Article

Physically based modelling of shallow landslide sediment yield at a catchment scale

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Abstract

 A shallow landslide erosion and sediment yield component, applicable at the basin scale, has been incorporated into the physically based, spatially distributed, hydrological and sediment transport modelling system, SHETRAN. The component determines when and where landslides occur in a basin in response to time-varying rainfall and snowmelt, the volume of material eroded and released for onward transport, and the impact on basin sediment yield. Derived relationships are used to link the SHETRAN grid resolution (up to 1 km), at which the basin hydrology and final sediment yield is modelled, to a subgrid resolution (typically around 10–100 m) at which landslide occurrence and erosion is modelled. The subgrid discretization, landslide susceptibility and potential landslide impact are determined in advance using a geographic information system (GIS), with SHETRAN then providing information on temporal variation in the factors controlling landsliding. The ability to simulate landslide sediment yield is demonstrated by a hypothetical application based on a catchment in Scotland.

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... The difficulty in predicting the location of individual slope failures, which can be referred to the simplified representation of the processes, as well as to the difficulty of accounting for the spatial variability of soils, still limits their systematic use for landslide hazard assessment. Modelling the contribution of landslides to sediment yield (Burton and Bathurst 1998;Bathurst et al. 2006) is a further step in the analysis of the interactions between slope instability and the river system. ...
... We recall here some of the simplest methods to compute the distance travelled by debris flows, which can be applied to a fast preliminary assessment of the possible interactions between debris flows in steep tributaries and the rivers in main valleys, and some more sophisticated two-dimensional numerical models suitable for a more detailed analysis of debris-flow propagation and deposition. Burton and Bathurst (1998) incorporated a module for debris-flow runout distance, which includes the assessment of the fraction of material that is delivered to the channel system, into the physically based model SHETRAN (Ewen, Parkin, and O'Connell 2000). The rules for debris-flow propagation and stopping defined by Burton and Bathurst (1998) have been successfully integrated into procedures for debris-flow susceptibility assessment at regional scales (Cavalli and Grisotto 2006). ...
... Burton and Bathurst (1998) incorporated a module for debris-flow runout distance, which includes the assessment of the fraction of material that is delivered to the channel system, into the physically based model SHETRAN (Ewen, Parkin, and O'Connell 2000). The rules for debris-flow propagation and stopping defined by Burton and Bathurst (1998) have been successfully integrated into procedures for debris-flow susceptibility assessment at regional scales (Cavalli and Grisotto 2006). ...
Chapter
The interactions between landslides (including debris flows) and river systems are a topic of great relevance for both the understanding of the evolution of mountain basins and channel networks and the implications for watershed management and flood-hazard control. Landslides and debris flows cause sudden and spatially concentrated pulses of sediment to travel from hillslopes and small lateral channels to main rivers. One of the most dramatic outcomes is the blockage of the receiving stream by landslide dams. Even when channel blockage does not occur, the impacts on the river system are remarkable, influencing geomorphological and sedimentological settings of valley floors. Channel aggradation, which is one of the most common outcomes of sediment pulses delivered from landslides to river systems, favours channel widening and lateral instability, including avulsion. The interactions of landslides and debris flows with rivers during major floods are similar to those occurring during normal flow conditions, but they are characterized by faster evolution and higher intensity of the involved processes. Due to the generally high transport capacity of the receiving stream during floods, sediment pulses from landslides lead to increased sediment transport. However, channel instability due to the aggradation of channel beds and floodplains, which occurs if sediment input exceeds the transport capacity, may severely increase the flood hazard. During floods, the probability of the receiving stream becoming blocked can be lowered because high discharge can erode and entrain landslide accumulations and debris-flow deposits, but there is a higher probability of paroxysmal evolution (fast filling of the landslide lake and erosion of the landslide dam) if channel damming does occur. This chapter aims to outline, with examples from the literature and the experience of the author, different types of interactions of landslides and debris flows with floods in mountain gravel-bed rivers (section 17.2), and present an overview on the approaches suitable to predict the occurrence of landslides and debris flows and their linkage with river systems, with attention to both the temporal and spatial scales of the processes (section 17.3). Section 17.4 summarizes the space scale at which different types of instability influence the river system, and discusses hazard prediction and management issues. Finally, section 17.5 presents some conclusions and delineates aspects that could deserve attention in future research.
... In this context, many procedures and models have been developed to assess sediment volumes mobilised from landslide source areas, and their transfer to the channel network (Borga et al., 2014;Bovis and Dagg, 1988;Burton and Bathurst, 1998;Gregoretti and Dalla Fontana, 2008;Prancevic et al., 2014;Tiranti et al., 2016). Most of them are modular approaches aiming to estimate the soil-involved volume, predicting the downslope evolution, and assessing the travel distance from the source area. ...
... • volume balance approach (Berti and Simoni, 2007;Crosta et al., 2003;Iverson et al., 1998); • limiting topographic methods (Burton and Bathurst, 1998;Ikeya, 1989); • empirical equations (Cannon, 1989;Fannin and Wise, 2001;Heim, 1932;Hsü, 1975;Rickenmann, 1999;Rickenmann and Zimmermann, 1993;Scheidegger, 1973;Toyos et al., 2008); • dynamic models (Iverson and Denlinger, 2001;Lancaster et al., 2003;O'Brien et al., 1993); ...
... Such studies underlined the considerable variability of sediment delivery ratio and noted a correlation with the site characteristics (e.g., landslide volume, distance to the stream, hillslope gradient, junction angles). Burton and Bathurst (1998) proposed a rule-based debris flow transport model based on simple assumptions on transport and deposition processes: (i) if slope inclination N10°, soil movement continues downslope; (ii) if slope inclination is between 4°a nd 10°, deposition starts spreading uniformly over the path; (iii) if slope inclination is b4°, the sediment transport halts and all remaining material deposits. ...
Article
In mountainous-forested landscape, quantifying the materials produced at hillslope scale that effectively reach the channel network with a given probability is currently challenging, due to the uncertainties in modelling the frequency-magnitude distribution of failures and in determining the sediment connectivity between unstable areas and channel network. The purpose of this study is to develop a modular approach to assess the sediment source areas and the probability of mobilization from hillslope, and to estimate the probability of sediment input to the streams proposing a new connectivity index. The first goal was faced adopting a 3D probabilistic slope stability method that includes the spatially distributed characteristics of forest coverage. The second aim was tackled by comparing sediment travel distance and the minimum-topographic distance to reach the nearest stream. A simple deposition model was applied to estimate the percentage of the sediment entering into the stream network. The methodology was tested on three headwater catchments in northern Italian Alps. The outputs were landslide susceptibility maps, which showed robust performances when compared to the available landslide inventories (AUC > 0.726), and maps of the probability that sediment reaches the channel network. In this way, it was possible to identify which areas are the most susceptible to landsliding, how many sediment materials can be mobilised with a given probability, and which is the degree of sediment connectivity with the channel system. Results obtained for the tested catchments, compared with data available from the literature, showed that the proposed methodology is of general validity, especially for those territories characterized by rainfall-triggered landslides and forest coverage. This study, then, provides a robust framework to improve debris-flow risk management and to implement watershed management strategies, such as planning forestry operations or positioning retention structures addressed to increase slope stability and to reduce sediment delivery.
... Secondo i dati di Vandre (1985) il valore di α è pari a 0.4 e quindi, adottando le soglie di 219 pendenza precedentemente descritte ed adattando di conseguenza l'approccio per il calcolo 220 della distanza di arresto proposto da (Burton & Bathurst, 1998), si può determinare l'arresto 221 della colata quando (eq. 6): 222 (5) dove W è la distanza d'arresto, Δh è la differenza di quota tra il punto di innesco e il punto in cui inizia la fase di rallentamento (e deposito) e α una frazione derivata empiricamente. ...
... 6): 222 (5) dove W è la distanza d'arresto, Δh è la differenza di quota tra il punto di innesco e il punto in cui inizia la fase di rallentamento (e deposito) e α una frazione derivata empiricamente. Secondo i dati di Vandre (1985) il valore di α è pari a 0.4 e quindi, adottando le soglie di pendenza precedentemente descritte ed adattando di conseguenza l'approccio per il calcolo della distanza di arresto proposto da (Burton & Bathurst, 1998), si può determinare l'arresto della colata quando (eq. 6): L'analisi del profilo non viene effettuata per le aste torrentizie che non presentano punti d'innesco di colate detritiche oppure nel caso in cui lungo il reticolo siano individuate zone di probabile inizio di colata ma non punti di rallentamento o arresto. ...
Article
Il presente studio nasce dall’esigenza degli uffici della Regione del Veneto di predisporre una procedura finalizzata alla valutazione della pericolosità sui conoidi alluvionali classificati come zone d’attenzione geologica nei Piani di Assetto Idrogeologico dei bacini montani del territorio regionale. Al fine di individuare un procedimento oggettivo per la valutazione della pericolosità sono state identificate e proposte metodologie di raccolta dati e di analisi atte ad individuare la tipologia del processo da investigare. Nell’ambito dello studio sono stati inoltre sviluppati strumenti per condurre e facilitare la raccolta dati del sistema bacinoconoide e software liberamente disponibili (https://github.com/ HydrogeomorphologyTools) per l’identificazione lungo il reticolo idrografico delle aree di potenziale innesco, rallentamento e deposito di colate detritiche e per il calcolo della distanza di arresto, finalizzato all’assegnazione di una priorità d’indagine dei conoidi. Il presente contributo presenta inoltre i risultati delle analisi in quattro aree test situate nelle province di Vicenza, Treviso e Belluno.
... As discussed earlier, vegetation reduces soil moisture due to interception, infiltration and ET (Ziemer, 1981;Simon and Collison, 2002;Rinaldi and Darby, 2007;Pollen-Bankhead and Simon, 2010). According to Burton and Bathurst (1998), slope stability depends on soil water content and the thickness of the saturated soil layer; the higher the soil water content is, the higher the positive pore water pressure and the lower apparent cohesion are, which significantly decreases shear strength. Preti (2013) showed that soil water content in shallow soils is significantly reduced during rainstorms if vegetation is present. ...
... Preti (2013) showed that soil water content in shallow soils is significantly reduced during rainstorms if vegetation is present. However, only a few studies were found in the literature that quantified or modelled the hydrological effects of vegetation in landslide mitigation (e.g., Burton and Bathurst, 1998;Greenwood et al., 2004;Kuriakose et al., 2006;Preti, 2013;Hwang et al., 2015;Liu et al., 2016). ...
Article
Large wood (LW) is an important element in riparian and mountain ecosystems and influences geomorphic controls, particularly in torrents and mountain rivers. Despite several advantages, LW can also exacerbate flood damage near infrastructure due to logjams or backwater rise and is often treated as a potential hazard. In an attempt to reduce such problems, channel slopes and banks are often clear cut in practice. This leads to a debate between the opinions of different scientists as well as stream and forest managers, where it is difficult to find a compromise between optimizing risk mitigation and eco-morphological functionality. Regarding risk mitigation due to LW, situations where the positive effects of vegetation succumb to negative effects should be identified to distinguish if shrubs or small trees (DBH < 10 cm) are more suitable to maintain streambank and hillslope stability. However, drastically removing vegetation can severely influence the ecosystem which should be avoided. In the case where large trees (DBH > 10 cm) have the potential to reduce the magnitude and frequency of recruitment processes, practices for forest management need to be optimized. Based on literature research, this article summarizes state of the art knowledge of vegetation effects on LW recruitment processes. In doing so, it focuses on three main recruitment processes: hydraulic bank erosion, geotechnical bank erosion and hillslope failure. Hydraulic bank erosion is responsible for delivering high volumes of sediment as well as LW in mountain catchments by removing streambank material through excess shear stress. The positive effects of vegetation can be quantified and implemented in modeling approaches through the adjustment of discharge-specific resistance coefficients or by using stochastic approaches. Geotechnical bank erosion and hillslope failure contribute to LW recruitment through failure. Root reinforcement is predominately the most important effect on how vegetation stabilizes streambanks and hillslopes. Based on the information mentioned above, a flow chart was formulated that uses specific criteria to define conditions in which forest management should be performed to mitigate potential LW recruitment without drastically removing all trees.
... The whole basin is divided into grids and the model quantifies slope failures at each grid cell on the basis of a factor-of-safety analysis with the infinite slope model (Burton and Bathurst, 1998) through use of spatially-distributed soil and vegetation parameters. Stochastic slope failure results are generated using probabilistic distributions of four soil and vegetation parameters, details of which are given below failed material is routed downslope with a rule-based scheme that determines sediment delivery to streams. ...
... The mass wasting component in DHSVM is stochastic in nature in that it calculates the FS based on user-defined probabilistic distributions of soil cohesion, angle of internal friction, root cohesion, and vegetation surcharge. For the infinite planar type shallow failure, the FS is given by (Burton and Bathurst, 1998 ...
Article
Landslide occurrences, which result in significant casualties, economic losses, and ecological impacts, have been increasing worldwide over the last few decades. Thus, it is crucial for future landslide susceptibility to be considered when making long-term plans for timber extraction. Two factors that are known to reduce soil strength and increase landslide susceptibility are clear cutting (due to reduced root contributions to soil strength) and degree of soil saturation. Therefore, as projected climate change is expected to result in storms with higher intensity precipitation in many mountainous regions, these areas are likely to become more susceptible to landslide activity resulting in potentially severe consequences to aquatic habitat due to increased sediment loads. There is a need to investigate potential management plans that simultaneously protect the economic viability of the forest industry and the ecosystem services of the forest. The primary objectives of this study are to explore the impact of timber harvesting on landslide susceptibility under climate change and to create high resolution (10 m) landslide susceptibility maps to inform land management decisions in an altered climate. The Distributed Hydrology Soil Vegetation Model (DHSVM), a physically-based hydrology model that has been improved to incorporate mass wasting and erosion processes, was used to assess the sensitivity of landslide susceptibility to timber extraction. To investigate the impacts of climate change on landslide susceptibility we applied downscaled output from two General Circulation Models (GCMs) with two greenhouse gas (GHG) emission scenarios, A1B and B1, for the year 2045. The areal extent classified with a high landslide susceptibility increased on average by 7.1% and 10.7% for the B1 and A1B GHG emissions scenarios, respectively. The landslide susceptibility maps produced in this study can enable forest managers to plan for climate change by identifying areas that are more prone to landslide activity under altered climate conditions. The methodologies developed herein can be used by forest managers around the world to better assess landslide potential.
... Landslides play an important role in determining sediment yield from a watershed [19,20]. Several studies attempted to establish the landslide component on total sediment yield [21][22][23][24][25][26]. For example, Burton and Bathurst [21] developed a physically-based model-SHETRAN to estimate the landslide-related sediment yield. ...
... Several studies attempted to establish the landslide component on total sediment yield [21][22][23][24][25][26]. For example, Burton and Bathurst [21] developed a physically-based model-SHETRAN to estimate the landslide-related sediment yield. Schuerch et al. [22] monitored the sediment yield in a small catchment and compared the different sediment source supplied to the channels. ...
Article
Full-text available
Accurate and reliable estimates of sediment yields from a watershed and identification of unstable stream reaches due to sediment-related disaster are crucial for watershed management, disaster prevention, and hazard mitigation purposes. In this study, we added hydrodynamic and sediment transport modules in a recently developed model to estimate sediment yields and identify the unstable stream reaches in a large-scale watershed (> 100km2). The calibrated and verified models can well reproduce the flow discharge and sediment discharge at the study site, the Shihmen Reservoir Watershed in Taiwan, during several typhoon events. For the scenario applications, the results revealed that the contribution (> 96%) of landslides on sediment supply is much more significant than compared to soil erosion (< 4%). The sediment contribution from the upstream of the hydrological station-Yufeng is approximately 36–55% of the total sediment supply for the rainfall events of 25, 50, 100, and 200 years return period. It also indicates that 22–52% of sediment still remain at foot of the slope and the streams, which become a potential source for sediment hazards in the future. Combining with the bed erosion and deposition depths, flow-induced shear stress from the SRH-2D model, and probability of slope failure within 250 m of stream reaches, the relatively stability of stream reaches can be identified. The results could provide the water resource authorities for reference to take precautionary measures in advance on the stream reaches with high-degree instability.
... Vanacker et al. (2003) and Gabet et al. (2004) use total unit soil weight for both layers. A more physically sound representation uses a moist unit soil weight for the unsaturated soil layer and saturated unit soil weight for a saturated soil layer (e.g., Burton and Bathurst, 1998;Sidle and Ochiai, 2006). The two-layer approaches use static values of moist unit soil weight and saturated unit soil weight, and do not take into account the impact of dynamic moisture condition for slope stability analysis. ...
... The infinite slope method (Skempton and DeLory, 1957) calculates safety factors as the ratio of resisting forces to driving forces. The infinite slope stability model as adapted by the several researchers (e.g., Montgomery and Dietrich 1994;van Westen and Terlien 1996;Acharya et al., 2006;Ray and De Smedt, 2009) is C s+C r ,(, YwV an <P FS= s r + y e Hsin0 1-m tanG where The VIC-3L model (Liang et al., 1994) The critical value for slope failure, defined by the ratio of resisting force to the sliding force on a slope, is 1 (Skempton and DeLory, 1957;Westen and Terlien 1996;Burton and Bathurst, 1998;Acharya et al, 2006;Ray and De Smedt, 2009). Depending on the soil, vegetation and climatic characteristics of the region, a slope may or may not fail at this critical safety factor value. ...
Thesis
Full-text available
Landslides are common throughout the world and can be triggered by earthquakes, volcanoes, floods, and heavy continuous rainfall in mountainous regions. For most types of slope failure, soil moisture plays a critical role because increased pore water pressure reduces the soil strength and increases stress. The combined effect of soil moisture in unsaturated soil layers and pore water pressure in saturated soil layers is critical to accurately predict landslides. However, dynamic in-situ soil moisture profiles are rarely measured on regional or global scales. The dynamic soil moisture can be estimated by a soil vegetation atmosphere transfer (SVAT) model or satellite. While a SVAT model can estimate soil moisture profile, satellite estimates are limited to the upper thin surface (0-5 cm). However, considering the complex database needed for a SVAT model, satellite data can be obtained quickly and may produce promising results in less data-rich regions at the global scale. While no previous landslide studies have used remotely-sensed soil moisture data, Advanced Microwave Scanning Radiometer (AMSR-E) has the potential to be useful in characterizing soil moisture profiles. First this study investigated relationships among landslides, AMSR-E soil moisture and Tropical Rainfall Measuring Mission (TRMM) in landslide prone regions of California, U.S., Leyte, Philippines and Dhading, Nepal. Then, a modified infinite slope stability model was developed and applied at Cleveland Corral, California, US and Dhading Nepal, using variable infiltration capacity (VIC-3L) soil moisture and AMSR-E soil moisture to develop dynamic landslide susceptibility maps at regional scale. Results show a strong relationship among remotely sensed soil moisture, rainfall and landslide events. Results also show a modified infinite slope stability model that directly includes vadose zone soil moisture can produce promising landslide susceptibility maps at regional scale using either VIC-3L or AMSR-E soil moisture. Vadose zone soil moisture has a significant role in shallow slope failure. Results show promising agreement between the susceptible area predicted by the model and the actual slope movements and slope failures observed in the study region. This model is quite reasonable to use in shallow slope stability analysis at a regional or global scale. Recommended Citation Ray, Ram Lakhan, "Landslide susceptibility mapping through enhanced dynamic slope stability analysis using earth observing satellite measurements" (2009). Doctoral Dissertations. 502. https://scholars.unh.edu/dissertation/502
... Prediction of locations of landslides within a particular rainstorm event remains challenging, highlighting issues of parameterisation, calibration and verification, and computation intensity. Parameterising subsurface mechanical and hydraulic properties in mountainous terrain remains a significant challenge, particularly because of the heterogeneity of these properties across these landscapes, the lack of systematic empirical measurement of these parameters for slopes, and poor understanding of the statistical distribution of properties at this scale (Burton and Bathurst, 1998). These issues of parameterisation mean that calibration of models is often best done using the historical landslide record. ...
... Dymond et al., 2016). Burton and Bathurst (1998) developed one of the earliest approaches to assess the contribution of shallow landslide erosion to catchment sediment yield using the model SHETRAN (Ewen, 1995). The approach determines when and where landslides occur in a catchment in response to time-varying rainfall and snowmelt, the volume of material eroded, and the impact on catchment sediment yield. ...
Article
Shallow, rainfall-triggered landslides are an important catchment process that affect the rate and calibre of sediment within river networks and create a significant hazard, particularly when shallow landslides transform into rapidly moving debris flows. Forests and trees modify the magnitude and rate of shallow landsliding and have been used by land managers for centuries to mitigate their effects. We understand that at the tree and slope scale root reinforcement provides a significant role in stabilising slopes, but at the catchment scale root reinforcement models only partially explain where shallow landslides are likely to occur due to the complexity of subsurface material properties and hydrology. The challenge of scaling from slopes to catchments (from 1-D to 2-D) reflects the scale gap between geomorphic process understanding and modelling, and temporal evolution of material properties. Hence, our understanding does not, as yet, provide the necessary tools to allow vegetation to be targeted most effectively for landslide reduction. This paper aims to provide a perspective on the science underpinning the challenges land and catchment managers face in trying to reduce shallow landslide hazard, manage catchment sediment budgets, and develop tools for catchment targeting of vegetation. We use our understanding of rainfall-triggered shallow landslides in New Zealand and how vegetation has been used as a tool to reduce their incidence to demonstrate key points.
... The majority of slope instability situations are the result of rainfall; specifically rainfall-induced landslides. Research from many disciplines, including engineering geology, soil mechanics, hydrology, and geomorphology, has focused on this subject; the introduction of Geographical Information Systems (GIS) software has made a significant contribution to landslide risk assessment [4,[10][11][12][13]. Various deterministic modeling applications are available for use at different scales [14], such as distributed Shallow Landslide Analysis Models (dSLAMs), which employs physical variables [9,15]. ...
... At the catchment scale, the SHALSTAB model uses steady-state hydrological processes and the infinite slope approach [8], whereas the SINMAP model [16] employs both uncertainty parameters and raster-based GIS images. SHETRAN [10] and TRIGRS [23] performed hydrological and spatial temporal modeling for saturated or unsaturated soil conditions. GEOtop-FS [6] is capable of handling soil layers separately, whereas PROBSTAB [24,25] can be combined with the STARWARS hydrologic model to consider multiple soil parameters. ...
Article
Full-text available
Landslide susceptibility models are important for public safety, but often rely on inaccessible or unaffordable software and geospatial data. Thus, affordable and accessible landslide prediction systems would be especially useful in places that lack the infrastructure for acquiring and analyzing geospatial data. Current landslide susceptibility models and existing methodologies do not consider such issues; therefore, this study aimed to develop an accessible and affordable landslide susceptibility modeling application and methodology based on open-source software and geospatial data. This model used TRIGRS (asc format) and QGIS (Digital Elevation Models (DEMs) extracted from GeoTIFF format) with widely accessible environmental parameters to identify potential landslide risks. In order to verify the suitability of the proposed application and methodology, a case study was conducted on Lantau Island, Hong Kong to assess the validity of the results, a comparison with 1999 landslide locations. The application developed in this study showed a good agreement with the four previous landslide locations marked as highly susceptible, which proves the validity of the study. Therefore, the developing model and the cost-effective approach, in this study simulated the landslide performance well and suggested the new approach of the landslide prediction system.
... 41 Cain, 1980;Wieczorek and Glade, 2005;Guzzetti et al, 2007;Guzzetti et al, 2008, and 42 reference therein); 3) by spatially distributed physical-deterministic modelling (e.g. Anderson 43 and Lloyd, 1991;Montgomery and Dietrich, 1994;Wu and Sidle, 1995;Borga et al, 1998;44 Pack et al, 1998;Burton and Bathurst, 1998;Van Beek, 2002, Baum et al, 2008;). The 45 heuristic models are mainly used in first assessments of hazard for regional planning. ...
Article
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The vast majority of shallow landslides and debris flows are precipitation initiated. Therefore, regional landslide hazard assessment is often based on empirically derived precipitation-intensity-duration (PID) thresholds and landslide inventories. Generally, two features of precipitation events are plotted and labelled with (shallow) landslide occurrence or non-occurrence. Hereafter, a separation line or zone is drawn, mostly in logarithmic space. The practical background of PID is that often only meteorological information is available when analyzing (non-) occurrence of shallow landslides and, at the same time, the conceptual idea is that precipitation information is a good proxy for both meteorological trigger and hydrological cause. Although applied in many case studies, this approach suffers from indistinct threshold, many false positives as well as limited physical process understanding. Some first steps towards a more hydrologically based approach have been proposed in the past, but these efforts received limited follow-up. Therefore, the objective of our paper is to: (a) critically analyse the concept of PID thresholds for shallow landslides and debris flows from a hydro-meteorological point of view, and (b) propose a novel trigger-cause conceptual framework for lumped regional hydro-meteorological hazard assessment. We will discuss this based on the published examples and associated discussion. We discuss the PID thresholds in relation to return periods of precipitation, soil physics and slope and catchment water balance. With this paper, we aim to contribute to the development of a stronger conceptual model for regional landslide hazard assessment based on physical process understanding and empirical data.
... In the same way, modelling has been used to quantify spatially distributed soil erosion rates, shallow landslides and sediment yields (e.g. Burton and Bathurst, 1998;de Jong et al., 1999), key processes to understand sediment connectivity. Although advances in field data acquisition techniques together with computational improvements to modelling have provided new opportunities to study connectivity, mapping water and sediment pathways, their changes through time, quantifying the amount of water and sediments being transferred from sources to sinks (e.g. ...
Article
Connectivity has become a key issue in the study of processes acting in hydro-geomorphic systems and has strong implications on the understanding of their behaviour. Given the high complexity of hydro-geomorphic systems and the large variety of the processes controlling the efficiency of water and sediment transfer through a catchment, mapping hydrological and sediment connectivity is fundamental to understand the linkages between different parts of the system and the role played by system configuration, natural landforms and man-made structures in favouring or obstacolating the continuity of runoff and sediment pathways. Furthermore, the analysis of changes on connectivity through time can help to investigate the effect of both natural and anthropic disturbance on water and sediment fluxes and associated processes. This special issue aimed to shed light on the latest advances inmapping water and sediment connectivity by means of field measurements, modelling and geomorphometric approaches along with quantitative methods for the analysis of connectivity temporal evolution.The special issue is composed of twenty-one papers presenting a huge variety of topics dealing with hydrological and sediment connectivity and their changes through time in different geographical andclimatic regions of the world, at different spatial and temporal scales. This special issue highlights the importance of connectivity assessment to properly address sediment and water-related issues and to improve management strategies in hydro-geomorphic systems.
... Mass movements are one of the most important geomorphic hazard in the Himalaya where the damage caused by the landslides/debris flows is ~ 30% of the total damage caused by landslides globally (Li, 1990). The human population explosion and urban expansion has exacerbated the landslide threat in Himalaya (Burton and Bathurst, 1998). The primary factors responsible for M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT landslide/debris flow occurrence in the Himalaya are local terrain conditions, slope-forming materials, topography, groundwater, and land cover ; in addition to these, strong winds, intense rainfall and earthquakes have become dominant triggers (Soeters and Van Westen, 1996). ...
Article
The Shyok-Nubra Valley situated in the NW Himalaya of India represents a dynamic environment where continuous tectonics has influenced the landscape, geologic and geomorphic processes. With existence of communities in such an environment it becomes very essential to document and understand the natural hazards. This paper provides a preliminary documentation and understanding of the natural hazards and their drivers, mechanisms and impacts in this region. Here, seismicity is poorly understood, and the earthquake hazards are primarily associated with collapse of building (Type-I and II) structures. Intense deformation has made the mountainous terrain very fragile, weak and highly susceptible to mass movements. The region is susceptible to floods and GLOFs, based on OSL dating, we report two flooding events (bracketed between 8.5 ± 0.4 and 7.5 ± 0.4 ka) and the increase in sedimentation rate over a period of 4.3 ka. Here, major settlements are on active fans that are highly vulnerable to numerous hazards. Fan hazard risk assessment in the Diskit area enabled identification of four hazard prone zones that should be avoided for any developmental work. Although the frequency of cloudburst and rain-storms has increased, very little is understood about the climate and its variability in this region. The region is prone to snow avalanche risk, but most of the settlements are located in the low susceptibility zone. The aeolian geomorphic processes are dominant in the region and desertification is prominent in some areas. This work provides a suitable context for resolving problems related to natural hazards susceptibility and developmental works in this region.
... One of the main factors which predict damage is slope, which is closely related to the velocity of the debris flow ( Guinau et al. 2007). On slopes between 4° and 10°, debris flow comes to a halt, and on gentle slopes less than 4°, the debris and all the remaining materials are deposited (Burton and Bathurst 1998;Cavalli et al. 2017). In the study area, the slope angle distribution shows a slightly different pattern between level 1 and the other classes. ...
Article
To mitigate the damage caused by debris flows resulting from heavy precipitation and to aid in evacuation plan preparation, areas at risk should be mapped on a scale appropriate for affected individuals and communities. We tested the effectiveness of simply identifying debris-flow hazards through automated derivation of surface curvatures using LiDAR digital elevation models. We achieved useful correspondence between plan curvatures and areas of existing debris-flow damage in two localities in Japan using the analysis of digital elevation models (DEMs). We found that plan curvatures derived from 10m DEMs may be useful to indicate areas that are susceptible to debris flow in mountainous areas. In residential areas located on gentle sloping debris flow fans, the greatest damage to houses was found to be located in the elongated depressions that are connected to mountain stream valleys. Plan curvature derived from 5m DEM was the most sensitive indicators for susceptibility to debris flows.
... For instance, stratigraphy (or layering of soil Landslides Original Paper deposit), the variation of soil thickness, and the accuracy of DTM (digital terrain model) could cause uncertainties in the physically based model approach Ho et al. 2012;Corominas et al. 2014;Cuomo and Iervolino 2016). Therefore, uncertainty has been recognized as an important cause of the discrepancy between simulated and observed distributions of landslide occurrences (Burton and Bathurst 1998). Recently, a probabilistic approach has been adopted with the physically based model to provide a systematic and quantitative way to account for the uncertainties involved in the physical slope model and in the material properties (Park et al. 2013;Rossi et al. 2013;Raia et al. 2014;Lee and Park 2016;Salciarini et al. 2017). ...
Article
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The occurrence of landslides is controlled by various interrelated spatial and climatic factors, some of which cannot be determined accurately in detail and others that can be determined only with large degrees of uncertainty. Therefore, uncertainties pervade the field of landslide susceptibility analysis, and so the recognition and assessment of uncertainties is of paramount importance in this analysis. In particular, in a physically based model that has been widely used in regional landslide susceptibility analysis, uncertainties are inevitably involved since reliable information required to estimate input parameters in physically based models is frequently limited in extent and has an imperfect quality. In addition, some uncertainties related to measured geotechnical parameters of slope materials may be nonstochastic, but rather cognitive, arising from incomplete information. Under such conditions of limited information, it is more appropriate to adopt the fuzzy set theory. Therefore, in this study, the fuzzy set theory, coupled with interval MC simulation and the vertex method, was adopted for physically based landslide susceptibility analysis to properly handle uncertainty propagation through a physical slope model. The proposed fuzzy-based approach was applied to the study area to evaluate landslide susceptibility for the regional area, and subsequently, to evaluate the performance of the proposed approach, the analysis results were compared with landslide inventory. In addition, a probabilistic and a deterministic analysis were also carried out to compare with the fuzzy-based analysis results. The fuzzy approach showed better performance than the probabilistic and deterministic analyses and was more robust against variation in input parameters than other approaches. Therefore, in a regional-scaled landslide susceptibility analysis using a physically based model, the fuzzy approach can control the uncertainties appropriately and is particularly advantageous when the amount of reliable input data is very limited.
... Among hydro-geomorphic processes, rainfall-induced shal- low landslide is a threatening hazard in many mountain- ous watersheds around the world. Deterministic landslide models are widely applied to construct landslide suscepti- bility maps for management and hazard mitigation (Montgomery and Dietrich, 1994;Wu and Sidle, 1995;Burton and Bathurst, 1998;Borga et al., 1998;Pack et al., 1998). Pre- vious studies have proven that soil wetness caused by rain storms plays a crucial role in triggering landslides. ...
Article
This study anatomized algorithm effects of specific contributing area (SCA) on soil wetness estimation, consequently landslide prediction, in SHALSTAB. A subtropical mountainous catchment during three typhoon invasions is targeted. The peak 2-day rainfall intensity of the three typhoons: Haitang, Mindulle and Herb are 144, 248 and 327 mm/day, respectively. We use modified success rate (MSR) to retrieve the most satisfying mean condition for model parameters in SHALSTAB at three rainfall intensities and respective pre-typhoon NDVI themes. Simulation indicates that algorithm affects the prediction of landslide susceptibility (i.e. FS, Factor of Safety) significantly. Based on fixed NDVI and the mean condition, we simulate by using full scale rainfall intensity from 0 to 1200 mm/day. Simulations show that predicted unstable area coverage increases non-linearly as rainfall intensity increases for all algorithms yet with different increasing trends. Compared to Dinf, D8 always gives lower coverage of predicted unstable area during three typhoons. By contrast, FD8 gives higher coverage areas. The absolute difference (compared to Dinf) in predicted unstable area ranges from ∼−3% to +4% (per-cent watershed area). The relative difference (compared to Dinf) ranges from −15% to as high as +40%. The maximum absolute and relative differences in unstable area prediction occur around the condition of 100-300 mm/day, which is common in subtropical mountainous region. Theoretical relationship among slope, rainfall intensity, SCA and FS value was derived in which FS values are very sensitive to algorithms in the field of slope from 37 to 52degree. Results imply any comparison among SCA-related landslide models or engineering application of rainfall return period analysis must base on the same algorithm to obtain comparable results. This study clarifies the SCA algorithm effect on FS prediction and deepens our understanding on landslide modeling.
... ISM is the oldest, simplest, and most widely used among LEMs (Selby, 1993;Pack et al., 1998;Montgomery and Dietrich, 1994;Burton and Bathurst, 1998;Borga et al., 2002;Arnone et al., 2011;Lepore et al., 2013). Its main feature is modeling the slope failure considering it as planar and parallel to the slope surface. ...
Article
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Slope Stability Models (SSMs) are valuable tools used as decision support in land management to mitigate catastrophic effects caused by rainfall-induced shallow landslides. In particular, SSMs incorporating the presence and influence of vegetation allow for the evaluation of how trees influence relative slope stability and how forest management could ensure the root reinforcement effect in space and time. By implementing empirical knowledge about complex mechanical and hydrological processes, SSMs have been realized by employing different modeling approaches and methods, becoming suitable for different contexts and scales of analysis. Recent SSMs increasingly consider vegetation both as a mechanism to counteract the triggering process of shallow landslides and as a manageable and modifiable tool for mitigating hazards. This review aims to analyze the state-of-the-art of SSMs applicable to vegetated slope areas, investigating those that consider root reinforcement and some of the most cited SSMs in the literature that neglect this effect instead. After classification and exposition on the spatial and temporal dimension of the analysis, modeling approaches, and complexity, we discuss the identification of the most suitable Slope Stability Model (SSM) for individual applications considering four fundamental aspects: modeling approaches, the analysis scale, and purpose, and the output data. Although all SSMs allow for risk analysis by quantifying the factor of safety, only a few allow for an accurate assessment of how changes in vegetation structure, due to the occurrence of natural and human disturbances, also affect the stability of a studied area. Such information is critical to identifying land management criteria to preserve and enhance the protection effect. The improvement of data collection and measurement techniques to obtain parameters for stability analysis required the development of new SSMs able to exploit the improved detail of information, thus allowing for increasingly accurate analyses.
... On the other hand, the TRIGRS model, or any other similar physically based numerical model (e.g., Montgomery and Dietrich, 1994;Burton and Bathurst, 1998;Malet et al., 2005;Rigon et al., 2006;Simoni et al., 2008;Anagnostopoulos and Burlando, 2012;Von Ruette et al., 2013;Mergili et al., 2014), has inherent computer storage and processing limitations that impose careful selection of an appropriate modelling strategy. Parallelization of the existing TRIGRS code (Alvioli and Baum, 2016; available in GitHub 3 ) was a first step, but further efforts are needed to produce physically-based models for the timing and spatial distribution of rainfall-induced shallow landslides that can be used efficiently for climate impact studies. ...
Article
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The relation between climate change and its potential effects on the stability of slopes remains an open issue. For rainfall induced landslides, the point consists in determining the effects of the projected changes in the duration and amounts of rainfall that can initiate slope failures. We investigated the relationship between fine-scale climate projections obtained by downscaling and the expected modifications in landslide occurrence in Central Italy. We used rainfall measurements taken by 56 rain gauges in the 9-year period 2003 – 2011, and the RainFARM technique to generate downscaled synthetic rainfall fields from global climate model projections for the 14-year calibration period 2002–2015, and for the 40-year projection period 2010–2049. Using a specific algorithm, we extracted a number of rainfall events, i.e. rainfall periods separated by dry periods of no or negligible amount of rain, from the measured and the synthetic rainfall series. Then, we used the selected rainfall events to force TRIGRS v. 2.1, the Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model. We analyzed the results in terms of variations (or lack of variations) in the pluviometric thresholds for the possible initiation of landslides, in the probability distribution of landslide size (area), and in landslide hazard. Results showed that the downscaled rainfall fields obtained by RainFARM can be used to single out rainfall events, and to force the slope stability model. Results further showed that while the rainfall thresholds for landslide occurrence are expected to change in future scenarios, the probability distribution of landslide areas are not. We infer that landslide hazard in the study area is expected to change in response to the projected variations in the rainfall conditions. We expect that our results will contribute to regional investigations of the expected impact of projected climate variations on slope stability conditions and on landslide hazards.
... (2) empirical, lumped-statistical, by relating rainfall information to the observed occurrence (e.g., Caine, 1980;Wieczorek and Glade, 2005;Guzzetti et al., 2007, 2008, andreference therein); and (3) by spatially distributed physicaldeterministic modeling (e.g., Anderson and Lloyd, 1991;Montgomery and Dietrich, 1994;Wu and Sidle, 1995;Borga et al., 1998;Burton and Bathurst, 1998;Pack et al., 1998;Van Beek, 2002;Baum et al., 2008). The heuristic models are mainly used in first assessments of (landslide) hazards for regional planning. ...
Article
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Many shallow landslides and debris flows are precipitation initiated. Therefore, regional landslide hazard assessment is often based on empirically derived precipitation intensity-duration (ID) thresholds and landslide inventories. Generally, two features of precipitation events are plotted and labeled with (shallow) landslide occurrence or non-occurrence. Hereafter, a separation line or zone is drawn, mostly in logarithmic space. The practical background of ID is that often only meteorological information is available when analyzing (non-)occurrence of shallow landslides and, at the same time, it could be that precipitation information is a good proxy for both meteorological trigger and hydrological cause. Although applied in many case studies, this approach suffers from many false positives as well as limited physical process understanding. Some first steps towards a more hydrologically based approach have been proposed in the past, but these efforts received limited follow-up.Therefore, the objective of our paper is to (a) critically analyze the concept of precipitation ID thresholds for shallow landslides and debris flows from a hydro-meteorological point of view and (b) propose a trigger–cause conceptual framework for lumped regional hydro-meteorological hazard assessment based on published examples and associated discussion. We discuss the ID thresholds in relation to return periods of precipitation, soil physics, and slope and catchment water balance. With this paper, we aim to contribute to the development of a stronger conceptual model for regional landslide hazard assessment based on physical process understanding and empirical data.
... However, in catchment areas in the mountains, human activities greatly influence ground surface conditions and vegetation cover. Human development and road construction are generally believed to compromise slope stability and trigger landslides and debris flows (Burton and Bathurst, 1998;Chung et al., 1995;Gorsevski et al., 2006). One of the main reasons for this is that road construction changes the terrain at the toe of a slope, which compromises the continuity of water flow and reduces the ability of the slope to drain, in turn reducing its stability. ...
Article
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Development in mountainous areas is inevitable in countries with high population densities, but the actual relationship between development and landslides remains uncertain. Clarifying the key current or historical factors resulting in landslides is crucial for hazard prevention and mitigation. This study focused on the Shihmen Reservoir catchment in Taiwan. Two combinations of explanatory variables in five different years (1946, 1971, 2001, 2004, and 2012) collected from a geodatabase and digital archives were used to conduct proximity and discrete logistic regression analyses. The results demonstrate that landslides increased dramatically from 1946 to 2012 in the catchment area. The proximity and overlapping of human development with landslides increased. However, the logistic regression results indicated that variation in susceptibility to landslides was due to natural causes, with the exception of historical deforestation and newly constructed road systems. Therefore, well-recovered historical woodland sites might currently be landslide-prone areas. We suggest that cumulative historical events should be considered as explanatory variables in future landslide prediction analysis.
... Since debris flows may occur with variable intensity, especially with regard to kinematic aspects, along the various parts of the channel network, it is important to identify the channel reaches prone to debris-flow propagation, deceleration, and stopping. It has been reported in the literature that a debris flow can start depositing the transported material on slopes of about 6°-10° and usually stopping at values around 3°-5° (Burton and Bathurst 1998;Benda 1985;Vandre 1985). Accordingly, following a cautionary approach, the proposed procedure classifies the raster cells in the slope range of 3°-8° and below 3° as deceleration and stopping, respectively. ...
Article
The assessment of the areas endangered by debris flows is a major issue in the context of mountain watershed management. Depending on the scale of analysis, different methods are required for the assessment of the areas exposed to debris flows. While 2-D numerical models are advised for detailed mapping of inundation areas on individual alluvial fans, preliminary recognition of hazard areas at the regional scale can be adequately performed by less data-demanding methods, which enable priority ranking of channels and alluvial fans at risk by debris flows. This contribution focuses on a simple and fast procedure that has been implemented for regional-scale identification of debris-flow prone channels and prioritization of the related alluvial fans. The methodology is based on the analysis of morphometric parameters derived from Digital Elevation Models (DEMs). Potential initiation sites of debris flows are identified as the DEM cells that exceed a threshold of slope-dependent contributing area. Channel reaches corresponding to debris flows propagation, deceleration and stopping conditions are derived from thresholds of local slope. An analysis of longitudinal profiles is used for the computation of the runout distance of debris flows. Information on erosion-resistant bedrock channels and sediment availability surveyed in the field are taken into account in the applications. A set of software tools was developed and made available (https://github.com/HydrogeomorphologyTools) to facilitate the application of the procedure. This approach, which has been extensively validated by means of field checks, has been extensively applied in the eastern Italian Alps. This contribution discusses potential and limitations of the method in the frame of the management of small mountain watersheds.
... 3. Métodos basados en los procesos físicos (por ejemplo Burton y Bathurst, 1998;Montgomery y Dietrich, 1994;Montrasio, Valentino y Losi, 2011;Pack, Tarboton y Goodwin, 1998;Wu y Sidle, 1995). Entre los factores que influencian los desliza- mientos superficiales desencadenados por lluvias, las propiedades de la vegetación tienen una con- tribución importante. ...
Article
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El presente artículo evalúa la susceptibilidad a ocurrencia de deslizamientos superficiales, empleando un método que permite modelar en grandes áreas de terreno, cuantificando la contribución de los árboles a la estabilidad mediante tres parámetros principales: interceptación de lluvia, refuerzo aportado por las raíces y sobrecarga debida a su peso. Se utiliza un modelo de interceptación para determinar la lluvia disponible para infiltración y su distribución temporal durante la misma. Se describen varios modelos hidrológicos, implementados en TRIGRS, y que según las condiciones iniciales permiten estimar la presión de poros. Esta variable se incluye en el modelo revisado de estabilidad de taludes infinitos, el cual considera los términos de refuerzo de las raíces y sobrecarga, permitiendo modelar la estabilidad en términos del factor de seguridad en toda una cuenca. Finalmente, se simulan diferentes escenarios de densidad arbórea en una cuenca del Valle de Aburrá y se comparan los resultados con una modelación realizada sin considerar el efecto de los árboles en la estabilidad.
... Doten et al. (2006) upgraded the model to include soil loss and sediment transport from four major processes: hillslope erosion, forest road erosion, mass wasting, and channel routing using a discrete approximation to the kinematic wave equation. Hillslope erosion is based on the System Hydrologique European sediment (SHESED) model (Burton & Bathurst, 1998;Wicks & Bathurst, 1996) and incorporates overland flow and raindrop impact. ...
Article
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A new paradigm of simulating suspended sediment load (SSL) with a Land Surface Model (LSM) is presented here. Five erosion and SSL algorithms were applied within a common LSM framework to quantify uncertainties and evaluate predictability in two steep, forested catchments (>1,000 km²). The algorithms were chosen from among widely used sediment models, including empirically based: monovariate rating curve (MRC) and the Modified Universal Soil Loss Equation (MUSLE); stochastically based: the Load Estimator (LOADEST); conceptually based: the Hydrologic Simulation Program-Fortran (HSPF); and physically based: the Distributed Hydrology Soil Vegetation Model (DHSVM). The algorithms were driven by the hydrologic fluxes and meteorological inputs generated from the Variable Infiltration Capacity (VIC) LSM. A multiobjective calibration was applied to each algorithm and optimized parameter sets were validated over an excluded period, as well as in a transfer experiment to a nearby catchment to explore parameter robustness. Algorithm performance showed consistent decreases when parameter sets were applied to periods with greatly differing SSL variability relative to the calibration period. Of interest was a joint calibration of all sediment algorithm and streamflow parameters simultaneously, from which trade-offs between streamflow performance and partitioning of runoff and base flow to optimize SSL timing were noted, decreasing the flexibility and robustness of the streamflow to adapt to different time periods. Parameter transferability to another catchment was most successful in more process-oriented algorithms, the HSPF and the DHSVM. This first-of-its-kind multialgorithm sediment scheme offers a unique capability to portray acute episodic loading while quantifying trade-offs and uncertainties across a range of algorithm structures.
... Empirical relationships are based on the sediment volume to be deposited (Ikeya, 1981;Rickenmann, 1999;García-Ruiz et al., 2002;Yu et al., 2006;Zhang et al., 2013;von Ruette et al., 2016) or topography (Cannon, 1989;Fannin and Wise, 2001;Lorente et al., 2003;McDougall, 2017;Prochaska et al., 2008;Tang et al., 2012;Vandre, 1985). Topographic methods require the channel slope (Prochaska et al., 2008) or elevation difference (Vandre, 1985;Burton and Bathurst, 1998). Their advantage is that they do not require an estimate of debris flow volume. ...
Article
The Wenchuan area has become highly susceptible to landslides and debris flows since the earthquake occurred on 2008. A detailed debris flow hazard assessment is necessary to provide information for future risk management. Debris flow runout on a depositional fan is an important factor for assessing debris flow hazard, and its estimate becomes essential for the planning of the mitigation works that must be built. We therefore developed two simple empirical relationships based both on univariate and multivariate approaches, which provide the runout distance using the data for 134 channelized debris flow events in 134 catchments in the Wenchuan earthquake zone. We generated a correlation matrix of the debris flow runout distances and the relevant variables. Because of the high correlations, the independent variable debris flow volume (VD) was selected for the univariate approach. Using a multicollinearity analysis and a stepwise regression technique, the catchment (basin) internal relief (H), and VD were used to develop a multivariate runout relationship. The coefficients of the variables were obtained using 80% of the dataset (training dataset); the remaining 20% was used for test of estimated performance by comparing the computed runout distances with observed values. The validation demonstrated that the proposed relationships are suitable for estimating the runout distances of debris flows on depositional fans in the Wenchuan earthquake zone. The univariate runout relationship has the advantage of being simple, whereas the multivariate runout relationship provides higher accuracy. Additionally we rearranged and reformulated existing relationships using the same training dataset and compared the results with those from the relationships here proposed. The estimations provided by our relationships were the closest to the observed values. The presented approaches may be applied to estimate debris flow runout distances in other areas after they are retrained using local datasets.
... Les modèles hydrologiques ont depuis longtemps inclus les processus liés à la végétation tels que l'interception des précipitations par la canopée, l'évapotranspiration, l'infiltration et la résistance à l'écoulement de surface [Wigmosta et al., 1994]. Certains de ces modèles hydrologiques peuvent être couplés à des modules d'érosion et de transport de sédiments afin de calculer les flux de sédiments (DHSVM [Doten et al., 2006], SHETRAN [Burton and Bathurst, 1998], SWAT [Betrie et al., 2011], WEPP (Water Erosion Prediction Project) [Flanagan and Nearing, 1995] ou AnugaSed par exemple). Néanmoins ces modèles sont conçus pour fonctionner sur de petites échelles de temps, échelle évènementielle ou annuelle, en raison de leurs performances de calcul qui ne permettent pas de simulations sur le long terme. ...
Thesis
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S’il est bien connu que la végétation peut affecter l’érosion, le dépôt de sédimentset l’évolution à long terme du relief, la nature de cette interaction et la manièredont elle devrait être modélisée ne sont pas manifestes et peuvent dépendre du sited’étude. Comprendre les modes d’action de la végétation est indispensable pour interpréter les formes actuelles du paysage et reconstituer l’histoire de l’érosion d’une part, et pour prédire les dynamiques érosives et morphologiques de ces systèmes dans un contexte de changement climatique global d’autre part. L’objectif de la thèse est d’identifier la nature et l’amplitude de l’impact de la végétation sur l’érosion dans le cadre des terrains marneux de l’Observatoire de Draix-Bléone. Nous avons travaillé sur deux bassins de l’Observatoire de taille et de lithologie similaires mais possédant une couverture végétale contrastée : le Laval, principalement dénudé, et le Brusquet, entièrement reboisé à la fin du XIXème siècle dans le cadre de travaux de restauration entrepris sur les Alpes-de-Haute-Provence. Dans un premier temps, nous avons mené une analyse morphométrique afin d’investiguer les liens entre des indicateurs caractérisant la morphologie des bassins et la végétation. L’analyse met en évidence un lien prépondérant entre pente et végétation. Dans un second temps, afin de rendre compte de ce couplage fort entre la végétation, la topographie et l’érosion, nous avons construit un modèle d’évolution géomorphologique avec la librairie Landlab et introduit l’effet de la végétation dans ce modèle. Nous avons employé une procédure de calibration de type leave-one-out" et de validation croisée afin de calibrer et de tester simultanément l’efficacité des prédictions du modèle. Le modèle est forcé avec les séries chronologiques de crues observées sur les deux bassins versants. Les résultats des simulations indiquent que les processus de transport sur versants dépendent fortement de la couverture végétale, alors que les processus de transport dans le réseau de drainage ne semblent pas être affectés par la présence de végétation. En outre, le modèle permet d’apporter un éclairage nouveau et de conclure que, sur ce site d’étude, la végétation agit principalement sur l’érosion en réduisant l’érodabilité du sol, donc en augmentant sa cohésion, plutôt qu’en réduisant le ruissellement de surface. Enfin, le modèle ainsi que la méthodologie proposés dans ce travail de thèse, constituent un outil intéressant pour la quantification et l’évaluation des opérations de revégétalisation et de reboisement antérieures ainsi que orienter de futurs travaux de restauration.
... On one hand, hydrological models have long included vegetation-related processes such as canopy interception of precipitation, evapotranspiration, infiltration and overland-flow resistance (Wigmosta, Vail, and Lettenmaier, 1994). Some of these hydrological models can be coupled with erosion and sediment transport modules to calculate sediment fluxes (DHSVM: ; Doten, Bowling, Lanini, Maurer, and Lettenmaier, 2006;SHETRAN: ;Burton and Bathurst, 1998;SWAT: ;Betrie, Mohamed, van Griensven, and Srinivasan, 2011; or AnugaSed, for instance). However, such models are designed to work at small timescales (event scale, or annual), and they do not honor the feedbacks of runoff generation, erosion or topographic change. ...
Article
While it is well‐recognized that vegetation can affect erosion, sediment yield, and over longer time scales landform evolution, the nature of this interaction and how it should be modeled is not obvious and may depend on the study site. In order to develop quantitative insight into the magnitude and nature of vegetation's influence on catchment erosion, we build a landscape evolution model to simulate erosion in badlands then calibrate and evaluate it against sediment yield data for two catchments with contrasting vegetation cover. The model couples hillslope gravitational transport and stream alluvium transport. Results indicate that hillslope transport processes depend strongly on the vegetation cover whereas stream transport processes do not seem to be affected by the presence of vegetation. The model performance in prediction is found to be higher for the denuded catchment than for the reforested one. Moreover, we find that vegetation acts on erosion mostly by reducing soil erodibility rather than by reducing surface runoff. Finally, the methodology we propose can be a useful tool to evaluate the efficiency of previous revegetation operations, and provide guidance for future restoration work.
... Among the methods for evaluating landslide susceptibilities, physical-model based analysis estimates the stability by treating a slope as a specific physical model and inputting slope information [19,20]. This method enables susceptibility analysis regardless of the information about landslide occurrence location information, so it is possible to analyze the susceptibility of an area before landslides occur [21]. ...
Article
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Every year, many countries carry out landslide susceptibility analyses to establish and manage countermeasures and reduce the damage caused by landslides. Because increases in the areas of landslides lead to new landslides, there is a growing need for landslide prediction to reduce such damage. Among the various methods for landslide susceptibility analysis, statistical methods require information about the landslide occurrence point. Meanwhile, analysis based on physical slope models can estimate stability by considering the slope characteristics, which can be applied based on information about the locations of landslides. Therefore, in this study, a probabilistic method based on a physical slope model was developed to analyze landslide susceptibility. To this end, an infinite slope model was used as the physical slope model, and Monte Carlo simulation was applied based on landslide inventory including landslide locations, elevation, slope gradient, specific catchment area (SCA), soil thickness, unit weight, cohesion, friction angle, hydraulic conductivity, and rainfall intensity; deterministic analysis was also performed for the comparison. The Mt. Umyeon area, a representative case for urban landslides in South Korea where large scale human damage occurred in 2011, was selected for a case study. The landslide prediction rate and receiver operating characteristic (ROC) curve were used to estimate the prediction accuracy so that we could compare our approach to the deterministic analysis. The landslide prediction rate of the deterministic analysis was 81.55%; in the case of the Monte Carlo simulation, when the failure probabilities were set to 1%, 5%, and 10%, the landslide prediction rates were 95.15%, 91.26%, and 90.29%, respectively, which were higher than the rate of the deterministic analysis. Finally, according to the area under the curve of the ROC curve, the prediction accuracy of the probabilistic model was 73.32%, likely due to the variability and uncertainty in the input variables.
... Cislaghi and Bischetti (2019) proposed a modular approach to couple slope stability modelling and connectivity. Similar methods have been used for modelling sediment delivery from debris flows (Burton and Bathurst, 1998), surface erosion (Poeppl et al., 2019;Zhao et al., 2020;Najafi et al., 2021b), and large wood recruitment to streams (Rigon et al., 2012;Lucía et al., 2015). These approaches adopt either physical or statistical models to predict slope stability, followed by a prediction of run-out length to determine the degree of connectivity. ...
Article
In silvopastoral environments, landslide erosion results in loss of productive soils and pasture. Sediment delivered to streams from landslides contributes to the degradation of freshwater and marine receiving environments by smothering benthic habitats and increasing turbidity, light attenuation, and sediment-bound contaminants. Biological mitigation is an important strategy in pastoral environments to combat landslide erosion and improve the health of downstream aquatic ecosystems. Using lasso logistic regression, we investigate determinants of sediment connectivity for a landslide-triggering storm event in 1977 in the Wairarapa, New Zealand. Furthermore, we develop the first morphometric connectivity model to predict the likelihood of sediment delivery to streams following landslide initiation. We explore a range of connectivity scenarios by defining a set of sinks and simulating varying rates of sediment generation during flood events of increasing magnitude. The likelihood of sediment delivery is greatly enhanced where landslide deposits coalesce. Besides scar size variables, overland flow distance and vertical distance to sink were the most important morphometric predictors of connectivity. When scar size variables were removed from the connectivity model, median AUROC was reduced from 0.88 to 0.75. By coupling landslide susceptibility and connectivity predictions in a modular form, we quantify the cost effectiveness of targeted versus non-targeted approaches to shallow landslide mitigation. Sediment delivery ratios range from 0.21 to 0.29, equating to an event sediment yield of 3548 t km⁻² to 9033 t km⁻². Targeted mitigation of landslide-derived sediment is approximately an order of magnitude more cost-effective than a non-targeted approach. Compared with a pasture-only baseline, a 34% reduction in sediment delivery can be achieved by increasing slope stability through spaced tree planting on 6.5% of the pastoral land. The maximum reduction achievable through comprehensive coverage of widely spaced planting is 56%. The landslide connectivity model provides an objective method to support management decisions relating to mitigation of landslide erosion and sediment delivery to streams.
... The superficial deposits that are found on the valley's slopes consist of calcareousdolomitic chaotic material with loose and sharp-edged fragments. [37][38][39]. The effects of rainfall on sediment yield are obvious and the sediment yield increases with an increase in the gravel percentage [40,41]. ...
Article
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Landslides are a serious geohazard worldwide, causing many casualties and considerable economic losses every year. Rainfall-induced shallow landslides commonly occur in mountainous regions. Many factors affect an area’s susceptibility, such as rainfall, the soil, and the slope. In this paper, the effects of rainfall intensity, rainfall pattern, slope gradient, and soil type on landslide susceptibility are studied. Variables including soil volumetric water content, matrix suction, pore water pressure, and the total stress throughout the rainfall were measured. The results show that, under the experimental conditions of this paper, no landslides occurred on a 5° slope. On a 15° slope, when the rainfall intensity was equal to or less than 80 mm/h with a 1 h duration, landslides also did not happen. With a rainfall intensity of 120 mm/h, the rainfall pattern in which the intensity gradually diminishes could not induce landslides. Compared with fine soils, coarser soils with gravels were found to be prone to landslides. As the volumetric water content rose, the matrix suction declined from the time that the level of infiltration reached the position of the matrix. The pore water pressure and the total stress both changed drastically either immediately before or after the landslide. In addition, the sediment yield depended on the above factors. Steeper slopes, stronger rainfall, and coarser soils were all found to increase the amount of sediment yield.
... The replacement of forests by agriculture and settlements is thought to cause severe erosion and landslides (Glade, 2003;Soini, 2005;Chuang & Shiu, 2017). The growing population of the hills demand better communication and mobility that in turn give rise to metalled road construction that are generally believed to compromise slope stability and trigger landslides as well as debris flows (Burton & Bathurst, 1998;Chuang & Shiu, 2017). ...
Chapter
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The Himalayan mountains are highly prone to landslides, and every year a multitude of slide events take place along its entire ranges. Darjeeling Himalayan region of West Bengal is not an exception and also highly prone to landslides. In the Darjeeling Himalayan extents, landslides are the major threat to the lives and properties of the people and also hamper the connectivity and commerce of the region aggravating lopsided development and poor economic condition. Considering the magnitude of landslide frequency and its extremities, this study aims to develop a landslide probability index (LPI) for the projection of landslide probabilities at the village level. The proposed methodology of the LPI is based on the weighted sum method of multi-criteria decision-making processes that involve eight explicitly localised proxy/indicator quantitative analysis, normalisation and weight assignment. The result of the derived LPI is divided into 4 distinct classes, viz. (a) very high landslide probability class comprising 45 villages, (b) high landslide probability class consists of 138 villages, (c) moderate landslide probability class includes 109 villages and (d) 56 villages are in low landslide probability class. It is evident from the study that the nature of landslide phenomenon is resulting from the interaction of contributing physical indicators, i.e. fragile lithology shares 34.58% in the radar diagram as the prime contributor of landslides in the DHR followed by drainage density at 17.91% and high degree of slope at 14.77%, and identification of such drivers of landslide probability can also be used in developing targeted adaptation planning and interventions.
... Another model called SHEETRAN is established to analyze the impact of rainfall on landslide and sediment transport. It is applied to the Luefregat River Basin [30][31][32]. The effects of rainfall on sediment yield is obvious [33]. ...
Preprint
Landslides are serious geological hazards that become a disaster worldwide, causing a large number of casualties and economic losses every year. There are many factors affecting landslide susceptibility, such as rainfall, soil and slope. Each of them has an important role in the process of slope losing stability. In this paper, the effects of rainfall intensity, rainfall pattern, slope gradient and soil type on landslide susceptibility are studied. In the process of rainfall-induced landslide, the relevant physical quantities of soil changes continuously. Their values and processes are closely related to the time of landslide occurrence. Hence, the variation of soil volumetric water content, matrix suction, pore water pressure and total stress throughout the rainfall are measured. As the results, soil type, slope gradient and rainfall intensity have a large influence on landslide susceptibility. The occurrence of landslides has a prerequisite that the slope is greater than or equal to 15°. The rainfall intensity needs to be not less than 80 mm/h. The difference of rainfall pattern also affects the landslide susceptibility. The rainfall pattern with rainfall intensity peak at the later stage is more likely to induce landslide. Coarser soils with gravels are prone to landslides when other conditions are the same. Steeper slopes, stronger rainfall, and coarser soils can all increase the amount of sediment yield.
... Debris flow is also one of the most frequent mass movement processes and plays an important role in moving sediment from steep regions to river system. Its high flow velocity, long runoff and impact forces, combined with poor temporal predictability, cause debris flow and its avalanches to be one of the most hazardous landslides types, because it can occur rapidly, with little warning, and exert great impulsive loads on objects in its paths; even small debris flow can strip vegetation, block drainage ways, damage structures, and endanger human life (Burton and Bathurst 1998;Liu and Tang 1995;Liu and Lei 2003). Direct debris-flow damage includes loss of human life, destruction of houses, damage to roads, environmental damage from product spills and many other losses that are difficult to quantify. ...
... landslides, as a sediment source in addition to diffuse hillslope erosion processes (e.g. Bathurst and Burton, 1998;Doten et al. 2006;Coulthard et al. 2013). However, they do not explicitly track the sediment produced by the different sediment sources in space and time and therefore cannot reconstruct the sediment provenance at the outlet. ...
Article
A hydrology‐sediment modelling framework based on the model Topkapi‐ETH combined with basin geomorphic mapping is used to investigate the role of localized sediment sources in a mountain river basin (Kleine Emme, Switzerland). The periodic sediment mobilization from incised areas and landslides by hillslope runoff and river discharge is simulated in addition to overland flow erosion to quantify their contributions to suspended sediment fluxes. The framework simulates the suspended sediment load provenance at the outlet and its temporal dynamics, by routing fine sediment along topographically‐driven pathways from the distinct sediment sources to the outlet. We show that accounting for localized sediment sources substantially improves the modelling of observed sediment concentrations and loads at the outlet compared to overland flow erosion alone. We demonstrate that the modelled river basin can shift between channel‐process and hillslope‐process dominant behaviour depending on the model parameter describing gully competence on landslide surfaces. The simulations in which channel processes dominate were found to be more consistent with observations, and with two independent validations in the Kleine Emme, by topographic analysis of surface roughness and by sediment tracing with 10Be concentrations. This research shows that spatially explicit modelling can be used to infer the dominant sediment production process in a river basin, to inform and optimise sediment sampling strategies for denudation rate estimates, and in general to support sediment provenance studies.
... Frictional resistance of the soil is affected by the presence of water and pore water pressure. As the quantity of interstitial fluid rises, the soil weight increases, further destabilizing the slope [11]. ...
Chapter
Two dimensional (2D) slope stability investigations are the most regularly uti-lized techniques among the designers because of their effortlessness. Determin-ing factor of safety against a potential failure is the main objective in predicting stability of slope. On the off chance if the factor of safety is determined to be suf-ficiently huge, the slope is considered to be steady (safe). On the off chance that it is 1.0 or less it is perilous. In this study, Variables such as soil water content and land temperature of 20 selected points were estimated during field observation. Samples that were collected from the site were analyzed in the geotechnical labor-atory to determine the field moisture content, cohesion, angle of shearing re-sistance and density. The principal parameter, soil moisture (ω) is obtained from the experimental methods for 20 selected points. Then remote sensing perspective is utilized to calculate the safety factors of the expressway slope stability. Cartosat information is used to infer a few pivotal variables engaged with the assurance of slope stability. Maps of soil mechanical factors, for example, cohesion of the soil (c), angle of shearing resistance (ø), and unit weight of the soil (γ) are obtained by correlating with soil moisture (ω) in the model maker. Cartosat-1 Digital Ele-vation Model (DEM) data is used in determining another significant variable, the slope angle (α). Factor of safety (FOS) computations depends on infinite slope stability models for shallow landslides are computed using SAGA GIS software.
... Gray and Megahan, 1981;Greenway, 1987;Philips and Watson, 1994). Modern landslide models, simulating the effect of vegetation on slope stability, therefore take both the modification of the soil moisture regime and the influence of root cohesion on the soil mantle into account (Anagnostopoulos et al., 2015;Burton and Bathurst, 1998;Cuo et al., 2008;Schwarz et al., 2010). ...
Article
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Forests have an important regulating function on water runoff and the occurrence of shallow landslides. Their structure and composition directly influence the risk of hydrogeomorphic processes, like floods with high sediment transport or debris flows. Climate change is substantially altering forest ecosystems, and for Central Europe an increase in natural disturbances from wind and insect outbreaks is expected for the future. How such changes impact the regulating function of forest ecosystems remains unclear. By combining methods from forestry, hydrology and geotechnical engineering we investigated possible effects of changing climate and disturbance regimes on shallow landslides. We simulated forest landscapes in two headwater catchments in the Eastern Alps of Austria under four different future climate scenarios over 200 years. Our results indicate that climate-mediated changes in forest dynamics can substantially alter the protective function of forest ecosystems. Climate change generally increased landslide risk in our simulations. Only when future warming coincided with drying landslide risk decreased relative to historic conditions. In depth analyses showed that an important driver of future landslide risk was the simulated vegetation composition. Trajectories away from flat rooting Norway spruce (Picea abies (L.) Karst.) forests currently dominating the system towards an increasing proportion of tree species with heart and taproot systems, increased root cohesion and reduced the soil volume mobilized in landslides. Natural disturbances generally reduced landslide risk in our simulations, with the positive effect of accelerated tree species change and increasing root cohesion outweighing a potential negative effect of disturbances on the water cycle. We conclude that while the efficacy of green infrastructure such as protective forests could be substantially reduced by climate change, such systems also have a strong inherent ability to adapt to changing conditions. Forest management should foster this adaptive capacity to strengthen the protective function of forests also under changing environmental conditions.
... Therefore, studies on debris flows have become crucially important because of the economic and social losses that these phenomena can cause. In recent years, many studies have concentrated on the modelling of torrential flows (O'Brien et al., 1993;Burton and Bathurst, 1998;Crosta and Frattini, 2003;Armanini et al., 2009;Hungr and McDougall, 2009;Horton et al., 2013;Gregoretti et al., 2016), giving particular importance to the triggering of debris flows events. The triggering mechanism is a complex phenomenon that depends on different variables. ...
Article
The research focuses on the assessment of the conditions for debris flow triggering in three very active mountain catchments. The study areas are the following: Rudan torrent (Vodo di Cadore, Mount Antelao in the Dolomites, Italy), Chiesa torrent (Pieve di Livinallongo, Mount Col di Lana, in the Dolomites, Italy) and Rebaixader torrent (border between the regions of Catalonia and Aragon, Axial Pyrenees area, Spain). Due to the differences among these basins and related source areas where debris flows originate, the knowledge on the link between geo-morphic conditions and driving mechanisms for debris flow activation is outlined. The study of debris flow initiation is carried out through a hydrological approach and a slope stability analysis. The hydrological analysis is supported by the calibration of intensity-duration curves of triggering rainfalls coupled with a distributed rainfall-runoff model. The analysis is corroborated using literature equations to compute critical discharges for sediment motion at the different levels of terrain deformation. The main results highlight the following: (i) a quite narrow range of triggering water discharges (0.03-0.16 m 3 /s) and shear stresses (267-413 N/m 2), promoting a new insight on the specific hazard mitigation; (ii) the quantification of a second stage of bed breakage, in some circumstances capable of amplifying the debris flow magnitude; and (iii) a minimum critical rainfall duration needed to effectively entrain the phenomenon (12-22 min) that might help to define more precise alert conditions. Finally, the geomorphologic differences among basins revealed two main typologies in terms of driving the triggering mode: flow rate dominant in the Rudan-type basins and mixed (flow rate plus slope stability conditioned) in the Chiesa-Rebaixader-type basins.
... For example, the SWMM model has been widely used in many cities to simulate water movement in both urban surface and drainage systems (Bisht et al., 2016;Giron� as et al., 2010;Li et al., 2016;Sun et al., 2014). The SHALSTAB model is used to simulate and predict the occurrence of rainfall-triggered landslides (Burton and Bathurst, 1998;Dietrich and Montgomery, 1998;Gorsevski et al., 2006). ...
Article
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Human exposure to threats from natural hazards is generally estimated using a static approach with the fixed number of people located in hazard-prone zones; however, in reality this number varies due to population mobility. This study proposes a human–hazard coupled City Model (HazardCM) for accurately calculating city spatiotemporal dynamic exposure to different hazards. It includes four components: an urban environment module, agent-based model, city–hazard coupler, and dynamic exposure assessment. Rainfall-triggered natural hazards under extreme hydrometeorological events were modeled in Lishui, China. Scenarios covering different magnitudes, timings and locations, and return periods of hazards were investigated to derive the spatial distribution and evolution of human exposure. This model is the first that different natural hazards have been analyzed within a unified framework using a dynamic method and offers a new way to investigate exposure's space–time characteristics while considering the dynamic nature of both humans and hazards.
... The selection of a proper DEM spatial resolution is a crucial step in any landslide susceptibility research and significantly affects the susceptibility zonation (Lee et al. 2004;Wu et al. 2007;Qin et al. 2013;Yang et al. 2014;Trigila et al. 2015;Cama et al. 2016;Sbroglia et al. 2018;Schlögel et al. 2018). Burton and Bathurst (1998) applied a dual-resolution method to predict shallow landslide hazards in Scotland and found that the prediction ability of this approach is sound. Dietrich and Montgomery (1998) studied data at 2, 6, 10, and 30 m spatial resolution, determining that finer resolutions result in a higher predictive accuracy in landslide susceptibility analysis. ...
Article
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The selection of an appropriate map resolution is highly important for landslide susceptibility assessment. No consistent objective criteria, however, are currently applied to the choice of map resolution. This research, in conjunction with slope units, explores the effect of digital elevation model (DEM) resolution on susceptibility modelling using three statistical models (frequency ratio, index of entropy, and weight of evidence). Seven different spatial resolutions (30, 40, 50, 60, 70, 80, and 90 m) and three statistical models are investigated. For each resolution, we compare the performance of the three models using area under curve (AUC) analysis. The results show that, independent of the statistical models, the best performances are produced at 70 m DEM resolution. This highlights that finer resolutions do not necessarily lead to higher predictive accuracy in landslide susceptibility mapping. Rather, the frequency ratio model seems to be optimal for the coarser resolutions (i.e. 70, 80, and 90 m).
... On the other hand, many numerical models for assessing the susceptibility to rainfall-92 induced shallow landslides at regional (catchment) scale have been developed and utilized 93 (Burton & Bathurst, 1998;Brunsden, 1999 r.slope stability (Mergili et al., 2014). Simple infiltration models, such as the Green-Ampt 103 model (Mein & Larson, 1973;Chen & Young, 2006), and more sophisticated infiltration 104 models following Darcy's law (Richards, 1931;Irmay, 1954;Van Genuchten, 1980) have 105 also been adopted. ...
Article
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The frequency of snowmelt-induced soil slope instabilities is increasing in some seasonally cold regions because of climate change. Reliable hazard assessment and risk mitigation of snowmelt-induced landslides require physically-based prediction models. However, existing models either apply only at the slope scale or assume precipitation as the sole landslide trigger. In doing so, they neglect the complexity and coupled nature of the thermo-hydro-mechanical processes leading to slope instability in seasonally cold regions (such as snow accumulation and melting, infiltration and surface runoff, soil saturation, pore water pressure buildup and dissipation). Here, we present a spatially distributed and sequentially coupled numerical model to simulate snowmelt-induced slope instabilities at the catchment scale. The model accounts for temperature-dependent changes in the soil hydraulic behavior related to changes in water state by means of a routine implemented in a geographic information system. We verified the performance of the model using a case study of spring snowmelt-induced soil slope failures that occurred after the 2004 Mid-Niigata earthquake in Japan. Considering limitations and simplifications, the model was able to predict the triggering condition, magnitude, and spatial distribution of the snowmelt-induced landslides with a satisfactory degree of accuracy. We believe that the robustness and simplicity of our numerical approach make it suitable for implementation in early warning systems.
... Physical, empirical and statistical approaches are used to analyse debris flow, which expresses the presumption of a debris flow occurring in an area with respect to its geomorphologic characteristics (Blais-Stevens and Behnia, 2016). Physically based approaches (Carrara et al., 2008;Burton and Bathurst, 1998) are more applicable to analysing physical and mechanical factors in independent catchments. The empirical model belongs to qualitative evaluation and is too subjective to be convincing. ...
Article
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The existence of debris flows not only destroys the facilities but also seriously threatens human lives, especially in scenic areas. Therefore, the classification and susceptibility analysis of debris flow are particularly important. In this paper, 21 debris flow catchments located in Huangsongyu Township, Pinggu District, Beijing, China, were investigated. Besides field investigation, a geographic information system, a global positioning system and remote-sensing technology were applied to determine the characteristics of debris flows. This article introduced a clustering validity index to determine the clustering number, and the fuzzy C-means algorithm and factor analysis method were combined to classify 21 debris flow catchments in the study area. The results were divided into four types: debris flow closely related to scale–topography–human activity, topography–human activity–matter source, scale–matter source–geology and topography–scale–matter source–human activity. Nine major factors screened from the classification result were selected for susceptibility analysis, using both the efficacy coefficient method and the combination weighting. Susceptibility results showed that the susceptibility levels of 2 debris flow catchments were high, 6 were moderate and 13 were low. The assessment results were consistent with the field investigation. Finally, a comprehensive assessment including classification and susceptibility evaluation of debris flow was obtained, which was useful for risk mitigation and land use planning in the study area and provided a reference for the research on related issues in other areas.
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Landslide is a major hydro¬geological hazard that affects large parts of Himalayan area of Uttarakhand state in India. The developments in Geo-spatial technologies have opened the doors for detailed and accurate assessment of landslide prone area. This paper deals with a use of temporal remote sensing data and geographical information systems for landslide mapping. Six categories of controlling factors for landslides i.e. slope gradient, aspect, lithology, land use land cover (LULC), drainage density, lineament density are defined in this study. Normalized Difference Vegetation Index (NDVI) has been generated to identify the vegetated and non-vegetated area. During the study, it is clearly reveals that a total number of about 695 landslides spots covering an area of 2.30 sq. km. were mapped from Landsat-OLI-TRS image of 2015 whereas a total number of 157 landslides covering an area of 1.60 sq. km. were mapped from Landsat-ETM+ image of the year 2005. This study is valuable for hazard zonation, mitigation purpose and regional planning in the Himalayan area.
Article
This study proposes an original approach for predicting shallow translational slide hazards, which are triggered by irregular rainfall events, via the method of zonation at a regional scale in emergency situations. The proposed model incorporates the infinite slope method in a GIS platform to assess hazard and risk associated with slope instability. This application can be integrated into the emergency management software SIMGE 1.0., SGE 2.0. The objective of the work is to provide a quick tool for managing emergencies and predicting shallow rainfall-induced landslides (RILs). The originality of this approach includes the relationship between two variables (m, Z)—with m being a hydrological pattern of steady state simulating the effects of rain that cause translational slides and Z being the characteristic sliding depth based on the bounded lithological unit. This method provides hazard maps, including zonation based on a factor of safety towards shallow landslides, where stable and unstable conditions (depending on precipitation) are determined for managing emergencies. This approach was applied in the Guadalmansa River basin, in Benahavis, Málaga (Andalusia), where numerous shallow landslides occurred in 2010, caused by extreme rainfall events, and a lithological unit has been isolated for this research (Alpujarride schist). The results obtained through this method have been verified after analysing the studied area's landslide inventory.
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Concurrency in extreme precipitation-induced events including flooding, landslides and associated debris flow result in massive loss of life, damage to infrastructures, and widespread disruption to socioeconomic activities. Despite recent advances in the field of risk hazard modeling, we lack a systematic framework to model and assess the impact of extreme precipitation induced concurrent hazards on infrastructure lifelines including road networks. Here we develop an integrated framework to study the effect of concurrent hazards i.e., landslide, debris flow, and flood on regional road networks. Our spatiotemporal 1-D simulations of shallow landslides and debris flows in combination with the 2-D hydrodynamic model for floods indicate that even highly localized concurrent events have potential to induce widespread and prolonged disruptions to the regional road networks. We illustrate the proposed framework's application to assess the functionality loss from the individual and concurrent events induced by extreme precipitation. Our results show that not accounting for concurrence in these correlated hazards could result in underestimation of functionality losses by 71 %, which in turn can undermine the pre-disaster preparedness and post-disaster recovery efforts.
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Located in a mountainous area of south-eastern Brazil, the municipality of Campos do Jordão has been hit by several landslides in recent history. Among those events, the landslides of early 2000 were significant in terms of the number of deaths (10), the population affected and the destruction of infrastructure that was caused. The purpose of this study is to assess the relative contribution of natural and human factors to triggering the landslides of the 2000 event. To achieve this goal, a detailed geotechnical survey was conducted in three representative slopes of the area to obtain geotechnical parameters needed for slope stability analysis. Then, a set of numerical experiments with GEO-SLOPE software was designed, including separate natural and anthropic factors. Results showed that natural factors, that is, high-intensity rainfall and geotechnical conditions, were not severe enough to trigger landslides in the study area and that human disturbance was entirely responsible for the landslide events of 2000. Since the anthropic effects used in the simulations are typical of hazardous urban areas in Brazil, we concluded that the implementation of public policies that constrain the occupation of landslide susceptible areas are urgently needed.
Thesis
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Hydrosedimentological connectivity is defined as the integrated transfer of water and sediments between compartments of the catchment, from any possible source to a given control point in a system where the transport vector is water. The study of hydrosedimentological connectivity contributes to the understanding of sediment dynamics in catchments. From the understanding of the elements that influence on hydrosedimentological connectivity, it is possible to determine connectivity degrees in a spatially-distributed and temporally-variable manner for a catchment. One way to evaluate this dynamic is through the use of indexes, however, a large part of the connectivity indexes, currently, consider only structural components, allowing a distribution varying only spatially. The present work had as main objective to develop a new index of hydrosedimentological connectivity (IHC) from the integration of functional and structural aspects of connectivity, allowing spatio-temporal variation. Mountain catchments in Brazil tend to have high degrees of connectivity, as they have well-distributed rainfall throughout the year and offer fewer possibilities for sediment deposition. This fact directly interferes with its hydrosedimentological dynamics. The Mascarada River catchment has a high altimetric range. Therefore, this catchment was used as a study area for the papers that make up this dissertation. The hydrosedimentological monitoring was carried out in the study catchment, through the installation of a hydrosedimentological station and three precipitation gauges. For the IHC development, different variables were evaluated, as a function of two components: structural connectivity and functional connectivity. Regarding the structural component, the use of high-resolution digital terrain models was proved to be important for the calculation of the physical variables of the landscape, such as the slope and length of the flow path. Still, in relation to the structural part, the water and sediment impedance was proved to be effective when calculated from the Manning coefficient, mainly in the forest-cover catchment. The landslides scars showed higher values of sediment connectivity, as they represent areas of exposed soil and superimposed on the preferential flow paths, acting as sediment sources in the catchment. Considering the importance of the functional aspect, precipitation characteristics were inserted in the IHC calculation, which allowed the evaluation of hydrosedimentological connectivity based on the space-time variation at the event scale at the catchment outlet. The IHC maximum and mean values showed a positive correlation (runoff volume 0.88 and 0.69; peak flow 0.83 and 0.63, respectively) with the values monitored at the catchment outlet. The preferential flow paths on the hillslopes, raised in the field survey, presented higher IHC values, which demonstrated consistency in the landscape representation by the index since the validation of connectivity is still a scientific big challenge. At the end of this study, the IHC was easily applied, with a simple structure and easily available input data. This index can contribute to the catchment management, providing spatialized information on the reach of sediments in the catchment in relation to their sources, in addition to identifying these sources.
Chapter
Landslides are among one of the most devastating natural disasters affecting millions of people, causing tens of thousands of deaths and resulting in millions to billions of dollars of damage annually. Examination of historical data suggests an increase in the number of slope failures along with an increase in the two major triggers—an increase in the number of significant earthquakes and wetter than average annual precipitations. These trends highlight the continued need to improve landslide science and understanding. This paper presents a summary of the recent advances in knowledge pertinent to the methods of slope stability and deformation analyses starting with the state of practice as detailed by Prof. J. Michael Duncan in 1996. Specifically, the paper focuses on the improvements to the computational and graphical capabilities with the widespread use and availabilities of computers, the ability to perform macro level stability analysis for regions, the advent of probabilistic slope stability analyses, developments in slope stability analyses of unsaturated slopes, and new methods to perform deformation analyses. Several case studies highlighting these advances are also included.
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Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas and the awareness of LWD as a risk is becoming more and more relevant. The recruitment of “fresh” large woody debris has been documented to play a significant role of the total amount of wood transported during flood events in mountain catchments. Predominately, LWD recruitment due to hydraulic and geotechnical bank erosion and shallow landslides contribute to high volumes of wood during floods. Quantifying the effects of vegetation on channel and slope processes is extremely complex. This manuscript therefore presents the concepts that are being implemented in a new modelling framework that aims to improve the quantification of vegetation effects on LWD recruitment processes. One of the focuses of the model framework is the implementation of the effect of spatio-temporal distribution of root reinforcement in recruitment processes such as bank erosion and shallow landslides in mountain catchments. Further, spatio-temporal precipitation patterns will be considered using a probabilistic approach to account for the spatio-temporal precipitation variability to estimate a LWD recruitment correction coefficient. Preliminary results are herein presented and discussed in form of a case study in the Swiss Prealps.
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The potentially important influence of climate change on landscape evolution and on critical zone processes is not sufficiently understood. The relative contribution of hydro‐climatic factors on hillslope erosion rates may significantly vary with topography at the watershed scale. The objective of this study is to quantify the hydro‐geomorphic behavior of two contrasting landscapes in response to different climate change scenarios in the Luquillo Critical Zone Observatory, a site of particular geomorphological interest, in terms of hillslope erosion and rainfall‐triggered landslides. We investigate the extent to which hillslope erosion and landslide occurrence remains relative invariant with future hydro‐climatic perturbations. The adjacent Mameyes and Icacos watersheds are studied, which are underlain by contrasting lithologies. A high resolution coupled hydro‐geomorphic model based on tRIBS (Triangulated Irregular Network‐based Real‐time Integrated Basin Simulator) is used. Observations of landslide activity and hillslope erosion are used to evaluate the model performance. The process‐based model quantifies feedbacks among different hydrologic processes, landslide occurrence, and topsoil erosion and deposition. Simulations suggest that the propensity for landslide occurrence in the Luquillo Mountains is controlled by tropical storms, subsurface water flow, and by non‐climatic factors, and is expected to remain significant through 2099. The Icacos watershed, which is underlain by quartz diorite, is dominated by relatively large landslides. The relative frequency of smaller landslides is higher at the Mameyes watershed, which is underlain by volcaniclastic rock. While projections of precipitation decrease at the study site may lead to moderate decline in hillslope erosion rates, the simulated erosional potential of the two diverse landscapes likely remains significant.
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Landslides are a significant process shaping the landscape of many Caribbean islands, where the geology and climate contribute to their prevalence. The ubiquitous steep slopes resulting from tectonic and volcanic forces provide abundant locations for landslide occurrence. The warm, wet climate influences the material involved with landsliding and serves as the most common mechanism for their initiation. The seasonal pattern of rainfall punctuated with intense storms is an efficient means for triggering landslides in this region. Most landslide types are found within the Caribbean. Debris flows and slides are by far the most prevalent form, along with earthflows, rockslides, rockfalls, and slumps. -from Authors
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It is impractical to address the long-term effect of forest man- agement strategies on erosion, sedimentation, and the resultant damage to fish habitat experimentally because to do so would require studying large watersheds for a century or more. Monte Carlo simulations were conducted on three hypothetical 10 000 ha, fifth-order forested watersheds. One wa- tershed was left undisturbed, one was completely clearcut and roaded in a decade, and one was cut at the rate of 1% each year. Each cutting strategy was repeated in succeeding centuries.
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A distributed, physically based slope stability model (dSLAM), based on an infinite slope model, a kinematic wave groundwater model, and a continuous change vegetation root strength model, is presented. It is integrated with a contour line-based topographic analysis and a geographic information system (GIS) for spatial data extraction and display. The model can be run with either individual rainfall events or long-term sequences of storms. These inputs can be either actual storm records or synthesized random events based on Monte Carlo simulation. The model is designed to analyze rapid, shallow landslides and the spatial distribution of safety factor (FS) in steep, forested areas. It can investigate the slope stability problem in both temporal and spatial dimensions, for example, the impact of timber harvesting on slope stability either at a given time or through an extended management period, the probability of landslide occurrence for a given year, and the delivery of landslide sediments to headwater streams. The dSLAM model was applied in a steep, forested drainage of Cedar Creek in the Oregon Coast Ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975. Simulated volume and number of failures were 733 m(3) and 4, respectively. These values agreed closely with field measurements following the 1975 storm. However, the effect of parameter uncertainty may complicate this comparison. For example, when soil cohesion values of 2.0 and 3.0 kPa were used, the failure volume changed by factors of 2.04 and 0.41, respectively, compared with the average condition of 2.5 kPa used in the simulation. For soil depths 30% higher and lower than the standard condition, the failure volume changed by factors of 2.0 and 0.27, respectively. When maximum root cohesion changed from 12.5 kPa (average condition) to 10 kPa, the failure volume increased 1.73-fold; for the case of 15 kPa, the failure volume changed by a factor of 0.55. The simulated failures caused by the storm were mostly in hollows. The simulations show that the spatial distribution of FS is controlled mainly by topography and timber-harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms. Most areas with FS < 3.0 corresponded with the distribution of blocks clear-cut in 1968, and all elements with FS < 2.0 were in areas clear-cut in 1968. Areas with low FS (1.0-1.6) expanded dramatically during the rainstorm and decreased at a slow rate after the storm. Factors of safety in hollows declined sharply during the storm.
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Determination of where and under what conditions a slope might fail is an important aspect for planning and conducting activities in forested drainage basins. Using currently employed techniques for modeling of basins and accepted geotechnical principles, a mathematical model has been developed that can aid in this determination. The model has been applied to one basin in Oregon and is currently being tested on another Oregon site and one in Southern Alaska. -from Authors
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In order to predict the sites of surface mountain slope failures induced by heavy rainfall in a granite area, a new method is proposed. The field to be tested is transferred into a digital landform model with 10 m grid space: water tables in a surface soil layer are calculated using a groundwater movement model; the tables together with topographical factors are used to define the degree of danger of a unit slope by an infinite slope stability analysis method. -from Authors
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Reports a method of designating areas in danger of debris flows, after researching many disasters. The dangerous area of a debris flow is identified by the starting point of deposition, ending point, deposit length, spread width and local topography. Relationships which may be quantified include 1) starting point of deposition: 2) ending point of deposition: 3) deposit length: 4) spread width. -from Author
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A fundamentally-based, soil erosion and sediment transport model which is incorporated with a distributed-system hydrologic model (ANSWERS) was developed. Erosion rates are related to hydrologic and hydraulic variables; soil characteristics; and surface and geographic conditions. The model was tested with data from two small agricultural watersheds of less than 10 ha in area.-from Authors
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Published records of the rainfall intensities and durations associated with shallow landsliding and debris flow activity suggests a limiting threshold for this type of slope instability. The limit has the general form: I = 14.82 D-0.39 and is best defined for rainfall durations between 10 minutes and 10 days.
Article
A model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near-surface through flow and slope stability models. The hydrologic model TOPOG (O'Loughlin, 1986) predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries. The slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity. The steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding. The spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high-resolution digital elevation data are available: Tennessee Valley in Marin County, California; Mettman Ridge in the Oregon Coast Range; and Split Creek on the Olympic Peninsula, Washington. Model predictions in each of these areas are consistent with spatial patterns of observed landslide scars, although hydrologic complexities not accounted for in the model (e.g., spatial variability of soil properties and bedrock flow) control specific sites and timing of debris flow initiation within areas of similar topographic control.
Article
Five models are investigated for determining the percentage delivery of sediment to streams for shallow landslides that evolve into debris flows. Models I-III are based on debris flow run-out distance, Model IV on snow avalanche run-out distance. For these it is assumed that percentage delivery is 100% for slopes above 10 degrees and zero for slopes below 4 degrees. For intermediate slopes, delivery is based on the run-out distance estimate. Model V, derived from field data, estimates percentage delivery directly without the need for slope conditions. The model performances are investigated using 100 hypothetical hillslopes and a limited database on landslide sediment delivery in Idaho. Model IV performs best but Model I is a close second and its design (run-out distance varying with elevation drop) may be preferable for modeling purposes. Model II (run-out distance varying with debris flow slope and volume) provides a conservative upper limit on percentage delivery. Parallel use of models to provide bounds on the percentage delivery estimate is recommended. The assumption of no deposition at slopes above 10 degrees is found to be not entirely correct and requires further research.
Article
During exceptionally heavy rains, debris avalanches may occur anywhere in forested mountains of the eastern United States. Examples from New Hampshire to North Carolina indicate that they are most probable when 5 or more inches of rain fall in a 24-hour period on steep (25-40°) slopes where soils are less than 36 inches deep. Risk increases with amount of summer rain and decreases with decreasing slope. As a practical matter, little can be done to prevent debris avalanching. That such disturbances may contribute large amounts of stream sediment should be considered in dealing with nonpoint stream pollution. Millions of loads were carried down at one grand avalanche into the Ammonoosuc, when a grand waterspout broke upon the mountain in the fall of the year 1836. Rocks and trees of the largest dimension presented no obstacle to its course (Hill 1839).
Article
A hydrological forecasting model is presented that attempts to combine the important distributed effects of channel network topology and dynamic contributing areas with the advantages of simple lumped parameter basin models. Quick response flow is predicted from a storage/contributing area relationship derived analytically from the topographic structure of a unit within a basin. Average soil water response is represented by a constant leakage infiltration store and an exponential subsurface water store. A simple non-linear routing procedure related to the link frequency distribution of the channel network completes the model and allows distinct basin sub-units, such as headwater and sideslope areas to be modelled separately. The model parameters are physically based in the sense that they may be determined directly by measurement and the model may be used at ungauged sites. Procedures for applying the model and tests with data from the Crimple Beck basin are described. Using only measured and estimated parameter values, without optimization, the model makes satisfactory predictions of basin response. The modular form of the model structure should allow application over a range of small and medium sized basins while retaining the possibility of including more complex model components when suitable data are available.
Article
SHESED is introduced as a physically based, spatially distributed erosion and sediment yield component for the existing SHE hydrological modelling system, for use at the catchment scale. For hillslopes (represented spatially by the SHE grid square network) SHESED simulates soil erosion by raindrop impact, leaf drip and sheet overland flow (without rilling), and the transport of the eroded material by overland flow. For channels the component simulates the erosion of bed material and the downstream transport of this material together with that supplied by overland flow. In the channel sediment routing procedure it is assumed that the flow can carry any available load of fine sediments (less than 0.062 mm in diameter) but for coarser sediments the load is limited by the calculated capacity transport rate of the flow. The channel component also allows for bed armouring. Application of SHESED to rainfall-induced sediment yield events at two agricultural catchments (areas 5.1 and 6.4 ha) in Iowa shows generally good reproduction of the observed temporal variations in sediment yield. Application to a 3.3 km reach of the East Fork River, Wyoming, for a 37 day period shows good reproduction of observed sediment discharge magnitudes but some discrepancy in the timing of the simulated sediment discharge peak.
Article
The paper forms the first part of an introduction to the SHE, a physically-based, distributed, catchment modelling system produced jointly by the Danish Hydraulic Institute, the British Institute of Hydrology and SOGREAH (France) with the financial support of the Commission of the European Communities. The SHE developed from the perception that conventional rainfall/runoff models are inappropriate to many pressing hydrological problems, especially those related to the impact of man's activities on land-use change and water quality. Only through the use of models which have a physical basis and allow for spatial variations within a catchment can these problems be tackled. The physical basis and flexible operating structure of the SHE allows the model to use as many or as few data as are available and also to incorporate data on topography, vegetation and soil properties not normally included in catchment models. It does not require a lengthy hydrometeorological record for its calibration and its distributed nature enables the spatial variability in catchment inputs and outputs to be simulated. However, the large amount of data required by the model means that new operation methodologies must be evolved. Thus spatial scale effects or simply a lack of data may create significant uncertainties in the values of the catchment parameters used in a simulation. These uncertainties will give rise to corresponding uncertainties in the predictions. However, the SHE is able to quantify these uncertainties by carrying out sensitivity analyses for realistic ranges of the parameter values. Even when there is a lack of data, therefore, the SHE can act as a valuable “decision-support system”.
Article
The paper forms the second part of an introduction to the SHE, a physically-based, distributed catchment modelling system produced jointly by the Danish Hydraulic Institute, the British Institute of Hydrology and SOGREAH (France) with the financial support of the Commission of the European Communities. The SHE is physically-based in the sense that the hydrological processes of water movement are modelled either by finite difference representations of the partial differential equations of mass, momentum and energy conservation, or by empirical equations derived from independent experimental research. Spatial distribution of catchment parameters, rainfall input and hydrological response is achieved in the horizontal by an orthogonal grid network and in the vertical by a column of horizontal layers at each grid square. Each of the primary processes of the land phase of the hydrological cycle is modelled in a separate component as follows: interception, by the Rutter accounting procedure; evapotranspiration, by the Penman-Monteith equation; overland and channel flow, by simplifications of the St. Venant equations; unsaturated zone flow, by the one-dimensional Richards equation; saturated zone flow, by the two-dimensional Boussinesq equation; snowmelt, by an energy budget method. Overall control of the parallel running of the components and the information exchanges between them is managed by a FRAME component. Careful attention has been devoted to a modular construction so that improvements or additional components (e.g. water quality and sediment yield) can be added in the future. Considerable operating flexibility is provided through the ability to vary the level of sophistication of the calculation mode to match the availability or quality of the data.
Article
The accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways. This paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using TOPMODEL. Distributed moisture status is predicted in TOPMODEL on the basis of spatial indices that depend on flow path definition. The sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients. A strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application.
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