a spatially distributed model for the dynamic prediction of sediment erosion and transport in mountainous forested watersheds 1 erosion and sediment transport in a temperate forested watershed are predicted with a new sediment model that represents the main sources of sediment generation in forested environments mass wasting hillslope erosion and road surface erosion within the distributed hydrology soil vegetation model dhsvm environment the model produces slope failures on the basis of a factor of safety analysis with the infinite slope model through use of stochastically generated soil and vegetation parameters failed material is routed downslope with a rule based scheme that determines sediment delivery to streams sediment from hillslopes and road surfaces is also transported to the channel network a simple channel routing scheme is implemented to predict basin sediment yield we demonstrate through an initial application of this model to the rainy creek catchment a tributary of the wenatchee river which drains the east slopes of the cascade mountains that the model produces plausible sediment yield and ratios of landsliding and surface erosion when compared to published rates for similar catchments in the pacific northwest a road removal scenario and a basin wide fire scenario are both evaluated with the model

experimental study of incipient motion in mixed size sediment transport rates of five sediments were measured in a laboratory flume three of these sediments had the same mean size the same size distribution shape and different values of grain size distribution standard deviation the critical shear stress for incipient motion of the individual size fractions within these sediments was estimated as that shear stress that produced a small dimensionless transport rate the sorting of the sediment mixture had little effect on the critical shear stress of individual fractions once the median size d50 of the mixture and a fraction s relative size di d50 are accounted for our data combined with previously published data show a remarkably consistent relation between the critical shear stress of individual fractions and the fraction s relative grain size despite a broad variation in the available data of mixture sorting grain size distribution shape mean grain size and grain shape all fractions in a size mixture begin moving at close to the same value of bed shear stress during steady state transport conditions this result is apparently true for transport systems where the transport rates of individual fractions are determined solely by the flow and bed sediment recirculating systems as well as for systems where the fractional transport rates are imposed on the system feed systems this equivalence in initial motion results is important because natural transporting systems often show attributes of both types of behavior in an unknown combination

estimating critical stream power for bedload transport calculations in gravel bed rivers the physical basis of bagnold s equation for critical stream power is examined although the general approach is well founded the original equation can be criticised for 1 failing to distinguish between the grain size in transport and the grain size that represents bed roughness 2 requiring a knowledge of critical flow depth in addition to gross channel properties 3 failing to allow for hiding and protrusion effects on the mobility of mixed size stream beds more general equations are presented which overcome these limitations they require a knowledge of channel slope but not depth the analysis suggests that the presence of form resistance in addition to grain roughness does not affect the calculation of critical power critical power is expected to depend more sensitively on grain size between reaches than within reaches

shallow landslide hazard assessment using a physically based model and digital elevation data a model for the analysis of topographic influence on shallow landslide initiation is applied to an experimental mountain basin where high resolution digital elevation data are available the cordon catchment 5 km2 located in northern italy the model delineates those areas most prone to shallow landsliding due to surface topographic effects on hydrologic response the model is composed of two parts a steady state model for shallow sub surface runoff and an infinite slope coulomb failure model which assumes that the soil is cohesionless at failure an inventory of landslide scars is used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions the model reproduces the observed distribution of landslide locations in a consistent way although spatial variations in soil strength and transmissivity which are not accounted for in the model influence specific distribution of landslide areas within regions of similar topographic control

numerical analysis on influence of principal parameters of topography on hillslope instability in a small catchment this study was conducted to identify the influence of three principal parameters constituting topography slope inclination soil depth and slope length on hillslope instability in a small catchment known as higashifukubegawa of shikoku island western japan the typhoon rainfall of 19 20 october 2004 was significant in causing a total of seven slope failures in the catchment though other rainfall events of various intensities in the same year did not cause failure to understand the influence of the three principal parameters numerical modeling of seepage and slope stability was performed in slope profiles constructed by varying the three parameters across their permissible range prepared from the seven slope failures of higashifukubegawa in geostudio geostudio tutorials includes student edition lessons geo slope international ltd calgary 2005 v 4 the change in porewater pressure and slope mass weight due to variation in values of principal parameters was used to interpret the change in factor of safety or instability the results showed that 1 instability increases with increase in the values of all three selected parameters across their range in higashifukubegawa with remarkable decreasing trend in factors of safety 2 slope inclination and soil depth were observed to affect instability through change in both unsaturated zone moisture content and mobilizing force of slope mass 3 but with slope length the unsaturated zone moisture content was not found to change considerably which implies that the instability due to slope length is mainly governed by change in slope mass weight overall this study has dealt in great detail with how hillslope instability changes with principal parameters of topography under the same simulating conditions of hydrological and geo mechanical parameters

mapping of risk and susceptibility of shallow landslide in the city of sao paulo brazil abstract in the city of sao paulo where about 11 million people live landslides and flooding occur frequently especially during the summer these landslides cause the destruction of houses and urban equipment economic damage and the loss of lives the number of areas threatened by landslides has been increasing each year the objective of this article is to analyze the probability of risk and susceptibility to shallow landslides in the limoeiro river basin which is located at the head of the aricanduva river basin one of the main hydrographic basins in the city of sao paulo to map areas of risk we created a cadastral survey form to evaluate landslide risk in the field risk was categorized into four levels based on natural and anthropogenic factors r1 low risk r2 average risk r3 high risk and r4 very high risk to analyze susceptibility to shallow landslides we used the shalstab shallow landsliding stability mathematical model and calculated the distribution frequency df of the susceptibility classes for the entire basin finally we performed a joint analysis of the average risk concentration rc and risk potential rp we mapped 14 risk sectors containing approximately 685 at risk homes more than half of which presented a high r3 or very high r4 probability of risk to the population in the susceptibility map 41 of the area was classified as stable and 20 as unconditionally unstable although the latter category accounted a smaller proportion of the total area it contained a concentration rc of 41 of the mapped risk areas with a risk potential rp of 12 we found that the locations of areas predicted to be unstable by the model coincided with the risk areas mapped in the field this combination of methods can be applied to evaluate the risk of shallow landslides in densely populated areas and can assist public managers in defining areas that are unstable and inappropriate for occupation

shallow groundwater response to rainfall on a forested headwater catchment in northern coastal california implications of topography rainfall and throughfall intensities on peak pressure head generation the pore water pressure head that builds in the soil during storms is a critical factor for the prediction of potential slope instability we report findings from a 3 year study of pressure head in 83 piezometers distributed within a 13 ha forested catchment on the northern coast of california the study s primary objective was to observe the seasonal and storm based dynamics of pressure head at a catchment scale in relation to observed rainfall characteristics and in situ topography to better understand landscape patterns of pressure head an additional goal was to determine the influence of the interaction between rainfall and forest canopy in altering delivery of water and pressure head during the large storms necessary to induce landsliding we found that pressure head was highly variable in space and time at the catchment scale pore pressures peaked close to maximum rainfall intensity during the largest storms measured the difference between rainfall and throughfall delivered through the canopy was negligible during the critical landslide producing peak rainfall periods pore pressure was spatially variable within the catchment and did not strongly correlate with surficial topographic features only 23 of the piezometers located in a variety of slope positions were found to be highly responsive to rainfall topographic index statistically explained peak pressure head at responsive locations during common storms but not during the larger storms with potential to produce landslides drainage efficiency throughout the catchment increased significantly in storms exceeding 2 to 7 months peak pressure head return period indicated by slowing or cessation of the rate of increase of pressure head with increasing storm magnitude this asymptotic piezometric pattern persisted through the largest storm measured during the study faster soil drainage suppressed pressure head response in larger storms with important process implications for pore pressure development and landslide hazard modelling copyright 2012 john wiley sons ltd

a physically based model for the topographic control on shallow landsliding 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

effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central japan landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention we examined the effects of forest harvesting on the frequency of landslides and debris flows in the sanko catchment central japan using nine aerial photo periods covering 1964 to 2003 these photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912 geology and slope gradient are rather uniformly distributed in the sanko catchment facilitating assessment of forest harvesting effects on mass wasting without complication of other factors trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10 fold higher than in control sites total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5 8 10 3 m 3 km 2 compared with 1 3 10 3 m 3 km 2 in clearcuts 25 yr indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability because landslide scars continue to produce sediment after initial failure sediment supply from landslides continues for 45 yr in the sanko catchment to estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions copyright 2007 john wiley sons ltd

the timing and magnitude of coarse sediment transport events within an upland temperate gravel bed river this paper describes the application of a new instrument to continuously measure bedload transport an impact sensor to a 72 km2 test catchment in the yorkshire dales northern england data from a network of impact sensors are linked to repeat surveys of channel morphological response to get a better understanding of the conditions that lead to sediment generation and transfer results suggest certain areas of the catchment act as key sediment sources at the annual time scale with material being quickly delivered to the lower parts of the catchment along the steep bedrock channel sediment transfer within the tributaries occurs in significantly smaller magnitudes than within the main channel but it moves more frequently and at different times of the year with transfer rates being strongly conditioned by larger scale valley geomorphology the lower 5 6 km reach sees a significant reduction in gradient and a widening of the valley this permits significant accumulation within the channel which has persisted for many years this lower reach is very sensitive to changes in sediment supply and there is good agreement between changes in bedload transport data and the surveyed channel response these observations have major implications for how river management projects should be developed in upland environments especially those where large scale geomorphological controls have a major impact upon the sediment transfer process evidence suggests that where river management restricts lateral movement of the channel and transfer of sediment into floodplain storage changes in sediment supply can lead to areas of severe accumulation acceleration of bank erosion and exacerbated flood risk

critical specific stream power in gravel bed rivers experiments with marked pebbles were carried out on different sized rivers of the belgian ardenne catchment areas varying from less than 1 km2 to 2700 km2 specific stream power required to cause bedload movement was evaluated and critical values were obtained three types of relationship between critical specific stream power 0 and grain size d were established the values for 0 in the largest river the ourthe were the lowest and were close to the values obtained for mountainous rivers carrying large boulders in medium sized rivers catchment area between 40 and 500 km2 the critical unit stream power was higher it is likely that it is due to the bedform s greater resistance this resistance would use up some of the energy that can cause movement and transport of bedload the amount of resistance of the bedform can be expressed as bedform shear stress determined by the relationship between grain shear stress that determines movement and transport of the bedload and the total shear stress this ratio varies between 0 4 and 0 5 in the medium sized rivers compared to 0 7 in the ourthe in headwater streams less than 20 km2 there is greater loss of energy due to bedform resistance 0 3 critical specific stream power is higher in this third type of river than in the other two

alice assessment of landslides induced by climatic events a single tool to integrate shallow and deep landslides for susceptibility and hazard assessment abstract the increasing evolution of urban areas in landslide prone regions and the modification of precipitation due to global climate change have led to a growing need for landslide hazard assessment lha for local land management and security services lha is based on the definition of the spatial and temporal probability of landslide occurrences and is split into three steps i a phenomenon inventory ii a landslide susceptibility analysis and iii a landslide hazard analysis nevertheless in practice essential information is often missing and lha corresponds most of the time to landslide susceptibility assessment acquired by expert knowledge this article presents a physical based model alice assessment of landslides induced by climatic events that can integrate different types of landslides shallow and deep with different sizes this tool can be used at the meso or broader scale 1 25 000 to 1 10 000 of work according to expert knowledge however a calibration must be carried out to fit observations and to take uncertainties into account thus a specific strategy is applied to the model on a study site located in the french south alps where numerous different landslide types were observed and analyzed after calibration on a small representative area the best fitted parameters are applied to a larger area for different types of landslides three landslide susceptibility maps shallow translational landslides rotational landslides and complex landslides are produced and the different susceptibility classes are compared with a landslide susceptibility map produced by a geomorphological approach the different susceptibility envelopes computed by the model are well integrated into the high susceptibility envelopes defined by the so called expert geomorphological approach thus the tool makes it possible to improve the mapping of potentially unstable areas by taking into account parameters such as the groundwater level in different surficial formations or the geotechnical values of landslide prone formations that experts are not always able to integrate alice is therefore proven to be a useful tool for mapping potential landslide prone areas if the tool is well calibrated taking into account the expert vision of the field different landslide types and different triggering factors including rainfall and seismic acceleration

long term modelling of landslides for different forest management practices long term effects of different forest management practices on landslide initiation and volume were analysed using a physically based slope stability model the watershed based model calculates the effects of multiple harvesting entries on slope stability by accounting for the cumulative impacts of a prior vegetation removal on a more recent removal related to vegetation root strength and tree surcharge four sequential clearcuts and partial cuts with variable rotation lengths were simulated with or without leave areas and with or without understorey vegetation in a subwatershed of carnation creek vancouver island british columbia the combined in nite slope and distributed hydrologic models used to calculate safety factor revealed that most of the simulated landslides were clustered within a 5 to 17 year period after initial harvesting in cases where suf cient time c 50 years lapsed prior to the next harvesting cycle partial cutting produced fewer landslides and reduced landslide volume by 1 4 to 1 6 fold compared to clearcutting approximately the same total landslide volume was produced when 100 per cent of the site was initially clearcut compared to harvesting 20 per cent of the area in successive 10 year intervals a similar nding was obtained for partial cutting vegetation leave areas were effective in reducing landsliding by 2 to 3 fold retaining vigorous understorey vegetation also reduced landslide volume by 3 8 to 4 8 fold the combined management strategies of partial cutting increasing rotation length provision of leave areas and retention of viable understorey vegetation offer the best alternative for minimizing landslide occurrence in managed forests copyright 2003 john wiley sons ltd

a contour based topographic model for hydrological and ecological applications a digital model for discretizing three dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described from this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area element area slope and aspect this form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon the model therefore has wide potential application for representing the three dimensionality of natural terrain and water flow processes in the fields of hydrology sedimentology and geomorphology three example applications are presented and discussed they are the prediction of zones of surface saturation the prediction of the distribution of potential daily solar radiation and the prediction of zones of erosion and deposition in a catchment

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

critical discharge for entrainment of poorly sorted gravel entrainment criteria for gravel sized particles on river beds are usually defined in terms of shear stress but some workers have proposed that critical discharge relationships are more reliable and more convenient the critical shear stress in poorly sorted gravels is known from recent work to depend much more on relative than absolute grain size it is shown that this effect can be included in a semi theoretical equation for the critical unit discharge to move individual grain sizes in a poorly sorted bed comparisons with published data on critical discharges in a variety of rivers show that both the sensitivity of critical discharge to grain size and the absolute levels of critical discharge are predicted quite well however any prediction of critical discharge is sensitive to the assumptions made first about flow resistance and secondly about the critical stress to move average sized particles

incorporation of the effect of concentration of flow into the kinematic wave equations and its applications to runoff system lumping abstract the usual kinematic wave equations are revised to consider the interaction between surface flow and subsurface flow in mountainous watersheds having curved surfaces covered with a layers of uniform thickness a function which represents watershed surface geometry which is called the geometric pattern function in the paper is incorporated into the basic equations of the kinematic wave model and the depth flow relation equation for the surface subsurface flow system is derived when the watershed surface is linearly converging or diverging its geometric pattern function has a linear form and numerical simulations for such cases are given here if the geometric pattern function is regarded as a new parameter of the kinematic wave model then the kinematic wave flow model becomes very flexible in fact when the lateral inflow is spatially uniform the model may be used as a simple model of a stream network system using this simplified model a method of transformation of the kinematic wave flow model of a stream system into a lumped runoff model which we call a reservoir cascade model is developed

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

a distributed slope stability model for steep forested basins 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 m3 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

a spectral clustering search algorithm for predicting shallow landslide size and location the potential hazard and geomorphic significance of shallow landslides depend on their location and size commonly applied one dimensional stability models do not include lateral resistances and cannot predict landslide size multidimensional models must be applied to specific geometries which are not known a priori and testing all possible geometries is computationally prohibitive we present an efficient deterministic search algorithm based on spectral graph theory and couple it with a multidimensional stability model to predict discrete landslides in applications at scales broader than a single hillslope using gridded spatial data the algorithm is general assuming only that instability results when driving forces acting on a cluster of cells exceed the resisting forces on its margins and that clusters behave as rigid blocks with a failure plane at the soil bedrock interface this algorithm recovers predefined clusters of unstable cells of varying shape and size on a synthetic landscape predicts the size location and shape of an observed shallow landslide using field measured physical parameters and is robust to modest changes in input parameters the search algorithm identifies patches of potential instability within large areas of stable landscape within these patches will be many different combinations of cells with a factor of safety less than one suggesting that subtle variations in local conditions e g pore pressure and root strength may determine the ultimate form and exact location at a specific site nonetheless the tests presented here suggest that the search algorithm enables the prediction of shallow landslide size as well as location across landscapes

simulation of density driven frictional downslope flow in z coordinate ocean models abstract an important component of the ocean s thermohaline circulation is the sinking of dense water from continental shelves to abyssal depths such downslope flow is thought to be a consequence of bottom stress retarding the alongslope flow of density driven plumes in this paper the authors explore the potential for explicitly simulating this simple mechanism in z coordinate models a series of experiments are performed using a twin density coordinate model simulation as a standard of comparison the adiabatic nature of the experiments and the importance of bottom slope make it more likely that the density coordinate model will faithfully reproduce the solution the difficulty of maintaining the density signal as the plume descends the slope is found to be the main impediment to accurate simulation in the z coordinate model the results of process experiments suggest that the model solutions will converge when the z coordinate model has sufficient vertical resolution to resolve the bottom viscous laye

the impacts of logging on landslide activity at clayoquot sound british columbia abstract the objective of this study was to investigate the impacts of logging on landslide activity in clayoquot sound on the west coast of vancouver island british columbia a total of 1004 landslides were documented in order to test the hypothesis that areas affected by logging activities show different density frequency and magnitude characteristics of landsliding than areas unaffected by logging the frequency of landslides in logged terrain was found to be nine times higher than in undisturbed forest an exponential increase in landslide frequency within the area logged was observed on a large watershed scale failures in logged terrain occur on gentler slopes than in natural terrain partly because fewer slopes steeper than 40 have been logged debris slides and debris flows are the most frequently occurring mass movements initiating mostly from road fill failures and from within cutblocks most landslides initiated on se facing slopes with the highest landslide frequency near the coast and diminishing exponentially further inland this pattern of activity most likely reflects the greater impact of severe storms arriving from the pacific with winds dominating from the southeast concave and straight slopes are most susceptible to landslide initiation a preliminary examination of geologic control on the frequency of landslides suggests that the quatsino formation the island plutonic suite and the sicker group are significantly above the average rate further work is needed to identify and quantify factors confounding the trends and correlations identified in this overview study results obtained in this study will be used to implement changes in forest management

a derived flood frequency distribution using horton order ratios a flood frequency distribution is derived from assumed climatic distributions and the geomorphologic unit hydrograph guh model of catchment response the derived distribution is tested on two appalachian mountain catchments and shows good agreement with historical data because the guh is rooted in catchment shape and geomorphology this derived frequency distribution may be a promising vehicle for studying the effect of catchment shape on flood frequency characteristics furthermore it is felt that the question of catchment homogeneity and similarity necessary for regional flood estimation can also be studied through the guh derived flood distribution

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

analysis of a small debris slide in coastal alaska on october 1 1980 a moderately intense storm at trap bay alaska triggered a small debris slide in a forested midslope depression that was instrumented to record the maximum piezometric rise although the return period for the storm was 2 years 54 3 68 cm of the total rain fell during the final 3 h causing the soil mantle to become nearly saturated this resulted in an average maximum pore water pressure of 2 2 kpa at the sliding surface causing failure analysis of the mechanics of the failure showed that an apparent cohesion of 2 0 kpa probably due to rooting strength was acting on the 43 hillslope calculated factors of safety for such thin partially saturated soils are very sensitive to small changes in apparent cohesion and should be used with caution on such sites

predicting shallow landslide size and location across a natural landscape application of a spectral clustering search algorithm predicting shallow landslide size and location across landscapes is important for understanding landscape form and evolution and for hazard identification we test a recently developed model that couples a search algorithm with 3 d slope stability analysis that predicts these two key attributes in an intensively studied landscape with a 10 year landslide inventory we use process based submodels to estimate soil depth root strength and pore pressure for a sequence of landslide triggering rainstorms we parameterize submodels with field measurements independently of the slope stability model without calibrating predictions to observations the model generally reproduces observed landslide size and location distributions overlaps 65 of observed landslides and of these predicts size to within factors of 2 and 1 5 in 55 and 28 of cases respectively five percent of the landscape is predicted unstable compared to 2 recorded landslide area missed landslides are not due to the search algorithm but to the formulation and parameterization of the slope stability model and inaccuracy of observed landslide maps our model does not improve location prediction relative to infinite slope methods but predicts landslide size improves process representation and reduces reliance on effective parameters increasing rainfall intensity or root cohesion generally increases landslide size and shifts locations down hollow axes while increasing cohesion restricts unstable locations to areas with deepest soils our findings suggest that shallow landslide abundance location and size are ultimately controlled by covarying topographic material and hydrologic properties estimating the spatiotemporal patterns of root strength pore pressure and soil depth across a landscape may be the greatest remaining challenge

geomorphic and paleoclimatic implications of latest pleistocene radiocarbon dates from colluvium mantled hollows california radiocarbon analyses of charcoal from basal colluvium in 11 california hollows show a clustering of dates between 9000 and 15 000 b p an indication that changes in the storage and discharge of colluvium from hillslopes accompanied the pleistocene holocene transition hollows are sites of topographically induced convergence and deposition of colluvial debris and evacuation of this debris was apparently more thorough and possibly more frequent in the latest pleistocene perhaps due to a combination of changes in vegetation and rainfall characteristics one hypothesis is that greater storm intensities occurred in the latest pleistocene and induced a higher frequency of landslides in hollows and a regional extension of channel heads upslope relative to the holocene during the last pleistocene california hollows apparently contained smaller volumes of colluvium in storage the increased storage of debris during the holocene may have resulted in a diminished supply of sediment to stream channels

experiments on surface structure and partial sediment transport on a gravel bed eight flume experiments were conducted to study the development of bed surface texture and structure in the presence of partial bed material transport the experiments have two phases a no feed degradational phase followed by a feeding phase a surface structure of irregular reticulate stone nets and clusters was developed before sediment feeding commenced bed load transport equaled or slightly exceeded the fed supply except at the highest feed rate the bed structure was maintained but bed surface texture fined with increasing sediment load the two phenomena may coexist because the largest grains on the bed moved only very sporadically the actual sediment transport rates were much less than the expected rate calculated from the ratio of bed surface grain size to transported grain size the difference reflects the increase in bed stability introduced by the bed structure between 17 and 47 of the bed shear stress is estimated to be carried by the structure 4 being absorbed by the load while the bed grains carried the balance of the stress bed material transport is exceedingly sensitive to bed surface structure and grain size which raises concerns about the realizable precision of grain size measurements and characterization of the structure

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

assessing shallow landslide hazards using the trigrs and shalstab models serra do mar brazil the hillslopes of the serra do mar a system of escarpments and mountains that extend more than 1500 km along the southern and southeastern brazilian coast are regularly affected by heavy rainfall that generates widespread mass movements causing large numbers of casualties and economic losses this paper evaluates the efficiency of susceptibility mapping for shallow translational landslides in one basin in the serra do mar using the physically based landslide susceptibility models shalstab and trigrs two groups of scenarios were simulated using different geotechnical and hydrological soil parameters and for each group of scenarios a and b three subgroups were created using soil thickness values of 1 2 and 3 m simulation results were compared to the locations of 356 landslide scars from the 1985 event the susceptibility maps for scenarios a1 a2 and a3 were similar between the models regarding the spatial distribution of susceptibility classes changes in soil cohesion and specific weight parameters caused changes in the area of predicted instability in the b scenarios both models were effective in predicting areas susceptible to shallow landslides through comparison of areas predicted to be unstable and locations of mapped landslides such models can be used to reduce costs or to define potentially unstable areas in regions like the serra do mar where field data are costly and difficult to obtain

forecasting and validation of landslide susceptibility using an integration of frequency ratio and neuro fuzzy models a case study of seorak mountain area in korea landslides susceptibility maps were constructed in seorak mountain area korea using an integration of frequency ratio and adaptive neuro fuzzy inference system anfis in geographical information system gis environment landslide occurrence areas were detected in the study by interpreting aerial photographs and field survey data landslide locations were randomly selected in a 50 50 ratio for training and validation of the models respectively topography geology soil and forest databases were also constructed maps relevant to landslide occurrence were assembled in a spatial database using the constructed spatial database 17 landslide related factors were extracted the adaptive anfis model with different types of membership functions mfs was then applied for landslide susceptibility mapping in the study area two landslide susceptibility maps were prepared using the different mfs the frequency ratio model was also applied to the landslide susceptibility mapping for comparing with the probabilistic anfis model finally the resulting landslide susceptibility maps were validated using the landslide locations which were not used for training the anfis the validation results showed 75 57 accuracy using the generalized bell shaped mf model 74 94 accuracy using the sigmoidal 2 mf model and 73 07 accuracy using frequency ratio model these accuracy results show that an anfis can be an effective tool in landslide susceptibility mapping

debris flow initiation and sediment recharge in gullies landslides that enter gullied low order drainages can either initiate debris flow or stop depositing sediment in the channel this process is one of the most common ways that debris flows initiate but little attention to date has been paid to evaluating the factors that affect whether or not the initial landslide will become a debris flow or deposit sediment in the channel statistically significant parameters that determine whether slope failures become debris flows or act to recharge in channel sediment are channel gradient angle of entry of failure into the channel initial failure volume and the amount of in channel stored sediment steeper channels low angles of entry lower volumes of in channel sediment and larger initial failures were more likely to result in debris flows this study found that as the volume of in channel stored sediment increased the volume of initial failure required to initiate a debris flow also increased this result calls into question the simple supply limited model of cyclical debris recharge and debris flow in low order gullied drainages and suggests a negative feedback mechanism between debris accumulation and debris flow susceptibility

deterministic approach for susceptibility assessment of shallow debris slide in the darjeeling himalayas india abstract high magnitude rainfall triggers numerous shallow debris slides in the darjeeling himalayas causing widespread damage to the environment loss of life and property thin soil cover and steep topography make the region vulnerable to debris slides the objective of the present study is to assess the susceptibility of the eastern part of darjeeling himalayas covering about 330 km2 to shallow debris slides through the functional relationship of hillslope hydrology and mechanical properties of slope materials deterministic approach based shallow landsliding stability shalstab model following mohr coulomb failure law was adopted to assess landslide susceptibility topographical parameters were derived from 8 m resolution cartosat 1 digital elevation model dem and mechanical properties of soil were obtained from an analysis of 15 soil samples for slope stability assessment the topographical and soil parameters were put into three different scenarios i assuming the surface entirely free from vegetation model 1 ii involving the role of vegetation root cohesion model 2 and iii surcharge of vegetation buildings and other structures along with root cohesion model 3 these predictive models were used to classify the area into various susceptibility classes with specific amounts of critical rainfall qc the result shows that 28 9 and 10 of the study area come under unconditionally unstable class in the three models respectively about 22 land in model 1 and 42 in each model 2 and model 3 come under unconditionally stable class protective capacity of roots against debris slide played a significant role in model 2 and model 3 performance of models was validated by comparison of observed predicted landslide areas and the area under the receiver operating characteristic roc curve it is found that the overall success rate of all the three models is relatively low 56 60 to 64 50 thus it may be concluded that the shalstab model in assessing landslide should either not be used at all at a regional level in the himalayas or be used only with great caution along with additional field and lab data

a low dimensional physically based model of hydrologic control of shallow landsliding on complex hillslopes hillslopes have complex three dimensional shapes that are characterized by their plan shape profile curvature of surface and bedrock and soil depth to investigate the stability of complex hillslopes with different slope curvatures and plan shapes we combine the hillslope storage boussinesq hsb model with the infinite slope stability method the hsb model is based on the continuity and darcy equations expressed in terms of storage along the hillslope solutions of the hsb equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function the presented model is composed of three parts a topography model conceptualizing three dimensional soil mantled landscapes a dynamic hydrology model for shallow subsurface flow and water table depth hsb model and an infinite slope stability method based on the mohr coulomb failure law the resulting hillslope storage boussinesq stability model hsb sm is able to simulate rain induced shallow landsliding on hillslopes with non constant bedrock slope and non parallel plan shape we apply the model to nine characteristic hillslope types with three different profile curvatures concave straight convex and three different plan shapes convergent parallel divergent in the presented model the unsaturated storage has been calculated based on the unit head gradient assumption to relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method the results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability therefore it can be concluded that the presented dynamic slope stability model hsb sm can be used safely for slope stability analysis on complex hillslopes our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others whilst divergent convex hillslopes remain stable even after intense rainfall in addition the relation between subsurface flow and hillslope stability has been investigated our analyses show that the minimum safety factor fs occurs when the rate of subsurface flow is a maximum in fact by increasing the subsurface flow stability decreases for all hillslope shapes copyright 2008 john wiley sons ltd

resistance to shallow landslide failure through root derived cohesion in east coast hill country soils north island new zealand measured shear strength cohesion and friction of airfall derived east coast hill country regolith is insufficient for the maintenance of existing regolith depth slope angle relationships in the catchment of lake waikopiro in northern hawke s bay new zealand if these regoliths are attributed with an additional increment of cohesion derived mechanically from a turf mat membrane existing depth slope angle distributions are explicable sites where failure has occurred have been measured and back analysis used to derive a range of values for additional mechanical cohesion values are in the range 0 2 7 6 kpa consistent with earlier findings this range is narrowed further to 0 7 6 9 kpa with assumptions regarding soil moisture status at failure copyright 1999 john wiley sons ltd

prediction of rainfall induced shallow landslides in the loess plateau yan an china using the trigrs model in this work a transient rainfall infiltration and grid based regional slope stability model trigrs was implemented in a case study of yan an city northwest china in this area widespread shallow landslides were triggered by the 12 july 2013 exceptional rainstorm event a high resolution dem soil parameters from in situ and laboratory measurements water table depths the maximum depth of precipitation infiltration and rain gauge corrected precipitation of the event were used as inputs in the trigrs model shallow landslides triggered on the same day were used to evaluate the modeling results the summarized results are as follows i the characteristics and distribution of thirty five shallow landslides triggered by the 12 july 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth area and volume less than 3 m 200 m2 and 1000 m3 respectively ii four intermediate factor of safety fs maps were generated using the trigrs model to represent the scenarios 6 12 18 and 24 hours after the storm event the area with fs 1 increased with the rainfall duration the percentage of the area with fs 1 was 0 2 3 3 3 8 and 5 1 for the four stages respectively twenty four hours after the rainstorm trigrs predicted that 1255 grid cells failed which is consistent with the field data iii trigrs generated more satisfactory results at a given precipitation threshold than sinmap which is ideal for landslide hazard zoning for land use planning at the regional scale comparison results showed that trigrs is more useful for landslide prediction for a certain precipitation threshold also in the regional scale iv analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation copyright 2016 john wiley sons ltd

spatial characterization of root reinforcement at stand scale theory and case study abstract we propose a new upscaling approach for quantify root reinforcement at the stand scale using the spatially explicit root bundle model rbm for describing pullout force displacement behavior coupled with a model for lateral root distribution the root distribution model was calibrated using data of two excavated soil profiles and validated with measurements of root distribution along the scarp of an artificially rainfall triggered landslide in a vegetated hillslope above the rhine river in northern switzerland results show that the model overestimates small root density 1 3 mm diameter leading to an error in estimated maximum root reinforcement of about 28 for comparison the most commonly used model of wu overpredicts root reinforcement by a factor of 3 the spatial variability of estimated maximum root reinforcement within the forest stand is high ranging from 0 to 20 kpa most soil reinforcement by roots occurs close to the tree stem or in zones where root systems overlap the new approach provides a detailed description of maximum root reinforcement on a slope an essential element for the prediction of shallow landslides and the management of protection forests

reconceptualising coarse sediment delivery problems in rivers as catchment scale and diffuse this paper assesses river channel management activities in the context of the interaction between coarse sediment delivery climate change river channel response and flood risk it uses two main sources of evidence 1 an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods and 2 a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network the field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself extreme events that could occur at any time in the year i e they are not dependent on wet antecedent conditions were crucial for sediment delivery however sustained high river flows were responsible for the majority of transfer within the river itself application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s regardless of the climate downscaling scenario used first approximations suggested that this would translate into annual bed level aggradation rates of between 0 10 and 0 20 m per year in the downstream main channel reaches second the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in channel simulation with river flows scaled for climate change to the 2050s and 2080s short term sedimentation could result in similar magnitude increases in inundated area for 1 in 0 5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude finally we were able to develop an alternative approach to river management in relation to coarse sediment delivery based upon reducing the rates of coarse sediment delivery through highly localised woodland planting under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem thus the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process with a much more explicit focus on the catchment scale if our river systems are to become more insulated from the impacts of future climate changes

entrainment of gravel from naturally sorted riverbed material the critical dimensionless shear stress ci required to entrain a given size particle di was computed from extensive bedload transport measurements in three self formed rivers that have naturally sorted gravel and cobble bed material the value of ci was determined to be significantly affected by the size distribution of the riverbed material for bed particles between 0 3 to 4 2 times the median diameter of the subsurface bed material d50 the average critical dimensionless shear stress ci is equal to ci 0 0834 di d50 0 872 with a coefficient of determination of 0 980 for bed particles larger than 4 2 times d50 ci appears to approach a constant value of approximately 0 020 in a noneroding channel thus ci varies from 0 25 to 0 020 for a given particle depending on the ratio of di to d50 previous investigations of the hydraulic conditions required to entrain coarse riverbed material have reported critical shear stress values ranging from 0 25 to 0 020 for a given particle size this analysis indicates that virtually all of the variation is due to differences in the subsurface bed material size distribution this analysis shows that ci varies almost inversely proportional to the particle diameter for a nonuniform bed material therefore bed particles between 0 3 to 4 2 times d50 are entrained at nearly the same discharge an investigation of the hydraulic characteristics and bed material mobility of 24 self formed gravel bed rivers in colorado determined that particles as large as the median diameter of the bed surface were entrained by discharges equal to the bankfull stage or less particles as large as the 90th percentile fraction were entrained by the bankfull discharge in nine of the rivers studied consequently in these rivers a significant fraction of the riverbed was entrained rather frequently over a period of years although the transport rate was very small