Numerical estimation of probability distribution of impingement of saltation gravel on irregular bed

Ryota Tsubaki, Yoshihisa Kawahara, Kenta Ayaka

Tuesday 30 june 2015

9:00 - 9:15h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 4A. Sediment - Erosion

Abrasion is a main factor of a detachment of algae attached to the riverbed cobbles during floods. The amount of algae to be detached is related to location, momentum and angle of the saltation gravel that impinges to the riverbed cobbles. The impingement conditions differ depending on the size of both saltation gravel and riverbed cobbles. In this study, the trajectory of gravel (d=0.5 to 3 cm) saltation on the channel consists of cobbles (d=20cm) is calculated using Moving Particle Semi-implicit (MPS) method (Koshizuka and Oka 1996). The saltation gravel is modeled by a group of moving (virtual) particles to take into account the size and shape of the physical gravel particle. The calculating domain has dimensions of 60 cm by 60 cm by 30 cm. The periodical boundary conditions for both streamwize and transverse directions are applied to simulate repeated contact between the saltation particle and the channel bed. The channel bed is modeled by using a number of fixed particles to represent the irregular bed shape. The statistics of the calculated trajectory are compared with those of experimental and theoretical values. Then, the spatial distributions of impingement probability and intensity are calculated based on the simulated particle trajectory. Finally, the efficiency of the algae detachment and its relation to the particle size are discussed.