scholarly journals Confluence Dynamics in a Modelled Large Sand-Bed Braided River

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1829
Author(s):  
Haiyan Yang ◽  
Peitong Cong
Keyword(s):  
Laboratory Experiments ◽  
Controlling Factors ◽  
Dynamic Processes ◽  
Suspended Sediment Transport ◽  
Braided River ◽  
Complex Flow ◽  
Field Surveys ◽  
Braided Rivers ◽  
Bed Deformation ◽  
Morphologic Changes

Confluences are key morphological nodes in braided rivers where flow converges, creating complex flow patterns and rapid bed deformation. Field surveys and laboratory experiments have been carried out to investigate the morphodynamic features in individual confluences, but few have investigated the evolution processes of confluences in large braided rivers. In the current study, a physics-based numerical model was applied to simulate a large lowland braided river dominated by suspended sediment transport, and analyze the morphologic changes at confluences and their controlling factors. It was found that the confluences in large braided rivers exhibit some dynamic processes and geometric characteristics that are similar to those observed in individual confluences arising from two tributaries. However, they also show some unique characteristics that may result from the influence of the overall braided pattern and especially of their neighboring upstream channels.

scholarly journals Modelling confluence dynamics in large sand-bed braided rivers

2018 ◽  
Author(s):  
Haiyan Yang ◽  
Zhenhuan Liu
Keyword(s):  
Field Survey ◽  
Experimental Studies ◽  
Controlling Factors ◽  
Dynamic Processes ◽  
Suspended Sediment Transport ◽  
Braided River ◽  
Complex Flow ◽  
Braided Rivers ◽  
Bed Deformation ◽  
Morphologic Changes

Abstract. Confluences are key morphological nodes in braided rivers where flow converges, creating complex flow patterns and rapid bed deformation. Field survey and laboratory experimental studies have been carried out to investigate the morphodynamic features in individual confluences, but few have investigated the evolution process of confluences in large braided rivers. In the current study a physics-based numerical model was applied to simulate a large lowland braided river dominated by suspended sediment transport, and analyzed the morphologic changes at confluences and their controlling factors. It was found that the confluences in large braided rivers exhibit some dynamic processes and geometric characteristics that are similar to those observed in individual confluences arising from two tributaries. However, they also show some unique characteristics that are result from the influence of the overall braided pattern and especially of neighboring upstream channels.

scholarly journals Physical Modeling of Landward Scour Due to Tsunami Bore Overtopping Seawall

2018 ◽  
Vol 203 ◽  
pp. 01003
Author(s):  
Raidan Maqtan ◽  
Badronnisa Yusuf ◽  
Saiful Bahri Hamzah
Keyword(s):  
Froude Number ◽  
Laboratory Experiments ◽  
Negative Relationship ◽  
Structural Performance ◽  
Flow Depth ◽  
Initial Water ◽  
Field Surveys ◽  
Strong Positive Relationship ◽  
Strong Negative Relationship ◽  
Wave Forms

many of the post tsunami field surveys which conducted by researchers revealed that, the failure due to scour at the landward toe of the seawall due to overtopping of tsunami wave forms one of the important types of coastal defence structures failure and constitutes one of the biggest threats to their structural performance. This study was intended to investigates the scour profile induced by tsunami bores at the landward toe of the vertical seawall and to discuss the effects of the parameters; tide level, incident bore Froude number Fb, incident bore height Hb, overtopping flow Froude number Fo, and overtopping flow depth Ho on the maximum scour depth induced at the landward toe of the seawall. A set of laboratory experiments were conducted at National Hydraulic Research Institute of Malaysia (NAHRIM) with the tichnique of dam break to generate the bore like tsunami. The experiments showed that the initial water level upstream of the seawall has a significant effect on the scour profile and there is a strong negative relationship exists with Froude number of the incident bore and a strong positive relationship exists with Froude number of the overtopping flow depth above the crest of the seawall.

Soil in braided rivers: An overlooked component of braided river morphodynamics

2014 ◽  
pp. 445-452
Author(s):  
N Bätz ◽  
E Verrecchia ◽  
S Lane
Keyword(s):  
Braided River ◽  
Braided Rivers

scholarly journals ANALYSIS OF TSUNAMI SCOUR AROUND SQUARE STRUCTURES USING A PUMP-DRIVEN FLOW METHOD

2020 ◽  
pp. 8
Author(s):  
Rafael Aranguiz ◽  
Oscar Link ◽  
Jose Aliaga ◽  
Oscar Briones ◽  
Ruben Alarcon ◽  
...  
Keyword(s):  
Solitary Waves ◽  
Laboratory Experiments ◽  
Maximum Flow ◽  
Sediment Deposition ◽  
Scour Depth ◽  
Flow Depth ◽  
Field Surveys ◽  
Flow Method ◽  
Tsunami Scour ◽  
Tsunami Event

Estimation of the maximum scour depth is important for defining the size and depth of building foundations in order to avoid failure during a tsunami event (Jayaratne, et al 2016). Traditionally, tsunami scour has been studied in laboratory experiments that use solitary waves. However, it has been demonstrated that this type of wave does not represent well a real tsunami (Madsen et al, 2008). In addition, results from field surveys are based on the scour depth after the tsunami event, studying only the maximum flow depth, and ignoring other hydrodynamic features such as velocity and wave period, as well as sediment deposition. The main objective of this research is to estimate maximum tsunami scour around rectangular structures as a function of realistic tsunami variables.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/ykb-JyL7lsE

scholarly journals Sedimentary facies analysis of the fluvial systems in the Siwalik Group, Karnali River section, Nepal Himalaya, and their significance for understanding the paleoclimate and Himalayan tectonics

2016 ◽  
Vol 51 ◽  
pp. 11-26 ◽  
Author(s):  
Ashok Sigdel ◽  
Tetsuya Sakai
Keyword(s):  
River System ◽  
Precipitation Pattern ◽  
Braided River ◽  
River Section ◽  
Meandering River ◽  
Braided Rivers ◽  
Facies Associations ◽  
Siwalik Group ◽  
Himalayan Tectonics ◽  
Flood Flow

Fluvial sediments of the Siwalik successions in the Himalayan Foreland Basin are one of the most important continental archives for the history of Himalayan tectonics and climate change during the Miocene Period. This study reanalyzes the fluvial facies of the Siwalik Group along the Karnali River, where the large paleo-Karnali River system is presumed to have flowed. The reinterpreted fluvial system comprises fine-grained meandering river (FA1), flood-flow dominated meandering river with intermittent appearance of braided rivers (FA2), deep and shallow sandy braided rivers (FA3, FA4) to gravelly braided river (FA5) and finally debris-flow dominated braided river (FA6) facies associations, in ascending order. Previous work identified sandy flood-flow dominated meandering and anastomosed systems, but this study reinterprets these systems as a flood-flow dominated meandering river system with intermittent appearance of braided rivers, and a shallow sandy braided system, respectively. The order of the appearance of fluvial depositional systems in the Karnali River section is similar to those of other Siwalik sections, but the timing of the fluvial facies changes differs. The earlier appearance (3-4 Ma) of the flood-flow dominated meandering river system in the Karnali River section at about 13.5 Ma may have been due to early uplift of the larger catchment size of the paleo-Karnali River which may have changed the precipitation pattern i.e. intensification of the Indian Summer Monsoon. The change from a meandering river system to a braided river system is also recorded 1 to 3 Ma earlier than in other Siwalik sections in Nepal. Differential and diachronous activities of the thrust systems could be linked to change in catchment area as well as diachronous uplift and climate, the combination of which are major probable causes of this diachronity.

scholarly journals Short communication: Challenges and applications of structure-from-motion photogrammetry in a physical model of a braided river

2019 ◽  
Vol 7 (1) ◽  
pp. 97-106 ◽  
Author(s):  
Pauline Leduc ◽  
Sarah Peirce ◽  
Peter Ashmore
Keyword(s):  
Structure From Motion ◽  
Short Communication ◽  
Successful Implementation ◽  
Braided River ◽  
Large Dataset ◽  
Automatic Target Detection ◽  
Braided Rivers ◽  
Digital Elevation ◽  
Communication Challenges ◽  
Close Range

Abstract. For extending the applications of structure-from-motion (SfM) photogrammetry in river flumes, we present the main challenges and methods used to collect a large dataset (>1000 digital elevation models, DEMs) of high-quality topographic data using close-range SfM photogrammetry with a resulting vertical precision of ∼1 mm. Automatic target detection, batch processing, and considerations for image quality were fundamental to the successful implementation of the SfM technique on such a large dataset, which was used primarily for capturing details of gravel-bed braided river morphodynamics and sedimentology. While the applications of close-range SfM photogrammetry are numerous, we include sample results from DEM differencing, which was used to quantify morphology change and provide estimates of water depth in braided rivers, as well as image analysis for mapping bed surface texture. These methods and results contribute to the growing field of SfM applications in geomorphology and close-range experimental settings in general.

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