Large‐scale modelling of highly braided and laterally confined reach of a sand‐bed river

Abstract

Morphological processes in sand‐bed braided rivers are highly complicated and dynamic, and it is challenging to fully comprehend and predict them quantitatively or even qualitatively. In this paper, we report the application of a physics‐based model with a single sediment fraction (D50 = 0.23 mm), based on field data, to simulate the morphodynamic processes of a large‐scale braided system in a wide valley of the middle Yarlung Tsangpo River in China. The model is capable of reproducing the evolution of large braided patterns at both microscopic and macroscopic scales, and simulating the formation of a high‐intensity braided reach from an initial lateral flat bed under lateral valley confinement. A narrow strip zone of braided corridor presents long‐term concentrated anabranches in the wide valley reach. Moreover, sensitivity analyses suggest that physics‐based modelling can simulate the multi‐thread river pattern even with relatively coarse grids and a large morphological acceleration factor. The model results show that active riverbed movement occurs and additional chutes are encouraged during flooding, while rising water level makes subchannels merge so that the statistical braiding index decreases. Conversely, only about 40% of the total channels are active in transporting sediment at low‐discharge stages, resulting in a local and slow bed scouring. The planimetric confinement of width variations and valley curvatures acts as a primary control on the local braided corridor and the forced bar assemblages. Width variations restrict the section‐average stream power for a given discharge event, while valley curvatures regulate velocity distribution through several control points. Moreover, the activities of riparian vegetation and sandstorm can interfere with the ability of rivers to braid in the corridor area, which requires much more attention in the follow‐up research.

Channel morphological activation of large braided rivers in response to climate-driven water and sediment flux change in the Qinghai-Tibet Plateau

“…It should be noted that this method is not necessary in all cases of braided river segmentation. For braided rivers with wide branches, such as the Yarlung Tsangpo River on the southern QTP, in which the branch width is larger than 30 m (Han et al, 2023;Shampa and Ali, 2019;You et al, 2022), can simply use the Global Otsu method to extract water bodies. Small branches (<10 m) are commonly exist in braided rivers in the SRYR (Ma et al, 2021), which is suitable for the application of Local Otsu + Lowpath method.…”

Analysis of Flood Water Level Variation in the Yichang–Chenglingji Reach of the Yangtze River after Three Gorges Project Operation

“…The theoretical relationship between the resistance of river channels and various morphological parameters is one of the research focuses currently [13,25,[29][30][31]. Moreover, quantifying various morphological parameters remains challenging in river dynamics due to the complex and dynamic river morphological processes, difficulty in obtaining high-resolution data across large river networks, a lack of measurements in remote or inaccessible regions, limited understanding of the complex interactions among morphological parameters, and influences from natural and anthropogenic changes [32][33][34][35][36]. On the other hand, the flood level in the YCR is also affected by the backwater for Dongting Lake.…”

Morphological Model for Erosion Prediction of India’s Largest Braided River Using MIKE 21C Model

“…A number of articles have reviewed existing approaches to numerical modelling in fluvial geomorphology, and erosion prediction (Murray and Paola, 1994;Webb, 1995;De Vriend, 2001;Malmaeus and Hassan, 2002;Olsen, 2003;Mosselman, 2004;Jang and Shimizu, 2005;Doeschl et al, 2006;Coulthard et al, 2007;Jang and Shimizu, 2007;Spasojevic and Holly, 2008;Thomas and Chang, 2008;Takebayashi and Okabe, 2009;Tucker and Bradley, 2010;Schuurman and Kleinhans, 2011;Van De Wiel et al, 2011;Mosselman, 2012;Lajeunesse et al, 2013;Liedermann et al, 2013;Nicholas, 2013;Pirot et al, 2014;Sun et al, 2015;Williams et al, 2016b;Yang et al, 2017;Javernick et al, 2018;Kasprak et al, 2019;Weisscher et al, 2020;Saadona et al, 2021;Bürgler et al, 2022;Stecca and Hicks, 2022;Wang et al, 2022;Han et al, 2023;Khanh et al, 2023;Pareta and Pareta, 2023;Stecca et al, 2023). In recent years, there has been a growing adoption of physics-based numerical models for modelling fluvial processes (Webb, 1995;De Vriend, 2001;Jang and Shimizu, 2005;Tuck...…”

“…Wang et al (2022) proposed a one-dimensional model simulating bed and bank changes in the Lower Yellow River's braided reach during flood seasons, integrating modules for flow-sediment transport, bed deformation, and bank erosion/accretion. Han et al (2023) successfully simulated the large-scale braided system evolution in the middle Yarlung Tsangpo River, China, using a physics-based model with D 50 = 0.23 mm, capturing both microscopic and macroscopic changes, including the formation of a high-intensity braided reach from an initial lateral flatbed under lateral valley confinement. Khanh et al (2023) used the Mike 21FM hydrodynamic model to assess sediment transport changes in the Tien River, crucial for understanding riverbed evolution in the Cao Lanh district.…”