simulated effect of a forest road on near surface hydrologic response and slope stability forest management practices often result in significant changes to hydrologic and geomorphic responses at or near the earth s surface a well known but not fully tested hypothesis in hillslope hydrology geomorphology is that a near surface permeability contrast caused by the surface compaction associated with forest roads can result in diverted subsurface flow paths that produce increased up slope pore pressures and slope failure the forest road focused on in this study is located in a steep forested zero order catchment within the h j andrews experimental forest oregon a three phase modelling effort was employed to test the aforementioned hypothesis i two dimensional vertical slice steady state heterogeneous saturated subsurface flow simulations at the watershed scale for establishing the boundary conditions for the catchment scale boundary value problem in ii ii two dimensional vertical slice transient heterogeneous variably saturated subsurface flow simulations at the catchment scale for estimating near surface hydrologic response and pore pressure distributions and iii slope stability analyses using the infinite slope approach driven by the pore pressure distributions simulated in ii for assessing the impact of the forest road both observed and hypothetical rainfall events are used to drive the catchment scale simulations the results reported here support the hypothesis that a forest road can have an effect on slope stability the permeability contrast associated with the forest road in this study led to a simulated altering of slope parallel subsurface flow with increased pore pressures up slope of the road and for a large rainfall event a slope failure prediction copyright 2005 john wiley sons ltd

deriving mechanisms and thresholds for cliff retreat in soft rock cliffs under changing climates rapidly retreating cliffs of the suffolk coast uk abstract understanding changing thresholds and mechanisms for retreat in soft rock cliffs is important under changing climates this can be achieved through combining detailed field observation long term process and morphological monitoring and numerical modelling the cliffs of the suffolk coast southern north sea have exhibited long term 1883 2010 recession rates of 3 5 m a 1 rising to 4 7 m a 1 in the period 1993 2010 annual to biannual ground survey data and the application of gis techniques to digitised records of changing shoreline position from historic maps and aerial photography reveal considerable decadal scale variations in cliff recession within which are nested inter annual fluctuations in rates of retreat archival datasets on significant periods of onshore winds and their interaction with high water levels including the incidence of storm surges and rainstorm events are used to determine thresholds for cliff base erosion and its propagation upwards through the cliff profile in addition the geo slope dynamic coupled hydrology stability model is used to establish thresholds for cliff face failures driven by variations in rainfall inputs retreat mechanisms are complex governed by cliff geology both as a primary control on suction loss and through its interaction with basal marine conditions the study allows a general model of cliff retreat for soft rock cliffs to be put forward whereby a resistant basal platform is overlain by more erodible weakly and moderately cemented sands and gravels in this model the varying balance between marine and terrestrial forcing factors are reflected in low 7 m a 1 modes of cliff retreat

snow depth in eastern europe in relation to circulation patterns rotated principal components of the 500 hpa geopotential heights in the euro atlantic sector are used as indicators of circulation pattern intensity daily snow cover depth data for the years 1951 95 from 71 eastern european stations are examined maps of linear correlation coefficient between monthly change in snow depth and rotated principal components are presented the positive and negative extremes of each circulation pattern are analyzed and positive and negative snow depth signals indicated a daily analysis of relationships between snow depth and circulation pattern is performed for three locations the strongest impact of the atmospheric circulation on changes in snow depth is observed in the south and west of the study area where the eastern european ee and central european circulation patterns are found to have the greatest impact the north atlantic oscillation nao impact on the snow depth in eastern europe is limited to the beginning and the end of winter snow cover has low variability in northeastern europe where the scandinavian sc pattern is of greatest importance and low sensitivity to change in the atmospheric circulation the decrease in snow cover depth observed in spring is related to the nao sc and ee patterns the latter being important for snow cover depth fluctuations over northeastern europe in april

transient seepage model for saturated unsaturated soil systems a geotechnical engineering approach a two dimensional finite element model is proposed to simulate transient seepage for complex groundwater flow systems the complete soil system is treated as a continuum encompassing flow in both saturated and unsaturated zones in the unsaturated zone the air phase is assumed to be continuous and open to atmospheric pressure the coefficient of permeability of the unsaturated soil is assumed to be a function of pore water pressure the governing differential equation is derived within a framework familiar to geotechnical engineers the stress state variables and the constitutive relationships for an unsaturated soil are used in the derivation the finite element solution to the governing differential equation is based on the galerkin weighted residual method the nonlinearity of the equation is solved by iterative procedures the finite element formulation is implemented into a computer model named trasee the model can be applied to a wide variety of problems involving complex boundary conditions and geo

modelled atmospheric response to changes in northern hemisphere snow cover the surface boundary conditions are altered in a numerical simulation of january climate by prescribing a higher and b lower than average snow extent over northern hemisphere land masses the anomalies in snow cover are shown to have quite a strong impact on the mean climatic state associated with an increase in the areal extent of the snow there is a significant reduction in temperature throughout the lower troposphere there are also large increases in sea level pressure over most land areas significant responses in the mass field are also seen at 500 hpa where reductions in atmospheric thickness lead to significant negative anomalies in the height field responses are also seen non locally over both the north pacific and north atlantic basins the impact of increased snow on cyclone tracks is also examined a reduction in cyclones is noted over both continents and over the western sectors of both ocean basins over the north atlantic basin this reduction extends across over europe significantly weakening the storm track in the north pacific cyclone density is reduced in the west while in the east there is actually a strengthening of the storm tracks there are corresponding changes in the genesis of cyclones in both of these regions the change in cyclogenesis intensity and density is demonstrated to be associated with changes in baroclinicity between the two experiments the anomalous snow boundary conditions lead to significant changes in the meridional temperature gradients over both ocean basins which impact on the baroclinic zones

north american snow depth and climate teleconnection patterns abstract snow atmosphere relationships have been studied for nearly half a century but the primary focus has been on snow extent variability largely because of the relative scarcity of snow depth data a recently released north american snow depth dataset with extensive spatial coverage and multidecadal temporal duration provides a new opportunity to compare snow depth climate relationships with snow extent climate relationships over north america robust concurrent lead and lag correlations are observed between snow depth and two major climate modes the pacific decadal oscillation pdo and the pacific north america pna pattern across north america and throughout the snow season in contrast snow extent exhibits a less coherent relationship with pdo and pna except in late spring which can be interpreted as a residual of the snow depth climate mode relationship a regional signature for the snow depth pdo pna relationship is also identified centered over interior central western north america

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

groundwater modelling of a weathered gneissic cover knowledge of the groundwater regime which is generally necessary in studying the stability of slopes is of fundamental importance in the analysis of landslides involving intensely weathered rocks as in the case of a landslide in the western sila massif southern italy reactivated by heavy and prolonged rainfall for this landslide the total absence of displacements during the actual quiescence period and the long return period of the critical rainfall events did not allow measurement of the critical pore pressures capable of reactivating the landslide to solve such a problem a saturated unsaturated flow model was calibrated taking into account in situ pore pressure measurements acquired over a long period of time the analyses permitted determination of the role played by the hydraulic heterogeneity of the involved soils and the hydraulic boundary conditions for simulation of the response of in situ pore pressures to rainfall such conditions were therefore used to predict the critical unknown valu

mid depth freshening in the north pacific subtropical gyre observed along the jma repeat and woce hydrographic sections 1 we report a freshening at mid depth in the north pacific subtropical gyre by using long term repeat hydrographic data along the 137 e section and one time hydrographic data along the world ocean circulation experiment hydrographic program whp p2 and p3 sections north of 15 n along the 137 e section we estimated a linear freshening trend of 0 0015 yr between the main thermocline and the salinity minimum layer of the north pacific intermediate water mainly caused by isopycnal surface deepening due to warming and by westward shifts of the salinity minimum tongue due to strengthening of the subtropical gyre furthermore along the whp p2 section the linear freshening trend could be classified into several groups according to longitude such spatial differences in the freshening trend seem to reflect differences in the formation processes and mid depth pathways of the salinity minimum waters

effects of soil moisture dynamics on slope failure at hyrum reservior utah field observations of shoreline conditions at hyrum reservoir utah were conducted during the summers of 1991 to 1993 a process of bluff retreat is described for a multiple layered bluff environment of sand and clay layers failure is initiated by wetting and drying of clay sediments which produces horizontal cracks within bluff material these cracks appear to penetrate to a depth of approximately 100 150 mm before initiating vertical cracking in the sediments the vertical cracks are propagated by continued drying of the surface sediment ultimately leading to failure of the bluff material the physical dimensions of sediment blocks succumbing to this mechanism range from a few hundred millimetres up to 3 m on a side with a depth of approximately 100 150 mm the mechanism described here appears to operate optimally when the supply of subsurface moisture is abundant and nearly continuous throughout the spring and early summer reservoir draw down large capillary fringe effects in the bluff and periodic wetting from upslope undrained hollows are the dominant moisture controls at this site moisture delivery to the face is strongly influenced by anisotropy of saturated hydraulic conductivity in the alternating clay and sand layers and related differences in sediment texture

multiple seepage faces on layered slopes and their implications for slope stability analysis this study provides an analysis of the water table configuration and pore pressure distribution in layered hillsides a finite element model was used to simulate two dimensional saturated unsaturated steady state flow through layered slopes a laboratory sand tank experiment was used to verify the physical foundation of the mathematical model it is shown that layered slopes feature multiple seepage faces perched water tables and wedge shaped unsaturated zones the pore pressure distribution and the distribution of multiple seepage faces are strongly dependent on the position of the impeding layers and their hydraulic properties predictions of pore pressure fields based on homogeneous saturated analyses may be significantly in error when applied to problems on layered slopes slope stability analyses on layered slopes that do not take into account the presence of unsaturated wedges beneath the impeding layers can lead to overdesign of the stable slope angle key words groundwater conditions unsatu

nao impact towards the springtime snow disappearance in the western eurasian continent 1 the atmospheric control over the disappearance of snow in western eurasia and its relationship to the north atlantic oscillation nao are investigated while the nao has a strong effect on the lower tropospheric temperature in the region its ability to force control over the snow extent is confined to western europe in january and february successive composite differences and heat budget analysis reveals a northeastward propagation of snow cover anomaly maintained by an anomalous zonal heat advection related to the nao from january to march and the intrusion of warm climatological southerly maintaining the snow anomaly until april

processes of coastal bluff erosion in weakly lithified sands pacifica california usa abstract coastal bluff erosion and landsliding are currently the major geomorphic processes sculpting much of the marine terrace dominated coastline of northern california in this study we identify the spatial and temporal processes responsible for erosion and landsliding in an area of weakly lithified sand coastal bluffs located south of san francisco california using the results of a five year observational study consisting of site visits terrestrial lidar scanning and development of empirical failure indices we identify the lithologic and process controls that determine the failure mechanism and mode for coastal bluff retreat in this region and present concise descriptions of each process bluffs composed of weakly cemented sands unconfined compressive strength ucs between 5 and 30 kpa fail principally due to oversteepening by wave action with maximum slope inclinations on the order of 65 at incipient failure periods of significant wave action were identified on the basis of an empirical wave run up equation predicting failure when wave run up exceeds the seasonal average value and the bluff toe elevation the empirical relationship was verified through recorded observations of failures bluffs composed of moderately cemented sands ucs up to 400 kpa fail due to precipitation induced groundwater seepage which leads to tensile strength reduction and fracture an empirical rainfall threshold was also developed to predict failure on the basis of a 48 hour cumulative precipitation index but was found to be dependent on a time delay in groundwater seepage in some cases

climate variability in the north pacific thermocline diagnosed from oxygen measurements an update based on the u s clivar co2 repeat hydrography cruises 1 new observations of oxygen variability in the north pacific ocean are reported on the basis of comparison of the u s climate variability and predictability and carbon clivar co2 repeat hydrography sections conducted along 30 n 2004 and 152 w 2006 with the earlier world ocean circulation experiment woce data and other cruises along these sections the largest changes in apparent oxygen utilization aou continue to occur as found in earlier north pacific repeat section analyses within the thermocline on 26 6 kg m 3 which is the densest isopycnal to outcrop in the open north pacific in climatological data in the northeastern north pacific along 152 w where a total of five cruises 1980 1984 1991 1997 and 2006 spanning a period of 26 years are available the aou changes correspond to an overall increase in aou on 26 6 kg m 3 from the 1980s early 1990s to 2006 however from 1997 to 2006 a decrease in aou is observed within the boundary region between the subtropical and subpolar gyres at 40 45 n along the center axis of the subtropical gyre at 30 n where two cruises are available 1994 and 2004 aou has also substantially increased on 26 6 kg m 3 from 1994 to 2004 in the eastern part of the section the repeat section data along 152 w and 30 n are consistent with a pattern of decadal scale ventilation anomalies that originate in the northwestern pacific possibly through variability including cessation of the 26 6 kg m 3 outcrop travel eastward along the subtropical subpolar gyre boundary and enter the northern portion of the subtropical gyre along the way for the 152 w aou data within the gyre boundary region 40 45 n good agreement exists with the close by time series data from ocean station p 50 n 145 w where a bidecadal cycle in aou has been observed in contrast a sensible correlation with the pacific decadal oscillation could not be found

dynamics of kuroshio path variations in a high resolution general circulation model 1 a long lived 2 year typical large meander lm path of the kuroshio is reproduced in a high resolution general circulation model gcm simulation with realistic topography and the life cycle formation maintenance and disappearance of the lm is studied the formation of the lm is triggered by a pair of upper layer anticyclonic and cyclonic eddies on the kuroshio with the cyclonic one on the downstream side upon reaching the western side of the shikoku basin south of japan these anomalies induce a lower layer anticyclonic eddy they enhance each other while they are carried eastward by the kuroshio specifically the southward flow on the eastern side of the lower anticyclonic eddy carries the upper cold cyclonic eddy offshore resulting in the southward deflection of the kuroshio path large meander these processes can be understood as a growth of baroclinic instability a stationary lm is established when the westward tendency caused by the beta effect owing to the large meridional displacement counterbalances the eastward tendency caused by the combination of advection and vortex induction owing to the curvature of the kuroshio path large scale disturbances from the upstream tend to strengthen the lm through baroclinic energy conversion in contrast small scale disturbances from the upstream grow locally along the meandering kuroshio front through baroclinic energy conversion they extract cold waters from the cold cyclonic eddy of the lm as they flow away to the east the horizontal extent of the cold cyclonic eddy is reduced and the meander is carried eastward since the advection effect dominates over the beta effect that weakens as a result of the smaller meridional extent

the development of multiple seepage faces on layered slopes this study provides an analysis of the water table configuration and hydraulic head distribution in layered hillsides a finite element model was used to simulate two dimensional saturated unsaturated steady state flow through layered slopes a laboratory sand tank experiment was used to verify the physical foundation of the mathematical model it is shown that layered slopes feature multiple seepage faces perched water tables and wedge shaped unsaturated zones the hydraulic head distribution and water table configuration are strongly dependent on the position of the impending layers and the ratio of the hydraulic conductivity between adjacent layers this work has geotechnical implications with regard to slope stability and the control of groundwater inflows into excavations it has hydrogeological implications with regard to flow path analysis in contamination studies it has geomorphological implications with respect to landform development by mass movements and surface water erosions and to drainage network development through piping

instability caused by a seepage impediment in layered fill slopes the underlying cause of loose fill slope failures in hong kong has been attributed to static liquefaction during heavy rainfall a series of centrifuge model tests and numerical analyses were condu

roles of the okhotsk sea and gulf of alaska in forming the north pacific intermediate water recently obtained world ocean circulation experiment woce sections and pre woce hydrography are used to study the water mass structure and formation and transformation of north pacific intermediate water npiw five neutral density surfaces are selected and mapped encompassing npiw from 400 to 900 m in the subtropical latitudes with a distance of 100 m between a pair of surfaces npiw is defined as a subtropical gyre salinity minimum which is well followed by a neutral density surface n 26 9 formation and transformation of npiw is examined by the mapped turner angle on neutral density surfaces apparent diffusive double diffusion is found in the alaskan gyre on n 26 5 neutral surface in the northwest subpolar gyre and the okhotsk sea on n 26 9 neutral surface and mainly in the okhotsk sea on the two deep neutral surfaces n 27 2 and n 27 4 these diffusive regions indicate transformation sources for npiw along with additional information of potential vorticity and stream function it is found that there are two different npiw formation sources one in the gulf of alaska characterized by high potential vorticity and the other in the okhotsk sea characterized by low potential vorticity the former lies shallower at n 26 2 26 5 but its effect deepens to npiw core density level at n 26 8 on the basis of potential vorticity distribution the latter includes the influence of the northwest subpolar gyre and extends much deeper to n 27 4 we call them gulf of alaska intermediate water gaiw and okhotsk intermediate water oiw respectively gaiw contributes to npiw in the eastern part of the subtropical gyre east of date line whilst oiw dominates in the west and entire lower part of npiw seasonal flow stream function mapped on neutral surfaces shows that the contribution of gaiw to npiw occurs mainly in the wintertime because in winter a significant northward shift of zero wind stress curl makes the gulf of alaska an additional source for npiw

interannual variability of wintertime snow cover across the northern hemisphere abstract digitized maps of northern hemisphere snow cover derived from visible satellite imagery are examined to assess the interannual variability of snow cover in winter months for years 1972 90 the secular trend of winter snow cover over the landmasses of eurasia and north america during this period is extremely small in december and january a decreasing trend of somewhat larger magnitude is observed in eurasian snow cover in february fluctuations of detrended interannual snow cover anomalies averaged over the eurasian and north american continents are positively correlated by subdividing the continents into longitudinal sectors it is determined that this intercontinental relationship is due to high correlations between european and north american sectors the relationship of snow cover fluctuations to large scale circulation anomalies is described using lime series of teleconnection pattern indices derived from monthly mean geopotential height fields a pattern of height anomalies resembling the n

examination of the seepage face boundary condition in subsurface and coupled surface subsurface hydrological models a seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions water table fluctuations and flow patterns its handling in hydrological models especially under complex conditions such as heterogeneity and coupled surface subsurface flow has not been extensively studied in this paper we compare the treatment of the seepage face as a static dirichlet versus dynamic boundary condition we assess its resolution under conditions of layered heterogeneity we examine its interaction with a catchment outlet boundary and we investigate the effects of surface subsurface exchanges on seepage faces forming at the land surface the analyses are carried out with an integrated catchment hydrological model numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the landscape evolution observatory the results show that the static boundary condition is not always an adequate stand in for a dynamic seepage face boundary condition especially under conditions of high rainfall steep slope or heterogeneity that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role and that seepage faces at the land surface are not always controlled by subsurface flow the paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way is applicable to unstructured grids and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

pathways of the north pacific intermediate water identified through the tangent linear and adjoint models of an ocean general circulation model 1 this study develops a strategy for tracing a target water mass and applies it to analyzing the pathway of the north pacific intermediate water npiw from the subarctic gyre to the northwestern part of the subtropical gyre south of japan in a simulation of an ocean general circulation model this strategy estimates the pathway of the water mass that travels from an origin to a destination area during a specific period using a conservation property concerning tangent linear and adjoint models in our analysis a large fraction of the low salinity origin water mass of npiw initially comes from the okhotsk or bering sea flows through the southeastern side of the kuril islands and is advected to the mixed water region mwr by the oyashio current it then enters the kuroshio extension ke at the first ke ridge and is advected eastward by the ke current however it deviates southward from the ke axis around 158 e over the shatsky rise or around 170 e on the western side of the emperor seamount chain and enters the subtropical gyre it is finally transported westward by the recirculation flow this pathway corresponds well to the shortcut route of npiw from mwr to the region south of japan inferred from analysis of the long term freshening trend of npiw observation copyright 2013 john wiley sons ltd

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is

role of atmospheric circulation with respect to the interannual variability in the date of snow cover disappearance over northern latitudes between 1988 and 2003 1 this paper analyzes the main spatial patterns in the dates of snow cover disappearance variability over northern latitudes between 1988 and 2003 the dates of snow cover disappearance were calculated using satellite passive microwave data from the special sensor microwave imager spatial and temporal patterns were obtained using principal components analysis in the s mode we identified eight components each representing a large region characterized by homogeneous interannual variability in the dates of snow cover disappearance we found that atmospheric circulation summarized by means of teleconnection indices had an important impact on the date of snow cover disappearance for most of these regions a role is played by the arctic oscillation in western siberia the spring east atlantic west russian pattern in central siberia and the pacific north