river morphology
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2021 ◽  
Author(s):  
Paul J. Southard ◽  
Joel P. L. Johnson ◽  
Daniella Rempe ◽  
Ashley M Matheny

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3437
Author(s):  
Huang Dai ◽  
Toshiki Iwasaki ◽  
Yasuyuki Shimizu

Sediment supply plays an essential role in river morphology. However, the specific impact of sediment supply on river morphology is not apparent. According to the hydrograph boundary layer (HBL) concept, upstream riverbed changes caused by the imbalance between sediment supply and the capacity can propagate only a limited length and have a negligible effect on the riverbed beyond such a short length. We performed a two-dimensional morphodynamic calculation to test the concept of HBL, which was proposed under a one-dimensional simulation, meaning that the concept of HBL is still valid for plane changes in river morphology. We employed an unsteady flow with equilibrium or constant sediment supply in a straight, modeled gravel-bedded channel with an unerodible bank to simulate alternate bar morphodynamics. The results show that regardless of the sediment supply condition, the alternate bar features formed downstream of the HBL are considerably similar. This suggests that sediment disturbance at the upstream end has a negligible effect on the mobile-bed dynamic processes, including alternate bar formation and development downstream of the HBL.


2021 ◽  
pp. 1-25
Author(s):  
Amit Segev ◽  
Itay J. Reznik ◽  
Uri Schattner

Abstract The Yarmouk River gorge extends along the Israel–Jordan–Syria border junction. It marks the southern bound of the Irbid–Azraq rift and Harrat Ash Shaam volcanic field at their intersection with the younger Dead Sea Transform plate boundary. During the last ∼13 Ma, the gorge has repeatedly accumulated basaltic units, chronologically named the Lower, Cover, Yarmouk and Raqqad Basalt formations. We examined their origin and distribution through aerial photos, and geological and geophysical evidence. Our results define a southern Golan magmatic province, which includes exposed Miocene (∼13 Ma) basalts, gabbro–diabase intrusions below the gorge and the adjacent Dead Sea Transform valley, and numerous Pliocene–Pleistocene volcanic sources along the gorge. Cover Basalt (∼5.0–4.3 Ma) eruptions formed two adjacent 0–100 m thick plateaus on the transform shoulder before flowing downslope to fill the topographically lower Dead Sea Transform valley with ∼700 m thick basalts. Later incision of the Yarmouk River and displacement along its associated fault divided the plateaus and formed the gorge. The younger Yarmouk (0.8–0.6 Ma) and Raqqad (0.2–0.1 Ma) basalts erupted in the upper part of the gorge from volcanos reported here, and flowed downstream toward the Dead Sea Transform valley. Consequently, eruptions from six phreatic volcanic vents altered the Yarmouk River morphology from sinuous to meandering. Our results associate the ∼13 Ma long southern Golan volcanism with the proposed SW-trending extensional Yarmouk Fault, located east of the Dead Sea Transform. Hence, the Yarmouk volcanism is associated with the ongoing Harrat Ash Shaam activity, which is not directly linked to the displacement along the Dead Sea Transform.


Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2588
Author(s):  
Hao-Che Ho ◽  
Yen-Ming Chiang ◽  
Che-Chi Lin ◽  
Hong-Yuan Lee ◽  
Cheng-Chia Huang

The change in movable beds is related to the mechanisms of sediment transport and hydrodynamics. Numerical modelling with empirical equations and the simplified momentum equation is the common means to analyze the complicated sediment transport processing in river channels. The optimization of parameters is essential to obtain the proper results. Inadequate parameters would cause errors during the simulation process and accumulate the errors with long-time simulation. The optimized parameter combination for numerical modelling, however, is rarely discussed. This study adopted the ensemble method to simulate the change in the river channel, with a single model combined with multiple parameters. The optimized parameter combinations for a given river reach are investigated. Two river basins, located in Taiwan, were used as study cases, to simulate river morphology through the SRH-2D, which was developed by the U.S. Bureau of Reclamation. The input parameters related to the sediment transport module were randomly selected within a reasonable range. The parameter sets with proper results were selected as ensemble members. The concentration of sedimentation and bathymetry elevation was used to conduct the calibration. Both study cases show that 20 ensemble members were good enough to capture the results and save simulation time. However, when the ensemble members increased to 100, there was no significant improvement, but a longer simulation time. The result showed that the peak concentration and the occurrence of time could be predicted by the ensemble size of 20. Moreover, with consideration of the bed elevation as the target, the result showed that this method could quantitatively simulate the change in bed elevation. With both cases, this study showed that the ensemble method is a suitable approach for river morphology numerical modelling. The ensemble size of 20 can effectively obtain the result and reduce the uncertainty for sediment transport simulation.


2021 ◽  
Vol 6 (2) ◽  
Author(s):  
Jazaul Ikhsan ◽  
Indrasweri NK

Debris flows triggered by Merapi eruption in 2010 have impacts on the environment and social condition along the rivers on the volcano, especially in Pabelan River. Material resulted from debris flows could change on morphology and porosity of riverbed surface material, as well as the capacity of sediment. Therefore, it is important to study the influence of Merapi eruption in 2010 on environmental and social conditions in Pabelan River. To determine the river morphology was used Ronsgen method. To calculate porosity of riverbed surface material was used the equation was proposed by Sulaiman. Einstein equation was used to calculate sediment transport. To investigate the social conditions, damage land and sand mining activity were used as parameters. The result has shown that morphology types at confluence Progo-Pabelan Rivers, Srowol Bridge, and Pabelan Bridge 1 were D5b, D5b and E5, respectively. Sedimentation has occurred in the segment between the confluence of Progo-Pabelan Rivers and Srowol Bridge. Erosion has taken place in the segment between Srowol Bridge and Pabelan Bridge 1. The riverbank collapses took place along the river and it gave a negative impact on social conditions. The sand mining activity was intensive, and the activity has a positive impact on the economical inhabitants.


2021 ◽  
Author(s):  
Guo-An Yu ◽  
He Qing Huang ◽  
Weipeng Hou

<p>Incised valleys or steep slopes in tectonic active mountain areas are normally in a critical equilibrium state which is highly fragile and prone to deviate under exotic disturbances (e.g., earthquake, heavy precipitation, or even human activities), inducing mass movements (e.g., landslides, avalanche, and/or debris flows). Mass movements have great impacts on fluvial processes and may even reshape valley morphology, hence are powerful drivers to river evolution in those environments. Unfortunately, compared to the mass movements themselves (e.g., occurrence time, volume, dynamics and underlying mechanisms), less attention has been paid to the fluvial processes (in a short/intermediate-term) and the long-term evolution of river morphology corresponding to (and after) those mass movements (especially catastrophic ones). This motivates the current work.</p><p>The southeast Tibet, located on the east Qinghai-Tibet Plateau, is one of the most active regions globally in terms of tectonic motion and rates of uplift. Rivers in the lower Yalung Tsangpo basin in this area are investigated to understand the morphodynamics influenced by modern and historical mass movements and examine the feedbacks of fluvial processes to mass movements. River reaches influenced by typical mass movements were chosen for detailed field surveys, including: (1) the upper part of the Yalung Tsangpo Grand Canyon which has been seriously impacted by avalanches and debris flows from tributary gullies originating at glacial mountains of Namcha Barwa and Gyala Peri; (2) the lower reach of the Yigong River covering the Yigong Landslide from the Zhamunong Gully; (3) the lower reach of the Palong River influenced by debris flows from Guxiang and Tianmo gullies; and (4)  the upper and middle reaches of the Palong River (extending roughly from Ranwu Lake to the upstream of Guxiang Lake) influenced by glacial processes and other induced mass movements since the last glacial maximum. Remote sensing images before and after the large-scale mass movements in recent decades were also used to track the corresponding river morphology variation.</p><p>Due to very high transport rate and volume of sediment incoming, mass movements have caused dramatic channel processes in east Tibet. Some even dammed the river, forming knickpoints and reshaping valley morphology. The morphology of the valleys in this area normally show alternating sections of gorges and wide valleys, with a staircase-like longitudinal profile. The gorge sections exhibit single and deeply incised channels with a high-gradient channel bed and terraces. In contrast, the wide valley sections consist of lakes, braided or anabranching channels, gentle bed gradients, and thick alluvial deposits. In recent decades, mass movements (mostly debris flows), occurred more frequently through gullies in the reaches of gorge sections than through gullies along the wide valley sections. Mass movements deviate river morphology and slope from (quasi-)equilibrium to non-equilibrium state, however, with attendant rapid sediment incoming, valley bottom siltation and erosion benchmark rising, it triggers a negative feedback which drives the river morphology to a new round of development towards equilibrium.</p>


2021 ◽  
Author(s):  
Rachel Hurley ◽  
Marianne Olsen ◽  
David Pettersen Eidsvoll ◽  
Nina Buenaventura ◽  
Asle Økelsrud ◽  
...  

<p>Several guidelines have been developed that describe methods for analysing riverine macroplastic flows. No single method has emerged as the standard approach for sampling plastic waste in rivers. This reflects the difficulty in establishing a global ‘one size fits all’ approach for river systems: there is significant variability in river morphology, hydrology, and geomorphology across the world and these differences necessitate adaptations of existing methods or the development of new approaches to assess macroplastic flows. In addition, there is a wide range of different potential objectives underpinning the monitoring of riverine macroplastic contamination, including assessments of plastic export, sources, transport, or accumulation. These generate different research questions, which require different solutions, and may necessitate the collection of data in different forms.</p><p>Nevertheless, there is an international demand for generating monitoring datasets that are comparable and can be used to create a holistic picture of macroplastic contamination across the globe. For the reasons listed above, harmonisation – through thorough method validation and quality assurance and control (QA/QC) – is likely to be more important than standardisation in this context. Additionally, in some cases there remains a disconnect between the types of data that are produced in monitoring activities and those which are desired by potential end users of the data. It is valuable, therefore, to increase the communicability of datasets and establish a common language for riverine macroplastic contamination. This study undertakes a critical review of existing methodologies for assessing macroplastic flows in river systems and identifies: i) what component of the macroplastic load is measured by each technique; ii) how can these methods be validated; iii) what QA/QC procedures could be implemented to increase the quality, robustness, and harmonisation of monitoring outputs; and iv) how can outputs be tailored to different uses of monitoring data.</p>


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