mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

transport processes in the tropical warm pool boundary layer part ii vertical structure and variability abstract the structure of the intertropical convergence zone itcz cloud topped marine atmospheric boundary layer away from the most intense mesoscale convective systems during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare is investigated eight vertical profiles taken by the australian cessna research aircraft are analyzed representing the successive influence of a growing small cluster of precipitating cumulus upon the subcloud layer on the basis of conclusions from a spectral analysis in part i of this study results are partitioned into contributions from three distinct categories a small scale 2 km processes corresponding to meso scale motions associated mainly with the action of precipitating cumulus clouds and larger motions and c extreme processes corresponding to contributions from e

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

scaling gridded river networks for macroscale hydrology development analysis and control of error a simple and robust river network scaling algorithm nsa is presented to rescale fine resolution networks to any coarser resolution the algorithm was tested over the danube river basin and the european continent coarse resolution networks at 2 5 5 10 and 30 min resolutions were derived from higher resolution gridded networks using nsa and geomorphometric attributes such as river order shape index and width function these parameters were calculated and compared at each resolution simple scaling relationships were found to predict decreasing river lengths with coarser resolution data this relationship can be used to correct river length as a function of grid resolution the length corrected width functions of the major river basins in europe were compared at different resolutions to assess river network performance the discretization error in representing basin area and river lengths at coarser resolutions were analyzed and simple relationships were found to calculate the minimum number of grid cells needed to maintain the catchment area and length within a desired level of accuracy this relationship among geomorphological characteristics such as shape index and width function derived from gridded networks at different resolutions suggests that a minimum of 200 300 grid cells is necessary to maintain the geomorphological characteristics of the river networks with sufficient accuracy

improvements in large scale drainage networks derived from digital elevation models 1 this paper presents an improved algorithm for deriving drainage networks for coarse gridded distributed hydrological models based on relatively fine resolution digital elevation models the proposed algorithm aims to reproduce actual drainage networks more closely when applied in regions with meandering rivers running in parallel and for cell sizes of the order of 10 kilometers to achieve this goal the cotat algorithm of reed 2003 was improved introducing another parameter related to the minimum upstream flow path into the cell besides the area threshold the proposed algorithm was tested by applying it to the catchments of the rivers tapajos 530 000 km 2 and grande 145 000 km 2 in south america results show that drainage networks are generally improved by the proposed algorithm needing only minor manual corrections

2 d rotation behavior of a rigid ellipse in confined viscous simple shear numerical experiments using fem abstract the rotation behavior of rigid elliptical inclusions adherent to the viscous matrix in simple shear flow is investigated using a 2 d finite element numerical model several simulations were performed using different ratios s between shear zone width and inclusion s least principal axis a computational strategy was devised to calculate pressure and viscous forces exerted on the inclusion and deduce its angular velocity for large s values results agree remarkably well with theoretical predictions while for small s values results deviate significantly from theory but are in agreement with previous analogue experiments the numerical model provided detailed and coherent information about the physical parameters involved in the process e g pressure strain rate and vorticity distributions within the model

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

a rigid circular inclusion in an anisotropic host subject to simple shear abstract the solution for velocity and rate of deformation in an incompressible homogeneously anisotropic viscous host embedding a cylindrical rigid inclusion subjected to a far field shearing parallel to the anisotropy direction is presented the rotation rate of the inclusion is equal to half the ambient shear rate independently of the anisotropy factor the flow in the matrix localizes into conjugate shear bands sub parallel to the anisotropy directions as the anisotropy factor increases the presented anisotropic analytical solution which neglects the bending stiffness approximates the flow in a layered medium in the limit of infinitely thin layers an initially planar layering is deflected adjacent to the inclusion and fold trains propagate into the host with progressing deformation numerical simulations show that the structural development leads to a decrease in the inclusion rotation rate and eventually to inclusion stagnation at high strains the fold shapes become more angular and the fold trains reach further out into the host as the anisotropy factor is increased increasing the layering thickness up to only 9 layers intercepting the inclusion has no significant effect on how the layer inclusion rotation rate evolves with strain a coarse layering in the host leads to a strongly reduced outreach of the fold trains and the absence of tight folds the analytical solution which is derived for a planar anisotropy in the host can be employed to approximate the structural development for a weakly anisotropic host or small deformation structural development of an anisotropic medium plays a major role in determining the system behavior for large deformation

a methodology for preserving channel flow networks and connectivity patterns in large scale distributed hydrological models physiographic data are often used to parameterize hydrological models and in the past physiographic parameters have often been derived manually however this can be a lengthy and unreliable process particularly for application to a gridded hydrological or atmospheric model applied to large or continental scale basins an important attribute of gridded models is drainage direction current methods that determine drainage directions for large or continental scale basins by general circulation models gcms route flow using lowest neighbour algorithms these methods however do not reflect the hydrology of the basin subunit this paper proposes a method of parameterizing hydrological models with physiographic data using the arclnfo macro language to create an interface between the topographic parameterization topaz software and the watflood hydrological model the interface uses output raster data created by topaz i e drainage identification to supply physiographic parameters required by watflood the interface watpaz is an expert system based on a manual method of deriving parameters for the watflood distributed model the watpaz interface uses grouped response units to subdivide the watershed this allows large drainage basins to be subdivided at a scale that allows computational efficiency while preserving the hydrological variability of the watershed to test whether the watpaz method improves the current gcm methodology for determining drainage directions watpaz is applied on a local basin wolf creek a regional scale basin athabasca and a continental scale basin mackenzie an examination of flow directions derived from this new method with current gcm methods is carried out the results indicate that a substantial improvement is made to flow routing within the basin using the channel network to determine drainage directions for each segment

hydraulic causes for basin hydrograph skewness it has been suggested that hydrograph skewness depends on the relative dominance between hillslope and channel network transport processes where the former ones make the hydrograph positively skewed while the latter tends to make it negatively skewed more recently however the role of river hydraulics in shaping the hydrograph has been highlighted we present a set of numerical modelling experiments using a hydrodynamic model of river networks in which we investigate how channel hydraulics influence the shape of the hydrograph particularly its skewness we further investigate the influence of baseflow rainfall intensity cross section geometry and basin scale on unit hydrograph response we show that river hydraulics has a decisive role because positively skewed hydrographs may occur even when water inputs to the river network are negatively skewed and in catchments whose width function is also negatively skewed we show additional results related to the effect of the degree of non linearity in the relationship between celerity and discharge the effects of baseflow and rainfall intensity these further confirm that hydraulic factors may be decisive in determining hydrograph shape

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

application of the promethee technique to determine depression outlet location and flow direction in dem with the fast growing progress of computer technologies spatial information on watersheds such as flow direction watershed boundaries and the drainage network can be automatically calculated or extracted from a digital elevation model dem the stubborn problem that depressions exist in dems has been frequently encountered while extracting the spatial information of terrain several filling up methods have been proposed for solving depressions however their suitability for large scale flat areas is inadequate this study proposes a depression watershed method coupled with the preference ranking organization method for enrichment evaluations promethees theory to determine the optimal outlet and calculate the flow direction in depressions three processing procedures are used to derive the depressionless flow direction 1 calculating the incipient flow direction 2 establishing the depression watershed by tracing the upstream drainage area and determining the depression outlet using promethee theory 3 calculating the depressionless flow direction the developed method was used to delineate the shihmen reservoir watershed located in northern taiwan the results show that the depression watershed method can effectively solve the shortcomings such as depression outlet differentiating and looped flow direction between depressions the suitability of the proposed approach was verified

determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network abstract distributed hydrological models require a detailed definition of a watershed s internal drainage structure the conventional approach to obtain this drainage structure is to use an eight flow direction matrix d8 which is derived from a raster digital elevation model dem however this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed this is largely due to limitations of the d8 approach and the lack of information over flat areas and pits the d8 approach alone is also unable to differentiate lakes from plain areas to avoid these problems a new approach using a digital river and lake network drln as input in addition to the dem has been developed this new approach allows for an accurate fit between the drln and the modelled drainage structure which is represented by a flow direction matrix and a modelled watercourse network more importantly the identification of lakes within the modelled network is now possible the proposed approach which is largely rooted in the d8 approach uses the drln to correct modelled flow directions and network calculations for dem cells overlapped by the drln flow directions are determined using drln connections only the flow directions of the other dem cells are evaluated with the d8 approach which uses a dem that has been modified as a function of distance to the drln the proposed approach has been tested on the chaudiere river watershed in southern quebec canada the modelled watershed drainage structure showed a high level of coherence with the drln a comparison between the results obtained with the d8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure the proposed approach will benefit hydrological models which require data such as a flow direction matrix a river and lake network and sub watersheds for drainage structure information

validation of a new global 30 min drainage direction map abstract digital drainage direction maps are a prerequisite for analyzing the flow of water on the land surface of the earth for continental or global studies the most appropriate and most frequently used resolution for such data sets appears to be 30 longitude by latitude in this paper we present the new global drainage direction map ddm30 a 30 raster map of surface drainage directions which organizes the earth s land area into drainage basins and provides the river network topology ddm30 was generated by first upscaling two drainage direction maps ddms at higher resolutions the resulting map was then extensively corrected in an iterative manner by comparison against vectorized high resolution river maps and other geographic information finally it was co referenced to the locations of 935 gauging stations provided by the global runoff data centre grdc which again involved manual corrections ddm30 was validated against drainage basin areas from the literature against the given upstream areas of the grdc stations and most importantly against information from hydro1k a data set based on a hydrologically corrected 1 km digital elevation model which is thought to afford the best information on surface drainage currently available at the global scale in the course of the validation the quality of ddm30 was compared to three other 30 ddms the validation results show that ddm30 provides a more accurate representation of drainage directions and river network topology than the other 30 ddms

a morphology independent methodology for quantifying planview river change and characteristics from remotely sensed imagery abstract remotely sensed imagery of rivers has long served as a means for characterizing channel properties and detection of planview change in the last decade the dramatic increase in the availability of satellite imagery and processing tools has created the potential to greatly expand the spatial and temporal scale of our understanding of river morphology and dynamics to date the majority of gis and automated analyses of planview changes in rivers from remotely sensed data has been developed for single threaded meandering river systems these methods have limited applicability to many of the earth s rivers with complex multi channel planforms here we present the methodologies of a set of analysis algorithms collectively called spatially continuous riverbank erosion and accretion measurements scream scream analyzes planview river metrics regardless of river morphology these algorithms quantify both the erosion and accretion rates of riverbanks from binary masks of channels generated from imagery acquired at two time periods additionally the program quantifies the area of change between river channels and the surrounding floodplain and area of islands lost or formed between these two time periods to examine variations in erosion rates in relation to local channel attributes and make rate comparisons between river systems of varying sizes the program determines channel widths and bank curvature at every bank pixel scream was developed and tested on rivers with diverse and complex planform morphologies in imagery acquired from a range of observational platforms with varying spatial resolutions validation and verification of scream generated metrics against manual measurements show no significant measurement errors in determination of channel width erosion and bank aspects scream has the potential to provide data for both the quantitative examination of the controls on erosion rates and for the comparison of these rates across river systems ranging broadly in size and planform morphology

influence of a permanent low friction boundary on rotation and flow in rigid inclusion viscous matrix systems from an analogue perspective abstract natural occurrences and recent experimental work show that a low friction inclusion matrix boundary can be responsible for antithetical rotation and development of stable shape preferred orientations in simple shear the flow of a viscous matrix around a rigid inclusion to which it may or may not be adherent is still not well studied but it is relevant to the understanding of the behaviour of structural elements in mylonite zones we used two dimensional 2 d analogue experiments to address these issues the experimental results with a permanent low friction inclusion matrix boundary nonadherent mode show the following 1 the rotation behaviour of inclusions in this mode is markedly different from the theoretical predictions and experimental results for the adherent mode 2 inclusions with aspect ratio equal to 1 rotate synthetically at a rate that depends upon inclusion shape and orientation 3 ellipse rectangle and lozenge shaped inclusions rotate antithetically when starting with their greatest axis parallel to the shear direction 4 back rotation is limited in all cases studied and the angle between the inclusion greatest axis and the shear direction represents a stable orientation which depends on inclusion aspect ratio and shape 5 a metastable orientation exists which is strongly dependent upon inclusion shape and aspect ratio and separates fields of antithetic and synthetic rotation our experimental results show that the overall flow pattern is bow tie shaped in adherent and nonadherent modes however there are major differences in the way the matrix flows near the inclusion i in the nonadherent mode the nearby matrix flows past the inclusion whereas in the adherent mode the nearby matrix flows with and follows the inclusion therefore in the adherent mode passive marker lines parallel to the shear direction and streamlines show considerable deflections at the inclusion crests in marked contrast with their straight character in the nonadherent mode ii stagnation points or closed flow lines near the inclusion were not observed in the nonadherent mode which means that there is no closed separatrix around the inclusion in this mode despite the fact that the overall flow shape is bow tie iii in the adherent mode the line of flow reversal is stable throughout deformation but in the nonadherent mode it changes position and orientation with progressive shearing this shifting of the line of flow reversal can be an important factor controlling rotation behaviour in the nonadherent mode iv in the nonadherent mode the inclusion behaviour is similar to that observed in confined flow v the flow pattern in the nonadherent mode provides an explanation for the observed lack of drag folds associated with small scale rigid inclusions in mylonites

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

applications of inclusion behaviour models to a major shear zone system the nordfjord sogn detachment zone in western norway rigid inclusion models have reached a stage where one should be able to use them to obtain quantitative values from ductile shear zones we used natural data collected in three sites and combined analogue and theoretical modelling to assess vorticity strain nature of rigid inclusion matrix interface and confinement in the large scale ductile nordfjord sogn detachment zone nsdz of the caledonides of western norway our study shows that 1 the observed shape preferred orientation spo at higher structural levels of the nsdz at site 1 gjervika can be explained by simple shear pure shear simple shear ratio sr 0 associated with a slipping inclusion matrix interface 2 the observed spo at deeper structural levels of the nsdz at site 2 near sandane can be produced by simple shear associated with a significant amount of shortening across the shear zone sr z 1 acting upon rigid inclusions in slipping contact with the enclosing matrix 3 observed back rotated boudins deeper in the nsdz at site 3 biskjelneset can form in confined flow associated with a considerable amount of shortening across the shear zone sr 0 4 4 the observed tails of porphyroclasts indicate a minimum at least local strain of ca g z 20 5 the clasts in the studied shear zones strongly depart from jeffery s model jeffery g b 1922 the motion of ellipsoidal particles immersed in a viscous fluid proceedings of the royal society of london a102 161e179 the large scale extensional nsdz under investigation shows evidence of strain partitioning rocks vary from protomylonites to ultramylonites and the simple shear and pure shear components are heterogeneously distributed therefore we conclude that flow in the nsdz was very heterogeneous both at the kilometre and the metre scale however the present study suggests that the amount of shortening across the shear plane throughout the nsdz increases with depth and the flattening component contributes to exhumation of the eclogite facies rocks in its footwall 2007 elsevier ltd all rights reserved

numerical modelling of porphyroclast and porphyroblast rotation in anisotropic rocks abstract the rotational behaviour of rigid objects in a weaker rock matrix during deformation has been the subject of many field experimental and numerical modelling studies often centred on the question whether objects rotate or not in non coaxial deformation with numerical studies gaining increasing popularity and importance we here provide an overview of the results published so far and provide new simulations originally shape and orientation were investigated while the emphasis shifted to rheology and slip between object and matrix in the nineties of the last century due to improved numerical techniques anisotropic rheology has become the focus of most recent studies indicating that it is a primary factor in the rotation behaviour of objects we present new simulations investigating the role of anisotropy on different scales relative to the object and show how this influences the rotation rate as well as the inclusion patterns in case of syntectonically growing porphyroblasts these simulations show that a variety of factors play a role to determine the rate and sense of rotation of objects the variability of the inclusion patterns that can develop necessitates extreme caution in the kinematic interpretation of these structures when observed in the field

deriving flow directions for coarse resolution 1 4 km gridded hydrologic modeling 1 the national weather service hydrology laboratory nws hl is currently testing a grid based distributed hydrologic model at a resolution 4 km commensurate with operational radar based precipitation products to implement distributed routing algorithms in this framework a flow direction must be assigned to each model cell a new algorithm referred to as cell outlet tracing with an area threshold cotat has been developed to automatically accurately and efficiently assign flow directions to any coarse resolution grid cells using information from any higher resolution digital elevation model although similar to previously published algorithms this approach offers some advantages use of an area threshold allows more control over the tendency for producing diagonal flow directions analyses of results at different output resolutions ranging from 300 m to 4000 m indicate that it is possible to choose an area threshold that will produce minimal differences in average network flow lengths across this range of scales flow direction grids at a 4 km resolution have been produced for the conterminous united states

a simple model of convective drafts accounting for the perturbation pressure term abstracta simple anelastic two column model of convective updraft accounting explicitly for the perturbation pressure term is developed there is no vertical wind shear in the environment and two

river reach length and slope estimates for large scale hydrological models based on a relatively high resolution digital elevation model application of regular grid based distributed hydrological models requires information related to river drainage networks such as flow directions flow accumulated areas basin delineation and length and slope of river reaches for every grid cell most of those data may be extracted automatically from digital elevation models dem however when dealing with large basins available dems are usually in higher spatial resolution than the model grid upscaling procedures have therefore been developed to extract low resolution flow directions and flow accumulated areas from relatively high resolution dems this paper presents a new methodology which extends the upscaling method to automatically extract length and slope of river reaches for large scale grid based hydrological models the proposed method is new and is believed to be the first attempt to produce such information automatically from dems the methodology was applied to parts of the uruguay river basin in south america using the globally wide available dem produced by the shuttle radar topography mission srtm 90m quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks which were assumed to be correct it was shown that the proposed methodology adequately assigns river lengths to every model cell while ensuring that the whole length of the streams is considered the effect of dem resolution on calculated river length errors was analyzed by resampling the srtm dem to three different cell sizes with best results obtained for the higher resolution dem the modification of the original high resolution dem through the process known as stream burning was also tested largely improving the quality of the results finally optimal distance transforms were used for the calculation of distance increments instead of euclidean local distances giving results that were generally better the quality of results for calculated slope values could not be assessed because no reliable data were available for comparison

improving hydrological information acquisition from dem processing in floodplains extraction of hydrological information from digital elevation models dems is a required step when conducting any spatially distributed hydrological modelling in particular automated methods are proposed to extract the drainage structure from the dem however a realistic river network is not always derived from conventional dem processing methods indeed inaccuracy occurs in flat areas corresponding to floodplains in these areas additional sources of information are required to extract the correct drainage direction from the dem in this study it is demonstrated that traditional approaches of dem preprocessing such as the commonly known stream burning fail to provide correct maps of drainage directions and catchment areas when the extension of flat areas is large a new method is proposed to take advantage of available imagery data this method is based on a double dem burning process dem is first burned in the main rivers using the channel network and then in the floodplain using the spatial distribution of floodplains provided by classified satellite images in this sense the method has been referred to as the floodplain burning approach or simply fb approach spatial distribution of floodplains is derived from a multitemporal sar image classification a system of equations is used to vary the elevation offset required to be burnt in each cell representing the floodplain according to the minimal distance from the channel network which is calculated by a distance transformation the fb approach was applied to a sub basin located within the larger amazon river basin the region is characterized by large floodplain extensions basin delineation maps derived from the new method were compared with those obtained from the traditional stream burning method and highlighted more realistic results copyright 2008 john wiley sons ltd

rotation of rigid elliptical cylinders in viscous simple shear flow analogue experiments we used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness and for very small ratios s between shear zone width z and the shortest principal axis e2 of the ellipse that constitutes the base of the elliptical cylinder 3 5 s z e2 1 2 former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and or a very large ratio between shear zone thickness and inclusion size s 1 and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow except for inclusions with infinite axial ratio our results depart greatly from the analytical predictions experiments were carried out at constant shear zone thickness but variable s and degree of coupling at the inclusion matrix interface the results show that 1 confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness even for synthetic rotation 2 the deviation in the angular velocity and or in the sense of rotation increases as s approaches 1 and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane and 3 a slipping inclusion matrix interface greatly enhances deviation from theoretical predictions with antithetic rotations to as much as 20

perturbation pressure at the base of cumulus clouds in low shear abstract we examine the pressure fields wound the cloud base updraft of three cumulus clouds observed in environments with low vertical shear of the horizontal wind near cloud base these fields are compared to the corresponding pressure fields beneath convective clouds embedded in moderate to large shear all of the pressure fields are derived from aircraft measurements taken during the 1981 cooperative convective experiment ccope the pressure fields associated with these low shear clouds are weaker than those for the clouds in higher shear furthermore the low shear fields are not consistently dominated by the dynamic pressure created by the interaction of the cloud base updraft with the vertical shear of the horizontal wind the weaker dynamic pressure is due to the smaller size and intensity of the cloud base updraft as well as the smaller vertical shear of the horizontal wind the reduction of the dynamic pressure allows buoyancy effects on the pressure field to become more apparent

on the effect of digital elevation model accuracy on hydrology and geomorphology this study compares published cartometric and photogrammetric digital elevation models dems of various grid spacings with a ground truth data set obtained by ground survey and studies the implications of these differences on key hydrologic statistics inferred catchment sizes and stream networks from published dems were found to be significantly different than those from the ground truth in most instances furthermore the width functions and cumulative area relationships determined from the published dems were found to fall consistently outside the 90 confidence limits determined from the ground truth for more than 60 of the relationship suggesting that these hydrologic properties are poorly estimated from published dems however the slope area relationships determined from published dems were found to be less sensitive to catchment shape size and stream network with the relationship falling outside the 90 confidence limits for less than 40 of the relationship for all catchments identified from the published dems a published relationship linking the horizontal resolution with the vertical accuracy of the dem was tested predicting a horizontal resolution of about 10 m for the published dems tested

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

deformation around rigid particles the influence of slip at the particle matrix interface abstract theoretical and previous experimental studies of rigid particle structures have only considered the behaviour of rigid particles for which the interface between particle and matrix is coherent in natural rocks the boundary behaviour may cover the whole range from free slip to complete coherence examples where slip may be promoted include crack seal deformation during the development of pressure shadows core mantle structures where the mantle is composed of much weaker fine recrystallized material and crystallizing magmas or partially molten rocks where grain boundaries are lubricated by the melt phase analogue scale model experiments have been performed under pure shear and simple shear conditions to compare the particle rotation and the flow in the matrix for both slipping and non slipping particle matrix interfaces when slip does occur particles rotate faster in pure shear and slower in simple shear than for non slip leading to the more rapid development of a shape preferred orientation the preferred orientation tends to be bimodal in simple shear flow the flow and finite strain patterns in the matrix are also strongly influenced by slip at the interface and porphyroclast systems can develop geometries with ambiguous or contradictory shear senses dependent on the original particle orientation in multi particle experiments slip on the interfaces enhances strong strain localization in non linear viscous material to produce patterns very similar to natural s c fabrics

analogue modelling of the influence of shape and particle matrix interface lubrication on the rotational behaviour of rigid particles in simple shear abstract the rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear couette flow was studied in 2d rock analogue experiments the influence of particle shape elliptical vs monoclinic aspect ratio and the nature of the matrix particle interface lubricated vs unlubricated was investigated both matrix pdms and lubricant liquid soap were linear viscous with a viscosity ratio of ca 10 4 without lubricant the rotational behaviour of all particles closely approximates the jeffery theory lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation in general for elliptical particles rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle for thick mantles initially 10 of the volume of the particle rotation rates are faster than jeffery theory for very thin mantles they are markedly slower compared with thick mantles particularly when the long axis is nearly parallel to the shear direction rotation rates are never strictly zero so true stabilization does not occur however for more elongate particles axial ratio 6 rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population in experiments the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain in natural examples of porphyroclast systems the weak mantle continually develops by recrystallization and or cataclasis of the rigid clast core and a steady state between production and thinning could be attained potentially leading to true stabilization for particles with a high axial ratio

rotation behaviour of rigid inclusions in multiple association insights from experimental and theoretical models many rocks are representative of inclusion matrix systems where rigid inclusions float on a ductile matrix the geological analogues of such inclusion matrix systems are theoretically modelled with the help of jeffery s 1922 theory in recent years there have been a number of reinvestigations on the rotational motion of rigid inclusions to account for some geological observations that are not yet predicted in models based on jeffery s theory adding to this effort this paper investigates the effects of 1 inclusion concentration and 2 the degree of coherence at the inclusion matrix interface on the rotation behaviour of rigid inclusions in a multiple inclusion system during simple shear deformation shear box experiments were run on models containing multiple identical elliptic cylinders of wax mimicking rigid inclusion embedded within putty representing ductile matrix two sets of experiments were performed with and without lubrication at the inclusion matrix interfaces each model had an isolated inclusion to reveal the variation of rotations of single and multiple inclusions increase in inclusion concentration results in contrasting rotation behaviour of isolated and multiple inclusions initially oriented parallel to the shear direction when the interfaces were not lubricated inclusions in multiple association rotated antithetically whereas the isolated one almost remained stationary in models wherein the inclusion matrix interfaces were lubricated with liquid soap both isolated and multiple inclusions rotated antithetically but the isolated inclusion rotated at a lower rate with increasing inclusion concentration the difference in the rates of antithetic rotation between isolated and multiple inclusions tended to be larger in both lubricated and non lubricated conditions the sense of rotation of isolated as well as multiple inclusions initially oriented perpendicular to the shear direction was always synthetic irrespective of the nature of the interface lubricated or non lubricated however the instantaneous rotation rates of inclusions in multiple association were higher than that of the isolated inclusions disposed in the same orientation rotation of inclusion in an inclusion matrix system is basically induced by the traction exerted by the flowing matrix on the surface of the inclusion during deformation employing a hydrodynamic model it is shown that mutual mechanical interaction among inclusions which is a function of inclusion concentration modifies the stresses at the inclusion matrix interface to a large extent moment calculations reveal that inclusions oriented parallel to the shear direction experience an antithetic moment in response to the normal stress components the magnitude of which increases with increasing inclusion concentration this implies that rotation of shear parallel inclusions in antithetic sense is favoured by higher inclusion concentration on the other hand inclusions oriented perpendicular to shear direction experience a moment that induces synthetic rotation the magnitude of the synthetic moment is larger for larger inclusion concentration leading to increase in the rate of synthetic rotation using the theoretical model the moments are calculated as a function of the aspect ratio of inclusions and the inferences based on this moment calculation are complemented with experimental findings

carving and adaptive drainage enforcement of grid digital elevation models 1 an effective and widely used method for removing spurious pits in digital elevation models consists of filling them until they overflow however this method sometimes creates large flat regions which in turn pose a problem for the determination of accurate flow directions in this study we propose to suppress each pit by creating a descending path from it to the nearest point having a lower elevation value this is achieved by carving i e lowering the terrain elevations along the detected path carving paths are identified through a flooding simulation starting from the river outlets the proposed approach allows for adaptive drainage enforcement whereby river networks coming from other data sources are imposed to the digital elevation model only in places where the automatic river network extraction deviates substantially from the known networks an improvement to methods for routing flow over flat regions is also introduced detailed results are presented over test areas of the danube basin

convective momentum transport and perturbation pressure field from a cloud resolving model simulation this study uses a 2d cloud resolving model to investigate the vertical transport of horizontal momentum and to understand the role of a convection generated perturbation pressure field in the momentum transport by convective systems during part of the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period it shows that convective updrafts transport a significant amount of momentum vertically this transport is downgradient in the easterly wind regime but upgradient during a westerly wind burst the differences in convective momentum transport between easterly and westerly wind regimes are examined the perturbation pressure gradient accounts for an important part of the apparent momentum source in general it is opposite in sign to the product of cloud mass flux and the vertical wind shear with smaller magnitude examination of the dynamic forcing to the pressure field demonstrates that the linear forcing representing the interaction between the convective updrafts and the large scale wind shear is the dominant term while the nonlinear forcing is of secondary importance thus parameterization schemes taking into account the linear interaction between the convective updrafts and the large scale wind shear can capture the essential features of the perturbation pressure field the parameterization scheme for momentum transport by zhang and cho is evaluated using the model simulation data the parameterized pressure gradient force using the scheme is in excellent agreement with the simulated one the parameterized apparent momentum source is also in good agreement with the model simulation other parameterization methods for the pressure gradient are also discussed

the influence of matrix rheology and vorticity on fabric development of populations of rigid objects during plane strain deformation abstract the influence of vorticity and rheology of matrix material on the development of shape preferred orientation spo of populations of rigid objects was experimentally studied experiments in plane strain monoclinic flow were performed to model the fabric development of two populations of rectangular rigid objects with object aspect ratios rob 2 and 3 the density of the rigid object populations was 14 of the total area objects were dispersed in a newtonian and a non newtonian power law matrix material with a power law exponent n of 1 2 the kinematic vorticity number wn of the plane strain monoclinic flow was 1 0 8 and 0 6 with finite simple shear strain of 4 6 3 0 and 0 9 respectively in experiments with rob 3 the spo is strongly influenced by wn and the material properties of the matrix deformation of a power law matrix material and low wn resulted in a stronger spo than deformation of a linear viscous matrix and high wn strain localization coupled with particle interaction plays a significant role in the development of a shape preferred orientation high strain simple shear zones separate trains of rigid objects that are surrounded by low strain zones with wn lower than the bulk wn in fabrics involving populations of objects with rob 2 rheology of the matrix materials does not systematically influence the intensity of the spo

estimating cell to cell land surface drainage paths from digital channel networks with an application to the amazon basin cell to cell surface flow paths are commonly derived from gridded digital elevation models dem by choosing the direction of steepest descent to one of the eight surrounding cells however adequate dems often are not available we developed a topography independent method for creating gridded land and stream drainage direction maps based on corrected vector river networks we applied it to the digital chart of the world river network in the amazon basin gridded at 0 0058 resolution in this basin low relief and poor topographic data have prevented the effective use of dem based methods we geo registered 224 hydrographic gages against the processed network and compared extracted vs published drainage areas drainage areas ranged from 227 to 4 620 000 km 2 median relative error was 4 5 increasing in smaller basins to 94 in basins 2000 km 2 the effective limit of reliability may differ from 2000 km 2 across the basin the drainage direction map and derivative datasets represent an improvement over existing datasets for regional research in the amazon basin methods exploiting vector networks complement terrain approaches and combined they may yield advances in the automated extraction of drainage maps and handling of topologically realistic river systems q 2005 elsevier b v all rights reserved

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

an analytical solution in 2d for the motion of rigid elliptical particles with a slipping interface under a general deformation a mathematical model for rigid inclusions with a slipping interface immersed in a general 2d homogeneous deformation is developed under bulk pure shear inclusions are expected to rapidly approach the stretching axis when compared to the behaviour of inclusions with no slip at the interface the derived model predicts synthetic and antithetic motion into a stable orientation under simple shear and thereafter the inclusion makes an antithetic angle with the shear direction under simple shear rotation rates can be higher or lower than those of no slip inclusions depending on orientation a direct relationship between object inclination to the shear direction and the vorticity of the bulk flow is predicted the model compares well with published analogue and numerical experiments

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

controls on the geometry of tails around rigid circular inclusions insights from analogue modelling in simple shear abstract we used analogue modelling to investigate the factors controlling tail geometry in porphyroclast systems results show that 1 inclusions can develop in both slipping and non slipping modes but inclusions only form in the latter 2 inclusions develop when the mantle production rate is constant and the mantle is transected by the separatrix inclusions form when the mantle is initially outside the separatrix and later comes inside this line 3 in the slipping mode the wedge shaped tail of inclusions always has a straight external surface parallel to the shear plane whereas in the non slipping mode the external surface is curved inwards external embayments 4 together with earlier theoretical results and inclusions always show stair stepping of tails when embedded in a viscous matrix under homogeneous simple shear deformation 5 maximum stair stepping occurs in the slipping mode and is at least equal to the inclusion diameter if our models bear significant similarity to nature then i the straight or curved character of inclusions could mean that they had respectively a slipping or non slipping interface with the surrounding recrystallized matrix and ii inclusions may result from shear deformation under retrogressive metamorphic conditions in thrust systems

extraction and representation of nested catchment areas from digital elevation models in lake dominated topography this paper presents a new method for extracting flow directions contributing upslope areas and nested catchments from digital elevation models in lake dominated areas existing tools for acquiring descriptive variables of the topography such as surface flow directions and contributing areas were developed for moderate to steep topography these tools are typically difficult to apply in gentle topography owing to limitations in explicitly handling lakes and other flat areas this paper addresses the problem of accurately representing general topographic features by first identifying distinguishing features such as lakes in gentle topography areas and then using these features to guide the search for topographic flow directions and catchment marking lakes are explicitly represented in the topology of a watershed for use in water routing nonlake flat features help guide the search for topographic flow directions in areas of low signal to noise this combined feature based and grid based search for topographic features yields improved contributing areas and watershed boundaries where there are lakes and other flat areas lakes are easily classified from remotely sensed imagery which makes automated representation of lakes as subsystems within a watershed system tractable with widely available data sets

influence of a low viscosity layer between rigid inclusion and viscous matrix on inclusion rotation and matrix flow a numerical study abstract we have used 2 d finite element modelling to investigate the influence of a permanent low viscosity layer between matrix and inclusion on matrix flow and inclusion rotation under viscous simple shear flow rigid inclusions of different shape circle square ellipse lozenge rectangle and skewed rectangles and aspect ratio r were used the calculated matrix flow pattern is neither bow tie nor eye shaped it is a new flow pattern that we call cat eyes shaped which is characterized by i straight streamlines that slightly bend inwards at the inclusion s crests ii elongate eye shaped streamlines on each side of the inclusion iii stagnation points in the centre of the eyes iv absence of closed streamlines surrounding the inclusion v changes in flow configuration with inclusion orientation the lines of flow reversal bend and tilt closed streamline circuits may disappear and streamlines may bend outwards at the inclusion s crests concerning inclusion rotation the numerical results show that i a low viscosity layer lvl makes inclusions with r 1 rotate synthetically but the rotation rate depends upon shape circle or square and orientation therefore shape matters in the slipping mode ii all studied shapes with r 1 rotate antithetically when starting with the greatest principal axis e 1 parallel to the shear direction 0 iii rotation is limited because there is a stable equilibrium orientation se for all studied shapes with r 1 iii there is also an unstable equilibrium orientation ue and both se and ue depend upon inclusion s r and shape the present numerical results closely agree with previous results of analogue experiments with a permanent low viscosity interface only minor deviations related with small shape differences were detected

how does modifying a dem to reflect known hydrology affect subsequent terrain analysis summary many digital elevation models dems have difficulty replicating hydrological patterns in flat landscapes efforts to improve dem performance in replicating known hydrology have included a variety of soft i e algorithm based approaches and hard techniques such as stream burning or surface reconditioning e g agree or anudem using a representation of the known stream network these methods trench or mathematically warp the original dem to improve how accurately stream position stream length and catchment boundaries replicate known hydrological conditions however these techniques permanently alter the dem and may affect further analyses e g slope this paper explores the impact that commonly used hydrological correction methods stream burning agree aml and anudem v4 6 3 and anudem v5 1 have on the overall nature of a dem finding that different methods produce non convergent outcomes for catchment parameters such as catchment boundaries stream position and length and differentially compromise secondary terrain analysis all hydrological correction methods successfully improved calculation of catchment area stream position and length as compared to using the dem without any modification but they all increased catchment slope no single method performing best across all categories different hydrological correction methods changed elevation and slope in different spatial patterns and magnitudes compromising the ability to derive catchment parameters and conduct secondary terrain analysis from a single dem modification of a dem to better reflect known hydrology can be useful however knowledge of the magnitude and spatial pattern of the changes are required before using a dem for subsequent analyses

polyphase variscan emplacement of exotic terranes morais and braganca massifs onto iberian successions evidence from 40ar 39ar mineral ages abstract the braganca and morais nappe complexes comprise internally imbricated continental tectonic units including schists deformed metagranite granulite and local eclogite and a structurally underlying ophiolite nappe high pressure assemblages in some of the continental sequences were variably retrogressed during an amphibolite facies metamorphic overprint by contrast rocks within the ophiolite nappe display prograde amphibolite facies assemblages hornblende concentrates from both tectonic units exposed in the braganca nappe complex record 40 ar 39 ar plateau and isotope correlation ages of c 385 390 ma a similar date is recorded by hornblende within mylonitic amphibolite ophiolite protolith along a ductile thrust which separates the two major nappe units muscovite within blastomylonitic metagranite lagoa augen gneiss in upper structural levels of the morais massif records 370 375 ma 40 ar 39 ar plateau ages muscovite within phyllinite developed along a ductile thrust separating the gneiss from the structurally underlying ophiolite nappe records a 375 ma age together the 40 ar 39 ar data suggest that a regionally significant early variscan amphibolite facies metamorphism occurred prior to c 385 390 ma early devonian this was associated with ductile imbrication of continental and ophiolite structural units with resultant formation of a composite nappe complex the composite nappe complex must have been maintained at relatively high structural levels throughout the remaining variscan evolution because there is no evidence for post 370 ma rejuvenation of intracrystalline argon systems in any of crystalline structural units examined this is in marked contrast to a significant late devonian c 330 ma locally high pressure metamorphism which is recorded in structurally underlying elements of the lower allochthon part of a foreland thrust complex composed of metasedimentary units with iberian protolith affinities together available chronologic constraints indicate emplacement of the previously assembled composite nappe complex into its present relative structural position at c 330 ma with resultant deformation and metamorphism of structurally underlying components of the iberian thrust complex

mineral lineation produced by 3 d rotation of rigid inclusions in confined viscous simple shear abstract the solid state flow of rocks commonly produces a parallel arrangement of elongate minerals with their longest axes coincident with the direction of flow a mineral lineation however this does not conform to jeffery s theory of the rotation of rigid ellipsoidal inclusions reis in viscous simple shear because rigid inclusions rotate continuously with applied shear in 2 dimensional 2 d flow the rei s greatest axis e1 is already in the shear direction therefore the problem is to find mechanisms that can prevent the rotation of the rei about one axis the vorticity axis in 3 d flow the problem is to find a mechanism that can make e1 rotate towards the shear direction and so generate a mineral lineation by rigid rotation about two axes 3 d analogue and numerical modelling was used to test the effects of confinement on rei rotation and for narrow channels shear zone thickness over inclusion s least axis wr 1 can rotate backwards from an initial orientation w e1 parallel to the shear plane in great contrast to jeffery s model 3 back rotation is limited because inclusions reach a stable equilibrium orientation 4 most importantly and in contrast to jeffery s model and to the 2 d simulations in 3 d the confined rei gradually rotated about an axis orthogonal to the shear plane towards an orientation with e1 parallel to the shear direction thus producing a lineation parallel to the shear direction the modelling results lead to the conclusion that confined simple shear can be responsible for the mineral alignment lineation observed in ductile shear zones

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

airborne measurements of terrain induced pressure perturbations airborne measurement of the horizontal pressure field using differential gps technology has been established during the last few years accurate aircraft measurement of the horizontalpressure gradientforce requires an independent determination of the height of the airborne platform above some reference level here the authors demonstrate a differential gps technique that uses data from a fixed reference station to refine the vertical position of the aircraft a series of research flight legs by the university of wyoming king air research aircraft uwka were conducted during the winter seasons of 2008 and 2009 over the medicine bow mountains in southern wyoming flight patterns consisted of a series of geographically fixed parallel legs along a quasi isobaric surface above the mountainous terrain allowing the finescale mapping of the horizontal pressure or geopotential height field the removal of the large scale gradient and tendency isolates the terrain induced pressure perturbation field results obtained using differential gps measurements of aircraft height show that the medicine bow range induces pronounced horizontal pressure perturbations with a leeside region of low pressure downwind of the crest in two cases on 11 february 2008 and 20 february 2009 a wind maximum is found downwind of the elevated terrain consistent with this pressure gradient simulations of these two cases were performed using the weather research and forecasting model wrf the wrf height patterns for the time of the uwka flight matched the general isobaric height patterns observed simulations and observations consistently show that the cross mountain acceleration is stronger when the perturbation pressure gradient is larger

preferred orientation developed by rigid markers in two dimensional simple shear strain a theoretical and experimental study abstract in a homogeneous two dimensional deformation linear markers embedded in a viscous matrix develop a preferred orientation along the principal axis of the strain ellipse theoretical analysis of marker rotation under two dimensional simple shear is used to derive an orientation distribution function this function shows that the relative density maximum increases with progressive strain its value being equal to the major minor strain ellipse axis ratio moreover the density is equal to the unity along the lines of no finite longitudinal strain experimentally observed preferred orientation is in good agreement with the expected theoretical distribution

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

path based methods for the determination of nondispersive drainage directions in grid based digital elevation models 1 path based methods for the determination of nondispersive drainage directions in grid based digital elevation models are presented these methods extend the descriptive capabilities of the classical d8 method by cumulating the deviations between selected and theoretical drainage directions along the drainage paths it is shown that either angular or transversal deviations can be employed accordingly two classes of methods designated d8 lad eight drainage directions least angular deviation and d8 ltd eight drainage directions least transversal deviation are developed detailed tests on four synthetic drainage systems of known geometry and on the liro catchment central italian alps indicate that the proposed methods provide significant improvement over the d8 method for the determination of drainage directions and drainage areas