Flow Resistance of Inertial Debris Flows

A relatively simple and versatile numerical model known as DAN, developed by Oldrich Hungr for the assessment of landslide mobility, has been enhanced to incorporate the consideration of a trapezoidal-shaped flow channel for more realistic modelling purposes. This enhanced debris mobility model (DMM) has been programmed to run on a spreadsheet and has been calibrated against detailed landslide data in Hong Kong. In contrast to previous work, the enhanced DMM eliminates the limitations inherited from the assumption of a rectangular flow channel with frictionless side boundaries. When using DMM, no predefined width of landslide is needed. The DMM simulates landslide mobility with the flow resistance on the whole wetted perimeter of the channel, calculates the surface width of the landslide based on the cross-sectional geometry of the channel, and is capable of predicting a lobe-shaped debris deposition area. This technical note presents details of the enhancement to the DAN formulation.Key words: landslides, debris flows, runout analysis, landslide mobility, dynamic modelling, numerical methods.

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Effects of Grain-Size Composition on Flow Resistance of Debris Flows: Behavior of Fine Sediment

Journal of Hydraulic Engineering ◽

10.1061/(asce)hy.1943-7900.0001586 ◽

2019 ◽

Vol 145 (5) ◽

pp. 06019004

Author(s):

Yuichi Sakai ◽

Norifumi Hotta ◽

Takahiro Kaneko ◽

Tomoyuki Iwata

Keyword(s):

Grain Size ◽

Debris Flows ◽

Flow Resistance ◽

Size Composition ◽

Fine Sediment ◽

Grain Size Composition

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Variable hydrograph inputs for a numerical debris-flow runout model

10.5194/nhess-2021-352 ◽

2021 ◽

Author(s):

Andrew Mitchell ◽

Sophia Zubrycky ◽

Scott McDougall ◽

Jordan Aaron ◽

Mylène Jacquemart ◽

...

Keyword(s):

Time Series ◽

Debris Flow ◽

Debris Flows ◽

Flow Resistance ◽

Numerical Models ◽

Natural Variability ◽

Simple Method ◽

Models And Modelling ◽

Model Topography ◽

Inflow Conditions

Abstract. Debris flows affect people and infrastructure around the world, and as a result, many numerical models and modelling approaches have been developed to simulate their impacts. Observations from instrumented debris-flow channels show that variability in inflow depth, velocity and discharge in real debris flows is much higher than what is typically used in numerical simulations. However, the effect of this natural variability on numerical model outputs is not well known. In this study, we examine the effects of using complex inflow time series within a single-phase runout model utilizing a Voellmy flow-resistance model. The interactions between model topography and flow-resistance were studied first using a simple triangular hydrograph, which showed simulated discharges change because of local slopes and Voellmy parameters. Next, more complex inflows were tested using time series based on 24 real debris-flow hydrographs initiated from three locations. We described a simple method to scale inflow hydrographs by defining a target event volume and maximum allowable peak discharge. The results showed a large variation in simulated flow depths and velocities arising from the variable inflow. The effects of variable inflow conditions were demonstrated in simulations of two case histories of real debris flows, where the variation in inflow leads to significant variations in the simulation outputs. The real debris-flow hydrographs were used to provide an indication of the range of impacts that may result from the natural variability in inflow conditions. These results demonstrate variation in inflow conditions can lead to reasonable estimates of the potential variation in impacts.

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Alluvial Steep Channels: Flow Resistance, Bedload Transport Prediction, and Transition to Debris Flows

Gravel-Bed Rivers ◽

10.1002/9781119952497.ch28 ◽

2012 ◽

pp. 386-397 ◽

Cited By ~ 20

Author(s):

Dieter Rickenmann

Keyword(s):

Debris Flows ◽

Flow Resistance ◽

Bedload Transport ◽

Transport Prediction

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Comparison of flow resistance relations for debris flows using a one-dimensional finite element simulation model

Natural Hazards and Earth System Science ◽

10.5194/nhess-6-155-2006 ◽

2006 ◽

Vol 6 (1) ◽

pp. 155-165 ◽

Cited By ~ 78

Author(s):

D. Naef ◽

D. Rickenmann ◽

P. Rutschmann ◽

B. W McArdell

Keyword(s):

Finite Element ◽

Debris Flows ◽

Flow Resistance ◽

Flow Behavior ◽

Equations Of Motion ◽

One Dimensional ◽

Averaged Equations ◽

Dimensional Finite Element ◽

To Come ◽

The One

Abstract. This paper describes a one-dimensional finite element code for debris flows developed to model the flow within a steep channel and the stopping conditions on the fan. The code allows the systematic comparison of a wide variety of previously proposed one-phase flow resistance laws using the same finite element solution method. The one-dimensional depth-averaged equations of motion and the numerical model are explained. The model and implementation of the flow resistance relations was validated using published analytical results for the dam break case. Reasonable agreement for the front velocities and stopping location for a debris-flow event in the Kamikamihori torrent in Japan can be achieved with turbulent flow resistance relations including "stop" terms which allow the flow to come to rest on a gently sloping surface. While it is possible to match the overall bulk flow behavior using relatively simple flow resistance relations, they must be calibrated. A sensitivity analysis showed that the shape of the upstream input hydrograph does not much affect the flow conditions in the lower part of the flow path, whereas the event volume is much more important.

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