the effect of lateral channel contraction on dam break flows laboratory experiment summary this paper presents an investigation of dam break flow in a channel with lateral contraction an experiment was carried out in a laboratory flume by instantaneous removal of a plate the problem was studied in a smooth prismatic channel of rectangular cross section over horizontal dry bed at a certain distance downstream from the dam location two symmetrical triangular shaped lateral sidewall obstacles were installed to generate converging diverging channel reach thus it points out the abrupt variation of topography in floodplain for practical applications adopted measuring technique digital image processing detected the flood wave propagation quite well thereby synchronous recording of the flow through the entire channel with three cameras the continuous free surface profiles and stage hydrographs were obtained without disturbing the flow the experimental data were compared with the results of rans based numerical simulation comparisons between measured and computed results show good agreement

modelling a paleo valley glacier network using a hybrid model an assessment with a stokes ice flow model modelling paleo glacier networks in mountain ranges on the millennial timescales requires ice flow approximations hybrid models calculating ice flow by combining vertical shearing shallow ice approximation and longitudinal stretching shallow shelf approximation have been applied to model paleo glacier networks on steep terrain yet their validity has not yet been assessed quantitatively moreover hybrid models consistently yield higher ice thicknesses than last glacial maximum geomorphological reconstructions in the european alps here we compare results based on the hybrid parallel ice sheet model pism and the stokes model elmer ice on the rhine glacier a catchment of the former european alpine icefield for pism we also test two magnitudes of flux limitation in a scheme that reduces shearing velocities we find that the flux limitation typically used in pism yields significantly reduced shearing speeds and increases ice thicknesses by up to 500 m partly explaining previous overestimations however reducing the ice flux limitation allows the hybrid model to minimize this mismatch and captures sliding speeds ice thicknesses ice extent and basal temperatures in close agreement with those obtained with the stokes model

shallow shelf approximation as a sliding law in a thermomechanically coupled ice sheet model 1 the shallow shelf approximation a balance of membrane stresses for ice flow is an effective sliding law for ice sheet modeling our use of it as a sliding law becomes a standard model for ice stream flow when the sliding velocity is large 100 m a 1 and faster following schoof 2006a we describe the basal resistance as plastic till for which the yield stress is given by a mohr coulomb formula pore water pressure is related to basal melt rate the velocity field used in the mass continuity and conservation of energy equations is an average of velocities from the shallow shelf approximation and the nonsliding shallow ice approximation using this scheme our model has realistic time dependent ice streams which exhibit the range of surface velocities seen in actual ice streams we demonstrate the model at high spatial resolution 5 km grid over multiple millenia using its implementation in the parallel ice sheet model numerical experiments show that the entire scheme is stable with respect to many parameter changes some experiments reveal significant ice stream variability in a hypothetical steady climate with characteristic cycles on the order of 1000 years we believe this is the first practical whole ice sheet model with a unified treatment of vertical shear stresses and membrane stresses it is capable of high resolution thermomechanically coupled multimillenia simulations of ice sheets containing ice streams

application of a polythermal three dimensional ice sheet model to the greenland ice sheet response to steady state and transient climate scenarios abstract steady state and transient climate change computations are performed with the author s three dimensional polythermal ice sheet model simulation code for polythermal ice sheets for the greenland ice sheet the distinctive feature of this model is the detailed consideration of the basal temperate ice layer in which the water content and its impact on the ice viscosity are computed its transition surface to the cold ice region is accounted for by continuum mechanical jump conditions on this interface the simulations presented include steady states subject to a range of physical parameters and two different climates present and glacial conditions as well as three types of transient scenarios namely i sinusoidal milankovic period forcing ii paleoclimatic forcing from the greenland ice core project core reconstruction and iii future greenhouse warming forcing

inactive and relict rock glaciers of the deboullie lakes ecological reserve northern maine usa lobate talus slopes in the deboullie lakes ecological reserve dler of northern maine exhibit parabolic profiles characteristic of inactive and relict talus derived rock glaciers vegetated rock glacier surfaces suggest that the landforms are no longer active and lobes comprising two dler rock glaciers document periods of past growth observations of perennial subsurface ice are supported by datalogger temperature measurements indicating that sporadic permafrost exists throughout the dler we compare the dler rock glaciers along with similar features elsewhere in new england and adjacent quebec to the modern alpine permafrost distribution results indicate that a mean annual temperature cooling of 68c is required to promote active rock glacier growth ages of plant remains recovered from the basal sediments of a local pond constrain deglaciation to before 11 320 14 c a bp and core stratigraphy and organic content reveal that a periglacial environment persisted during the early postglacial era thus we hypothesise that the dler rock glaciers were active during lateglacial time despite the lack of glacier activity in the region we take this to suggest that north eastern us rock glaciers formed in response to mean annual temperatures skewed towards the frigid winters of the younger dryas chronozone copyright 2009 john wiley sons ltd

experimental study on dam break waves for silted up reservoirs the overall dam break phenomenon is currently well understood for reservoirs filled with water however many dams face serious problems of reservoir sedimentation thus regarding risk management the influence of a large amount of sediment in the reservoir on dam break wave propagation is of great importance experimental investigations were performed to investigate the influence of the silting degree of reservoirs and grain size distribution on wave heights and velocities dam break waves in silted up reservoirs are the result of a two phase flow formed by a layer of water over a layer of saturated sediments in which complex phenomena occur simultaneously sediments flow such as a viscous fluid from the dam breach until complete stoppage and clear water flows over the sediments creating bed load transport the final sediment deposition cone the flow of the positive front and maximum wave heights were studied an empirical formula is proposed to describe the celerity of the positive wave front in the case of silted up reservoirs

on estimating length fluctuations of glaciers caused by changes in climatic forcing the reaction of alpine glaciers to shifts in the equilibrium line altitude ela is calculated by using a two dimensional numerical model to solve the full equations for the velocity and stress fields full system model in the absence of basal motion rates of advance and retreat of the snout of typically sized alpine glaciers are found to be insensitive to the details of the flow at the snout even when the glaciers are far from steady state a comparison of results obtained with a full system model and a shallow ice approximation sia model yields no significant differences in advance or retreat rates this assumption has been implicitly made in numerous previous climatic studies and is here shown to be well justified using a realistic mass balance altitude feedback only slight model dependent changes in steady state lengths are found the relative importance of mass balance and glacier dynamics for the transient response of alpine glaciers to changes in the ela is given a precise meaning by determining the model dependent additional shifts in ela needed for the sia and the full system models to produce identical changes in length for alpine glaciers these additional shifts in ela are on the order of 10 m which is within the error range of ela estimates it follows that at least in the absence of significant basal motion there is no need to include the effects of horizontal stresses when calculating the reaction of alpine glaciers to climatic changes attention should focus on accurate determination of the mass balance distribution and model tuning to give realistic ice thickness distributions

improvement of a 2 d sia ice flow model application to glacier de saint sorlin france a number of improvements have been made to an existing two dimensional ice flow model applied to an alpine glacier analysis of the results of the existing model revealed several shortcomings the first concerns the lack of mass conservation of the applied alternating direction implicit adi scheme a semi implicit si scheme is therefore proposed and the effects on mass conservation assessed by a comparison with the adi scheme the comparison is first carried out with a simple theoretical glacier for which the improvement is significant concerning the real case of glacier de saint sorlin france the initial deviation in mass conservation was much less pronounced such that the new scheme although improving mass conservation does not significantly change the modelled dynamics however other shortcomings that have a more profound impact on the modelling of glacier behaviour have been identified the ice thickness may become negative over some gridpoints leading to an inconsistency the problem is partly resolved by incorporating extra checks on critical gridpoints at the glacier border finally with the help of ice particle tracking unrealistic ice settlement above the bergschrund has been identified as the main reason for spurious dynamic effects and has been corrected

three dimensional numerical modeling of dam break flows with sediment transport over movable beds abstracta three dimensional 3d numerical model has been developed to simulate dam break flows with sediment transport over movable beds the hydrodynamic model solves the 3d reynolds averaged navier stokes equations using a finite volume method on collocated hexahedral meshes the volume of fluid vof technique with the compressive interface capturing scheme for arbitrary meshes is used to track the water surface boundary the sediment transport model solves the nonequilibrium transport equations of suspended load and bed load separately and in turn calculates the resulting bed change a moving mesh technique is adopted to track the time evolution of bed topography the grid moving velocity and computational cell volume change due to the moving mesh are taken into consideration when the hydrodynamic and sediment transport equations are discretized the developed model has been tested using several experimental dam break flows over movable beds the calculated temporal and spatial variations of water a

high resolution finite volume method for shallow water flows a high resolution time marching method is presented for solving the two dimensional shallow water equations the method uses a cell centered formulation with collocated data rather than a space staggered approach spurious oscillations are avoided by employing monotonic upstream schemes for conservation laws muscl reconstruction with an approximate riemann solver in a two step runge kutta time stepping scheme a finite volume implementation on a boundary conforming mesh is chosen to more accurately map the complex geometries that will occur in practice these features enable the model to deal with dam break phenomena involving flow discontinuities subcritical and supercritical flows and other cases the method is applied to several bore wave propagation and dam break problems

development of tongue shaped and multilobate rock glaciers in alpine environments interpretations from ground penetrating radar surveys abstract rock glaciers occur as lobate or tongue shaped landforms composed of mixtures of poorly sorted angular to blocky rock debris and ice these landforms serve as primary sinks for ice and water storage in mountainous areas and represent transitional forms in the debris transport system accounting for 60 of all mass transport in some alpine regions observations of active flowing alpine rock glaciers indicate a common association between the debris that originates from cirque headwalls and the depositional lobes that comprise them the delivery of this debris to the rock glacier is regulated primarily by the rate of headwall erosion and the point of origin of debris along the headwall these factors control the relative movement of individual depositional lobes as well as the overall rate of propagation of a rock glacier in recent geophysical studies a number of alpine rock glaciers on prins karls forland and nordenskioldland svalbard norway and the san juan mountains of southwest colorado usa have been imaged using ground penetrating radar gpr to determine if a relationship exists between the internal structure and surface morphology results indicate that the overall morphologic expression of alpine rock glaciers is related to lobate deposition during catastrophic episodes of rockfall that originated from associated cirque headwalls longitudinal gpr profiles from alpine rock glaciers examined in this study suggests that the difference in gross morphology between the lobate and tongue shaped rock glaciers can be attributed primarily but not exclusively to cirque geometry frequency and locations of debris discharge within the cirque and the trend and magnitude of valley gradient in relation to cirque orientation collectively these factors determine the manner in which high magnitude debris discharges which seem to be the primary mechanism of formation accumulate to form these rock glaciers

an enthalpy formulation for glaciers and ice sheets polythermal conditions are ubiquitous among glaciers from small valley glaciers to ice sheets conventional temperature based cold ice models of such ice masses cannot account for that portion of the internal energy which is latent heat of liquid water within temperate ice so such schemes are not energy conserving when temperate ice is present temperature and liquid water fraction are however functions of a single enthalpy variable a small enthalpy change in cold ice is a change in temperature while a small enthalpy change in temperate ice is a change in liquid water fraction the unified enthalpy formulation described here models the mass and energy balance for the three dimensional ice fluid for the surface runoff layer and for the subglacial hydrology layer together in a single energy conserving theoretical framework it is implemented in the parallel ice sheet model results for the greenland ice sheet are compared with those from a cold ice scheme this paper is intended to be an accessible foundation for enthalpy formulations in glaciology

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

last glacial maximum climate in new zealand inferred from a modelled southern alps icefield abstract we present a simulation of the new zealand southern alps icefield at the last glacial maximum lgm c 30 000 20 000 calendar years ago ka in an attempt to constrain the climate of that period we use a 500 m resolution ice sheet model parameterised using empirical glaciological climatological and geological data specific to the model domain to simulate the entire southern alps icefield we find that an lgm cooling of at least 6 6 5 c is necessary to bring about valley glaciers that extend beyond the mountains however climate topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain and in order to remain within geologically reconstructed lgm limits we find that the lgm cooling was most likely associated with a precipitation regime up to 25 drier than today wetter than present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence these results perhaps indicate that either the westerly air masses affecting new zealand during the lgm were drier than today or that they were weaker or zonally displaced with respect to present

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

rock glaciers and related periglacial landforms in the sierra nevada ca usa inventory distribution and climatic relationships abstract rock glaciers and related periglacial rock ice features rifs are abundant yet overlooked landforms in the sierra nevada california where they occur in diverse forms we mapped 421 rifs from field surveys and grouped these into six classes based on morphology and location these categories comprise a greater range of frozen ground features than are commonly described in rock glacier surveys mapped features extended from 2225 to 3932 m modern mean 3333 m occurred mostly on nnw to nne aspects and ranged in apparent age from modern to relict late pleistocene many of the smaller features mapped here are not readily discernible with remote e g air photo observation field surveys remain the best approach for their detection we interpreted the presence of outlet springs basal lakes suspended silt in outlet streams and fringing phreatophytic vegetation in addition to morphologic indications of current rock movement as evidence for interstitial ice either persistent or seasonal the six classes were distinct in their geographic settings and morphologic conditions indicating process level differences to assess modern climate we intersected mapped locations with the 30 arcsec prism climate model discriminant analysis indicated significant differences among the climate means of the classes with the first three canonical vectors describing 94 of the differences among classes mean annual air temperatures maat for modern features ranged from 0 3 to 2 2 c mean precipitation ranged from 1346 to 1513 mm we calculated differences between modern and pleistocene temperatures in two ways one based on elevation differences of modern and relict rifs 662 m and standard lapse rate the other using prism estimates for the first we estimate the difference in maat as 3 9 c range 2 2 to 7 9 c from prism the difference was 3 3 c range 1 0 to 6 1 c in that persistent snowfields and glaciers are retreating in the sierra nevada under warming climates rifs will likely become increasingly important in prolonging water storage during the warm season and providing small but distributed water reserves for biodiversity and runoff their presence and water contributions would benefit by further hydrologic study

one dimensional modeling of dam break flow over movable beds a one dimensional model has been established to simulate the fluvial processes under dam break flow over movable beds the hydrodynamic model adopts the generalized shallow water equations which consider the effects of sediment transport and bed change on the flow the sediment model computes the nonequilibrium transport of bed load and suspended load the effects of sediment concentration on sediment settling and entrainment are considered in determining the sediment settling velocity and transport capacity in particular a correction factor is proposed to modify the van rijn formulas of equilibrium bed load transport rate and near bed suspended load concentration for the simulation of sediment transport under high shear flow conditions the governing equations are solved by an explicit finite volume method with the first order upwind scheme for intercell fluxes the model has been tested in two experimental cases with fairly good agreement between simulations and measurements the sensitivities of the model results to parameters such as the sediment nonequilibrium adaptation length manning s roughness coefficient and the proposed correction factor have been verified the proposed model has also been compared to an existing model and the results indicate the new model is more reliable

subsurface investigation of a rock glacier using ground penetrating radar implications for locating stored water on mars 1 the discovery of rock glacier like features on mars suggests the presence of flowing or once flowing ice rock mixtures these landforms which include lobate debris aprons concentric crater fill and lineated valley fill hold significant promise as reservoirs of stored water ice that could be used as fuel sources for human exploration of mars and provide a frozen record of the climatic history of the planet to understand the deformation and distribution of ice within these landforms fundamental descriptions of their internal structure and development are required to this end a ground penetrating radar investigation was initiated using rock glaciers in the san juan mountains of colorado as surrogates for similar martian landforms results obtained from one of these rock glaciers show that the interior of the landform is composed of a layered permafrost matrix of ice sediment and ice lenses that comprise thicker depositional units formed through high magnitude debris falls folds in the uppermost layers correspond to the surface expression of ridges and furrows suggesting that compressive stresses originating in the accumulation zone are transmitted downslope through the rock glacier rock glacier features on mars may also consist of layered permafrost which would suggest a history of development involving seasonal frost accumulation and or water influx from below in terms of water storage within martian analogs consideration must include the possibility that some water ice may be stored in relatively pure form within lenses and vein networks such as observed in the surrogate rock glacier of this study

dam break in channels with 90 bend in practice dam break modeling is generally performed using a one dimensional 1d approach for its limited requirements in data and computation however for valleys with multiple sharp bends such a 1d model may fail for predicting as well the maximum water level as the wave arrival time this paper presents an experimental study of a dam break flow in an initially dry channel with a 90 bend with refined measurements of water level and velocity field the measured data are compared to some numerical results computed with finite volume schemes associated with roe type flux calculation the 1d approach reveals the expected limits while a full two dimensional 2d approach provides fine level prediction and rather satisfactory information about the arrival time a hybrid approach is now proposed mixing the 1d model for the straight reaches and local 2d models for the bends the compatibility of the roe fluxes at the interfaces requires a careful formulation but the resulting scheme seems able to capture reflection and diffraction processes in such a way that the results are really good in what concerns the water level

climatic patterns over the european alps during the lgm derived from inversion of the paleo ice extent abstract quaternary climate has been dominated by alternating glacial and interglacial periods while the timing and extent of past ice caps are well documented local variations in temperature and precipitation as a response to cyclic glaciations are not resolved resolving these issues is necessary for understanding regional and global climate circulation in particular the impact of the cold high pressure zone above the fennoscandian ice cap on the position of the jet stream in europe and a possible change in the direction and the source of moisture flow are still debated here we reconstruct climate conditions that led to the observed ice extent in the european alps during the last glacial maximum lgm using a new inverse method to reconstruct the spatially variable position of the equilibrium line altitude ela we investigate whether the alpine lgm ice cap dominantly received precipitation in the south due to a strong southward shift of the westerlies in midlatitudes we report inversion results that enable us to estimate the role of climate inversion method parameters ice dynamics flexure and topography in modulating the inferred equilibrium line altitude our main finding is the increase of the position of the ela from west to east and from north to south of the mountain range which suggest dominant moisture delivery over the alps during the lgm relatively similar to today

experimental study and numerical verification of silted up dam break abstract in this study multiphase flood waves caused by failure of silted up dams have been scrutinized experimentally and efficacy of the public domain cfd software openfoam numerical models to represent such phenomenon is evaluated experimental observations are sparse on dam break for reservoirs with high sediment depths called silted up reservoirs sediment layer in this case may behave as a viscous fluid and produce a complex multi layer flow of air and water overtopping a sediment layer massive sediment quantities can have a substantial impact on the wave propagation pattern caused by dam break this study contributes to an experiment based understanding of dam break phenomenon with silted up reservoir and elaborates the propagation of multi layer waves herein different hydraulic conditions were experimentally observed including 8 different upstream sediment depths in the range of 0 0 24 m and 4 downstream initial water levels of 0 0 02 0 04 and 0 05 m which collectively created 32 scenarios the resulted waves were filmed by high speed cameras and data were extracted through image processing an open source cfd software namely openfoam was employed to simulate the experiments using two distinct numerical approaches volume of fluid vof and eulerian results of both numerical approaches were in good agreement with the experimental measurements with mae and rmse error values varying from 0 006 m to 0 031 m and 0 008 m to 0 043 m respectively 2 to 10 and 2 6 to 14 with respect to the reservoir height of 0 3 m the eulerian approach showed marginally superior performance to vof especially in cases with high sediment depths which is likely due to accommodating phase mixing a wide collection of high quality data is made available online in the appendix data and could be utilized in future studies

dam break wave front celerity this work is concerned with the role that friction and inertia effects can play on the magnitude of dam break wave front celerity classic analytical solutions are presented a large collection of experimental data is used covering a wide range of different initial conditions fixed bed or mobile bed five types of bed material dry or wet bed downstream and with or without bed step to overcome the limitations of analytical solutions a numerical model is used the model is based on the shallow water approach with contact load dominated sediment transport and it makes use of developments recently made in the study of sheet flows the analytical and numerical results are compared with experimental data it was found that the celerity is mainly dictated by the friction coefficient by the sediment inertia by the initial downstream water depth and by the initial bed step height for good data fitting the friction coefficient must be influenced by the type of bed fixed or mobile in the latter the coefficient must vary with the bed material characteristics the dissimilarities between the experimental analytical and numerical results are interpreted

sediment transport and morphodynamics generated by a dam break swash uprush coupled vs uncoupled modeling the present work analyzes the hydro morphodynamics characterizing the swash region during the uprush stage a comparison is illustrated between the sediment transport measured in a series of dam break experiments and that predicted by the numerical hydro morphodynamic model of postacchini et al 2012 the primary aim is to investigate the differences arising between the weakly coupled or uncoupled model and the measurements in terms of hydrodynamics tip celerity and sediment transport the hydrodynamics are well described by the model and results have been used to calibrate both friction factor and subgrid turbulent viscosity comparison of numerically computed tip celerity with experimental data reveals a fairly good agreement i e a mean error of about 10 while modeled sediment transport differs by about 40 from the available data no evident differences are found between results obtained from the coupled and uncoupled model runs 2 for the celerity and 11 for the sediment transport rate at the tip suggesting that for the specific flow under investigation at the leading edge of the swash front hydro morphological coupling is not an issue of fundamental importance however for the special case here of a swash forced by a dam break scour occurs at the dam location and in this case the erosion of the bed is significantly larger in the uncoupled model