strontium isotopes and rare earth elements as tracers of groundwater lake water interactions lake naivasha kenya abstract strontium isotope compositions and rare earth element ree concentrations are presented for groundwater and surface water samples collected from the lake naivasha watershed in the east african rift kenya the chief objective of the study is to test the suitability of rees in conjunction with sr isotopes as tools for investigating groundwater lake water interactions in general the ree concentrations and 87 sr 86 sr ratios support the authors earlier investigations where cl mass balance 18 o d and he isotopes were employed to study groundwater lake water interactions in the naivasha watershed the ree data suggest that a significant amount of the groundwater south of lake naivasha i e 50 85 consists of lake water recharge to the aquifer system specifically mixing calculations conducted using ree data of lake naivasha water and groundwaters indicate that between 70 and 85 of groundwater directly south of the lake is likely lake water these values are somewhat higher than the authors previous estimates determined with conservative stable h isotopes d 50 70 for both cases however the data demonstrate that water originating in lake naivasha contributes significantly to the underlying groundwater flow system hence supporting earlier evidence that the lake s freshness reflects rapid loss of water and dissolved solutes to the local groundwater system overall lake and groundwater sr isotope compositions support seepage of lake water into the underlying aquifer along the lake s south shore the 87 sr 86 sr data also provide additional insight into the geochemical evolution of waters of the lake naivasha watershed indicating that the initial source of sr to these waters is likely chemical weathering reactions involving basaltic rocks within the recharge zones of the watershed along the rift valley flanks furthermore with increasing residence time of groundwaters within the aquifer system and flow down and along the rift valley floor sr isotope compositions of groundwaters become more radiogenic reflecting rock water interactions with chemically differentiated and radiogenic peralkaline rhyolite volcanic rocks the importance of the longer aquifer residence times and radiogenic source rocks is especially apparent for geothermal waters of the olkaria geothermal field that have 87 sr 86 sr ratios i e 0 70747 similar to local comendites

chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

persistence in intra annual snow depth distribution 1 measurements and topographic control 1 terrestrial and airborne laser scanning tls and als techniques have only recently developed to the point where they allow wide area measurements of snow distribution in varying terrain in this paper we present multiple tls measurements showing the snow depth development for a series of precipitation events we observe that the pattern of maximum accumulation is similar for the two years presented here correlation up to r 0 97 storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms based on the strong link between accumulation patterns and terrain we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns this approach of winstral et al 2002 which describes wind exposure and shelter was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance furthermore a high sensitivity to the local wind direction was demonstrated we suggest that winstral et al s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

the major ion composition of silurian seawater one hundred fluid inclusions in silurian marine halite were analyzed in order to determine the major ion composition of silurian seawater the samples analyzed were from three formations in the late silurian michigan basin the a 1 a 2 and b evaporites of the salina group and one formation in the early silurian canning basin australia the mallowa salt of the carribuddy group the results indicate that the major ion composition of silurian seawater was not the same as present day seawater the silurian ocean had lower concentrations of mg2 na and so42 and much higher concentrations of ca2 relative to the ocean s present day composition furthermore silurian seawater had ca2 in excess of so42 evaporation of silurian seawater of the composition determined in this study produces kcl type potash minerals that lack the mgso4 type late stage salts formed during the evaporation of present day seawater the relatively low na concentrations in silurian seawater support the hypothesis that oscillations in the major ion composition of the oceans are primarily controlled by changes in the flux of mid ocean ridge brine and riverine inputs and not global or basin scale seawater driven dolomitization the mg2 ca2 ratio of silurian seawater was 1 4 and the k ca2 ratio was 0 3 both of which differ from the present day counterparts of 5 and 1 respectively seawaters with mg2 ca2 2 e g modern seawater facilitate the precipitation of aragonite and high magnesian calcite therefore the early paleozoic calcite seas were likely due to the low mg2 ca2 ratio of seawater not the pco2 of the silurian atmosphere

transport of soluble salts in a large semiarid basin river murray australia median annual concentrations of cl so4 hco3 na k mg and ca increase greatly downstream in the river murray along its 2500 km route to the sea chloride increases from less than 2 mg l 1 near the headwaters to about 170 mg l 1 near the downstream end of the main channel water near the head of the river has hco3 balanced by similar equivalents of na ca and mg while higher salinity water in the downstream half of the river is dominated by na and cl sources of these dissolved ions include a sea derived airborne salts contributing essentially all of the cl br and 80 of the na and b rock derived ions from weathering of sedimentary rock and soil minerals contributing most of the observed hco3 80 of the ca and 20 25 of the mg and so4 much of the change in chemistry along the axis of the murray is due to influx of saline groundwater which has a major ion composition similar to sea water inflows of irrigation drainage water also enhance downstream transport of salts especially hco3 the stable isotope composition of the river murray 2h and 18o begins with relatively depleted heavy isotope abundances 47 8 in the uplands of the southeastern margin of the murray darling basin increasing steadily by 30 and 6 respectively due to evaporative enrichment from river surfaces and influx of drainage returned from irrigation diversions despite the similarity of groundwater major ion chemistry to that of sea water stable isotope compositions of groundwaters clearly demonstrate that water molecules from past marine incursions have been completely flushed from the system similarly the cl br ratios of groundwaters are not appreciably different from seawater values indicating that dissolution of fossil evaporites does not contribute significant salt to the groundwaters or the river

simulation of the net snow accumulation along the wilkes land transect antarctica with a regional climate model regional climate modelling in conjunction with accumulation measurements collected on antarctic traverses of the international trans antarctic scientific expedition itase is presented as a tool for extending the spatial coverage of field measurements the modelling of part of east antarctica spanned the 7 year epoch 1980 86 where data covering the same period are available the agreement between simulation and observation is improved when a parameterization of the snow surface redistribution processes such as wind erosion is included in the regional climate model the modelled spatial distribution of the net snow mass transported in the boundary layer over coastal east antarctica indicates that this mass is a significant component of the surface mass balance

adaptation of the near surface wind to the development of sand transport a model of wind blown sand transport is described with particular emphasis on the feedback between the grain cloud and the near surface wind the results from this model are used to develop owen s 1964 hypothesis that the grain layer behaves so far as the flow outside it is concerned as increased aerodynamic roughness whose height is proportional to the thickness of the layer the hypothesis is developed to show the influence this dynamic roughness has on the turbulent boundary layer above the saltation layer two processes are identified which influence the path of the system towards equilibrium the first is the feedback between the near surface wind and the grain cloud in which the quantity of sand transported is limited by the carrying capacity of the wind the second is due to the temporal development of an internal boundary layer in response to the additional roughness imposed on the flow above the grain layer by the grain cloud a similarity is noted between the temporal response of a turbulent boundary layer to sand transport and the spatial response of a turbulent boundary layer downstream of a step increase in surface roughness finally it is noted that the work may have important implications for transport rate prediction in unsteady winds

the impact process in aeolian saltation two dimensional simulations a critical event in the trajectory of a sand grain saltating in air is its interaction with the surface we examine the phenomenon of grain bed impacts in two dimensions using a combination of dynamical computer simulations analytical models and physical reasoning the results indicate that the grain bed collisions can be treated as two body collisions with the bed particle assuming an effective mass greater than its true mass also the presence of geometrical surface irregularities has a strong bearing on the interaction between saltating and surface grain populations as well as on the formation of small scale bedforms

fine scale modeling of the boundary layer wind field over steep topography 1 this paper describes the adaptation of wind fields to steep and complex terrain using fine scale numerical modeling the work is motivated by the need of high resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes applying the nonhydrostatic and compressible atmospheric prediction model advanced regional prediction system arps to steep alpine topography the boundary layer flow was simulated and evaluated against measurements the adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated the topography used in our study has a length scale of 500 m a typical height of 150 m and maximum slopes of 45 numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration this analysis indicates that a high resolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small scale flow features such as speed up separation and recirculation the onset of flow separation is highly sensitive to initial and boundary conditions slope angle and surface roughness the results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced the simulated wind fields have been used to drive a numerical three dimensional snow drift model which is presented in a companion paper by lehning et al 2008

the last phase of the storegga slide simulation of retrogressive slide dynamics and comparison with slide scar morphology the prehistoric storegga slide one of the world largest known submarine slides took place about 8200 years ago most likely the slide was triggered by an earthquake in a steeper slope area in the distal part of the slide the present day s morphology of the slide area indicates that major parts of the slide took place as a sequential failure process spreading successively from the far end to the present shelf edge numerical simulations illustrating this retrogressive back stepping behaviour are presented for the last phase of the storegga slide as it reached today s upper headwall the applied rheological model is based on a bingham fluid with a history dependent yield strength and consistency

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

assessment of river flow with significant lateral inflow through reverse routing modeling the discharge hydrograph estimation in rivers based on reverse routing modeling and using only water level data at two gauged sections is here extended to the most general case of significant lateral flow contribution without needing to deploy rainfall runoff procedures the proposed methodology solves the saint venant equations in diffusive form also involving the lateral contribution using an head driven modeling approach where lateral inflow is assumed to be function of the water level at the tributary junction the procedure allows to assess the discharge hydrograph at ends of a selected river reach with significant lateral inflow starting from the stage recorded there and without needing rainfall data specifically the mast 1d hydraulic model is applied to solve the diffusive wave equation using the observed stage hydrograph at the upstream section as upstream boundary condition the other required data are 1 the observed stage hydrograph at the downstream section as benchmark for the parameter calibration 2 the bathymetry of the river reach from the upstream section to a short distance after the downstream gauged section the method is validated with different flood events observed in two river reaches with a significant intermediate basin where reliable rating curves were available selected along the tiber river in central italy and the alzette river in luxembourg very good performance indices are found for the computed discharge hydrographs at both the channel ends and along the tributaries the mean nash sutcliffe value nsq at the channel ends of two rivers is found equal to 0 99 and 0 86 for the upstream and downstream sites respectively the procedure is also validated on a longer stretch of the tiber river including three tributaries for which appreciable results are obtained in terms of nsq for the computed discharge hydrographs at both the channel ends for three investigated flood events

stable isotopic and geochemical characteristics of groundwater in kherlen river basin a semi arid region in eastern mongolia summary inorganic solute ion concentrations and stable isotopes of oxygen and hydrogen in groundwater river water and precipitation were investigated to gain insight into the groundwater recharge process in the kherlen river basin a semi arid region in eastern mongolia the solute constituents in the river water main stream were of ca hco3 type spatially invariant and low in concentration groundwater in the upstream region was also characterized by a ca hco3 type though all ion concentrations were higher than in the river water on the other hand the chemical composition of the groundwater in the midstream region southern and eastern was spatially variable and the na mg2 cl and hco 3 concentrations were considerably higher than in the river water and upstream groundwater the stable isotopic compositions showed an evaporation effect on the groundwater and river water as well as an altitude effect in the precipitation and river water preferential recharge by relatively large rainfall events is thought to have caused the depleted isotopic ratio in the groundwater in the dry regions the stable isotope chemical and hydrological data suggest that the main stream water of the kherlen river is recharged by precipitation that falls in a headwater region at an altitude of more than 1650 m and that the interaction between the groundwater and river water is not dominant in the midstream and downstream regions of the river basin

geochemistry of the upper han river basin china 3 anthropogenic inputs and chemical weathering to the dissolved load abstract the study focuses on the chemical and trace element compositions of the dissolved load in the upper han river the water source area of the middle route of china s south to north water transfer project water samples were collected in the high flow period and analyzed for cations by inductively coupled plasma atomic emission spectrometer and anions by ionic chromatography respectively in order to understand the contributions of anthropogenic activities and rock weathering to river solutes as well as the associated co2 consumption in the carbonate dominated basin the river waters have a mean tz of 2674 eq l ranging from 1034 3 to 4611 6 eq l which is significantly higher than that of the global river waters calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major species in the basin there are three major reservoirs carbonates silicates and agriculture urban effluents contributing to the dissolved load in the river chemical weathering rate is approximately 53 1 t km2 yr with respective carbonate and silicate weathering rates of 47 5 t km2 yr 19 8 mm kyr and 5 6 t km2 yr 2 1 mm kyr the co2 consumption is estimated to be 64 69 109 mol yr and 9 69 109 mol yr by carbonate and silicate weathering respectively the contribution of the anthropogenic inputs to the dissolved load is estimated to be 16 7 demonstrating the strong impacts of human activities on water chemistry

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

estimation of the electrostatic charge of individual blowing snow particles by wind tunnel experiment there are some reports on the measurement of the charge to mass ratio of blowing snow particles but there are few studies concerned with individual snow particle charge we measured the charge to mass ratios using snow particles selected according to size and discussed individual charges experiments were conducted in a cryogenic wind tunnel charge to mass ratios measured in our experiment were all negative and their absolute values tended to increase with a decrease in particle diameter individual snow particle charges were calculated from the average of particle diameter distributions the charges were all approximated by the power function of diameter at each temperature assuming that the coefficient of these approximations is a function of air temperature we could easily predict the individual snow particle charge

the influence of drought and anthropogenic effects on groundwater levels in orissa india summary investigating the response of groundwater levels to the extreme weather events provides essential information for sustainable planning and management of water resources the aim of this study was to identify and quantify the groundwater level trend of the state orissa india to understand the forcing mechanism of droughts in conjunction with the anthropogenic pressure using the non parametric mann kendall statistical procedure the pre and post monsoon groundwater level records of 1002 monitoring stations during the period 1994 2003 were analyzed the results show that the drawdowns due to deficient rainfall during dry years high temperatures and anthropogenic pressure have not been recovered through the recharge in wet years however this study does not determine whether drought high temperatures or anthropogenic effects have had largest influence on the groundwater levels decline the cases of significant water table declines are higher in number than those expected to occur by chance in the pre monsoon season 59 of the monitoring stations experienced groundwater declines as against 51 in the post monsoon season for the study area as a whole this could be interpreted that the fluctuation is not a part of noise but that a signal is being identified further the trend result showed wide spatial and seasonal differences irrespective of seasons the consolidated rock formation that covers 80 of the geographical area experienced significant water table decline however the semi consolidated and unconsolidated formations experienced water table decline in the pre monsoon summer season only the vulnerable sites where the groundwater level declined significantly were identified so that recharge measures could be taken up

stable isotopes as an indicator of evaporation in the river murray australia the stable isotope composition of water d and 18o and chloride concentrations were measured monthly at 26 stations along the river murray australia and several major tributaries from december 1988 to june 1989 the first four months had low natural runoff plus large irrigation diversions from storage reservoirs the following three months had much higher up to a factor of 5 river discharge deuterium and oxygen 18 compositions had a maximum range of 50 and 9 respectively from headwaters to mouth chloride concentrations increased downstream with a maximum range from 1 to 180 10 3 kg m 3 these trends can be attributed to 1 evaporation from storage facilities and river channels 2 inflows of irrigation drainage water enriched in heavy isotopes and 3 inflows of saline groundwater water losses by evaporation from the river surface and irrigation areas amounted to about 40 15 of releases from reservoir storage based on the integrated enrichment of deuterium which is comparable to the total transpiration flux within the basin about half of the chloride acquired by the murray as it traversed the middle third of the basin during summer months appears to have resulted from return flows of irrigation drainage water

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

major element chemistry of the changjiang yangtze river the chemistry of major elements ca mg na k hco3 so4 cl and si in the river water of the changjiang yangtze river was studied based on continuously monitored data at 191 stations in the drainage basin for the period 1958 1990 the results show that the total dissolved solid tds concentration of the changjiang varies over an order of magnitude throughout the basin 49 7 518 1 mg l with a medium tds concentration of 205 9 mg l about three times the global average in contrast the tds at a given main channel station varies only slightly in different seasons with a variation factor less than 2 0 despite a substantial water dilution in the summer flood season the major element chemistry of the changjiang is mainly controlled by rock weathering with the anion hco3 and the cation ca dominating the major ion composition due to the abundance of carbonate rocks in the basin a persistently increasing trend has been observed in the concentrations of so4 and to a lesser extent cl in the changjiang a signature of considerable anthropogenic impacts e g acid deposition flux calculations at datong the most downstream main channel station without tidal influence indicate that the changjiang transports ca 154 106 tons year of tds to the sea second only to the amazon in the world

measurements and one dimensional model calculations of snow transport over a mountain ridge wind transport of snow can cause an additional snow load on leeward slopes which often has a considerable influence on avalanche danger for a quantitative assessment of this process a model is proposed which calculates the snow transport over a two dimensional mountain ridge based on input measurements of wind speed and precipitation since the topography is idealized the model is focused on the snow mass that is transported over the ridge and no statements are made about the exact snow distribution over the slopes three transport modes are distinguished snow transport in saltation snow transport in suspension and preferential deposition of precipitation suspension is modelled with a one dimensional diffusion equation and for the saltation layer a newly developed model based on the microscale physical processes is implemented the effect of speed up of the wind over the ridge is included by assuming an analytical wind profile with a maximum wind speed at a few meters above the ridge advective effects are taken into account in a parameterization of the turbulent shear stress profile the model is compared with measurements taken at the experimental snowdrift site gaudergrat in the parsenn area switzerland and good agreement is obtained between calculated and measured results

saltating particles over flat beds measurements of ejection and impact velocities trajectory lengths and maximum rise heights of sand grains median diameters 118 and 188 m in saltation over a flat sand bed in a wind tunnel have been obtained from the digitization of multiple image photo graphs the mean angle of ejection is found to be about 30 o from the horizontal rather than 90 o with mean vertical ejection velocity of about 2u where u is the friction velocity trajectories of saltating grains have been computed using the measurements of the initial ejection velocities and the mean velocity profile of the air flow

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

grain size dependence of eolian saltation lengths during snow drifting eolian saltation a primary process in the transport of fine granular material by wind produces a variety of geophysical effects on earth and other planetary surfaces wind tunnel experiments were carried out to investigate the dependence of saltation on grain size the saltation length of snow particles was estimated at size intervals of 0 05 mm in diameter by measuring local vertical mass fluxes in 17 snow collectors arrayed at the lee end of the snow surface the measured mean saltation length of snow particles of 0 01 1 mm in diameter ranged from 0 1 to 1 0 m at wind velocities of 5 10 m s mean saltation length decreased with increasing diameter and decreasing wind speed we suggest that the probability of the saltation length of a particle at each diameter is described by a monotonically decreasing distribution function that is the shorter the saltation length the higher the frequency of its occurrence one ramification of this distribution is that the mean saltation length does not imply the dominance of saltating particles of this length

wind blown flux rates derived from drifts at arctic snow fences historically there has been considerable interest in establishing the relationship between wind blown snow flux q and wind speed by monitoring the drift growth at snow fences in arctic alaska during three winters we computed q for 36 distinct transport events each fence was instrumented with depth sounders to measure deposition rates the majority of events 31 occurred between november and february despite winter extending from october to june on average five substantial snow deposition events sdes occurred at each fence per winter the mean flux during sdes was 0 16 0 19 and 0 29 kg s 1 m 1 at barrow imnavait creek and franklin bluffs respectively the differences in q explained by the different wind regimes at the three sites to place these flux measurements in perspective we reviewed all previous experimental values of q with special attention to height and time over which the fluxes were measured the new data help fill a range of wind speeds 12 18 m s 1 where prior results have been sparse combined the full data define a diffuse cloud best represented by upper and lower bounding equations q u 1 3 10 3 w 2 5 and q l 3 3 10 9 w 6 5 where w is wind speed 5 m s 1 we suggest that these bounds rather than a single equation provide the best way to estimate snow fluxes

a muskingum based methodology for river discharge estimation and rating curve development under significant lateral inflow conditions abstract quite often the discharge at a site is estimated using the rating curve developed for that site and its development requires river flow measurements which are costly tedious and dangerous during severe floods to circumvent the conventional rating curve development approach perumal et al in 2007 and 2010 applied the variable parameter muskingum stage hydrograph vpms routing method for developing stage discharge relationships especially at those ungauged river sites where stage measurements and details of section geometry are available but discharge measurements are not made the vpms method enables to estimate rating curves at ungauged river sites with acceptable accuracy but the application of the method is subjected to the limitation of negligible presence of lateral flow within the routing reach to overcome this limitation this study proposes an extension of the vpms method henceforth known herein as the vpms l in method for enabling the streamflow assessment even when significant lateral inflow occurs along the river reach considered for routing the lateral inflow is estimated through the continuity equation expressed in the characteristic form as advocated by barbetta et al in 2012 the vpms l in is tested on two rivers characterized by different geometric and hydraulic properties 1 a 50 km reach of the tiber river in central italy and 2 a 73 km reach of the godavari river in the peninsular india the study demonstrates that both the upstream and downstream discharge hydrographs are well reproduced with a root mean square error equal on average to about 35 and 1700 m 3 s 1 for the tiber river and the godavari river case studies respectively moreover simulation studies carried out on a river stretch of the tiber river using the one dimensional hydraulic model mike11 and the vpms l in models demonstrate the accuracy of the vmps l in model which besides enabling the estimation of streamflow also enables the estimation of reach averaged optimal roughness coefficients for the considered routing events

two dimensional numerical modelling of surface wind velocity and associated snowdrift effects over complex mountainous topography a new experimental software for blowing snow sytron2 is pre sented it takes advantage of the previous limited realization sytron1andof the entire real time operational environment of the automatic chain safran crocus mepra scm it runs presently on a rectangular grid with a mesh size of about 45m covering an area of 3 0 3 0km 2 around the observation test site col du lac blanc french alps 2700m a s l near the alpe d huez ski resort sytron2 is initialized with a realistic snowpack representation derived fromthe scmoutputs andcoupledto awind fieldcom puted by the new samver model the final aim is to build a fully embedded tool sui table for representing snowdrift effects with a better resolution at different specific locations the different tools and operators used are described as well as the field valida tion processes which are based on remote identification of the eroded and accumulated areas using digital pictures

chemical mixing model of streamflow generation at la selva biological station costa rica abstract la selva biological station occupies an area of lowland tropical rainforest in central costa rica sodium and chloride data were used to quantify the mixing proportions of local runoff and geothermal groundwater at several sites throughout the stream channel system in late april at the end of the dry season the fraction of streamflow accounted for by geothermal groundwater varied spatially between 0 and 0 85 indicating a significant contribution to streamflow and to stream solute loads from geothermal groundwater at some sites in general higher inputs of geothermal groundwater were found at lower elevations over half the flow from one basin the salto was due to geothermal groundwater suggesting a minimum annual runoff of about 0 7 m of geothermal groundwater from this basin a plot of na cl vs fraction of geothermal groundwater revealed watershed scale chemical differences between the two major drainage systems the sura and the salto differences that were not apparent from a traditional two solute plot of cl vs na concentration a small 21 mm storm produced relatively little change in mixing proportions as most throughfall was apparently retained in the relatively dry soils

recharge mechanisms and geochemical processes in a semi arid sedimentary basin eastern cape south africa abstract stable isotope 18 o and 2 h and geochemical signatures are used to gain some insight into recharge processes and groundwater salinization mechanisms in a semi arid rangeland catchment the 665 km 2 catchment is underlain by fractured lower beaufort sandstones and mudstones and is intruded by several dolerite dykes chloride and isotopic relationships suggest that chloride ions in ground water are of meteoric origin the hypothesized recharge and salinization mechanism is that large storm events periodically dissolve accumulated surficial meteoric salts and after a period of evaporative enrichment at or near the soil surface leach them into the ground water geochemical variations imply that spatial differences exist in recharge volumes in evaporative enrichment or in the extent of leaching of surficial salts meteoric sodium chloride contributes greater than 90 of the dissolved sodium except at low salinities where cation exchange processes yield additional sodium inputs in exchange for dissolved calcium and magnesium at high salinities this process reverses and sodium is adsorbed releasing calcium and magnesium this process accounts for up to 40 of the dissolved calcium and magnesium contributions from geochemical weathering are relatively uniform in spite of highly variable salinities which implies that residence times are also relatively uniform

geochemistry of the dissolved load of the changjiang basin rivers anthropogenic impacts and chemical weathering abstract this study focuses on the chemical and sr isotopic compositions of the dissolved load of the rivers of the changjiang basin one of the largest riverine systems in the world water samples were collected in august 2006 from the main tributaries and the main changjiang channel the chemical and isotopic analyses indicated that four major reservoirs carbonates silicates evaporites and agriculture urban effluents contribute to the total dissolved solutes the overall chemical weathering carbonate and silicate rate for the changjiang is approximately 40 ton km2 year or 19 mm kyr similar to that of the ganges brahmaputra system and the basin is characterized by carbonate and silicate weathering rates ranging from 17 to 56 ton km2 year and from 0 7 to 7 1 ton km2 year respectively in the lower reach of the changjiang main channel the weathering rates are estimated to be 36 and 2 2 ton km2 year for carbonates and silicates respectively it appears that sulphuric acid may dominate chemical weathering reactions for some sub basins the budgets of co2 consumption are estimated to be 646 109 and 191 109 mol year by carbonate and silicate weathering respectively the contribution of the anthropogenic inputs to the cationic tds of the changjiang is estimated to be 15 20 for the most downstream stations our study suggested that the changjiang is strongly impacted by human activities and is very sensitive to the change of land use

hydrogeochemical characteristics of central jianghan plain china the central jianghan plain is the semi closed basin in the middle reaches of yangtze river a total of 78 water samples targeting groundwater were collected from 75 sites in this study site the area between yangtze river and han river including rivers and lakes for temperature ph electrical conductivity ec total dissolved solids tds and ion composition measurements correlation matrix was used to assess the geochemical and anthropogenic processes the most confined groundwater was grouped into hco3 ca mg while phreatic groundwater and surface water had a more diversified hydrochemistry the spatial variation in overall water quality as well as comparison with who world health organization standards for drinking water is illustrated mn as and no3 concentrations were found to exceed the allowable limits for drinking water of who guidelines and they also show remarkable spatial variations abnormally high nitrate concentration up to 150 190 mg l was found only in phreatic groundwater which suggested that the nitrate pollution might be caused by agricultural activities the present study may be helpful in further studies concerning water quality issues in this area where groundwater is a vital source for drinking and other activities

numerical modeling of blowing and drifting snow in alpine terrain in mountainous regions snow transport due to wind significantly influences snow distribution and as a result avalanche danger a physically based numerical two layer model is developed to simulate blowing and drifting snow in alpine terrain one layer describes the driving wind field and the transport in suspension the description is based on the atmospheric boundary layer equations using an e model for the turbulent closure the second layer describes the transport due to saltation including erosion and deposition of snow here conservation equations for mass and momentum are formulated for the mixture of snow and air particle trajectory calculations are used to parameterize quantities characterizing the saltation layer both layers are mutually coupled by boundary conditions a two way coupling between particles and airflow is taken into account comparisons between simulation results and field measurements around an alpine crest show encouraging results

wind tunnel experiments on blowing snow blowing snow was produced artificially in a cold wind tunnel and various measurements were conducted including particle diameters concentrations saltation lengths heat transport and electric charge the mean diameter of blowing snow particles decreased only slightly with increasing height in the saltation layer standard deviation was large and velocities were scattered in a wide range suggesting the complex dynamic process on taking off the mean saltation length ranged from a few cm to 40 cm increasing with wind velocity

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

hydrochemical characteristic and interaction process of surface and groundwater in mid lower reach of hanjiang river china hanjiang river the largest tributary of yangtze faces environmental pressures from south to north water transfer project and anthropogenic influences in order to reveal the chemical characteristics of river and contribution of groundwater to the river along mid lower reaches of hanjiang river field works have been conducted in wet and dry seasons the major ion compositions are characterized by the dominance of ca2 and hco3 in surface water and groundwater as a result calcite weathering is a dominant process for surface water and groundwater additionally dolomite weathering also contributes to hydrochemical evolution in the groundwater of the basin stable isotopes 18o d show that both surface and groundwater most probably originate from present day precipitation isotopic of both surface water and groundwater can provide greater confidence in identifying the weathering and extent of interaction processes it was found that river water was mainly recharged by tributaries in wet season while recharged by groundwater in dry season dissolved solute flux from tributaries and groundwater to the river was estimated by water balance budget model and environmental tracer mass balance approach tributaries and groundwater contribute to mid lower reach of hanjiang river in wet season and dry season respectively from section h1 to h9 there were 455 4 kg s of total dissolved solute tds transferred from tributaries to the main channel and 99 8 kg s of tds fluxed from groundwater to river water in dry season

chemical and physical weathering in the min jiang a headwater tributary of the yangtze river abstract the min jiang is a major headwater tributary of the yangtze chang jiang its source is in the undeveloped eastern tibetan plateau but it flows through the heavily populated sichuan four rivers basin on its way to join the yangtze main channel the dissolved major element composition was determined in the tibetan headwaters at the rising stage and at four hydrologic stations in a monthly time series the min jiang is alkaline and has high dissolved load compared to other world rivers carbonate weathering dominates especially in the source region of the min jiang main channel and silicate weathering and evaporite dissolution gain some importance in the dadu he tributary the si na k ratios of the dissolved load and the clay mineralogy of the bed material suggest that silicate weathering in the watershed is superficial i e soluble cations are being preferentially leached many major elements show lower concentrations at high summer discharge but there is also additional input such that the concentration discharge relationship is not purely a result of dilution the discharge weighted total dissolved solid tds flux based on data from the three upstream monitoring stations is 10 10 6 tons year 6 of the yangtze at mouth and the chemical denudation rate as measured by tds yield is 115 tons km 2 year for the min jiang higher than the average yangtze basin 85 tons km 2 year the common extrapolation using annual average discharge and spot sampling of dissolved and suspended material during rising or falling stage can reasonably estimate chemical fluxes to 20 but seriously underestimate the physical flux sampling the peak flash flow is critical for the suspended particulate material concentrations of so 4 cl and ca are significantly elevated as the river debouches onto the populated sichuan basin

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

distribution of snow drifts on ridge slopes measurements and theoretical approximations during several winters the positions and magnitudes of excess snow deposits or denudation zones caused by wind have been evaluated on the flanks of regular elongated mountain ridges the surveys were carried out by conventional measurements of mass balance according to angle of slope 10 to 35 shape of crest hump or wedge shaped and orientation to the wind various patterns of snow deposition may be found it is shown that on ridges oriented perpendicularly to the main wind direction north west during snow storms near periodic snow deposits may be expected on the lee slope on the windward side there is a denudation zone near the crest the measurements indicate that lee slopes of mean slope angle are buried in mid winter under twice as much snow as the adjacent windward slopes however the ridge system as a whole accumulates the same amounts of snow as do areas of flat terrain theoretical approximations based on theories of potential flow and semi empi rical plume models are used to simulate the presumed dispersion of snow the model calculations intended as diagnostic tools suggest that snow may be diffused and deposited on lee slopes in a plume like manner similar to other particulate matter snowfall together with low level blowing snow as an additional source of suspended particles appears to increase the snow deposits mainly on the foot of steeper ridges

observations of collisions of saltating grains with a granular bed from high speed cine film high speed photography was used to record saltating sand grains colliding with a horizontal noncohesive bed of similarly sized grains impacting grain bed interaction is discussed in general the process as observed from the films is then described in terms of the apparent bed contact length abcl and various parameters of the impacting grains and any ejected grains examples are given of typical behaviour of bed grains in response to impacting grains of different sizes saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments so that previously buried grains become available for entrainment this process is discussed in relation to the potential release of dust particles into the airflow

energy and momentum conserving model of splash entrainment in sand and snow saltation despite being the main sediment entrainment mechanism in aeolian transport granular splash is still poorly understood we provide a deeper insight into the dynamics of sand and snow ejection with a stochastic model derived from the energy and momentum conservation laws our analysis highlights that the ejection regime of uniform sand is inherently different from that of heterogeneous sand moreover we show that cohesive snow presents a mixed ejection regime statistically controlled either by energy or momentum conservation depending on the impact velocity the proposed formulation can provide a solid base for granular splash simulations in saltation models leading to more reliable assessments of aeolian transport on earth and mars

field observations on spatial variability of surface hoar at the basin scale inclination and wind exposure within an area of about 3 km 2 four automatic weather stations were located within the study area one on level terrain and three across a ridge despite the good instrumentation the correlation between surface hoar growth and calculated sublimation rate was poor distinct spatial patterns of surface hoar growth were found surface hoar crystals were frequently larger at the ridge site than in the surroundings of the automatic weather station on level terrain the variation in surface hoar formation was mainly due to different prevailing wind regimes during the formation periods the surroundings of the automatic weather station on level terrain were under the influence of local katabatic winds that dried up the air so that growth conditions were locally less favorable our observations suggest that predicting surface hoar formation for complex alpine terrain on the basis of data from an automatic weather station the standard procedure in avalanche forecasting seems nearly impossible unless at least the local wind regime is known at high resolution 10 m for both surface hoar formation and surface hoar destruction observations suggest wind conditions to be most crucial for spatial variation

a process based model of snow drifting this physics based two phase flow model of the mass balance of drifting snow calculates the transport of snow through saltation and suspension and recognizes the important role of in transit sublimation on surface erosion rates measurements of the vertical gradient of drifting snow mass flux and wind speed in the surface boundary layer indicate the total flux of saltating snow increases linearly with wind speed and is sensitive to the transport threshold the total flux of suspended snow requires saltation to become established and increases with the cube of both the total flux of saltating snow and the wind speed the total suspended flux quickly becomes the dominant transport mode as wind speeds increase beyond threshold levels and comprises more than 90 of the total flux for wind speeds greater than 15 m s i sublimation rates estimated from wind speed temperature and humidity are sufficiently balanced by snow surface erosion rates to ablate completely snow packs with depths of the order 200 mm a typical value for steppe and prairie environments

using 222rn to examine groundwater surface discharge interaction in the rio grande de manati puerto rico 222rn was used in the karst drainage basin of the rio grande de manati in puerto rico to study groundwater surface flow relationships locations of groundwater influx along two sections of the rio grande de manati were identified the 222rn measurements were used together with stream discharge data in a mass balance equation to quantify the groundwater inputs the investigation established that both of the sections of the rio manati surveyed not only gained groundwater but lost surface flow it was calculated that the river gained about 1 2m3s 1 and lost 0 5m3s 1 to the aquifer between ciales and united states geological survey gauging station 5 between united states geological survey gauging stations 6 and 7 groundwater influx and stream flow loss occurred simultaneously with groundwater inputs equalling surface discharge losses of 4m3s 1 the study successfully demonstrated the innovative application of 222rn as a geochemical tracer in examining groundwater surface flow relationships in a karst system

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

mountain snow distribution governed by an altitudinal gradient and terrain roughness 1 the heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer the snow distribution affects water resources natural hazards such as avalanches and ecology while a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone we present a model of the mean snow depth in topographic control units as a function of two terrain parameters the conventional elevation plus a fractal roughness parameter for this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner the model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation this unusually simple relationship holds for clusters of the snow depths of small topographical units by applying fractal analysis we describe the roughness of the terrain and use this parameter for the prediction of snow deposition rougher terrain holds less snow than smoother terrain this finding is important not only for avalanche warning or eco hydrological applications but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions

quantifying groundwater discharge to cockburn river southeastern australia using dissolved gas tracers 222rn and sf6 groundwater discharge to the cockburn river southeast australia has been estimated from comparison of natural 222rn activities in groundwater and river water interpreted using a numerical flow model that simulates longitudinal radon activities as a function of groundwater inflow hyporheic exchange evaporation gas exchange with the atmosphere and radioactive decay an injection of sf6 into the river to estimate the gas transfer velocity assisted in constraining the model previous estimates of groundwater inflow using 222rn activities have not considered possible input of radon due to exchange between river water and water in the hyporheic zone beneath the streambed in this paper radon input due to hyporheic exchange is estimated from measurements of radon production by hyporheic zone sediments and rates of water exchange between the river and the hyporheic zone total groundwater inflow to the cockburn river is estimated to be 18500 m 3 d although failure to consider hyporheic exchange would cause overestimation of the volume of groundwater inflow by approximately 70 copyright 2006 by the american geophysical union

snow saltation threshold measurements in a drifting snow wind tunnel wind tunnel measurements of snowdrift in a turbulent logarithmic velocity boundary layer have been made in davos switzerland using natural snow regression analysis gives the drift threshold friction velocity ut assuming an exponential drift profile and a simple drift to friction velocity relationship measurements over 15 snow covers show that ut is influenced more by snow density and particle size than by ambient temperature and humidity and varies from 0 27 to 0 69 m s 1 schmidt s threshold algorithm and a modified version used in snowpack a snow cover model agree well with observations if small bond sizes are assumed using particle hydraulic diameters obtained from image processing bagnold s threshold parameter is 0 18 roughness lengths z0 vary between snow covers but are constant until the start of drift threshold roughness lengths are proportional to u 2 t the influence of macroscopic objects on the roughness length is shown by the lower values measured over the smooth and flat snow surface of the wind tunnel 0 04 z0 0 13 mm compared to field measurements mean drifting snow grain sizes for mainly new and partly decomposed snow are 100 175 mm and independent of surface particle size this paper describes the results of a series of experiments investigating the form of the wind velocity boundary layer over a snow surface with and without drift this information is essential to help calculate the energy balance at the snow surface and also to assess mass movement of snow by wind the process of drift is important both over relatively flat terrain such as antarctic regions where it contributes to mass balance and also in mountainous terrain where accumulation on steep slopes can contribute to the danger of avalanches the velocity boundary layer over a surface is often de scribed by a log law where the wind speed at a particular height is a function of the surface friction velocity u and aerodynamic roughness length z0 stull 1988 the param eters uand z0 are then used to model the fluxes of heat and water vapour from the surface which are important not only for snowpack development marks and dozier 1992 lehn ing and others 2002b but also for mass balance calculations cline 1997 liston and sturm 1998 box and others 2004 aerodynamically rough solid surfaces have roughness lengths independent of u schlichting and gersten 2003 the same does not always hold over granular surfaces such as snow or sand above the threshold friction velocity ut particles will be entrained and transported by drift at low wind speeds this drift will be predominantly saltation where particles follow parabolic paths over the surface bagnold 1941 p 10 37 these drifting particles increase the aerodynamic roughness of the surface owen 1964 summarized earlier research relating to the aerodynamic effects of drifting particles and developed a theoretical framework to explain this effect together these suggest two

hydrochemical characteristics of aquifers near sutherland in the western karoo south africa the western karoo depends entirely on groundwater for domestic and agricultural use an understanding of the chemical evolution of the groundwater provides insight into the interaction of water with the environment and contributes to better resource management descriptive statistics correlation matrices and factor analysis together with stable isotope data were used to gain an understanding of the hydrochemical processes of the groundwaters in the fractured rocks around sutherland in the western karoo the main processes influencing the groundwater chemistry are salinisation mineral precipitation and dissolution cation exchange and human activity the stable isotope data indicate that the infiltration of evaporated water is partly responsible for the occurrence of saline subsurface waters the ionic oxygen and hydrogen stable isotope composition of the groundwaters suggests that the effects of localised topography are one of the overriding factors controlling the groundwater chemistry in higher lying areas ca hco3 2 type waters are prevalent while in topographical flat areas nacl type waters dominate in areas where water collects close to or at the surface saline soils are formed from these areas salts are leached to the subsurface during significant recharge periods these findings are important in that they contribute to the identification of suitable locations for developing groundwater resources that could yield a relatively better quality water q 2001 elsevier science b v all rights reserved

variable parameter mccarthy muskingum routing method considering lateral flow summary the fully mass conservative variable parameter mccarthy muskingum vpmm method recently proposed by perumal and price 2013 for routing floods in channels and rivers without considering lateral flow is extended herein for accounting uniformly distributed lateral flow contribution along the reach the proposed procedure is applied for studying flood wave movement in a 24 2 km river stretch between rottweil and oberndorf gauging stations of neckar river in germany wherein significant lateral flow contribution by intermediate catchment rainfall prevails during flood wave movement the geometrical elements of the cross sectional information of the considered routing river stretch without considering lateral flow are estimated using the robust parameter estimation rope algorithm that allows for arriving at the best performing set of bed width and side slope of a trapezoidal section the performance of the vpmm method is evaluated using the nash sutcliffe model efficiency criterion as the objective function to be maximized using the rope algorithm the twenty seven flood events in the calibration set are considered to identify the relationship between total rainfall and total losses as well as to optimize the geometric characteristics of the prismatic channel width and slope of the trapezoidal section based on this analysis a relationship between total rainfall and total loss of the intermediate catchment is obtained and then used to estimate the lateral flow in the reach assuming the lateral flow hydrograph is of the form of inflow hydrograph and using the total intervening catchment runoff estimated from the relationship the uniformly distributed lateral flow rate q l at any instant of time is estimated for its use in the vpmm routing method all the 27 flood events are simulated using this routing approach considering lateral flow along the reach many of these simulations are able to simulate the observed hydrographs very closely the proposed approach of accounting lateral flow using the vpmm method is independently verified by routing flood hydrograph of 6 flood events which are not used in the total rainfall vs total loss relationship established for the intervening catchment of the studied river reach close reproduction of the outflow hydrographs of these independent events using the proposed vpmm method accounting for lateral flow demonstrate the practical utility of the method

snow particle characteristics in the saltation layer shadowgraphy was employed to study snow saltation in boundary layer wind tunnel experiments with fresh naturally deposited snow the shadowgraphy method allowed for a temporally and spatially high resolution investigation of snow particle characteristics within a measurement area of up to 50 mm x 50 mm snow particle size and number characteristics and their variation with height in the saltation layer were analysed the following observations and findings were made for the saltation layer 1 the particle number decreases exponentially with height 2 the mean particle diameter is fairly constant with a very slight tendency to decrease with height 3 the maximum particle diameter decreases linearly with height and 4 the snow particle size distribution can be adequately described by gamma probability density functions the shape and scale parameters of the gamma distribution were found to vary systematically though only slightly with height over ground and between experiments with different snowpack characteristics

back analysis of drifting snow measurements over an instrumented mountainous site the nemo numerical model of drifting snow whose general outlines are presented in this paper is based on a physical model for saltation and turbulent diffusion the model needs a set of input parameters including fall velocity threshold shear velocity shear velocity mass concentration and roughness which are obtained from empirical formulae and wind speed measured at a given height to better determine the required field data in an alpine context our experimental site col du lac blanc 2700 m a s l french alps was first equipped with one anemometer and blowing snow acoustic sensors which proved not to be accurate enough for research purposes in the current state of development even though a new calibration curve was used we therefore set up a snow particle counter and we returned to the traditional robust mechanical traps and a 10 m mast with six anemometers two temperature sensors and a depth sensor to better determine friction velocity and aerodynamic roughness based on the studied drifting snow events we conclude 1 the proportionality of the aerodynamic roughness to the square of the friction velocity was confirmed but with a varying proportionality ratio depending on the snowdrift event 2 values of s u f were relatively well approximated by empirical formulae from data originating from antarctica and 3 snowdrift concentration profiles obtained by pomeroy s semi empirical formulae for the saltation layer coupled with a theoretical approach for the diffusion layer overestimated the concentration profiles for the studied blowing snow event

snow atmosphere coupled simulation at dome c antarctica using a snow atmosphere coupled model the evolution of the surface and near surface snow temperature is modeled at dome c antarctica during the period 20 30 january 2010 firstly the detailed multilayer snow model crocus is run in stand alone mode with meteorological input forcing data provided by local meteorological observations the snow model is able to simulate the evolution of surface temperature with good accuracy it reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well secondly a fully coupled 3 d snow atmosphere simulation is performed with the arome regional meteorological model for which the standard single layer snow parameterization is replaced by crocus in spite of a poor simulation of clouds the surface and near surface snow temperatures are correctly simulated showing neither significant bias nor drifts during the simulation period the model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower this study highlights the potential of snow atmosphere coupled models over the antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions

channel pattern change downstream from a reservoir an example of wandering braided rivers reservoir induced channel pattern change is an issue of significance both in theory and engineering practice based on data from three major wandering braided rivers in china namely the yongdinghe the hanjiang and the yellow rivers as well as a laboratory experimental study this paper deals with channel pattern change downstream from reservoirs complex response in channel adjustment has been observed in the field and as a result a three stage descriptive model has been established to describe the course of channel pattern change also the three stages have been simulated successfully by a laboratory physical model although the observed tendency of channel pattern change of the three rivers is quite different which has been a matter of controversy for many years among chinese researchers it can be satisfactorily explained by the present complex response model because of different boundary conditions the duration of the three stages for the three rivers is different so the channel pattern change of the three rivers shows a different tendency at each specific stage the present study suggests that schumm s qualitative model for river channel metamorphosis should be modified when used for predicting reservoir induced channel pattern change on a wandering braided river because the model has not taken into consideration the changing erosional resistance of channel boundary material and therefore the resultant feedback effect it cannot predict the whole course of channel pattern change over a long period

real time flood forecasting downstream river confluences using a bayesian approach abstract accurate forecast stages at river sections is of paramount importance to properly address flood forecasting and warning systems ffwss operating in real time the forecast values can be provided by flood wave routing models to be implemented when gauged sections are operative along the channel different models have been proposed in the literature and the forecast can be approached by neglecting or involving the contribution of lateral inflows among the latter recently stafom rcm stage forecasting model rating curve model has been proposed assuming a lateral contribution uniformly distributed along the reach therefore the model application is not suitable for future stage prediction at hydrometric sections located just downstream river confluences to overcome this issue we propose a methodology that exploits the probabilistic forecast estimated at a gauged site on a tributary through a bayesian approach and the probabilistic relationship between the stages recorded here and the ones at a downstream site located along the main channel where the forecasted stage estimate is of interest the paglia river basin in central italy is selected as case study the results indicate that the procedure can be useful to address real time hydraulic risk management even at river sections located downstream important confluences provided that gauged sites are operative along the tributary

temporal variability of accumulation at neumayer station antarctica from stake array measurements and a regional atmospheric model in this study we investigate the ability of the regional atmospheric model racmo to represent temporal variations of antarctic accumulation using weekly stake array measurements from neumayer station the model uses ecmwf reanalyses data to force the atmospheric variables at the lateral boundaries of the model domain accumulation is defined as precipitation minus sublimation generally the model represents the synoptic situations that lead to precipitation reasonably well the amounts of accumulation are however usually lower in the model than in the measurements it cannot be distinguished whether the model underestimates precipitation or whether this effect is due to the redistribution of snow by the wind which is not taken into account in the model but affects the accumulation at the measuring site significant differences between model and measurements also occur in cases of net ablation due to wind erosion or when accumulation was due to snowdrift from southwest without precipitation observed

wind influence on snow depth distribution and accumulation over glaciers 1 in mountain regions wind is known to cause snow redistribution while physically based models of snow redistribution have been developed for flat to gently rolling terrain extension of these findings to steep terrain has been limited by the complexity of wind fields in such areas in this study we applied a nonhydrostatic and compressible atmospheric prediction model to steep alpine topography and compared the results to a fully distributed data set of snow depth estimations the results show reduced horizontal wind velocity as well as an increasing downward vertical wind velocity over areas with the largest winter accumulation which are mostly glacierized we show that the wind velocity normal to the local surface which should be zero in a nondivergent flow field and is a direct measure of increased or decreased local deposition is a function of small scale features of local topography the correlation between wind fields snow accumulation and glacierization suggests that accurate modeling of wind fields over glacierized areas in complex terrain is a key factor for understanding the mass balance distribution of glaciers

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers

major ion chemistry in the headwaters of the yamuna river system chemical weathering its temperature dependence and co 2 consumption in the himalaya abstract the yamuna river and its tributaries in the himalaya constitute the yamuna river system yrs the yrs basin has a drainage area and discharge comparable in magnitude to those of the bhagirathi and the alaknanda rivers which merge to form the ganga at the foothills of the himalaya a detailed geochemical study of the yrs was carried out to determine i the relative significance of silicate carbonate and evaporite weathering in contributing to its major ion composition ii co2 consumption via silicate weathering and iii the factors regulating chemical weathering of silicates in the basin the results show that the yrs waters are mildly alkaline with a wide range of tds 32 to 620 mg l 1 in these waters the abundances of ca mg and alkalinity which account for most of tds are derived mainly from carbonates many of the tributaries in the lower reaches of the yamuna basin are supersaturated with calcite in addition to carbonic acid sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering silicate weathering in yrs basin contributes on average 25 molar basis of total cations on a basin wide scale silicate weathering however does not seem to be intense in the basin as evident from low si na k in the waters 1 2 and low values of chemical index of alteration cia in bed sediments 60 co2 drawdown resulting from silicate weathering in the yrs basin in the himalaya during monsoon ranges between 4 to 7 105 moles km 2 y 1 this is higher than that estimated for the ganga at rishikesh for the same season the co2 consumption rates in the yamuna and the ganga basins in the himalaya are higher than the global average value suggesting enhanced co2 drawdown in the southern slopes of the himalaya the impact of this enhanced drawdown on the global co2 budget may not be pronounced as the drainage area of the yrs and the ganga in the himalaya is small the co2 drawdown by silicates in the yrs basin is marginally higher than the reported values of co2 release from oxidation of organic rich sediments estimated using re as a proxy this comparison shows the need to constrain co2 sources and sinks better to balance its budget in a regional scale the results also show that silicate weathering rate in the yrs basin is 10 mm ky 1 and on the ganga basin it is 5 mm ky 1 which are several times lower than the carbonate weathering rates the significantly higher silicate weathering rate observed in the yrs basin seems to be governed by rapid physical erosion in this region the apparent activation energy for overall silicate weathering in the yrs basin derived from na and si concentrations and water temperature ranges from 50 to 80 kj mol 1 these values are comparable to those reported for granitoid weathering in natural watersheds and feldspar weathering in laboratory experiments this study brings to light the sources contributing to major ions enhanced chemical weathering rates in the yamuna river basin and interdependence of silicate weathering on physical erosion and temperature