recognition of 18β h oleanane in several crudes and tertiary upper cretaceous sediments definition of a new maturity parameter abstract ekweozor et al chem geol 27 11 28 and 29 37 first discovered an unknown compound with a gc retention time very close to that of the 18 h olenane peak in oils and tertiary sediments of the nigerian delta this compound was called j several authors wang et al advances in organic geochemistry 1981 pp 108 113 wiley chichester 1983 schoelle et al ibid pp 156 163 reported the occurrence of 18 h oleanane without underlying the presence of j because of their coelution in this study the presence of j has been confirmed in more than 150 rock extracts and 19 oils from different countries and is identified as the 18 h oleanane by comparison to retention time and mass spectrum and by its coelution with an authentic standard apart from tertiary sediments the 18 h and 18 h oleananes have also been found in upper cretaceous sediments which extends the occurrence of these compounds back in age a maturity correlation has been found between the relative concentration of 18 h oleanane and 18 h oleanane in fact an increase in the 18 h 18 h oleanane ratio has been observed with increasing depth in several wells the 18 h 18 h oleanane ratio has been correlated with other classical maturity parameters i e ts tm ro and tmax

double flood basalts and plume head separation at the 660 kilometer discontinuity several of the world s flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years these double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle this detached plume head eventually triggers the first flood basalt event the remaining conduit forms a new plume head which causes the second eruptive event the second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head in general agreement with observations regarding double flood basalts

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

reach scale floodplain inundation dynamics observed using airborne synthetic aperture radar imagery data analysis and modelling summary in this paper we use an airborne synthetic aperture radar to map river flood inundation synoptically at fine spatial resolution 1 2 m along a 16 km reach of the river severn west central england images were obtained at four times through a large flood event between 8th and 17th november 2000 and processed using a statistical active contour algorithm to yield the flood shoreline at each time intersection of these data with a high vertical accuracy survey of floodplain topography obtained from airborne laser altimetry permitted the calculation of dynamic changes in inundated area total reach storage and rates of reach dewatering in addition comparison of the data to gauged flow rates the measured floodplain topography and map data giving the location of embankments and drainage channels on the floodplain yields new insights into the factors controlling the development of inundation patterns at a variety of scales finally the data were used to assess the performance of a simple two dimensional flood inundation model lisflood fp and allows us for the first time to validate the dynamic performance of the model this process is shown to give new information into structural weaknesses of the model and suggests possible future developments including the incorporation of a better description of floodplain hydrological processes in the hydraulic model to represent more accurately the dewatering of the floodplain

numerical simulation of floodplain hydrology despite the extensive research into hillslope and channel interactions in headwater catchments surprisingly little attention has been paid to such processes in lowland rivers in particular previous studies have not addressed the influence of hillslope contributions and have concentrated solely on in bank floods rather than more complex out of bank cases accordingly we combine field monitoring and numerical modeling to study hillslope floodplain and channel interactions for a lowland river piezometric precipitation and river stage data were used to parameterize and test a new two dimensional finite element model of saturated unsaturated flow applied to two vertically aligned cross sections through a lowland floodplain data for two major out of bank flood events were simulated which appeared to show the presence of a significant unsaturated zone extending up to 5 m below the surface the model simulated reasonably well the pressure head field that was recorded at a number of piezometers located internal to the computational domain on each transect and we conclude that floodplain hydrology is predominately a two dimensional lateral process three dimensional down reach flow effects would seem to become more significant at the beginning and end of each event the simulations also showed that the unsaturated zone remained close to saturation at all times and that it was not significant in terms of the floodplain hydrology examination of velocity vector patterns showed the formation of a strong groundwater ridge within the floodplain this led to the development of strong velocities directed toward hillslope areas as the inundation front approached the hillslope floodplain junction this suggests that surface water may move into hillslope areas adjoining the floodplain during major floods thus the extent of the hyporheic zone may be larger than previously thought

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

geometric and structural river channel complexity and the prediction of urban inundation recent research modelling floodplain inundation processes has concentrated on issues surrounding the level of physical topographical and numerical solver complexity needed to represent floodplain flows adequately however during flooding episodes the channel typically still conveys the bulk of the flow despite this the effect of channel physical processes and topographic complexity on model results has been largely unexplored to address this the impact of channel cross section geometry channel long profile variability and the representation of hydraulic structures on floodplain inundation are explored using a coupled dynamic 1d 2d hydraulic model estry tuflow of the carlisle floods of january 2005 these simulations are compared with those from a simplified 1d 2d model lisflood fp in this case the simpler model is sufficient to simulate the far field peak flood elevations however comparison of channel dynamics suggests that the full shallow water approximation used by estry tuflow gives a more robust performance when models calibrated on maximum floodplain water elevations are used to predict channel water levels examination of the response of estry tuflow to variations in channel geometric complexity shows that downstream variations in the channel long profile are more important than cross section variability for obtaining a dataset independent calibration the results show in general that as model physical complexity is increased calibrated parameters become less effective and as a consequence the values of performance measures reduce less rapidly away from the optimum value this means that often more physically complex models are less likely to yield different optimum parameter values when calibrated on different datasets resulting in a more robust numerical model lastly the inclusion of bridge structures can simulate substantial local backwatering effects but the variability in observed water and wrack marks is such that it is not possible to discern the effect of the bridges at this site in the post event observational dataset copyright 2011 john wiley sons ltd

geochemical and petrographic characterization of humic coals considered as possible oil source rocks abstract recently several groups of authors have argued that coals should be considered as possible source rocks for oil as well as being source rocks for gas the present study was undertaken with the objective of evaluating the various methods of characterization of maturation levels and oil potentials of coals from within the oil window it was found that the degree of maturation of a coal could not be specified exactly no matter what parameter describing coal rank was used this lack of precision obviously makes it difficult to compare coals especially from the point of view of their petroleum potential which varies during the course of coalification furthermore quantitative evalution of the oil potential of coals is difficult particularly the present day petrographic concept of exinite does not seem very well adapted to this quantitative evaluation differences in oil potential might in fact be better explained by the relative proportions of the various vitrinite macerals which are present rather than by the proportion of exinite in the coal

heat flow on the hawaiian swell and lithospheric reheating most oceanic volcanic centres caused by hotspot activity are surrounded by sea floor that is unusually shallow for its age1 2 there is increasing evidence that swells found on older sea floor like the hawaiian swell have formed from a broad scale reheating and thinning of the lithosphere as it passes over a mantle hotspot3 4 if the formation and subsequent disappearance of these swells are controlled by thermal processes they should have an above normal heat flux we present here the results from 95 new heat flow measurements on the hawaiian swell along the older part of the swell the heat flow is 20 25 higher than the normal heat flow for crust of this age this anomaly is consistent with the observed swell uplift the shape and amplitude of the heat flow anomaly require that the reheating be largely confined to the lower half of the lithosphere

the potential influence of radiative heat transfer on the formation of megaplumes in the lower mantle abstract recent seismic tomographic models have revealed broad low velocity anomalies in the lower mantle beneath africa and the central pacific which suggest a break in the symmetry between hot and cold regions in lower mantle dynamics we have considered the possible impact from radiative heat transfer which can be described by a nonlinear temperature dependent coefficient in the thermal conductivity in 2d numerical simulations results for rayleigh numbers up to 106 show a strong stabilizing influence from radiative heat transfer on mantle upwellings and the production of extremely hot thermal anomalies in the interior this nonlinearity is responsible for producing a strong attractor in the mantle convective system which greatly simplifies its time dependent dynamics the possible link of the simplified lower mantle time dependent dynamics with polar wander is discussed the main point here is that slow time dependence of the huge anomalies in the lower mantle can be the main mechanism controlling long term rotational dynamics

biological markers and carbon isotope composition of organic matter in the upper cretaceous coals and carbonaceous shale succession jiza qamar basin yemen origin type and preservation abstract bituminous coals and carbonaceous shales located in the jiza qamar basin on the eastern yemen were analysed based on a combined investigation of organic geochemistry and petrology to define the palaeodepositional environment condition organic matter inputs and their thermal maturity carbon isotope compositions and various biomarkers were performed on coals and carbonaceous shales within the upper cretaceous mukalla formation in the jiza qamar basin the 13 c values range from 29 2 to 24 5 with average values around 26 7 whereas the organic carbon contents in most sediment samples are consistently high 3 indicating that the organic matter in the mukalla coal and carbonaceous shale sediments has a predominantly terrigenous origin with slightly marine influence during burial this has also been identified from kerogen microscopy which is characterized by dominance of vitrinite and liptinite organic matter the investigated biomarkers indicated that the mukalla coals and carbonaceous shales contain high contribution of land plants with a minor aquatic organic matter input that was deposited in a fluvial to deltaic environments and preserved under relatively oxic conditions this has been achieved from acyclic isoprenoids terpane and sterane biomarkers of a saturated hydrocarbon and dibenzothiophene alkylnaphthalene and methylphenanthrene biomarkers of an aromatic hydrocarbon based on the analysed biomarker thermal maturity indicators it may be deduced that the mukalla coals and carbonaceous shales in the jiza qamar basin have entered an early mature to mature stages for hydrocarbon generation this is also supported by vitrinite reflectance values of 0 63 0 83 ro indicative that these sediments have reached oil window maturity

inferring the viscosity and the 3 d density structure of the mantle from geoid topography and plate velocities summary in a dynamic earth mantle mass heterogeneities induce gravity anomalies surface velocities and surface topography these lateral density heterogeneities can be estimated on the basis of seismic tomographic models recent papers have described a realistic circulation model that takes into account the observed plate geometry and is able to predict the rotation vectors of the present plates the relationship between the surface observables and the heterogeneities is sensitive to the viscosity stratification of the mantle here we use this model combined with a generalized least squares method in order to infer the viscosity profile of the earth from the surface observations and to get some new insight into the 3 d density structure of the mantle the computed radial viscosity profile presents a continuous increase of more than two orders of magnitude the asthenosphere has a viscosity close to 2 x lo2 pa s no sharp discontinuity is requested at the upper lower mantle interface the largest viscosity 7 x 10 pas is reached in the middle of the lower mantle at greater depth approaching the core mantle boundary the viscosity decreases by one order of magnitude the model suggests that the well known degree 2 and order 2 anomaly in the transition zone of the upper mantle is merely the signature of the slabs it also slightly increases the degree 2 and order 0 in the lower mantle and decreases it in the upper mantle in other words the inversion requests a hotter lower mantle beneath the equator and a colder upper mantle at the same latitudes

steady plumes in viscously stratified vigorously convecting three dimensional numerical mantle convection models with mobile plates 1 we present results from three dimensional 3 d cartesian geometry computations featuring vigorous high rayleigh number mantle convection in a system incorporating stiff tectonic plates with dynamically determined time dependent velocities we track plume related hot spot motion while calculating associated synthetic hot spot tracks allowing us to estimate plume migration rates relative to plate motion rates plate like surface motion is achieved explicitly by specifying both the plate geometry and rigidity however plate velocities evolve dynamically in response to the buoyancy distribution within the convecting system including buoyancy within the plate itself we find that convection is characterized by downwelling sheets and varying numbers of 3 d upwelling structures when the lower mantle to upper mantle viscosity ratio is varied from 9 to 90 as the lower mantle viscosity is increased relative to the upper mantle viscosity the upwellings in the calculations evolve into vigorous active plumes characterized by long narrow thermal conduits with broad disk like heads the total number shape and persistence of the plumes are affected by the specified viscosity stratification in the calculations our findings indicate that hot spots associated with mantle plumes drift by smaller distances in comparable amounts of time when the lower mantle viscosity is increased relative to the upper mantle viscosity in cases with a high lower mantle to upper mantle viscosity ratio the depth of the flow aligned with plate motion is diminished and the plate scale return flow is integrated into a deep unorganized sluggish layer as a result plume conduit morphology in the lower mantle of such calculations is less influenced by plate motion than in calculations with a small difference between upper mantle and lower mantle viscosity for lower mantle viscosities 30 times and 90 times greater than the upper mantle viscosity the lower mantle velocity field is dominated locally by active plumes anchored in the lower thermal boundary layer of the convecting system and plume migration rates are typically only about 10 of the overriding plate velocity in such cases we also find that plume related hot spots persist for periods that we estimate to be between 0 55 and 1 1 plume transit times

the oleananes origin maturation and limits of occurence in southern nigeria sedimentary basins oleananes occur within well defined age and paleogeographic boundaries in the sedimentary province of southern nigeria thus signifying that the biomarkers may be analogous to index fossils in anambra syncline lower benue trough the biomarkers are found in rocks which are as old as late upper cretaceous in tertiary niger delta the concentration composition and distribution of the oleananes in rocks and oils are determined mainly by palaeodepositional environment and thermal history and are independent of age and geographical location of specific samples oleanane content varies with increasing burial depth with peak concentration coinciding within rm range 0 4 0 6 implying early generation of hydrocarbons from the basin s typically resin rich kerogens it is evident that the oleanane content parameter is superior to the hopane and sterane isomerisation indices for monitoring thermal maturation in the delta and for differentiating paralic from paralic marine source facies as well as early from late generated oils

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

sterane isomerisation and moretane hopane ratios in crude oils derived from tertiary source rocks the extent of sterane isomerisation reactions and the moretane hopane ratios of 234 crude oils taken world wide from a wide variety of source rocks of differing geological ages have been measured this data indicates that in 78 crude oils derived from tertiary source rocks sterane isomerisation reactions as determined by the 20s 20s 20r ration of the c29 5 h 14 h 17 h normal steranes and the c29 iso iso normal ratio iso 5 h 14 h 17 h are mainly incomplete and sometimes considerably so in addition the same crude oils have 17 h 21 h moretane 17 h 21 h hopane ratios which are significantly greater predominantly in the range 0 10 0 30 than those of crude oils derived from older mature source rocks mainly less than 0 1 this data for crude oils lends support to the hypothesis proposed by mackenzie and mckenzie 1983 for source rock extracts that the time temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in tertiary sediments is generally insufficient despite generation of crude oil at relatively high temperatures an alternative hypothesis is that the incomplete sterane isomerisation of tertiary crude oils may be due to generation of these crude oils from their deltaic land plant containing source rocks under low heating conditions a third hypothesis proposes that the tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration although possible in particular instances such a mechanism does not appear to be generally applicable since in that case the phenomenon would then appear to be restricted to the tertiary the higher moretane hopane ratios of the tertiary crude oils could suggest that constraints similar to those applying in sterane isomerisation also operate in the conversion of moretane to 17 h hopane

the interaction of plumes with the transition zone under continents and oceans abstract the dynamics of mantle flow with phase transitions can be influenced by the presence of a thick continental lithosphere especially for the 400 km phase transition we have studied the effects of the continental lithosphere on the mantle convection with the two major phase transitions at 400 km and 660 km a 2 d model with an aspect ratio 8 box was used in which the surface was divided into two domains oceanic and continental the continental lithosphere is modeled by a highly viscous 200 km thick lid which is 100 times stiffer than the oceanic part we also consider the consequences of plate reconfiguration by switching instantaneously the underlying rheological structure of the oceanic and continental domains a depth dependent viscosity with an additional jump at 660 km depth was employed other depth dependent properties employed are the thermal expansivity and the thermal diffusivity both internal and basal heating configurations were studied our results show that there are distinct differences in the mode of interaction of plumes with the transition zone under continents and oceans much larger stationary plumes are developed in the lower mantle under continents and erupt from time to time into the upper mantle creating a very hot continental upper mantle plumes under oceans are weaker but produce fast horizontal jets when the plumes impinge upon the surface very large plumes are formed in the internally heated cases because of the presence of depth dependent properties in the lower mantle creating a thick bottom boundary layer this thick thermal boundary layer is swept upward under the continents by a large scale flow in the lower mantle these results can be important for the interpretation of seismic tomography under africa and the central pacific

efficient incorporation of channel cross section geometry uncertainty into regional and global scale flood inundation models this paper investigates the challenge of representing structural differences in river channel cross section geometry for regional to global scale river hydraulic models and the effect this can have on simulations of wave dynamics classically channel geometry is defined using data yet at larger scales the necessary information and model structures do not exist to take this approach we therefore propose a fundamentally different approach where the structural uncertainty in channel geometry is represented using a simple parameterisation which could then be estimated through calibration or data assimilation this paper first outlines the development of a computationally efficient numerical scheme to represent generalised channel shapes using a single parameter which is then validated using a simple straight channel test case and shown to predict wetted perimeter to within 2 for the channels tested an application to the river severn uk is also presented along with an analysis of model sensitivity to channel shape depth and friction the channel shape parameter was shown to improve model simulations of river level particularly for more physically plausible channel roughness and depth parameter ranges calibrating channel manning s coefficient in a rectangular channel provided similar water level simulation accuracy in terms of nash sutcliffe efficiency to a model where friction and shape or depth were calibrated however the calibrated manning coefficient in the rectangular channel model was 2 3 greater than the likely physically realistic value for this reach and this erroneously slowed wave propagation times through the reach by several hours therefore for large scale models applied in data sparse areas calibrating channel depth and or shape may be preferable to assuming a rectangular geometry and calibrating friction alone

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

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

time dependent convection with non newtonian viscosity we have used a numerical model of bottom heated two dimensional convection in boxes of aspect ratios 2 5 and 4 0 to study the differences in time dependent convection between newtonian and stress dependent viscosity the onset of time dependence due to boundary layer instability is found at approximately the same effective rayleigh number for both rheologies however with increasing rayleigh number the temporal and spatial fluctuations in the flow field become much more pronounced with non newtonian rheology also the tendency for breakup of long cells into smaller ones is stronger the presence of stress dependent rheology can cause long wavelength lateral viscosity variations up to an order of magnitude this result could have strong implications for the interpretation of mantle viscosity from postglacial rebound

coupled 1d quasi 2d flood inundation model with unstructured grids a simplified numerical model for simulation of floodplain inundation resulting from naturally occurring floods in rivers is presented flow through the river is computed by solving the de saint venant equations with a one dimensional 1d finite volume approach spread of excess flood water spilling overbank from the river onto the floodplains is computed using a storage cell model discretized into an unstructured triangular grid flow exchange between the one dimensional river cells and the adjacent floodplain cells or that between adjoining floodplain cells is represented by diffusive wave approximated equation a common problem related to the stability of such coupled models is discussed and a solution by way of linearization offered the accuracy of the computed flow depths by the proposed model is estimated with respect to those predicted by a two dimensional 2d finite volume model on hypothetical river floodplain domains finally the predicted extent of inundation for a flood event on a stretch of river severn united kingdom by the model is compared to those of two proven two dimensional flow simulation models and with observed imagery of the flood extents

a simple raster based model for flood inundation simulation in this paper the development of a new model for simulating flood inundation is outlined the model is designed to operate with high resolution raster digital elevation models which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation this consists of a one dimensional kinematic wave approximation for channel flow solved using an explicit finite difference scheme and a two dimensional diffusion wave representation of floodplain flow the model is applied to a 35 km reach of the river meuse in the netherlands using only published data sources and used to simulate a large flood event that occurred in january 1995 this event was chosen as air photo and synthetic aperture radar sar data for flood inundation extent are available to enable rigorous validation of the developed model 100 50 and 25 m resolution models were constructed and compared to two other inundation prediction techniques a planar approximation to the free surface and a relatively coarse resolution two dimensional finite element scheme the model developed in this paper outperforms both the simpler and more complex process representations with the best fit simulation correctly predicting 81 9 of inundated and non inundated areas this compares with 69 5 for the best fit planar surface and 63 8 for the best fit finite element code however when applied solely to the 7 km of river below the upstream gauging station at borgharen the planar model performs almost as well 83 7 correct as the raster model 85 5 correct this is due to the proximity of the gauge which acts as a control point for construction of the planar surface and the fact that here low lying areas of the floodplain are hydraulically connected to the channel importantly though it is impossible to generalise such application rules and thus we cannot specify a priori where the planar approximation will work simulations also indicate that for this event at least dynamic effects are relatively unimportant for prediction of peak inundation lastly consideration of errors in typically available gauging station and inundation extent data shows the raster based model to be close to the current prediction limit for this class of problem q 2000 elsevier science b v all rights reserved

the accuracy of sequential aerial photography and sar data for observing urban flood dynamics a case study of the uk summer 2007 floods in this paper we examine for the first time the potential of remote sensing to monitor flood dynamics in urban areas and constrain mathematical models of these processes this is achieved through the development of a unique data set consisting of a series of eight space borne synthetic aperture radar sar and aerial photographic images of flooding of the uk town of tewkesbury acquired over an eight day period in summer 2007 previous observations of urban flooding have used single image and wrack mark data and have therefore been unable to adequately chart the propagation and recession of flood waves through complex urban topography by using a combination of space borne radar and aerial imagery we are able to show that remotely sensed imagery particularly from the new terrasar x radar can reproduce dynamics adequately and support flood modelling in urban areas we illustrate that image data from different remote sensing platforms reveal sufficient information to distinguish between models with varying degrees of channel floodplain connectivity particularly toward the end of the recession phase of the event for this test case our results also show that high resolution sar imagery even when acquired from satellites can reveal important hydraulic characteristics difficult to simulate with current dynamic flood models hence it is established at least for this test case and event that sar imagery from as far as several hundred kilometers from the earth s surface can deliver important information about floodplain dynamics that can be used to identify and help build suitable models even in built up environments

interpretation of the d zone at the base of the mantle dependence on assumed values of thermal conductivity a common assumption in modeling dynamic processes in the earth s lower mantle is that thermal conductivity is sensibly constant throughout the lower mantle and equal to approximately 4 w m 1 k 1 this value is the result of extrapolation using a linearized theory with estimated parameters for lattice contributions to thermal conductivity furthermore this value is highly dependent on the assumed geotherm excluding theoretical uncertainties in the extrapolation recent experimental data for the pressure dependence of conductivity coupled with a revised geotherm lead to substantially higher estimated values for the lower mantle the hypothesis that the seismically resolved anomalous zone at the base of the mantle d is a thermal boundary layer can be questioned in this case of a higher estimation for thermal conductivity

viscosity undulations in the lower mantle the dynamical role of iron spin transition a b s t r a c t a proper determination of the lower mantle viscosity profile is fundamental to understanding earth geodynamics based on results coming from different sources several models have been proposed to constrain the variations of viscosity as a function of pressure stress and temperature while some models have proposed a relatively modest viscosity variation across the lower mantle others have proposed variations of several orders of magnitude here we have determined the viscosity of ferropericlase a major mantle mineral and explored the role of the iron high to low spin transition viscosity was described within the elastic strain energy model in which the activation parameters are obtained from the bulk and shear wave velocities those velocities were computed combining first principles total energy calculations and the quasi harmonic approximation as ar esult of a strong elasticity softening across the spin transition there is a large reduction in the activation free energies of the materials creep properties leading to viscosity undulations these results suggest that the variations of the viscosity across the lower mantle resulting from geoid inversion and postglacial rebound studies may be caused by the iron spin transition in mantle minerals implications of the undulated lower mantle viscosity profile exist for both down and up wellings in the mantle we find that a viscosity profile characterized by an activation free energy of g z0 300 400 kj mol based on diffusion creep and dilation factor 0 5b etter fits the observed high velocity layer at mid mantle depths which can be explained by the stagnation and mixing of mantle material our model also accounts for the growth of mantle plume heads up to the size necessary to explain the large igneous provinces that characterize the start of most plume tracks

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

small scale sublithospheric continental mantle deformation constraints from sks splitting observations summary it is generally believed that azimuthal seismic anisotropy is an important property of the subcontinental mantle and that this is a relatively small scale phenomenon compared with anisotropy of the oceanic mantle during recent years shear wave splitting has come to be viewed as the most direct diagnostic of azimuthal anisotropy the magnitude of the splitting delay times can often rule out a crustal source of anisotropy however it is not yet clear whether the source of anisotropy lies within the lithosphere or the sublithosphere it is essential to know the scale of lateral variations and the distribution of anisotropy with depth in order to understand the origin of this phenomenon here we describe a way to constrain the depth of the anisotropy by studying the lateral variation of the splitting parameters at neighbouring seismic stations we use sks and skks phases recorded at the nars nl array a relatively dense network of broad band stations separated by about 50 km fresnel zones at different depths are calculated for these phases the depth of the anisotropy is constrained by the criterion that fresnel zones corresponding to different splitting observations should not overlap variability in the splitting measurements for events with different directions of approach recorded at one station and for single events recorded at various stations provides evidence for a non homogeneously distributed source of anisotropy located below the array at different depths we show that this variability in the measurements cannot be due to effects of crustal scattering our results indicate that the anisotropy is partly located in the sublithospheric mantle at about 400 km depth this suggests that the deformation in this region is subject to significant lateral variations

evolution of starting mantle plumes a comparison between numerical and laboratory models abstract laboratory experiments on the initiation and development of mantle plumes suggest the formation of a bulbous plume head that grows in time by entrainment of surrounding material followed by a thin feeder conduit this type of plume is generally not seen in numerical models of mantle convection to better determine the possible differences between numerical and laboratory experiments we have numerically reproduced a published laboratory experiment on plume initiation theoretical predictions for the growth of the plume head have been verified and the experiments allowed for a new determination of a similarity constant models with a constant viscosity fluid show much less entrainment simulations using a plume rising from a thermal boundary layer with an olivine type temperature dependence show that most of the source material is contained in the plume head and that the conduit is largely composed of entrained material simulations with a more realistic non newtonian rheology show that plumes can rise much faster through the mantle which will lead to higher temperatures of the plume head at the earth s surface compared to what experiments with newtonian rheology suggest

cooling of the earth in the archaean consequences of pressure release melting in a hotter mantle a model is presented to describe the cooling of the earth in the archaean at the higher archaean mantle temperatures pressure release melting starts deeper and generates a thicker basaltic or komatiitic crust and depleted harzburgite layer compared with the present day situation intrinsic compositional stability and lack of mechanical coherency renders the mechanism of plate tectonics ineffective it is proposed that the archaean continents stabilised early on top of a compositionally stratified root in the archaean oceanic lithosphere hydrated upper crust can founder and recycle through its high pressure phase eclogite eclogite remelting and new pressure release melting generates new crustal material migration of magma and latent heat release by solidification at the surface provides an efficient mechanism to cool the mantle by several hundreds of degrees during the archaean this can satisfactorily explain the occurrence of high extrusion temperature komatiites and lower extrusion temperature basalts in greenstone belts as being derived from the same source by different mechanisms

a technique for the calibration of hydraulic models using uncertain satellite observations of flood extent this paper presents a methodology to calibrate hydraulic models using possibility of inundation maps derived from satellite imagery the study was performed on a river reach of the lower dee uk where a coarse resolution image envisat asar and high resolution satellite image ers 2 sar were acquired at the same time during the december 2006 flood event ten different flood extent maps were derived from the two flood images by using five different procedures to process these data these flood extent maps were used to perform a sensitivity analysis of a simple raster based inundation model lisflood fp the sensitivity analysis enabled us to investigate the capability of the two different resolution images to calibrate the friction parameters of the flood inundation model the analysis showed that the optimal parameters of the model depend on the type of satellite image used to evaluate the model as well as on the particular procedure used to derive the flood extent map finally the study developed a novel methodology to calibrate flood inundation models by comparing the model results to a possibility of inundation map obtained by combining the ten different flood extent maps

geochemical modelling in rapidly subsiding basins abstract geochemical modelling in rapidly subsiding basins presents some puzzling questions in trying to clarify them two african basins related to different domains were studied the high tertiary and quaternary sedimentation rate is a common feature of the two basins in each of them present heat flow values were computed in different wells on the basis of temperature stratigraphic and petrophysical data using a one dimensional finite element mathematical model the resulting distributions show in some cases irregular patterns which are examined in detail to outline their possible causes extrapolation of the present thermal regime to the past generally gives computed maturity values considerably higher than those obtained experimentally the experimental data include vitrinite reflectance values rock eval pyrolysis results sterane and hopane isomerization and sterane aromatization hypotheses about thermal history are made in order to explain the areal maturity distribution they are checked comparing computed maturity values and experimental ones by combining experimental data and results of the modelling exercise we conclude that the high sedimentation rate independent of the tectonic domain in which it occurs can induce noticeable and peculiar thermal anomalies

hard turbulent thermal convection and thermal evolution of the mantle this article summarizes the results of hard turbulent convection obtained in laboratory experiments and numerical simulations its applications to mantle convection are illustrated by two dimensional numerical solutions to 1 newtonian 2 non newtonian convection and 3 newtonian convection with multiple phase transitions in newtonian mantle convection the transition from soft to hard turbulence is marked by the appearance of disconnected plumes spectral analysis of the time series of the nusselt number reveals the presence of a spectral scaling subrange for hard turbulence but not for soft turbulence in hard turbulence there is correspondence between the spectra in frequency and wavenumber domains the slope of the seismic wave spectra measured from seismology suggests that the mantle convection today is strongly time dependent the transition to hard turbulence takes place at much lower nusselt numbers for non newtonian than for newtonian rheology for the mantle this would have important ramifications non newtonian plumes behave quite differently from newtonian ones in that large curvatures are developed in their trajectories in the hard turbulent regime mantle convection with phase transitions tends to become more layered with increasing rayleigh numbers the style of mantle convection might have changed from a layered to a more whole mantle type of flow with time catastrophic overturns associated with strong gravitational instabilities in the transition zone could be responsible for superplume events

melting instabilities in the transition zone abstract melting in the transition zone could result from the rapid passage of hot upwelling through the perovskite spinel phase transition a large temperature increase could be produced above the perovskite to spinel transition by both viscous heating and a nonlinear positive feedback between temperature dependent viscosity and latent heat release the rise times for these instabilities have been estimated to be about 10 ma these instabilities were triggered by the episodic downwelling instabilities which preceded the flush events of cold material in layered mantle convection with phase transitions these results would suggest that melting in the transition zone would have had a greater tendency to occur in the past and might have caused the generation of komatiites in the archean

the interaction of a plume with a rheological boundary a comparison between two and three dimensional models the discrete nature of volcanic hot spot chains whose origin is believed to be related to mantle plumes is suggestive that the plumes feeding them may be pulsating a possible origin of the pulsations is the interaction of mantle plumes with a rheological interface in the transition zone we have studied the time dependent three dimensional interaction of an upwelling mantle plume with a rheological interface that separates a newtonian lower mantle from a newtonian upper mantle with a lower viscosity previous two dimensional 2 d work demonstrates that when a hot plume enters a non newtonian layer with lower viscosity the hot material is carried from the interface in pulsating diapiric events a purely newtonian analog to this model mimics this behavior in a qualitative manner if the viscosity contrast across the interface is larger than 2 orders of magnitude in this work we have used this newtonian model to make three dimensional 3 d modeling feasible a combined spectral finite difference code has been employed to solve the 2 d and 3 d convection equations in cartesian coordinates we have varied the rayleigh number scaled to the constant viscosity of the lower mantle between 104 and 105 and the viscosity contrast of the layers between 10 and 1000 in 2 d situations with low viscosity contrasts a plume thins in a steady state fashion as it enters the upper layer at moderate and higher viscosity contrasts above 50 the plume shows a pulsating behavior this transition from thinning to pulsating is found to be strongly dependent on viscosity contrast and only moderately dependent on rayleigh number the frequency of the pulsations is linearly dependent on rayleigh number and viscosity contrast in three dimensions the plume thins less and is therefore less susceptible to disruption by shear and the plume moves through the upper layer in a steady state fashion this disappearance of pulsating behavior in three dimensions indicates a case where conclusions about plume dynamics in two dimensions do not apply to 3 d situations

interaction between the mid atlantic ridge and the azores hot spot during the last 85 myr emplacement and rifting of the hot spot derived plateaus 1 multiple and single beam bathymetric data are compiled over the azores plateau to produce a 1 km 1 km grid between latitudes 32 n and 49 n and longitudes 22 w and 43 w mantle bouguer anomalies are then calculated from this grid and the satellite derived gravity these grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis the elevated seafloor of the azores plateau is interpreted as resulting from the interaction of a mantle plume with the mid atlantic ridge mar the presence of a large region of elevated seafloor associated with a thick crust between the great meteor seamounts and the azores platform on the africa plate and less developed conjugate structures on the north america plate favors genetic relations between these hot spot derived structures this suggests that a ridge hot spot interaction has occurred in this region since 85 ma this interaction migrated northward along the ridge axis as a result of the sse absolute motion of the africa plate following a direction grossly parallel to the orientation of the mar kinematic reconstructions from chron 13 35 ma to the present allow a proposal that the formation of the azores plateau began around 20 ma and ended around 7 ma a sharp bathymetric step is associated with the beginning of important melt supply around 20 ma the excess of melt production is controlled by the interaction of the ridge and hot spot melting zones the geometry and distribution of the smaller scale features on the plateau record episodic variations of the hot spot melt production the periodicity of these variations is about 3 5 myr following the rapid decrease of widespread volcanism the plateau was subsequently rifted from north to south by the mid atlantic ridge since 7 ma this rifting begins when the mar melting zone is progressively shifted away from the 200 km plume thermal anomaly these results bear important consequences on the motion of the africa plate relative to the azores hot spot they also provide an explanation to the asymmetric geochemical signature of the azores hot spot along the mid atlantic ridge

petroleum source bed evaluation of tertiary niger delta reply a total of 63 sidewall and drill cutting shale samples obtained from a depth slice of 800 to 3650 m in two onshore and two offshore wells located respectively in the eastern and western niger delta basin nigeria were analyzed for organic matter type concentration and thermal maturity dominant sedimentary kerogens were the humic and mixed types organic carbon contents of the sediments ranged from 0 4 to 4 4 and the degree of thermal evolution as evidenced by vitrinite reflectance r sub 0 odd even ratios oer 2c sub 29 c sub 28 c sub 30 and variations of the ratios of the concentration of soluble organic matter to total organic carbon content som toc were within the ranges 0 2 to 0 7 4 0 to 1 0 and 10 to 240 respectively on the basis of the variation of the maturation parameters the onset of mature source beds in the onshore and offshore delta were delimited at approximately 3375 and 2900 m respectively the inferred threshold temperature was about 95 sup 0 c the results of the present study support the hypothesis that the main source beds of the niger delta basin are the deeply buried paralic or paralic marine facies

remote sensing of volumetric storage changes in lakes three dimensional remote sensing promises a giant leap forward for surface water hydrology in much the same way that radar altimetry transformed physical oceanography however the complex geometries of small terrestrial water bodies introduce difficulties particularly with respect to trade offs between changing water depth and inundation area we use in situ measurements of water surface stage h dt and remotely sensed area a to compute time varying storage changes s in nine lakes of the peace athabasca delta canada despite their identical geomorphic setting regression slopes between h and a vary significantly between lakes primarily from a predictable area effect but also small bathymetric variations between basins on average lateral contraction expansion versus stage adjustment contributes as little as 7 versus 93 to as much as 76 versus 24 of overall storage change s we conclude that both surface area and h dt rather than just either alone must be measured to confidently estimate s from space copyright 2009 john wiley sons ltd

interactions between subgrid scale resolution feature representation and grid scale resolution in flood inundation modelling numerical modelling of flood inundation over large and complex floodplains often requires mesh resolutions coarser than the structural features e g buildings that are known to influence the inundation process recent research has shown that this mismatch is not well represented by conventional roughness treatments but that finer scale features can be represented through porositybased sub grid scale treatments this paper develops this work by testing the interactions between feature representation sub grid scale resolution and mesh resolution it uses as the basis for this testing a 2d diffusion based flood inundation model which is applied to a 2004 flood event in a topologically complex upland floodplain in northern england results showed serious degradation of model predictions without explicit representation of features like walls inclusion of such features through raising mesh cell elevations where intersected by a feature resulted in a major improvement in model predictions in terms of reduced inundation extent to make such treatments physically realistic and notably so that the full potential for floodplain storage is included it was shown that a sub grid scale treatment also needed to be included the effects of this combined treatment was the recovery of more plausible floodplain friction values as well as a sensitivity to friction that allows for more effective representation of floodplain friction effects such as vegetation

sedimentology and characteristics of dispersed organic matter in tertiary niger delta origin of source rocks in a deltaic environment organic matter in tertiary strata of the niger delta is mainly a mixture of types ii and iii kerogen as defined by pyrolysis has a high pristane phytane ratio 1 and is composed of the macerals vitrinite and minor liptinite the main palynofacies are structured woody material opaque organic matter cuticles pollen and spores and minor amorphous organic matter the geochemistry petrology palynofacies and distribution data indicate a predominantly terrestrial and detrital source of the organic matter irrespective of facies formation or age the distribution and abundance of the organic matter are related to both the age of the strata and depositional environment the most significant variation is the decline in mean total organic carbon toc content from late eocene 2 2 toc to pliocene strata 90 toc and an associated general decline in pyrolysis defined hydrogen index hi and pristane phytane ratio the decrease in toc and hi in younger strata reflects increased dilution of a nearly constant supply of terrestrial organic matter with the generally higher sedimentation rates of younger strata a simple linear dilution model accounts for about 50 of the variance in measured toc the low pristane phytane ratio of younger strata may reflect less oxidizing depositional conditions the variation in organic matter with depositional environments and environmental depth zones defined by foraminiferal assemblages is significant although less important than variation due to age the highest toc and hi values occur in nonmarine swamp marsh and floodplain deposits reflecting proximity to the organic source beach barrier and offshore bar facies have lower toc and hi values due to selective winnowing of organic matter and greater oxidation from continental to transition marine depth zones a marked decline in toc and hi occurs as a result of dilution selective transport and oxidation of the organic matter from transitional to bathyal depth zones little variation is found in toc but a general increase is found in hi which reflects a relative increase in more hydrogen rich autochthonous organic matter in all facies autochthonous organic matter comprises less than 20 of the toc no interpretable variation appears in maceral or palynofacies abundance with sediment type which probably reflects the homogeneity of the organic matter paradoxically no rich source rocks occur in the tertiary succession in the niger delta and as conventionally measured the strata have little or no oil generating potential the poor quality of the source rocks has been more than compensated for by their great volume by the excellent migration routes provided by interbedded permeable sands and possibly by the relatively rapid rate of maturation niger delta type of source rock although an end member in terms of general source rock composition appears to be relatively typical of tertiary deltas

numerical and experimental study on two dimensional flood flows with and without structures the behavior of two dimensional 2d flood flows and the hydrodynamic force acting on structures are investigated numerically and experimentally numerical simulations are performed using a model based on the finite volume method with an unstructured grid system and the flux difference splitting technique experiments on flood propagation in a flood plain with and without structures were conducted so as to obtain a comprehensive verification of the model front positions depths and surface velocities of flood flows as well as hydrodynamic forces on structures were observed comparisons of numerical results against these experimental data show that the model can predict 2d flood flows and the force on structures with reasonable accuracy

multi scale assessment of overflow driven lateral connectivity in floodplain and backwater channels using lidar imagery overflow driven lateral connectivity significantly influences the spatial distribution and diversity of floodplain habitats and biota proper understanding of lateral connectivity in floodplain and backwater channels is therefore critical for assessment of river quality and for targeting management or restoration actions in this study we present a methodological framework for spatial and temporal assessments of overflow driven lateral connectivity at two spatial scales bypass reach and backwater channel firstly we compute the relative elevations as well as overflow discharge duration and frequency using a simple raster based method that uses a lidar digital elevation model dem rating curves and streamflow time series subsequently we analyse the accuracy of this approach with respect to the accuracy of a dem and evaluate its further applications altogether four 10 km long bypass reaches and 11 backwater channels are analysed located along the rhone river corridor in france the results proved the precision of the method to be affected by the lidar dem accuracy which was on average more precise in a typically homogeneous floodplain setting rather than for backwater channel plugs with pronounced topographic complexity and usually riparian forest canopy amongst the four studied reaches bregnier cordon proved to have the greatest flooding dynamics followed by belley and chautagne the hydrological connectivity pattern of pierre benite differed significantly three longitudinal patterns of hydrological connectivity of backwater channels displayed stepwise advancement of the water the presented results can be used to assess ecological potential of floodplain habitats and their historic and prospective evolution through time copyright 2014 john wiley sons ltd

effects of depth variations in creep laws on the formation of plates in mantle dynamics we have studied the influences of depth varying rheologies on the structure of mantle convection and the near surface flow fields upwelling flows crossing the upper lower mantle boundary become considerably thinner and faster streamlines are concentrated near the surface and other plate like characteristics are enhanced by this type of rheological stratification in which the averaged effective viscosity of the upper mantle is about two orders of magnitude lower than that of the lower mantle the presence of a lithosphere with a higher non linear dependence in the flow law further promotes plate like behavior plate like character of the top boundary layer is encouraged by a decreasing depth dependent viscosity in the non newtonian upper mantle and by greater convective vigor

mantle convection as a boundary layer phenomenon summary the boundary layer nature of vigorous thermal convection is explored using high resolution numerical solutions to the governing hydrodynamic equations these solutions are obtained for a series of idealized models of the earth s mantle in which the viscosity is assumed to be constant a detailed analysis of the local energy balance within the horizontal and vertical thermal boundary layers is presented in terms of which a test of the fundamental assumptions of boundary layer theory is provided the results of this test have important geophysical consequences since the asymptotic predictions of boundary layer theory have been employed extensively in the context of thermal history modelling although boundary layer theory closely predicts the correct power law behaviour of various quantities it does not determine their absolute values accurately vertical advection is shown to play an important role in the energy balance within horizontal boundary layers at all rayleigh numbers horizontal and vertical advection dominate the energy balance within vertical plumes while horizontal diffusion plays a very minor role when heating is partially from within the fluid vertical advection into the upper thermal boundary layer can produce significant departures in the thermal structure from that found when heating is entirely from below for a free upper boundary this results in a relative flattening of the variations of surface topography and heat flow across the convection cells for a constant velocity upper boundary similar to plate motion the bathymetry flattens but the heat flow does not this result agrees with marine observations rigidity of the thermal boundary layer below the upper surface is not included explicitly in the model and it is not known whether the inclusion of this feature in future models would significantly alter the topographic expression if not the observed departure of the oceanic bathymetry from a 6 dependence at old ocean floor ages could be attributed to a small amount of internal heating in a mantle wide convective circulation

role of floodplain sediments in reducing the nitrate concentration of subsurface run off a case study in the cotswolds uk discharge of groundwater from a limestone aquifer through floodplain sediments is associated with a large decrease in the nitrate concentration of the water results are presented to show that only a small amount of this reduction is caused by dilution of groundwater by water already present within the floodplain sediments most of the effect is an active reduction process most probably biological denitrification the nitrate reduction process appears to operate independently of surface vegetation type and tends to be focused in specific regions of the floodplain where sediments are anaerobic and carbon rich the results suggest that active denitrification can operate throughout the winter when nitrate concentrations in groundwater are at their highest and that the process remains effective even during periods of maximum run off the results show that undrained floodplains can be used as buffer zones to protect surface waters from groundwater polluted with agriculturally derived nitrate

investigating the influence of minor hydraulic structures on modeling flood events in lowland areas investigating the influence of minor hydraulic structures on modeling flood events in lowland areas

effects of depth dependent thermal expansivity on mantle circulations and lateral thermal anomalies the influences of depth dependent thermal expansivity on the structure of newtonian thermal convection and lateral thermal anomalies are studied in an aspect ratio ten box the effects of the depth dependent expansivity are to produce large aspect ratio cells with a few relatively stationary upwellings the lateral thermal anomalies in the lower mantle are greatly diminished by depth dependent expansivity this together with a decrease in the temperature derivative of seismic velocities in the lower mantle would support the low level of lateral heterogeneities found in recent tomographic studies

flooding dynamics on the lower amazon floodplain 1 hydraulic controls on water elevation inundation extent and river floodplain discharge 1 modeling the routing of flood waters across large floodplains is challenging because flows respond to dynamic hydraulic controls from complex geomorphology vegetation and multiple water sources in this study we analyzed the topographic and hydrologic controls of inundation dynamics of a large floodplain unit 2440 km2 along the lower amazon river we combined land topography derived from the shuttle radar topography mission srtm with underwater topography derived from an extensive echo sounding survey to generate a seamless digital elevation model dem floodplain inundation was simulated using lisflood fp which combines one dimensional river routing with two dimensional overland flow and a local hydrological model for the first time accurate simulation of filling and drainage of an amazon floodplain was achieved with quantification of changes in water elevation flooding extent and river floodplain exchange we examined the role of diffuse overbank versus channelized flows on river floodplain exchange diffuse overbank flows represent 93 of total river to floodplain discharge and 54 of floodplain to river discharge floodplain discharge during high water was four times higher than field observation values when the srtm v 4 dem with no correction was used for simulation because of a 4 4 m elevation bias originating from residual motion errors of the srtm interferometric baseline

comparing the performance of a 2 d finite element and a 2 d finite volume model of floodplain inundation using airborne sar imagery the performances of a finite volume model sfv and finite element model telemac 2d in reproducing inundation on a 16 km reach of the river severn united kingdom are compared predicted inundation extents are compared with 4 airborne synthetic aperture radar images of a major flood event in november 2000 and these are used to calibrate 2 values of manning s n for the channel and floodplain the four images are shown to have different capacities to constrain roughness parameters with the image acquired at low flow rate doing better in determining these parameters than the image acquired at approximately peak flow this is assigned to the valley filling nature of the flood and the associated insensitivity of flood extent to changes in water level the level of skill demonstrated by the models when compared with inundation derived using a horizontal water free surface also increases as flow rate drops the two models show markedly different behaviours to the calibration process with telemac showing less sensitivity and lower optimum values for manning s n than sfv when the models are used in predictive mode calibrated against one image and predicting another sfv performs better than telemac copyright 2007 john wiley sons ltd

three dimensional models of mantle flow across a low viscosity zone implications for hotspot dynamics the influence of a shallow low viscosity zone on the planform of infinite prandtl number rayleigh benard convection has been investigated at rayleigh numbers ra ranging from 1 5 103 to 3 105 a viscosity contrast of130 has been set between the low and high viscosity layers for ra exceeding about 3 104 and no slip conditions at the top and bottom boundaries a hexagonal convective planform is systematically observed free slip boundary conditions lead to the development of a square convective planform the flow is ascending along the center of the cells and is strongly narrowed in the low viscosity layer a moving top boundary does not destabilize significantly these plumes as long as the drift velocity is lower than the upwelling velocity in the low viscosity layer a higher drift velocity of the upper boundary rapidly induces the formation of convective rolls at ra of 3 105 unsteady flow occurs along the descending currents when the convective cells have the horizontal size predicted by the linear theory this time dependence is prevented when the cells are smaller suggesting that there is a competition between the aspect ratio and the steadiness of the cells such a reduction of the horizontal dimensions of the cells with increasing ra has been observed in large experiments these results show that a moderate viscosity drop at shallow depth in the mantle compatible with the geoid and bathymetric data at hotspot swells induces a marked asymmetry between the upper and lower convective boundary layers this promotes the development of ascending plumes large at depth and very narrow a few tens of kilometers in section below the lithosphere these plumes are very stable in time and space it is inferred that the channelling of the ascending plumes induced by a viscosity drop precludes the development of secondary convection in a top low viscosity layer

pulsating diapiric flows consequences of vertical variations in mantle creep laws abstract recent laboratory work has suggested that the rheology of the lower mantle may be newtonian we have studied the time dependent dynamics of plumes interacting with a rheological interface separating an upper non newtonian mantle and a newtonian lower mantle pulsating diapiric structures with fast time scales are promoted by the interaction of the rising plumes with this rheological boundary surface heat flow signals are discernible as pulses which remain relatively stationary they correlate well with the localized upwellings just below the surface the presence of a mobile lithosphere from increasing the non newtonian power law index helps to produce a large scale circulation in the upper mantle which draws large hot patches away from nearby upwellings in our calculations the resultant averaged effective viscosity of the non newtonian upper mantle is about two orders of magnitude lower than that of the newtonian lower mantle a viscously stratified newtonian model produces more incoherent and broad scale diapiric structures and is less efficient for generating sharply varying time dependent thermal signatures

predicting floodplain inundation raster based modelling versus the finite element approach we compare two approaches to modelling floodplain inundation a raster based approach which uses a relatively simple process representation with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation and a finite element hydraulic model aiming to solve the full two dimensional shallow water equations a flood event on a short c 4 km reach of the upper river thames in the uk is simulated the models being validated against inundation extent as determined from satellite synthetic aperture radar sar imagery the unconstrained friction parameters are found through a calibration procedure where a measure of fit between predicted and observed shorelines is maximized the raster and finite element models offer similar levels of performance both classifying approximately 84 of the model domain correctly compared with 65 for a simple planar prediction of water surface elevation further discrimination between models is not possible given the errors in the validation data the simple raster based model is shown to have considerable advantages in terms of producing a straightforward calibration process and being robust with respect to channel specification copyright 2001 john wiley sons ltd

estimation of river discharge propagation speed and hydraulic geometry from space lena river siberia 1 moderate resolution imaging spectroradiometer modis derived measurements of lena river effective width we display a high predictive capacity r2 0 81 mean absolute error 60 90 km 2 3 time valley width satellite derived we q rating curves and hydraulic geometry b exponents converge upon stable values b 0 48 indicating transferability of the discharge retrieval method between different locations put another way at length scales exceeding 60 90 km all subreaches display similar behavior everywhere at finer reach length scales e g 0 25 1 km longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space while at least one gauging station is required for calibration results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems

dynamical consequences of depth dependent thermal expansivity and viscosity on mantle circulations and thermal structure the effects of both depth dependent thermal expansivity and depth dependent viscosity on mantle convection have been examined with two dimensional finite element simulations in aspect ratio ten boxes surface rayleigh numbers between 107 and 6 107 have been considered the effects of depth dependent properties acting singly or in concert are to produce large scale circulations with a few major upwellings the interior of the mantle is cooled by the many cold instabilities which are slowed down and eventually swept about by the large scale circulation the interior temperature of the mantle can be influenced by the trade off between depth dependent properties and internal heating for chondritic abundance of internal heating and depth dependent thermal expansivity the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic the thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth dependent properties whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant over several hundred degrees depth dependent properties also encourage the formation of a stronger mean flow in the upper mantle which may be important for promoting long term polar motions

the effects of shallow rheological boundaries in the upper mantle on inducing shorter time scales of diapiric flows the authors report on a study of pulsating diapiric flow in the upper mantle they study the effect of introducing new phase boundaries in the mantle on such flow basic models have an interface at a depth of 670 km in the rheological properties the authors study the effect of introducing another phase boundary at a depth close to 400 km

upper mantle heterogeneities and dynamics the width of geochemical and residual elevation anomalies along the mid ocean ridge system decrease as both the distance between migrating ridge segments and related hotspots and the local geochemical dispersion in the anomalies increase these observations provide further evidence that flows of mantle plumes in the upper mantle are deflected by migrating ridge sinks once they override hotspots

floodplain friction parameterization in two dimensional river flood models using vegetation heights derived from airborne scanning laser altimetry two dimensional 2 d hydraulic models are currently at the forefront of research into river flood inundation prediction airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction the paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2 d flood models to specify a friction factor at each node of the finite element model mesh the only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height different sets of flow resistance equations are used to model channel sediment short vegetation and tall and intermediate vegetation the scheme was tested in a modelling study of a flood event that occurred on the river severn uk in october 1998 a synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent the modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain the variable friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration copyright 2003 john wiley sons ltd

the role of recrystallization in the preferred orientation of olivine abstract the effects of recrystallization on the preferred orientation in olivine have been studied the recrystallization mechanisms studied include grain growth the deformation induced grain boundary migration digbm and subgrain rotation sgr grain boundary migration is involved in the first two but not in sgr significant preferred orientation was found only in the latter two where dislocations are involved the combined microstructural and fabric preferred orientation observations indicate that the grain boundary migration produces strong preferred orientation when the driving force is the dislocation energy but not when the grain boundary energy is the driving force the nature of preferred orientation due to dislocation related recrystallization digbm or sgr was found to depend on the mechanism of recrystallization the digbm produces preferred orientation in which the low dislocation density grains with unfavourable orientation for easy slip dominate thereby significantly altering the preferred orientation formed by dislocation glide in contrast sgr does not essentially alter the deformation fabric and therefore the fabric associated with sgr recrystallization is related to the geometry of flow the present results demonstrate that the existence of seismic anisotropy in the upper mantle is strong evidence for the dislocation mechanism s of deformation and suggest that care must be exercised in applying the results of laboratory fabric studies made for a particular mechanism of recrystallization to the earth s interior where the dominant mechanism s of dynamic recrystallization can be different

rheological transition in mantle convection with a composite temperature dependent non newtonian and newtonian rheology numerical simulations of mantle convection with a composite temperature dependent newtonian and non newtonian creep law have revealed a transition in the dominant creep mechanism with the increasing vigour of convection newtonian creep is found to dominate in the low rayleigh number regime with sufficiently high effective rayleigh number the overall creep mechanism in the convective flow becomes non newtonian the transitional rayleigh number increases strongly with the activation energy these results would suggest a scenario that in the early epochs of earth the flow in the mantle would have been governed by non newtonian rheology and would have exhibited both strong spatial and temporal fluctuations with time the flow mechanism would behave like a newtonian fluid and would have a different time dependent character in time dependent newtonian dominated flows there are still localized features with distinctly non newtonian character our analysis of the relative contributions to the lateral viscosity field supports the idea that the inference of the nature of lateral viscosity heterogeneities by seismic tomography may be strongly contaminated by the dominant non newtonian contributions to the total lateral viscosity field

modelling planetary dynamics by using the temperature at the core mantle boundary as a control variable effects of rheological layering on mantle heat transport abstract in planetary convection there has been a great emphasis laid on the usage of the rayleigh number as a control parameter for describing the vigor of convection however realistic mantle rheology not only depends on temperature pressure strain rate and composition but also on the nature of the dominant creep mechanism which varies with pressure and also with temperature it is difficult to study the effects of varying influences from the convective strength without also changing the mantle flow law in the process we have adopted the approach of using as the sole control parameter the temperature at the core mantle boundary t cmb in modelling planetary dynamics with a composite non newtonian and newtonian rheology which is temperature dependent in the upper mantle and both temperature and pressure dependent in the lower mantle increasing the t cmb strengthens convective vigor and leads to a non linear increase of averaged temperature heat flow and root mean squared velocity the interior viscosity decreases strongly with t cmb and internal heating due to radioactivity a viscosity maximum is found in the horizontally averaged viscosity profile at a depth around 2000 km this viscosity hill moves downward with diminishing amplitude in the face of increasing dissipation number and internal heating the bottom third of the lower mantle appears to be superadiabatic as a consequence of the stiff lower mantle rheology the scaling relationship between the nusselt nu number and t cmb shows a relatively insensitive increase of nu with t cmb in terms of an effective rayleigh number of the whole system ra e the power law exponent of the nu ra e relationship is very low around 0 12 strong pressure dependence of lower mantle rheology and its large volume relative to the entire mantle would induce a much lower cooling rate of the planet than previous models based on parameterized convection with a temperature dependent viscosity

using post flood surveys and geomorphologic mapping to evaluate hydrological and hydraulic models the flash flood of the girona river spain in 2007 summary this paper analyzes the girona river spain flash flood occurred on the 12th of october 2007 combining hydrological and hydraulic modeling with geomorphologic mapping and post flood survey information this research aims to reproduce the flood event in order to understand and decipher the flood processes and dynamics on a system of prograding alluvial fans the hydrological model tetis was used to characterize the shape and dimension of the october 2007 girona river hydrograph subsequently the flood event was reproduced using the free surface flow module of the model riverflow2d the combination of hydrological and hydraulic models was evaluated using post flood surveys defining maximum flooded area and flood depths then simulations with different peak discharges were carried out to estimate the hydro geomorphologic response of the girona river floodplain through the identification of the activation thresholds in different geomorphic elements results showed that the unit peak discharge of the october 2007 flood event 5 m3 s 1 km 2 was among the largest ever recorded in the area according to the existing literature likewise the hydraulic model showed a good performance in reproducing the flood event fita 76 rmse 0 65 m and nse 0 6 despite the complexity of the case an ephemeral and ungauged river the model simulation revealed the existence of an activation pattern of paleochannels and alluvial fans which was altered by the presence of some anthropogenic disturbances this multidisciplinary approach proved to be a useful strategy for understanding flash flood processes in ungauged catchments it allowed understanding the mechanisms governing floods in alluvial fans systems and it represented a solid contribution for early warning plans and risk mitigation policies

ultrafast mantle plumes and implications for flood basalt volcanism in the northern atlantic region abstract recent geochemical and geochronological data on paleocene flood basalts from west greenland se greenland and the british isles show that volcanic activity at these widely separated locations commenced nearly simultaneously around 61 62 ma ago and that the duration of this initial phase of flood basalt magmatism was of the order of a few million years or less a small fast moving upper mantle plume which rapidly spreads out horizontally on encountering the base of the lithosphere appears to be a viable mechanism to explain these observations however in order to reconcile the idea of an ultrafast plume with the observed plate velocities a physical mechanism is needed for inducing a separation of timescales between the plume speed and the surrounding mantle circulation thermal convection with a non newtonian temperature and depth dependent rheology provides such a mechanism wherein extremely fast plumes ascending at velocities between one to tens of meters per year can be produced in an otherwise slowly convecting mantle moving at cm yr this transport mechanism is capable of bringing up very hot matter from the transition zone to the lithosphere the fast upward velocities lead to the production of high viscous heating rates surrounding the plume upon impinging the lithosphere it is thus possible to explain the near simultaneous onset of magmatism in west greenland se greenland and the british isles in the early tertiary by a fast moving mantle plume spreading out horizontally with a velocity of around 0 5 m yr for resolving numerically the thermal mechanical state of these strongly time dependent mantle flows extremely high spatial resolution on the kilometer scale is required finally we suggest the possibility that the source of the fast upper mantle plume under iceland may be rooted in the lower mantle this is consistent with the recent findings by seismic tomography of a deep mantle plume under iceland

mantle plumes pinched in the transition zone abstract we have employed an axisymmetric spherical shell model with the two major phase transitions and variable viscosity to study the dynamical processes associated with both regular mantle plumes and superplumes which can develop spontaneously in strongly time dependent situations this model is heated both from below and from within and the viscosity varies according to the temperature pressure and the phase boundaries we have studied the physical processes due to the interactions between the different types of plumes and superplumes with the transition zone which can shed light on some new understanding of intraplate volcanism the interaction between the plume and the two major phase transitions gives rise to the production of a reservoir of plume material localized in the transition zone the spinel to olivine phase transition induces the ejection of very fast plume material within a very thin vertical channel towards the surface the spreading of this plume is controlled by the upper mantle circulation stable plumes which extend throughout the mantle for several hundred million years can produce volcanism with an age progression of the seamounts other plumes which are bent and move relative to the global circulation may generate chaotic surface volcanism with a very limited age progression of the seamounts plume plume collision produces a superplume growing from the core mantle boundary cmb the interaction between superplumes and the perovskite to spinel phase transition generates a thick thermal boundary layer in which the upper mantle can serve as the site for the launching of new smaller plumes stress fields associated with the superplume have the largest magnitude at the cmb and just below the 670 km discontinuity they may be associated with seismic anisotropy found there

optimal cross sectional spacing in preissmann scheme 1d hydrodynamic models choosing a suitable set of cross sections for the representation of the natural geometry of a river is important for the efficiency of one dimensional 1d hydraulic models but only few guidelines are available for the selection of the most suitable distance between cross sections depending on the hydraulic problem at hand this issue is investigated by examining models of a 55 km reach of the river po italy and a 16 km reach of the river severn united kingdom for both of which high quality laser scanning altimetry are available the high resolution digital terrain models of the two river reaches enabled the construction of a series of hypothetical topographical ground surveys with different spacing between cross sections which could be used as input to a standard 1d model unet both historical and synthetic flood events for the two river reaches were simulated and the results were then analyzed to quantify the accuracy associated with each resolution and to assess how survey resolution impacts the performance of standard 1d models the study results agree with the available suggestions in the literature and provide useful guidelines for 1d hydrodynamic modeling

a subgrid channel model for simulating river hydraulics and floodplain inundation over large and data sparse areas 1 this paper presents a new computationally efficient hydraulic model for simulating the spatially distributed dynamics of water surface elevation wave speed and inundation extent over large data sparse domains the numerical scheme is based on an extension of the hydraulic model lisflood fp to include a subgrid scale representation of channelized flows which allows river channels with any width below that of the grid resolution to be simulated the scheme is shown to be numerically stable and scalable before being applied to an 800 km reach of the river niger in mali the niger application focused on the performance of four different model structures a model without channels two dimensional 2 d model a model without a floodplain one dimensional 1 d model a model of the main channels and floodplain 1 d 2 d model and the subgrid approach developed here inclusion of both the channel network and the floodplain was shown to be essential meaning that large scale models of this region including routing models for land surface schemes will require a floodplain component including subgrid scale channels on the floodplain changed inundation dynamics over the delta significantly and increased simulation accuracy in terms of water level wave propagation speed and inundation extent furthermore only the subgrid model showed a consistent parameterization when calibrated against either gauge or icesat water level data suggesting that connectivity provided by small channels is a strong control on the hydraulics of the floodplain or at the very least that low resolution gridded hydraulic models require additional connectivity to represent the delta flow dynamics

oleanane parameter verification by quantitative study of the biomarker occurrence in sediments of the niger delta abstract the variation of the absolute concentration of oleananes in three selevted sedimentary columns of the tertiary niger delta is paralleled by the corresponding oleanane parameter op profile thereby confirming that the latter can be utilized for estimating the relative contribution of terrigenous organic matter it is shown that op features a dynamic range especially at the oil generative window ogw and can precisely delimit the top of the ogw which for the niger delta is shown to coincide approximately with the 80 c isotherm and ro 0 55 this study provides the first direct evidence of the inadequacy of vitrinite reflectance as a maturity parameter for type iii kerogen furthermore based on the new findings an alternative model for oleanene oleanane interconversions in the geosphere is proposed

rise of starting plumes through mantle of temperature pressure and stress dependent viscosity the evolution of size and excess temperature of starting plumes is calculated as a function of 1 newtonian and power law stress dependent mantle rheology and 2 buoyancy flux into the plume through a feeding conduit in mantle of temperature and pressure dependent viscosity the initial size and excess temperature that allow plumes starting at the core mantle boundary to reach the base of the lithosphere 200 k or more warmer than the surroundings are determined for a range of conditions the results suggest that starting plumes can be divided into slow and fast plumes slow plumes become large and cool through entrainment of the surroundings during ascent so that they are likely to have little impact on the evolution of the lithosphere fast plumes on the other hand rise so rapidly that cooling and entrainment become unimportant they reach the lithosphere while they are still hot often with an excess temperature similar to that at the source and are likely to strongly perturb the lithosphere the change from slow to fast plumes occurs over a small increase in plume buoyancy at the source particularly in power law mantle small buoyancy flux through the conduit affects only slow plumes whereas high flux causes plumes of different initial radius to reach the lithosphere with similar radius and excess temperature the results suggest that the study of important starting plumes those that will have considerable geological consequences can be simplified to that of 1 nonentraining constant radius thermals plume heads isolated from the source for small buoyancy flux and 2 nonentraining plumes for high flux in all cases most entrainment occurs in the lower mantle comparison between power law and newtonian mantle viscosities suggests that the upper mantle will respond as a power law fluid because it yields lower effective viscosity when submitted to the buoyancy stress of plumes than does a corresponding newtonian mantle the power law response of the upper mantle is unlikely to considerably influence ascent time of plumes but it will considerably change the way plumes interact with the lithosphere

determining the petroleum generating potential of coal using organic geochemistry and organic petrology abstract the ardjuna basin of northwest java is typical of many tertiary basins in that it contains high wax crude oil pyrolysis gas chromatography revealed that potential precursors of long chain waxy paraffins are present in coals of the talang akar formation and are most abundant in those that are rich in matrix liptinite conversely it was not possible to estimate waxy oil generating potential using rock eval because pyrolysates from talang akar coal are mainly comprised of naphthenic and aromatic compounds these being derived from resinite and fluorescing vitrinite because of a controlling influence by the abundance of these macerals changes in hydrogen index could not be used to assess maturity resinite and related macerals might play an especially important role in petroleum expulsion as evidenced by their high genetic potential and hence inherent capability of saturating the source rock pore system it is speculated that their maturation products while not constituting typical crude oil might pervade the coal fabric deactivate adsorptive sites and hence facilitate the expulsion of waxy oil that is generated from matrix liptinite

the effects of spatial resolution and dimensionality on modeling regional scale hydraulics in a multichannel river as modeling capabilities at regional and global scales improve questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics this study uses the hydrodynamic model lisflood fp to simulate patterns of water surface elevation wse depth and inundation extent across a 90 km anabranching reach of the tanana river alaska to provide boundary conditions we collected field observations of bathymetry and wse during a 2 week field campaign in summer 2013 for the first time at this scale we test a simple raster based model s capabilities to simulate 2 d in channel patterns of wse and inundation extent additionally we compare finer resolution 25 m 2 d models to four other models of lower dimensionality and coarser resolution 100 500 m to determine the effects of simplifying process representation results indicate that simple raster based models can accurately simulate 2 d in channel hydraulics in the tanana also the fine resolution 2 d models produce lower errors in spatiotemporal outputs of wse and inundation extent compared to coarse resolution 1 d models 22 6 cm versus 56 4 cm rmse for wse and 90 versus 41 critical success index values for simulating inundation extent incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers rmse in spatially distributed wse by at least 16 as a result better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global scale models

the interaction of plume heads with compositional discontinuities in the earth s mantle the effects of compositional discontinuities of density and viscosity in the earth s mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique three specific problems are considered 1 a plume head rising away from a deformable interface 2 a plume head passing through an interface and 3 a plume head approaching the surface of the earth for the case of a plume attached to a free surface the calculated time dependent plume shapes are compared with experimental results two principal modes of plume head deformation are observed plume head elongation or the formation of a cavity inside the plume head the inferred structure of mantle plumes namely a large plume head with a long tail is characteristic of plumes attached to their source region and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high to low viscosity region as a rising plume head approaches the upper mantle most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle if the plume head moves from a high to low viscosity region the plume head becomes significantly elongated and for the viscosity contrasts thought to exist in the earth could extend from the 670 km discontinuity to the surface plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry the dynamic surface topography induced by plume heads is bell shaped when the top of the plume head is at depths greater than about 0 1 plume head radii as the plume head approaches the surface and spreads the dynamic topography becomes plateau shaped the largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical and the surface expression of these stresses is likely to be dominated by radial extension as the plume spreads compressional stresses on the surface are produced beyond the edges of the plume consequently extensional features will be produced above the plume head and may be surrounded by a ring of compressional features

hydraulic visibility using satellite altimetry to parameterize a hydraulic model of an ungauged reach of a braided river what hydraulic information can be gained from remotely sensed observations of a river s surface in this study we analyze the relationship between river bed undulations and water surfaces for an ungauged reach of the xingu river a first order tributary of the amazon river this braided reach is crosscut more than 10 times by a envisat environmental satellite track that extends over 100 km rating curves based on a modeled discharge series and altimetric measurements are used including the zero flow depth z0 parameter which describes river s bathymetry river widths are determined from jers japanese earth ressources satellite images hydrodynamic laws predict that irregularities in the geometry of a river bed produce spatial and temporal variations in the water level as well as in its slope observation of these changes is a goal of the surface water and ocean topography satellite mission which has a final objective of determining river discharge first the concept of hydraulic visibility is introduced and the seasonality of water surface slope is highlighted along with different flow regimes and reach behaviors then we propose a new single thread effective hydraulic approach for modeling braided rivers flows based on the observation scales of current satellite altimetry the effective hydraulic model is able to reproduce water surface elevations derived by satellite altimetry and it shows that hydrodynamical signatures are more visible in areas where the river bed morphology varies significantly and for reaches with strong downstream control the results of this study suggest that longitudinal variations of the slope might be an interesting criteria for the analysis of river segmentation into elementary reaches for the surface water ocean topography mission that will provide continuous measurements of the water surface elevations the slopes and the reach widths

turbulent open channel flows with variable depth across the channel the flow of water in straight open channels with prismatic complex cross sections is considered lateral distributions of depth mean velocity and boundary shear stress are derived theoretically for channels of any shape provided that the boundary geometry can be discretized into linear elements the analytical model includes the effects of bed generated turbulence lateral shear turbulence and secondary flows experimental data from the science and engineering research council serc flood channel facility are used to illustrate the relative importance of these three effects on internal shear stresses new experimental evidence concerning the spatial distribution of reynolds stresses yx and zx is presented for the particular case of compound or two stage channels in such channels the vertical distributions of zx are shown to be highly nonlinear in the regions of strongest lateral shear and the depth averaged values of yx are shown to be significantly different from the depth mean apparent shear stresses the importance of secondary flows in the lateral shear layer region is therefore established the influence of both reynolds stresses and secondary flows on eddy viscosity values is quantified a numerical study is undertaken of the lateral distributions of local friction factor and dimensionless eddy viscosity the results of this study are then used in the analytical model to reproduce lateral distributions of depth mean velocity and boundary shear stress in a two stage channel the work will be of interest to engineers engaged in flood channel hydraulics and overbank flow in particular

development of diapiric structures in the upper mantle due to phase transitions solid state phase transitions in time dependent mantle convection can induce diapiric flows in the upper mantle when a deep mantle plume rises toward phase boundaries in the upper mantle the changes in the local thermal buoyancy local heat capacity and latent heat associated with the phase change at a depth of 670 kilometers tend to pinch off the plume head from the feeding stem and form a diapir this mechanism may explain episodic hot spot volcanism the nature of the multiple phase boundaries at the boundary between the upper and lower mantle may control the fate of deep mantle plumes allowing hot plumes to go through and retarding the tepid ones

floodplain roughness parameterization using airborne laser scanning and spectral remote sensing abstract floodplain roughness parameterization is one of the key elements of hydrodynamic modeling of river flow which is directly linked to exceedance levels of the embankments of lowland fluvial areas the present way of roughness mapping is based on manually delineated floodplain vegetation types schematized as cylindrical elements of which the height m and the vertical density the projected plant area in the direction of the flow per unit volume m 1 have to be assigned using a lookup table this paper presents a novel method of automated roughness parameterization it delivers a spatially distributed roughness parameterization in an entire floodplain by fusion of casi multispectral data with airborne laser scanning als data the method consists of three stages 1 pre processing of the raw data 2 image segmentation of the fused data set and classification into the dominant land cover classes khat 0 78 3 determination of hydrodynamic roughness characteristics for each land cover class separately in stage three a lookup table provides numerical values that enable roughness calculation for the classes water sand paved area meadows and built up area for forest and herbaceous vegetation als data enable spatially detailed analysis of vegetation height and density the hydrodynamic vegetation density of forest is mapped using a calibrated regression model herbaceous vegetation cover is further subdivided in single trees and non woody vegetation single trees were delineated using a novel iterative cluster merging method and their height is predicted r 2 0 41 rse 0 84 m the vegetation density of single trees was determined in an identical way as for forest vegetation height and density of non woody herbaceous vegetation were also determined using calibrated regression models a 2d hydrodynamic model was applied with the results of this novel method and compared with a traditional roughness parameterization approach the modeling results showed that the new method is well able to provide accurate output data the new method provides a faster repeatable and more accurate way of obtaining floodplain roughness which enables regular updating of river flow models

dynamical effects of a temperature and pressure dependent lower mantle rheology on the interaction of upwellings with the transition zone we have examined the consequences of a temperature and pressure dependent lower mantle viscosity on the interaction of upwellings with the two major phase transitions the viscosity used is only temperature dependent in the upper mantle but assumes both temperature and pressure dependences in the lower mantle the activation enthalpy increases with depth dependence scaled after experimental melting curves of lower mantle components we have employed a two dimensional cartesian box with an aspect ratio of five and a mantle layer thickness of 2900 km using an extended boussinesq model with a depth dependent thermal expansivity latent heat release and viscous dissipation have been included in the temperature equation we have considered models both without and with a viscosity jump a factor of 8 across the 660 km boundary the range of averaged rayleigh numbers ra considered lies between 2 106 and 107 a major effect of this temperature and pressure dependent rheology is the stabilization of the upwelling plumes and the increase of viscous heating in the bottom portion of these plumes the impingement of these heated plumes at the endothermic phase boundary causes the development of secondary plumes to rise into the upper mantle shear heating together with the latent heat release produces large temperature increases in the plumes passing through the transition zone which may cause melting in the deep upper mantle although the average rayleigh number in the case of temperature and pressure dependent viscosity is around a factor of 5 lower than in a case with purely temperature dependent viscosity the resulting flow is only slightly less layered which is contrary to the earlier finding of christensen and yuen 1985 the tendencies for the development of secondary plumes and high temperatures inside the upwellings are enhanced by the viscosity jump at the 660 km boundary in this situation few nearly steady vigorous upwellings exist in the lower mantle while in the upper mantle vigorous time dependent convection takes place for an averaged rayleigh number of 107 the system becomes layered with many thin plumes appearing in the lower mantle