investigation of the variability of floc sizes on the louisiana shelf using acoustic estimates of cohesive sediment properties abstract vertical profiles of suspended sediment concentration and floc size estimated from acoustic backscatter are used together with turbulent shear estimates to investigate cohesive sediment flocculation under different flow conditions concentration measurements by optical backscatter sensors at two levels are used to calibrate the acoustic backscatter intensity a strong correlation is observed between suspended sediment concentration and turbulence intensity mean size of flocs increases toward the bottom except within the bottom few centimeters where floc breakage is observed due to strong turbulence simultaneous shear rate and floc size profiles show that low shear promotes flocculation at low concentrations increasing turbulence intensity increases the amount of sediment in the water column but decreases the floc size indicating floc breakage thus these effects are seen at cm scale vertical resolution in the field for the first time the results support previously published numerical experimental and lower resolution field studies

modeling of rainfall triggered shallow landslide by integrating hydrological modeling with the infinite slope stability analysis a rainfall triggered shallow landslide model was developed by iverson water resour res 36 1897 1910 2000 in iverson s model the infiltration capacity is assumed to be equivalent to the saturated hydraulic conductivity for finding pressure heads analytically however for general infiltration process the infiltration capacity should vary with time during the period of rain and the infiltration rate is significantly related to the variable infiltration capacity to avoid the unrealistically high pressure heads iverson employed the beta line correction by specifying that the simulated pressure heads cannot exceed those given by the beta line in this study the suitability of constant infiltration capacity together with the beta line correction for hydrological modeling and landslide modeling of hillslope subjected to a rainfall is examined by amending the boundary condition at ground surface of hillslope in iverson s model the modified iverson s model with considering general infiltration process is developed to conduct this examination the results show that the unrealistically high pressure heads from iverson s model occur due to the overestimation of infiltration rate induced from the assumption that the infiltration capacity is identical to the saturated hydraulic conductivity considering with the general infiltration process the modified iverson s model gives acceptable results in addition even though the beta line correction is applied the iverson s model still produces greater simulated pressure heads and overestimates soil failure potential as compared with the modified iverson s model therefore for assessing rainfall triggered shallow landslide the use of constant infiltration capacity together with the beta line correction needs to be replaced by the consideration of general infiltration process

scale invariance of soil moisture variability and its implications for the frequency size distribution of landslides abstract power spectral analyses of soil moisture variability are carried out from scales of 100 m to 10 km on the microwave remotely sensed data from the washita experimental watershed during 1992 the power spectrum s k has an approximate power law dependence on wave number k with the exponent 1 8 this behavior is consistent with the behavior of a stochastic differential equation for soil moisture at a point and it has important consequences for the frequency size distribution of landslides we present the cumulative frequency size distributions of landslides induced by precipitation in japan and bolivia as well as landslides triggered by the 1994 northridge california earthquake large landslides in these regions despite being triggered by different mechanisms have a cumulative frequency size distribution with a power law dependence on area with an exponent ranging from 1 5 to 2 we use a soil moisture field with the above statistics in conjunction with a slope stability analysis to model the frequency size distribution of landslides in our model landslides occur when a threshold shear stress dependent on cohesion pore pressure internal friction and slope angle is exceeded this implies a threshold dependence on soil moisture and slope angle since cohesion pore pressure and internal friction are primarily dependent on soil moisture the cumulative frequency size distribution of domains of shear stress greater than a threshold value with soil moisture modeled as above and topography modeled as a brownian walk is a power law function of area with an exponent of 1 8 for large landslide areas this distribution is similar to that observed for landslides the effect of strong ground motion from earthquakes lowers the shear stress necessary for failure but does not change the frequency size distribution of failed areas this is consistent with observations this work suggests that remote sensing of soil moisture can be of great importance in monitoring landslide hazards and proposes a specific quantitative model for landslide hazard assessment

hydromechanical triggering of landslides from progressive local failures to mass release 1 water infiltrating during intense rainfall on steep slopes gradually weakens the wet soil mass inducing localized failures that may initiate a cascade of load redistributions and successive failures propagating across a hillslope the challenge of linking the progressive nature of local events culminating in an abrupt landslide is addressed by a new hydromechanical triggering model that links key hydrologic processes with threshold based mechanical interactions a hillslope is represented as assembly of soil columns interconnected by frictional and tensile mechanical bonds represented as virtual bundles of fibers increasing water load exerted on mechanical bonds causes gradual failure of fibers until restraining forces are exceeded following failure at the soil bedrock interface the load on a column is redistributed to its neighbors via intact mechanical primarily tensile bonds which in turn may also fail and transmit the load downslope as compressive stresses when soil internal compressive strength is exceeded a load bearing column may liquefy and initiate a landslide release that could propagate downslope or retrogressively upslope the model reproduces observed power law frequency magnitude relationships of landslides with exponents ranging between 1 0 and 2 2 in agreement with landslide inventory data we applied a criticality measure defined by ramos 2011 to evaluate the specific influences of slope angle soil texture and root reinforcement on attainment of hillslope criticality in which a small local failure may trigger release of a large soil mass the model provides new insights on the conditions giving rise to an abrupt transition from a seemingly stable hillslope to a catastrophic landslide

instruments for particle size and settling velocity observations in sediment transport in this paper we describe two sensors for measurement of particle size distribution and settling velocity distribution these measurements are critical to the correct estimation of the true sediment concentration in the field as well as to evaluating models for transport rates of sediments a multi angle measurement of laser scattering is made and inverted to obtain the particle size distribution since small angle scattering is relatively insensitive to particle composition the size distribution measurements are robust and do not require particle refractive index it is shown that with a knowledge of the size distribution true particulate volume concentration can be obtained unaffected in calibration by changes in particle size distribution the data from bottom boundary layer experiments using the instrument show the presence of temporal variability in size distribution associated with the strength of forcing of the boundary layer the importance of these observations lies in the implication that historical data acquired with single parameter optical or other sensors needs to be revisited in the second instrument analyzing the observation of size distributions during settling in a settling column produces settling velocity estimates in this case the history of concentration of each size class is examined to determine the settling velocity without invoking any assumptions of settling regime settling velocity data from a field experiment off the new jersey coast fit the model wf na 0 45 10 23 a 1 2 n

topographic controls of landslides in rio de janeiro field evidence and modeling landslides are common features in the serra do mar located along the southeastern brazilian coast most of them associated with intense summer storms specially on the soil mantled steep hillslopes around rio de janeiro city where the favelas slums proliferated during the last few decades on february 1996 hundreds of landslides took place in city of rio de janeiro triggered by intense rainstorms since then many studies have been carried out in two experimental river basins in order to investigate the role played by the topographic attributes in controlling the spatial distribution of landslides inside them landslide scars and vegetation cover were mapped using aerial photographs and field observations a detailed digital terrain model 4 m 2 resolution of the basins was generated from which the main topographic attributes were analyzed producing maps for slope hillslope form contributing area and hillslope orientation by comparing these maps with the spatial distribution of the landslide scars for the 1996 event a landslide potential index lpi for the many classes of the different topographic attributes was defined at the same time field experiments with the guelph permeameter were carried out and a variety of scenarios were simulated with the shalstab model a process based mathematical model for the topographic control on shallow landslides the results suggest that most of the landslides triggered in the studied basins were strongly influenced by topography while vegetation cover did affect landslide distribution between the topographic attributes hillslope form and contributing area played a major role in controlling the spatial distribution of landslides therefore any procedure to be used in this environment towards the definition of landslide hazards need to incorporate these topographic attributes d 2003 elsevier b v all rights reserved

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

load redistribution rules for progressive failure in shallow landslides threshold mechanical models rainfall induced landslides are often preceded by progressive failures that culminate in abrupt mass release local failure progression is captured by a landslide hydro mechanical triggering lht model that represents the soil mantle as interacting columns linked by tensile and compressive mechanical bonds mechanical bonds may fail at a prescribed threshold leaving a modeling challenge of how to redistribute their load to neighboring intact soil columns we employed an elastic spring block model to analytically derive redistribution rules defined by the stiffness ratio of compressive to tensile bonds these linear elastic rules were generalized to real soil using measurable young s modulus and poisson s ratio results indicate that local failure characteristics of ductile like soils e g clay are reproduced by low stiffness ratios whereas global failure of brittle sandy soils corresponds to large stiffness ratios systematic analyses yield guidelines for selecting load redistribution rules for failure of geological materials and mass movement phenomena represented by discrete threshold mechanics

atypical peri gondwanan granodiorite tonalite magmatism from southern iberia origin of magmas and implications abstract an ensemble of fifteen granodiorite tonalite plutons and minor intrusions was generated during cambro ordovician times ca 498 462 ma at the margin of gondwana which occupies a large portion of the central iberian zone of the iberian massif spain and portugal this ensemble is known as the beira extremadura batholith beb which is mainly composed of tonalities and granodiorites 90 vol and shows an atypical composition with values of asi alumina saturation index 1 2 on average and marked calc alkaline affinity in terms of major and trace elements shrimp zircon u pb ages of 476 7 ma 476 6 ma and 474 7 ma for montanchez santa cruz de la sierra and valdemorales tonalites respectively coincide within uncertainty with the age of other lower ordovician beb intrusions analysis of phase relations and comparisons with experimental results on cotectic liquid compositions indicate that these atypical rocks represent calc alkaline magmas that carried exogenous pelitic restites from depth assimilation of partially molten metasediments by invasion of calc alkaline magmas is a plausible explanation model mixing of experimental calc alkaline liquids and ediacaran metasedimentary rocks yields that 20 up to 40 in samples of the santa cruz pluton of assimilated metagreywackes and metapelites is required to account for geochemical atypical compositions departing from a main cotectic array of calc alkaline systems the processes of melting or melting plus assimilation are favored by addition of water rich fluids we propose a tectonic scenario of crustal extension and metasomatized mantle melting that supplied hydrous intermediate magmas to the crust triggering crustal melting and massive assimilation of metasediments

the effect of periodic stratification on floc size distribution and its tidal and vertical variability geum estuary south korea abstract to understand the spatiotemporal variability in the floc size distribution the factors controlling floc size and the timing of flocculation with sediment flux in the periodically stratified geum estuary korea simultaneous measurements of current salinity suspended sediment concentration ssc and floc size distributions were analyzed and floc size was compared with stratification turbulence ssc and sediment flux salinity measurements indicated that the water column was stratified during ebb and well mixed during flood consistent with the process of strain induced periodic stratification coincident with periodic stratification was an ebb flood asymmetry in floc size where coarser multimodal and variable distributions occurred during the stratified ebb whereas finer unimodal and relatively constant distributions occurred during the well mixed flood vertically flocs coarsened downward during the stratified ebb and were vertically homogenous during the well mixed flood the ebb flood asymmetry in floc size was due to the ebb flood asymmetry in stratification and turbulence furthermore while floc size decreased with turbulence the ssc increased with turbulence as a consequence large flocs occurred with relatively small ebb directed fluxes whereas small flocs occurred with relatively large flood directed fluxes overall these observations indicate that the variability of the floc size distribution in periodically stratified estuaries is different than in well mixed estuaries and that ebb directed fluxes may be more flocculated than flood directed fluxes in these systems

the role of biophysical cohesion on subaqueous bed form size biologically active fine grained sediment forms abundant sedimentary deposits on earth s surface and mixed mud sand dominates many coasts deltas and estuaries our predictions of sediment transport and bed roughness in these environments presently rely on empirically based bed form predictors that are based exclusively on biologically inactive cohesionless silt sand and gravel this approach underpins many paleoenvironmental reconstructions of sedimentary successions which rely on analysis of cross stratification and bounding surfaces produced by migrating bed forms here we present controlled laboratory experiments that identify and quantify the influence of physical and biological cohesion on equilibrium bed form morphology the results show the profound influence of biological cohesion on bed form size and identify how cohesive bonding mechanisms in different sediment mixtures govern the relationships the findings highlight that existing bed form predictors require reformulation for combined biophysical cohesive effects in order to improve morphodynamic model predictions and to enhance the interpretations of these environments in the geological record

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

weathering profile of non welded ignimbrite and the water infiltration behavior within it in relation to the generation of shallow landslides the mechanism underlying rain induced shallow landslides of non welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile according to our study of ito ignimbrite in southern kyushu japan rhyolitic volcanic glass the primary component of ignimbrite is first hydrated and dissolved forming halloysite halloysite near ground surface is then transported through the ignimbrite by infiltrating water and becomes clogged in interstices to form clay bands suction monitoring across a weathering profile indicated that downward infiltration of water is disrupted once by a zone of less permeable clay bands and again at the weathering front this disruption at the front is caused by a capillary barrier effect caused by the structure where finer weathered material overlies coarser fresh material this results in a well defined weathering front particularly beneath a slope where water flux is parallel to the front whereas the front is transitional beneath a ridge top where the front is nearly horizontal and the water flux is normal to the front infiltrating water from rain increases the weight of weathered material and decreases the suction within the material which is the final trigger of a shallow landslide of non welded ignimbrite long term weathering which proceeds on the order of years provides slide material

hydrodynamics and sedimentation induced by large scale coastal developments in the keum river estuary korea abstract the macro tidal keum river estuary located in the eastern yellow sea has been suffering siltation and morphological change since 1994 to understand the effects of the large scale coastal developments on the sedimentation processes in the estuary hydrodynamic and sedimentary data collected from 1985 to 2002 were analyzed and numerical experiments of hydrodynamics were performed the sedimentation rate in the estuary increased by a factor of 1 9 from 3 5 10 6 to 6 7 10 6 m 3 y 1 after the construction of a dam in the upper reaches of the estuary in 1994 large part of the estuary is veneered by the muddy sediments noticeably which were rarely found before dam construction since then siltation has concentrated in the upper estuary rather than the lower the upstream transport and accumulation of fine grained sediments is due to 1 the change to flood dominance in the main channel i e the relative intensification of flood current and the flood directed residual current and 2 the decrease in transport capacity in the upper estuary i e the marked decrease in current velocity which was induced by dam construction the former has resulted in the ebb dominance of the gaeya channel a distributary in the north of the main channel the tidal pumping of fine sediments was reinforced not by the freshwater saltwater interaction but by the residual tidal circulation the sediment fluxes observed in 2001 2002 demonstrate year round net inflow both at the entrance of the jetties and at the gaeya channel which implies that the sediments delivered by the keum river are entirely confined to the estuary incapable of escaping to the sea the net inward transport of fine sediments may accumulate pollutants adsorbed to or absorbed in the sediment grains in the estuary thus deteriorating the benthic environment gradually and the water quality eventually

laboratory evaluation of the lisst in a stratified fluid a laboratory study to evaluate the performance of a laser in situ scattering and transmissometry lisst in a stratified environment is presented light passing through a stratified turbulent fluid is scattered due to changes in the index of refraction in natural water bodies density stratification due to surface heating and fresh water salt water mixing is widespread therefore in situ instruments designed to measure particle size based on the principle of laser diffraction such as the lisst are likely to encounter operational limits under stratified conditions results from a laboratory study show that salinity fluctuations cause small angle forward scattering patterns that are indistinguishable from particle scattering for a type c lisst which measures particles in the 2 5 to 500 m range the scattering is confined primarily to the inner 9 rings under salinity stratification ranging from 2 to 10 ppt experiments conducted with stratification and particles reveal that the type c lisst can distinguish particle size distributions so long as the median particle size is smaller than about 128 m

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

modelling the probability of occurrence of shallow landslides and channelized debris flows using geotop fs this paper describes a coupled distributed hydrological geotechnical model geotop fs which simulates the probability of occurrence of shallow landslides and debris flows we use a hydrological distributed model geotop which models latent and sensible heat fluxes and surface runoff and computes soil moisture in 3 d by solving richards equation numerically together with an infinite slope geotechnical model geotop fs the combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled in particular the model has been conceived to make direct use of field surveys geotechnical characteristics and soil moisture measurements in the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined to account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes the safety factor is computed with a probabilistic approach in order to determine the likelihood of slope failures soil parameters are assigned distributions instead of single deterministic values the analysis presented was carried out for an alpine watershed located in the friuli region italy for which some geological and geotechnical data were available in the past this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events the distributed coupled geotop fs model was calibrated by reproducing some of these events and validated in order to map future failure probabilities

modelling snow failure with a fibre bundle model dry snow slab avalanches initiate from a failure in a weak snow layer below a cohesive slab snow is considered as a porous ice structure and the strength distribution of the single elements of this structure i e grains and bonds between grains shows a high degree of disorder on the bond or microstructural level the failure process is believed to start if the fracturing of bonds between snow grains is not balanced by the formation of new bonds we use a statistical fracture model a fibre bundle model to study the failure process in a weak snow layer the model consists of fibres of various strengths representing single snow grains between two rigid plates which represent the slab above and the substratum below the weak layer the fibres deform in a linear elastic manner and break instantly at their rupture strength broken fibres may sinter re bond and regain strength after a finite sintering time we show that the different characteristic times for breaking and sintering lead to the rate dependence of snow strength this is to our knowledge the first statistical model to reproduce the ductile to brittle transition which snow exhibits with increasing strain rate when the model is applied to simulate experimental stress strain curves for different strain rates the model and experimental results are in fair agreement

linkage of sediment supply and transport processes in miyagawa dam catchment japan 1 linkages between sediment supply by episodic geomorphic processes obtained from aerial photographs and field surveys and sediment transport estimated from changes in sediment deposition behind a large dam were investigated in the miyagawa dam catchment central japan a total of 6667 landslides were confirmed in the period from 1965 to 2000 on the basis of seven temporal pairs of aerial photographs both the occurrence of landslides and discharge into the dam lake affect sediment yield indicating that fluvial systems in miyagawa dam catchment are supply limited with respect to sediment sediment yields are affected by not only the initial failed volume of landslides but also the mobility of landslides and debris flows in miyagawa dam catchment percentages of landslides reaching channels varied from 56 in 1997 2000 to 75 in 1976 1981 and were correlated with maximum hourly rainfall in addition the mobility of debris flows was higher during periods with high maximum instantaneous discharge compared to lower discharge suggesting that the water content both in initially failed materials and transported sediment controlled their mobility topography also affected the mobility of landslides debris flows for catchments 0 1 km2 the percentage of channel network length impacted by debris flows decreased with increasing catchment area due to reduced channel gradient thus both the magnitude of rainfall runoff events and the catchment topography affect how landslide sediment contributes to sediment yield at the large catchment scale

development of progressive landslide failure in cohesive materials the development of progressive failure in slopes is a poorly understood process and relatively few advances in terms of the mechanics of the development of failure have been made since 1967 however advances in the understanding of the development of fractures in brittle materials provide new insights into landslide mechanics in addition the link between the deformation mechanism and movement type allows interpretation of displacement records to determine the mechanisms acting within a slope this paper utilizes these insights into deformation processes combined with reinflation stress path triaxial experiments to propose a new model for the development of a progressive first time failure within a slope this model is able to explain the development of failure when the factor of safety is greater than unity the existence of saito linearity a linear trend when the reciprocal of velocity prior to failure is plotted against time during tertiary creep and the development of failures during periods of apparently increasing normal effective stress

characteristics of the size distribution of recent and historical landslides in a populated hilly region despitetheavailabilityofstudiesonthefrequencydensityoflandslideareasinmountainousregions frequency areadistributions of historical landslide inventories in populated hilly regions are absent this study revealed that the frequency area distribution derived from a detailed landslide inventory of the flemish ardennes belgium is significantly different from distributions usually obtainedinmountainousareaswherelandslidesaretriggeredbylarge scalenaturalcausalfactorssuchasrainfall earthquakesorrapid snowmelt instead the landslide inventory consists of the superposition of two populations i e i small b1 2 10 2 km 2 shallow complexearthslides that areat most30yrold and ii large n1 2 10 2 km 2 deep seatedlandslides that areolder than100yr both subpopulations are best represented by a negative power law relation with exponents of 0 58 and 2 31 respectively this study focused on the negative power law relation obtained for recent small landslides and contributes to the understanding of frequency distributions of landslide areas by presenting a conceptual model explaining this negative power law relation for small landslides in populatedhilly regions according to the model hilly regions canberelatively stable under the present dayenvironmental conditions andlandslidesaremainlytriggeredbyhumanactivitiesthathaveonlyalocalimpactonslopestability therefore landslidescausedby anthropogenic triggers are limited in size and the number of landslides decreases with landslide area the frequency density of landslide areas for old landslides is similar to those obtained for historical inventories compiled in mountainous areas as apart from the negative power law relation with exponent 2 31 for large landslides a positive power law relation followed by a rollover is observed for smaller landslides however when analysing the old landslides together with the more recent ones the present day higher temporal frequency of small landslides compared to large landslides obscures the positive power law relation and rollover 2007 elsevier b v all rights reserved

a model of propagating brittle failure in heterogeneous media i consider a nonelastodynamic model for the propagation of brittle failure in a heterogeneously stressed medium numerical simulation shows a power law distribution of failure sizes with a slope not far different from the size distribution of seismic events the time history of calculated failure activity is not consistent with observed seismic behavior and some explanations and implications are discussed

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement

landslides on coastal sage scrub and grassland hillslopes in a severe el nino winter the effects of vegetation conversion on sediment delivery during the 1997 1998 el nino record rainfall triggered 150 shallow landslides within a 9 5 km2 area near santa barbara cal ifornia they were studied to analyze the sediment delivery to val ley floors from landslides in coastal sage scrub and converted grasslands the conversion of coastal sage to grasslands primarily to provide pasturage for cattle is common in the region and the landscape s response may affect water quality reservoir infilling and debris flow hazards we explore the relationship between lateral root reinforcement and landslide volume by developing a slope stability analysis that incorporates root cohesion along the sides of the failure the stability analysis correctly predicts an inverse re lationship between landslide volume and hillslope angle in the sage the volumes of failures in the grasslands do not vary systemati cally with slope and are generally smaller than those in the sage from aerial photograph analysis and field mapping we find that there are 22 9 failures per square kilometer in the grasslands com pared to 13 2 failures per square kilometer in the sage despite the lower failure density in the coastal sage greater failure volumes and longer transport distances delivered more sediment to valley floors with a specific volumetric flux of 2 8 3 10 2 m 3 m 1 for this el nino compared to 1 73 10 2 m 3 m 1 in the grasslands we con clude that the conversion from vegetation with stronger and deeper roots coastal sage to vegetation with weaker and shallower roots grass has caused a pulse of increased landsliding in the grasslands because the soils are currently too thick for the prevailing root reinforcement we suggest that over time soils in the grassland hollows will become thinner as the evacuation by landslides is re peated until the landsliding rate declines to balance the soil sup plied from local colluvium production and diffusive processes upslope

settling velocity and mass settling flux of flocculated estuarine sediments new formulations are presented for the settling velocity and mass settling flux the product of settling velocity and sediment concentration of flocculated estuarine mud physics based formulae for these are developed based on assumptions of a two class floc population microflocs and macroflocs in quasi equilibrium with the flow the settling velocities of microflocs and macroflocs are related to floc size and density via the kolmogorov microscale as a function of turbulent shear stress and sediment concentration including height dependence and floc density dependence coefficients in the formulae are calibrated against an existing large data set of in situ observations of floc size and settling velocity from northern european estuaries various measures of performance show that the resulting formulae achieve an improved level of agreement with data compared with other published prediction methods the new formulae with the original calibration coefficients perform well in tests against independent measurements made in two estuaries

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

channel curvature effects on estuarine circulation in a highly stratified tropical estuary the sao francisco river estuary brazil abstract the effects of the channel curvature on estuarine circulation were assessed in the sao francisco river estuary this estuary is a deltaic front system with a highly stratified salinity distribution the assessment was based on field experiments where currents and salinity and temperature were monitored during a semi diurnal tidal cycle in two cross sections with distinct curvatures radii of 2 and 8 km the least squares method was used to determine the mean velocity residual velocity and the tidal velocity amplitude and phase for the m2 harmonic the results for the m2 harmonic were compared to an analytical solution that considers a simplified momentum balance between barotropic pressure gradient and bottom friction the model skill for these two results was 0 44 and 0 63 for sections a and b respectively the differences between these results indicate that there are other dynamically influential forces for the longitudinal momentum balance besides those included in the analytical solution the baroclinic pressure gradient presented values two orders of magnitude greater than the bottom friction demonstrating the dynamic importance of this force although centrifugal acceleration is a component of the lateral momentum balance it also plays a role in the distribution of longitudinal currents in the cross section displacing the maximum currents towards the exit of the curve in addition to the channel curvature effect the influence of the bathymetry was also observed on the tidal amplitude in the cross sections and on the depth averaged residual longitudinal velocities along the sections with the highest average speed in the shallowest areas of each section

the cycle of turbulent dissipation in the presence of tidal straining in regions of large horizontal density gradient tidal straining acts to produce a periodic component of stratification that interacts with turbulent mixing to control water column structure and flow a 25 h series of measurements of the rate of dissipation of turbulent kinetic energy e in the liverpool bay region of freshwater influence rofi have revealed the form of this interaction and indicate substantial differences from regions where horizontal gradients are weak in the rofi system there is a pronounced difference between flood and ebb regimes during the ebb the water column stratifies and strong dissipation is confined to the lower half of the water column by contrast during the flood stratification is eroded with complete vertical mixing occurring at high water and high values of dissipation 3 mw m23 extending throughout the water column the cycle of dissipation is therefore predominantly semidiurnal in the upper layers whereas near the bottom boundary the principal variation is at the m4 frequency as observed in regions of horizontal uniformity toward the end of the flood phase of the cycle tidal straining produces instabilities in the water column that release additional energy for convective mixing confirmation of increased vertical motions throughout the water column during the late flood and at high water is provided by measurements of vertical velocity and the error velocity from a bottom mounted acoustic doppler current profiler

observations of suspended sediment stratification from acoustic backscatter in muddy environments abstract vertical profiles of suspended sediment concentration estimated from acoustic backscatter are used to re examine the relation between sediment stratification and floc size in a cohesive sedimentary environment concentration measurements by optical backscatter sensors at two vertical levels are used to calibrate the acoustic backscatter intensity in spite of the complexities due to the rapidly changing flow and cohesive sediment properties the estimates of sediment concentration reproduce well the observations together with the vertical profiles of suspended sediment concentration measured current profiles are used to calibrate a one dimensional vertical 1dv boundary layer numerical model for combined wave current flow on muddy beds the numerical simulations are used to investigate the effect of the floc size on the vertical structure of the suspended sediment concentration profile for similar flow conditions smaller flocs result in more mixed profiles with higher concentration in the upper water column and lower near bed concentration this is the first time this effect is seen in direct field observations and confirms previously published numerical results

the importance of tidal and lateral asymmetries in stratification to residual circulation in partially mixed estuaries measurements collected in the york river estuary virginia demonstrate the important impact that tidal and lateral asymmetries in turbulent mixing have on the tidally averaged residual circulation a reduction in turbulent mixing during the ebb phase of the tide caused by tidal straining of the axial density gradient results in increased vertical velocity shear throughout the water column during the ebb tide in the absence of significant lateral differences in turbulent mixing the enhanced ebb directed transport caused by tidal straining is balanced by a reduction in the net seaward directed barotropic pressure gradient resulting in laterally uniform two layer residual flow however the channel shoal morphology of many drowned river valley estuaries often leads to lateral gradients in turbulent mixing tidal straining may then lead to tidal asymmetries in turbulent mixing near the deeper channel while the neighboring shoals remain relatively well mixed as a result the largest lateral asymmetries in turbulent mixing occur at the end of the ebb tide when the channel is significantly more stratified than the shoals the reduced friction at the end of ebb delays the onset of the flood tide increasing the duration of ebb in the channel conversely over the shoal regions where stratification is more inhibited by tidal mixing there is greater friction and the transition from ebb to flood occurs more rapidly the resulting residual circulation is seaward over the channel and landward over the shoal the shoal channel segregation of this barotropically induced estuarine residual flow is opposite to that typically associated with baroclinic estuarine circulation over channel shoal bathymetry

landslide rupture and the probability distribution of mobilized debris volumes 1 landslide driven erosion is controlled by the scale and frequency of slope failures and by the consequent fluxes of debris off the hillslopes in this paper we tackle the magnitude frequency part of the process and develop a theory of initial slope failure and debris mobilization that reproduces the heavy tailed distributions probability density function or pdfs observed for landslide source areas and volumes landslide rupture propagation is treated as a quasi static noninertial process of simplified elastoplastic deformation with strain weakening debris runout is not considered the model tracks the stochastically evolving imbalance of frictional cohesive and body forces across a failing slope and uses safety factor concepts to convert the evolving imbalance into a series of incremental rupture growth or arrest probabilities a single rupture is simulated with a sequence of weighted coin tosses with weights set by the growth probabilities slope failure treated in this stochastic way is a survival process that generates asymptotically power law tail pdfs of area and volume for rock and debris slides predicted scaling exponents are consistent with analyses of landslide inventories the primary control on the shape of the model pdfs is the relative importance of cohesion over friction in setting slope stability the scaling of smaller shallower failures and the size of the most common landslide volumes are the result of the low cohesion of soil and regolith whereas the negative power law tail scaling for larger failures is tied to the greater cohesion of bedrock

fiber bundle model for multiscale modeling of hydromechanical triggering of shallow landslides 1 sudden and rapid mass movements associated with landslides and snow avalanches present a hazard to life and infrastructure yet their predictions and triggering mechanisms remain poorly understood statistical methods and correlative studies have been used to produce landslide or avalanche susceptibility maps often with limited physical basis mechanistic approaches based on factor of safety computation seldom represent the progressive transition from local failure events to a landslide and in general do not include heterogeneities associated with land cover or with subsurface material properties and hydrologic pathways focusing on rainfall induced shallow landslides we propose the use of the fiber bundle model fbm a generic yet powerful and adaptable model used in modeling fatigue and fracture of complex and disordered materials the primary strength of the fbm is its ability to represent the progressive failure of cracks and shear zones and the ruptures of highly heterogeneous bonding elements that are present in soils at all scales the model also provides a natural framework for interpretation of acoustic emission signatures from failing slopes which may form the basis of a monitoring and warning system

a seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the 17 january 1994 northridge california earthquake abstract one of the most significant effects of the 17 january 1994 northridge california earthquake m 6 7 was the triggering of thousands of landslides over a broad area some of these landslides damaged and destroyed homes and other structures blocked roads disrupted pipelines and caused other serious damage analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes we analyzed the frequency distribution and geometries of triggered landslides in the santa susana 7 5 quadrangle an area of intense seismic landslide activity near the earthquake epicenter landslides occurred primarily in young late miocene through pleistocene uncemented or very weakly cemented sediment that has been repeatedly folded faulted and uplifted in the past 1 5 million years the most common types of landslide triggered by the earthquake were highly disrupted shallow falls and slides of rock and debris far less numerous were deeper more coherent slumps and block slides primarily occurring in more cohesive or competent materials the landslides in the santa susana quadrangle were divided into two samples single landslides 1502 and landslide complexes 60 which involved multiple coalescing failures of surficial material we described landslide morphologies by computing simple morphometric parameters area length width aspect ratio slope angle to quantify and rank the relative susceptibility of each geologic unit to seismic landsliding we calculated two indices 1 the susceptibility index which is the ratio given as a percentage of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit and 2 the frequency index given in landslides per square kilometer ls km2 which is the total number of landslides within each geologic unit divided by the outcrop area of that unit susceptibility categories include very high 2 5 landslide area or 30 ls km2 high 1 0 2 5 landslide area or 10 30 ls km2 moderate 0 5 1 0 landslide area or 3 10 ls km2 and low

sediment resuspension flocculation and settling in a macrotidal estuary national natural science foundation of china 40876043 papd fund china scholarship council 2010832427 mel young scientist visiting fellowship melrs0938

analytical and observational relations between landslide volume and surface area 1 a remarkable field observation is that landslides of different sizes from different locations around the globe and triggered by different mechanisms all seem to follow a single relation with their volume to surface area ratio following a power law of 1 4 this paper presents an analytical examination of the shape of landslides on the basis of limit equilibrium principles involving the exact mathematical solution of the failure mode the obtained analytical relation between the volume and the surface area of a landslide agrees well with the function obtained from the field observations and hence a mechanical basis is given to the previously poorly understood field observations in addition this paper presents a new graphical interpretation of the factor of safety associated with slope stability analysis and its relation to the probability of failure

landslide volumes and landslide mobilization rates in umbria central italy abstract a catalogue of 677 landslides of the slide type was selected from a global database of geometrical measurements of individual landslides including landslide area al and volume vl the measurements were used to establish an empirical relationship to link al in m2 to vl in m3 the relationship takes the form of a power law with a scaling exponent 1 450 covers eight orders of magnitude of al and twelve orders of magnitude of vl and is in general agreement with existing relationships published in the literature the reduced scatter of the experiential data around the dependency line and the fact that the considered landslides occurred in multiple physiographic and climatic environments and were caused by different triggers indicate that the relationship between vl and al is largely independent of the physiographical setting the new relationship was used to determine the volume of individual landslides of the slide type in the collazzone area central italy a 78 9 km2 area for which a multi temporal landslide inventory covering the 69 year period from 1937 to 2005 is available in the observation period the total volume of landslide material was vlt 4 78 107 m3 corresponding to an average rate of landslide mobilization l 8 8 mm yr 1 exploiting the temporal information in the landslide inventory the volume of material produced during different periods by new and reactivated landslides was singled out the wet period from 1937 to 1941 was recognized as an episode of accelerated landslide production during this 5 year period approximately 45 of the total landslide material inventoried in the collazzone area was produced corresponding to an average rate of landslide mobilization l 54 mm yr 1 six times higher than the long term rate the volume of landslide material in an event or period was used as a proxy for the magnitude of the event or period defined as the logarithm base 10 of the total landslide volume produced during the event or period with this respect the new relationship to link al and vl is a starting point for the adoption of a quantitative process based landslide magnitude scale for landslide events

in situ geophysical and hydro geochemical monitoring to infer landslide dynamics pegairolles de l escalette landslide france the pegairolles de l escalette landslide is located in the central part of the languedoc region southern france it corresponds to a deep seated landslide 50 m of thickness with extremely slow slip displacement 3 4 mm year in this area the current landslide activity is associated with intense precipitation events 300 500 mm in a few days and the related dissolution of triassic evaporite layers at depth considering a relatively simple geological context and a landslide mainly controlled by slope hydrogeology this site constitutes a natural observatory to study the impact of large rain events on slope kinematics this work is based on complete and original instrumentation deployed in two nearby boreholes since 2012 the landslide is investigated down to 65 m depth by two in situ permanent observatories for geophysical electrical resistivity and deformation metric sensor spacing daily and seasonal data acquisition and hydrogeochemical monitoring pressure ph temperature electrical conductivity fluid sampling 4 depths monthly data acquisition the data recorded during the five years of investigations help us to characterize the active slip zones in the underground as well as the seasonal dynamics of the different hydrogeological units within the slope we also observe a heavy rainfall event characterized by both electrical resistivity and geochemical changes down hole which suggest different time responses of the system to the meteorological solicitations these first results point out the relevance of the downhole monitoring to progress towards a better understanding of internal landslide processes in relation to climate forcing

criticality in earthquakes good or bad for prediction abstract through the analysis of the correlation functions in simulations of an earthquake model the critical properties of the system are studied simulations are performed in a more realistic modification of the olami feder christensen model of earthquakes and result in uncorrelated avalanches distributed following a power law with weak signs of foreshocks and aftershocks the spatial autocorrelation function of the system and other structural variables are computed in every step of the simulation the spatial autocorrelation between points separated from each other by a constant distance equal to 1 4 and 1 8 of the linear size of the system shows large variations temporally correlated with the time series of avalanche size i e spatial correlation values are in average very high before a large earthquake very small after a large earthquake and they evolve between these two states however the temporal average of the spatial autocorrelation over the whole simulation shows values close to zero result that is in contradiction with the idea that the correlation length is of the same order as the linear size of the system diverging in an infinite system which is the main signature of a critical scenario by averaging the autocorrelation in smaller time windows the critical properties of temporal states can be used as an indication of upcoming catastrophic events the structural variables are also correlated with the occurrence of large avalanches suggesting the possibility of monitoring these variables in order to achieve prediction

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

landslide erosion controlled by hillslope material landslide erosion is a primary control of landscape relief a wide ranging analysis of landslide geometry shows that soil based landslides are generally less voluminous than landslides that involve the failure of bedrock and provides refined metrics for estimating the volume of a landslide from the area of the failure

power law correlations of landslide areas in central italy abstract we have studied the frequency area statistics of landslides in central italy we consider two data sets data set a contains 16 809 landslide areas in the umbria marche area of central italy they represent a reconnaissance inventory of very old old and recent modern landslides the noncumulative frequency area distribution of these landslides correlates well with a power law relation exponent 2 5 over the range 0 03 km 2 a l 2 data set b contains 4233 landslides that were triggered by a sudden change in temperature on 1 january 1997 resulting in extensive melting of snow cover an inventory of these snow melt triggered landslides was obtained from aerial photographs taken 3 months after the event these landslides also correlate well with a power law relation with exponent 2 5 over the range 0 001 km 2 a l 2 we show that the correlation of data set b is essentially identical to the correlation of 11 000 landslides triggered by the 17 january 1994 northridge california earthquake we attribute a rollover for small landslides in data set a to incompleteness of the record due to erosion and other processes and to limitations in the reconnaissance mapping technique used to complete the inventory on the other hand we conclude that rollovers for small landslides in data set b and the california earthquake data are real and are associated with the surface morphology we conclude that the power law distribution is valid over a wide range of landslide areas and discuss possible reasons we also discuss the contribution of the snow melt and earthquake triggered landslide events to the total landslide inventory

mass settling flux of fine sediments in northern european estuaries measurements and predictions abstract this study describes a new flocculation model which was based entirely on observations of settling floc spectra and turbulent shear stresses acquired primarily from a series of in situ experiments conducted in several european estuaries the synthesis identified that the key components which best quantitatively describe a floc population are the changes in the macrofloc 160 m and microfloc settling velocities ws macroem and ws microem together with how the suspended matter is distributed across each floc sub population spm ratioem the ws macroem algorithm displayed an increase in settling velocity at low shear stresses due to flocculation enhanced by shear and floc disruption at higher stresses for the same concentration the transition being a turbulent shear stress of about 0 36 n m 2 the combination of the three algorithms into a single equation to predict mass settling flux msf em estimated the total flux of the 157 measured floc samples with a cumulative error 1 and 5 mm s 1 were both in error by an average of 86 and 41 respectively a concentration settling parameterisation and the van leussen techniques under predicted the total cumulative flux by 35 and 38 respectively furthermore the analysis indicated that the various existing methods all incurred high predictive errors at times under estimating by over 70 as concentration levels rose in close proximity to the bed the findings of this study demonstrate the new manning floc settling velocity mfsv empirical model has flexibility in adapting to a wide range of both turbulent shear stress and suspended sediment concentration estuarine conditions

internal soil moisture response to rainfall induced slope failures and debris discharge article i nfo predictions of rainfall induced fast moving mass flow and or debris flows require better knowledge of the mechanism controlling the debris discharge of slopes in debris source areas a series of rainfalltests on 0 32 m deep 0 7 m high 1 35 m wide sandy slopes resting on a bi linear impermeable rigid base was performed soil moisture content and solid discharge measurements were performed to gain insights into the rainfall induced retrogressiveslopefailure thesolid ordebris dischargeisaresultof thewash outof the fluidizedslopetoeby the interflow along the soil bedrock interface characteristics of the failure process for the slopes are represented by mass wasting curves or solid discharge qs vs time t curves which are functions of the rainfall intensity and or the cumulative rainfall the mass wasting curves have inflection points representing transitions from minor toe failures into remarkable retrogressive failures the first inflection point of the soil moisture vs t curve measured at the soil bedrock interface signaling the arrival of the descending wet front may serve as a precursor for predicting the onset of an abrupt solid discharge induced by shallow slope failures the time of peak water content measured at the soil bedrock interface may approximate the time of 5 total solid volume discharge up to the time of 5 of total slope volume discharge a fully saturated state sr 100 was never observed at the 0 2 m below surface zone however it was observed along the soil bedrock interfaceat near toezoneof the slope regardlessof theintensityof rainfallinvestigated retrogressive failures were essentially associated with nonuniformly distributed water content in the slope for both the 0 2 m below surface zone and the soil bedrock interface a more uniform distribution of sr along the full height of the slope was found for slopes subjected to high rainfall intensities of 47 and 65 mm h than that for the slope subjected to a low rainfall intensity of 23 mm h at the inflection point of the qs vs t curve and 5 of total solid volume discharge values of sr at a certain distance from the toe for the soil bedrock interface were higher than those measured at the same distance fromthe toefor the 0 2 m below surface zone indicating the effect of infiltration induced interflowalong the soil bedrock interface and its effects on the fluidization of the slope toe and the retrogressive failure of the slope

floc properties in the turbidity maximum of a mesotidal estuary during neap and spring tidal conditions in order to improve the understanding of how fine cohesive matter behaves during different tidal conditions within an estuary turbidity maxima high quality in situ data is of a prime requirement as part of the european commission cosinus project a series of measurements were carried out in the upper reaches of the tamar estuary to investigate how flocculated mud properties vary within the turbidity maximum zone floc populations were sampled at regular intervals using the optical inssev instrument the floc data was supplemented by simultaneous time series of near bed profiles of turbulent shear stress and suspended particulate matter the proportion of macroflocs 160 m changed significantly across the turbidity maximum before the passage of the turbidity maximum the total floc mass tended to be equally divided between the macroflocs and microflocs on neaps whilst on springs the macroflocs contributed 60 70 at spring tides a peak near bed spm concentration of 6 g l 1 was measured in the turbidity maximum this was over an order of magnitude higher than observed at neaps the turbulence measurements showed significant drag reduction at spm concentration gradients above 3 6 kg m 4 within the turbidity maximum the macrofloc proportion rose rapidly until they contributed at least 75 of the floc dry mass during neap conditions and at spring tides this reached in excess of 90 96 an abundance of fast settling macroflocs from spring tides accounted for a time series average of 83 of the mass settling flux where as during neap tides the macroflocs contributed 15 less to the settling flux rate this was partly due to a time series averaged macrofloc settling velocity of 3 9 mm s 1 from the spring tidal data 2 1 mm s 1 higher than for neap tide conditions during the turbidity maximum passage at springs macroflocs reached 2 2 mm in diameter these flocs had settling velocities of up to 16 6 mm s 1 but effective densities were less than 50 kg m 3 which means they would be prone to break up when settling to a region of high shear at the opposite and of the scale low turbidity and quiescent slack water conditions severely restricted floc production

factors controlling floc settling velocity along a longitudinal estuarine transect a 147 km longitudinal transect of flocculated cohesive sediment properties in san francisco bay sfb was conducted on june 17th 2008 our aim was to determine the factors that control floc settling velocity along the longitudinal axis of the estuary the inssev lf video system was used to measure floc diameters and settling velocities at 30 stations at a distance of 0 7 m above the estuary bed floc sizes d ranged from 22 m to 639 m and settling velocities ws ranged between 0 04 mm s 1 and 15 8 mm s 1 during the longitudinal transect nearbed turbulent shear stresses throughout the transect duration were within the 0 2 0 5 pa range which typically stimulates flocculation growth the individual d ws floc density plots suggest the suspended sediments encountered throughout sfb were composed of both muddy cohesive sediment and mixed sediments flocs mass weighted population mean settling velocity wsmass ranged from 0 5 mm s 1 to 10 mm s 1 the macrofloc and microfloc demarcation at 160 m sub populations demonstrated parameterised settling velocities which spanned nearly double the range of the sample mean settling velocities wsmean the macroflocs tended to dominate the suspended mass up to 77 of the ambient suspended solid concentration ssc from san pablo bay to carquinez strait the vicinity of the turbidity maximum zone microfloc mass was particularly significant typically 60 100 of the ssc in the northern section of south bay and most of central bay the transect took eleven hours to complete and was not fully synoptic during slack tide larger and faster settling flocs deposited accounting for most of the longitudinal variability the best single predictor of settling velocity was water velocity 39 min prior to sampling not suspended sediment concentration or salinity resuspension and settling lags are likely responsible for the lagged response of settling velocity to water velocity the distribution of individual floc diameters and settling velocities indicates that floc density for a given floc diameter varies greatly a small portion a few percent of suspended sediment mass in sfb is sand sized and inclusion of sand in flocs appears likely fractal theory for cohesive sediment assumes that there is a single primary particle size that flocculates which is not the case for these types of mixed sediment flocs the wide variability in the physical biological and chemical processes which contribute to flocculation within sfb means that spatial floc data is required in order to accurately represent the diverse floc dynamics present in the bay system the importance in determining accurate estimates of floc density has been highlighted by the sfb data as these provide the basis for realistic distributions of floc dry mass and the mass settling flux across a floc population however although video floc sampling devices can produce the various floc property trends observed in sfb good survey practice is still paramount one can see that if the sampling coverage i e data collection frequency is poor this could lead to potential mis interpretations of the data and only limited conclusions may be drawn from such a restricted survey for example a limited survey i e only 3 stations compared to the 10 stations in the full survey in south bay produces an under estimate in both the macrofloc sscmacro distribution by a factor of four and the wsmacro by a factor of two to develop sediment transport numerical models for sfb high quality floc size and settling data are needed to understand and simulate the depositional qualities of both suspended cohesive sediment and mixed sediments in san francisco bay this study has shown that the most pragmatic solution is a physically based approach whereby the detailed flocs d vs ws spectra are parameterised in terms of their macrofloc and microfloc properties this aids in model calibration whilst retaining more of the dynamical aspects of the floc populations all forms of flocculation are dynamically active processes therefore it is important to also include both ssc and turbulence functions together with the floc data

an advanced process based distributed model for the investigation of rainfall induced landslides the effect of process representation and boundary conditions extreme rainfall events are the major driver of shallow landslide occurrences in mountainous and steep terrain regions around the world subsurface hydrology has a dominant role on the initiation of rainfall induced shallow landslides since changes in the soil water content affect significantly the soil shear strength rainfall infiltration produces an increase of soil water potential which is followed by a rapid drop in apparent cohesion especially on steep slopes of shallow soils this loss of shear strength can lead to failure even in unsaturated conditions before positive water pressures are developed we present hydrolisthisis a process based model fully distributed in space with fine time resolution in order to investigate the interactions between surface and subsurface hydrology and shallow landslides initiation fundamental elements of the approach are the dependence of shear strength on the three dimensional 3 d field of soil water potential as well as the temporal evolution of soil water potential during the wetting and drying phases specifically 3 d variably saturated flow conditions including soil hydraulic hysteresis and preferential flow phenomena are simulated for the subsurface flow coupled with a surface runoff routine based on the kinematic wave approximation the geotechnical component of the model is based on a multidimensional limit equilibrium analysis which takes into account the basic principles of unsaturated soil mechanics a series of numerical simulations were carried out with various boundary conditions and using different hydrological and geotechnical components boundary conditions in terms of distributed soil depth were generated using both empirical and process based models the effect of including preferential flow and soil hydraulic hysteresis was tested together with the replacement of the infinite slope assumption with the multidimensional limit equilibrium analysis the results show that boundary conditions play a crucial role in the model performance and that the introduced hydrological preferential flow and soil hydraulic hysteresis and geotechnical components multidimensional limit equilibrium analysis significantly improve predictive capabilities in the presented case study