Assessing a numerical cellular braided-stream model with a physical model
Braidedchannel ; Channel geometry ; Concept ; Fluvial dynamics ; Model ; Numerical model ; Stream
The AA. test the representation of braidedchannel 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.
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
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
to discriminate between channels with single and multi-thread velocity fields.
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 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
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
from which measurements can be reliably made. They can also be related directly to bar theory for braided pattern development.
Asynchronous terrace development in degrading braidedchannels
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 braidedchannels in a laboratory flume and in a degrading braided
This paper describes a process of terrace development in rapidly degrading channels that produces a physically continuous terrace tread that consists of temporally nonsynchronous segments. Moreover, the AA. show that lower terraces developed
Channel pattern change downstream from a reservoir: an example of wandering braided rivers
Bank erosion ; Braidedchannel ; 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
model proposed by Schumm (1977) for prediction of channel changes.
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.
Modelling bedload yield in braided gravel bed rivers
Braidedchannel ; 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 braidedchannel. 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
River channel changes of the Subansiri in Assam, India
Assam ; Bank erosion ; Braidedchannel ; Channel geometry ; India ; Meander ; Photointerpretation ; Stream ; Twentieth Century
, 1970 and satellite imagery of 1990. The types of changes taking place in the Subansiri river channel are grouped into 4 categories. The river channel seems to make a remarkable change from a meandering pattern in 1920 towards a braided pattern by 1990
The sequential changes in the position of banklines as a result of bank erosion, as well as various changes in the channel have been studied in the Subansiri river in Assam, India. The study was carried out from available topographic maps of 1920
as seen from gradual increase in overall braiding intensity.
Evolution of mid-channel bars in a braided river and complex response to reservoir construction : an example from the middle Hanjiang River, China
Bank erosion ; Braidedchannel ; Carrying capacity ; Channel geometry ; China ; Dam ; Discharge ; Hydraulic works ; Runoff ; Stream
Using the middle Hanjiang River as an example, this paper deals with the development of mid-channel bars in a braided river, as controlled by channel boundary conditions, runoff and sediment load, as well as reservoir construction. Relations have
been established between indices describing the mid-channel bars and the controlling variables, such as the channel width, the percentage silt-clay content in the channel boundary and the energy expenditure of flowing water. Bank erosion exerts a marked
influence on the development of mid-channel bars after reservoir construction. A descriptive model showing the complex response has been established.
The effects of survey frequency on estimates of scour and fill in a braided river model
Alberta ; Braidedchannel ; 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 braidedchannel evolution, and identifies specific channel kinetics that cause scour-fill compensation. By using a small-scale physical
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 braidedchannel kinetics.
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
Alberta ; Braidedchannel ; 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
Channel adjustment and a test of rational regime theory in a proglacial braided stream
Alberta ; Braidedchannel ; Canada ; Channel geometry ; Discharge ; Grain size distribution ; Gravel ; Proglacial lake ; Sediment load ; Stream
The AA. analyze the historical trends in channel pattern and the contemporary downstream changes in channel geometry, grain size, and gradient in the gravel bed, proglacial Sunwapta River, Alberta. The rational equations incorporate the effect
of grain size and slope on channel width and the effect of width and grain size on channel slope. The regime equations are successful even though they were devised for single channel gravel streams. The results confirm the influence of grain size on channel
pattern thresholds and demonstrates, using spatial transitions in channel pattern, that channel pattern predictions based on stream power alone are inadequate.
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.
Channel pattern discrimination based on the relationship between channel slope and width
Braidedchannel ; Carrying capacity ; Channel geometry ; Comparative study ; Cross section ; Discriminant analysis ; Fluvial dynamics ; Longitudinal section ; Mathematical model ; Meander ; Model ; River bed ; Roughness ; Slope gradient ; Stream
The classic channel slope-discharge relationship proposed by Leopold and Wolman (1957) for channel pattern discrimination has been tested by a large database including 4 types of rivers : gravel-bed meandering rivers, gravel-bed braided rivers, sand
-bed meandering rivers and sand-bed braided rivers. The result shows that this relationship cannot discriminate channel patterns well when both gravel- and sand-bed rivers are considered. The channel width-bankfull discharge relationship suggested by XU
(1996) for discrimination of channel patterns of sand-bed rivers in China, is also tested in this study by the same database. Discussion of the results.
A large and geographically diverse data set consisting of meandering, braiding, incising, and post-incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds
of channel pattern and instability. An energy-based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics. The logistic regression approach developed in this study
provides an alternative tool for risk-based management of fluvial systems in the context of channel modifications and watershed disturbances.
Variability of bedload transport and channel morphology in a braided river hydraulic model
Carrying capacity ; Channel geometry ; Fluvial processes ; Meander ; Model ; River bed ; Stream
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
Bedload transport processes in a braided gravel bed river model
Applied hydrology ; Carrying capacity ; Channel geometry ; Flow ; Fluvial processes ; Model ; New Zealand ; South Island
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.
to descriptions in the literature of the braiding process. A new model for mid-channel bar growth is presented which helps explain the long-term development of the confluence-diffluence unit.
This paper provides data on the spatial and temporal pattern of surface velocity as mid-channel bar growth is initiated downstream of a fixed junction scour in a generic scale flume model. These flume data and interpretations are compared
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.