RESULT AND DISCUSSION

RESULT AND DISCUSSION

Simulations were performed with the hydrograph of debris discharge The result obtained from the simulation shows a reasonable value and input parameters shown in Table 1 in order to reproduce the

when the volumes estimated by the field investigation are compared amount of mobilized debris, the deposits at the channel, and the

to those obtained from the simulation. About 4,270m 3 of total sediment amount that flowed passed to alluvial fan area. Debris flow volume

discharge volume passed through the alluvial fan as obtained from flowing through 1D channel into 2D region can be calculated as

the simulation while field data was estimated to be approximately follows:

3,990m 3 . The accuracy of the result obtained from the simulation model is about 93% as compared to the real in-situ measurements. Conversely, there are slight differences in the volumes obtained. The

Q out =Q in +V bed -D bed

differences may be due to the estimated geometry values that are being used during simulation.

Where: Q

out : the total debris flow volume into the 2D region (m );

Q in : supplied debris flow volume (m 3 );

V : debris flow volume of moveable bed (m bed 3 );

D bed 3 : debris flow deposition volume in 1D area (m ). After putting the above parameters into formula (8), we can get:

Q := 1,700 + 2,850 – 279.71 = 4,270.29m 3 out .

Figure 7: Inflow sediment volume and volume that passed to alluvial fan KANAKO) a. Volume from field data, b. Volume from simulation and condition of river bed after debris flow

From the simulation, the deposited tend to occurs when the gradient

CONCLUSION

of profile moves from steep to gentle area. Volume of sediment at each calculation point can be obtained from the simulation which

KANAKO is a user friendly numerical simulation package with shows whether a deposition or erosion takes place in the channel

easy to understand manual and simple portrayal of Graphical User during debris flow event. There are two points of major deposition

Interface (GUI). The software is developed based on theoretical when the slope gradient decreases which is at 582m accumulating

principles of debris flow and supported by laboratory experiment and about 15m 3 of sediment and 567-558m gathering about 316m 3 of field data. It is suitable in analyzing the mechanism and potential

sediment. behaviors having controlled by important factors such as channel gradient and hydrograph. In this study, simulation by KANAKO has been successful in showing the amount of sediment volumes and processes of deposition and erosion along the channel. KANAKO has also successfully showed the flow depth and sediment thickness in alluvial fan area.

Results obtained from the reproduction simulations have demonstrated

a reasonable performance of the simulation model and provide a useful mechanism and outputs that will help in the assessment of the risks as well as in the planning and to provide preventive measures whether in the form of structural or non-structural measures. By

Figure 8: Variation of sediment thickness at alluvial fan area

comparing between the developed and present numerical models with real events, a reliable decision can be made in evaluating the most suitable and accurate model to determine the total discharge volume, run-out distance, flow depth and thickness of alluvial deposited.

Figure 9: Flow depth at alluvial fan area

From the simulation, it shows that the debris floods occur in the whole area of the alluvial fan after running out from the channel outlet. The alluvial fan area is a narrow road and based on the simulation, at least

a 0.04m flow depth and maximum flow depth of 0.25m after it passes the road. The maximum sediment thickness is more than 3m located at the entrance of alluvial fan. This indicate that during debris flow incident, road certainly impassable because have been filled with 3m thick of sediment.