Simulation of debris flows in the Central Andes ba

Authors: Martin Mergili Wolfgang Fellin Stella M Moreiras Johann Stötter

Publish Date: 2011/09/07

Volume: 61, Issue: 3, Pages: 1051-1081

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Abstract

A GISbased model framework designed as a raster module for the Open Source software GRASS was developed for simulating the mobilization and motion of debris flows triggered by rainfall Designed for study areas up to few square kilometres the tool combines deterministic and empirical model components for infiltration and surface runoff detachment and sediment transport slope stability debris flow mobilization and travel distance and deposition The model framework was applied to selected study areas along the international road from Mendoza Argentina to Central Chile The input parameters were investigated at the local scale The model was run for a number of rainfall scenarios and evaluated using field observations and historical archives in combination with meteorological data The sensitivity of the model to a set of key parameters was tested The major scope of the paper is to highlight the capabilities of the model—and of this type of models in general—as well as its limitations and possible solutionsDebris flows are rapid mass movements of water and debris representing a considerable hazard when interfering with people buildings or infrastructures They are often triggered by heavy or prolonged rainfall or by extreme snow melt Mobilization of debris flow material often occurs due to translational or rotational failure of saturated or undercut slopes or due to entrainment of regolith by surface runoff or by the debris flow itself Various models exist for simulating the involved subprocesses eg particle entrainment regolith hydrology slope stability or debris flow motion More integrated GISbased approaches as attempted for example by Burton and Bathurst 1998 or by Wichmann 2006 are extremely valuable for a quick assessment of debris flow hazard as a response to defined meteorological and hydrological conditions The present paper describes a method for integrated modelling of debris flows from triggering to deposition based on the software GRASS GIS As an Open Source GIS package with focus on raster processing GRASS facilitates model development distribution and evaluation the program code is freely accessible and new modules may be added by anybody Therefore the entire scientific community has the chance to contribute to the evaluation of the model and the further development of the program code The present paper focuses on the assessment of the potentials and limitations of the model—and of this type of models in general—and on its sensitivity to certain key input parameters For this purpose various combinations of parameter settings were evaluated using six small catchments in the Central Andes Argentina and ChileAt first glance the term debris flow does not always refer to exactly the same process Some authors rather consider it as landslide with a fluidlike motion Burton and Bathurst 1998 Corominas et al 2003 Moreiras 2004a b others consider it as runoff with very high sediment concentration Rickenmann 1999 O’Brien 2003 However these two approaches are not necessarily contradictory—they rather depend on whether the observer has a geotechnical or a hydrological background As stated by Rickenmann 1999 debris flows are phenomena intermediate between landslides and runoff Many debris flow events in the real world share features of both types of processes but most of them have a clear tendency to the one or the other Some authors distinguish between debris flows on slopes originating from landslides and debris flows in channels mobilized in or near to the stream bed Wichmann 2006 Process chains coupling landslides runoff and debris flows are commonIntegrated simulation models for debris flows require the inclusion of model components for all relevant subprocesses whereby the most important are slope stability detachment by surface runoff both of them including hydraulic triggers and debris flow motion The following review focuses on methods applicable in combination with Geographic Information Systems GISVarious authors have suggested predominantly or fully empirical sediment transport equations for example Schoklitsch 1962 Yalin 1963 Yang 1973 Bagnold 1980 Low 1989 Govers 1990 Rickenmann 1990 or Abrahams et al 2001 The Rickenmann 1990 equation—only including bedload—is best suited for relatively steep channels and high load Hessel and Jetten 2007The motion of debris flows shows properties different from the flow of clear water requiring specialized and complex methods to be modelled in a fully deterministic way Savage and Hutter 1989 Hungr 1995 Iverson 1997 Chau and Lo 2004 modified the model of Takahashi et al 1992 in order to model flow path and deposition of debris flows threatening the Leung King Estate Hong Kong China based on a GIS Implementation of the SavageHutter theory into GIS is a challenge because of nonrectangular coordinate systems used Mergili et al 2008

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