keeping the edge a numerical method that avoids knickpoint smearing when solving the stream power law the stream power equation is commonly used to model river incision into bedrock although specific conditions allow an analytical approach finite difference methods fdms are most frequently used to solve this equation fdms inevitably suffer from numerical smearing which may affect their suitability for transient river incision modeling we propose the use of a finite volume method fvm which is total variation diminishing tvd to simulate river incision in a more accurate way the tvd fvm is designed to simulate sharp discontinuities making it very suitable to simulate river incision pulses we show that the tvd fvm is much better capable of preserving propagating knickpoints than fdms using niagara falls as an example comparison of numerical results obtained using the tvd fvm with analytical solutions shows a very good agreement furthermore the uncertainty associated with parameter calibration is dramatically reduced when the tvd fvm is applied the high accuracy of the tvd fdm allows correct simulation of transient incision waves as a consequence of older uplift pulses this implies that the tvd fvm is much more suitable than fdms to reconstruct regional uplift histories from current river profile morphology and to simulate river incision processes in general

numerical simulation of overbank processes in topographically complex floodplain environments this article presents results from an investigation of the hydraulic characteristics of overbank flows on topographically complex natural river floodplains a two dimensional hydraulic model that solves the depth averaged shallow water form of the navier stokes equations is used to simulate an overbank flow event within a multiple channel reach of the river culm devon uk parameterization of channel and floodplain roughness by the model is evaluated using monitored records of main channel water level and point measurements of floodplain flow depth and unit discharge modelled inundation extents and sequences are assessed using maps of actual inundation patterns obtained using a global positioning system observational evidence and ground photographs simulation results suggest a two phase model of flooding at the site which seems likely to be representative of natural floodplains in general comparison of these results with previous research demonstrates the complexity of overbank flows on natural river floodplains and highlights the limitations of laboratory flumes as an analogue for these environments despite this complexity frequency distributions of simulated depth velocity and unit discharge data closely follow a simple gamma distribution model and are described by a shape parameter that exhibits clear systematic trends with changing discharge and floodplain roughness such statistical approaches have the potential to provide the basis for computationally efficient flood routing and overbank sedimentation models copyright 2002 john wiley sons ltd

a sensitivity analysis of meteoric infrasound 1 we perform a multicomponent sensitivity analysis of how the physical and dynamical parameters that characterize a meteor in fall affect the ground overpressure and period of a plausible emitted n wave signal the nonlinear propagation model used throughout is based upon whitham s nonlinearization method which is modified to take into account a stratified atmosphere we use sensitivity indices derived using a fourier amplitude sensitivity test to measure how the meteor parameters uncertainties affect the uncertainty in the overpressure and period of an emitted n wave the investigated parameters include the azimuth entry angle diameter drag coefficient density and initial velocity of the meteor as well as the atmosphere the method is used to re examine the crater forming meteorite fall near carancas peru 2007 we obtain good agreement between the simulated signals and observed waveforms it is shown that ground overpressure uncertainty depends on the atmospheric uncertainties that are strongly correlated with the unknown trajectory whereas the period is governed by the diameter uncertainties finally we consider new waveform parameters that help characterize the meteor

hillslope storage and rainfall amount thresholds as controls of preferential stormflow summary shallow saturated subsurface flow is a dominant runoff mechanism on hillslopes of headwater catchments under humid temperate climate its timing and magnitude is significantly affected by the presence of preferential pathways reliable prediction of runoff from hillslope soils under such conditions remains a challenge in this study a quantitative relationship between rainfall stormflow and leakage to bedrock for hillslopes where lateral preferential runoff represents a dominant part of the overall response was sought combined effects of temporal rainfall distribution and initial hillslope saturation antecedent moisture conditions on stormflow leakage to bedrock and overall water balance were evaluated by conducting simulations with synthetic rainfall episodes a two dimensional dual continuum model was used to analyze hydrological processes at an experimental hillslope site located in a small forested headwater catchment long term seasonal simulations with natural rainfall indicated that leakage to bedrock occurred mostly as saturated flow during major runoff events the amount of rainfall needed to initiate stormflow appeared as a dynamic hillslope property depending on temporal rainfall distribution initial hillslope storage and the spatial distribution of soil water within the hillslope no single valued rainfall threshold responsible for triggering stormflow was found rainfall stormflow as well as rainfall leakage relationships were found highly nonlinear for low initial hillslope saturations temporal rainfall distribution affected the amount of rainfall necessary to initiate stormflow more than it did the amounts of stormflow or leakage to bedrock in spite of a simple hillslope geometry with constant slope and parallel soil atmosphere and soil bedrock interfaces considered in the analysis the applied model predicted a hysteretic behavior of storage discharge relationship the results showed a mutual interplay of components of hillslope water balance exposing a nonlinear character of the hillslope response the study provided a quantitatively coherent insight in the hydraulic functioning of hillslopes where preferential flow constitutes a dominant part of stormflow

thermoluminescence dating of the kamil impact crater egypt thermoluminescence tl dating has been used to determine the age of the meteorite impact crater at gebel kamil egyptian sahara previous studies suggested that the 45 m diameter structure was produced by a fall in recent times less than 5000 years ago of an iron meteorite impactor into quartz arenites and siltstones belonging to the lower cretaceous gilf kebir formation the impact caused the complete fragmentation of the impactor and the formation of a variety of impactites e g partially vitrified dark and light materials present as ejecta within the crater and in the surrounding area after a series of tests to evaluate the tl properties of different materials including shocked intra crater target rocks and different types of ejecta we selected a suite of light colored ejecta that showed evidence of strong thermal shock effects e g partial vitrification and the presence of high temperature and pressure silica phases the abundance of quartz in the target rocks including the vitrified impactites allowed tl dating to be undertaken the variability of radioactivity of the intracrateric target rocks and the lack of direct in situ dosimetric evaluations prevented precise dating it was however possible to constrain the impact in the 2000 bc 500 ad range if as we believe the radioactivity measured in the fallback deposits is a reliable estimate of the mean radioactivity of the site the narrower range 1600 400 bc at the 2 confidence level can be realistically proposed

piezometric response in zones of a watershed with lateral preferential flow as a first order control on subsurface flow characterizing zones of a watershed based on the water table is used to understand and predict internal watershed processes in watersheds dominated by lateral preferential flow the water table response typically shows a distinct hydraulically limited pattern this response is characterized by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases we expected that this response would be related to the contributing area since nearby hillslope excavations showed that the development of preferential flow network was positively correlated with the contributing area the watershed was stratified into three predetermined zones and installed 25 piezometers to measure the water table dynamics the objectives were 1 to characterize the water table runoff relationship 2 to prove preferential flow by observable characteristics and 3 to test the feasibility of identifying areas within a watershed that are dominated by lateral preferential flow watershed zones were not well defined and there was no strong relationship between the hydraulically limited response and observable watershed characteristics although zones might still be useful for grouping the hillslope processes the piezometric response may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow copyright 2010 john wiley sons ltd

geological and geophysical investigation of kamil crater egypt we detail the kamil crater egypt structure and refine the impact scenario based on the geological and geophysical data collected during our first expedition in february 2010 kamil crater is a model for terrestrial small scale hypervelocity impact craters it is an exceptionally well preserved simple crater with a diameter of 45 m depth of 10 m and rayed pattern of bright ejecta it occurs in a simple geological context flat rocky desert surface and target rocks comprising subhorizontally layered sandstones the high depth to diameter ratio of the transient crater its concave yet asymmetric bottom and the fact that kamil crater is not part of a crater field confirm that it formed by the impact of a single iron mass or a tight cluster of fragments that fragmented upon hypervelocity impact with the ground the circular crater shape and asymmetries in ejecta and shrapnel distributions coherently indicate a direction of incidence from the nw and an impact angle of approximately 30 to 45 newly identified asymmetries including the off center bottom of the transient crater floor downrange maximum overturning of target rocks along the impact direction and lower crater rim elevation downrange may be diagnostic of oblique impacts in well preserved craters geomagnetic data reveal no buried individual impactor masses 100 kg and suggest that the total mass of the buried shrapnel 100 g is approximately 1050 1700 kg based on this mass value plus that of shrapnel 10 g identified earlier on the surface during systematic search the new estimate of the minimum projectile mass is approximately 5 t

the flux of small near earth objects colliding with the earth asteroids with diameters smaller than approximately 50 100 m that collide with the earth usually do not hit the ground as a single body rather they detonate in the atmosphere these small objects can still cause considerable damage such as occurred near tunguska siberia in 1908 the flux of small bodies is poorly constrained however in part because ground based observational searches pursue strategies that lead them preferentially to find larger objects a tunguska class event the energy of which we take to be equivalent to 10 megatons of tnt was previously estimated to occur every 200 300 years with the largest annual airburst calculated to be approximately 20 kilotons kton tnt equivalent ref 4 here we report satellite records of bolide detonations in the atmosphere over the past 8 5 years we find that the flux of objects in the 1 10 m size range has the same power law distribution as bodies with diameters 50 m from this we estimate that the earth is hit on average annually by an object with approximately 5 kton equivalent energy and that tunguska like events occur about once every 1 000 years

spatio temporal variability of piezometric response on two steep alpine hillslopes information on the main drivers of subsurface flow generation on hillslopes of alpine headwater catchments is still missing therefore the dominant factors controlling the water table response to precipitation at the hillslope scale in the alpine bridge creek catchment northern italy were investigated two steep hillslopes of similar size soil properties and vegetation cover but contrasting topography were instrumented with 24 piezometric wells sixty three 63 rainfall runoff events were selected over three years in the snow free months to analyse the influence of rainfall depth antecedent moisture conditions hillslope topographic characteristics and soil depth on shallow water table dynamics piezometric response expressed as percentage of well activation and water peak magnitude was strongly correlated with soil moisture status as described by an index combining antecedent soil moisture and rainfall depth hillslope topography was found to be a dominant control only for the convex divergent hillslope and during wet conditions timing of water table response depended primarily on soil depth and topographic position with piezometric peak response occurring later and showing a greater temporal variability at the hillslope bottom characterized by thicker soil the relationship between mean hillslope water table level and standard deviation for all wells reflected the timing of the water table response at the different locations along the hillslopes the outcomes of this research contribute to a better understanding of the controls on piezometric response at the hillslope scale in steep terrain and its role on the hydrological functioning of the study catchment and of other sites with similar physiographic characteristics copyright 2014 john wiley sons ltd

a 1 d morphodynamic model for rill erosion 1 the key objective of this paper is to develop a 1 d hydrodynamic and sediment transport model namely rill1d that handles transcritical flows over abrupt changes e g formation of pool crests and width change in a single rill and also predicts changes in rill bed elevation replication of rill conditions in terms of flow and bed evolution changes necessitated the use of an enhanced tvd maccormack scheme with implementation of tseng s surface gradient method to provide an oscillation free solution over formed pool crests the model at the end of each time step calculates the flow depth velocity and bed shear stress and provides changes in bed elevation and grain size distribution within a cell the hydrodynamic performance of rill1d is evaluated by comparing its results with either analytical solutions or experimental observations from various benchmark tests with rigid bed conditions that include 1 formation of a hydraulic jump in a rectangular channel 2 steady subcritical and transcritical flow without a shock over a hump 3 formation of a hydraulic jump in a converging diverging frictionless channel and 4 flows over step pools it is shown that the enhanced tvd maccormack scheme adequately simulates transcritical flows by preserving the mass conservation and reducing the artificial numerical error the scheme also approximates satisfactorily depth and velocity for a single rill with a fixed bed consisting of steps and pools except near the pool headwalls where a backroller forms with negative velocities the sediment component of rill1d is evaluated by two field investigations of single rills with mobile beds with the field data the code is tested for its ability to reproduce measured values of sediment transport rates a sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model rill1d performs reasonably well in these simulations in terms of sediment prediction rates and fared adequately in terms of replicating rill bed morphology

simple spatially distributed models for predicting flood inundation a review abstract in this paper we review recent progress in the use of reduced complexity models for predicting floodplain inundation we review the theoretical basis for modelling floodplain flow with simplified hydraulic treatments based on a dimensional analysis of the one dimensional shallow water equations we then review how such schemes can be applied in practice and consider issues of space discretization time discretization and model parameterisation before going on to consider model assessment procedures we show that a key advantage of reduced complexity codes is that they force modellers to think about the minimum process representation necessary to predict particular quantities and act as a check on any tendency to reductionism at the same time however the use compared to standard hydraulic codes of strong simplifying assumptions requires us to also address the question how simple can a model be and still be physically realistic we show that by making explicit this debate about acceptable levels of abstraction reduced complexity codes allow progress to be made in addressing a number of long standing debates in hydraulics

modelling hydrodynamics in the rio parana argentina an evaluation and inter comparison of reduced complexity and physics based models applied to a large sand bed river abstract depth averaged velocities and unit discharges within a 30 km reach of one of the world s largest rivers the rio parana argentina were simulated using three hydrodynamic models with different process representations a reduced complexity rc model that neglects most of the physics governing fluid flow a two dimensional model based on the shallow water equations and a three dimensional model based on the reynolds averaged navier stokes equations flow characteristics simulated using all three models were compared with data obtained by acoustic doppler current profiler surveys at four cross sections within the study reach this analysis demonstrates that surprisingly the performance of the rc model is generally equal to and in some instances better than that of the physics based models in terms of the statistical agreement between simulated and measured flow properties in addition in contrast to previous applications of rc models the present study demonstrates that the rc model can successfully predict measured flow velocities the strong performance of the rc model reflects in part the simplicity of the depth averaged mean flow patterns within the study reach and the dominant role of channel scale topographic features in controlling the flow dynamics moreover the very low water surface slopes that typify large sand bed rivers enable flow depths to be estimated reliably in the rc model using a simple fixed lid planar water surface approximation this approach overcomes a major problem encountered in the application of rc models in environments characterised by shallow flows and steep bed gradients the rc model is four orders of magnitude faster than the physics based models when performing steady state hydrodynamic calculations however the iterative nature of the rc model calculations implies a reduction in computational efficiency relative to some other rc models a further implication of this is that if used to simulate channel morphodynamics the present rc model may offer only a marginal advantage in terms of computational efficiency over approaches based on the shallow water equations these observations illustrate the trade off between model realism and efficiency that is a key consideration in rc modelling moreover this outcome highlights a need to rethink the use of rc morphodynamic models in fluvial geomorphology and to move away from existing grid based approaches such as the popular cellular automata ca models that remain essentially reductionist in nature in the case of the world s largest sand bed rivers this might be achieved by implementing the rc model outlined here as one element within a hierarchical modelling framework that would enable computationally efficient simulation of the morphodynamics of large rivers over millennial time scales

topographic controls on shallow groundwater dynamics implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall run off response and has been linked to the export of solutes from uplands to streams we sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences footslope backslope shoulder a spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet up from summer through winter in a small till mantled research catchment we demonstrate that the spatial patterns of shallow water table extent and duration and therefore hydrologic connectivity had a strong seasonal signature during the low antecedent soil moisture conditions typically associated with the growing season water tables were patchy discontinuous and only the wettest near stream footslope areas were consistently hydrologically connected with the stream network during the dormant season footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network in the largest storm events the typically driest landforms shoulder slopes established shallow transient water tables suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network in addition we found significant differences p 0 05 in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events these results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements determining hydrologic connectivity between watershed elements as well as for understanding solute transport in catchments copyright 2010 john wiley sons ltd

exploring the frequency size relationships of pipe collapses in different morphoclimatic regions abstract piping is an important land degradation process that occurs in almost all climatic zones this study analyses for the first time the frequency size distribution of different types of pipe collapses pcs sinkholes and compound depressions related to the coalescence of sinkholes compound sinkholes and elongated blind gullies exploring the frequency size relationships of pcs provides critical morphometric information about this hazardous erosion and ground stability process as well as its impact on hillslope denudation hillslope channel coupling and landscape development the analysis has been performed with field based inventories of pcs from five catchments located in two different morphoclimatic environments one in the semi arid ebro depression ne spain valpalmas catchment and four in the humid bieszczady mts se poland in total 724 pcs were mapped among which 335 pcs in valpalmas and 389 pcs in the bieszczady mts the morphometric analyses were based on the major axis the maximum length or width and area of the pcs despite differences between study areas from ne spain and se poland related to climate conditions rainfall regime soil water storage capacity spatial pattern of pipe networks vegetation cover and land use empirical cumulative frequency curves of pcs show similar patterns in all study sites indicating similar overall effects of piping erosion the size distribution of the inventoried pcs can be modelled satisfactorily with logarithmic functions with high goodness of fit values r2 0 93 for each type of pc and the combined set of pcs sinkholes and compound sinkholes blind gullies mapped in each area and in the five catchments together the pcs mapped in valpalmas are displaced towards larger dimensions attributable to local factors the applicability and limitations of frequency size relationships of pcs for geomorphological studies and hazard assessment are discussed

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

hillslope threshold response to rainfall 1 a field based forensic approach summary hillslope threshold response to storm rainfall is poorly understood basic questions regarding the type location and flow dynamics of lateral subsurface flow remain unanswered even at our most intensively studied field sites here we apply a forensic approach where we combined irrigation and excavation experiments at the well studied maimai hillslope to determine the typology and morphology of the primary lateral subsurface flowpaths and the control of bedrock permeability and topography on these flowpaths the experiments showed that downslope flow is concentrated at the soil bedrock interface with flowpath locations controlled by small features in the bedrock topography lateral subsurface flow is characterized by high velocities several orders of magnitude greater than predicted by darcy s law using measured hydraulic conductivities at the site we found the bedrock to be moderately permeable and showed that vertical percolation of water into the bedrock is a potentially large component of the hillslope water balance our results suggest that it is the properties of the bedrock topography and permeability that control subsurface flow at maimai and the soil profile plays a less significant role than previously thought a companion paper incorporates these findings into a conceptual model of hydrological processes at the site to explore the generalities of whole hillslope threshold response to storm rainfall

dem based modelling of surface runoff using diffusion wave equation a digital elevation model dem based overland flow routing model was developed for computation of surface runoff for isolated storm events the model operates on a grid or cell basis and routes the rainfall excess generated over the cells following the dem derived drainage paths to the catchment outlet the rainfall excess for each cell of the catchment was computed using the philip two term infiltration model utilizing the physical properties of the cell the overland flow was described by a finite volume based numerical solution of the diffusion wave approximation of the st venant equations the cell physical properties such as topographic characteristics land use soil etc were extracted from published maps for discretized cells of the catchment using a geographic information system the results of model application indicate that the model satisfactorily predicted the runoff hydrograph the cell based structure of the model allowed for generation of spatially distributed catchment information in terms of the model computed variables such as the depth of flow and discharge

gebel kamil the iron meteorite that formed the kamil crater egypt abstract the 45 m in diameter kamil impact crater was formed 10 g inferred from the density map compiled in this study is 3400 kg field data indicate that the iron bolide approached the earth s crust from the northwest 305 340 n travelling along a moderately oblique trajectory upon hypervelocity impact the projectile was disrupted into thousands of fragments shattering was accompanied by some melting of the projectile and of the quartz arenite target rocks which also suffered shock metamorphism

interflow dynamics on a low relief forested hillslope lots of fill little spill author s du e rhett jackson c klaus j mcdonnell jj griffiths na williamson mf greco jl bitew m abstract 2016 we evaluated the occurrence of perching and interflow over and within a sandy clay loam argillic horizon within first order low relief forested catchments at the savannah river site srs in the upper coastal plain of south carolina we measured soil hydraulic properties depths to the argillic layer soil moisture shallow groundwater behavior interflow interception trench flows and streamflow over a 4 year period to explore the nature and variability of soil hydraulic characteristics the argillic topography and their influence on interflow generation perching occurred frequently within and above the restricting argillic horizons during our monitoring period but interflow was infrequent due to microtopographic relief and associated depression storage on the argillic layer surface high percolation rates through the argillic horizon particularly through soil anomalies also reduced the importance of interflow interflow generation was highly variable across eleven segments of a 121 m interception trench hillslopes were largely disconnected from stream behavior during storms hillslope processes were consistent with the fill and spill hypothesis and featured a sequence of distinct thresholds vertical wetting front propagation to the argillic layer saturation of the argillic followed by local perching filling of argillic layer depressions and finally connectivity of depressions leading to interflow generation analysis of trench flow data indicated a cumulative rainfall threshold of 60 mm to generate interflow a value at the high end of the range of thresholds reported elsewhere

shock metamorphism and impact melting in small impact craters on earth evidence from kamil crater egypt kamil is a 45 m diameter impact crater identified in 2008 in southern egypt it was generated by the hypervelocity impact of the gebel kamil iron meteorite on a sedimentary target namely layered sandstones with subhorizontal bedding we have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign february 2010 in order to investigate shock effects recorded in these rocks ejecta samples reveal a wide range of shock features common in quartz rich target rocks they have been divided into two categories as a function of their abundance at thin section scale 1 pervasive shock features the most abundant including fracturing planar deformation features and impact melt lapilli and bombs and 2 localized shock features the least abundant including high pressure phases and localized impact melting in the form of intergranular melt melt veins and melt films in shatter cones in particular kamil crater is the smallest impact crater where shatter cones coesite stishovite diamond and melt veins have been reported based on experimental calibrations reported in the literature pervasive shock features suggest that the maximum shock pressure was between 30 and 60 gpa using the planar impact approximation we calculate a vertical component of the impact velocity of at least 3 5 km s 1 the wide range of shock features and their freshness make kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures

case study influence of morphological changes on flooding in jingjiang river the middle reach of the yangtze river customarily called the jingjiang river together with its diversion channels and dongting lake form a large complicated drainage system in the last five decades significant geomorphological changes have occurred in the drainage system including the shrinkage of diversion channels contraction of dongting lake changes in the rating curve at the luoshan station and cutoffs of the lower jingjiang river these changes are believed to be the cause of the occurrence of abnormal floods in the jingjiang river qualitative analyses suggest that the first three factors aggravate the flood situation in the lower jingjiang river while the last factor seems beneficial for flood prevention to quantitatively evaluate these conclusions a finite volume numerical model was constructed a series of numerical simulations were carried out to test the individual and combined effects of the aforementioned four factors and these simulations showed that high flood stages in the jingjiang river clearly are related to the geomorphological changes

target projectile interaction during impact melting at kamil crater egypt abstract in small meteorite impacts the projectile may survive through fragmentation in addition it may melt and chemically and physically interact with both shocked and melted target rocks however the mixing mingling between projectile and target melts is a process still not completely understood kamil crater 45 m in diameter egypt generated by the hypervelocity impact of the gebel kamil ni rich ataxite on sandstone target allows to study the target projectile interaction in a simple and fresh geological setting we conducted a petrographic and geochemical study of macroscopic impact melt lapilli and bombs ejected from the crater which were collected during our geophysical campaign in february 2010 two types of glasses constitute the impact melt lapilli and bombs a white glass and a dark glass the white glass is mostly made of sio 2 and it is devoid of inclusions its negligible ni and co contents suggest derivation from the target rocks without interaction with the projectile 2 o 3 0 84 18 7 wt feo t 1 83 61 5 wt and nio 2 melt that eventually solidified as white glass behaved as an immiscible liquid and did not interact with the projectile during the excavation stage dark glass melt engulfed and coated the white glass melt target fragments and got stuck to iron meteorite shrapnel fragments this model could also explain the common formation of white and dark glasses in small impact craters generated by iron bodies e g wabar

formation of a small impact structure discovered within the agoudal meteorite strewn field morocco a relic impact structure was recognized within the strewn field of the agoudal iron meteorite the heavily eroded structure has preserved shatter cones in a limestone basement and remnants of autochthonous and allochthonous breccias fragments of iron incorporated into the allochthonous breccia have a chemical composition ni 5 16 wt ir 0 019 ppm similar to that of the agoudal meteorite supporting a syngenetic origin of the strewn field and the impact structure the total recovered mass of agoudal meteorite fragments is estimated at approximately 500 kg the estimated size of the se nw oriented strewn field is 6 2 km model calculations with minimal preatmospheric size show that a similar meteorite strewn field plus one small crater with observed shock effects could be formed by fragmentation of a meteoroid approximately 1 4 m in diameter with an impact angle of approximately 60 from the horizontal however the most probable is an impact of a larger 3 4 m diameter meteoroid resulting a strewn field with approximately 10 craters 10 30 m in diameter each plus numerous meteorite fragments the calculated scattering area of meteorite shrapnel ejected from these impact craters could completely cover the observed strewn field of the agoudal meteorite

agricultural land degradation by piping erosion in chaco plain northwestern argentina abstract soil piping has been pointed out as an important water erosion agent in a wide range of climatic regions it is responsible for high soil losses in loess derived soils the goal of this study is to evaluate the factors that are acting in the generation of piping processes and explain the mechanism of pipe collapse initiation the study was carried out in loess derived soils located in a rural area of the chaco plain between tucuman and santiago del estero provinces in northwestern argentina pipe collapse types were described and soil loss estimation was performed factors influencing the process were studied under six different categories i e physico chemical and soil mechanical soil mineralogical microstructural biological and land use properties in the study area pipes took place in agricultural fields principally in pastures with slope gradients between 1 and 3 soil pipe collapse occurred in the area as a consequence of sudden wetting of the collapsible soils during summer storms pipe collapse forms vertical pipes or macropores that provide pathways for runoff directly into the soil pipe network in addition tension cracks adjacent to pipe collapses can provide pathways for preferential flow from the surface to the soil pipe network with successive water infiltration the size of the pipes tends to increase and evolves to advanced stages of the process by internal erosion and eventually more pipe collapse blind gully formation is the final step of the piping process after the pipes roof collapse

hydrologic connectivity and threshold behavior of hillslopes with fragipans and soil pipe networks many concepts have been proposed to explain hydrologic connectivity of hillslopes with streams hydrologic connectivity is most often defined by qualitative assessment of spatial patterns in perched water tables or soil moisture on hillslopes without a direct linkage to water flow from hillslopes to streams this form of hydrologic connectivity may not explain the hydrologic response of catchments that have network s of preferential flow paths e g soil pipes which can provide intrinsic connectivity between hillslopes and streams duplex soils are known for developing perched water tables on hillslopes and fostering lateral flows but the connectivity of localized perched water tables on hillslopes with soil pipes has not been fully established the objectives of this study were to characterize pipeflow dynamics during storm events the relationships between perched water tables on hillslopes and pipeflows and their threshold behavior two well characterized catchments in loess soil with a fragipan were selected for study because they contain multiple laterally extensive over 100 m soil pipe networks hillslopes were instrumented with shallow wells adjacent to the soil pipes and the wells and pipe collapse features were equipped with pressure transducers perched water tables developed on hillslopes during a wetting up period october december and became well connected spatially across hillslope positions throughout the high flow period january march the water table was not spatially connected on hillslopes during the drying out april june and low flow july september periods even when perched water tables were not well connected water flowing through soil pipes provided hydrologic connectivity between upper hillslopes and catchment outlets correlations between soil pipeflow and perched water tables depended on the size and location of soil pipes the threshold relationship between available soil moisture index plus storm precipitation asi p and pipeflow was dependent on the season and strongest during dry periods and not high flow seasons this study demonstrated that soil pipes serve as a catchment backbone of preferential flow paths that provide intrinsic connectivity between upper hillslopes and streams

soil pipe collapses in a loess pasture of goodwin creek watershed mississippi role of soil properties and past land use little is known about the association of soil pipe collapse features with soil properties or land use history three loess covered catchments in northern mississippi usa were characterized to investigate these relationships soil pipe collapses were characterized for their size type feature and spatial location along with soil properties across the three catchments although mapped as the same soil one of the catchments did not contain pipe collapse features while the other two had 29 4 and 15 4 pipe collapses per hectare these loess soils contained fragipan layers that are suspected of perching water thereby initiating the piping processes pipe collapses associated with subsurface flow paths were not always consistent with surface topography the surface layer tended to be non erodible while layers below even the upper fragipan layers were susceptible to erosion by pipeflow soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible these anthropic soils were previously gullies that were filled in in the 1950s when forested areas assumed to have been established when land was previously converted from crop to forest land were converted to pasture three decades after this land use change from forest to pasture pipe collapses became evident in contrast the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production the surface horizons above the lower fragipan layer were completely removed during this period thus the top soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed this study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role copyright 2015 john wiley sons ltd

numerical simulation of relatively wide shallow channels with erodible banks a two dimensional numerical model was developed to simulate relatively wide shallow rivers with an erodible bed and banks composed of well sorted sandy materials a moving boundary fitted coordinate system was used to calculate water flow bed change and bank erosion the cubic interpolated pseudoparticle method was used to calculate flow which introduced little numerical diffusion the sediment transport equation for the streamline and transverse transport was used to estimate bed and bank evolution over time while considering the secondary flow bank erosion was simulated when the gradient in the cross sectional direction of the banks was steeper than the submerged angle of repose because of bed erosion near the banks the numerical model reproduced the features of central bars well such as bar growth channel widening due to divergence of the flow around the bars scour holes at the lee of the bars and the increase of bar size with time these features were in accordance with the observations for laboratory experiments it also reproduced the features of braided rivers such as the generation of new channels and abandonment of old channels the bifurcation and confluence of channels and the lateral migration of the channels the model showed that the sediment discharge rate fluctuated with time one of the dynamic features observed in braided channels

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

morphological modeling using a fully coupled total variation diminishing upwind biased centered scheme high resolution morphological modeling of fluvial processes with complex rapidly varying flows has been limited so far by model accuracy or computational efficiency one of the most widely used numerical algorithms is based on the total variation diminishing method solved by either upwind or centered approaches an upwind scheme preserves high accuracy but is complex and computationally demanding whereas the simplicity and efficiency of a centered approach compromise the accuracy the present paper extends a recent upwind biased centered scheme originally developed for clear water and scalar transport over a rigid bed to sediment laden flows over an erodible bed it does so by developing a fully coupled 2 d mathematical model using a finite volume method for structured grids the complete set of noncapacity based governing equations involving the effects of bed deformation and sediment density variation as well as the influences of turbulence and sediment diffusion and the temporal and spatial scales needed for sediment adaptation is solved at one time to obtain synchronous solutions for the entire computational domain for stability a two stage splitting approach together with a second order runge kutta method is employed for the source terms the model is verified in a number of tests covering a wide range of complex sediment laden flows the model is demonstrated to accurately simulate shock waves and reflection waves but also rapid bed deformations at high sediment transport rates the combination of high numerical accuracy and computational efficiency makes the model an important tool to forecast flood events in morphologically complex areas

godunov type solution of curvilinear shallow water equations this paper presents details of a second order accurate godunov type numerical model of the two dimensional conservative hyperbolic shallow water equations written in a non orthogonal curvilinear matrix form and discretized using finite volumes roe s flux function is used for the convection terms and a nonlinear limiter is applied to prevent spurious oscillations validation tests include frictionless rectangular and circular dam breaks an oblique hydraulic jump jet forced flow in a circular basin and vortex shedding from a vertical surface piercing cylinder the results indicate that the model accurately simulates sharp fronts a flow discontinuity between subcritical and supercritical conditions recirculation in a basin and unsteady wake flows

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

ephemeral gully erosion by preferential flow through a discontinuous soil pipe abstract subsurface flow through soil pipes can contribute to ephemeral gully erosion but these soil pipes are cut off when tillage fills in the gully the objective was to determine the effect of flow through discontinuous soil pipes on ephemeral gully erosion experiments were conducted on 150 cm long by 100 cm wide soil beds with an artificial soil pipe at the upper end that extended 50 cm into the soil immediately above a water restricting horizon the combination of rainfall with pipe flow produced extensive 63 kg soil losses by mass wasting the mode of mass wasting appeared to be sudden cataclysmic pop out failures total soil loss by sheet erosion with rainfall and pipe flow combined 13 6 kg was four times higher than by rainfall alone 3 4 kg under rainfall with pipe flow soil loss by mass wasting was nearly 20 times higher than sheet erosion from rainfall alone soil conservation practices that treat surface runoff process alone may be ineffective if subsurface flow is contributing

analysis of a prehistoric egyptian iron bead with implications for the use and perception of meteorite iron in ancient egypt tube shaped beads excavated from grave pits at the prehistoric gerzeh cemetery approximately 3300 bce represent the earliest known use of iron in egypt using a combination of scanning electron microscopy and micro x ray microcomputer tomography we show that microstructural and chemical analysis of a gerzeh iron bead is consistent with a cold worked iron meteorite thin fragments of parallel bands of taenite within a meteoritic widmanstatten pattern are present with structural distortion caused by coldworking the metal fragments retain their original chemistry of approximately 30 wt nickel the bulk of the bead is highly oxidized with only approximately 2 4 of the total bead volume remaining as metal our results show that the rst known example of the use of iron in egypt was produced from a meteorite its celestial origin having implications for both the perception of meteorite iron by ancient egyptians and the development of metallurgical knowledge in the nile valley

modeling of two dimensional overland flow a two dimensional hydrodynamic and numerical model for overland flow is developed in this paper the model allows spatial variations in hillslope physical characteristics including surface roughness infiltration and microtopography the accuracy of the model is tested by comparison with characteristic based solutions and experimental data the results of these tests indicate that the model is accurate and has good stability and convergence properties the application of the model to two dimensional overland flow on hillslopes is demonstrated by applying it to surfaces with spatially variable roughness infiltration and microtopography these simulations show that microtopography is the dominant factor causing spatial variation in overland flow depth velocity and direction

transient two dimensional simulation of real flood events in a mediterranean floodplain the application of a two dimensional 2d finite volume numerical model to real flood events in the ebro river is presented the hydraulic model used is based on the 2d transient shallow water equations on the irregular bed that are able to compute flow advance over a dry bed this study involves the reliable simulation of not only the flood wave advance but also the drying process in a series of events of different magnitude the importance of the correct characterization of the roughness coefficient and the topography is emphasized in the study the former is estimated from a previous classification of structurally homogeneous habitats and the latter is defined by merging the digital terrain model data with a hydraulic river bed elevation reconstruction algorithm the calibration of the full model resulting from the roughness bed river and flow simulation models is based on field measurements of the flooded area for two steady discharges the validation is performed by comparing the numerical results with the water levels measured during five flood events at certain times with the flooded area and time series of continuous point measurements of water depth during different situations throughout the year because the model provides correct predictions of the surface processes both for low and high flow discharges the simulation results are used to analyze the present floodplain hydrodynamics in the same way different topographic scenarios on the basis of changes in the hydraulic river floodplain connectivity are generated to analyze their potentially beneficial effect in the floodplain geomorphic dynamics doi 10 1061 asce hy 1943 7900 0000565 2012 american society of civil engineers ce database subject headings unsteady flow overland flow hydration dewatering flood plains shallow water mediterranean sea simulation author keywords unsteady surface flow wetting drying finite volume shallow water hydrodynamic floodplain hydraulic bed reconstruction

how do disconnected macropores in sloping soils facilitate preferential flow runoff from hillslopes is generated by processes such as infiltration excess and saturation overland flow subsurface stormflow and subsurface return flow preferential flow through macropores can affect any one of these runoff generation processes field studies at the hitachi ohta experimental watershed in japan have noted that self organization processes may manifest the connectivity of such subsurface flow paths particularly via macropores from hillslopes to stream channels it is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at hitachi ohta where subsurface flow and streamflow respond to thresholds of wetness numerical solutions to the three dimensional richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes shapes and orientations solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions the preferential flow network expands as the degree of saturation increases the expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain although the individual macropores are disconnected it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion in addition to the importance of these findings related to stormflow generation in catchments they add support to the concept of self organization of subsurface flow systems in soils copyright 2010 john wiley sons ltd

landscape controls on the hydrology of stream riparian zones abstract increased knowledge of hydrology is essential to an understanding of the water quality function of stream riparian zones we examined the effect of upland surficial aquifer size topography and riparian sediment lithology on the subsurface hydrology of eight riparian sites on glacial till and outwash landscapes in southern ontario canada riparian sites had a permanent subsurface hydrologic connection to the adjacent upland in landscapes where upland permeable sediment depths were 2 15 m in contrast a hydrologic connection was absent in summer and autumn at riparian sites with 5 where the riparian zone was level to gently sloping

microscopic impactor debris in the soil around kamil crater egypt inventory distribution total mass and implications for the impact scenario we report on the microscopic impactor debris around kamil crater 45 m in diameter egypt collected during our 2010 geophysical expedition the hypervelocity impact of gebel kamil ni rich ataxite on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due se sw of the crater extending 300 000 m2 up to 400 m from the crater in agreement with previous determination of the impactor trajectory the microscopic impactor debris include vesicular masses spherules and coatings of dark impact melt glass which is a mixture of impactor and target materials si fe and al rich glass plus fe ni oxide spherules and mini shrapnel documenting that these products can be found in craters as small as few tens of meters in diameter the estimated mass of the microscopic impactor debris 20 t likely 50 60 t

finite volume model for shallow water equations with improved treatment of source terms a simple yet precise relation between the flux gradient and the bed slope source term is presented which produces a net force within the cell with an inclined water surface but ensures still water condition when there is no flow across the boundaries the proposed method consists of calculating the pressure term based on the water depths at the cell vertices which may be computed by a higher order scheme and the bed slope source term by a centered discretization technique the methodology is demonstrated with a godunov type upwind finite volume formulation the inviscid fluxes are calculated using roe s approximate riemann solver and a second order spatial accuracy is obtained by implementing multidimensional gradient reconstruction and slope limiting techniques the accuracy and applicability of the numerical model is verified with a couple of test problems and a real flow example of tidal water movement in a stretch of river hooghly in india

anatomy of a young impact event in central alberta canada prospects for the missing holocene impact record small impact events recorded on the surface of earth are signifi cantly underrepresented based on expected magnitude frequency relations we report the discovery of a 36 m diameter late holocene impact crater located in a forested area near the town of whitecourt alberta canada although undetectable using visible imagery the presence of the crater is revealed using a bare earth digital elevation model obtained through airborne light detection and ranging lidar the target material comprises deglacial quaternary sediments with impact ejecta burying a late holocene soil dated to ca 1100 14 c yr b p most of the 74 iron meteorites 0 1 1196 g recovered have an angular exterior morphology these meteorites were buried at depths 25 cm and are interpreted to result from fragmentation of the original projectile mass either at low altitude or during the impact event impact of the main mass formed the simple bowl shaped impact structure associated with an ejecta blanket and crater fi ll the increasing availability of lidar data for many terrestrial surfaces will serve as a useful tool in the discovery of additional small impact features

laboratory experiments of tsunami runup on a circular island laboratory experiments of a 7 2 m diameter conical island were conducted to study three dimensional tsunami runup the 62 5 cm tall island had 1 on 4 side slopes and was positioned in the center of a 30 m wide by 25 m long flat bottom basin solitary waves with height to depth ratios ranging from 0 05 to 0 20 and source lengths ranging from 0 30 to 7 14 island diameters were tested in water depths of 32 and 42 cm twenty seven capacitance wave gages were used to measure surface wave elevations at incident and four radial transects on the island slope maximum vertical runup measurements were made at 20 locations around the perimeter of the island using rod and transit a new runup gage was located on the back or lee side of the island to record runup time series

discontinuous galerkin finite element method for simulation of flood in crossroads a numerical solution of the two dimensional saint venant equations is presented for the study of the propagation of the floods through the crossroads of the city the numerical scheme is a runge kutta discontinuous galerkin method rkdg with a slope limiter the work studies the robustness and the stability of the method the study is organized around three aspects the prediction of the water depths the location of the right and oblique hydraulic jumps in the crossing and especially the distribution of the flow discharges in the downstream branches the objective of this paper was to use the rkdg method in order to simulate supercritical flow in crossroads and to compare these simulations with experimental results and to show the advantage of this rkdg method compared to a second order finite volume method a good agreement between the proposed method and the experimental data was found the method is then able to simulate the flow patterns observed experimentally and to predict accurately the water depths the location of the hydraulic jumps and the discharge distribution in the downstream branches

earth impact effects program a web based computer program for calculating the regional environmental consequences of a meteoroid impact on earth we have developed a web based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on earth www lpl arizona edu impacteffects this paper details the observations assumptions and equations upon which the program is based it describes our approach to quantifying the principal impact processes that might affect the people buildings and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions the program requires six inputs impactor diameter impactor density impact velocity before atmospheric entry impact angle the distance from the impact at which the environmental effects are to be calculated and the target type sedimentary rock crystalline rock or a water layer above rock the program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse the thermal radiation emitted by the impact generated vapor plume fireball and the intensity of seismic shaking the program also approximates various dimensions of the impact crater and ejecta deposit as well as estimating the severity of the air blast in both crater forming and airburst impacts we illustrate the utility of our program by examining the predicted environmental consequences across the united states of hypothetical impact scenarios occurring in los angeles we find that the most wide reaching environmental consequence is seismic shaking both ejecta deposit thickness and air blast pressure decay much more rapidly with distance than with seismic ground motion close to the impact site the most devastating effect is from thermal radiation however the curvature of the earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon

efficient disruption of small asteroids by earth s atmosphere accurate modelling of the interaction between the atmosphere and an incoming bolide is a complex task but crucial to determining the fraction of small asteroids that actually hit the earth s surface most semi analytical approaches have simplified the problem by considering the impactor as a strengthless liquid like object pancake models1 2 but recently a more realistic model has been developed that calculates motion aerodynamic loading and ablation for each separate particle or fragment in a disrupted impactor3 4 here we report the results of a large number of simulations in which we use both models to develop a statistical picture of atmosphere bolide interaction for iron and stony objects with initial diameters up to 1 km we show that the separated fragments model predicts the total atmospheric disruption of much larger stony bodies than previously thought in addition our data set of 1 000 simulated impacts combined with the known pre atmospheric flux of asteroids with diameters less than 1 km5 6 7 8 9 10 11 12 elucidates the flux of small bolides at the earth s surface we estimate that bodies 220 m in diameter will impact every 170 000 years

hillslope riparian stream connectivity and flow directions at the panola mountain research watershed to obtain a better understanding of water s journey from the hillslope to the stream water level time series from 26 groundwater wells in a hillslope riparian study area in the panola mountain res

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

computing nonhydrostatic shallow water flow over steep terrain flood and dambreak hazards are not limited to moderate terrain yet most shallow water models assume that flow occurs over gentle slopes shallow water flow over rugged or steep terrain often generates significant nonhydrostatic pressures violating the assumption of hydrostatic pressure made in most shallow water codes in this paper we adapt a previously published nonhydrostatic granular flow model to simulate shallow water flow and we solve conservation equations using a finite volume approach and an harten lax van leer and einfeldt approximate riemann solver that is modified for a sloping bed and transient wetting and drying conditions to simulate bed friction we use the law of the wall we test the model by comparison with an analytical solution and with results of experiments in flumes that have steep 31 or shallow 0 3 slopes the law of the wall provides an accurate prediction of the effect of bed roughness on mean flow velocity over two orders of magnitude of bed roughness our nonhydrostatic law of the wall flow simulation accurately reproduces flume measurements of front propagation speed flow depth and bed shear stress for conditions of large bed roughness

catastrophic collapse of water supply reservoirs in urban areas in recognition of the risks associated with the catastrophic collapse of a water supply reservoir a computer mofel was developed to predict the progress of the ensuing flood the fractional step method is used to solve the two dimensional shallow water wave equations on an unstructured triangular grid the finite volume method with a first order approximate riemann solver is used to solve the homogeneous equations euler s method is used to solve the ordinary differential equation operator verification of the model is achieved by comparing the model results with analytical solutions as well as documented published results with very good agreement the model is applied to a case study involving the sudden collapse of a water supply reservoir these reservoirs are generally located in elevated positions in residential areas and represent a potential risk to life and property the model is conservative robust efficient and capable of simulating the wetting and drying processes it resolves shocks simulates flow around complex geometry and obstacles and includes the influence of steep bed slopes and friction

the kamil crater in egypt we report on the detection in southern egypt of an impact crater 45 meters in diameter with a pristine rayed structure such pristine structures are typically observed on atmosphereless rocky or icy planetary bodies in the solar system this feature and the association with an iron meteorite impactor and shock metamorphism provides a unique picture of small scale hypervelocity impacts on earth s crust contrary to current geophysical models ground data indicate that iron meteorites with masses of the order of tens of tons can penetrate the atmosphere without substantial fragmentation

fully coupled approach to modeling shallow water flow sediment transport and bed evolution in rivers 1 our ability to predict complex environmental fluid flow and transport hinges on accurate and efficient simulations of multiple physical phenomenon operating simultaneously over a wide range of spatial and temporal scales including overbank floods coastal storm surge events drying and wetting bed conditions and simultaneous bed form evolution this research implements a fully coupled strategy for solving shallow water hydrodynamics sediment transport and morphological bed evolution in rivers and floodplains pihm hydro and applies the model to field and laboratory experiments that cover a wide range of spatial and temporal scales the model uses a standard upwind finite volume method and roe s approximate riemann solver for unstructured grids a multidimensional linear reconstruction and slope limiter are implemented achieving second order spatial accuracy model efficiency and stability are treated using an explicit implicit method for temporal discretization with operator splitting laboratory and field scale experiments were compiled where coupled processes across a range of scales were observed and where higher order spatial and temporal accuracy might be needed for accurate and efficient solutions these experiments demonstrate the ability of the fully coupled strategy in capturing dynamics of field scale flood waves and small scale drying wetting processes

finite volume two dimensional unsteady flow model for river basins the paper presents a two dimensional unsteady flow model rbfvm 2d based on the finite volume method with a combination of unstructured triangular and quadrilateral grids in a river basin system the attractive feature of this model is that it calculate of the mass and momentum flux across each side of elements as a riemann problem which is solved using the osher scheme this feature enables this model to deal with the wetting and drying processes for flood plain and wetland studies dam breaking phenomena involving discontinuous flows subcritical and supercritical flows and other cases the computations of tributary inflows and regulated flows through gates weirs and culverts or bridges are also included sample applications of this model to two dam break problems showed fairly satisfactory results also this model was applied to a portion of the kissimmee river basin in florida for flow simulations and the results agreed well with the field and laboratory data in a physical model study of this ri

2d shallow water model using unstructured finite volumes methods this paper presents a two dimensional 2d shallow water numerical model which is based on the resolution of the saint venant equation using the unstructured finite volumes method combined with green s theorem technique the model has been validated by several benchmarks the numerical results obtained from the model are in good agreement with the analytical or experimental ones the paper also presents an application of this model to flood diversion from the red river into a water retention zone for the purpose of reducing flood threat at hanoi capital of vietnam

hydrodynamics of turbid underflows i formulation and numerical analysis a mathematical model is developed for unsteady two dimensional single layer depth averaged turbid underflows driven by nonuniform noncohesive sediment the numerical solution is obtained by a high resolution total variation diminishing finite volume numerical model which is known to capture sharp fronts accurately the monotone upstream scheme for conservation laws is used in conjunction with predictor corrector time stepping to provide a second order accurate solution flux limiting is implemented to prevent the development of spurious oscillations near discontinuities the model also possesses the capability to track the evolution and development of an erodible bed due to sediment entrainment and deposition this is accomplished by solving a bed sediment conservation equation at each time step independent of the hydrodynamic equations with a predictor corrector method the model is verified by comparison to experimental data for currents driven by uniform and nonuniform sediment

surf zone dynamics simulated by a boussinesq type model part i model description and cross shore motion of regular waves abstract this is the first of three papers on the modelling of various types of surf zone phenomena in this first paper part i the model is presented and its basic features are studied for the case of regular waves the model is based on two dimensional equations of the boussinesq type and it features improved linear dispersion characteristics possibility of wave breaking and a moving boundary at the shoreline the moving shoreline is treated numerically by replacing the solid beach by a permeable beach characterized by an extremely small porosity run up of nonbreaking waves is verified against the analytical solution for nonlinear shallow water waves the inclusion of wave breaking is based on the surface roller concept for spilling breakers using a geometrical determination of the instantaneous roller thickness at each point and modelling the effect of wave breaking by an additional convective momentum term this is a function of the local wave celerity which is determined interactively the model is applied to cross shore motions of regular waves including various types of breaking on plane sloping beaches and over submerged bars model results comprise time series of surface elevations and the spatial variation of phase averaged quantities such as the wave height the crest and trough elevations the mean water level and the depth averaged undertow comparisons with physical experiments are presented the phaseaveraged balance of the individual terms in the momentum and energy equation is determined by time integration and quantities such as the cross sectional roller area the radiation stress the energy flux and the energy dissipation are studied and discussed with reference to conventional phase averaged wave models the companion papers present cross shore motions of breaking irregular waves swash oscillations and surf beats part ii and nearshore circulations induced by breaking of unidirectional and multidirectional waves part iii

crater morphology in sandstone targets the memin impact parameter study hypervelocity 2 5 7 8 km s 1 impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass target pore space saturation target projectile density contrast and target layer orientation on crater size and shape crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation craters in water saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone morphometric analyses of the resultant craters 5 40 cm in diameter reveal features that are characteristic of all of our experimental craters regardless of impact conditions i a large central depression within a fragile light colored central part and ii an outer spallation zone with areas of incipient spallation two different mechanical processes grain fragmentation and intergranular tensile fracturing are recorded within these crater morphologies zone i approximates the shape of the transient crater formed by material compression displacement comminution and excavation flow whereas ii is the result of intergranular tensile fracturing and spallation the transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models the dimensions of this transient and of the final crater show the same trends both increase in volume with increasing impact energy and with increasing water saturation of the target pore space the relative size of the transient crater in percent of the final crater volume decreases with increasing projectile mass and velocity signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

dissecting the variable source area concept subsurface flow pathways and water mixing processes in a hillslope summary this study uses an instrumented trenched 0 5 ha hillslope in the southern tier of new york state usa to provide new data and insights on how variable source areas and associated flow pathways form and combine to connect rainfall with downstream water flows across a hillslope measurements of water fluxes in the trench upslope water table dynamics surface and bedrock topography and isotopic and geochemical tracers have been combined for a four dimensional space time characterization of subsurface storm flow responses during events with dry antecedent conditions infiltrating rainwater was found to percolate through a prevailing fragipan layer to deeper soil layers with much 33 71 of the total discharge of the hillslope originating from deeper water flow below the fragipan during storm events with wet antecedent conditions and large rainfall amounts shallow lateral flow of event and pre event water above the fragipan occurred and was one magnitude greater than the deeper water flow contribution spatial surface and subsurface water quality observations indicate that water from a distance of up to 56 m contributed runoff from the hillslope during storm events in addition mobilization of total dissolved phosphorus tdp with subsurface flow played a greater role than with overland or near surface flow during all events tdp loads were highest in the total discharge during peak flows 8 11 5 kg ha 1 d 1 except during the largest storm event when tdp concentrations were highly diluted these results have implications for strategies to protect streams and other downstream water recipients from waterborne nutrient and pollutant loading

lagrangian modeling of the dynamics of river and floodplain flow a new lagrangian dynamic river model is described the model solves the coupled one dimensional hydrostatic flow equations separately in a main river channel and in adjacent floodplains using a two stage predictor corrector scheme the lateral interaction between the main channel and floodplains due to both advective exchange arising from lateral pressure gradients and turbulent exchange due to lateral shear is included the lagrangian moving grid eliminates numerical diffusion and oscillations commonly experienced in eulerian models and can accurately simulate wave propagation and nonlinear steepening until wave breaking the lagrangian moving grid is dynamically adaptive providing variable resolution as the moving fluid parcel s length changes either because the cross sectional flow area or the flow depth changes as the wave moves down a channel of variable cross section the model also allows flows over dry beds and moving boundaries to be handled efficiently the model was successfully validated

cosmic ray exposure and pre atmospheric size of the gebel kamil iron meteorite cosmogenic he ne and ar as well as the radionuclides 10be 26al 36cl 41ca 53mn and 60fe have been determined on samples from the gebel kamil ungrouped ni rich iron meteorite by noble gas mass spectrometry and accelerator mass spectrometry ams respectively the meteorite is associated with the kamil crater in southern egypt which is about 45 m in diameter samples originate from an individual large fragment individual as well as from shrapnel concentrations of all cosmogenic nuclides stable and radioactive are lower by a factor 3 4 in the shrapnel samples than in the individual assuming negligible 36cl decay during terrestrial residence indicated by the young crater age 85 cm i e a pre atmospheric mass 20 tons with a preferred radius of 115 120 cm 50 60 tons the analyzed samples came from a depth of approximately 20 cm individual and approximately 50 80 cm shrapnel the size of the gebel kamil meteoroid determined in this work is close to estimates based on impact cratering models combined with expectations for ablation during passage through the atmosphere folco et al 2010 2011

two dimensional flood routing on steep slopes program routweir represents a two dimensional flood routing model designed to analyze two dimensional flow caused by rainfall and runoff flooding events input to the program consists of known geometry topography initial conditions and boundary conditions the geometry and bathymetry of the flood plain are represented by a grid of interconnecting triangular elements initial water levels are prescribed to correspond to the normal water elevations in the river channel boundary conditions are prescribed by a discharge hydrograph at the upstream boundary of the river basin and by the water surface elevations at the ocean boundary the interior water elevations and discharges are computed allowing flooding and drying to take place in the triangular elements of the grid based on a conservation of water volume equation and a surface slope dependent dynamic equation output consists of time histories of watersurface elevations and peak elevations in both tabular and graphical form routweir has been successfully calibrated against recorded flood levels in the rio culebrinas basin in puerto rico and has been used in that basin in a federal flood insurance study a versatile computer program routweir can be applied to many flood routing problems it is particularly suited for wide river basins with large bottom slopes and for normally dry areas subject to extensive flooding