Analysis of a small debris slide in coastal Alaska

Elektronisch veröffentlicht auf dem Publikationsserver der Universität Potsdam: http://opus.kobv. de/ubp/volltexte/2008/1640/ urn:nbn:de:kobv:517-opus-16402 [http://nbn-resolving.de/urn:nbn:de:kobv:517-opus16402] SummaryAs land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In addition to the loss of biodiversity, land-use change potentially deteriorates regional water cycles, which may have undesirable effects for local populations such as decreased water supply during dry seasons, enhanced flooding in the rainy season, or deterioration of drinking water quality.Montane rainforests in the south Ecuadorian Andes are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. Depending on the rainfall regime, the potential disturbance-induced decrease of Ks may become relevant for regional watersheds.My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatialtemporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) 'recovery' from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure.In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uniand bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect.Regarding variogram modeling, I encouraged restricted maximum likelihood estimation becau...

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“…This is especially true for high-intensity storms following wet antecedent conditions (Sidle and Swanston, 1982).…”

Section: Influence Of Landslides On Hydrological Flowpathsmentioning

confidence: 99%

Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

Zimmermann

Elsenbeer

2008

Journal of Hydrology

126

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“…Because of these limitations, slope failure can occur (Tohari et al, 2007). In general, rainfall-induced slope failures are caused by increased pore pressure and seepage force during periods of intense rainfall (Anderson and Sitar, 1995;Sidle and Swanston, 1982;Wang and Sassa, 2003;Sitar et al, 1993). Previous studies have been conducted to understand the failure mechanism of a slope, and to determine the point of initiation of failure.…”

Section: Introductionmentioning

confidence: 99%

Behavior analysis by model slope experiment of artificial rainfall

Park

2016

Nat. Hazards Earth Syst. Sci.

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Abstract. In this study, we performed a model slope experiment with rainfall seepage, and the results were compared and verified with the unsaturated slope stability analysis method. In the model slope experiment, we measured the changes in water content and matric suction due to rainfall seepage, and determined the time at which the slope failure occurred and the shape of the failure. In addition, we compared and verified the changes in the factor of safety and the shape of the failure surface, which was calculated from the unsaturated slope stability analysis with the model experiment. From the results of experiment and analysis, it is concluded that the unsaturated slope stability analysis can be used to accurately analyze and predict rainfall-induced slope failure. It is also concluded that in seepage analysis, setting the initial conditions and boundary conditions is very important. If engineers will use the measured porewater pressure or matric suction, the accuracy of analysis can be enhanced. The real-time monitoring system of porewater pressure or matric suction can be used as a warning of rainfall-induced slope failure.

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“…The literature and various studies performed on shallow landslides or "soil slips" reveal that they have caused heavy damage in different environmental conditions all over the world (Kesseli, 1943;Campbell, 1975;Govi and Sorzana, 1980;Govi and Mortara, 1981;Sidle and Swanston, 1982;Ellen and Wieczorek, 1988). Important contributions on the matter, referring to the Italian territory, are the data collection carried out by the Piedmont Region after the 1994 flood (Sutera Sardo et al, 1996;Campus et al, 1998) and the scientific notes, concerning similar types of events, in other regions: Campania in 1998 (Cascini et al, 2000(Cascini et al, , 2003Olivares 2001;Olivares and Picarelli, 2001), Umbria in 2004 (Cardinali et al, 2006), Tuscany in 1996 (Delmonaco et al, 2003) and Emilia Romagna in 2000 (Emilia Romagna ReCorrespondence to: L. Montrasio (lorella.montrasio@unipr.it) gion, Report 2002).…”

Section: Introductionmentioning

confidence: 99%

A model for triggering mechanisms of shallow landslides

Montrasio

Valentino

2008

Nat. Hazards Earth Syst. Sci.

201

109

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Abstract. Rainfall-induced shallow landslides, also called "soil slips", are becoming ever more frequent all over the world and are receiving a rising interest in consequence of the heavy damage they produce. At the University of Parma, a simplified physically based model has been recently set up for the evaluation of the safety factor of slopes which are potentially at risk of a soil slip. This model, based on the limit equilibrium method applied to an infinite slope, takes into account some simplified hypotheses on the water down-flow and defines a direct correlation between the safety factor of the slope and the rainfall depth. In this paper, this model is explained in detail and is used in a back analysis process to verify its capability to foresee the triggering instant of rainfall-induced shallow landslides for some recent case studies in the Emilia Romagna Apennines (Northern Italy). The results of the analyses and of the model implementation are finally shown.

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Analysis of a small debris slide in coastal Alaska

Cited by 118 publications

References 6 publications

Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

Behavior analysis by model slope experiment of artificial rainfall

A model for triggering mechanisms of shallow landslides

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