Assessing a numerical cellular braided-stream model with a physical model
Braided channel ; Channel geometry ; Concept ; Fluvial dynamics ; Model ; Numerical model ; Stream
The AA. test the representation of braided channel morphodynamics in the Murray-Paola model, MP model, against the known characteristics (mainly from a sequence of high resolution digital elevation models) of a physical model of a braided stream
. It achieves this by initiating the model from real braided topography rather than white noise. This extension of the application of the MP model is used to identify characteristics that are not reproduced, to investigate their causes, propose modifications
and discuss both the implications for the formation of braiding and alternative modelling strategies.
Geomorphological studies of braided rivers still lack a consistent measurement of the complexity of the braided pattern. Several simple indices have been proposed and two (channel count and total sinuosity) are the most commonly applied. A series
of experiments was run using small-scale physical models of braided rivers in a 3 m x 20 m flume. Sampling criteria for braid indices and their comparability were assessed using constant-discharge experiments. Sample hydrographs were run to assess the effect
of flow variability. Functional relationships between channel pattern and, for example, discharge, are sensitive to the choice of braid index. At present, channel count indices give the best combination of rapid measurement, precision, and range of sources
from which measurements can be reliably made. They can also be related directly to bar theory for braided pattern development.
Alberta ; Braided channel ; Canada ; Channel geometry ; Comparative study ; Model ; Sediment transport ; Stream
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
Bedload transport processes in a braided gravel bed river model
A 1:50 scale hydraulic model was designed, based on Froude number similarity and using hydrological and sediment data from a small braided gravel-bed river (the North Branch of the Ashburton River, Canterbury, New Zealand). The qualitative results
of the experiments using steady flows and unsteady flows reveal the nature of bedload transport (BLT) processes in braided rivers, particularly regarding variability of BLT in braided rivers.
Channel morphology and bed load pulses in braided, gravel-bed streams
Small-scale hydraulic laboratory models based on Froude modelling criteria were used to investigate : 1) the influence of gradient and discharge on the average cross-sectional geometry and channel pattern of braided streams| b) the temporal
variability of braided stream morphology at constant gradient and discharge| c) the relationship between this temporal variability in morphology, the occurrence of bed-load pulses and the nature of bed-load transfer processes in gravel-bed braided streams.
Direct measurement of three-dimensional flow fields and morphological evolution of the anabranches in the braided Brahmaputra-Jamuna River, Bangladesh, were undertaken to investigate the interactions between fluvial processes and anabranch
morphology. These data were used to elucidate the circumstances leading to the bifurcation of a single channel, with a topic of fundamental importance to understanding the physical processes responsible for braiding. An empirical relationship was established
Modelling bedload yield in braided gravel bed rivers
Braided channel ; Carrying capacity ; Channel geometry ; Discharge ; Gravel ; Model ; New Zealand ; Numerical model ; Sediment load ; South Island ; Stream
This paper outlines an approach for estimating the annual bedload yield of a braided channel. This procedure is based on the extension of the theory of flow and sediment transport in braided rivers recently presented by Paola (1996). The potential
This work is aimed at the characterization of the morphology of braided streams, in order to assess whether the system reaches a steady state under constant flow conditions and, in that case, to determine how it can be described and on which
the occurence of a steady state. A set of parameters was considered, such as the braid plain width and the number and typology of branches and nodes. Results point out that a relationships exists between braiding morphology and 2 dimensionless parameters
, related to total water discharge and stream power. The paper ends with a discussion on different width definitions and on the relationship between width and discharge, that distinctively characterize the braided pattern.
The effects of survey frequency on estimates of scour and fill in a braided river model
Alberta ; Braided channel ; Canada ; Carrying capacity ; Channel geometry ; Fluvial dynamics ; Model ; Sediment transport ; Spatial analysis ; Stream
This study examines the magnitude of bias associated with compensation events that occur at the temporal scale of braided channel evolution, and identifies specific channel kinetics that cause scour-fill compensation. By using a small-scale physical
model it is possible to essentially eliminate compensation resulting from variation in discharge by maintaining constant discharge. Also, river-bed topography can be mapped relatively easily and frequently using a flume. Hence, a small-scale braided
gravel-bed river model is used in this study to examine the magnitude and nature of scour-fill and to relate the spatial pattern of compensation to braided channel kinetics.
Chaos and order. The channel geometry of gravel bed braided rivers in Geomorphological models. Theoretical and empirical aspects.
During their studies in Butramo basin, Calabria, the AA. became convinced that the braided rivers are not at all chaotic, but are extremely well regulated fluvial systems with an optimum efficiency in carrying both water and bed load.
Asynchronous terrace development in degrading braided channels
in the upstream portion of a degrading channel may correlate with higher terrace surfaces developed farther down channel. The results are based upon data collected and observations made in degrading braided channels in a laboratory flume and in a degrading braided
Gravel transport and morphological change in braided Sunwapta River, Alberta, Canada
Alberta ; Braided stream ; Canada ; Carrying capacity ; Channel geometry ; Fluvial erosion ; Fluvial processes ; River bed ; Sediment budget ; Sediment transport
The relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated, daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial Sunwapta River, Alberta
Bed load transport in braided gravel-bed stream models
This paper presents the results of bed load transport measurements from several small-scale gravel braided streams formed at various combinations of slope and constant discharge. These data present an opportunity to investigate the form of sediment
transport relationships for braided streams, assess the extent to which the model results may be directly applicable to field prototypes, and investigate the nature of temporal fluctuations around the mean transport rate.
Channel pattern change downstream from a reservoir: an example of wandering braided rivers
Bank erosion ; Braided channel ; Channel geometry ; China ; Experimentation ; Fluvial erosion ; Model ; Reservoir ; Stream
This study will deal with the downstream channel pattern change by a comparison between three famous wandering braided rivers in China, namely, the Yongdinghe, the hanjiang, and the Yellow Rivers. Firstly, there is a discussion on the qualitative
Bank erosion ; Braided channel ; Erosion ; Fluvial processes ; Model ; Network ; Sediment transport ; Slope gradient ; Stream
The AA. examine some of the detailed characteristics of this cellular computer model. They show the qualitative form of the braiding produced by the model is generally insensitive to changes in most of the numerical parameters used in the model
. The most crucial parameter choice is the use of a non-linear exponent (>1) to describe the relation between sediment flux and local stream power. In addition, the AA. show that there is a simple and apparently fundamental connection between braided-stream
Terminal Pleistocene braided to meandering transition in rivers of the Southeastern USA
Braided channel ; C 14 dating ; Channel geometry ; Climatic variation ; Georgia (USA) ; Meander ; North Carolina ; Palaeo-environment ; Palaeohydrology ; Pleistocene ; South Carolina ; Stream ; United States of America
Thirteen paleomeanders on the oldest parts of meander belts on floodplains in the Coastal Plain of Georgia and the Carolinas (southeastern USA) were selected for radiocarbon dating to determine the onset of meandering following braiding during
the Late Pleistocene during Oxygen Isotope Stage 2. The radiocarbon ages were compared to previously reported Late Pleistocene ages for braid bars and eolian dunes.
Variability of bedload transport and channel morphology in a braided river hydraulic model
The objectives of this paper are: 1) to assess variability in bedload transport and channel morphology in a 1:50 hydraulic model of a braided river under replicate runs, where all the controlling variables are held constant; 2) to investigate
Secondary flow in anabranch confluences of a braided, graveled-bed stream
This paper reports the results of field measurements made with the objective of documenting the primary (downstream) and secondary (cross-stream) flow fields. Measurements of the velocity components were made in two, active, braided river anabranch
Sediment size variation in a braided reach of the Sunwapta River, Alberta, Canada
The downstream diminution in sediment size in a braided reach of the proglacial Sunwapta River, was examined statistically to identify the sources of the observed variation about an expected exponential relationship between clast size and distance