Enrica Viparelli

University of South Carolina | USC · Department of Civil & Environmental Engineering

Gravel bed rivers often display pool‐riffle morphology. Downstream changes in channel width are often correlated with pool‐riffle topography. Considering self‐formed, alluvial, straight and single‐thread gravel‐bed rivers, here we provide an analytical solution for their equilibrium pool‐riffle morphology in the presence of spatially varying widths...

Convergent estuaries have been shortened by dam‐like structures worldwide. Here, we evaluate 31 long‐term water level stations and use a semi‐analytical tide model to investigate how landward‐funneling and a dam influence tidal and storm surge propagation in the greater Charleston Harbor region, South Carolina, where three rivers meet: the Ashley,...

Turbidity currents, which are stratified, sediment-laden bottom flows in the ocean or lakes, can run out for 100's to 1000's of kilometers in submarine channels without losing their stratified structure. Here we derive a layer-averaged, two-layer model for turbidity currents, specifically designed to capture long-runout. Previous models have captur...

Channel stability and sediment transport in gravel bed streams depend on temporally and spatially variable fluid forces, bed surface structures, armoring, and sediment supply/storage. Of particular interest here is the influence of sediment supply timing on bedload transport rate and grain size distribution, bed surface composition and channel morp...

Downstream width variations can generate pool‐riffle morphology under experimental conditions, in numerical simulations and natural river channels. The present understanding of how pool‐riffle morphology varies with sediment supply and caliber, however, is insufficient due to the limited range of sediment supply rates explored in previous experimen...

Convergent coastal-plain estuaries have been shortened by dam-like structures worldwide. We used 31 long-term water level stations and a semi-analytical tide model to investigate the influence of a dam and landward-funneling on tides and storm surge propagation in the greater Charleston Harbor region, South Carolina, where three rivers meet: the As...

Notwithstanding the large number of studies on bedforms such as dunes and antidunes, predicting equilibrium bedform type and geometry for a given flow regime, sediment supply and caliber remains an open problem. Here, we present results from laboratory experiments specifically designed to study how upper regime bedform type and geometry vary with s...

A robustly calibrated and validated hydrodynamic model depicts flow patterns over a topographically complex floodplain with a heterogeneous main channel levee. Simulations highlight floodplain inundation dynamics for two conditions, the passage of sub‐bankfull and overbank flood waves. Sub‐bankfull inundation commences with the passage of the flood...

The Waal Branch of the Rhine River has eroded over the last 150 years following channel straightening and narrowing. In 2014–2015 a pilot project replaced existing groynes over an 11 km long reach with three longitudinal training walls (LTWs) to mitigate channel bed erosion, among other purposes. Walls are lower than the river bank and split the fl...

Modeling transport, erosion, and deposition of nonuniform sediment over temporal intervals that are short compared to those characterizing channel bed aggradation and degradation remains an open problem due to the complex quantification of the sediment fluxes between the bed material load and the alluvial deposit. Parker, Paola, and Leclair in 2000...

Engineering modifications of rivers, e.g., dams or groynes, often induce long-term riverbed erosion, which can be mitigated with sediment nourishments. Here, we consider nourishments to mitigate channel bed erosion induced by channel narrowing, as opposed to the more common application downstream of dams. Our objective is to assess and quantify how...

Floodplain inundation has been viewed as a type of binary process set by the relative elevation between river stage and levee crest. However, recent reports in the literature show that this perception may have limited applicability. In particular, through‐bank channels, conduits that cross the main river levees or banks, facilitate conditions for a...

We present a novel approach for detecting surface water flows over flooded terrain. The approach requires a minimum of three stage measurements and can be applied to any inundated surface, across a range of temporal and spatial scales. This method creates new and robust opportunities for field observation and for validation of numerical simulations...

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 equilibr...

Rivers that traverse the terrestrial‐marine interface may have lower reaches that are influenced by both terrestrial and marine processes. However, only a handful of studies have focused on how the interactions of fluvial and tidal processes translate to channel geomorphology, and those are largely from delta/distributary systems. Here we quantify...

Intraslope basins, or minibasins, are topographic features of the continental slope that can be filled with sediment transported by submarine flows. These deposits may contain important hydrocarbon reservoirs. Here we present results of two-dimensional numerical simulations of multiple turbidity currents entering two linked minibasins. The numerica...

Plain Language Summary Over two thirds of the world's large rivers are heavily engineered. Human intervention has important consequences for river channels, which erode and aggrade in response to measures like dam construction, channelization, and diversion. Such bed level change can directly (and severely) affect flood safety, navigation, and ecol...

Recent studies reveal that low‐slope bedrock reaches (bedrock surface slope milder than ~5 m/km) are more common than previously thought and can be found in engineered rivers and densely populated deltas. Here we present a novel formulation of alluvial morphodynamics of low‐slope bedrock rivers transporting nonuniform bed material that accounts for...

Intermittent floodplain channels are low‐relief conduits etched into the floodplain surface and remain dry much of the year. These channels comprise expansive systems and are important because during low‐level inundation they facilitate lateral hydraulic connectivity throughout the floodplain. Nevertheless, few studies have focused on these floodpl...

Research on the morphodynamics of bedrock rivers has primarily focused on bedrock incision, and little is known about the alluvial morphodynamics of rivers with exposed bedrock surfaces. More specifically, there is a lack of information on the morphodynamics of low slope bedrock reaches due to the recent recognition of such systems. Here, we presen...

Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross‐laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms f...

The complex interactions between flow hydrodynamics, sediment transport, geometry, and changes in base level control the morphodynamic evolution of tidal channels, inlets, and estuaries. Research on these complex settings have involved decades of field, laboratory, and modeling work. Studies on the one-dimensional morphodynamic of well-mixed, tide-...

Different base level scenarios have been imposed to a sand-gravel laboratory Gilbert delta to gain insight on its dynamics under varying base level. Base level rise results in intensified aggradation over the topset, as well as a decrease in topset slope and topset surface coarsening, the signals of which migrate in an upstream direction. Preferent...

In response to changes in the upstream controls (i.e., the water discharge, the sediment supply rate, and the calibre of the load), engineered alluvial channels adjust their bed slope and bed surface texture to establish a new equilibrium state. Here we present and discuss various causes of degradational response of engineered channels to changes i...

Downstream fining of bed sediment in alluvial rivers is usually gradual but often an abrupt decrease in characteristic grain size occurs from about 10 to 1 mm, i.e. a gravel-sand transition (GST) or gravel front. Here we present an analytical model of GST migration that explicitly accounts for gravel and sand transport and deposition in the gravel...

Understanding of the formative conditions of fluvial bedforms is significant for both river management and geological studies. Diagrams showing bedform stability conditions have been widely used for the analyses of sedimentary structures. However, the use of discriminants to determine the boundaries of different bedforms regimes has not yet been ex...

When the water discharge, sediment supply, and base level vary around stable values, an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state (i.e. a dynamic or statistical equilibrium state). Here we present analytical relations describing the mean equilibrium geometry of an alluvial river...

In numerical models of gravel bed river morphodynamics the bed material is described as a mixture of sand and gravel. In these models sedimentation processes are generally simplified by dividing the channel bed deposit in two regions: one or more mixed layers whose particles can interact with the bedload, and the substrate whose grain size distribu...

The collection of time-sensitive data on real-life embankment failures and their analysis are essential steps to model breach processes and the consequential flood, which are of great importance for preparing emergency action plans. In this paper, data on 14 earthen embankments that failed or were damaged in the Midlands of South Carolina resulting...

Results from laboratory experiments on conservative density current confluence are reported. Hydraulic characteristics and morphodynamic consequences of the confluence of two continuous release density currents in a horizontal, 45° asymmetrical junction are examined and compared to those of terrestrial subaerial river junctions. It was observed tha...

There has been quite some debate on the relative importance of particle abrasion and grain size selective transport regarding the river profile form and the associated grain size trends in a graded alluvial stream. Here we present new theoretical equations for the graded alluvial river profile that account for the effects of particle abrasion and g...

The bankfull geometry of alluvial rivers is thought to be controlled by water and sediment supply, and characteristic sediment size. Here we demonstrate a novel finding: when bankfull shear velocity and bankfull depth are correlated against bed material grain size and bed slope, they are to first order independent of grain size and dependent on wat...

Bed material transported in geomorphically active gravel bed rivers often has a local source at nearby eroding banks and ends up sequestered in bars not far downstream. However, most 1-D numerical models for gravel transport assume that gravel originates from and deposits on the channel bed. In this paper, we present a 1-D framework for simulating...

Sorting and selective transport of particles by material density is important for understanding a wide range of processes, including the formation of mineral placers, deposition of mine tailings and routing of tracers and contaminants. This article describes an experimental study of the transport of mixtures of particles differing density in a sedi...

The lowermost Mississippi River, defined herein as the river segment downstream of the Old River Control Structure and hydrodynamically influenced by the Gulf of Mexico, extends for approximately 500 km. This segment includes a bedrock (or more precisely, mixed bedrock-alluvial) reach that is bounded by an upstream alluvial-bedrock transition and a...

The 1-D saltation–abrasion model of channel bedrock incision of Sklar and Dietrich (2004), in which the erosion rate is buffered by the surface area fraction of bedrock covered by alluvium, was a major advance over models that treat river erosion as a function of bed slope and drainage area. Their model is, however, limited because it calculates be...

The bankfull geometry of alluvial rivers is thought to be controlled by water and sediment supply, and characteristic sediment size. Here we demonstrate a novel finding: when bankfull shear velocity and bankfull depth are correlated against bed material grain size and bed slope, they are to first order independent of grain size and dependent on wat...

This research implements a recently proposed framework for meander migration, in order to explore the coevolution of planform and channel width in a freely meandering river. In the model described here, width evolution is coupled to channel migration through two submodels, one describing bank erosion and the other describing bank deposition. Bank e...

A one-dimensional model that is able to store the stratigraphy emplaced by a prograding delta is validated against experimental results. The laboratory experiment describes the migration of a Gilbert delta on a sloping basement into standing water, i.e., a condition in which the stratigraphy emplaced by the delta front is entirely stored in the dep...

Sediment sourced from river banks, either through widening or progressive meander bend migration, can represent an important component of a river's bed material load. However, sediment exchange with a floodplain is not necessarily even, and both the size distribution and overall rates of transfer into and out of a channel can influence the overall...

The 1-D saltation-abrasion model of channel bedrock incision of Sklar and Dietrich, in which the erosion rate is buffered by the surface area fraction of bedrock covered by alluvium, was a major advance over models that treat river erosion as a function of bed slope and drainage area. Their model is, however, limited because it calculates bed cover...

The Mississippi River delta is undergoing a catastrophic drowning, whereby 5,000 km2 of low-lying wetlands have converted to open water over at least the past eight decades, as a result of many anthropogenic and natural factors. Continued net land loss has been thought inevitable due to a decline in the load of total suspended sediment--both sand a...

A one-dimensional model that is able to store the stratigraphy emplaced by prograding bedforms with a downstream slip face is validated against experimental results. The laboratory experiment describes the migration of a Gilbert delta on a sloping basement into standing water, i.e. a condition in which the stratigraphy emplaced by the delta front (...

Developing accurate long-term, basin-scale sediment budgets using isotopic sediment fingerprints requires a sediment routing model that not only accounts for a range of sediment source terms (e.g. tributaries, surface erosion and erosion of bluffs and terraces) but also considers the variation in time of volume and tracer concentration for the sedi...

A numerical model that predicts the stratigraphy of a prograding Gilbert delta is presented. Such a Gilbert delta is formed when a river is flowing into a deep basin and the sediment transported by the river downstream avalanches downa steep slope.These deltas are characterized by thin and relatively low-slope topsets, steep foresets (the progradin...

The term "breaching" refers to the slow, retrogressive failure of a steep subaqueous slope, so forming a nearly vertical turbidity current directed down the face. This mechanism, first identified by the dredging industry, has remained largely unexplored, and yet evidence exists to link breaching to the formation of sustained turbidity currents in t...

Although sediment is a natural constituent of rivers, excess loading to rivers and streams is a leading cause of impairment and biodiversity loss. Remedial actions require identification of the sources and mechanisms of sediment supply. This task is complicated by the scale and complexity of large watersheds as well as changes in climate and land u...

A numerical model to predict ecological succession in deltaic environments has been developed in the context of the NCED (National Center for Earth-surface Dynamics) multidisciplinary effort on coastal restoration in Louisiana, where a considerable amount of land loss has been recorded in the last decades. The previous modeling effort of the NCED g...

Major changes in the morphology of the Trinity River in California, such as narrowing of the cross section and sedimentation of fine sediment in pools, occurred after the closure of a system of dams. These changes caused a dramatic reduction in the salmonid population and a resulting decline of the fishery. Gravel augmentation, regulated flood rele...

Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Presen...

As a river-carrying sediment mixture aggrade, it creates a stratigraphic signature that records this evolution. This stratigraphy is characterized by the vertical/horizontal variation of substrate grain size distribution. If a river degrades, it mines this stratigraphy, and transfers the sediment so accessed farther downstream. Although several num...

Rivers with poorly-sorted bed sediment create their own stratigraphy as they deposit sediment. Prediction of the subsequent river degradation into its own deposit requires knowledge of the spatial structure of the grain size variation of the deposit. The ultimate goal of the present work is the development, testing and verification against experime...

One way to study the mechanism of gravel bed load transport is to seed the bed with marked gravel tracer particles within a chosen patch and to follow the pattern of migration and dispersal of particles from this patch. In this study, we invoke the probabilistic Exner equation for sediment conservation of bed gravel, formulated in terms of the diff...

We have developed a sediment routing model of the Maple River, southern Minnesota, to test multiple hypotheses regarding the effects of natural and human disturbances on the contribution of sediment from multiple sources and transport of that sediment through the river network. The watershed-scale sediment dynamics are strongly influenced by two fa...

Downstream fining, i.e. the tendency for a gradual decrease in grain size in the downstream direction, has been observed and studied in alluvial rivers and in laboratory flumes. Its classical explanations include a) abrasion due to successive collisions of individual grains, and b) selective deposition, which occurs because coarser particles, being...

This study focuses on a numerical model of turbidity currents with reversing buoyancy, i.e., flows that are rendered heavier than the ambient water due to the presence of suspended sediment but that as sedimentation progresses become lighter than the ambient water due to a difference in temperature or salinity. The flows considered here may be eith...

Modeling sediment fluxes and pathways in complex landscapes is limited by our inability to accurately measure and integrate heterogeneous, spatially distributed sources into a single coherent, predictive geomorphic transport law. In this study, we partition the complex landscape of the Le Sueur River watershed into five distributed primary source t...

Aone-dimensional model describing bed evolution in awater-feed flume is presented.The model considers conditions of lower-regime plane bed. Sediment transport can be modeled as uniform in size or as a mixture of different grain sizes. As in some previous morphodynamic models with sediment mixtures, the active layer approximation has been introduced...

Floods in alluvial rivers are characterized by channels incision in the alluvial bed during the rising stage and their filling up in the falling stage; this phenomenon is well known and called scour and fill. In this work scour and fill during floods will be described as bar migration in the alluvial bed; when bar trough reaches the riverbank prote...