the role of feedback mechanisms in historic channel changes of the lower rio grande in the big bend region abstract over the last century large scale water development of the upper rio grande in the u s and mexico and of the rio conchos in mexico has resulted in progressive channel narrowing of the lower rio grande in the big bend region we used methods operating at multiple spatial and temporal scales to analyze the rate magnitude and processes responsible for channel narrowing these methods included hydrologic analysis of historic stream gage data analysis of notes of measured discharges historic oblique and aerial photograph analysis and stratigraphic and dendrogeomorphic analysis of inset floodplain deposits our analyses indicate that frequent large floods between 1900 and the mid 1940s acted as a negative feedback mechanism and maintained a wide sandy multi threaded river declines in mean and peak flow in the mid 1940s resulted in progressive channel narrowing channel narrowing has been temporarily interrupted by occasional large floods that widened the channel however channel narrowing has always resumed after large floods in 1990 and 1991 the active channel width of the lower rio grande has narrowed by 36 52 narrowing has occurred by the vertical accretion of fine grained deposits on top of sand and gravel bars inset within natural levees channel narrowing by vertical accretion occurred simultaneously with a rapid invasion of non native riparian vegetation tamarix spp arundo donax which created a positive feedback and exacerbated the processes of channel narrowing and vertical accretion in two floodplain trenches we measured 2 75 and 3 5 m of vertical accretion between 1993 and 2008 in some localities nearly 90 of bare active channel bars were converted to vegetated floodplain during the same period upward shifts of stage discharge relations occurred resulting in over bank flooding at lower discharges and continued vertical accretion despite a progressive reduction in stream flow thus although the magnitude of the average annual flood was reduced between 40 and 50 over bank flooding continued these changes reflect a shift in the geomorphic nature of the rio grande from a wide laterally unstable multi thread river to a laterally stable single thread channel with cohesive vertical banks and few active in channel bars

a study of a self generated stratospheric sudden warming and its mesospheric lower thermospheric impacts using the coupled time gcm ccm3 1 a stratospheric sudden warming episode was self consistently generated in the coupled national center for atmospheric research thermosphere ionosphere mesosphere and electrodynamics general circulation model climate community model version 3 time gcm ccm3 taking advantage of the unique vertical range of the coupled model ground to 500 km we were able to study the coupling of the lower and upper atmosphere in this warming episode planetary wave 1 is the dominant wave component in this warming event analysis of the wave phase structure and the wave amplitude indicates that the wave may experience resonant amplification prior to the peak warming the mean wind in the high latitude winter stratopause and mesosphere decelerates and reverses to westward due to planetary wave forcing and forms a critical layer near the zero wind lines the wind deceleration and reversal also change the filtering of gravity waves by allowing more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt which causes eastward forcing and reverses the westward jet in the mlt this also changes the meridional circulation in the upper mesosphere from poleward downward to equatorward upward causing a depletion of the peak atomic oxygen layer at 97 km and significant reduction of green line airglow emission at high latitudes and midlatitudes planetary waves forced in situ by filtered gravity waves in the mlt grow in the warming episode their growth and interaction with tides create diurnal and semidiurnal variabilities in the zonal mean zonal wind

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

global estimates of gravity wave parameters from gps radio occultation temperature data 1 gravity waves gws play critical roles in the global circulation and the temperature and constituent structures in the middle atmosphere they also play significant roles in the dynamics and transport and mixing processes in the upper troposphere and lower stratosphere and can affect tropospheric weather despite significant advances in our understanding of gws and their effects in different regions of the atmosphere in the past few decades observational constraints on gw parameters including momentum flux and propagation direction are still sorely lacking global positioning system gps radio occultation ro technique provides global all weather high vertical resolution temperature profiles in the stratosphere and troposphere the unprecedentedly large number of combined temperature soundings from the constellation observing system for meteorology ionosphere and climate and challenging minisatellite payload gps ro missions allows us to obtain gw perturbations by removing the gravest zonal modes using the wavelet method for each day we extended the gw analysis method of alexander et al 2008 to three dimensions to estimate the complete set of gw parameters including momentum flux and horizontal propagation direction from the gw temperature perturbations thus derived to demonstrate the effectiveness of the analysis we showed global estimates of gw temperature amplitudes vertical and horizontal wavelengths intrinsic frequency and vertical flux of horizontal momentum in the altitude range of 17 5 22 5 km during december 2006 to february 2007 consistent with many previous studies gw temperature amplitudes are a maximum in the tropics and are generally larger over land likely reflecting convection and topography as main gw sources gw vertical wavelengths are a minimum at equator likely due to wave refraction whereas gw horizontal wavelengths are generally longer in the tropics most of the waves captured in the analysis of the gps data are low intrinsic frequency inertia gws and the estimated intrinsic frequencies scaled by the coriolis parameter also show a strong maximum at equator enhanced wave fluxes are linked to convection topography and storm tracks among others as preliminary tests of the analysis in deriving horizontal propagation directions we compared the gps estimates with the corresponding estimates from the u s high vertical resolution radiosonde data using the conventional stokes parameters method and we also conducted a separate analysis of the gps data over the southern andes in south america we also showed the first global estimates of gw propagation directions from the gps data finally the sensitivity of the analysis to the temporal and spatial dimensions of the longitude latitude time cells and the uncertainties of the analysis and possible ways to reduce these uncertainties are discussed

the life cycle of the northern hemisphere sudden stratospheric warmings motivated by recent evidence of strong stratospheric tropospheric coupling during the northern hemisphere winter this study examines the evolution of the atmospheric flow and wave fluxes at levels throughout the stratosphere and troposphere during the composite life cycle of a sudden stratospheric warming the composite comprises 39 major and minor warming events using 44 years of ncep ncar reanalysis data the incipient stage of the life cycle is characterized by preconditioning of the stratospheric zonal flow and anomalous quasistationary wavenumber 1 forcing in both the stratosphere and troposphere as the life cycle intensifies planetary wave driving gives rise to weakening of the stratospheric polar vortex and downward propagation of the attendant easterly wind and positive temperature anomalies when these anomalies reach the tropopause the life cycle is marked by momentum flux and mean meridional circulation anomalies at tropospheric levels that are consistent with the negative phase of the northern hemisphere annular mode the anomalous momentum fluxes are largest over the atlantic half of the hemisphere and are associated primarily with waves of wavenumber 3 and higher

chemical and dynamical discontinuity at the extratropical tropopause based on start08 and waccm analyses 1 using isentropic trace gas gradients of o3 and co the discontinuity in the chemical composition of the upper troposphere ut and lower stratosphere ls is examined on middle world isentropes from 300 to 380 k the analysis is a follow up study of the dynamical discontinuity as represented by the potential vorticity pv gradient based tropopause which is based on the product of isentropic pv gradients and wind speed overall there is fairly good consistency between the chemical discontinuity in trace gas distributions and the pv gradient based tropopause trace gas gradients at the pv gradient based tropopause are stronger in winter than in summer revealing the seasonal cycle of the tropopause transport barrier the analysis of the trace gas gradients also identifies atmospheric transport pathways in the upper troposphere lower stratosphere utls several regions where trace gas gradients are found to be decoupled from the dynamical field indicate preferred transport pathways between the ut and ls in particular anomalous co and o3 gradients above eastern africa eastern asia and the west pacific are likely related to convective transport and anomalous o3 gradients over the north atlantic and north pacific are related to isentropic transport connected to frequent wave breaking the results indicate that the pv gradient based tropopause definition provides a good identification of the dynamical and chemical discontinuity and is therefore effective in locating the physical boundary in the utls

changes in hydrologic regime by dams dams have major impacts on river hydrology primarily through changes in the timing magnitude and frequency of low and high flows ultimately producing a hydrologic regime differing significantly from the pre impoundment natural flow regime this paper presents the analysis of pre and post dam hydrologic changes from dams that cover the spectrum of hydrologic and climatic regimes across the united states our overall goals are to document the type magnitude and direction of hydrologic shifts because of impoundment using the entire database for the national inventory of dams nid for dams possessing longstanding u s geological survey usgs gages downstream we identified 21 gage stations that met length of record criteria encompassing an array of types of dams and spanning four orders of magnitude in contributing watershed area to assess hydrologic changes associated with dams we applied a hydrologic model the indicators of hydrologic alteration iha supplemented with orientation statistics for certain hydrograph parameters dams had significant impacts on the entire range of hydrologic characteristics measured by iha for many characteristics the direction and significance of effects were highly consistent across the 21 sites the most significant changes across these sites occurred in minimum and maximum flows over different durations for low flows the 1 day through 90 day minimum flows increased significantly following impoundment the 1 day through 7 day maximum flows decreased significantly across the sites at monthly scales mean flows in april and may tend to decline while mean flows in august and september increase other significant adjustments included changes in annual hydrograph conditions primarily in the number of hydrograph reversals that has generally increased for almost all sites following impoundment the number of high pulses has increased following impoundment but the average length declines the mean rate of hydrograph rise and fall has declined significantly these results indicate that the major pulse of dam construction during the previous century has modified hydrologic regimes on a nationwide scale for large and small rivers

downstream hydrologic and geomorphic effects of large dams on american rivers abstract the hydrology and geomorphology of large rivers in america reflect the pervasive influence of an extensive water control infrastructure including more than 75 000 dams one hundred thirty seven of the very large dams each storing 1 2 km 3 10 6 acre feet of water or more alter the flows of every large river in the country the hydrologic effects of these very large dams emerge from an analysis of the stream gage records of 72 river reaches organized into 36 pairs one member of each pair is an unregulated reach above a dam whereas the other is a regulated reach downstream from the same structure comparison of the regulated and unregulated reaches shows that very large dams on average reduce annual peak discharges 67 in some individual cases up to 90 decrease the ratio of annual maximum mean flow 60 decrease the range of daily discharges 64 increase the number of reversals in discharge by 34 and reduce the daily rates of ramping as much as 60 dams alter the timing of high and low flows and change the timing of the yearly maximum and minimum flows in some cases by as much as half a year regional variation in rivers dams and responses are substantial rivers in the great plains and ozark ouachita regions have annual maximum mean flow ratios that are 7 times greater than ratios for rivers in the pacific northwest at the same time the ratio of storage capacity mean annual water yield for dams is greatest for interior western ozark ouachita and great plains rivers and least for pacific northwest streams thus in many cases those rivers with the highest annual variability have the greatest potential impact from dams because structures can exert substantial control over downstream hydrology the hydrologic changes by dams have fostered dramatic geomorphic differences between regulated and unregulated reaches when compared to similar unregulated reaches regulated reaches have 32 larger low flow channels 50 smaller high flow channels 79 less active flood plain area and 3 6 times more inactive flood plain area dams also affect the area of active areas the functional surfaces that are functionally connected to the present regime of the river regulated reaches have active areas that are 72 smaller than the active areas of similar unregulated reaches the geomorphic complexity number of separate functional surfaces per unit of channel length is 37 less in regulated reaches reductions in the size of hydrologically active functional surfaces are greatest in rivers in the great plains and least in eastern streams the largest differences in geomorphic complexity are in interior western rivers the shrunken simplified geomorphology of regulated large rivers has had direct effects on riparian ecology producing spatially smaller less diverse riparian ecosystems compared to the larger more complex ecosystems along unregulated reaches of rivers

initial ionospheric observations made by the new resolute incoherent scatter radar and comparison to solar wind imf 1 the first resolute incoherent scatter radar observations of the polar ionospheric f region show the fine control of the ionospheric plasma density and flow electric field by the solar wind interplanetary magnetic field imf a summary of 8 days of observations is presented and 10 imf bz southward turning events during this period are analyzed in terms of the time delay of plasma density enhancements and ionospheric convection intensification with respect to the timing of bz southward turning we find that ne enhancements are strongly tied to strong 5 nt imf bz southward turnings arrive 25 75 mins depending on mlt after the imf pulse arrives at the bowshock nose last as long as bz stays southward contain as small as 25 km horizontal substructures are altitudinally smooth a characteristic of a solar produced plasma the most predictable response of ionospheric convection is anti sunward flow intensification on average 25 mins after bz southward change

lateral erosion of the sacramento river california 1942 1999 and responses of channel and floodplain lake to human influences this study focused on a spatial and temporal analysis of the active channel and associated floodplain lakes using aerial photographs spanning five decades 1942 1962 1985 1999 over a 140 km long reach of the sacramento planimetric changes were analysed longitudinally and temporally to highlight the spatial structures and their evolution through time the results underline complex changes and space time pattern in bank erosion channel length and active channel width the bank erosion and also channel lengthening were higher between 1962 and 1985 than in the two periods studied before and after active channel width significantly decreased from 1942 to 1999 partly progressively from upstream to downstream with local widening whatever the studied periods similarly the floodplain lakes observed before 1942 1962 were significantly different in size and geometry from those which appeared during the most recent period the creation of lakes is less frequent after the 1940s with a secondary peak of occurrence during the 1962 1985 period the interpretation of these changes is complex because of various human pressures acting over different time scales bank protection flow diversion sediment starvation land use changes and various natural influences flood sequences through out the period geological setting the findings are discussed by comparison with previous work and highlight the important effect of dam impact on peak flow and sediment starvation modifying longitudinally hydraulic conditions within the channel but also the increase in riprap protection which induced change in bank erosion channel planimetry and floodplain lake characters geometry frequency of renewal variation in flood intensities is also observed as having positive effects on the bank erosion pattern secondarily land use changes also controlled bank erosion intensity copyright c 2010 john wiley sons ltd

equilibrium or indeterminate where sediment budgets fail sediment mass balance and adjustment of channel form green river downstream from flaming gorge dam utah and colorado this study examines bed and bank adjustment in the 105 km reach of the green river immediately downstream from flaming gorge dam by the use of historical aerial and oblique photographs analysis of current and abandoned stream gaging records and field observations although this segment has been previously characterized as sediment deficient these data show that sediment is accumulating in all reaches and that the bed has not degraded at any location where historical data are available adjustment is occurring through a combination of deposition of post dam sediment and stabilization of pre dam deposits resulting in a 10 30 reduction in average width of the channel all post dam surfaces are colonized by woody riparian vegetation the style of channel adjustment varies between geomorphically defined reaches in canyons dominated by debris fans and gravel bedded restricted meandering reaches gravel bars have become inactive and accumulated fine sediment in the sand bedded meandering reaches existing islands have increased in size and new mid channel islands have formed in all of these types of reaches post dam deposits line the banks and sediment has accumulated in side channels that previously separated islands from the bank these findings demonstrate that sediment budgets that show a balance between inputs and outputs cannot necessarily be interpreted to indicate channel equilibrium a sediment mass balance for 150 km reach between the dam and the first long term gage indicates approximate balance of inputs and outputs for the pre and post dam periods when uncertainty in budget components is considered the mass balance is indeterminate although the green river may have been in approximate equilibrium in the pre dam period we have shown that channel width is decreasing in the post dam period the post dam deposits constitute a small but a significant component of the sediment budget upstream from the first major tributary sediment is supplied to this reach by small tributaries and to a lesser extent erosion of pre dam alluvium downstream from the study area the volume of the post dam deposits is tiny relative to the volume of sediment input from the first major tributary d 2005 elsevier b v all rights reserved

principles of engineering geomorphology for managing channel erosion and bedload transport examples from french rivers abstract french rivers have been transformed by centuries of development to satisfy various social demands such as navigation hydro electric power production flood control or checking erosion these modifications have led to impacts that are detrimental to ecology to resources and to human interests in recent years increased public and management awareness of these problems has given way to new conceptions and objectives in the field of river engineering among which the goal of establishing sustainable long term management strategies is of the highest importance because many of these problems are directly or indirectly related to changes in the geomorphological functioning of fluvial systems there is a need to integrate a geomorphological approach into river engineering practices the principles of engineering geomorphology are developed here and are illustrated by examples taken from rivers that drain the french alps and their piedmont

estimation of error in bankfull width comparisons from temporally sequenced raw and corrected aerial photographs this study investigates the propagation of error through image to image comparison of 285 river bankfull width measurements of the afon trannon mid wales bankfull width is quantified from both aerial photographs analysed as rectified images in erdas imagine orthomax and raw images in paintshop pro a method for the robust estimation of bankfull width measurement error through temporal sequences of scanned aerial photographs is presented and the improvement in accuracy achieved using rectified imagery is quantified results from this study are placed in the context of previously published rates of bankfull width change from a wide range of river scales and the bankfull change rates for robust medium term analysis using approximately 1 10 000 historical aerial photography are identified

spatial disaggregation and aggregation procedures for characterizing fluvial features at the network scale application to the rhone basin france network scale heterogeneity in fluvial forms and processes has been analyzed for decades through the field based characterization of a reduced number of sites spatially continuous data sets are increasingly available at a national scale e g digital elevation models or aerial orthophotographs and open up new possibilities to investigate spatial structures in stream networks the paper introduces a gis methodological framework to support and automate the large scale characterization of the fluvial system based on spatial disaggregation and aggregation procedures the spatial disaggregation consists in the longitudinal discretisation of geographical objects into relatively high resolution spatial units to characterize fluvial features continuously along stream networks because rivers are heterogeneous and hierarchically organized the spatial aggregation aims to delineate statistically pattern or process based spatial units to answer questions at appropriate scales the paper develops the gis implementation of the disaggregation and aggregation procedures for characterizing stream networks in a geomorphic perspective we illustrate the approach on the rhone network focusing on the characterization of three geographical objects commonly used in classification schemes the streamline the valley bottom and the active channel the latter on a limited area the spatial aggregation is automated using the threshold test of pettitt 1979 to detect change points in univariate data series and delineate homogeneous spatial units throughout the stream network we provide three simple application examples to illustrate the potentialities of the spatial aggregation to investigate spatial heterogeneity in stream networks finally insights limitations and future challenging issues emerging from the application of the methodological framework are discussed

channel incision gravel mining and bedload transport in the rhone river upstream of lyon france canal de miribel the miribel canal is a former arm of the rhone embanked between 1848 and 1857 over a length of 18 km to improve navigation at low discharges the impact of this was a hydraulic tilting of the long profile characterised by 4 m of degradation upstream and 4 6 m of aggradation of bedload downstream this phenomenon increased downstream flooding since 1937 a diversion dam has controlled upstream water input thus reducing the transit of the pebble bedload however excessive harvesting of sands and gravels occurred between 1970 and 1980 resulting in a general lowering of the river bed and the accompanying water table with ecological consequences in the alluvial plain and for water supply this development made it all the more necessary to obtain knowledge about the bedload discharges passing through the miribel canal and more broadly about the hydraulic conditions as functions of the varying discharge calculation of shear stresses and grain size measurements on the lateral bars after several floods in 1989 90 show that movement of bed material is initiated at a discharge of 440 m3 s 1 equalled or exceeded 40 days year 1 and becomes general at 550 m3 s 1 equalled or exceeded 30 days year 1 transport discharge is thus relatively frequent and involves distal fluvio glacial deposits composed of fine grained materials potential transport calculated by the meyer peter formula is around 60 000 t year 1 for the range of discharges between 440 and 850 m3 s 1 for these discharge values the canal experiences a loss of materials without replacement from upstream for higher rates of discharge the floodgates let through an unknown quantity of materials which partially make up the loss gravel harvesting ceased in 1991 but the diversion dam will have to be operated in a different way in order to increase the input of bedload into the canal

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

the origin of stationary planetary waves in the upper mesosphere abstract satellite observations indicate that quasi stationary planetary waves often exist to at least 100 km in the winter mesosphere waves are also seen in the summer upper mesosphere a three dimensional numerical model was used to simulate these waves and to diagnose the physical processes involved the waves simulated in the model closely resemble observed waves several model runs that isolate specific processes are used to determine the relative importance of two forcing mechanisms in the model planetary waves that propagate from below are significantly damped at the altitude where gravity wave drag becomes large about 75 km in the winter midlatitudes or below if a reversal in the mean wind is encountered momentum forcing associated with breaking gravity waves that have been filtered by planetary scale wind variations below acts to generate planetary waves in the middle and upper mesosphere the amplitude from in situ forcing by gravity wave breaking exceeds the amplitude from the upward prop

spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits ain river france floodplain development is associated with lateral accretion along stable channel geometry along shifting rivers the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence which exhibit specific overflow patterns in this contribution the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river ain river france the sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137cs and unsupported 210pb sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain sedimentation rates range between 0 65 and 2 4 cm a1 over a period of 10 to 40 years the data provide additional information on the role of distance from the bank overbank flow frequency and channel geometry in controlling the sedimentation rate channel infills lower than adjacent floodplains exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain additionally channel degradation aggradation and bank erosion which reduce or increase the distance between the main channel and the cutoff channel aquatic zone affect local overbank flow magnitude and frequency and therefore sedimentation rates thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills last the dendrogeomorphic and 137cs approaches are cross validated for estimating the sedimentation rate within a channel infill

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

longitudinal variations in mesospheric winds evidence for gravity wave filtering by planetary waves abstract mesospheric horizontal wind data from the high resolution doppler image hrdi satellite instrument are used to investigate the longitudinal variation of nontidal winds in the upper mesosphere and their relationship with winds in the stratosphere the period covered by the study is late winter february mid march for 1992 1994 the results indicate that there is a negative correlation between longitudinal variations of the zonal winds in the stratosphere and those in the mesosphere and between longitudinal variations of the meridional winds in the stratosphere and mesosphere the data are examined to determine which of several possible causes is responsible the possibilities are 1 that planetary scale disturbances are produced in situ by gravity wave drag in the mesosphere that is not zonally symmetric because of filtering by the planetary waves in the stratosphere 2 that asymmetries are caused by longitudinal variations in gravity wave drag due to azonal source distributions that are coinc

effects of channel confinement on pioneer woody plant community structure composition and diversity along the river drome se france river embankments are one of the main causes of a loss in active channel movement the knock on effects of river channel stabilization include important shifts in the ecohydrological conditions in the protected zone behind embankments which has already been well exemplified however few authors have attempted to investigate changes to pioneer units of vegetation colonizing the active channel following the construction of dikes as a consequence we studied the structure composition and diversity of pioneer vegetation units dominated by willow and poplar along the river drome in two adjacent but contrasting river reaches an embanked reach and an unconstrained reach each subject to the same flow regime but offering very different hydrogeomorphological contexts for vegetation colonization our results clearly demonstrate that river embankments affect channel geometry a reduction in channel width from between 200 and 500 m to less than 100 m leads to steeper elevational gradients with an overall coarser grain size and consequently drier overall conditions on colonizable landforms in the channelized reach pioneer vegetation responded by colonizing landforms at higher elevations above the low water mark and by occurring in smaller units within the channelized study reach there was also a reduction in species diversity a homogenization in vegetation unit structure and a predominance of more drought tolerant ligneous species p nigra in pioneer vegetation units in the channelized study reach

temporal and spatial scales of geomorphic adjustments to reduced competency following flow regulation in bedload dominated systems abstract because of the combined effects of reduced sediment transport capacity and competency following flow regulation morphological changes are expected to occur in channels downstream from dams and specifically at tributary junctions where local inputs of water and sediment occur using a combination of historical aerial photographs mainstem and tributary channel pebble counts and hec ras flow modeling for two watersheds in south central vt one unregulated and the other regulated since 1961 we document the time series of post regulation channel narrowing and associated bar growth due to the influx of tributary sediment channel adjustments at regulated tributary junctions have been significant in ca 50 years following impoundment with channels downstream of the confluences narrowing over 15 after an initial ca 20 year lag before the onset of accelerated narrowing moreover flow modeling suggests that downstream of regulated confluences the modern median grain size d50 along the channel bed is immobile no significant channel narrowing has occurred either above or below unregulated tributary junctions or on the mainstem upstream of regulated confluences however greater channel sediment fining is observed upstream of regulated confluences than above unregulated confluences thus the primary mode of mainstem channel adjustment differs up and downstream of regulated tributaries these confluence effects have occurred where the tributary drainage area is only 0 2 times that of the mainstem well below the threshold ratio of 0 6 required for significant geomorphic effects at unregulated confluences highlighting the geomorphic scale shift of dams lastly we evaluate the downstream length required for a river to recover from the impacts of impoundment and demonstrate that even distal locations are impacted by flow regulation unlike the impacts of flow regulation in the western us where channel incision and bar erosion predominate following impoundment we find that in situations where bed incision is minimal and where sediment loads are low but bed caliber high bar growth and channel narrowing are significant adjustments at tributary junctions following impoundment therefore at our sites the effects of dams on reduced competency may be more profound than on reduced sediment transport capacity highlighting the importance of geologic and geomorphic settings in understanding fluvial responses to impoundment

sedimentation in the riparian zone of an incising river this paper focuses on one aspect of riparian zone change associated with channel incision it presents information on sedimentation within the riparian zone of the river garonne france derived from both historical and contemporary sources the riparian zone investigated is morphologically complex containing a remnant island and cut off channel information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross profile change as well as an assessment of changes in riparian zone sedimentation rates and patterns very significant changes are identified over the last 50 years a change from a multiple thread to single thread channel planform high rates of riparian zone sedimentation of the order of 0 5 to 2 5 cm a 1 clear spatial patterns in over bank sedimentation reflecting topographic and vegetational variations and flood event magnitude and a reduction in morphological and vegetational diversity through the period which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink copyright 2001 john wiley sons ltd

the seasonal evolution of planetary waves in the southern hemisphere stratosphere and troposphere seasonality in planetary wave structure in the southern hemisphere stratosphere and troposphere 1000 1 mb is studied based on eight years 1979 1986 of daily geopotential data emphasis is placed on the distinctive seasonality in the stratosphere along with tracing the stratospheric fluctuations into the troposphere time filtering is used to separate stationary and transient components maximum geopotential height variance is observed in the middle to upper stratosphere in late winter spring with a distinct secondary smaller maximum in late fall early winter these maxima sandwich the strongest mid winter zonal winds this sequence occurs approximately one month earlier in the upper stratosphere two corresponding peaks are observed in stratospheric zonal mean wind and temperature fluctuations the two maxima in stratospheric wave variance are not in agreement with observed seasonal changes in quasi geostrophic refractive index of the zonal mean flow the stratospheric geopotential variance maxima result from nearly equal amounts of stationary and transient zonal wave 1 fluctuations with transient wave 2 also contributing during late winter stationary wave 1 shows intriguing seasonal evolution the early winter maximum is predominantly equivalent barotropic whereas that of late winter spring is highly baroclinic in the stratosphere stratospheric poleward fluxes of heat and momentum both exhibit pronounced maxima during september october these result primarily from the stationary wave 1 contributions and the transients assume a secondary role although not as pronounced as the stationary wave seasonality seasonal differences in transient wave behaviour are also documented including three dimensional propagation characteristics and wave mean flow interaction diagnostics

global estimates of gravity wave momentum flux from high resolution dynamics limb sounder observations analyzed to derive global properties of gravity waves we describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs the wave vertical wavelength as a function of height and the horizontal wave number along the line joining each profile pair the analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis we examine global distributions of these gravity wave properties in the monthly mean and on an individual day and we also show sample instantaneous wave events observed by hirdls the results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow the high vertical and horizontal resolution afforded by the hirdls measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail mountain wave observations show clear propagation to altitudes in the mesosphere

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

microwave limb sounder observations of gravity waves in the stratosphere a climatology and interpretation high horizontal resolution temperature data from the microwave limb sounder mls are analyzed to obtain information about high intrinsic frequency gravity waves in the stratosphere global climatologies of temperature variance at solstice are computed using six years of data a linear gravity wave model is used to interpret the satellite measurements and to infer information about tropospheric wave sources globally uniform sources having several different spectral shapes are examined and the computed variances are filtered in three dimensional space in a manner that simulates the mls weighting functions the model is able to reproduce the observed zonal mean structure thus indicating that the observations reflect changes in background wind speeds and provide little information about the latitudinal variation of wave sources longitudinal variations in the summer hemisphere do reflect source variations since the modeled variances exhibit much less variation in this direction as a consequence of the zonal symmetry of the background winds a close correspondence between the mls variances and satellite observations of outgoing longwave radiation suggests that deep convection is the probable source for these waves the large variances observed over the tip of south america in winter are most certainly linked to orographic forcing but inferences about wave sources in northern hemisphere winter are difficult to make as a result of the high degree of longitudinal and temporal variability in the stratospheric winds comparisons of model results using different source spectra suggest that the tropospheric sources in the subtropics in summer have a broader phase speed spectrum than do sources at middle latitudes in winter

nature rehabilitation by floodplain excavation the hydraulic effect of 16 years of sedimentation and vegetation succession along the waal river nl abstract the ewijkse plaat is a floodplain along the waal river nl in 1988 the floodplain was excavated as part of a program for enlargement of the discharge capacity and was assigned as a nature rehabilitation area this paper describes the combined geomorphological and vegetation evolution of the floodplain until 16 years after the initial excavation using elevation data and data on vegetation structure derived from detailed aerial stereographic imagery the impact of these processes on flow velocity and water surface elevation was evaluated by using a hydraulic model within 16 years the excavated amount of sediment was redeposited in the area the dominant geomorphological process after excavation was vertical accretion of the floodplain which resulted in the formation of natural levees the amount of sedimentation was correlated to the across floodplain flow r 2 0 89 in the research period 41 of the sedimentation took place during two single major flood events the creation of pioneer stages by excavation promoted softwood forest establishment which influenced the sedimentation pattern significantly the landscape evolved toward structure rich vegetation nine years after excavation the initial hydraulic gain was lost by the combined effect of sedimentation and vegetation succession implications for river and nature management are discussed

historical geomorphic analysis 1932 2011 of a by passed river reach in process based restoration perspectives the old rhine downstream of the kembs diversion dam france germany the old rhine downstream of the kembs diversion dam is one of the largest by passed river reaches in the world 50 km it offers a unique opportunity to study the morphological effects of by passing and address physical and ecological restoration approaches in regulated rivers we conduct a space time analysis of channel adjustment over a period of 80 years 1932 to 2011 we examine planform changes from aerial photographs erosional and depositional patterns from vertical profiles sediment sizes within the active channel and the new established floodplain and we date riparian vegetation encroachment results show that the old rhine exhibited rapid response to the completion of the by passing scheme in the 1950s with a 26 narrowing in median active channel width between 1956 and 2008 from vegetation encroachment on dewatered channel margins mostly groyne fields the narrowing was accompanied by overbank fine sediment deposition 1 5 cm y 1 aggradation since 1950 as well as slight bed degradation 0 7 cm y 1 since 1950 we found no downstream propagation of active channel narrowing over time nor propagation of bed degradation the channel was already significantly adjusted prior to the diversion scheme following the nineteenth century river straightening and groyne construction by passing dewatering mainly provided new pioneer habitat for synchronous vegetation establishment and promoted channel stability by decreasing sediment transport owing to peak flow reduction the morphological budget calculated over the past 20 years estimated a downstream output for coarse sediments at 16 000 m3 y 1 with 80 originating from bed degradation and 20 from bank erosion without significant inputs from upstream the present day morphodynamics remain sensitive to changes because of dynamic bed armouring 2 1 this retrospective analysis permits us to discuss management strategies for altered rivers recommended activities are gravel reintroduction with particle sizes finer than the armoured river bed to enhance sediment transport and promote form dynamism under current flood magnitudes this should be coupled with river widening to allow for complex depositional patterns that benefit ecological habitats these actions should not be implemented without prior analysis of local sediment transfer processes based on in situ experiments and modelling

sediment flux to basins causes controls and consequences there is an increasing trend in the earth sciences towards the integration of many subdisciplines the sedimendatry basin is a fundamental focal point of many studies which as a consequence often neglects the complimentary drainage basin or catchment sedimentary basins provide a record of earth history reflecting the geographical lithological oceanographic and ecological development through the rock record drainage basins in comparison record ephemeral landscape evolution where topography is eroded and provides the flux of sediment to the basin the basin fill reflects the sediment flux from the hinterland and provides evidence of the dynamic geomorphic processes in context the drainage system and sedimentary basin can be regarded as a production line with sedimentary record giving valuable insight into long term landscape evolution and geomorphological processes illuminating the evolution of sedimentary basins this volume assesses the current position of understanding sediment supply to basins with the integration of the many sub disciplines in the earth sciences it documents a mix of hinterland and sedimentary basin studies with a gradation from orogenic belts to the deep marine the authors represent a wide spectrum of earth scientist with leaders in the science providing review papers and new directive papers in their field of specialization

case studies of the mesospheric response to recent minor major and extended stratospheric warmings 1 we have studied the mesospheric response to two recent stratospheric warmings by performing short term forecasts at medium 1 5 and high 0 5 spatial resolution under different gravity wave drag gwd scenarios we validated our models with our high altitude analysis that extends from 0 to 90 km for the minor warming of january 2008 reduced upper level orographic gwd weakened the downward residual circulation and cooled the mesosphere parameterized nonorographic gwd increased the simulated mesospheric cooling for the prolonged major warming of 2006 heavily attenuated orographic gwd led to pronounced cooling near 50 km during the extended phase of this event an unusually strong westerly polar vortex reformed in the lower mesosphere which allowed westward propagating nonorographic gravity waves to reach the mesosphere and break with net westward accelerations of over 50 m s 1 d 1 this in turn forced a strong residual circulation yielding descent velocities over 2 cm s 1 between 65 n and 85 n consistent with previous reports of enhanced downward transport of trace constituents the resulting adiabatic heating as evidenced by the unusually vertically displaced stratopause at 80 km is likely a direct consequence of this enhanced gravity wave driven descent high resolution simulations without parameterized gwd were closer to the analysis than medium resolution simulations with parameterized orographic gwd only but still did not fully simulate the mesospheric thermal response specifically the 80 km temperature enhancement was still underestimated in these simulations this suggests that higher spatial resolution is needed to adequately resolve extratropical gravity wave momentum fluxes

interannual variability of the stratospheric circulation in the southern hemisphere the variability from year to year of the seasonal evolution in the southern hemisphere stratosphere over a period of 10 years from 1980 to 1989 is investigated using the global geopotential height derived from the data from the stratospheric sounding unit on board the tiros noaa satellites as a measures of interannual variability the variance of the zonal mean geostrophic wind over the 10 years was calculated for each day although the major warming hardly occurs in the southern hemisphere stratosphere large variances can be observed during the winter and spring the maximum variances appear at low latitudes in late autumn move towards mid latitudes in midwinter and remain near 60 s in spring the seasonal movement of the zonal mean westerly jet in the southern hemisphere stratosphere can be classified into two categories in terms of the location of the maximum westerlies at the 1 mb level in midwinter namely hlj high latitude jet years with maximum westerlies around 50 s llj low latitude jet years with maximum westerlies around 40 s during the late winter the core of the westerly jet moves polewards earlier in hlj years in llj years in association with this earlier movement the growth of the amplitudes of planetary waves 1 and 2 during the period from winter to spring occurs earlier in hlj years than in llj years in autumn however the wave 1 amplitude only for llj years develops vigorously in the stratosphere and even the troposphere before the seasonal movement of the zonal mean westerly jet branches off into the two categories the appearances of hlj and llj years occur in groups of a few years this is quite different from the behaviour of the equatorial quasi biennial oscillation

fluvialcorridor a new arcgis toolbox package for multiscale riverscape exploration abstract both for scientists and river basin managers development of automated geographic information system gis tools is essential today to characterize riverscapes and explore biogeomorphologic processes over large channel networks since the 1990s gis toolboxes and add in programs have been used to characterize catchments however there is currently no equivalent to a planimetric and longitudinal characterization of fluvial corridor networks at multiple scales this paper describes fluvialcorridor a new gis toolbox this package allows the user i to extract a large set of riverscape features such as the main components of fluvial corridors from dem and vector layers e g stream network or valley bottom and ii to aggregate spatial features into homogeneous segments and metrics characterizing each of them the methodological frameworks involved have been previously described by alber and piegay 2011 leviandier et al 2012 and bertrand et al 2013 and this contribution focuses on the gis tools allowing the user to automatically operate them a case study on the drome river france is provided to illustrate the potential of the package both for geomorphologic understanding and target management actions fluvialcorridor has been developed for arcgis with the related native python library named arcpy and tested on arcgis 10 0 and 10 1 obviously each component of the package can be used separately however it also provides a complete workflow for fluvial corridor characterization even as the toolbox is continually under development and revision case study database fluvialcorridor package and guidelines are available online at http umrevs isig fr