Flow and sediment transport in a sharp river bend using a 3D-RANS model

Flow dynamics and sediment transport in a river bend have recently been studied using experimental and numerical investigations. A three-dimensional numerical modeling model named NaysCUBE was used in this study to describe the flow pattern and process of sediment transport in a sharp river bend as a complement to the prior work of the physical hydraulic model. The model uses the RANS equation to simulate flow where a fully complex 3D flow is governed. Despite the limitations of the RANS model, NaysCUBE well reproduces the flow pattern and turbulence phenomena in a movable bed channel with sharp curvature. Compared with data from a prior experiment, the morphological adjustment is simulated sufficiently. The three-dimensional flow structures are useful for determining the appropriate countermeasures for local scouring and riverbank protection.

Finding the optimum groin layout for the Konaweha river banks protection via 2D numerical modeling

River bank erosion has become a critical issue, especially for river bends with an alluvial soil type. Mostly, river bank erosions have caused structural failures because many national roads in Indonesia are placed near the river bend areas. Groins can reduce flow velocity, thereby increasing riverbank stability. However, most groins were installed in the river without impacting the river flow due to the improper design. This paper analyzes the use of groins placed at the river bend of the Konaweha River to protect the river bank with a length of 250 m from erosion. The evaluation employs 2D numerical modeling using MIKE21 FM to observe the influence of the groin on the river velocity, flow distribution pattern, and water level. Sixteen model scenarios with four groin configurations were tested for 25-year discharge, 2-year discharge, normal discharge 600 m3/s, and low discharge 197 m3/s to achieve the most effective plan. Based on the simulation results, Scenarios with five groins are recommended to reduce the flow velocity along the outer river bank from 2 to 0.3 m/s, thus minimizing the erosion. In addition, the spacing of groins being twice the groin length is recommended.

Incipient Motion of Gravel Bedload Considering the Secondary Flow in Bend

The transport of gravel bedload in river bend is one of the basic problems of river dynamics. However, both the complicated bend flow structure and the stochastic bedload transport make explaining the problem theoretically difficult. Flow is the power of the bedload transport, so obtaining the precise theoretical flow structure is fundamental. Through considering the velocity-dip phenomenon and giving the matched boundary conditions, we have obtained the completed three-dimensional bend flow structure in the previous study. Combining the flow structure and the influences of the two-way exposure, we did further research on the incipient motion of the gravel bedload in bend in this paper. It turns out that, because of the existence of the secondary flow, the particle in bend forced by both the longitude and the transverse velocities in the plane. The two-way velocities form an intersection angle which influences the incipient velocity and direction of the particle movement. Moreover, the non-uniform distribution of the bend flow structure along the cross-section decides the differences of the intersection angle, incipient velocity, transport speed of the bedload in the bed surface. Then, the above differences result in the change of the sediment gradation and partition behaviour of the bedload transport.

Analysis on The Effect of Groyne Type Impermeable Placement on Sediment Distribution in Lariang River Bend

Sedimentation and erosion caused by differences in discharge is a problem that often occurs at river bends. One of the functions of placing the groyne is to reduce the river flow velocity along the riverbank, accelerate sedimentation, and ensure the embankment or river bank's safety against scouring. This study aimed to determine the distribution of current velocity, distribution of riverbed shear stress, and sediment distribution to the effect of groyne placement. There are 7 (seven) simulation models used to get the most effective groyne placement. From the model simulation results by adding a groyne building on the river's outer bend for the simulation model scenario 2 to scenario 7, the largest sedimentation production is in scenario 3, namely the height of riverbed sediment deposits 230 hours of 1.094 m. Furthermore, the groyne building's effective placement is determined based on a maximum change in the riverbed scenario. In scenario 3, the placement and dimensions of the groyne length of 17.5 m; distance between groyne 24.4 m; the groyne is inclined upstream in the direction of flow 10°

A Review of Numerical Simulations of Secondary Flows in River Bends

River bends are one of the common elements in most natural rivers, and secondary flow is one of the most important flow features in the bends. The secondary flow is perpendicular to the main flow and has a helical path moving towards the outer bank at the upper part of the river cross-section, and towards the inner bank at the lower part of the river cross-section. The secondary flow causes a redistribution in the main flow. Accordingly, this redistribution and sediment transport by the secondary flow may lead to the formation of a typical pattern of river bend profile. It is important to study and understand the flow pattern in order to predict the profile and the position of the bend in the river. However, there are a lack of comprehensive reviews on the advances in numerical modeling of bend secondary flow in the literature. Therefore, this study comprehensively reviews the fundamentals of secondary flow, the governing equations and boundary conditions for numerical simulations, and previous numerical studies on river bend flows. Most importantly, it reviews various numerical simulation strategies and performance of various turbulence models in simulating the flow in river bends and concludes that the main problem is finding the appropriate model for each case of turbulent flow. The present review summarizes the recent advances in numerical modeling of secondary flow and points out the key challenges, which can provide useful information for future studies.

“The Wright Brothers” by Mikhail Zenkevich: Correspondence with Orville Wright and Other Contributors (1932–1933): New Archival Findings

As a result of the latest findings in the archives of Russia and the United States, the correspondence between Mikhail Zenkevich and Orville Wright is published for the first time (the originals in English are supplemented with the Russian translations). This correspondence was conducted between 1932–1933, which correlates to the time period Zenkevich was working on the first biography of the pioneer aviators in Russian, Brat’ia Rait (The Wright Brothers, 1933). Also included are excerpts from the letters of foreign literati and colleagues, such as Michael Gold, Harold Heslop, Maurice Becker, Helen Black, as well as domestic correspondents, K. K. Kuraev among them. The article deliberates upon the direct influence of the materials provided by O. Wright on the book. A review of the holdings on the theme of aviation in Zenkevich’s fund (IRLI Pushkinskii Dom) is provided. The examination of the little- known biographical details, as well as the parts of the poet’s epistolary legacy and his prosaic works, adds to the analysis. Taken together, this all has allowed for substantiation of certain presumptions about other possible sources of the book. The article interprets some literary features of Brat’ia Rait by tracing the development of the theme of aviation in the earlier poems by this former Acmeist, and by drawing parallels with some of his later short and long poems, such as “Al’timetr. Tragorel’ef” (Altimeter. Tragic Relief) and “Torzhestvo aviatsii” (The Triumph of Aviation), and a short novel “Na strezhen’” (On the River Bend) and fictional memoirs Muzhitskii Sfinks (The Peasant Sphinx). Finally, some intertextual parallels between “The Triumph of Aviation” and Edgar Allan Poe’s “The Raven,” translated by Zenkevich, are revealed. The conclusion is made that the materials received from O. Wright have subsequently influenced the long poem “The Triumph of Aviation” and other works by Zenkevich. The publication is equipped with detailed notes, commentaries and illustrations.

Features of the population organization of Myricaria bracteata in the riverbed of the Ursul River (Gorny Altai)

The article represents the analysis of the ontogenetic composition and demographic parameters of 3 cenopopulations of Myricaria bracteata in the riverbed of the Ursul River (Central Altai). It was found that the ontogenetic structure and density of individuals depend on the degree of formation of the phytocenosis and the influence of abiotic factors (features of the substrate, river bend). The invasive cenopopulation formed in a bend of the river in the absence of a phytocenotic pressure; the young normal cenopopulation formed in the river deflection on the grasscover stony shore, and the invasive-regressive cenopopulation formed on an island washed by the river.

ANALISIS DINDING PENAHAN TANAH DI DAERAH ALIRAN SUNGAI MENGGUNAKAN PROGRAM MIDAS GTS NX

A retaining wall at a river bend in Depok cannot hold the soil behind the wall that cause the wall collapses and the soil landslide. The retaining wall is using shallow foundation. Therefore, a new wall is needed to prevent the land from sliding. The research method was using finite element method and Midas GTS NX program using 1 boring log data, 40cmx40cm for pole size and three types of walls with different capping beam size. In this analysis, the value of L2 is smaller than L1, which indicated an unusual thing, in general the value of L2 is equal or greater than L1, L1 is length of the free pole and L2 is length of the pole through the ground surface. The value of L1 can increase due to the river currents that erode riverbeds. The analysis showed the three types of walls has fulfilled the maximum limit of lateral deformation 8.4cm and maximum limit moment from the brochure 224.2kNm. From the three types of wall, type 1 wall is selected with displacement value of 2.454cm and a maximum moment of 116.592kNm. Type 1 wall were chosen because it require a minimum cost of Rp 458.821.479,072 less than other types. Dinding penahan tanah disebuah tikungan sungai di Depok tidak dapat menahan tanah yang berada di belakangnya sehingga dinding tersebut roboh dan menyebabkan tanah di belakang dinding longsor. Dinding penahan tanah tersebut didesain dengan menggunakan pondasi dangkal. Oleh karena itu, diperlukan dinding penahan tanah yang baru dengan menggunakan tiang pancang untuk mencegah tanah tersebut longsor lagi. Metode penelitian dilakukan dengan menggunakan metode elemen hingga dengan bantuan program Midas GTS NX dengan menggunakan 1 data boring log, ukuran tiang 40cmx40cm dan tiga tipe dinding dengan ukuran capping beam yang berbeda. Dalam analisa ini, besarnya nilai L2 lebih kecil dari L1 yang menunjukkan hal tidak lazim yang pada umumnya besarnya nilai L2 sama atau lebih besar dari L1 dimana L1 merupakan panjang tiang bebas dan L2 merupakan panjang tiang menembus permukaan tanah. Besarnya nilai L1 dapat meningkat akibat adanya arus sungai yang menggerus dasar sungai. Hasil analisa menunjukkan ketiga tipe dinding telah memenuhi syarat batas maksimum deformasi lateral dinding sebesar 8.4cm dan batas maksimum momen dari brosur 224.2kNm. Dari ketiga tipe dinding tersebut dipilih dinding tipe 1 dengan nilai displacement sebesar 2.454cm dan momen maksimum 116.592kNm. Dinding tipe 1 dipilih karena membutuhkan biaya paling minimum sebesar Rp 458.821.479,072 lebih kecil dibandingkan dengan tipe lainnya.

Sustainable aquaculture development in oxbow lakes with emphasis on the involvement of women.

A total of 600 oxbow lakes are located in the southwestern part of Bangladesh, covering 5,488 ha. An oxbow lake (baor) is an old cut-off river bend, usually in the shape of a horseshoe. Pond aquaculture for women was introduced in oxbow lakes in 1995-1996 to allow their active participation in aquaculture as a livelihood activity. The shallow and silted parts of the baor were excavated into 0.5 to 1.5 ha size fishponds. This study was conducted in 1999 in two selected oxbow lakes in Jessore district to assess the technological and socio-economic effects of fish farming groups (FFGs) and pond aquaculture in oxbow lakes with emphasis on the involvement of women. Three categories of questions (socio-economic, technical and gender) were asked of FFG members. This study shows that initially when the women became involved in pond excavation and dike compaction, as members of the FFGs, most of their men members did not like this. As Bangladesh is a Muslim-dominant country, there is a general idea among men that women should not work outside together with men. However, after a few years, once the success of the women's fish farming activities and marketing became clear, their social status and respect in the society and family increased through their active participation in this process. A total of 23 oxbow lakes in five districts around Jessore, covering 1,400 ha, have been handed over from the Ministry of Land to the Department of Fisheries (DOF). Subsequently, the DoF transferred the user-rights to the beneficiaries for a period of 50 years.