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  • Flow modelling in gravel-bed rivers: rethinking the bottom boundary condition
  • England ; Grain size distribution ; Gravel ; Model ; River bed ; Roughness ; Simulation ; Stream ; Stream flow ; United Kingdom
  • A key problem in computational fluid dynamics (CFD) modelling of gravel-bed rivers is the representation of multi-scale roughness, which spans the range from grain size, through bedforms, to channel topography. These different elements of roughness
  • -resolution topography. The results show the ability of the model to capture the spatially-averaged flow field and, thus, illustrate its potential for representing flow processes in natural gravel-bed rivers. Finally, practical data requirements
  • do not clearly map onto a model mesh and use of simple grain-scale roughness parameters may create numerical problems. This paper presents CFD simulations for 3 cases: a plane bed of fine gravel, a plane bed of fine gravel including large, widely
  • -spaced pebble clusters, and a plane gravel bed with smaller, more frequent, protruding elements. Here, the spatially-averaged velocity and eddy viscosity are used to investigate the applicability of the model, compared with using the explicit high
  • 2011
  • Active width of gravel-bed braided rivers
  • The AA. compare theoretical predictions of active width in gravel-bed braided rivers with observations from Sunwapta River, (Alberta, Canada), and from a generic physical model of gravel braided rivers, to describe and measure trends and variability
  • in active width. From these empirical results, the AA. formulate a general relation that predicts active width over a range of braided river types and flow conditions. This paper also raises questions about differences between hydraulically-based numerical
  • model computations of instantaneous active width and observation of time-integrated morphological active width. Understanding these differences can give insight into the nature of bedload transport in braided rivers and the relationship to morphological
  • 2011
  • Magnitude and frequency relations of bankfull flows and bed-material entrainment in the Llano River watershed, Central Texas, USA
  • The physical geography of medium-sized rivers, focusing on the Southeastern and South-Central United States. Part II
  • Bassin-versant ; Capacité de charge ; Cours d'eau ; Crue ; Débit de pointe ; Ecoulement fluvial ; Etats-Unis ; Géométrie hydraulique ; Llano River ; Texas ; Transport sédimentaire
  • Bankfull channel geometry and bed-material entrainment are examined in the Llano River watershed in central Texas, which is characterized by mixed alluvial-bedrock boundaries and a highly variable flow regime. Field data, including cross-section
  • surveys and sediment samples from 17 sites, are coupled with one-dimensional hydraulic models and flood-frequency analyses to compute recurrence intervals of bankfull and entrainment conditions. Recurrence intervals of flows that entrain median-sized bed
  • material are consistently less than 1 year, whereas flows that define bankfull morphology range from 1 to 4 years (median of 1.75 years). Recurrence intervals of flows responsible for incipient entrainment of relatively coarse bed material are typically
  • 2011
  • Applied hydrology ; Flood ; Flow resistance ; River bed ; Roughness ; Sediment transport ; Stream ; Stream flow ; Turbulence
  • arise from characterizing mobile beds, bed topography and its evolution and how these factors control rates of change of average velocity as discharge rises along a given river reach. Different issues can be recognized as a function of the spatial
  • and temporal scales of investigation. More emphasis should be placed upon reach-scale investigations. Detailed studies of bed topography, its maintenance, its evolution (at the reach scale) and its interactions with macroturbulence structure and sediment
  • 2011
  • Increase in coarse sediment transport associated with disturbance of gravel river beds by signal crayfish (Pacifastacus leniusculus)
  • Biogenic process ; Carrying capacity ; Crustacea ; Ecosystem ; England ; Experimentation ; Invasive species ; Leicestershire ; River bed ; Roughness ; Sediment load ; Sediment transport ; Stream ; United Kingdom ; Zoogeomorphology
  • further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux.
  • A series of flume experiments, using loose and water-worked gravel beds of narrowly graded grain sizes that were exposed to 6 h of crayfish activity under low-velocity flows, showed a substantial increase in the number of grains entrained
  • 2011
  • Bed scouring downstream of hydraulic structures under steady flow conditions : experimental analysis of space and time scales and implications for mathematical modeling
  • Experimentation ; Hydraulic works ; Impact ; Mathematical model ; River bed ; Scouring ; Sediment transport ; Simulation ; Stream
  • 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. 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
  • 2011
  • The origin and development of the Nyl River floodplain wetland, Limpopo Province, South Africa: trunk-tributary river interactions in a dryland setting
  • Floodplain ; Humid environment ; Limpopo ; River bed ; Sedimentation ; South Africa
  • The Nyl River floodplain wetland, one of South Africa’s largest floodplain wetlands and a Ramsar site of international conservation importance, is located in an area of long-term and still active valley sediment accumulation. Creation
  • of accommodation space for sedimentation has previously been attributed to tectonic controls, but new investigations reveal that a more likely cause is progradation of coarse-grained tributary fans across the narrow river valley downstream of the main area
  • 2011
  • Spatial and temporal controls on historical channel responses – study of an atypical case: Someşu Mic River, Romania
  • Channel geometry ; Climatic variability ; Geomorphometry ; Historical period ; Human impact ; Hydraulic works ; River bed ; Romania ; Stream
  • In this paper the spatial and temporal responses of the Someşu Mic River to natural and anthropogenic controls over the past 150 years are analysed, based on a series of morphometric parameters extracted from 5 successive sets of topographic maps
  • and one set of orthophotos. The AA. aim to 1) identify the main controlling factors of the river's dynamics, 2) evaluate the natural mechanisms of change in time and space and 3) estimate the deterioration degree of these natural mechanisms due to human
  • 2011
  • Effects of turbulence on the transport of individual particles as bedload in a gravel-bed river
  • This study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel-bed river. The experimental design implemented in the Eaton-North River (Québec, Canada) is based
  • 2011
  • Nonlinearity and unsteadiness in river meandering : a review of progress in theory and modelling
  • Bibliography ; Channel geometry ; Classification ; Fluvial dynamics ; Meander ; Model ; River bed ; Sediment transport ; Stream ; Topography
  • . Hence they first derive a classification of river bends based on a systematic assessment of the various physical mechanisms affecting their morphodynamic equilibrium and their evolution in response to variations of hydrodynamic forcing. They then review
  • some recent developments which allow to treat analytically the flow and bed topography of mildly curved and long nonlinear bends subject to steady forcing, taking advantage of the fact that flow and bed topography in mildly curved long bends are slowly
  • 2011
  • Oxbow lakes as indicators of river channel change : Leaf River, Mississippi, USA
  • The physical geography of medium-sized rivers, focusing on the Southeastern and South-Central United States. Part II
  • Action anthropique ; Cours d'eau ; Etats-Unis ; Exploitation des graviers ; Géométrie hydraulique ; Lac-croissant ; Leaf River ; Mississippi ; Méandre
  • This study uses oxbow lakes to ascertain the extent and nature of change in a river's form, focusing on the effects of post-1950s floodplain gravel extraction on the geomorphology of the Leaf River in southeastern Mississippi, USA. Data from 12
  • cross-sections suggests that the present-day river is 35% wider and 12% shallower than the cross-sectional geometry in cutoffs that pre-date 1955. Field measurements reveal that the Leaf River was relatively stable from at least 1911 to the early 1940s
  • tributary that deprived downstream areas of bed load and created profile adjustments.
  • 2011
  • linking of bed morphologies with turbulent flow fields, the intriguing question of what causes trains of highly-ordered sediment waves to form in beds of river sediments, and how to define the important characteristics of a dune-covered bed, including
  • 2011
  • Tree establishment on bars in low-order gravel-bed mountain streams
  • Alberta ; Canada ; Flood ; Mountain ; Plant colonization ; Riparian vegetation ; River bed ; Rocky Mountains ; Sedimentation ; Stream ; Tree ; Vegetation
  • gravel-bed mountain streams that does not conform to the standard lateral accretion model of tree recruitment for larger rivers. It is suggested that vertical accretion results in sediment deposition patterns on bars that are often highly patchy
  • 2011
  • Vegetation succession prevents dry lake beds from becoming dust sources in the semi-arid steppe region of China
  • Here the AA. chose eight inland dry lakes, one outflow lake and one river on the southeast edge of the Inner Mongolian Plateau to investigate vegetation patterns along transects from lake bed to lake shore, and determine the relationships between
  • vegetation patterns and environmental factors. The results show that dry lake bed soils have high contents of fine particles. Also, soil salt content is the most critical control on vegetation succession on desiccated lake beds. The AA. suggest grazing should
  • 2011
  • Riffle-pool morphometry and stage-dependant morphodynamics of a large floodplain river (Vereinigte Mulde, Sachsen-Anhalt, Germany)
  • In this study a monitoring approach is employed that focuses on analysing cross-sectional and longitudinal channel geometry of a large floodplain river (Vereinigte Mulde, Sachsen-Anhalt) with a high temporal and spatial resolution, in order
  • to conclude from stage-dependant morphometric changes to riffle and pool maintaining processes. An index for the longitudinal amplitude of riffle-pool sequences, the bed undulation intensity or bedform amplitude, is introduced and proved to be highly
  • significant as a form parameter, its first derivative as a process parameter. The process of pool scour and riffle fill is addressed as bedform maintenance or bedform accentuation. It is indicated by increasing longitudinal bed amplitudes. According
  • to the observed dynamics of bed amplitudes, maintenance of riffle-pool sequence lags behind discharge peaks.
  • 2011
  • River channel and bar patterns explained and predicted by an empirical and a physics-based method
  • The AA. compare an empirical stream power-based classification and a physics-based bar pattern predictor. They present a careful selection of data from the literature that contains rivers with discharge and median bed particle size ranging over
  • flood, valley gradient and channel width predicted with a hydraulic geometry relation. ‘Thresholds’, above which certain patterns emerge, were identified as a function of bed sediment size. Bar theory predicts nature and presence of bars and bar mode
  • , here converted to active braiding index (Bi). The most important variables are actual width–depth ratio and nonlinearity of bed sediment transport. Results agree reasonably well with data.
  • 2011
  • Downstream effects of impounding a natural lake: the Snake River downstream from Jackson Lake Dam, Wyoming, USA
  • Aménagement hydraulique ; Barrage ; Bilan sédimentaire ; Cours d'eau ; Etats-Unis ; Gravier ; Géométrie hydraulique ; Snake River ; Transport sédimentaire ; Wyoming
  • Calibration of the transport relations was based on bed load transport data collected over a wide range of flows on the Snake River and its 2 major tributaries within the study area in 2006 and 2007. Comparison of actual flows with unregulated flows
  • magnitudes, common floods are capable of mobilizing the bed material. Calculations suggest that the Snake River was not in equilibrium before construction of JLD, but was naturally in sediment deficit. This result highlights the value of transport data
  • 2011
  • Modelling time varying scouring at bed sills
  • Discharge ; Flood ; Fluvial erosion ; Geotechnics ; Model ; Numerical model ; River bed ; Scouring ; Stream ; Stream flow
  • of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow
  • 2011
  • Aménagement hydraulique ; British Columbia ; Canada ; Chenal ; Cours d'eau ; Crue ; Granulométrie ; Gravier ; Sable ; Sédimentologie ; Transport sédimentaire ; Vedder River
  • The new channel (Vedder Canal) had a fine bed and a much lower slope than the gravel-bed river immediately upstream. Changes in morphology and sedimentology as gravel advanced into and along the Canal are documented using air photos, historical
  • advanced by the sequential development of discrete gravel tops on initially sandy alternate bars. Calculations show that even though the gravel bed at the head of the Canal is almost unimodal, size-selective transport during floods can account
  • 2011
  • Carrying capacity ; Digital elevation model ; Experimentation ; Fluvial hydrology ; Grain size distribution ; River bed ; River regime ; Roughness ; Sediment load ; Sedimentary structure ; Stream ; Topography
  • (zero sediment feeding) and recirculation. The objective is to quantify and evaluate the relationships between bed surface topography and sediment availability. The implications of these observations in terms of sediment transport and bed roughness
  • 2011