bank collapse processes in a valley bottom gully western iowa widening and bank slope reduction of a valley bottom gully in western iowa was correlated to increasing subsurface flow over a 36 year period to study bank collapse at this gully we measured rainfall air temperature hydraulic head near the banks and bank movement nearly continuously over a 2 year period styles of movement ranged from imperceptible creep to rapid slab collapses preceded by the formation of tension cracks parallel to the gully walls bank movement was commonly correlated to rainfall or snowmelt and associated head increases in the banks if the banks are modelled as a two dimensional slab with an adjacent tension crack partly filled with water measured heads were sufficient to cause bank failures through reduction of frictional support at the base of the slab during winter months air temperature variations across 0 c were correlated with bank movement during mildly subfreezing periods banks expanded and most but usually not all of this movement was recovered during above freezing periods this motion is attributed to frost heave followed by thawing deformation of the banks by heaving and thawing during winter may weaken them and prime them for failure during spring rains and snowmelt when the frequency of mass wasting events is highest copyright 2008 john wiley and sons ltd

stability of composite river banks the stability of a river bank depends on the balance of forces motive and resistive associated with the most critical mechanism of failure many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size geometry and structure of the bank the engineering properties of the bank material the hydraulics of flow in the adjacent channel and climatic conditions rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt clay bank erosion occurs by fluvial entrainment of material from the lower cohesionless bank at a much higher rate than material from the upper cohesive bank this leads to undermining that produces cantilevers of cohesive material upper bank retreat takes place predominantly by the failure of these cantilevers three mechanisms of failure have been identified shear beam and tensile failure the stability of a cantilever may be analysed using static equilibrium and beam theory and dimensionless charts for cantilever stability constructed application of the charts requires only a few simple measurements of cantilever geometry and soil properties in this analysis the effects of cracks and fissures in the soil must be taken into account these cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface following mechanical failure blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue hence the rate of bank retreat is fluvially controlled even though the mechanism of failure of the upper bank is not directly fluvial in nature this cycle of bank erosion undermining cantilever failure and fluvial scour of the toe operates over several flood events and has important implications for river engineering channel changes and the movement of sediment through fluvial systems

modeling deep water renewal in lake baikal temperature dissolved oxygen nutrients and chlorofluorocarbon 12 data obtained from lake baikal are used to describe deep water renewal in a deep temperate latitude lake observations are used to propose the physical mechanism governing convection and to formulate a model of deep ventilation the key physical mechanism governing deep water renewal is the so called thermobaric instability because the temperature of maximum density decreases with depth a lake can become conditionally unstable if the base of the cold mixed layer is displaced to a depth at which its temperature matches the local temperature of maximum density thereby resulting in sinking plumes an important consequence of this phenomenon is that deep temperate lakes such as baikal do not completely mix twice yearly instead deep ventilation is episodic a two dimensional model of a wind and buoyancy driven lake shows many strong mixing events and a fairly realistic seasonal cycle indicating that the hypothesis is physically realizable a filling box model is used to deduce the annually averaged fluxes necessary to produce a steady vertical distribution of tracers as observed good fits are obtained to oxygen and chlorofluorocarbon distributions by this model about 50 of the world s liquid freshwater is contained in the large deep lakes located in the temperate latitudes between 45 and 65 n see hutchinson 1957 of fundamental importance to such lakes is their ventilation time the time scale associated with renewal of deep water for it is the deep convection process that most strongly controls the internal redistribution of scalar properties such as dissolved oxygen nutrients and anthropogenic pollutants see wiiest et al 1988 however surprisingly few attempts to study and quantify ventilation in deep

atmospheric noble gases in lake sediment pore water as proxies for environmental change 1 lake sediment pore water has been proposed as a noble gas archive for paleoenvironmental reconstruction but appropriate experimental techniques have not been available until recently here we present noble gas concentrations measured in the sediment pore water of lake issyk kul kyrgyzstan which demonstrate for the first time the value of the sediment pore water archive for paleoclimate reconstruction the noble gas profiles in the sediment indicate that the salinity of the lake water during the mid holocene was more than twice its present value of 6 0 g kg implying a 200 m lower lake level

stability of streambanks formed in partially saturated soils and effects of negative pore water pressures the sieve river italy abstract streambanks of alluvial channels are usually composed of loose materials which are unsaturated in ambient conditions unsaturated soils are subject to negative pore water pressures which cause an apparent cohesion the latter is the main factor in allowing the stability of near vertical banks even during moderate in bank flow events the apparent cohesion can be strongly reduced as the material approaches full saturation therefore during the drawdown phase as the confining pressure of the water in the channel disappears a bank failure is likely to occur channel bed level lowering along the sieve river central italy has caused widespread bank instability a geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils in order to obtain relations between bank angle and height in limit equilibrium conditions a stability chart was obtained with curves for different apparent cohesion values and a stability analysis was performed taking into account the effects of flow events in order to investigate the pore pressure effects a series of piezo tensiometers were installed in a streambank of the sieve river data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall evapotranspiration and water stage variations a planar failure with a tension crack occurred in the upper cohesive part of the bank during december 1996 the safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material safety factor variations through time are therefore shown as a function of seasonal variations in matric suction

a time series of environmental tracer data from deep meromictic lake lugano switzerland an 11 yr 1990 2001 time series of tritium helium 3 3h 3he apparent water ages as well as one sulfur hexafluoride sf6 profile were used to study the development of the vertical mixing dynamics of the deep meromictic northern basin of lake lugano the density stratification of the water column was dominated by an increase in dissolved ions with depth which remained approximately constant during the 1990s the deep water temperature increased steadily during this period passing a threshold above which cooling of the surface water could force convection however increasingly mild winter temperatures prevented the occurrence of a turnover until 2005 the maximum apparent 3h 3he water age increased from about 16 yr in 1990 to 23 yr in 2001 the maximum apparent sf6 age in 2001 was 12 8 yr the large difference between the apparent 3h 3he and sf6 ages is at least partly due to nonlinear effects of mixing causing sf6 ages to underestimate the true mean deep water residence time whereas 3h 3he ages overestimate it the decreasing concentrations of 3h and 3he are more reliable indicators of the continuous deep water exchange in the lake than are the apparent ages budget calculations using the tracer concentrations reveal an annual renewal of the deep water below 100 m in depth by about 8 and enable the calculation of long term mean profiles of the effective vertical turbulent diffusivity kz no trend in the mixing intensity during the 1990s could be determined the radiogenic he flux into the lake is comparable to estimates of the whole crustal degassing flux

vertical turbulent diffusion and upwelling in lake baikal estimated by inverse modeling of transient tracers vertical turbulent diffusion coefficients upwelling velocities and oxygen depletion rates are estimated by inverse modeling of the concentrations of cfc 11 ccl3f cfc 12 ccl2f2 3h 3he and dissolved oxygen for the southern central and northern basin of lake baikal a model is developed that considers two regions in each basin of lake baikal 1 a surface mixed layer sml 400 m thick and 2 a deepwater column dwc below 400 m the smls are assumed to be well mixed in each of the dwcs passive tracers are transported by vertical turbulent diffusion and upwelling upwelling is generated by a depth dependent source of water because of density plumes propagating from the sml downward to larger depths this water is considered to contain the same tracer concentrations as the sml the tracer concentrations in the smls of the three basins are coupled to the atmosphere by gas exchange including water vapor transport and precipitation to the catchment by river inflow and outflow and to the neighboring basins via diffusive exchange and advection smls and dwcs of the same basin are connected by vertical turbulent diffusion density driven water transport and upwelling beginning at the turn of this century the tracers cfc 11 cfc 12 3h and 3he are modeled simultaneously to predict modern concentrations on the basis of the tracer data the vertical diffusion coefficient k is determined to be 4 6 10 4 m2 s 1 10 for the southern 6 3 10 4 m2 s 4 10 for the central and 1 7 10 4 m2 s 4 25 for the northern basin the vertical advective flux of water at 400 m water depth is calculated as 110 km3 yr 1 in the southern 70 km3 yr 1 in the central and 290 km3 yr 1 in the northern basin concentration of dissolved molecular oxygen is modeled by using the estimated transport parameters and by fitting for the unknown consumption rate inverse modeling of oxygen suggests that o2 depletion in the dwc can be described by a volume sink of 44 3 mgo2 m 3 yr 1 combined with an areal sink at the sediment water interface of 17000 3000 mgo2 m 2 yr 1

processes and forms of an unstable alluvial system with resistant cohesive streambeds as a response to channelization projects undertaken near the turn of the 20th century and in the late 1960s upstream reaches and tributaries of the yalobusha river mississippi usa have been rejuvenated by upstream migrating knickpoints sediment and woody vegetation delivered to the channels by mass failure of streambanks has been transported downstream to form a large sediment debris plug where the downstream end of the channelized reach joins an unmodified sinuous reach classification within a model of channel evolution and analysis of thalweg elevations and channel slopes indicates that downstream reaches have equilibrated but that upstream reaches are actively degrading the beds of degrading reaches are characterized by firm cohesive clays of two formations of palaeocene age the erodibility of these clay beds was determined with a jet test device and related to critical shear stresses and erosion rates repeated surveys indicated that knickpoint migration rates in these clays varied from 0 7 to 12 m a 1 and that these rates and migration processes are highly dependent upon the bed substrate resistant clay beds of the porters creek clay formation have restricted advancement of knickpoints in certain reaches and have caused a shift in channel adjustment processes towards bank failures and channel widening channel bank material accounts for at least 85 per cent of the material derived from the channel boundaries of the yalobusha river system strategies to reduce downstream flooding problems while preventing upstream erosion and land loss are being contemplated by action agencies one such proposal involves removal of the sediment debris plug bank stability analyses that account for pore water and confining pressures have been conducted for a range of hydrologic conditions to aid in predicting future channel response if the sediment debris plug is removed to improve downstream drainage care should be taken to provide sufficient time for drainage of groundwater from the channel banks so as not to induce accelerated bank failures published in 2002 john wiley sons ltd

natural cf4 and sf6 on earth the occurrence of cf4 and sf6 in natural fluorites caf2 is reported contents are found to be typically 200 2000 ppt mass for cf4 and 50 100 ppt mass for sf6 cf4 and sf6 were also detected in granites where fluorite is an accessory mineral cf4 and sf6 thus possess a large reservoir in the continental crust that by degassing can sustain natural atmospheric background levels of 40 ppt mole and up to 0 01 ppt mole respectively the article also discusses how natural sf6 may cause interference in hydrological tracer studies

effect of bank stability on geometry of gravel rivers a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel bed channel the new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability the bank stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment cementing by fines and binding of the sediment by root masses the two key parameters in the bank stability analysis are the median grain diameter of the bank sediment d50bank and the modified friction angle of the bank sediment a sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry this is supported by testing the theory on published field data the bank sediment size was assumed to equal the bed sediment size and the variation of the friction angle was investigated the estimated values are seen to increase systematically

correction to vertical turbulent diffusion and upwelling in lake baikal estimated by inverse modeling of transient tracers by f peeters r kipfer m hofer d m imboden and v m domysheva

exceptional mixing events in meromictic lake lugano switzerland italy studied using environmental tracers the deep northern basin of lake lugano was permanently stratified over the last 4 decades because of mineralization in response to strong eutrophication however two consecutive cold and windy winters 2004 2005 and 2005 2006 destabilized the water column and led to two exceptionally strong mixing events the conductivity temperature and depth time series data from 1995 to 2006 allowed the reconstruction of the evolution of the water body that made deep convective mixing possible over the years 1995 2006 the stability of the water column decreased continuously in winter reaching a neutral stability at the end of the study period the schmidt stability values observed in the winters of 2004 2005 and 2005 2006 were virtually zero analyses of helium isotopes tritium sulfur hexafluoride and chlorofluorocarbons in water samples collected immediately after the two mixing events revealed large changes in the tracer concentration profiles and permitted comparisons of the apparent water ages in lake lugano with previous measurements tracer concentration profiles became more homogeneous and approached atmospheric equilibrium concentrations in the time series the tracer data along with changes observed in the physical parameters of the water column demonstrate the considerable deepwater renewal and gas exchange with the atmosphere that has taken place

selective gravel entrainment and the empirical evaluation of flow competence the concept of flow competence is generally employed to evaluate velocities and bed stresses of river floods from the sizes of the largest sediment particles transported for the most part this evaluation has been empirical combining data from a number of separate flood events in different river systems those data are re examined and compared with empirical equations for the selective entrainment of gravel from deposits of mixed sizes it is found that the competence relationships trend counter to those obtained for selective entrainment indicating that the competence evaluations are affected by varying degrees of selective size entrainment individual data sets which have been employed to establish the flow competence relationships either show no trend on their own or yield a trend which runs counter to the competence equation instead being more compatible with the selective entrainment relationships in most instances the empirical competence equations greatly overestimate the hydraulics of flood flows and it is suggested that the better established selective entrainment equations be used for competence evaluations as well empirical equations are available for this purpose relating the dimensionless shields entrainment function or the bed shear stress to the diameter of the largest grain moved and to the median diameter of the deposit as a whole

deep water renewal in lake issyk kul 1 the deep water renewal rates of lake issyk kul are studied using the time dependent anthropogenically produced tracers sulfur hexafluoride sf 6 chlorofluorocarbons cfcs and tritium helium 3 sf 6 and the cfcs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the sf 6 apparent ages based on this model the mean age of the water below 100 m depth is 6 1 yrs the mean oxygen consumption rate for the same depth range is 6 4 mol kg 1 yr 1 and the mean remineralization rates for nitrate phosphate and silicate are 0 53 0 003 and 0 67 mol kg 1 yr 1 respectively

development and testing of riverbank stability analysis the ability to predict the stability of eroding riverbanks is a prerequisite for modeling alluvial channel width adjustments and a requirement for predicting bank erosion rates and sediment yield associated with bank erosion however there are a number of limitations of existing bank stability analyses that limit their physical basis and predictive ability some of these limitations are addressed through the development of a new bank stability analysis the new approach is applicable to steep cohesive nonlayered riverbanks that fail along planar failure surfaces pore water and hydrostatic confining pressure terms are included in the analysis the failure plane is not constrained to pass through the toe of the bank the predictive abilities of four bank stability analyses lohnes and handy 1968 huang 1983 osman and thorne 1988 and the present analysis were assessed using field data the new analysis is the most successful of the tested analyses in terms of predicting the stability of riverbanks wit

susceptibility and triggering scenarios at a regional scale for shallow landslides abstract the work aims at identifying susceptible areas and pluviometric triggering scenarios at a regional scale in calabria italy with reference to shallow landsliding events the proposed methodology follows a statistical approach and uses a database linked to a gis that has been created to support the various steps of spatial data management and manipulation the shallow landslide predisposing factors taken into account are derived from i the 40 m digital terrain model of the region an 15 075 km2 extension ii outcropping lithology iii soils and iv land use more precisely a map of the slopes has been drawn from the digital terrain model two kinds of covers prevalently coarse grained cg cover or fine grained fg cover were identified referring to the geotechnical characteristics of geomaterial covers and to the lithology map soilscapes were drawn from soil maps and finally the land use map was employed without any prior processing subsequently the inventory maps of some shallow landsliding events totaling more than 30 000 instabilities of the past and detected by field surveys and photo aerial restitution were employed to calibrate the relative importance of these predisposing factors the use of single factors first level analysis therefore provides three different susceptibility maps second level analysis however enables better location of areas susceptible to shallow landsliding events by crossing the single susceptibility maps on the basis of the susceptibility map obtained by the second level analysis five different classes of susceptibility to shallow landsliding events have been outlined over the regional territory 8 9 of the regional territory shows very high susceptibility 14 3 high susceptibility 15 moderate susceptibility 3 6 low susceptibility and finally about 58 very low susceptibility finally the maps of two significant shallow landsliding events of the past and their related rainfalls have been utilized to identify the relevant pluviometric triggering scenarios by using 205 daily rainfall series different triggering pluviometric scenarios have been identified with reference to cg and fg covers a value of 365 mm of the total rainfall of the event and or 170 mm d of the rainfall maximum intensity and a value of 325 mm of the total rainfall of the event and or 158 mm d of the rainfall maximum intensity are able to trigger shallow landsliding events for cg and fg covers respectively the results obtained from this study can help administrative authorities to plan future development activities and mitigation measures in shallow landslide prone areas in addition the proposed methodology can be useful in managing emergency situations at a regional scale for shallow landsliding events triggered by intense rainfalls through this approach the susceptibility and the pluviometric triggering scenario maps will be improved by means of finer calibration of the involved factors

a new technique for the automatic monitoring of erosion and deposition rates the rates and processes of erosion and deposition of soils and sediments are subjects of widespread and increasing concern in the earth and environmental sciences process inference from field studies however has been hampered by a lack of information on the precise magnitude frequency and timing of erosional and depositional activity because no automatic monitoring technique has hitherto been available i describe here an automatic photo electronic erosion pin peep system which apparently for the first time allows quasi continuous time series of erosion and deposition data to be collected example results from a river bank site show how the peep system helps to define the true temporal distribution of geomorphological change quantify the erosional impact of individual forcing events and discriminate between competing hypotheses of process control in erosional and depositional contexts the system should thus allow more effective testing of erosion models of high temporal resolution and facilitate a more rigorous linking of catchment sediment output to supply dynamics

distribution of helium and tritium in lake baikal the 3 h 3 he age of a water mass is a measure of the time that has passed since the water mass was last in contact with the atmosphere between 1992 and 1995 a detailed study of 3 h 3 he ages was conducted in lake baikal the deepest and largest lake by volume on earth to investigate deep water renewal in its three major basins maximum 3 h 3 he ages are 14 17 years in the southern basin 16 18 years in the central basin and 10 11 years in the northern basin rates of renewal of deep water with surface water deduced from volume weighted mean 3 h 3 he ages below 250 m depth are about 10 yr 1 in the southern and central basins and 15 yr 1 in the northern basin in the southern basin the mean 3 h 3 he age below 250 m depth increased steadily from 9 6 years in 1992 to 11 years in 1995 indicating a slight diminution in deep water renewal during this time bottom water renewal by large scale advection was estimated from the mass balance of 3 he in the 200 m thick bottom layer of each basin bottom water renewal rates in the northern basin were found to be between 80 and 150 km 3 yr 1 and in the central basin between 10 and 20 km 3 yr 1 whereas in the southern basin they were practically zero correlating oxygen and dissolved helium 4 concentrations with 3 h 3 he age allowed us to determine the mean hypolimnetic oxygen depletion rate in the water column 4 5 mol l 1 yr 1 as well as mean helium fluxes from the lake bottom 2 8 x 10 11 atoms m 2 s 1 in the northern basin and 1 3 x 10 11 atoms m 2 s 1 in the central and southern basins the helium isotope ratio of the terrigenic helium component injected from the lake bottom determined from measurements of water from hydrothermal springs in the vicinity of the lake was found to be 2 2 x 10 7

the nature of the meteoritic components of apollo 16 soil as inferred from correlations of iron cobalt iridium and gold with nickel concentrations of co ni ir and au in small samples of submature and mature soil from apollo 16 are highly variable correlations of fe co ir and au with ni indicate that the variation in siderophile element concentrations results from variation in the concentration of fe ni metal from these correlations the mean composition of the metal is inferred to be 5 6 ni and 0 36 co for a ni co ratio of 15 5 0 7 i e dissimilar to the chondritic ratio of 20 21 the fe ni metal is also characterized by low ir ni and ir au ratios compared to metal in ordinary chondrites metal with a similar composition is also found in metal rich noritic impact melt breccias that occur as discrete rocks as well as small clasts in ancient regolith breccias at apollo 16 mass balance models using lithophile element concentrations indicate that about 35 of the soil is noritic impact melt the fe ni metal associated with this component is sufficient to supply virtually all the ancient fe ni metal found in the typical apollo 16 soil 0 4 0 5 i e no other source is required the soil also contains 1 2 carbonaceous chondrite the concentration of this component appears to be relatively constant from sample to sample and does not contribute significantly to the variation in siderophile element abundances these two meteoritic components contribute nearly equal concentrations of ni to the typical apollo 16 soil

apparent loss of cfc 113 in the upper ocean we report and evaluate data of the chlorofluorocarbon cfc 113 in comparison with concurrent data for cfc 12 from cruises into the temperate north atlantic the tropical western pacific the eastern mediterranean and the weddell sea we consistently find cfc 113 deficiencies in the warmer upper waters which we interpret as cfc 113 depletion at rates of the order of 3 per year with possibly accelerated rates in the mixed layer or near the surface these results severely limit a tracer utility of cfc 113 in the warm upper waters of the ocean tracer applications in the deep waters of the ocean should be much less affected since cfc 113 loss in such waters appears to be far slower this also holds for the eastern mediterranean despite its rather warm deep waters for the weddell sea the data indicate a cfc 113 deficiency 20 in the shelf waters which converts into a similar deficiency in newly formed deep and bottom water such cfc 113 deficiency has to be accounted for in southern ocean tracer work future work is proposed to study cfc 113 loss in the ocean in additional detail and to elucidate the loss mechanism s on which our data give little clue

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

physical and chemical properties of the waters of saline lakes and their importance for deep water renewal lake issyk kul kyrgyzstan the relationships between electrical conductivity temperature salinity and density are studied for brackish lake issyk kul these studies are based on a newly determined major ion composition which for the open lake shows a mean absolute salinity of 6 06 g kg 1 the conductivity temperature relationship of the lake water was determined experimentally showing that the lake water is about 1 25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water based on these results an algorithm is presented to calculate salinity from in situ conductivity measurements applied to the field data this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores the algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20 c and 1 atm lake issyk kul water is about 530 g m 3 denser than seawater at the same salinity the temperature of maximum density at 1 atm is about 0 15 c lower than that for seawater diluted to the same salinity despite its small variations salinity plays an important role together with temperature changes in the static stability and in the production of deep water in this lake changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time uncharged silicic acid is negligible for the stability of the water column except near an 15 m thick nepheloid layer observed at the bottom of the deep basin copyright 2002 elsevier science ltd

third international symposium on stratified flows the third international symposium on stratified flows was convened on february 3 5 1987 in pasadena california one hundred and seventy six engineers and scientists representing 14 countries attended and presented papers on internal waves and their stability blocking and intrusion topographic effects rotating stratified flows turbulent stratified shear flows mixed layer dynamics and convection frontal phenomena and gravity currents plumes and thermals new results were also presented on direct numerical solution of the navier stokes equations this report provides a brief summary of the meeting presentations and comments upon the implications for the civil engineering profession

pore water pressure and streambank stability results from a monitoring site on the sieve river italy to investigate the role of pore water pressures in the stability of a streambank a series of tensiometers and piezometers was installed in a bank of the sieve river tuscany italy fluvial entrainment at the bank toe was monitored by repeated cross profiling erosion pins and marked pebbles fluctuations in matric suction measured at the tensiometers reflected the overall response of pore water pressures to rainfall evapotranspiration rising and drawdown of the river stage and variations in water table an expression was derived for the safety factor with respect to mass movement of the upper bank incorporating the failure criterion for unsaturated soils and the normal mohr coulomb criterion for saturated conditions variations in matric suction have important effects on the stability of the streambank during low flow periods the shear strength term due to the matric suction allows the bank to remain stable at a steep angle however during rainfall and flow events reduction in matric suction and increase in unit weight of the material from vertical and lateral infiltration may be sufficient to trigger a mass failure without development of significant positive pore water pressures during the rising limb of high flow events the factor of safety increases as a consequence of the stabilizing confining pressure of the water in the river despite a reduction in matric suction during drawdown in the river when the suction values are still low and the confining pressure in the river decreases to zero the factor of safety falls to lower values than those experienced prior to the runoff event measurements of fluvial entrainment reveal that although the processes mechanisms and the frequency of retreat of basal and upper bank zones differ significantly the amount of retreat at the bank toe due to fluvial erosion is comparable to that of the upper portion of the bank due to mass failure copyright 1999 john wiley sons ltd

transit time distributions in lake issyk kul 1 measurements of sulfur hexafluoride sf6 and chlorofluorocarbons cfcs are used to constrain the timescales for deep water renewal in lake issyk kul as these tracers have different tropospheric histories their combination provides more transport information than one tracer alone in particular from these measurements the mean and standard deviation of the distributions of transit times since water made last contact with the surface can be tightly constrained is older than the age determined from sf6 and younger than the ages from the cfcs and increases from around 4 yrs at 200 m to around 10 5 yrs at the deepest location 655 m also increases with depth and equals around 0 7 to 0 8 which corresponds to large ranges of transit times and implies mixing processes play a major role in the transport the approach used can also be applied to similar tracer measurements in the oceans and groundwaters to constrain transport in these geophysical systems

riverbank stability analysis i theory in this paper a slope stability analysis for steep banks is used in conjunction with a method to calculate lateral erosion distance to predict bank stability response to lateral erosion or bed degradation the failure plane angle failure block width and volume of failed material per unit channel length may be calculated for the critical case these parameters define the bank geometry following failure and form the starting point for subsequent analyses the calculation procedure is illustrated by a worked example following mass failure slump debris accumulates at the bank toe the debris is removed by lateral erosion prior to further oversteepening or degradation generating further mass failures any process based model for channel width adjustment must account for the combined effects of lateral erosion and mass instability in producing bank instability the approach adopted here represents a marked improvement over earlier work which does not account for changes in bank geometry due to lateral er