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Published in Quoc VO Thanh, Modeling of Hydrodynamics and Sediment Transport in the Mekong Delta, 2021
Channel thalweg, as the natural direction of a watercourse, is an important factor to reconstruct river topography. Incorporating the thalweg into the interpolator results in a continuous deepest channel. This makes the bed surface reconstructed more accurate. We introduced an efficient interpolation approach for generating river bathymetry from sparse cross-sectional data. We also found that the linear interpolation method is suggested for sparse data regions. However, it is difficult to identify the thalweg line based on sparse data. We suggest to generate the thalweg line by connecting splines of the deepest points from cross-section to cross-section. Besides, there is several studies considering the center line for reconstructing river bathymetry (Goff and Nordfjord, 2004; Legleiter and Kyriakidis, 2008; Merwade, 2009). This could lead to generating a discontinuous thalweg channel. Chen and Liu (2017) used the interpolation methods, namely linear interpolation, IDW and Natual Neighbor to resample cross-sections and found that the linear interpolation is the most efficient method to reproduce smooth topography and continuous thalweg trajectory.
Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
One may assess the erosion activity of a river by analyzing its long profile, given by the line obtained by plotting the elevations against the respective distances measured along the Thalweg, the deepest part of the streambed from the source to the mouth. The mouth represents the river base level, which is the lowest altitude, reached at the moment by erosion. The general base level is the medium sea level of the sea, where all continental waters outflow.
A Short Tour of Mathematical Morphology on Edge and Vertex Weighted Graphs
Published in Olivier Lézoray, Leo Grady, Image Processing and Analysis with Graphs, 2012
where ∇I is the normalized gradient of the image I. The gradient for a grey level image is Ii − Ij. As the weights are inverted, the maxima are considered instead of minima, and a thalweg is computed instead of watershed. A thalweg is the deepest continuous line along a valley. In the rest of the paper, we continue to use by convention the term “watershed” instead of “thalweg”.
Large debris flows in Chosica, Lima, Peru: the application of hydraulic infrastructure for erosion control and disaster prevention
Published in Australian Journal of Earth Sciences, 2020
S. P. Villacorta, K. G. Evans, K. Nakatani, I. Villanueva
These structures provide, with correct engineering design, the stability of the side slopes and riverbed of the streams and are especially useful to stop and stabilise large blocks and sediment mobilised by debris flows in basins with steep slopes. The main aim is to trap debris in the upstream area, then the thalweg slope of the channel reduces causing the loci of deposition to move upslope and cross-sections to become shallower. This reduces the kinetic energy of future flows causing the larger rocks and sediment to be deposited on more upstream areas and reducing the transport capacity of the flow. The fundamental aim of mitigation, with structures such as SABO dams, is to reduce flow velocity and sediment transported downstream thereby reducing the risk to human life and property (Mizuyama & Mizuno, 1997). In Japan, once SABO dams have trapped debris flow and depositional zones become full of sediment, it is proposed to remove sediment and secure the deposition zone area to achieve effective results (Horiguchi & Komatsu, 2019).
Hydraulic and turbulent flow characteristics beneath a simulated partial ice-cover
Published in Journal of Hydraulic Research, 2021
Baafour Nyantekyi-Kwakye, Ebenezer E. Essel, Karen Dow, Shawn P. Clark, Mark F. Tachie
Transport of sediment from riverbed and its banks due to the spatial and temporal distribution of turbulence changes the thalweg and bathymetry of rivers over time. Recent research on sediment transport processes have been reported for open channel flows (Kostaschuk, 2000; Kostaschuk et al., 2005) and ice-covered conditions (Lau & Krishnappan, 1985; Shen & Wang, 1995). The results highlight the dominant role of the interaction between water and sediment-laden bed on turbulent sediment transport processes. River ice formation in the northern hemisphere can alter the hydrodynamic characteristics of rivers during freeze-up. Typically, the first type of ice that forms is border ice due to the low velocities close to the banks. Over time, the entire river will be fully covered with ice depending on meteorological and hydraulic conditions. Border ice growth from each side of the riverbanks results in the formation of a partial ice cover (PIC) on the river, which is the focus of the present study. The simultaneous existence of open water and PIC makes the turbulent flow field complicated to analyse. In contrast to open channel flow, the presence of an ice cover modifies the flow regime over the entire river cross-section. There is the imposition of an additional boundary layer at the ice-covered zone (Chen et al., 2016; Shen & Wang, 1995; Teal et al., 1994; Zhong et al., 2018). The existence of these two boundary layers subjects the flow beneath ice covers to increased frictional resistance. Chen et al. (2015) proposed a two-layer hypothesis to divide the cross-sectional area of an ice-covered flow into two sections using the Einstein (1941) hydraulic separation theory. They also estimated the shear stresses at the bed, ice and sidewalls, which are essential for sediment transport and erosion. Although flow beneath PIC is complex, the majority of river ice research has focused on flow characteristics beneath full ice covers (Healy et al., 2002; Teal et al., 1994; Walker & Wang, 1997). For instance, Sukhodolov et al. (1999) investigated the turbulent flow behaviour beneath an intact ice cover on a river using a three-dimensional acoustic Doppler velocimeter (ADV). Sukhodolov et al. (1999) noted that the presence of an ice cover on a river complicated the turbulent flow structures compared to open water conditions. The spatial scales of turbulence were observed to be on the order of the river depth.