C12
Numerical Simulation on Debris-Flow Deposition and Erosion Processes Upstream of a Check
Dam with Experimental Verification
〇Badri Bhakta Shrestha, Hajime Nakagawa, Kenji Kawaike and Yasuyuki Baba
1. Introduction
The understanding of behavior and mechanism of debris flow and the study of preventive measures are very important. In this study, the numerical model is developed to reproduce the debris flow deposition and erosion processes upstream of a check dam.
2. Numerical Models and Laboratory Experiments The numerical simulations and experiments are performed for closed type and grid type check dams. To simulate the debris flow deposition upstream of a closed or a grid type check dam, a deposition model of upstream of a check dam and a model of blockage by large sediment particles in the case of a grid dam, are incorporated in the flow model of the debris flow. The riverbed erosion model under unsaturated bed condition is used to simulate the erosion process of deposited sediment upstream of a check dam by a
normal scale flood flow.
A rectangular flume of 5m long, 10cm wide and 13cm deep is set at 18o for the experiments. Check dams are set at 20cm upstream from end of the flume. Sediment bed of mean diameter dm=2.53mm with 1.9m long
and 7cm deep is positioned 2.8m upstream from the outlet of the flume. This sediment bed is saturated by water. Debris flow is produced by supplying a constant water supply 260cm3/sec for 10sec from upstream end of the flume. In the case of erosion, the water discharge is supplied at a rate of 260cm3/sec for 15sec after removing some large boulders initially deposited upstream of the check dam.
3. Results and Conclusions
Fig. 1 and Fig. 2 show the simulated and experimental results of deposition and erosion processes upstream of the check dam at different time steps respectively. The deposition and erosion models could calculate the debris flow deposition and erosion processes upstream of a check dam. The simulated results agree well with the experimental results. The deposited sediment upstream of a grid dam can be flushed out to the downstream effectively due to erosion process by a normal scale flood flow when some initially deposited large boulders are removed.
0 2 4 6 8 10 0 10 20 30 40 50 Distance (cm) D ep th (cm ) θ=18o Exp at 0.2sec Exp at 0.4sec Exp at 0.6sec Exp at 0.8sec Exp at 1sec Sim at 0.2sec Sim at 0.4sec Sim at 0.6sec Sim at 0.8sec Sim at 1sec a. Closed dam 0 2 4 6 8 10 0 10 20 30 40 50 Distance (cm) D ep th ( cm ) θ=18o
Exp at 0.2sec Exp at 0.4sec Exp at 0.6sec
Exp at 0.8sec Exp at 1sec Exp at 2sec
Sim at 0.2sec Sim at 0.4sec Sim at 0.6sec
Sim at 0.8sec Sim at 1sec Sim at 2sec
b. Grid dam, l/dmax=1.73
Fig. 1 Simulated and experimental results of debris
flow deposition upstream of a check dam. Fig. 2 Simulated and experimental bed variations of deposited sediment due to erosion process.
0 2 4 6 8 10 0 20 40 60 80 100 Distance (cm) D ep th (cm ) θ=18o
Initially deposited depth Exp at 4sec Exp at 8sec Exp at 12sec Sim at 4sec Sim at 8sec Sim at 12sec
