Experimental analysis and numerical simulation of bed elevation change in mountain rivers

Abstract

Studies of sediment transport problems in mountainous rivers with steep slopes are difficult due to rapid variations in flow regimes, abrupt changes in topography, etc. Sediment transport in mountainous rivers with steep slopes is a complicated subject because bed materials in mountainous rivers are often heterogeneous and contain a wide range of bed material sizes, such as gravel, cobbles, boulders, etc. This paper presents a numerical model that was developed to simulate the river morphology in mountainous rivers where the maximum bed material size is in the range of cobbles. The governing equations were discretized using a finite difference method. In addition, an empirical bed load formula was established to calculate the bed load transport rate. The flow and sediment transport modules were constructed in a decoupled manner. The developed model was tested to simulate the river morphology in an artificial channel and in the Asungjun River section of the mountainous Yangyang Namdae River (South Korea). The simulation results exhibited good agreement with field data.

Investigation of Shear Stress Distribution in a 90 Degree Channel Bend

“…The experiments can be carried out at a 25 Hz frequency in 1.0 minutes. Therefore, the device can record up to 1,500 data of the flow velocity per second in the V x , V y and V z directions [14,5]. Fig.3.…”

Experimental Investigation and Numerical Simulation of Morphological Changes in Natural Channel Bend

“…Bed load in natural rivers especially in steep slope rivers is often distributed with non-uniform size (Guan et al 2016;Dang and Park, 2016b). Therefore applying a bed load transport formula with uniform particle size, the calculated results often differ by orders of magnitude.…”

“…They reported that grain-size parameters have an important role on bed level variation. Dang and Park (2016b) reported that bed load in the mountain river often distributed into several different fractions and each particle size is subjected to the interaction of other particles. When non-uniform bed load is transported through channels, not only aggradation and degradation occur, but sorting also occurs in a similar way.…”

“…The numerical solution procedure description given full details can be found by referring to the previous publications (Dang and Park, 2016b).…”

“…In this work, the model performance assessment was based on the agreement of the simulated results and measured data together with the value of the statistical performance indices such as the Brier Skill Score (BSS) criteria, Root Mean Square Error (RMSE) and Mean Absolute Errors (MAE). BSS and RMSE are the criteria most widely used to assess the model performance with observed data (Dang and Park, 2016b;Davies et al 2002;Guan et al 2016). The BSS has been identified as the most appropriate criteria to determine the performance of the river morphology model (Davies et al 2002) because this criterion compares the model results to a baseline prediction.…”