event frequency and landscape stability on the floodplain systems of arid central australia abstract central australian floodplains contain landforms suggesting activity at three scales a set of large sand sheets sand threads and megaripple covered channels related to a few enormous floods the contemporary floodplain which consists of channels and levees floodouts unchannelled floodplains and floodbasins and erosion cell mosaics which result from local redistribution of sediment classical floodplain models do not fit these systems which behave more like low angle alluvial fans because they continue to accumulate sediment the sedimentary history of the central australian floodplains suggests that deposition in the last 10 000 years has been dominated by a few gigantic floods these events are not represented in the published slackwater deposit record but morphological evidence for them can be found in bedrock gorges as well as on floodplains since the last major flood channel levee systems have been growing slowly upwards and outwards and outwards from the mountain ranges away from these systems sediment supply is limited and the dominant process is local reworking this has intensified since the arrival of europeans 100 years ago and also as a result of increased flooding due to variations in rainfall

use of airborne imaging spectrometer data to map minerals associated with hydrothermally altered rocks in the northern grapevine mountains nevada and california abstract three flightlines of airborne imaging spectrometer ais data acquired over the northern grapevine mountains nevada and california were used to map minerals associated with hydrothermally altered rocks the data were processed to remove vertical striping normalized using an equal area normalization and reduced to reflectance relative to an average spectrum derived from the data an algorithm was developed to automatically calculate the absorption band parameters band position band depth and band width for the strongest absorption feature in each pixel these parameters were mapped into an intensity hue saturation ihs color system to produce a single color image that summarized the absorption band information this image was used to map areas of potential alteration based upon the predicted relationships between the color image and mineral absorption band individual ais spectra for these areas were then examined to identify specific minerals two types of alteration were mapped with the ais data areas of quartz sericite pyrite alteration were identified based upon a strong absorption feature near 2 21 m a weak shoulder near 2 25 m and a weak absorption band near 2 35 m caused by sericite fine grained muscovite areas of argillic alteration were defined based on the presence of montmorillonite identified by a weak to moderate absorption feature near 2 21 m and the absence of the 2 35 m band montmorillonite could not be identified in mineral mixtures calcite and dolomite were identified based on sharp absorption features near 2 34 and 2 32 m respectively areas of alteration identified using the ais data corresponded well with areas mapped using field mapping field reflectance spectra and laboratory spectral measurements

enhancement of extratropical cyclogenesis by a mesoscale convective system abstract considerable progress has been made in the past decades on understanding the life cycle of rapidly deepening winter cyclones however little attention has been paid to the role that mesoscale convective systems mcss play during extratropical cyclogenesis within weak baroclinic environments in this study the impact of an mcs on the subsequent surface cyclogenesis is investigated by extending the previously documented 21 h simulation of the 10 11 june 1985 pre storm squall line to 36 hours the model reproduces the meteorological events from the initiation to the dissipation of the squall system and then to the formation of a surface cyclone and the amplification of midlevel baroclinic waves as verified against all available observations it is found that the squall line is initiated ahead of a weak surface cold front with the aid of baroclinic forcing once initiated however the prefrontal squall system is primarily driven by the interaction of convectively generated circulations with a co

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

discrete frontal propagation in a nonconvective environment abstract surface discrete frontal propagation in a wintertime nonconvective environment is documented using conventional surface and upper air data and simulated using the psu ncar mesoscale model synoptic and mesoscale surface analyses show a cold front associated with a synoptic scale low pressure system propagating from northwest to southeast across the central united states apparently discrete frontal propagation occurs when the surface front dissipates and a new front forms approximately 500 km ahead of the original front with no compelling evidence of frontal passage in the intervening space upper air analyses indicate the infusion of three different airstreams into the frontal region resulting in the formation of a ribbon of low static stability air parallel to and several hundred kilometers in advance of the original front this static stability structure appears to be involved in the observed evolution of the front the development of precipitation over the intervening zone between the old

digital soil pattern recognition in the lower namoi valley using numerical clustering of gamma ray spectrometry data abstract digital soil mapping involves the use of ancillary data e g proximal and remotely sensed as surrogates for soil information to produce maps of soil type or classes two of the most popularly used sources of ancillary data are the proximally sensing electromagnetic em induction instruments and remotely sensed digital elevation model data dem however these data have limitations at the catchment level and are of limited use on predominantly flat alluvial landscapes respectively another option is the use of remotely sensed gamma ray ray spectrometry data which has successfully been used to map the regolith in this paper the use of ray spectrometry data i e potassium k uranium u thorium th and total count tc coupled with a numerical clustering algorithm i e fuzzy k means fkm algorithm is explored in order to identify geological and geomorphological units at the district and soil mapping units at a broader catchment level we do this by using the euclidean distance and the measures of fuzziness performance index fpi and normalized classification entropy nce to identify k 11 classes and a fuzziness exponent 2 0 for interpretation the k 11 classes produce contiguous classes which are consistent with geological and geomorphological interpretations of an eroded landscape alluvial lands and dust mantled alluvial lands at the district level at the sub catchment level the k 11 classes also match broad soil mapping units and also elucidate subtle differences of the alluvial lands which characterise the agriculturally significant parts of the lower namoi valley fuzzy canonical analysis shows that k and tc contribute most to the discrimination of the classes associated with the trachyte rich parts of the eroded landscape the alluvial lands and most of the dust mantled alluvial lands whilst u and th discriminate the basaltic outliers and other geomorphological units of the eroded lands we conclude that the approach allows soil management and landscape units to be identified with the information used as a first approximation to determine where soil sample locations need to be collected to validate the map units identified in order to better incorporate and characterise subsoil properties the inclusion of em signal data e g em38 or dualem 1 may also be appropriate

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

the formation of multiple fronts using two dimensional semi geostrophic frontogenesis models and three dimensional semi geostrophic baroclinic wave models it is shown that atmospheric development in the presence of non uniformities in pre existing temperature distributions may be expected to lead to the frequent occurrence of multiple frontal structures in general such non uniformities in the temperature distribution will be important if they significantly change the ambient temperature gradient the frontal structures associated with the irregularities tend to be very shallow they are possible candidates for the triggering mechanism for frontal troughs well behind a cold front and for shallow rainbands ahead of such a front however it seems that a separate mechanism is still necessary for the production of the middle level banded structures that are frequently observed

regional scale sedimentation process models from airborne gamma ray remote sensing and digital elevation data airborne gamma ray survey data were used to provide information on potassium thorium and uranium concentrations in surface soil and rock in arid central australia spatial patterns in these radioelements allow tracing of paths of sediment at catchment scale survey elevation data are combined with contour data to produce digital elevation models for terrain analysis tracing of sediment flow paths and modelling of extreme floods gamma ray data show consistent variation with slope a limited range of drainage areas and erosion deposition models derived from the conservation of mass equation supply limited sediment transport models give a reasonable reproduction of observed radioelement distribution but some elements of the distribution pattern reflect the area inundated by 500 1000 year floods rather than the effects of simple downslope movement partial area sediment supply models are derived by downstream accumulation of erosion and deposition rates calculated using the conservation of mass equation with transport laws based on slope alone and stream power comparison with observed radioelement patterns suggests that both transport laws apply in different parts of the landscape regional scale sediment transport models will require a range of models depending on location in the landscape and event frequency this approach may allow estimation of sediment delivery ratios copyright 2001 john wiley sons ltd

mesoscale coastal processes during gale iop 2 abstract during intensive observation period 2 of the genesis of atlantic lows experiment a number of mesoscale phenomena were observed with special and conventional observing systems over the land and coastal waters this study involved analysis of these data for the period 24 26 january 1986 in order to define the structure and dynamics of three features the coastal front a shallow cyclone that propagated along the coastal front modifying it as it moved northward and a low level jet that formed in the strong coastal pressure gradient field the coastal front formed in an existing pressure trough over the gulf stream as a result of both ageostrophic deformation and differential diabatic heating there existed considerable variability in the frontal strength and position on both the mesoalpha and mesobeta scales the level of strongest frontogenesis was near the surface with frontolysis calculated above 950 mb the marine atmospheric boundary layer mabl over the gulf stream was conducive to cyclon

mesoscale modeling of a cold front and its interaction with a diurnally heated land mass abstract a mesoscale numerical model incorporating a detailed planetary boundary layer scheme including momentum heat and moisture exchange with the lower boundary is used to study the change in structure of a dry summertime front as it moves towards a coastline two dimensional experiments show that the diurnal pressure fall over land causes a trough to form in the coastal region ahead of the approaching front frontogenesis at this mesoscale trough leads to the formation of a new front near the coast giving the appearance of strong acceleration of the original frontal system in the offshore region this process can occur over a wide range of times from early afternoon to late evening but no such acceleration occurs for fronts crossing the coast in the early morning hours these results indicate a tendency for more fronts to cross the coastline in the afternoon early evening period than at other times a statistic which is observed in southeast australia and oregon usa they also imply fronts sho

structure of the cold front observed in sesame ave iii and its comparison with the hoskins bretherton frontogenesis model abstract a cold front which passed through the dense network of the sesame ave severe environmental storms and mesoscale experiment atmospheric variability experiment on 25 26 april 1979 was investigated rawinsonde data collected from 23 special stations and 19 national weather service stations at three hour intervals for a 24 hour period were used along with hourly surface data radar summary charts and goes east satellite images severe storms formed along the surface front during this period the analysis focused on the vertical circulation across the frontal surface at low levels the major features of the cold frontal system that emerged from an analysis of this unique data set include a familiar direct vertical circulation with moist warm air ascending just above the surface front however the upgliding motion was intercepted by a secondary circulation at middle levels the analysis result was compared with model predictions of hoskins and bretherton 1972 as calculated by blumen 1980 sever

floodplain sediment disconnectivity at a tributary junction and valley constriction site in the fitzroy river basin queensland australia abstract many catchment scale sediment models assume connectivity from the top to the bottom of the catchment the purpose of this study is to provide evidence that particular topographic features can affect catchment connectivity and the transfer of sediment through the catchment this study investigates floodplain sediment deposition in a valley bottom constriction and tributary junction site within the fitzroy river basin a large semiarid subtropical catchment in ne australia these sites can cause backwater effects during flooding that enhance sediment deposition isotope analysis of floodplain sediment cores for cesium 137 and plutonium 239 240 is used to determine deposition rates since the 1960s results show overall higher deposition rates across the lower tributary floodplain proximal to the confluence and within the valley constriction reach deposition rates in the upper constriction reach were less than in the constriction reach but similar to rates reported by other studies in the fitzroy river basin however evidence suggests that the region of influence of the valley constriction on sediment deposition is dependent on flood size with large floods depositing sediment further upstream than the sampling sites of this study nevertheless the study shows evidence that backwater inducing features such as confluences of disparate channels can promote sediment deposition and cause a disconnection in the transfer of sediment from tributary to main channel the effect of these processes on storing sediment needs to be considered in catchment scale sediment budget models

frontogenesis over a mountain ridge abstract the interaction of developing two dimensional cold and warm frontal systems with a mesoscale mountain ridge is examined the flow of the rotating model atmosphere is assumed to be inviscid adiabatic and boussinesq the geostrophic momentum approximation is made an imposed horizontal deformation field forces the frontogenesis the nonlinear model equations are solved numerically in physical space using terrain following coordinates which incorporate the fully nonlinear lower boundary condition comparison of the model results with and without topography enables assessment of the impact of the mountain on the frontogenesis a scale analysis indicates that the most general problem of frontal interaction with an infinite mountain ridge encompasses a seven dimensional parameter space the scale analysis provides justification for die two dimensional geostrophic momentum approximation and defines an inverse richardson number as a measure of the importance of the ageostrophic advection sensitivity

application of airborne gamma ray imagery to assist soil survey a case study from thailand abstract airborne gamma ray imagery agri provides coarse resolution approximately 400 400 m pixel spatial information on gamma ray emitting elements i e potassium k thorium th and uranium u in the upper half meter of the soil these radioelements are a potential information source for soil mapping since their abundance is related to soil geochemistry specifically the chemical composition of parent materials and their weathering products resulting from geomorphic and pedogenic processes the aim of this study was to evaluate the potential of agri for improving digital soil survey process in two phases 1 a preliminary phase where hypotheses of soil landscape relationships are developed and 2 a phase where soil map unit boundaries are placed or revised the study also evaluated the match between agri and existing lithologic geopedologic and soil series maps the study was conducted in a well characterized complex soil landscape the 560 km2 upper pa sak watershed in petchaboon province thailand the relationship between gamma ray data and geological units was examined with box and whisker plots and confirmed by rock and soil samples rock and soil sample classifications were compared with the gamma ray image and to typical radioelement responses found in the literature to interpret agri data in terms of regolith and soil genesis we compared agri to two existing soil maps geopedologic and soil series maps first the geopedologic map was split into four maps according to the geopedologic hierarchy landscape lithology relief and landform at the latter lowest level soil units are also associated secondly soil series and geopedologic soil units were used to examine the distribution of radioelement response to selected soil characteristics parent material texture mineralogy and thickness the interpretations from best correlation in both soil maps were described in terms of the radioelement changes during pedogenic and geomorphic processes based on a review of literature and supported by soil samples in the hypotheses generating stage agri provided useful information in three forms single signal ratio and ternary images enhanced with a hill shaded dem by relating these to lithology material transport and internal pedogenetic processes agri correlated well with the classes of the geopedologic map 1 50 000 at the two higher levels landscape and lithology but to a lesser degree at the two lower levels relief and landform in geopedologic approach in the mapping stage agri showed deficiencies in the soil series map 1 50 000 made by conventional aerial photo analysis and limited field surveys especially in inaccessible areas but also in low relief terraces and flood plains which provided a basis for future field sampling to correct these deficiencies agri suggested new boundaries differentiating topsoil properties and the presence of plinthite despite its coarse resolution clustering of gamma ray and elevation data dem was carried out using fuzzy logic to generate various classification layers final map was produced using total weighted inverse distance of all the classes in a 3 by 3 window class label was assigned to the one with the largest total inverse distance over the entire set of fuzzy classification bands the result shows relatively higher classification accuracy for soil parent material differentiation overall accuracy of 72 as compared to the classification for soil types 67

a case study of extended east coast frontogenesis abstract a case study of extended coastal frontogenesis was done to examine the contributions of geostrophic versus observed wind deformation to frontogenesis and to determine the significance of a preexisting baroclinic zone along the atlantic coast as a condition for frontogenesis both geostrophic and observed with deformation play a role in the coastal frontogenesis the frontogenetical process involves a weak cyclone which strengthens the preexisting temperature gradient as it moves northward a moist baroclinic zone remains in place along the coast in the absence of strong cold advection in the wake of the weak cyclone the residual moisture enhanced baroclinicity and surface vorticity are important factors contributing to a second disturbance which intensifies as it moves northeastward to the coast along the frontal zone

facies sequences on a carbonate ramp the carboniferous limestone of south wales during early carboniferous times a major sea level rise led to the development of an extensive carbonate ramp over what is now south wales differential subsidence and sea level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho tectonic settings inner mid and outer ramp the inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence the sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments the peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing up cycles the sequence contains many subaerial breaks and tectonic uplift resulted in base level changes and fluvial incision the mid ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base sedimentation periodically exceeded sea level rise and subsidence and regressive progradational oolitic sand bodies developed the thickest of which are stacked units with up to four individual sand bodies storm processes were of major importance in this setting the outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major waulsortian reef mounds also developed none of the shallowing phases seen in the other ramp zones can be detected in this sequence subsidence and eustatic sea level rise seem to have been the major controls on deposition but the recognition of eustatic sea level falls is difficult the detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record

holocene paleofloods of the ross river central australia abstract the rivers of central australia rise in the macdonnell ranges and flow out across broad low relief plains into the surrounding desert the stratigraphy of the ross river plain records the areal extent and frequency of holocene floods this floodout plain is underlain by deeply weathered alluvial deposits characterized by red earth soils dated by thermoluminesence at 59 000 yr this old alluvium is covered by a sheet like deposit of very silty sand of probable eolian origin dated by thermoluminesence at 9200 900 yr the oldest holocene alluvium occurs as broad low relief bars and levee deposits flanking the modem channel and as low relief long wavelength bedforms that fan out across the plain this deposit resulted from a flood flow up to 10 km wide that covered the entire plain evidence for several large floods between 1500 and 700 yr b p is also preserved in a 500 to 1500 m wide paleochannel thus the surface features on the floodout plains are the product of a few rare large flood events this paleohydrologic record is additional evidence of the dynamic nature of the hydrometerological regime of central australia

sediment source tracing using environmental magnetism a new approach with examples from australia environmental magnetism can be used for sediment source tracing in situations such as stream junctions where two catchments deliver magnetically distinguishable well combined average source mixes to a trunk stream consistent mineral magnetic parameter relationships show that spatially and temporally constant magnetic mineral assemblages occur along reaches of natural streams for most of the confluence mixing situations examined it is possible to distinguish between tributaries using magnetic parameter relationships using these relationships relative tributary contributions to the resultant downstream mix can be quantified the method can be used for tracing suspended and bedload sediments so that the principal source catchments can be determined by a sequence of measurements at stream junctions along a drainage network there is considerable potential for using this new and easily applied method for studies of sediment delivery processes and sediment movement in fluvial environments

identifying large scale erosion and deposition processes from airborne gamma radiometrics and digital elevation models in a weathered landscape patterns of erosion and deposition are difficult to identify and measure at catchment and regional scale but it may be possible to infer their distribution from remote sensing using easily measured surrogate variables airborne geophysical surveys provide data on gamma ray emissions from surface and near surface material and allow estimation of k th and u content gamma ray signatures are largely determined by lithology but also change with weathering and with erosion and deposition and may be used as a partial surrogate for those processes comparison of gamma ray signatures with topographic characteristics closely related to sediment transport capacity downstream sorting of sediments and the extent of erosion and deposition shows strong linkages studies in four small catchments in southeastern australia indicate that k consistently increases as slopes become steeper while th and u may either increase or decrease this suggests the presence of fresh rock rather than weathered material and implies removal of material by erosion although some patterns may result from systematic changes in lithology across catchments analysis by lithology confirms the increase in k with slope in granites metamorphosed sediments and basalt and also shows a tendency for u to decrease with slope in the granites and basalt gamma ray emissions vary only slightly with catchment area a surrogate measure of water discharge suggesting that water erosion is limited or that discharge is not closely related to area gamma radiometric profiles down hillslopes averaged across the full range of gradients show that in most cases radioelements initially decrease probably reflecting increased weathering but then increase close to valley floors because of accumulation of fine sediments analysis by lithology confirms the increase in radioelements close to valley floors in granites and metamorphosed sediments but the trend is less clear in basalt gamma ray profiles down floodplains are variable and indicate the amount of deposition and accumulation of weathered material in valley openings and exposure of bedrock in valley constrictions simple erosion and deposition models based on the conservation of mass equation and applied to the four catchments show that all radioelements increase as the potential for deposition increases they reach a low point in zones of no net erosion or deposition and subsequently increase as erosion becomes more intense and weathered material is lost from slopes analysis by lithology largely confirms this pattern the usefulness of airborne geophysical survey data is limited by flight line spacing with most data being flown at a 200 400 m spacing in australia however general trends in erosion and deposition can still be distinguished and there is capacity for calibrating long term erosion and deposition models once better approaches to interpretation of gamma ray data have been developed copyright 2000 john wiley sons ltd

use of magnetic and radiometric measurements to investigate erosion and sedimentation in a british upland catchment in response to the potential shortcomings of single technique strategies in the investigation of erosion and sedimentation a combined magnetic and radiometric 13cs and 210pb approach has been undertaken in the upland watershed lake system of howden reservoir derbyshire by combining these techniques some assessment of sediment sources and the erosion status of the catchment has been achieved alone each approach would have been unable to determine unequivocally sediment provenance furthermore the parallel use of these measurements has highlighted limitations and or uncertainties in both the magnetic and 137cs techniques these problems reflect the particular soil characteristics and drainage conditions of this upland catchment despite the documented severity of peat erosion in the region howden reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation sediment yields total 127 7 t km 2 yr 1 including organic fraction 31 3 t km 2 yr 1 are however higher than in other british upland areas