available for proper field scale model verification. We then use the validated model to quantify the long-term (equilibrium) response of the schematic reach to changes in sediment supply magnitude and size distribution, as well as to changes in floodplain width. 

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2. Equilibrium of Self‐Formed, Single‐Thread, Sand‐Bed Rivers

   https://doi.org/10.1029/2021GL094591  

   Viparelli, E.; Eke, E. C. (October 2021, Geophysical Research Letters)

   Abstract Equilibrium geometry of single‐thread rivers with fixed width (engineered rivers) is determined with a flow resistance relation and a sediment transport relation, if characteristic discharge, sediment caliber and supply are specified. In self‐formed channels, however, channel width is not imposed, and one more relation is needed to predict equilibrium geometry. Specifying this relation remains an open problem. Here we present a new model that brings together a coherent train of research progress over 35 years to predict equilibrium geometry of single‐thread rivers from the conservation of channel and floodplain material. Predicted channel geometries are comparable with field observations. In response to increasing floodplain width, sand load and grain size, the equilibrium slope increases, bankfull depth and width decrease. As the volume fraction content of mud in the sediment load increases, bankfull width‐to‐depth ratio and slope decrease suggesting that mud load has a strong control on channel patterns and bankfull geometry. 

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3. Sediment Transport Potential in a Hydraulically Connected River and Floodplain‐Channel System

   https://doi.org/10.1029/2020WR028852  

   Sumaiya, Sumaiya; Czuba, Jonathan A.; Schubert, John T.; David, Scott R.; Johnston, Graham H.; Edmonds, Douglas A. (May 2021, Water Resources Research)

   Abstract Meandering river floodplains often contain intermittently flooded complex channel networks. Many questions remain as to the pervasiveness, function, and evolution of these floodplain channels. In this present work, we analyzed size‐specific sediment transport potential and assessed whether the channelized floodplain of the meandering East Fork White River near Seymour, Indiana is on a net erosional or depositional trajectory. We applied a two‐dimensional hydrodynamic model and used simulated model results to estimate the largest sediment size that can be moved in suspension and as bedload at various flows for grain size classes between 4 µm and 64 mm. We developed a probabilistic method that integrates the largest sediment size that can be moved at various flows to compute an effective grain size, which we compared to measured field data. Results show that the river is capable of supplying sand to the floodplain and these floodplain channels can transport sand in suspension and gravel as bedload. This suggests that sediment supplied from the river could be transported as bedload in floodplain channels. These floodplain channels are supply limited under the current hydrologic regime and the grain size distribution of the bed surface is set by the flow conditions; thus, these floodplain channels are net erosional. Finally, our proposed method of probabilistically integrating the largest sediment size that can be moved at various flows can be used to predict the upper end of the grain size distribution in suspension and in bed material, which is applicable to floodplains as well as coastal areas. 

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4. Sediment Routing and Floodplain Exchange (SeRFE): A Spatially Explicit Model of Sediment Balance and Connectivity Through River Networks

   https://doi.org/10.1029/2020MS002048  

   Gilbert, Jordan_T; Wilcox, Andrew_C (September 2020, Journal of Advances in Modeling Earth Systems)

   Abstract Sediment regimes, i.e., the processes that recruit, transport, and store sediment, create the physical habitats that underpin river‐floodplain ecosystems. Natural and human‐induced disturbances that alter sediment regimes can have cascading effects on river and floodplain morphology, ecosystems, and a river's ability to provide ecosystem services, yet prediction of the response of sediment dynamics to disturbance is challenging. We developed the Sediment Routing and Floodplain Exchange (SeRFE) model, which is a network‐based, spatially explicit framework for modeling sediment recruitment to and subsequent transport through drainage networks. SeRFE additionally tracks the spatially and temporally variable balance between sediment supply and transport capacity. Simulations using SeRFE can account for various types of watershed disturbance and for channel‐floodplain sediment exchange. SeRFE is simple, adaptable, and can be run with widely available geospatial data and limited field data. The model is driven by real or user‐generated hydrographs, allowing the user to assess the combined effects of disturbance, channel‐floodplain interactions and particular flow scenarios on the propagation of disturbances throughout a drainage network, and the resulting impacts to reaches of interest. We tested the model in the Santa Clara River basin, Southern California, in subbasins affected by large dams and wildfire. Model results highlight the importance of hydrologic conditions on postwildfire sediment yield and illustrate the spatial extent of dam‐induced sediment deficit during a flood. SeRFE can provide contextual information on reach‐scale sediment balance conditions, sensitivity to altered sediment regimes, and potential for morphologic change for managers and practitioners working in disturbed watersheds. 

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5. A mathematical model for bedrock incision in near‐threshold gravel‐bed rivers

   https://doi.org/10.1002/esp.5957  

   Gabel, Vanessa; Tucker, Gregory E; Campforts, Benjamin (July 2025, Earth Surface Processes and Landforms)

   Gravel‐bed rivers that incise into bedrock are common worldwide. These systems have many similarities with other alluvial channels: they transport large amounts of sediment and adjust their forms in response to discharge and sediment supply. At the same time, the occurrence of bedrock incision implies behaviour that falls on a spectrum between fully detachment‐limited ‘bedrock channels’ and fully transport‐limited ‘alluvial channels’. Here, we present a mathematical model of river profile evolution that integrates bedrock erosion, gravel transport and the formation of channels whose hydraulic geometry is consistent with that of near‐threshold alluvial channels. We combine theory for five interrelated processes: bedload sediment transport in equilibrium gravel‐bed channels, channel width adjustment to flow and sediment characteristics, abrasion of bedrock by mobile sediment, plucking of bedrock and progressive loss of gravel‐sized sediment due to grain attrition. This model contributes to a growing class of models that seek to capture the dynamics of both bedrock incision and alluvial sediment transport. We demonstrate the model's ability to reproduce expected fluvial features such as inverse power law scaling between slope and area, and width and depth consistent with near‐threshold channel theory, and we discuss the role of sediment characteristics in influencing the mode of channel behaviour, erosional mechanism, channel steepness and profile concavity. 

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